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NEUROANATOMY - I BY ADESEJI WASIU A. ALABI ADEOLA ADIGUN OLANIYI DEPARTMENT OF ANATOMY, UNIVERSITY OF ILORIN.

NEUROANATOMY - I

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Page 1: NEUROANATOMY - I

NEUROANATOMY - IBY

ADESEJI WASIU A.ALABI ADEOLA

ADIGUN OLANIYI

DEPARTMENT OF ANATOMY,UNIVERSITY OF ILORIN.

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Divisions of the Nervous System

2 main subdivisions: Central Nervous System

◦ the brain & spinal cord Peripheral Nervous System -

◦ groups of neurons called ganglia and peripheral nerves

◦ provides pathways to & from the central nervous system for electrochemical signals (impulses)

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The Peripheral Nervous System

Composed of 2 divisions: Somatic

◦ Provides sensory information (voluntary)◦ Transmits impulses to and from skeletal muscles - usually conscious actions

Autonomic ◦ motor system for viscera (smooth muscles & glands-involuntary)

◦ Autonomic is further divided into 2 subdivisions

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The Autonomic Nervous System

2 subdivisions of Autonomic: Sympathetic

◦ participates in body’s response to stress; fight or flight

Parasympathetic ◦ returns body to resting state & conserves resources

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Orientation of the PNS Dorsal roots carry sensory info to the spinal cord Ventral roots carry outgoing motor axons Peripheral nerves formed from dorsal & ventral roots Symmetry of PNS

◦ Arranged on 2 axis:◦ longitudinal: rostral to caudal ( head to tail)◦ dorsal to ventral (back to front)

Segmented:◦ 31 pairs of spinal nerves◦ 12 pairs of cranial nerves

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NeuronsThe basic and functional unit of the nervous system.Consist of a cell body (perikaryon) and processes arising from it.The processes arising from the cell body of a neuron are called neurites.Several short branching processes called Dendrites One longer process called an Axon

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Types of Neuron

1. UNIPOLAR

3. MULTIPOLAR

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SynapseSynapses are sites of junction between neurons.Types

axosomatic synapseaxoaxonal synapse dendro-axonic or dendro-dendriticsomato-dendritic

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Supporting cells of nervous system

Non conducting cells of the nervous systems.Collectively referred to as NeurogliaAstrocyteMicrogliaSchwann cellsOligodentrocytesThey provide mechanical support to neurons Serve as insulators and prevent neuronal impulsesfrom spreading in unwanted directions.

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The Central Nervous System

Consists of following Regions:◦ Spinal Cord◦ Brain

◦ Cerebrum◦ Cerebellum◦ Diencephalon: the caudal (posterior) part of the forebrain, containing the

epithalamus, thalamus, hypothalamus, and ventral thalamus and the third ventricle.

◦ Brain Stem◦ Midbrain◦ Medulla◦Pons

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Protection of the Brain & CNS

The skull & spinal column The Meninges

◦ 3 layers of tissue protecting brain◦ Dura mater

◦ outer tough layer ◦ Subdural space – normally small

◦ Arachnoid membrane ◦ next to dura mater◦ Subarachnoid space - spongy layer filled with cerebrospinal fluid

and blood vessels◦ Pia mater

◦ membrane that covers the brain Cerebrospinal fluid (CSF) - cushions brain; circulates around the brain & spinal cord

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The Spinal Cord- gross anatomy and internal structure

The spinal cord is roughly cylindrical in shape. It begins superiorly at the foramen magnum in the skull. It terminates inferiorly in the adult at the level of the lower border of the L1. In the young child, it usually ends at the upper border of L3.

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Spinal Cord (cont’d)ENLARGEMENTS

Cervical & lumbar enlargements

In the cervical region, it gives origin to the brachial plexus

In the lower thoracic and lumbar regions, it gives origin to the lumbosacral plexus

CONUS MEDULLARIS:

Inferiorly, the spinal cord tapers off into the conus medullaris.

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FILUM TERMINALE:

From the apex of conus medullaris

Prolongation of the pia mater, descends to be attached to the posterior surface

of coccyx.

