The Human Body E-Book

• Herausgeber: Amber Books Ltd
• Kategorie: Ratgeber
• Sprache: Englisch
• Veröffentlichungsjahr: 2017

Seitenzahl: 480

Beschreibung

Discover how the individual parts of The Human Body function and work together: in this accessible and fascinating examination, you can navigate through the body from head to toe, looking at each individual area. As you read The Human Body, you will find out incredible facts, such as:
• The average person produces about 0.75-1.1ml tears (lacrimal fluid) every day
• A marathon runner achieves 40 percent greater cardiac output than an untrained person
• Sneezes travel at 160km/h (100 mph)
Clear, jargon-free text describes the function of individual parts of the body, from the skull and brain to all the major organs, bone structures and nervous systems, giving a comprehensive insight into the parts of the body we take for granted. All artworks are annotated to make every element clear. If you need to know about The Human Body and how it works, this is the book for you.

Leseprobe

 

THE

HUMAN

BODY

An Illustrated Guide To Your Body and How It Works

General Editor: Professor Peter Abrahams

This digital edition first published in 2016

Published by Amber Books Ltd United House North RoadLondon N7 9DP United Kingdom

Website: www.amberbooks.co.uk Instagram: amberbooksltd Facebook: amberbooks Twitter: @amberbooks

Copyright © 2016 Amber Books Ltd

ISBN: 978-1-78274-287-6

All rights reserved. With the exception of quoting brief passages for the purpose of review no part of this publication may be reproduced without prior written permission from the publisher. The information in this book is true and complete to the best of our knowledge. All recommendations are made without any guarantee on the part of the author or publisher, who also disclaim any liability incurred in connection with the use of this data or specific details.

www.amberbooks.co.uk

 

Contents

Introduction

6

Head

8

Neck

66

Thorax

84

Upper Limbs

124

Abdomen

154

Reproductive System

182

Pelvis

196

Lower Limbs

202

The Whole Body System

232

Index

248

THE HUMAN BODY

Introduction

Medicine and our understanding of human anatomy has developed enormously over the last few hundred years, often due to the ground- breaking discoveries of a few radical thinkers.

OUR FASCINATION WITH OUR BODIES and how they work, why they go wrong, and what to do to heal them is boundless. Throughout history, countless theories, mostly erroneous, explaining anatomy and physiology have been dreamed up by all manner of physicians, surgeons, quacks, witchdoctors, alchemists, faith- healers, astrologers and charlatans, who in their day, were often well-respected and highly paid professionals.

Despite this catalogue of bad practice, the history of medicine is punctuated by brilliant discoveries and truly visionary thinking that has, against all the odds, hauled us into the modern era of medical science. Hippocrates, ‘the father of medicine’, practised medicine on the Greek island of Cos in the fifth century bc, and is undoubtedly the most famous and recognizable figure of them all. His achievement was to establish a specialist body of physicians who were governed by a strict code of ethics, and who employed observable scientific methods in their research. This laid the foundation for modern medical practice.

The four ‘humours’Hippocrates’ work had a profound influence on medicine, and his ideas were enthusiastically expanded by doctors in the centuries that followed. Unfortunately, his theories on anatomy and disease were factually inaccurate. He believed that four ‘humours’, (black bile, yellow bile, phlegm and blood) governed human health and that any illness

was a result of imbalances between them. With the exception of the monks, who grew herbs and plants with some genuine medicinal properties, factual inaccuracy was the trademark of medicine and anatomy during the Middle Ages. The ‘humours’theory was still widely held to be true, andChristian and Islamic religious beliefwas highly influential on medicaltheory. All sorts of theories, suchas blood letting, draining‘noxious fluids’ from the bodyor encouraging ‘excess fluids’to move about the bodyfreely were commonly putinto practice, oftenaccompanied by

In this 17th century diagram by Anastasius Kircher, the human body represents the world in microcosm, which is described as a living organism with metabolic processes.

apothecaries’ potions,which contained suchbizarre and infamousingredients as newt’s tonguesand worm’s livers.

With the arrival of the Renaissancein Italy in the late fourteenth century,medical science moved forward. Therediscovery of classical learning encouraged physicians to re-apply scientific methods to medical research, and leave behind the influence of religion and superstition. Great names from the period, such as Leonardo Da Vinci, put forward new ideas. He believed that in order to treat disease it was necessary to first learn about the body and its processes, learning that could ultimately only come through the dissection of human cadavers. Dissection was not,

6

INTRODUCTION

Surgeons can perform today what would have been a miracle only 200 years ago, with a patient survival rate that would have stunned early physicians.

however, a new idea. Claudius Galen, a highly influential second century physician, had dissected animals and had assumed that human anatomy followed the same patterns, an idea that became accepted wisdom for over 1500 years. But by the sixteenth century, the anatomist, Andreas Vasalius, showed Galen was wrong and revealed previously unknown anatomical structures in his book, de Humani Corporis Fabrica (the Fabric of the Human Body), in 1543. Procuring bodies for dissection, however, was neither easy or pleasant. The Church forbade human dissection, so anatomists across Europe infamously resorted to robbing graves and cutting down bodies from gallows in order to obtain fresh materials for their research. Other pioneering work recording what had been discovered was conducted by Da Vinci and Vasalius, who sought to accurately represent anatomical structure through detailed diagrams and illustrations.

Blood circulation

Still, these ideas and methods were controversial and often dismissed. In 1628, the English doctor, William Harvey, stunned the medical world when he published An Anatomical Disquisition on the Movement of the Heart and Blood. In this book, he showed that blood circulated around the body and further proposed that the heart pumped blood through arteries. He also realised the significance of the valves of the heart in controlling the flow of blood. Although his ideas were considered outlandish, this scientific method of research was again proved to be the way forward. His findings were confirmed by the invention of the microscope in the late seventeenth century: for the first time in history, scientists could observe more than the naked eye would allow.

By the end of the nineteenth century, many of the practices and procedures we now take for granted

were coming to the fore. Crude anaesthetics were developed by James Young Simpson, antiseptics were pioneered by Joseph Lister, and in 1896, Wilhelm Rontgen amazed the world with a new invention that allowed internal examination of the body without the need for surgery: the x-ray machine was born. Other ground-breaking work by figures such as Louis Pasteur, who established the link between germs and disease, and Karl Landsteiner, who discovered the four main blood groups, paved the way for much more complex surgery such as organ transplants. Surgeons can perform today what would have been a miracle only 200 years ago, with a patient survival rate that would have stunned early physicians.

