The Brain and Cranial Nerves

Biology 315. Anatomy and Physiology I. Chapter 14. The Brain and Cranial Nerves. Tortora and Grabowski, 13th edition. 2012. I. Brain Organization, Protection, and Nourishment. A. Major Parts of the Brain: brain stem, cerebellum, diencephalon, and cerebrum B. Blood Flow Through the Brain. : substantial; 20% cardiac output at rest; Lack of blood flow > a couple of minutes = permanent damage. Glucose supply must be constant (Sx of hyper/hypoglycemia) 1. Arterial supply A. internal carotid arteries B. Vertebral arteries. R. and L vertebral arteries join to become basilar artery inside the cranium 2.

Venous drainage: venous sinuses into internal jugular veins 3. Blood Brain Barrier: protective A) Tight jctns. seal endothelial cells of brain capillaries B. Astrocytes processes press up against capillary walls C. Lipid soluble substances pass easily; some other substances cross via AT, some slowly C. Protective coverings of the brain 1. Cranial meninges like spinal meninges: dura, arachnoid, pia 2. Extensions of dura separate parts of the brain *falx cerebri = separates the 2 hemispheres of cerebrum *falx cerebelli = separates the 2 hemispheres of the CBLM *tentorium cerebelli = separates the cerebrum from CBLM

D. Cerebrospinal Fluid; 1. Mechanical protection: shock absorber 2. Chemical protection: optimal chemical environment for accurate neuronal signaling. 3. Circulation/ medium for exchange of O2, nutrients, wastes, etc. 4. Produced in choroid plexuses = capillary networks and ependymal cells in ventricular walls; A. 1. Continuous circulation of CSF thru ventricles, spinal canal, and subarachnoid space. Lateral ventricles (separated by septum pellucidum) ? through Interventricular foramina? 3rd ventricle (in diencephalon) ? cerebral aqueduct of Sylvius in midbrain ? 4th ventricle in brain stem ?

Three openings in roof of 4th ventricle ? Subarachnoid space, central canal of spinal cord 5. Reabsorption into blood via : arachnoid villi in superior sagittal sinus 6. Production must equal reabsorption ! About 125 ml total at any time, maintain constant pressure. Read about hydrocephalus. II. The Brain Stem. = medulla, pons, midbrain. A. Medulla: a continuation of the spinal cord to the pons 1. White matter: both sensory and motor tracts are present A. Motor: Pyramids bulges on the anterior side of medulla: the pyramidal tract/ direct pathways *pyramidal decussation. 0% of right crosses to L, and 90% L crosses to R® side of brain controls most of L side of body. B. Sensory. *medial lemniscus: axons from gracile and cuneate nuclei through medulla, pons, midbrain. 2. Grey Matter: = nuclei A. Cardiovascular center (h. r. , force of contraction, b. v. diameter) B. Rhythmicity center for resp. rate C. Other: vomiting center; coughing center, etc. D. Olivary nuclei : lateral swelings E. Nuclei of posterior column system *gracile and cuneate nuclei F. Nuclei for cranial nerves VIII, IX, X, XI, XII. B. Pons (= bridge) , between medulla and pons. 1. Nuclei/ Gray matter pneumotaxic center, apneustic center; help control breathing *Nuclei for cranial nerves V, VI, VII, VIII. 2. White Matter : ascending sensory and descending motor tracts. C. Midbrain = mesencephalon; from pons to diencephalon 1. Cerebral aqueduct passes through here 2. White matter *cerebral peduncles = continuations of corticospinal, corticopontine, corticobulbar tracts + sensory tracts 3. Gray matter *Tectum = posterior side of midbrain. 2 sets of paired bumps. –superior colliculi ( visual reflexes, tracking images, pupillary reflex, accommodation reflex, etc. ) – inferior colliculi (auditory reflexes, e. . , startle reflex ) *substantia nigra (lack of dopamine here associated with Parkinson’s Disease) *red nucleus (rubro); synapses from tracts in cerebrum/CBLM re: coordination *Nuclei of Cranial Nerves III, IV. D. Reticular Formation: involves both grey matter and white matter, 1. through brainstem and into the diencephalon. 2. Both ascending (“sensory”) and descending (“motor”) neurons 3. Reticular Activating System: sensory axons which project to the cerebral cortex; Center for arousal, consciousness, etc. E. g. , a stroke to this area would result in a comatose state. III. Cerebellum A.

