Chapter 14 The Brain and Cranial Nerves

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Chapter 14The Brain and Cranial Nerves

• Largest organ in the body at almost 3 lb.• Brain functions in sensations, memory, emotions, decision

making, behavior

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Principal Parts of the Brain

• Cerebrum• Diencephalon

– thalamus & hypothalamus

• Cerebellum• Brainstem

– medulla, pons & midbrain

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Blood Supply to Brain• Arterial blood supply is branches from circle of

Willis on base of brain (page 699 or next slide)

• Vessels on surface of brain----penetrate tissue

• Uses 20% of our bodies oxygen & glucose needs

– blood flow to an area increases with activity in that area

– deprivation of O2 for 4 min does permanent injury

• at that time, lysosome release enzymes

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Subarachnoid Haemorrhage

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Middle Meningeal Artery –epidural

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Venous Drainage• Superior saggital sinus etc- in subdural

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Bridging Veins – subdural space

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Subdural Haemorrhage

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Protective Coverings of the Brain

• Bone, meninges & fluid

• Meninges same as around the spinal cord– dura mater

– arachnoid mater

– pia mater

• Dura mater extensions– falx cerebri

– tentorium cerebelli

– falx cerebelli

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Meninges

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Blood Brain Barrier

• Blood-brain barrier (BBB)– protects cells from some toxins and pathogens

• proteins & antibiotics can not pass but alcohol & anesthetics do

– tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries

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What goes in and What Doesn’t• Lipid Soluble- O2, CO2, ETOH, anesth all pass

easily the BBB

• Watersoluble, glucose, urea, creatinine, ions pass slowly or in the case of glucose, via active transport only

• BBB is not uniform throughout, some areas are more permeable and thus bacteria can get in

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Cerebrospinal Fluid (CSF)

• 80-150 ml (3-5oz)

• Clear liquid containing glucose, proteins, & ions

• Functions– mechanical protection

• floats brain & softens impact with bony walls

– chemical protection• optimal ionic concentrations for action potentials

– circulation• nutrients and waste products to and from bloodstream

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Origin of CSF

• Choroid plexus = capillaries covered by ependymal cells– 2 lateral ventricles, one within each cerebral hemisphere

– roof of 3rd ventricle

– fourth ventricle

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Drainage of CSF from Ventricles

• One median aperture & two lateral apertures allow CSF to exit from the interior of the brain

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Cerebral Perfusion Pressure

• CPP = MABP – ICP

• Cerebral auto regulation

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Hydrocephalus• Blockage of drainage of CSF (tumor,

inflammation, developmental malformation, meningitis, hemorrhage or injury

• Continued production cause an increase in pressure --- hydrocephalus

• In newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissue

• Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen

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Medulla Oblongata• Continuation of spinal cord• Ascending sensory tracts• Descending motor tracts• Nuclei of 5 cranial nerves• Cardiovascular center

– force & rate of heart beat– diameter of blood vessels

• Respiratory center– medullary rhythmicity area sets basic rhythm of breathing

• Information in & out of cerebellum• Reflex centers for coughing, sneezing, swallowing etc

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Injury to the Medulla

• Hard blow to the back of the head may be fatal• Cranial nerve malfunctions on same side as injury;

loss of sensation or paralysis of throat or tongue; irregularities in breathing and heart rhythm

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Pons

• One inch long• White fiber tracts

ascend and descend• Pneumotaxic &

apneustic areas help control breathing

• Middle cerebellar peduncles carry sensory info to the cerebellum

• Cranial nerves 5 thru 7

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Midbrain

• One inch in length• Extends from pons to

diencephalon• Cerebral aqueduct

connects 3rd ventricle above to 4th ventricle below

• Visual reflex centers and auditory relay (startle reflex)

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Midbrain in Section

• Cerebral peduncles---clusters of motor & sensory fibers

• Substantia nigra---helps controls subconscious muscle activity

• Red nucleus-- rich blood supply & iron-containing pigment– cortex & cerebellum coordinate muscular movements by sending

information here from the cortex and cerebellum

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Reticular Formation

• Scattered nuclei in medulla, pons & midbrain

• Reticular activating system– alerts cerebral cortex to sensory signals (sound of

alarm, flash light, smoke or intruder) to awaken from sleep

– maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles

• Motor function is involvement with maintaining muscle tone

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Cerebellum

• 2 cerebellar hemispheres and vermis (central area)• Function

– correct voluntary muscle contraction and posture based on sensory data from body about actual movements

– sense of equilibrium

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Cerebellum

• Transverse fissure between cerebellum & cerebrum• Cerebellar cortex (folia) & central nuclei are grey matter• Arbor vitae = tree of life = white matter

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Diencephalon Surrounds 3rd Ventricle

• Surrounds 3rd ventricle• Superior part of walls is thalamus

• Inferior part of walls & floor is hypothalamus

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Thalamus

• 1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass)

• Relay station for sensory information on way to cortex• Crude perception of some sensations

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Thalamic Nuclei

• Nuclei have different roles– relays auditory and visual impulses, taste and somatic sensations – receives impulses from cerebellum or basal ganglia– anterior nucleus concerned with emotions, memory and

acquisition of knowledge (cognition)

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Hypothalamus

• Dozen or so nuclei in 4 major regions – mammillary bodies are relay station for olfactory reflexes;

infundibulum suspends the pituitary gland

• Major regulator of homeostasis– receives somatic and visceral input, taste, smell & hearing information;

monitors osmotic pressure, temperature of blood

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Functions of Hypothalamus

• Controls and integrates activities of the ANS which regulates smooth, cardiac muscle and glands