Discovering human anatomy

So how much do we actually know about how our own body systems work and how can we better understand what the doctor or surgeon sees and does? The Human Body will show you what we are really made of through a thorough examination of human anatomy. The book is structured from the head to the toe, and is broken down into the head, neck, thorax, upper limbs, abdomen, reproductive system, pelvis, lower limbs and general body systems. In turn, each section examines the bones, muscles, nerves, soft tissue and organs and how they work and interact. This book is the beginning of a fascinating journey.

Techniques such as Magnetic Resonance Imaging (MRI) allow medical staff to gain a ‘sliced’ image through the body. This can be used to study tumours in soft tissue, such as the brain.

7

HEAD

The skull

The skull is the head’s natural crash helmet, protecting the brain and sense organs from damage. It is made up of 28 separate bones and is the most complex element of the human skeleton.

Frontal boneForms forehead and roof of orbital cavity

Supra-orbital notchHole or notch in the upper eye socket through which nerves and vessels pass

CalvariaThe vault of the skull (also called cranial vault or skull-cap); the upper part of the cranium that encloses the brain

GlabellaJoins the nasal bones and the frontal processes of the maxilla

NasionPoint of articulation between the two nasal bones and the frontal bone

Nasal bonePair of bones forming the bridge of the nose

Infra-orbital marginThe lower edge of the orbital opening

Body of mandibleHorseshoe-shaped bone that forms the lower jaw

Inferior nasal concha (turbinate)Enlarges the surface area of the nasal cavity

Nasal septumThin partition in the nasal cavity separating the nasal passages

OrbitCavity containing the eyeball and its assorted muscles, nerves and vessels; also known as the eye socket

Temporal boneOne of two bones that form part of the sides and base of the skull

Lesser wing of sphenoid bone One of two side wings extending from the body of the sphenoid bone

Zygomatic boneForms the cheekbone and side wall of the eye socket

Infra-orbital foramenThis is a hole through which blood vessels and a nerve pass

MaxillaOne of a pair of bones that form the upper jaw

Mental foramenHole through which nerves and vessels from the roots of the teeth pass to the lower lip and chin

The skull is the skeleton of the face and the head. The basic role of the skull is protecting the brain, the organs of special sense such as the eyes, and the cranial parts of the breathing and digestive system. It also provides attachment for

many of the muscles of the neck and head.

Although often thought of as a single bone, the skull is made up of 28 separate bones. For convenience, it is often divided into two main sections: the cranium and the mandible. The basis for

this is that, whereas most of the bones of the skull articulate by relatively fixed joints, the mandible (jawbone) is easily detached.

The cranium is then subdivided into a number of smaller regions, including:

• cranial vault (upper dome

   part of the skull)

• cranial base

• facial skeleton

• upper jaw

• acoustic cavities (ears)

• cranial cavities (interior of skull housing the brain).

8

HEAD

Illuminated skull

Most of the bones of the skull are connected by sutures – immovable fibrous joints. These, and the bones inside the skull, can be seen most clearly using a brightly illuminated skull.

Several of the bones of the skull are paired, with one on either side of the midline of the head. The nasal, zygomatic, parietal and temporal bones all conform to this symmetry. Others, such as the ethmoid and sphenoid

bones, occur singly along the midline. Some bones develop in two separate halves and then fuse at the midline, namely the frontal bone and the mandible (lower jaw).

The bones of the skull constantly undergo a

process of remodelling: new bone develops on the outer surface of the skull, while the excess on the inside is reabsorbed into the bloodstream. This dynamic process is facilitated by the presence of numerous cells and a good blood supply.

Occasionally, a deficiency in the cells responsible for reabsorption upsets the bone metabolism, which can result in severe thickening of the skull – osteopetrosis, or Paget’s disease – and deafness or blindness may follow.

Frontal sinusesPockets of air connected to the nasal passage; not fully understood, but believed to help shape the orbitals and provide binocular vision

Greater wing of sphenoid boneOne of two wings extending from the sphenoid bone

Crista galliAlso known as ‘cock’s comb’ – a crest-like projection from the ethmoid bone

Ethmoidal sinusMade up of eight to ten air cells within the outer mass of the ethmoidal bone

Superior orbital fissureSpace between the roof and side wall of the orbit through which vessels and nerves pass

Zygomatic archThin bridge of bone between the temporal and zygomatic bones

Nasal concha (turbinate)Shell-shaped bone that projects into the nasal cavity

Ramus of mandibleBone projecting upwards from the mandible behind the teeth; provides support for jaw muscles

Maxillary sinusPyramid-shaped sinus occupying the cavity of the maxilla

9

HEAD

Side of the skull

A lateral or side view of the skull clearly reveals the complexity of the structure, with many separate bones and the joints between them.

Frontal boneForms the forehead and upper parts of both orbits. At birth, consists of two halves which later join up

Lacrimal boneThe smallest bone of the face, contributing to the orbit (eye socket)

Parietal boneOne of a pair of bones forming the top and sides of the cranium

Coronal sutureThe joint between the frontal and parietal bones

PterionThe area where the frontal, parietal, squamous part of the temporal and greater wing of the sphenoid bones articulate

Nasal boneOne of a pair of narrow, rectangular bones forming the bridge and root of nose

Zygomatic boneForms prominent part of cheek, and some of the orbit

Lambdoid suture Occurs between the parietal and occipital bones

External acoustic meatus temporal bone The canal through to the middle and inner ears

Occipital boneSaucer-shaped bone which forms the back and part of the base of the cranium

Styloid process of temporal bone Finger-like bone to which muscles and ligaments attach

Zygomatic archHorizontal arch formed by zygomatic and temporal bones

MaxillaUpper jaw

Sphenoid boneForms the base of the cranium behind the eyes

Body of mandibleThe lower jaw

Mental foramenOpening for the passage of blood vessels and nerves

Mastoid process of temporal bone Protuberance extending behind ear; point of attachment for several neck muscles

Squamous (flat) part of temporal bone Forms part of side of cranium

Condyle of mandibleArticulates with temporal bone to form temporomandibular joint

Several of the bones of the skull are paired, with one on either side of the midline of the head. The nasal, zygomatic, parietal and temporal bones all conform to this symmetry. Others, such as the ethmoid and sphenoid bones, occur

singly along the midline. Some bones develop in two separate halves and then fuse at the midline, namely the frontal bone and the mandible (lower jaw).