Structure: 1. Tentorium cerebelli (dura separating the cerebrum from cerebellum) *groove called transverse fissure. 2. Central area: vermis Vs. Lateral lobes = CBLR hemispheres 3. Anterior vs. posterior lobes of each hemisphere 4. Flocculonodular lobe: small, on inferior surface. 5. CBLR cortex arranged in folia (leaves) 6. White matter = arbor vitae 7. CBLR nuclei: deeper nuclei, within white matter B. Connections with other parts of the brain 1. Inferior CBLR peduncle: white matter, connects CBLM to medulla 2. Middle CBLR peduncle: white matter, connects CBLM to pons (largest) 3.

Superior CBLR peduncle: white matter connects CBLM to midbrain and thalamus C. Functions: 1. Coordination, prediction, balance/equilibrium; does not initiate voluntary movement 2. Another way to say it: compares intended movements with what is actually happening in order to smooth and coordinate complex, skilled movements. Regulates posture and balance. May have a role in cognition and language processing IV. Diencephalon. : from brain stem towards cerebrum; surrounds 3rd ventricle A. Thalamus: 80% of diencephalon 1. Paired, oval masses of grey matter organized into nuclei 2. Two sides connected by intermediate mass of the thalamus . Sensory Function *: major relay center for most sensations that project to the cortex; *thalamus sorts out the modalities of sensation and sends them on. *only crude perception of sensation (pain, heat, pressure) in the thalamus itself *part of limbic system, connects to hypothalamus * associated with memory, emotions, etc. 4. Motor: relays info from CBLM and basal ganglia to primary motor cortex *contributes to RAS, autonomic activities. 5. Structure: *axonal fibers connecting the thalamus and cerebral cortextravel through the internal capsule, just lateral to the thalamus. Many nuclei involved in various functions: we will not distinguish these. Just recognize the complexity of this small organ. B. Hypothalamus: speaking of complex, small organs……. 12+ nuclei in 4 major regions. We will not cover specific nuclei. 1. Structures to know: * Supra-optic region: just superior to the optic chiasm * Mammillary bodies: 2 rounded projections assoc. with smell 2. Functions of the hypothalamus: *control/integration of ANS *hormone production (oxytocin; ADH; releasing factors to pituitary) *regulation of emotional/behavioral patterns (in concert with limbic system): rage, aggression, pain, pleasure, sexual arousal satiety center *thirst center *body temperature control (thermostat is here) *regulation of circadian rhythms, states of consciousness. C. Epithalamus: 1. pineal gland: secretes melatonin, which promotes sleepiness/ biological clock 2. some other nuclei associated with emotional response to odors. D. Subthalamus: tracts + nuclei Red nucleus + substantia nigra + subthalamic nuclei work with basal ganglia, CBLM, cerebrum to control body movements. E. Circumventricular Organs= Parts of the diencephalon which lie in the walls of the 3rd and 4th ventricles. They monitor changes in blood chemistry (they lack a BBB)

Includes: pituitary, part of hypothalamus, pineal, etc. V. Cerebrum: the “brains” of the matter. A. Basic Structure: 1. R and L cerebral hemispheres, connected at the corpus callosum (white matter) 2. Cerebral cortex = gray matter; deeper layers = white matter. 3. Folds of cortex = gyri / convolutions 4. Deepest grooves between gyri = fissures *longitudinal fissure separates hemispheres 5. Shallower grooves = sulci. B. Lobes of cerebrum 1. Frontal separated from Parietal by central sulcus *precentral gyrus = primary motor cortex *postcentral gyrus = primary sensory cortex 2.

Frontal lobe separated from Temporal lobe by lateral cerebral sulcus 3. Parietal lobe separated from Occipital lobe by parieto-occipital sulcus 4. Insula: lies within lateral cerebral sulcus, deep to parietal, frontal, and temporal lobes C. Cerebral white matter: 3 types of tracts 1. Association tracts: conduct nerve impulses between gyri within the same hemisphere 2. Commissural tracts: conduct nerve impulses between gyri in one cerebral hemisphere to other *anterior commissure *posterior commissure *corpus callosum 3. Projection tracts = conduct nerve impulses from cerebrum to lower parts of the