FISSURE & SULCI

In the midline anteriorly, the anterior median fissure.

On the posterior surface, a shallow furrow, the posterior median sulcus.

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SPINAL NERVES Along the entire length of the spinal cord are attached 31 pairs of spinal nerves Cervical …… 8 Thoracic …… 12 Lumbar …… 5 Sacral …… 5 Coccygeal …..1 Each connects to the spinal cord by 2 roots – dorsal and ventral. Each root forms from a series of rootlets that attach along the whole length of the spinal cord segment. Ventral roots are motor while dorsal roots are sensory. The 2 roots join to form a spinal nerve prior to exiting the vertebral column. Almost immediately after emerging from its intervertebral foramen, a spinal nerve will divide into a dorsal ramus, a ventral ramus, and a meningeal branch that re-enters and innervates the meninges and associated blood vessels. Each ramus is mixed. Joined to the base of the ventral rami of spinal nerves in the thoracic region are the rami communicantes. These are

sympathetic fibers. Dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs.

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Plexuses

Except for T2 to T12, all ventral rami branch extensively and join one another lateral to the vertebral column forming complicated nerve plexuses.

Within a plexus, fibers from different rami criss cross each other and become redistributed.

Internal Structure:

The spinal cord is composed of an inner core of gray matter, which is surrounded by an outer covering of white matter.

GRAY MATTER

On cross section; the gray matter is seen as an H-shaped pillar with anterior and posterior gray columns, or horns, united by a thin gray commissure containing the small central canal.

A small lateral gray column or horn is present in the thoracic and upper lumbar segments of the cord.

The amount of gray matter present at any given level of the spinal cord is related to the amount of muscle innervated at that level.

Thus, its size is greatest within the cervical and lumbosacral enlargements of the cord.

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Grey and White Matter of Spinal CordWHITE MATTER

• The white matter, may be divided into anterior, lateral, and posterior white columns or funiculi.

• The anterior column on each side lies between the midline and the anterior nerve roots;

• The lateral column lies between the anterior and the posterior nerve roots;

• The posterior column lies between the posterior nerve roots and the midline.

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Spinal Cord Nuclei and laminae

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Ascending and descending tracts of spinal cord ↑ Sensory

◦ Gracile tract◦ Leg position & vibration

◦ Cuneate tract◦ Arm position & vibration

◦ Dorsal spinocerebellar tract◦ Strength & muscle speed

◦ Ventral spinocerebellar tract◦ Modulation; interneurons

◦ Lateral spinothalamic tract◦ Pain & temperature

◦ Anterior spinothalamic tract◦ Light touch

◦ Spinocervical thalamic tract

◦ Kinesthetic movement & discriminative touch

↓ Motor◦ Corticospinal tract

◦ Speed & agility

◦ Reticulospinal tract◦ Differential facilitation of motor neurons

◦ Rubrospinal tract◦ Fix movement errors

◦ Lateral vestibulospinal tract◦ Extensor & posture

◦ Medial vestibulospinal tract◦ Flexor & head position

◦ Tectospinal tract◦ Head turning

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Clinical Anatomy of spinal cordDevelopmental anomalies: Spinal bifida

–meningomyelocoele, meningomyelocoele, rachischisis

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•Tabes dorsalis (syphilitic myelopathy)

–complication of advanced syphilis (Treponema pallidum)

•Damage to dorsal root ganglion (or spinal ganglion)

•degeneration (demyelination) of dorsal column fibres

•Loss of proprioceptive sense (position sense), and discriminative touch

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Lumbar puncture

•Gives access to the spinal subarachnoid space

•Needle inserted between L3/L4 or L4/L5

•Structures traversed during lumbar puncture:

–Skin

–Subcutaneous tissue

–Supraspinous ligament

–Interspinous ligament

–Ligamentum flavum

–Epidural tissue

–Spinal dura

–Arachnoid mater

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Epidural injections –Lumbar epidural 

•(for anaesthetic/analgesic injections) –Caudal epidural– Cervical/thoracic epidural  