The bones of the skull constantly undergo a process of remodelling:

new bone develops on the outer surface of the skull, while the excess on the inside is reabsorbed into the bloodstream.

This dynamic process is facilitated by the presence of numerous cells and also a good blood supply.

Occasionally, a deficiency in the cells responsible for reabsorption upsets the bone metabolism, which can result in severe thickening of the skull – osteopetrosis, or Paget’s disease – and deafness or blindness may follow.

10

HEAD

Inside the skull

The inside of the left half of the skull shows the large cranial vault (calvaria) and facial skeleton in section.

Comparing this photograph with the one of the skull’s exterior, many of the same bones can be seen, as well as additional structures. The bony part of the nasal septum (the dividing wall of the nasal cavity) consists of the vomer and the perpendicular plate of the ethmoid bone.

In this skull, the sphenoidal air sinuses are large. The pituitary fossa, containing the pea-sized, hormone-producing pituitary gland, projects down into the sinus. The circle marks the pterion, corresponding to the position marked on the external photograph.

The skull covers the brain, and skull fractures can lead to potentially life- threatening situations. If the side of the skull is fractured in the region of the temporal bone, the blood vessel of the middle meningeal artery may be damaged (extra dural haemorrhage). This vessel

supplies the skull bones and the meninges (outer coverings of the brain), and if ruptured, the escaping blood may cause pressure on vital centres in the brain. If not relieved, this can rapidly cause death. The artery is accessible to the surgeon if entry is made near the pterion.

Grooves for middle meningeal vessels Run upwards and backwards to the meninges, which are situated outside the brain

Coronal suture

Pituitary fossa (sella turcica)Compartment that contains the pituitary gland

Pterion

Orbital part of frontal boneForms part of eye socket

Parietal bone

Frontal air sinus

Nasal bone

Sphenoidal air sinus

Internal acoustic meatus in petrous part of temporal bone

Perpendicular plate of the ethmoid bone

Vomer

Palatine maxilla

Body of mandible

Occipital bone

Lambdoid suture

External occipital protuberance

Margin of foramen magnum

Ramus of mandible

Mandibular foramen

Angle of mandible

Pterygoid hamulus of medial pterygoid plate

11

HEAD

Top and base of the skull

The calvaria, or vault of the skull, is the upper section of the cranium, surrounding and protecting the brain.

Top of the skullexterior

Top of the skullinterior

BACK

FRONT

Occipital boneJust visible from above; also forms part of the back and base of skull

Sagittal sutureJoins the two parietal bones

Parietal tuberosityProtruberance at the side of the skull

Vertex‘Peak’ of the head

Parietal bonePaired, one on either side

Coronal sutureRuns between the frontal bone and the two parietal bones

‘Flat’ bone of parietalMade up of three layers: inner table, diplöe and outer table

Grooves for middle menigeal vessel Allow the passage of vessels to the meninges outside the brain

Frontal crestProjection from the frontal bone into the cranial cavity

Frontal boneForms the front section of the calvaria, and the forehead

The four bones that make up the calvaria are the frontal bone, the two parietals and a portion of the occipital bone.

These bones are formed by a process in which the original soft connective tissue membrane ossifies (hardens) into bone

substance, without going through the intermediate cartilage stage, as happens with some other bones of the skull.

Points of interest in the calvaria include:

• The sagittal suture running longitudinally from the

   lambdoid suture at the back of the head to the coronal suture.

• The vertex (highest point) of the skull; the central uppermost part, along the sagittal suture.

• The distance between the two parietal tuberosities is

   the widest part of the cranium.

• The complex, interlocking nature of the sutures which enable substantial skull growth in the formative years, and provide strength and stability in the adult skull.

12

HEAD

Base of the skull

This unusual view of the skull is from below. The upper jaw and the hole through which the spinal cord goes can be seen.

Incisive fossaDepression through to the root of the canine tooth

Median palatine sutureRuns between the two palatine processes of the maxillae

Palatine process of maxilla

Zygomatic bone

Horizontal plate of palatine bone Together with palatine processes of maxillae forms the hard palate

Zygomatic arch

VomerForms the division between nasal cavities

Sphenoid bone

Foramen ovale

Foramen lacerum

Carotid canal

Jugular foramen

Mastoid processProtrusion of the temporal bone

Mastoid notch

External occipital crest

External occipital protuberance

Foramen spinosum

Pharyngeal tubercleFrom which pharynx muscles hang

Stylomastoid foramen

Foramen magnumHole through which the spinal cord joins the brain stem

Mastoid foramen

The bones found in the midline region of the base of the skull (the ethmoid, sphenoid and part of the occipital bone) develop in a different way from those of the vault of the skull. They are derived from an earlier cartilaginous structure in a process called endochondral ossification.

The maxillae are the two tooth-bearing bones of the upper jaw, one on each side. The palatine processes of the maxillae and the horizontal plates of the palatine bones form the hard palate.

PALATE DEFECTS

A cleft palate occurs when the structures of the palate

do not fuse as normal before birth, creating a gap in the roof of the mouth. This links the oral and nasal cavities. If the gap extends through to the upper jaw, a harelip will become apparent on the upper lip. However, surgery can often improve the defect.

Children with narrow

palates and crowded teeth can have an orthodontic appliance fitted which gradually increases tension across the longitudinally running midline palatine.

Over a period of months, the edges of the suture are forced apart, allowing for the growth of new bone, and extra space for the teeth.

13

HEAD

Scalp

The scalp is composed of five layers of tissue that cover the bones of the skull. The skin is firmly attached to the muscles of the scalp by connective tissue which also carries numerous blood vessels.

Skull

SkinOuter layer of scalp; contains many hair follicles, sweat glands and sebaceous glands

Dense connective tissueSecond layer; binds the skin to the aponeurosis and contains many blood vessels

DiplöeLattice like tissue that lies between inner and outer layers of the skull

Surface of the brain Covered by the pia mater, the innermost layer of the meninges

AponeurosisFibrous tissue that connects the occipitalis muscle at the rear of the head to the frontalis muscle at the front

Temporalis muscleMuscle at the side of the head; it is attached to the lower jaw and can be felt when the teeth are clenched

Arachnoid materA thin, fibrous layer of the meninges between the dura mater and pia mater

Dura materTough fibrous membrane that lines the inside of the skull

Loose connective tissueEnables the upper layers of the scalp to move over the lowest layer, the pericranium

Diploic veinLocated inside the spongy bone of the skull

PericraniumDeepest layer of scalp, the pericranium is a membrane which covers the skull bones

The five layers of the scalp have been peeled back to show their relationship with the blood vessels and underlying bone.