CNS or from lower parts of CNS to the cerebrum *internal capsule (both ascending and descending fibers) D. Basal Ganglia: These are nuclei (but they are called ganglia) deep within cerebrum. 1. Names: know that these terms refer to basal ganglia. *globus pallidus *putamen) These two together = corpus striatum *caudate ) *substantia nigra/ subthalamic nuclei also considered part of / closely assoc. with basal ganglia. 2. Function: poorly understood. Generally coordinate movement. * muscle tone *subconscious, stereotyped, patterned movement, like swinging your arms when you walk *According to Guyton, Stimulation of centers near the subthalamic nuclei can cause rhythmic limb motions, including forward walking reflexes. This does not mean that the individual muscles of walking are controlled from this region, but simply that excitation of this region sends “command” signals to activate the cord centers where preprogrammed neuronal circuits then cause the actual walking movements. “ *e. g. , cat with lesions in certain areas can walk in normal fashion, but, when it comes to a wall, it simply butts its head against the obstruction and tries to keep on walking. Thus, the cat lacks purposefulness of locomotion. e. g. , equilibrium, working with CBLM *e. g. , maintain background muscle tone for intended movements, such as playing the piano, doing surgery, etc. *functions of basal ganglia poorly understood. Most information comes from studies of patients with specific lesions, nearly all of which involve dyskinesias. , such as chorea = random, gross, uncontrolled movement. These are often brisk, graceful, and may resemble fragments of purposeful movement athetosis = slow, writhing movements, often seen in CP hemiballismus = big, violent, forceful involuntary movements tremor = resting; as in Parkinsonism. also involved in some cognitive processes, emotional behaviors, etc. , with limbic system. E. Limbic system = a wishbone-shaped group of structures that encircle the brain stem and function in emotional aspects of behavior related to survival, especially involuntary aspects of behavior; acquisition of new memory; pleasure/ pain/ sex/ rage. The “emotional” brain. Some of the structures include: 1. Limbic lobe = rim of cerebral cortex on the medial surface of each hemisphere. Includes hippocampus (major site for memory acquisition) and other areas. 2. Dentate gyrus 3. Amygdala 4. Some thalamic nuclei 5. Some hypothalamus . Olfactory bulbs 7. Fornix 8. + others F. Brain Injuries: problems with oxygen supply, reoxygenation, direct tissue damage 1. Concussion: abrupt, temporary loss of consciousness; from a blow to the head or sudden stopping of a moving head. No obvious bruising of brain. 2. Contusion = bruising of brain due to trauma and includes leakage of blood from microscopic vessels; pia may be torn and allow blood to enter subarachnoid space. Usually a short loss of consciousness…… 3. Laceration = tear of the brain, usually from skull fracture or gunshot wound, includes bleeding into the brain and subarachnoid space.

Increased intracranial pressure. VI. Cerebral cortex areas and functions: Sensory vs. motor vs. association. A. Sensory areas. (Areas of cortex are referred to as numbers) 1. Primary somatosensory (or just sensory) cortex: postcentral gyrus and adjacent areas. Receives information about *touch, pressure, proprioception, temperature, tickle, itch, etc. , and localizes those to specific parts of the body *amount of area receiving impulses from particular part of the body depends on the number of receptors in that area, not the size of that area. E. g. , more area for fingertips than small of back. . Primary visual area: posterior tip of occipital lobe. Receives information about *color *shape *movement of visual stimuli 3. Primary auditory area : superior part of temporal lobe. Receives info. Re: *pitch *rhythm *loudness of sound 4. Primary gustatory area: base of postcentral gyrus. Impulses for taste. 5. Primary olfactory area: temporal lobe, on medial aspect. For smell B. Motor areas: 1. Primary Motor Area: (area 4) = precentral gyrus (UMN) 2. Broca’s speech area = frontal lobe, next to lateral cerebral sulcus. 97% of people have this structure in their left hemisphere.

For expressive speech If damaged, expressive aphasia C. Association Areas: some motor, some sensory 1. Somatosensory association area: posterior to postcentral gyrus *integrates and interprets sensations. Makes them meaningful, relates them to past sensations. 2. Visual association area: anterior to primary visual cortex in occipital lobe. *relates present/past visual experiences; recognition and evaluation of what is seen 3. Auditory association area: inferior and posterior to primary auditory cortex in temporal lobe. Lets you identify sound as music, speech, noise, etc. 4.

