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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