The scalp is the covering of the top of the head which stretches from the hairline at the back of the skull to the eyebrows at the front. It is a thick, mobile, protective covering for the skull, and it has five distinct layers, the first three of which are bound tightly together.

The skin of the scalp is the thickest in the body and the

hairiest. As well as its functions of hair-bearing and protection of the skull, the skin of the front of the scalp in particular has an important role in facial expression.

This is because many of the fibres of the scalp muscles are attached to the skin, allowing it to move backwards and forwards.

CONNECTIVE TISSUE

Under the skin, and attached firmly to it, is a layer of dense tissue which carries numerous arteries and veins. The arteries are branches of the external and internal carotid arteries, which interconnect to give a rich blood supply to all areas of the scalp. This layer of connective tissue is also

attached firmly to the underlying layer of muscle.

The connective tissue binds the skin to the muscle in such a way that even if the scalp is torn from the head in an accident, these three layers will remain together.

14

HEAD

Muscles of the scalp

The muscles of the scalp lie below the skin and a layer of connective tissue. They act to move the skin of the forehead and the jaw while chewing.

SkinOutermost layer of the scalp; bears hair

AponeurosisLayer of fibrous connective tissue which joins the front and rear sections of the occipitofrontalis muscle

OccipitalisOriginates in the occipital bone and joins aponeurosis; pulls scalp back

Temporalis muscleSituated at the side of the head and running down to the lower jaw; closes jaw and maintains position of the lower jaw while at rest

Dense connective tissueDirectly underneath, and bound to, the skin; carries arteries and veins which supply the scalp with blood

Frontalis muscleCovers forehead and dome of skull from the aponeurosis to the eyebrows; raises eyebrows and wrinkles forehead

Orbicularis oculiFlat muscle that surrounds the eye

Orbicularis orisThe sphincter muscle surrounding the mouth

The occipitalis muscle fixes the aponeurosis enabling the frontalis muscle to play a role in facial expression. The temporalis muscle is responsible for clenching the jaw.

The occipitofrontalis is a large muscle formed by two sections at the front and the back of the scalp, which are connected by a thin, tough, fibrous sheet (aponeurosis). The frontalis is the section of muscle over the forehead, arising from the skin overlying the eyebrow and passing back to become continuous with the

aponeurosis. This muscle acts to raise the eyebrows, thus wrinkling the forehead or pulling the scalp forward, as when frowning.

The occipitalis is the section of muscle that arises from the top of the back of the neck and passes forward to the aponeurosis. It acts to pull the scalp backwards.

The temporalis muscle lies

at the side of the scalp, above the ears, and runs from the skull down to the lower jaw. It is involved in the action of chewing.

LOOSE CONNECTIVE TISSUE

The fourth layer, underlying the muscle and aponeurosis, is a layer of loose connective tissue which

allows the layers above to move relatively freely over the layer below. It is at this level that the scalp may be torn away during accidents, such as the head going forward through the windscreen of a car.

The pericranium, the fifth layer of the scalp, is the tough membrane covering the bone of the skull itself.

15

HEAD

Brain

The brain is the part of the central nervous system that lies inside the skull. It controls many body functions including our heart rate, the ability to walk and run, and the creation of our thoughts.

Left cerebral hemisphere

Right cerebral hemisphere

Frontal poleThe most anterior part of the forebrain

Longitudinal fissureThe division between the two cerebral hemispheres

Superior frontal gyrus

Precentral gyrusContains the motor area of the cortex that controls the skeletal muscles. As well as moving the limbs, this part of the the cortex controls movement of the fingers, thumbs and lips

Precentral sulcus

Central sulcus Separates the frontal and parietal lobes

Postcentral gyrusContains the sensory area of the cortex

SulcusAn infolding of the cerebral cortex

Parieto-occipital sulcusForms a boundary between the parietal and occipital lobes

GyrusA raised ridge of cerebral cortex

Calcarine sulcusContains the visual part of the cortex

The brain comprises three major parts: forebrain, midbrain and hindbrain. The forebrain is divided into two halves, forming the left and right cerebral hemispheres.

HEMISPHERES

The cerebral hemispheres form the largest part of the forebrain. Their outer surface is folded into a

series of gyri (ridges) and sulci (furrows) that greatly increases its surface area. Most of the surface of each hemisphere is hidden in the depths of the sulci.

Each hemisphere is divided into frontal, parietal, occipital and temporal lobes, named after the closely related bones of the skull. Connecting the two

hemispheres is the corpus callosum, a large bundle of fibres deep in the longitudinal fissure.

GREY AND WHITE MATTER

The hemispheres consist of an outer cortex of grey matter and an inner mass of white matter.

• Grey matter contains nerve

   cell bodies, and is found in the cortex of the cerebral and cerebellar hemispheres and in groups of sub- cortical nuclei.

• White matter comprises nerve fibres found below the cortex. They form the communication network of the brain, and can project to other areas of the cortex and spinal cord.

16

HEAD

Inside the brain

A midline section between the two cerebral hemispheres reveals the main structures that control a vast number of activities in the body. While particular areas monitor sensory and motor information, others control speech and sleep.

Precentral gyrus

Central sulcus

Postcentral gyrus

Corpus callosumA thick band of nerve fibres, found in the depths of the longitudinal fissure that connects the cerebral hemispheres

Right cerebral hemisphereOne of two hemispheres that form the largest part of the forebrain

VentricleFluid-filled cavity

ThalamusDirects sensory information from the sense organs to the correct part of the cerebral cortex

Pineal glandPart of the epithalamus that synthesizes melatonin

Parieto-occipital sulcus Divides the occipital and parietal lobes

Calcarine sulcusWhere most of the primary visual cortex lies

CerebellumControls body movement and maintains balance; consists of grey matter on the outside and white matter on the inside

Optic nerveCarries visual information from the eye to the brain

Pituitary stalkThe pituitary gland is not included when the brain is removed from the skull

HypothalamusConcerned with emotions and drives, such as hunger and thirst; it also helps to control body temperature and the water-salt balance in the blood

MidbrainImportant in vision; links the forebrain to the hindbrain

PonsPart of the brainstem that contains numerous nerve tracts

Spinal cord

Medulla oblongataContains vital centres that control breathing, heart-beat and blood supply

SPEECH, THOUGHT AND MOVEMENT

The receptive speech area (Wernicke’s area) lies behind the primary auditory cortex and is essential for understanding speech. The prefrontal cortex has high- order cognitive functions, including abstract thinking, social behaviour and decision-making ability.