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Amyotrophic Lateral Sclerosis, ALS (or

Lou Gehrig’s Disease

• Upper and lower motor neuron disease – with gradual degeneration of

motor neurons – Progressive weakening of

skeletal muscles occurs • atrophy and fasciculation (fine

twitching) occur • May involve genetic factor

– Mutation of SOD1 gene (on xsome 21) reported

– FALS runs in family • Symptoms starts around 40-

60 years (more in men) • Patient may die from

respiratory failure – due to paralysis of diaphragm

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The Brain Remaining 6 areas of the CNS are part of the brain The control center of the body

◦ Regulates body activity; enables you to think  Surface is gray matter - 6 x 106 cell bodies / cc Under gray matter is white matter - formed of myelinated axons.

 Surface of the brain (neocortex) is convoluted◦ Increases surface area◦ ridges = gyri◦ grooves = sulci

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Forebrain, Midbrain, Hindbrain

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The Cerebral Hemispheres Largest region of brain; 7/8 by weight - Includes:

◦ Cerebral cortex – outer surface of gray matter◦ underlying white matter◦ 3 nuclei (clusters of related neurons):

◦ the basal ganglia◦ the hippocampal formation◦ the amygdala◦ these are masses of gray matter at the base of the cerebrum that serve the motor cortex

◦ paired cavities =   lateral ventricles ◦ Divided into 2 ‘half spheres’ = hemisheres

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The Cerebral Cortex The convoluted outer surface

◦ grooves = sulci◦ elevated regions = gyri

Composed of gray matter 2-5 mm thick Contains ~ 12 billion neurons Most of the cerebral cortex is concerned with processing sensory information or motor commands

2 bands of tissue – one sensory, one motor Divided into primary, secondary, & tertiary

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The Forebrain Telencephalon

◦ Olfactory bulb◦ Cerebral cortex◦ Basal telencephalon (basal ganglia)◦ Corpus callosum

◦ commissure between cerebral hemispheres◦ Internal capsule

◦ connections with brain stem◦ Lateral ventricles

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Lobes of the Cerebrum 2 sides called hemispheres Joined by a bridge = Corpus Callosum Separated by a deep fissure front to back Like 2 mirror images (but not quite) Divided into 4 lobes

◦ 1. Frontal◦ 2. Parietal◦ 3. Temporal◦ 4. Occipital

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Lobes of the Cerebrum

Parietal Lobe

Temporal Lobe

Frontal Lobe

Limbic Lobe

Occipital Lobe

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The Frontal LobeIntellectual functioningReasoningAggressionSexual behaviorSpeechSmellVoluntary movements

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The Parietal LobeBody sensory awareness (including taste)LanguageAbstract thought, especially mathBody imaging

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The Temporal LobeIncludes part of limbic system*Emotion*Interpretation of languageHearingMemory

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The Occipital LobeReceiving, interpreting, & discriminating visual stimuli Association of visual stimuli with memory

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Ventral View

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Sagittal Section

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Superolateral surface

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Superolateral surface

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Medial surface

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Medial surface

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Inferior surface

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White matter of Cerebral hemisphereThe surface of the cerebral hemisphere is covered by a thin layer of grey matter called the cerebral cortex.The greater part of the cerebral hemisphere deep to the cortex is occupied by white matter within which are embedded certain important masses of grey matter.These fibres may be: Association fibres that interconnect different regions of the cerebral cortex.Projection fibres that connect the cerebral cortex with other masses of grey

matter; and vice versa.Commissural fibres that interconnect identical areas in the two hemispheres.

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Internal capsuleThe internal capsule may be divided into the following parts. The anterior limb lies between the caudate nucleus medially, and the anterior part of

the lentiform nucleus laterally. The posterior limb lies between the thalamus medially, and the posterior part of the

lentiform nucleus on the lateral side. In transverse sections through the cerebral hemisphere the anterior and posterior

limbs of the internal capsule are seen to meet at an angle open outwards. This angle is called the genu (genu = bend).

Some fibres of the internal capsule lie behind the posterior end of the lentiform nucleus. They constitute its retrolentiform part.