Wernicke’s area – interpretive speech area ; interprets speech of others into your thoughts. Recognizes spoken words. If damaged, cannot understand speech. 5. Common integrative area: bordered by the main sensory association areas. Integrates sensations into meaning; transmits signals to other parts of the brain to cause the appropriate response. You can identify music as Beethoven’s Fifth; speech as that coming from Mom, etc. 6. Premotor area: just anterior to precentral gyrus. Deals with learned motor activities of a complex and sequential nature. E. g. , kicking a soccer ball; playing the piano; writing a word. . Frontal eye field: (with premotor area): controls voluntary scanning movements of the eyes used in e. g. , reading. D. Hemispheric Lateralization 1. Some asymmetry between hemispheres 2. Left hemisphere receives sensory info and sends motor info on/to right hemisphere 3. Most people: * left hemisphere more important for reasoning, numerical/scientific skills, language. *right hemisphere more for mesical/artistic awarenes, spatial/pattern perception, emotional content of language, facial recognition, etc. *identified via PET scans E. Brain waves = summation of all A Ps and graded potentials . Electroencephalogram/ EEG 2. Wave patterns *alpha= awake, resting with your eyes closed *beta = nervous system is active, with sensory input and mental activity *theta = in children and adults experiencing emotional stress and in disorders of the brain *delta = only present during deep sleep in adults, but also normally present in awake infants. VII. Cranial Nerves: 12 pairs; originate in brain and pass through foramina; part of PNS I. Olfactory : all sensory; nerve fibers pass from nasal olfactory epithelium through cribriform plate of the ethmoid to the olfactory bulb. >primary olfactory area in temporal lobe II. Optic ; all sensory. Optic nerve forms from ganglion cells in retina, travels through optic canal –> optic chiasm –> optic tracts. Medial half of optic nerve crosses to other side. –> lateral geniculate nucleus of thalamus –> primary visual cortex. Some connections to superior colliculus (from diencephalon) III. Oculomotor: primarily motor. (Midbrain) *SR, IR, IO, MR eye muscles + upper eyelid (lev. palp. superioris) *pupillary reflex IV. Trochlear : primarily motor (midbrain) *SO eye muscle V. Trigeminal: both (pons)

Ophthalmic nerve: touch/ pain/ thermal Maxillary nerve“ + maxillary teeth, upper lip Mandibular nerve“ + mandibular teeth, lower lip + motor to muscles of mastication VI. Abducens : primarily motor (pons) LR eye muscle VII. Facial: mixed (pons) Sensory: taste from anterior 2/3 of tongue + proprioception Motor: muscles of facial expression Parasympathetic: lacrimal glands, nasal glands, palatine glands, salivary glands VIII. Vestibulocochlear (Auditory or Acoustic) ; primarily sensory Vestibular: equilibrium; from semicircular canals, saccule, utricle of vestibular system, ends in pons

Auditory: hearing; from organ of Corti; to medulla IX. Glossopharyngeal : mixed (medulla) Sensory: taste from post. 1/3 of tongue, proprioceptors, stretch receptors in carotid sinus, chemoreceptors in carotid body. Motor: parasympathetic to parotid gland; stylopharyngeus muscle and pharyngeal muscles X. Vagus: mixed (medulla); Sensory: skin of external ear; proprioceptors in throat/neck muscles; visceral sensory receptors from thorax and abdomen Motor: Parasympathetic to everything down to left colic flexure (lungs, heart, gut) XI. Accessory (“Spinal Accessory” mixed; originates from medulla + spinal cord

Sensory: proprioceptors in muscles supplied by motor neurons, to medulla Motor: pharyngeal muscles, laryngeal, soft palate; sternomastoid + trapezius XII. Hypoglossal : mixed; (medulla) Sensory: from tongue; proprioception Motor: muscles of tongue Review cranial nerve tests (in lab manual) VIII. Development of Nervous System: omit IX. Aging and the Nervous System: slight decrease in brain mass with age. X. Disorders: Homeostatic Imbalances A. CVA: Hemorrhage; emboli/blood clots = stroke; atherosclerosis See risk factors: tPA given and somewhat effective if given within 3 hours of onset AND if it’s a CVA/stroke caused by a clot

B. TIAs : temporary cerebral dysfunction caused by impaired blood flow to the brain. Sx: dizzy; weak; headache; motor impairment; visual problems, etc. No permanent effects but predictive of higher risk of CVA C. Alzheimer Disease: cause: unknown; only about 1 % is known genetic structural abnormalities: loss of cholinergic neurons Beta-amyloid plaques deposited outside neurons Neurofibrillary tangles inside neurons long, slow death. Terminal event usually some complication of bed-ridden patients, such as pneumonia, UTI A Ch E inhibitors improves alertness/behavior in a small percentage of pts.

XI. Medical Terminology agnosia: inability to recognize the significance of sensory stimuli such as sounds, sights, smells, tastes, and touch apraxia: inability to carry out purposeful movements but the person is not paralyzed delirium: transient condition involving abnormal cognition, disordered attention, psychomotor behavior….. Dementia: permanent, progressive loss of intellectual abilities… personality, etc. Encephalitis: Lethargy: “functional sluggishness” condition Stupor: unresponsiveness from which a patient can be aroused only briefly and only by vigorous and repeated stimulation


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