Within the white matter of the cerebral hemispheres are several masses of grey matter, known as the basal ganglia. This group of structures is involved in aspects of motor function,

including movement programming, planning and motor programme selection and motor memory retrieval.

DIENCEPHALON

The medial part of the forebrain comprises the structures surrounding the third ventricle. These form the diencephalon which includes the thalamus, hypothalamus, epithalamus and subthalamus of either side. The thalamus is the last relay station for information from the brainstem and spinal cord before it reaches the cortex.

The hypothalamus lies below the thalamus in the floor of the diencephalon. It is involved in a variety of homeostatic mechanisms, and controls the pituitary gland which descends from its base. The anterior (front) lobe of the pituitary secretes substances that influence the thyroid and adrenal glands, and the gonads and produces growth factors. The posterior lobe produces hormones that increase blood pressure, decrease urine production and cause uterine contraction. The hypothalamus also influences

the sympathetic and parasympathetic nervous systems and controls body temperature, appetite and wakefulness. The epithalamus is a relatively small part of the dorso-caudal diencephalon that includes the pineal gland, which synthesizes melatonin and is involved in the control of the sleep/wake cycle.

The subthalamus lies beneath the thalamus and next to the hypothalamus. It contains the subthalamic nucleus which controls movement.

17

HEAD

Blood vessels of the brain

The arteries provide the brain with a rich supply of oxygenated blood.

Inferior (from below) view of the brain

Right hemisphere

Left hemisphere

Olfactory bulbsOrgans of smell

Cerebrum

Middle cerebral arteryThis is the main branch of the internal carotid artery, supplying blood to two- thirds of the cerebral hemisphere and many deep structures of the brain

Anterior cerebral artery Supplies blood to the frontal lobe and to the medial surface of the cerebral hemisphere

Circle of WillisCircle of communicating arteries at the base of the brain

Basilar arteryA large artery which lies on the inferior surface of the pons; divides to form the two posterior cerebral arteries

Vertebral arteryArises from the subclavian arteries, enters the skull through the foramen magnum to supply the brainstem, then fuses with its opposite number to form the basilar artery

Posterior cerebral artery Supplies blood to the inferior part of the temporal lobe and to the occipital lobe at the back of the brain

Cerebellum

Cerebellar arteriesBranches from the vertebral and basilar arteries that provide the blood supply to the cerebellum

Spinal cord

The human brain weighs about 1.4 kg and accounts for two per cent of our total body weight. However, it requires 15–20 per cent of the cardiac output to be able to function properly. If the blood supply to the the brain is cut for as little as 10 seconds we lose consciousness and, unless blood flow is quickly

restored, it takes only a matter of minutes before the damage is irreversible.

THE ARTERIAL NETWORK

Blood reaches the brain via two pairs of arteries. The internal carotid arteries originate from the common carotid arteries in the neck, enter the skull via the carotid canal and then branch

to supply the cerebral cortex. The two main branches of the internal carotid are the middle and anterior cerebral arteries.

The vertebral arteries arise from the subclavian arteries, enter the skull via the foramen magnum and supply the brainstem and cerebellum. They join, forming the basilar artery

which then divides to produce the two posterior cerebral arteries that supply, among other things, the occipital or visual cortex at the back of the brain.

These two sources of blood to the brain are linked by other arteries to form a circuit at the base of the brain called the ‘circle of Willis’.

18

HEAD

Veins of the brain

Deep and superficial veins drain blood from the brain into a complex system of sinuses. These sinuses rely on gravity to return blood to the heart as, unlike other veins, they do not possess valves.

The veins of the brain can be divided into deep and superficial groups. These veins, none of which have valves, drain into the venous sinuses of the skull.

The sinuses are formed between layers of dura mater, the tough outer membrane covering the brain, and they are unlike the veins in the rest of

the body in that they have no muscular tissue in their walls.

The superficial veins have a variable arrangement on the surface of the brain and many of them are highly interconnected. Most superficial veins drain into the superior sagittal sinus. By contrast, most of the deep veins, associated with

structures within the body of the brain, drain into the straight sinus via the great cerebral vein (vein of Galen).

FUNCTIONS OF THE SINUSES

The straight sinus and the superior sagittal sinus converge. Blood flows through the transverse and sigmoid sinuses and exits the

skull through the internal jugular vein before flowing back towards the heart.

Beneath the brain, on either side of the sphenoid bone, are the cavernous sinuses. These drain blood from the orbit (eye socket) and the deep parts of the face. This provides a potential route of infection into the skull.

Superior sagittal sinusThe largest of the venous sinuses; receives blood from many of the superficial cerebral veins and is also the site for reabsorption of cerebrospinal fluid into the circulation

Inferior sagittal sinusFound at the lower margin of the falx cerebri (a large fold in the dura mater separating the two cerebral hemispheres); receives blood from superficial veins

Straight sinusDrains blood from the inferior sagittal sinus and the deep cerebral veins via the great vein of Galen

Cavernous sinusDrains blood from the orbit, deep parts of the face and the pituitary gland

Inferior petrosal sinusAssociated with the petrous temporal bone of the skull, this sinus drains blood from the cavernous sinus into the internal jugular vein

Superior petrosal sinus Drains blood from the cavernous sinus into the transverse sinus

Transverse sinusConnects the confluence of the sinuses and the sigmoid sinus

Sigmoid sinusDrains blood from the transverse sinus to the internal jugular vein; so called because of its ‘S’ shape

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Ventricles of the brain

The brain ‘floats’ in a protective layer of cerebrospinal fluid – the watery liquid produced in a system of cavities within the brain and brainstem.

The brain contains a system of communicating (connected) cavities known as the ventricles. There are four ventricles within the brain and brainstem, each secreting cerebrospinal fluid (CSF), the fluid that surrounds and permeates the brain and spinal cord, protecting them from injury and infection.

Three of the ventricles – namely the two (paired) lateral ventricles and the third ventricle – lie within the forebrain. The lateral ventricles are the largest, and lie within each cerebral hemisphere. Each consists of a ‘body’ and three ‘horns’ – anterior (situated in the frontal lobe), posterior (occipital lobe) and inferior (temporal lobe). The third ventricle is a narrow cavity between the thalamus and hypothalamus.