Some other fibres pass below the lentiform nucleus (and not medial to it). These fibres constitute the sublentiform part of the internal capsule

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Functional areas

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The Primary Sensory & Motor Cortex

Primary Motor Cortex: ◦ controls voluntary movements of limbs & trunk◦ contains neurons that project directly to spinal cord to activate somatic motor neurons

Primary Sensory Areas ◦ receive information from peripheral receptors with only a few synaptic relays interposed

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Brodmann Areas Cytoarchitectural areas of neocortex Regions with similar cell structure Numbered

◦ each represents a functionally distinct area Examples:

◦ Area 17 is the primary visual cortex ◦ at the caudal pole of the occipital lobe

◦ Area 4 is the primary motor cortex ◦ primary auditory cortex on left side of temporal lobe near language center

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Secondary & Tertiary Areas Surrounding primary areas are higher order (secondary & tertiary) sensory & motor areas

◦ Process & integrate info coming from the primary sensory areas.

Higher order motor areas send complex info required for motor actions to primary motor areas 

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Association AreasThree other large regions of cortex surround the primary, secondary & tertiary areas Called association areas

In primates, association areas are majority of cortex

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Localization of Cortical Functions

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Lobes of the Brain & Associated Regions

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Integration of Brain FunctionsInteractions of all areas sensory, motor & motivational systems is essential for behavior.

Example: throw a ball - info about motion of ball, impact of ball, position of arms, legs, hands, etc. - sensory, motor, motivational systems

Anatomical organization of each major functional system (sensory, motor, motivational) follows 4 principles

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Principles of Anatomical Organization

Each system contains relay centers◦ These don’t just transmit info; also modify it◦ Most important relay center is the thalamus◦ almost all sensory info to cerebral cortex processed by thalamus

Each system is composed of several distinct pathways◦ Example: touch & pain

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Principles of Anatomical Organization (Cont.)

Each pathway is topographically organized◦ neural map - clustered functions

Most pathways cross the body’s midline◦ Thus each hemisphere controls the actions/sensations of the opposite side.

◦ Left side dominates language; right side -spatial perception, musical ability

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Diencephalon Thalamus & hypothalamus taken together Important structures found in the cerebrum Between the midbrain & cerebral hemispheres

◦ Thalamus◦ Hypothalamus ◦ Third ventricle

Retina and optic nerves ◦ develop from optic vesicle that pouches off from diencephalon during development

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The Thalamus & Hypothalamus Thalamus

◦ relay center - processes & distributes almost all sensory & motor info going to the cerebral cortex

◦ links nervous & endocrine system◦ emotional control

Hypothalamus◦ under the thalamus◦ regulates autonomic nervous system◦ connects to thalamus, midbrain & some cortical areas◦ Controls body temperature, thirst, hunger, emotional behavior

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Cerebellum The cerebellum consists of a part lying near the midline called the vermis, and of two lateral hemispheres.two surfaces, superior and inferiorDorsal to the pons & medulla Mostly white matter covered with a thin layer of gray matterPleated surface; divided into several lobesReceives sensory input from the spinal cord, motor info from the cerebral cortex & input about balance from receptors in the inner earTherefore, can coordinate planning & timing of voluntary muscle movement & maintain balance

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The Medulla Oblongata & Pons

Medulla Oblongata◦ Bottom (rostral) region of the brainstem◦ Regulates blood pressure and respiration; controls breathing, swallowing, digestion, heart & blood vessels.