• Synthesizes regulatory hormones that control the anterior pituitary

• Contains cell bodies of axons that end in posterior pituitary where they secrete hormones

• Regulates rage, aggression, pain, pleasure & arousal• Feeding, thirst & satiety centers• Controls body temperature• Regulates daily patterns of sleep

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Cerebrum (Cerebral Hemispheres)

• Cerebral cortex is gray matteroverlying white matter– 2-4 mm thick containing billions

of cells– grew so quickly formed folds

(gyri) and grooves (sulci or fissures)

• Longitudinal fissure separates left & right cerebral hemispheres

• Corpus callosum is band of white matter connecting left and right cerebral hemispheres

• Each hemisphere is subdivided into 4 lobes

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Lobes and Fissures • Longitudinal fissure (green)

• Frontal lobe

• Central sulcus (yellow)– precentral & postcentral gyrus

• Parietal lobe

• Parieto-occipital sulcus

• Occipital lobe

• Lateral sulcus (blue)

• Temporal lobe

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Basal Ganglia

• Connections to red nucleus, substantia nigra & subthalamus• Input & output with cerebral cortex, thalamus &

hypothalamus• Control large automatic movements of skeletal muscles

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Limbic System

• Parahippocampal & cingulate gyri & hippocampus• Emotional brain--intense pleasure & intense pain• Strong emotions increase efficiency of memory

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Brain Injuries• Causes of damage

– displacement or distortion of tissue at impact– increased intracranial pressure– infections– free radical damage after ischemia

• Concussion---temporary loss of consciousness– headache, drowsiness, confusion, lack of concentration

• Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF)

• Laceration--tearing of brain (fracture or bullet)– increased intracranial pressure from hematoma

Types of Injuries Cont

• Epidural bleed –arterial- Middle meningeal artery – retrograde unconsiousness -treated Burr holes

• SubDural Bleed –venous- bridging veins

• Subarchnoid bleed- arterial-Circle of Willis

• Moderate axonal injury

• Diffuse axonal tearing injury

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Sensory Areas of Cerebral Cortex

Receive sensory information from the thalamusPrimary somatosensory area = postcentral gyrus = 1,2,3Primary visual area = 17Primary auditory area = 41 & 42Primary gustatory area = 43

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Motor Areas of Cerebral Cortex

• Voluntary motor initiation– Primary motor area = 4 = precentral gyrus

• controls voluntary contractions of skeletal muscles on other side

– Motor speech area = 44 = Broca’s area• production of speech -- control of tongue & airway

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Association Areas of Cerebral Cortex (FYI)

• Somatosensory area = 5 & 7 (integrate & interpret)• Visual association area = 18 & 19 (recognize & evaluate)• Auditory association area(Wernicke’s) = 22(words become speech)• Gnostic area = 5,7,39 & 40 (integrate all senses & respond)• Premotor area = 6 (learned skilled movements such as typing)• Frontal eye field =8 (scanning eye movements such as phone book)

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Aphasia• Language areas are located in the left cerebral

hemisphere of most people• Inability to use or comprehend words = aphasia

– nonfluent aphasia = inability to properly form words• know what want to say but can not speak • damage to Broca’s speech area

– fluent aphasia = faulty understanding of spoken or written words

• faulty understanding of spoken or written words– word deafness = an inability to understand spoken words– word blindness = an inability to understand written words

• damage to common integrative area or auditory association area

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Hemispheric Lateralization• Functional

specialization of each hemisphere more pronounced in men

• Females have larger connections between 2 sides

• Damage to left side produces aphasia

• Damage to same area on right side produces speech with little emotional inflection

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The Spinal Cord• Extends from the foramen magnum of the

skull to L¹ or L² ; the dural and arachnoid membranes extend to the level of S², well beyond the end of the spinal cord which makes this an ideal location for a lumbar tap

• 31 pairs of spinal nerves attach to the cord by paired roots and exit from the vertebral column via the intervertebral foramina to travel to the body regions they serve

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The Spinal Cord

• It is about the width of a thumb for most of its length, but is enlarged in the cervical and lumbosacral regions, where the nerves serving the upper and lower limbs arise

• The collection of nerve roots at the inferior end of the vertebral canal is named the cauda equina

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The Spinal Cord: Gray Matter and Spinal Roots

• Looks like the letter “H” or a butterfly with the cross-bar of gray matter called the gray commissure that encloses the central canal

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The Spinal Cord: Gray Matter and Spinal Roots

• Dorsal and Ventral Roots: very short and fuse laterally to form the spinal nerves

• The spinal nerves form the peripheral nervous system

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The Spinal Cord: White Matter• Composed of myelinated and unmyelinated

nerve fibers that allow communication between different parts of the spinal cord and between the cord and brain

• (1) Ascending: up to higher centers (sensory inputs) (2) Descending: down to the cord from the brain or within the cord to lower levels (motor outputs) (3) Transversely: across from one side of the cord to the other (commissural fibers)

• Ascending and descending make up most of the white matter

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Spinal cord InjuriesThe following list outlines which muscle functions may be retained at

progressively lower levels of spinal cord transection.  C1–C3: no function maintained from the neck down; ventilator needed

for breathing

C4–C5: diaphragm, which allows breathing

C6–C7: some arm and chest muscles, which allows feeding, some dressing, and propelling wheelchair

T1–T3: intact arm function

T4–T9: control of trunk above the umbilicus  T10–L1: most thigh muscles, which allows walking with long leg braces

L1–L2: most leg muscles, which allows walking with short leg braces