HINDBRAIN VENTRICLE

The fourth ventricle is situated in the hindbrain, beneath the cerebellum. When viewed from above, it is diamond-shaped, but in sagittal section (see right) it is triangular. It is continuous with the third ventricle via a narrow channel called the cerebral aqueduct of the midbrain. The roof of the fourth ventricle is incomplete, allowing it to communicate with the subarachnoid space (see over).

This sagittal section of the brain and brainstem reveals the four ventricles and the foramina and aqueducts that connect them.

Lateral ventriclesPair of ventricles that lie in the forebrain; there is one lateral ventricle in each hemisphere

Anterior hornFrontal part of the lateral ventricle; lies in front of the interventricular foramen

BodyMain section of the lateral ventricle; formed from three horns (projections): anterior, inferior and posterior

Inferior hornPart of the lateral ventricle that lies in the temporal lobe

Posterior hornPart of the lateral ventricle that extends towards the occiptal pole (the back of the head)

Cerebral cortex

FRONTAL LOBE

OCCIPITAL LOBE

TEMPORAL LOBE

CEREBELLUM

Interventricular foramenChannel joining the two lateral and the single third ventricles; also known as the foramen of Monro

Third ventricleA single ventricle linked to the two lateral ventricles via the interventricular foramen

Cerebral aqueductChannel joining the third and fourth ventricles; passes the length of the midbrain

Median aperture (foramen of Magendie) An opening in the fourth ventricle that allows CSF to pass into the subarachnoid space

Spinal cord

Fourth ventricleCavity within the brainstem that extends to the central canal in the middle of the spinal cord

Left lateral recess (foramen of Luschka) Opening in the fourth ventricle that allows CSF to pass into the subarachnoid space

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Circulation of cerebrospinal fluid

Cerebrospinal fluid (CSF) is produced by the choroid plexus within the lateral, third and fourth ventricles.

Dura materThe outermost of the three meninges of the brain

Choroid plexus of the third ventricle Responsible for the production of cerebrospinal fluid

Arachnoid granulationsStructures through which CSF passes into the venous sinuses

Subarachnoid spaceGap between the arachnoid and pia meninges through which CSF circulates; arrows    indicate the direction of flow

Superior sagittal sinusA space receiving venous blood from the cerebral hemispheres

Arachnoid materThe middle of the three meninges of the brain

Lateral ventricle

Third ventricle

Interventricular foramen The opening through which CSF passes from the lateral ventricle to the third ventricle; blockage of this opening can lead to hydrocephalus

Cistern of the great cerebral vein An area where CSF can be sampled

Cerebral aqueductCarries CSF to the fourth ventricle

Pituitary glandRegulates the production of hormones

Lateral aperture of fourth ventricle Channel through which CSF passes into the sub arachnoid space

Central canal of spinal cordContinuous with the fourth ventricle and extending through the spinal cord

Choroid plexus of fourth ventricle Produces CSF

Cerebellomedullary cisternaOne of a number of cisternae (enlarged subarachnoid space) from where CSF can be sampled

Median apertureOpening in roof of fourth ventricle, allowing CSF to pass into the subarachnoid space

The arrows show the movement of CSF: blue denotes the route of the fluid through the ventricular system; yellow the route through the subarachnoid space.

The choroid plexuses are a rich system of blood vessels originating from the pia mater, the innermost tissue surrounding the brain. The plexuses contain numerous folds (villous processes) projecting into the ventricles, from which cerebrospinal fluid is produced.

From the choroid plexuses in the two lateral ventricles,

CSF passes to the third ventricle via the interventricular foramen. Together with additional fluid produced by the choroid plexus in the third ventricle, CSF then passes through the cerebral aqueduct of the midbrain and into the fourth ventricle. Additional fluid is produced by the choroid plexus in the fourth ventricle.

SUBARACHNOID SPACE

From the fourth ventricle, CSF passes out into the subarachnoid space surrounding the brain. It does this through openings in the fourth ventricle – a median opening (foramen of Magendie) and two lateral ones (foramina of Luschka). Once in the subarachnoid space, the CSF circulates to

surround the central nervous system. As CSF is produced constantly, it needs to be drained continuously to prevent build-up of pressure. This is achieved by passage of the CSF into the venous sinuses of the brain through protrusions (arachnoid granulations). These are particularly evident in the superior sagittal sinus.

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Cerebral hemispheres

The cerebral hemispheres are the largest part of the brain. In humans, they have developed out of proportion to the other regions, distinguishing our brains from those of other animals.

Lobes of the cerebral hemispheres

Rolandic fissureThe central sulcus

Frontal lobeConcerned with planning future actions and controlling movements

Parietal lobeConcerned with somatic sensation and body image

Parieto- occipital sulcus

Sylvian fissureAlso known as the lateral fissure

Temporal lobeConcerned with hearing and some aspects of learning, memory and emotion

Occipital lobeConcerned with interpreting the visual scene

The cerebral hemispheres are each divided into four lobes. They are named after the bones of the skull which lie over them.

The left and right cerebral hemispheres are separated by the longitudinal fissure which runs between them. Looking at the surface of the hemispheres from the top and side, there is a prominent groove running downwards, beginning about 1 cm behind the midpoint between the front and back of the brain.

This is the central sulcus or rolandic fissure. Further

down on the side of the brain there is a second large groove, the lateral sulcus or sylvian fissure.

LOBES OF THE BRAIN

The cerebral hemispheres are divided into lobes, named after the bones of the skull which lie over them:

• The frontal lobe lies in front of the rolandic fissure and above the sylvian fissure

• The parietal lobe lies

   behind the rolandic fissure and above the back part of the sylvian fissure; it extends back as far as the parieto-occipital sulcus, a groove separating it from the occipital lobe, which is at the back of the brain

• The temporal lobe is the area below the sylvian fissure and extends backward to meet the occipital lobe.

At the bottom of the sylvian fissure there is another distinct area known as the insula or island of Reil. This triangular region has been buried by the growth of the adjacent parts of the brain and is not normally visible unless the sylvian fissure is spread open.

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Functions of the cerebral hemispheres

Different regions of the cortex have distinct and highly specialized functions.

The cerebral cortex is divided into:

• Motor areas, which initiate and control movement. The primary motor cortex controls voluntary movement of the opposite side of the body. Just in front of the primary motor cortex is the pre-motor cortex and a third area, the

   supplementary motor area, lies on the inner surface of the frontal lobe. All of these areas work with the basal ganglia and cerebellum to allow us to perform complex sequences of finely controlled movements.