Pons ◦ Above medulla◦ links cerebellum to cerebrum; relays info from cerebral hemispheres to cerebellum

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The Midbrain Mesencephalon

◦ Tectum (roof) ◦ superior colliculus + inferior colliculus

◦ Tegmentum (floor) ◦ Cerebral aqueduct

Controls responses to sight (e.g. eye movements) Relay station of auditory & visual signals Motor control of some skeletal muscles

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The Brainstem Anatomically, from the bottom up:

◦ Medulla Oblongata◦ Pons◦ Midbrain

Taken together = brainstem◦ Contains all the nerves that connect the spinal cord with the cerebrum

◦ Receives sensory info from head, face, & neck◦ Motor neurons control muscles of head & neck◦ 12 pairs of cranial nerves carry input & output◦ Also involved in hearing, taste & balance

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The Limbic System A functional & evolutionary division, rather than anatomical

Group of structures in center of the brain above the brainstem:◦ hypothalamus◦ pituitary◦ hippocampus

◦ important role in memory◦ hippocampal gyrus◦ amygdala

◦ coordinates actions of the autonomic & endocrine systems

◦ involved in emotions

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Functions of the Limbic System

Sometimes called the “mammalian brain because most highly developed in mammals

One of the oldest areas of brain from an evolutionary standpoint

Maintains homeostasis: e.g. helps maintain temperature, blood pressure, heart rate, blood sugar

Also involved in emotional reactions needed for survival

4 F’s: fleeing, fighting, feeding.

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Visualizing the Limbic System

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Clinical Anatomy of Brain

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Ipsilateral/Contralateral The cerebral hemispheres are involved with inputs and outputs from the contralateral side of the body◦ Damage to neocortex causes problems on the opposite side

◦ In patients with epilepsy, surgeons occasionally cut corpus callosum to relieve seizures. Flash different pictures in each eye, patients could describe what they saw with right eye, but not left, but could pick out object - example: Heart = ART.

The cerebellum is involved with the control of movement on the ipsilateral side of the body.◦ Damage to the cerebellum causes motor deficits on the same side.

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Injury MechanismsThe brain is a complex and delicate organ, and one that is vulnerable to injury from a variety of different traumas. These include: Frontal Lobe Injury Occipital Lobe Injury Temporal Lobe Injury Side Impact Injury Coup/Contre-coup Injury Diffuse Axonal Injury Epidural Hematoma Subdural Hematoma

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Frontal Lobe InjuryThe frontal lobe of the brain can be injured from direct impact on the front of the head.

During impact, the brain tissue is accelerated forward into the bony skull. This can cause bruising of the brain tissue and tearing of blood vessels.

Frontal lobe injuries can cause changes in personality, as well as many different kinds of disturbances in cognition and memory.

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Occipital Lobe InjuryOccipital lobe injuries occur from blows to the back of the head.

This can cause bruising of the brain tissue and tearing of blood vessels.

These injuries can result in vision problems or even blindness.

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Temporal Lobe InjuryThe temporal lobe of the brain is vulnerable to injury from impacts of the front of the head.

The temporal lobe lies upon the bony ridges of the inside of the skull, and rapid acceleration can cause the brain tissue to smash into the bone, causing tissue damage or bleeding.

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Side Impact InjuryInjuries to the right or left side of the brain can occur from injuries to the side of the head.

Injuries to this part of the brain can result in language or speech difficulties, and sensory or motor problems.

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Coup/Contre-coup InjuryA French phrase that describes bruises that occur at two sites in the brain.

When the head is struck, the impact causes the brain to bump the opposite side of the skull. Damage occurs at the area of impact and on the opposite side of the brain.

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Diffuse Axonal InjuryBrain injury does not require a direct head impact. During rapid acceleration of the head, some parts of the brain can move separately from other parts. This type of motion creates shear forces that can destroy axons necessary for brain functioning.

These shear forces can stretch the nerve bundles of the brain.

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Diffuse Axonal InjuryThe brain is a complex network of interconnections. Critical nerve tracts can be sheared and stressed during an acceleration-type of injury.

Diffuse axonal injury is a very serious injury, as it directly impacts the major pathways of the brain.

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Epidural HematomaAn epidural hematoma is a blood clot that forms between the skull and the top lining of the brain (dura).

This blood clot can cause fast changes in the pressure inside the brain.

When the brain tissue is compressed, it can quickly result in compromised blood flow and neuron damage.

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Subdural HematomaA subdural hematoma is a blood clot that forms between the dura and the brain tissue.

The clot may cause increased pressure and may need to be removed surgically.

When the brain tissue is compressed, it can quickly result in compromised blood flow and tissue damage.

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