Chapter 14
The Brain and Cranial Nerves
•Largest organ in the body at almost 3 lb.
•Brain functions in sensations, memory, emotions, decision making, behavior
Principal Parts of the Brain
•Cerebrum
•Diencephalon
–thalamus & hypothalam= us
•Cerebellum
•Brainstem
–medulla, pons & midbr= ain
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
Blood Supply to Brain
•Arterial blood supply is branches from circle of Willis on base of brain (page 699)<= /p>
•Vessels on surface of brain----penetrate tissue
•Uses 20% of our bodies oxygen & glucose needs
–blood flow to an area inc= reases with activity in that area
–deprivation of O2 for 4 m= in does permanent injury
•at that time, lysosome release enzymes
•Blood-brain barrier (BBB)
–protects cells from some = toxins and pathogens
•proteins & antibiotics can not pass but alcohol & anesthetics do
–tight junctions seal toge= ther epithelial cells, continuous basement membrane, astrocyte processes covering capillaries
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 concentrati= ons for action potentials
–circulation
•nutrients and waste produ= cts to and from bloodstream
Drainage of CSF from Ventricles
•One median aperture & two lateral apertures allow CSF to exit from the inte= rior of the brain
Reabsorption of CSF
•Reabsorbed through arachnoid villi
–grapelike clusters of ara= chnoid penetrate dural venous sinus
•20 ml/hour reabsorption rate =3D same as production rate
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 expan= sion 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
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 are= a sets basic rhythm of breathing
•Information in & out of cerebellum
•Reflex centers for coughing, sneezing, swallowing etc
XII =3D Hypoglossal Nerve
•Controls muscles of tongue during speech and swallowing
•Injury deviates tongue to injured side when protruded
•Mixed, primarily motor
X =3D Vagus Nerve
•Receives sensations from viscera
•Controls cardiac muscle and smooth muscle of the viscera
•Controls secretion of digestive fluids
VIII =3D Vestibulocochlear Nerve
•Cochlear branch begins in medulla
–receptors in cochlea
–hearing
–if damaged deafness or ti= nnitus (ringing) is produced
•Vestibular branch begins in pons
–receptors in vestibular apparatus
–sense of balance
–vertigo (feeling of rotat= ion)
–ataxia (lack of coordinat= ion)
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
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
VII =3D Facial Nerve
•Motor portion
–facial muscles
–salivary & nasal and = oral mucous glands & tears
•Sensory portion
–taste buds on anterior 2/3’s of tongue
V =3D Trigeminal Nerve
•Motor portion
–muscles of mastication
•Sensory portion
–touch, pain, & temper= ature receptors of the face
•ophthalmic branch
•maxillary branch
•mandibular branch
Midbrain
•One inch in length
•Extends from pons to diencephalon
•Cerebral aqueduct connects 3rd ventricle above to 4th ventricle below
Cerebellum
•2 cerebellar hemispheres and vermis (central area)
•Function
–correct voluntary muscle contraction and posture based on sensory data from body about actual moveme= nts
–sense of equilibrium
Cerebellum
•Transverse fissure between cerebellum & cerebrum
•Cerebellar cortex (folia) & central nuclei are grey matter
•Arbor vitae =3D tree of life =3D white matter
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
Hypothalamus
•Dozen or so nuclei in 4 major regions
–mammillary bodies are rel=
ay
station for olfactory reflexes;
infundibulum suspends the pituitary gland
•Major regulator of homeostasis
–receives somatic and visc= eral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood
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
Epithalamus
•Pineal gland
–endocrine gland the size = of small pea
–secretes melatonin during darkness
–promotes sleepiness &= sets biological clock
•Habenular nuclei
–emotional responses to od= ors
Subthalamus & CVO
–sites of entry of HIV virus into brain (dementia)
Cerebrum
(Cerebral Hemispheres)
•Cerebral
cortex is gray matter
overlying white matter
–2-4 mm thick containing
billions
of cells
–grew so quickly formed fo=
lds
(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 hemisph= eres