• Sensory areas, which receive and integrate

   information from sensory receptors around the body. The primary somatosensory area receives information from sensory receptors on the opposite side of the body about touch, pain, temperature and the position of joints and muscles (proprioception).

• Association areas, which

   are involved with the integration of more complex brain functions – the higher mental processes of learning, memory, language, judgment and reasoning, emotion and personality.

Primary motor cortexControls voluntary movement of the opposite side of the body; electrical stimulation in this area will produce movement of specific muscle groups

Primary somatosensory cortexReceives information from sensory receptors on the opposite side of the body about touch, pain, temperature and the position of joints and muscles

Auditory association cortex Concerned with the interpretation of the meaning and significance of sounds

Visual association areaConcerned with recognizing the meaning of visual information and relating it to previous experience

Broca’s areaConcerned with the production of speech; in about 97 per cent of people this area is located on the left-hand side of the brain

Primary auditory cortex Processes basic features of sound such as pitch and rhythm

Primary visual cortexReceives visual information from the eyes relating to the opposite half of the field of vision

Some of the major functional areas of the cerebral cortex are mapped onto this side view of the human brain.

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Thalamus

The thalamus is a major sensory relay and integrating centre in the brain, lying deep within its central core. It consists of two halves, and receives sensory inputs of all types, except smell.

Dorsomedial nucleusIntegrates information about mood and instinct

Lateral posterior nucleusInvolved in the integration of sensory information

PulvinarIntegrates somatic sensations and auditory and visual information

Internal medullary laminaEncloses intralaminar nuclei which help control alertness

Anterior nucleusInvolved in aspects of memory and emotion

Ventral anterior nucleusInvolved in the control of voluntary movement

Ventrolateral nucleusInvolved in the control of voluntary movement

Lateral geniculate bodyRelays visual information to the occipital lobe of the cerebral cortex

Ventral posterolateral nucleusRelays information about pain, touch, pressure, temperature, vibration and taste to sensory areas of the cerebral cortex

The thalamus is composed of a number of distinct nuclei (masses of nerve cells). Each of these nuclei receives sensory input from a different source and relays it to a specific region of the brain.

The thalamus is made up of paired egg-shaped masses of grey matter (cell bodies of nerve cells) 3–4 cm long and 1.5 cm wide, located in the deep central core of the brain known as the diencephalon, or ‘between brain’.

The thalamus makes up about 80 per cent of the diencephalon and lies on either side of the fluid-filled third ventricle.

The right and left parts of the thalamus are connected to each other by a bridge of

grey matter – the massa intermedia, or interthalamic adhesion.

NEUROANATOMY

The front end of the thalamus is rounded and is narrower than the back, which is expanded into the pulvinar. The upper surface of the thalamus is covered with a thin layer of white matter – the stratum zonale. A second layer of white matter – the external medullary lamina –

covers the lateral surface.

Its structure is very complex and it contains more than 25 distinct nuclei (collections of nerve cells with a common function).

These thalamic nuclear groups are separated by a vertical Y-shaped sheet of white matter – the internal medullary lamina. The anterior nucleus lies in the fork of the Y, and the tail divides the medial and lateral nuclei and splits to enclose the intralaminar nuclei.

These can be subdivided into several groups:

• Anterior nuclei

• Medial nuclei

• Lateral nuclei

Divided into a larger ventral group and a smaller dorsal group

• Intralaminar, midline and reticular nuclei

• Posterior nuclei

• pulvinar

• medial geniculate body

• lateral geniculate body

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Hypothalamus

The hypothalamus is a complex structure located in the deep core of the brain. It regulates fundamental aspects of body function, and is critical for homeostasis – the maintenance of equilibrium in the body’s internal environment.

Paraventricular nucleusSynthesizes the hormone oxytocin; in females, this causes milk production in the mammary glands and contraction of the uterine walls in childbirth

Corpus callosumA band of nerve fibres that connects the left and right cerebral hemispheres

Dorsomedial and ventromedial nucleus Concerned with the control of hunger and thirst

Pituitary glandHormones released from this gland are under the direct control of the hypothalamus

Suprachiasmatic nucleusConcerned with controlling the sleep–wake cycle

Supraoptic nucleusProduces vasopressin (antidiuretic hormone), which increases water reabsorption in the kidneys

Like the thalamus, the hypothalamus is composed of a number of nuclei. These nuclei are involved in the control of autonomic (unconscious) functions.

The hypothalamus is a small region of the diencephalon; it is the size of a thumbnail and weighs only about four grams. It lies below the thalamus and is separated from it by a shallow groove, the hypothalamic sulcus. The hypothalamus is just

behind the optic chiasm, the point where the two optic nerves cross over as they travel from the eyes towards the visual area at the back of the brain.

Several distinct structures stand out on its undersurface:

• The mammillary bodies –

   two small, pea-like projections which are involved in the sense of smell

• The infundibulum or pituitary stalk – a hollow structure connecting the hypothalamus with the posterior part of the

   pituitary gland (neurohypophysis) which lies below it

• The tuber cinereum or median eminence – a greyish-blue, raised region surrounding the base of the infundibulum.

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Limbic system

The limbic system is a ring of interconnected structures that lies deep within the brain. It makes connections with other parts of the brain, and is associated with mood and memory.

The limbic system is a collection of structures deep within the brain that is associated with the perception of emotions and the body’s response to them.

The limbic system is not one, discrete part of the brain. Rather it is a ring of interconnected structures surrounding the top of the brainstem. The connections between these structures are complex, often forming loops or circuits and, as with much of the brain, their exact role is not fully understood.

STRUCTURE

The limbic system is made up from all or parts of the following brain structures:

• Amygdala – this almond- shaped nucleus appears to be linked to feelings of fear and aggression

• Hippocampus – this structure seems to play a part in learning and memory

• Anterior thalamic nuclei – these collections of nerve cells form part of the thalamus. One of their roles seems to lie in the control of instinctive drives

• Cingulate gyrus – this connects the limbic system to the cerebral cortex, the part of the brain that carries conscious thoughts

• Hypothalamus – this regulates the body’s internal environment, including blood pressure, heart rate and hormone levels. The limbic system generates its effects on the body by sending messages to the hypothalamus.

