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The Brain Anatomy and Physiology Membranes cover the brain and spinal cord • Membranes are called meninges • Three layers: dura mater, arachnoid mater, and pia mater • Dura mater is outer, arachnoid is middle, pia is innermost. Meninges Meninges Meninges • Between the arachnoid and pia maters is the subarachnoid space, which contains cerebrospinal fluid. • A series of spaces in the brain, called ventricles, also contain cerebrospinal fluid. Cerebrospinal Fluid • Is secreted by specialized capillaries of the dura mater layer. These special tissues are called choroid plexuses. • The fluid circulates through the ventricles and is reabsorbed into the blood Cerebrospinal Fluid • The pressure remains fairly constant, as fluid is secreted and absorbed continuously • The brain and spinal cord “float” in the fluid, which supports and protects them • Also controls ions and carries waste to blood Pressure can be measured, and samples of fluid can be taken to diagnose infections Meningitis Meninges become inflamed, may be viral or bacterial Major Regions of the Brain • Cerebrum: largest part; sensory and motor functions, higher reasoning skills • Diencephalon: processes sensory info • Cerebellum: coordinate voluntary muscle • Brain Stem: regulates visceral activities Cerebrum • Divided into lobes • Lobes are named after the skull bones they underlie • Two hemispheres divided by corpus callosum • Convoluted surface • Outermost part is the cerebral cortex Cerebrum Cerebrum Cerebral Cortex Diencephalon • Located between cerebral hemispheres and above the midbrain • Contains the thalamus, hypothalamus, optic tracts, posterior pituitary gland, pineal gland Diencephalon Brain Stem • Connects cerebrum to the spinal cord • Consists of midbrain, pons, medulla oblongata Functions of Brain Stem • Relay center • Reflex center • Medulla oblongata contains regulatory centers for heart rate, constriction and dilation of blood vessels, respiration Cerebellum • Reflex center for integrating sensory information concerning the position of body parts • Coordinates complex skeletal muscle movements Hemisphere Dominance • Everyone uses both hemispheres in basic functions • Right side controls motor functions of the left side; left side controls motor functions of the right side. (stroke) Hemisphere Dominance • Most people have a dominant hemisphere, although you can be equally right and left brained • “Right brained” or “left brained” refers to which hemisphere is dominant • Determines your manner of thinking; they are not the same! Hemisphere Dominance Left Brain thinkers are • Logical and sequential • Rational • Analytical • Objective • Look at the parts Right brain thinkers are • Random • Intuitive • Holistic • Synthesizing • Subjective • Look at wholes Hemisphere Dominance “Right brains” often choose as careers • Athletes • Entrepreneurs • Sales • Artist • Musician • Craftsman • dancer Hemisphere Dominance “Left brains” often choose careers in • Law • Accounting • Science • Medicine Cranial Nerves • Twelve pairs of cranial nerves arise from the inferior side of the brain • 1st pair comes from cerebrum • Other 11 pairs originate from brain stem • Lead to parts of the head, neck, and trunk Each nerve has a name and a roman numeral A Career Cut Short by Spinal Cord Injury The Spinal Cord • Two functions: conduct nerve impulses; reflex center • Is part of the CNS • Is a nerve column going down from brain into the vertebral column • Ends near the 1st or 2nd lumbar vertebrae • Surrounded by meninges, which continue below the L1 and L2 vertebrae Where would you do a spinal tap to collect CSF without damaging the spinal cord? Spinal Cord • A cross section shows a core of gray matter surrounded by white matter • Gray matter = unmylenated axons and neuron cell bodies • White matter = masses of mylenated axons Notice the three layers of meninges • The white matter contains 3 sections of longitudinal bundles called nerve tracts (posterior, anterior, and lateral) • Ascending tracts of nerves carry sensory information to the brain • Descending tracts carry motor impulses to muscle or glands Spinal Cord posterior lateral Anterior Spinal Nerve Tracts Posterior section of white matter contains only ascending nerve tracts The anterior and lateral sections of white matter contain both ascending and descending nerve tracts Spinal Nerves • Coming off the spinal cord are 31 pairs of spinal nerves • Grouped and labeled according to the level of vertebrae they come from • These nerves are part of the PNS C1-C8; T1-T12; L1-L5; S1-S5 Spinal Nerves • The 31 pairs branch out to serve various parts of the body • Which nerve serves which parts of the body can be seen on a dermatome map Autonomic vs Somatic nervous Systems • Somatic: motor pathways of PNS that lead to the skin and skeletal muscles • Autonomic: happens without conscious effort— maintains homeostasis by regulating smooth muscles, blood pressure, breathing rate, heart rate, etc. Two Divisions of Autonomic • Sympathetic, which prepares the body for stressful, emergency situations • Parasympathetic, which is most active during ordinary, restful conditions, and returns the body to normal conditions after the emergency Autonomic Nerve Fibers • Are arranged slightly differently than somatic nerve fibers • A pathway from the brain or spinal cord to the skeletal muscle contains two neurons instead of just one Page 241 in your textbook Autonomic Nerve Fibers • The first neuron leaves the brain or spinal cord and joins with a mass of neurons called a ganglion. This neuron is preganglionic. The second neuron that leaves the ganglion is called postganglionic Autonomic Neurotransmitters • Acetylcholine is the neurotransmitter secreted by preganglionic fibers of both the sympathetic and parasympathetic divisions. The postganglionic fibers of the parasympathetic also secrete acetylcholine • Norepinephrine is the neurotransmitter secreted by the postganglionic fibers of the sympathetic division. Autonomic Control • Brain and spinal cord control most of its activities • Medulla oblongata receives sensory impulses and send motor responses • Hypothalamus regulates body temp, hunger, thirst, water and electrolyte balances. • Other brain areas control autonomic system during emotional stress