•Each hemisphere is subdivided into 4 lobes
Lobes and Fissures
•Longitudinal fissure (gre= en)
•Frontal lobe
•Central sulcus (yellow)
–precentral & postcentral gyrus
•Parietal lobe
•Parieto-occipital sulcus<= /p>
•Occipital lobe
•Lateral sulcus (blue)
•Temporal lobe
•=
Insula
Limbic System
•Emotional brain--intense pleasure & intense pain
•Strong emotions in=
crease
efficiency of memory
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
Sensory Areas of Cerebral Cortex
Receive sensory information from the thalamus
&nbs= p; Primary somatosensory area =3D postcentral gyrus =3D 1,2,3
&nbs= p; Primary visual area =3D 17
&nbs= p; Primary auditory area =3D 41 & 42
&nbs= p; Primary gustatory area =3D 43
&nbs= p;
Motor Areas of Cerebral Cortex
•Voluntary motor initiation
–Primary motor area =3D 4 = =3D precentral gyrus
•controls voluntary contractions of skeletal muscles on other side
–Motor speech area =3D 44 = =3D Broca’s area
•production of speech -- control of tongue & airway
Association Areas of Cerebral Cortex
•Somatosensory area =3D 5 = & 7 (integrate & interpret)
•Visual association area = =3D 18 & 19 (recognize & evaluate)
•Auditory association area(Wernicke’s) =3D 22(words become speech)
•Gnostic area =3D 5,7,39 &= amp; 40 (integrate all senses & respond)
•Premotor area =3D 6 (lear= ned skilled movements such as typing)
•Frontal eye field =3D8 (s= canning eye movements such as phone book)
Aphasia
•Language areas are located in the left cerebral hemisphere of most people
•Inability to use or comprehend words =3D aphasia
–nonfluent aphasia =3D inability to properly form words
•know what want to say but= can not speak
•damage to Broca’s s= peech area
–fluent aphasia =3D faulty understanding of spoken or written words
•faulty understanding of s= poken or written words
–word deafness =3D an inability to understand spoken words
–word blindness =3D an inability to understand written words
Hemispheric Lateralization
•Functional specialization= of each hemisphere more pronounced in men
•Females have larger conne= ctions between 2 sides
•Damage to left side produ= ces aphasia
•Damage to same area on ri= ght side produces speech with little emotional inflection
Electroencephalogram (EEG)
•Brain waves are millions of nerve action potentials in cerebral cortex
–diagnosis of brain disord= ers (epilepsy)
–brain death (absence of activity in 2 EEGs 24 hours apart)
•Alpha -- awake & resting
•Beta -- mental activity
•Theta -- emotional stress
•Delta -- deep sleep
II -- Optic Nerve
•Connects to retina supplying vision
I -- Olfactory Nerve
•Extends from olfactory mucosa of nasal cavity to olfactory bulb
•Sense of smell
Aging & the Nervous System
•Years 1 to 2
–rapid increase in size due to increase in size of neurons, growth of neuroglia, myelination & development of dendritic branches
•Early adulthood until death
–brain weight declines until only 93% by age 80
–number of synaptic contacts declines
–processing of information diminishes
–conduction velocity decreases
–voluntary motor movements slow down
–reflexes slow down
Cerebrovascular Accident (CVA)
•Third leading cause of death after heart attacks and cancer
•2 types of strokes
–ischemic due to decreased blood flow
–hemorrhagic due to rupture of blood vessel
•Risk factors
–high blood pressure, high cholesterol, heart disease, diabetes, smoking, obesity, alcohol
•Tissue plasminogen activator (t-PA) used within 3 hours of onset will decrease permanent disability
Transient Ischemic Attack (TIA)
•Episode of temporary cerebral dysfunction
•Cause
–impaired blood flow to the brain
•Symptoms
–dizziness, slurred speech, numbness, paralysis on one side, double vision
–reach maximum intensity almost immediately
–persists for 5-10 minutes & leaves no deficits
•Treatment is aspirin or anticoagulants; artery bypass grafting or carotid endarterect= omy
Alzheimer Disease (AD)
•Dementia =3D loss of reasoning, ability to read, write, talk, eat & walk
•Afflicts 11% of population over 65
•Loss of neurons that release acetylcholine
•Plaques of abnormal proteins outside neurons
•Tangled protein filaments within neurons
•Risk factors -- head injury, heredity
•Beneficial effects of estrogen, vitamin E, ibuprofen & ginko biloba