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Lecture 11

Week/Lecture 11: Brain and Cranial Nerves.pdf

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Humber College
BIOL 171

Brain and Cranial Nerves Spinal nerves are organized into plexuses The Brain sensations, memory, emotions, decision making, movement brain communicates with the body via the spinal cord and 12 pairs of cranial nerves Main parts of the Brain cerebrum cerebellum diencephalon thalamus hypothalamus brainstem midbrain pons medulla Ventricles four hollow chambers within the brain 2 lateral ventricles (1 in each cerebral hemisphere) not "1st and 2nd" ventricles, but "the lateral ventricles" 3rd ventricle (medial to thalamus) 4th ventricle (between cerebellum and brainstem) pituitary gland works with nervous and endocrine system optic chiasm optic nerves cross into optic chiasm, enter optic tract to brain brain stem Blood Supply to Brain branches from the circle of Willis blood is sent to circle of Willis, then is transported across the brain where needed brain is 2% of body weight, but consumes 20% of oxygen and glucose blood flow to brain regions increases with neuronal activity Protective Coverings of the Brain bone, meninges, CSF meninges same as around the spinal cord (dura, arachnoid and pia maters) dural sinus (carries venous blood — jugular veins — heart) dural partitions (falx cerebri, tentorium cerebelli, falx cerebelli) extend into fissures, support brain from moving in skull falx cerebri fills space between hemispheres tentorium cerebelli divides cerebrum from cerebellum Blood-Brain Barrier consists of: brain capillary endothelial cells joined by tight junctions continuous basement membrane processes of astrocytes wrap around capillaries as extra barrier prevents passage of many toxins and pathogens (proteins, antibiotics can't cross; glucose, alcohol, anesthetics can) Cerebrospinal fluid clear, colourless liquid in which the brain floats (slows movement of brain) 80-150 mL- fills ventricles, surrounds CNS protects brain, spinal cord transports nutrients and metabolic wastes proves stable chemical environment (homeostatic balance of chemicals) specialized fluid in specialized place Flow of Cerebrospinal Fluid secreted from choroid plexuses (capillaries covered by ependymal cells) in walls of ventricles leaves ependymal cells and enters lateral ventricles specialized capillaries; majority of fluid in CSF is made in blood plexus: network ependymal: glial cells Passage of CSF lateral ventricle — interventricular foramen — 3rd ventricle — cerebral aqueduct — 4th ventricle 4th ventricle — median and lateral apertures — subarachnoid space OR central canal of spinal cord subarachnoid space: outside of brain cerebral aqueduct: small tube that transports CSF Reabsorption of CSF CSF returns to blood via arachnoid villi (grapelike clusters of arachnoid mater protruding into dural sinuses) arachnoid villi forces CSF out of subarachnoid space CSF drains to dural sinuses then to jugular veins Brainstem (3 regions) midbrain extends from pons (inferiorally) to diencephalon co-ordination of muscle movements (along with cerebellum) visual and auditory reflex centres cranial nerves 3+4 arise from midbrain pons bridge between medulla and midbrain centres that control patterns of breathing cranial nerves 5-7 arise from pons medulla oblongata continuation of spinal cord contains: ascending and descending tracts pathways to/from cerebellum nuclei of 5 cranial nerves vital control centres: cardiac centre (rate/force of heartbeat) vasomotor centre (blood pressure; constriction/dilation of blood vessels) respiratory centre (rate/depth of breathing) misc. centres: coughing, sneezing, hiccuping, swallowing, vomiting, sweating Reticular Formation diffuse network of neurons in medulla, pons, midbrain helps regulate muscle tone Reticular Activating System (RAS) regulates level of consciousness RAS "disconnects" when sleeping so no information coming or going (until a problem arises) if a problem: alerts cerebrum to sensory signals (afferent pathways run through RAS to thalamus) cerebrum is aroused to deal with problem can recognize light flashes, sounds, somatic signals RAS cannot recognize smell (smoke) pain signals create increased arousal throughout brain Cerebellum vermis (worm-like) in centre of superior surface 2 hemispheres automatic processing centre compares motor commands with input from proprioceptors monitors motor commands and makes sure they are co- ordinating to create right muscle action maintains posture, muscle tone, balance co-ordinates, smooths complex sequences of skilled muscle movements cerebellar peduncles attach cerebellum to brainstem superior cerebellar peduncle motor to midbrain (minor changes in motor movements) middle cerebellar peduncle motor to pons (voluntary movements) inferior cerebellar peduncle sensory from midbrain (balance) Diencephalon made up of thalamus and hypothalamus thalamus forms lateral walls of 3rd ventricle relay centre for auditory, visual, taste, somatic impulses (not smell) receives impulses from spinal cord, brainstem, cerebellum, basal nuclei role in awareness, emotions, memory, cognition acts as "phone operator": plugs in/connects info from different areas hypothalamus controls ANS and endocrine system major regulator of homeostasis controls: water and electrolyte balance food intake body temperature heart rate hormone secretion sleep patterns emotions (pain, pleasure, rage, aggression) sexual response Cerebral Topography Lobes and Fissures surface folded into gyri (outward fold of brain tissue), separated by sulci (shallow grooves) and fissures (deep grooves) longitudinal fissure (divides cerebrum into 2 hemispheres) central sulcus (runs laterally, through centre of brain)
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