Medial view of the limbic system within the brain

Cingulate gyrusConnects the limbic system to the cerebral cortex

AmygdalaAlmond-shaped mass of grey matter which has links with the olfactory system

HypothalamusRegion of the forebrain concerned with regulating the body’s internal environment

HippocampusThis plays an important role in converting new information into long-term memories

The limbic system connections encircle the upper part of the brainstem. They link with other parts of the brain and are associated with emotion.

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Connections of the limbic system

The limbic system has connections with the higher centres of the brain in the cortex, and with the more primitive brainstem. It not only allows the emotions to influence the body, but also enables the emotional response to be regulated.

The developing brain

The cerebral cortexThis outer layer of the brain evolved last, and is related to higher intellect

The brainstemThis part of the brain evolved first, and is responsible for self- preservation and aggression

The limbic systemThis system developed secondly and enabled the emotions necessary for mammalian existence, which include caring for offspring

The three layers of the brain evolved one by one over thousands of years. Each is responsible for different bodily and intellectual functions.

The human brain can be considered to be made up of three parts. These parts have evolved one after another over the millennia.

BRAINSTEM

The ‘oldest’ part of the brain, in evolutionary terms, is the brainstem, which is concerned largely with unconscious control of the internal state of the body. The brainstem can be seen as a sort of ‘life support system’.

LIMBIC SYSTEM

With the evolution of mammals came another

‘layer’ of brain, the limbic system. The limbic system allowed the development of feelings and emotions in response to sensory information. It is also associated with the development of newer – in evolutionary terms – behaviours, such as closeness to offspring (maternal bonding).

CEREBRAL CORTEX

The final layer of the human brain is shared to some extent with higher mammals. It is the cerebral cortex, the part of the brain that allows

humans to think and reason. With this part of the brain, individuals perceive the outside world and make conscious decisions about their behaviour and actions.

ROLE OF THE LIMBIC SYSTEM

The limbic system lies between the cortex and the brainstem and makes connections with both. Through its connections with the brainstem, the limbic system provides a way in which an individual’s emotional state can influence the internal state of the

body. This may prepare the body perhaps for an act of self-preservation such as running away in fear, or for a sexual encounter.

The extensive connections between the limbic system and the cerebral cortex allow human beings to use their knowledge of the outside world to regulate their response to emotions. The cerebral cortex can thus ‘override’ the more primitive limbic system when necessary.

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Basal ganglia

The basal ganglia lie deep within the white matter of the cerebral hemispheres. They are collections of nerve cell bodies that are involved in the control of movement.

The common term basal ganglia is, in fact, a misnomer, as the term ganglion refers to a mass of nerve cells in the peripheral nervous system rather than the central nervous system, as here. The term basal nuclei is anatomically more appropriate.

COMPONENTS

There are a number of component parts to the basal nuclei which are all anatomically and functionally closely related to each other. The parts of the basal nuclei include:

• Putamen. Together with the caudate nucleus, the putamen receives input from the cortex

• Caudate nucleus. Named for its shape, as it has a long tail, this nucleus is continuous with the putamen at the anterior (front) end

• Globus pallidus. This nucleus relays information from the putamen to the pigmented area of the midbrain known as the substantia nigra, with which it bears many similarities.

GROUPING

Various names are associated with different groups of the basal nuclei. The term corpus striatum (striped body) refers to the whole group of basal nuclei, whereas the striatum includes only the putamen and caudate nuclei. Another term, the lentiform nucleus, refers to the putamen and the globus pallidus which, together, form a lens-shaped mass.

Head of caudate nucleus

Internal capsuleFan-shaped white matter passing between basal ganglia, giving it a striped appearance

PutamenReceives input from the cerebral cortex

Globus pallidusPart of the lentiform nucleus in the brain

Tail of caudate nucleus

ThalamusMass of grey matter located in each side of the forebrain

A

B

A

B

Locator

This stepped section through the brain shows the basal nuclei located deep within the cerebral hemispheres. These nerve cell bodies control movement.

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Structure and role of the basal ganglia

The overall shape of the basal ganglia (nuclei) is complex, and is hard to imagine by looking at two-dimensional cross-sections.

Caudate nucleus

Thalamus

Lentiform nucleusConsists of putamen and globus pallidus

Amygdala

Tail of caudate nucleus

This diagram shows the brain in three dimensions. The size and shape of the basal ganglia can be seen in relation to other structures.

When seen in a three- dimensional view, the size and shape of the basal nuclei, together with their position within the brain as a whole, can be appreciated more easily.

In particular, the shape of the caudate nucleus can now be understood – it connects at its head with the putamen, then bends back to arch over

the thalamus before turning forwards again. The tip of the tail of the caudate nucleus ends as it merges with the amygdala, part of the limbic system (concerned with unconscious, autonomic functions).

ROLE OF THE BASAL NUCLEI

The functions of the basal

nuclei have been difficult to study because they lie deep within the brain and are therefore relatively inaccessible. Much of what is known of their function derives from the study of those patients who have disorders of the basal nuclei that lead to particular disruptions of movement and posture, such as

Parkinson’s disease.

A summary of what is currently known about the function of the basal nuclei is that: they help to produce movements which are appropriate; and they inhibit unwanted or inappropriate movements.

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Cerebellum

The cerebellum, which means ‘little brain’, lies under the occipital lobes of the cerebral cortex at the back of the brain. It is important to the subconscious control of movement.

The cerebellum has two hemispheres, one on either side of the worm-like vermis. The surface of the cerebellum is made up of thin folds (folia).

VermisCentral ‘wormlike’ portion of cerebellum which lies between two lateral hemispheres

PonsPart of the brainstem linking the medulla oblongata and the thalamus

Medulla oblongataUpper end of the spinal cord and lowest part of the brainstem

Flocculonodular lobeSmall, propeller-shaped lobe which lies on the underside of the cerebellum; made up of flocculus and central nodule (part of the vermis)

Central canal of spinal cord

Anterior lobeRelatively small lobe, separated from posterior lobe by deep primary fissure

Posterior lobeLargest of the three lobes, extending from primary fissure on upper surface of cerebellum to the posterolateral fissure on the underside

FoliaFine folds on surface of cerebellum, arranged transversely

The part of the brain known as the cerebellum lies under the occipital lobes of the cerebral cortex at the back of the head. The vital roles of the cerebellum include the co-ordination of movement and the maintenance of balance and posture. The cerebellum

works subconsciously and so an individual is not aware of its functioning.

STRUCTURE

The cerebellum is composed of two hemispheres which are bridged in the midline by the vermis. The hemispheres extend laterally (sideways)

and posteriorly (backwards)