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Central Nervous System • Brain • Cerebrum • Cerebellum • Diencephalon • Brain stem • Spinal Cord • Gray matter - cerebral cortex; outer layer of the brain • White matter - fibers beneath cortex and corpus callosum (fibers that connect the two halves of cerebral cortex) • Area of brain responsible for higher-order behaviors (learning, intelligence, awareness, etc.) Cerebrum Cerebrum • Gyri (gyrus): folds (rises) in cerebral hemispheres • Sulci (sulcus): shallow grooves • Divides the cerebral hemispheres into lobes • Fissures: deep grooves separating the gyri • Longitudinal fissure: prominent groove that divides cerebrum into right and left cerebral hemispheres Cerebellum • Located just caudal to cerebrum • Area of brain responsible for coordinated movement, balance, posture, and complex reflexes Diencephalon • Passageway between brain stem and cerebrum • Structures associated with diencephalon: • Thalamus, hypothalamus, and pituitary gland Brain Stem • Connection between brain and spinal cord • Medulla oblongata • Pons • Midbrain • Area of brain responsible for basic (subconscious, autonomic) functions of the body • HR • Breathing, coughing, sneezing, • BP • Many of the cranial nerves originate from this area of brain • Connective tissue layers that surround brain and spinal cord • Contain blood vessels, fluid, and fat • Supply nutrients and oxygen to the superficial tissues of the brain and spinal cord • Provide some cushioning and distribution of nutrients for CNS Meninges Meninges • Three layers: 1.Dura mater - tough, fibrous 2.Arachnoid - delicate, spiderweb-like 3.Pia mater - very thin; lies directly on surface of brain and spinal cord CSF—in subarachnoid space (Contains CSF) Cerebrospinal Fluid • Fluid between Arachnoid and Pia mater and in canals and ventricles inside brain and central canal of spinal cord • Provides cushioning function • May play role in regulation of autonomic functions such as respiration and vomiting Blood-Brain Barrier • Separates the capillaries in the brain from the nervous tissue • Capillary walls in the brain have no fenestrations; covered by cell membranes of glial cells • Prevents many drugs, proteins, ions, and other molecules from readily passing from the blood into the brain Cranial Nerves • 12 nerve pairs in PNS that originate directly from brain • Numbered in Roman numerals from I through XII (1 through 12) • Each nerve may contain axons of motor neurons, axons of sensory neurons, or combinations of both Spinal Cord • Medulla: central part of spinal cord • Composed of gray matter • A lot of nerve processing occurs here (not just in brain) • Central canal – center of medulla Spinal Cord • Cortex: outer part of spinal cord • White matter • Myelinated and unmyelinated nerve fibers • Surrounds the gray matter Spinal Cord • Dorsal and Ventral Nerve Roots emerge as Spinal Nerves from between each pair of adjacent vertebrae • Dorsal nerve roots contain sensory fibers • Ventral nerve roots contain motor fibers • Spinal nerve is a mix of sensory and motor neurons Autonomic Nervous System • Controls automatic functions at subconscious level • Sympathetic nervous system - nerves emerge from thoracic and lumbar vertebral regions (thoracolumbar system) • Parasympathetic nervous system - nerves emerge from brain and sacrum (cranial-sacral) Table 13-3. Effects of Sympathetic and Parasympathetic Nervous Systems Sympathetic System Parasympathetic System Effect Effect Heart rate Increases Decreases Force of heart contraction Increases No significant effect Diameter of bronchioles Increases (dilates) Decreases (constricts) Diameter of pupil Increases (dilates) Decreases (constricts) GI motility, secretions,and blood flow Decreases Increases Diameter of skin blood vessels Decreases No significant effect Diameter of muscle blood vessels Increases No significant effect Diameter of blood vessels to kidney Decreases No significant effect Neurotransmitters and Receptors • Sympathetic nervous system • 1º neurotransmitter—norepinephrine • Adrenergic neurons - neurons that release norepinephrine • Epinephrine/norepinephrine also released from adrenal medulla • To elicit an effect, effector organ must contain receptor for epi/norepi Neurotransmitters and Receptors • Smooth/Cardiac muscles may constrict or dilate in response to epi/norepi 1. α1- adrenergic receptors – cause vasoconstriction of skin, GI tract, and kidney [don’t need to digest, make urine, or bleed profusely} 2. β1-adrenergic receptors - increase heart rate and force of contraction 3. β2-adrenergic receptors - cause bronchodilation (relaxation) Neurotransmitters and Receptors • Parasympathetic nervous system • 1º neurotransmitter—acetylcholine • Cholinergic neurons - release acetylcholine • 2 types: • Nicotinic receptors • Muscarinic receptors Summary: receptor types Reflexes • Somatic reflexes - involve contraction of skeletal muscles • Autonomic reflexes - regulate smooth muscle, cardiac muscle, and endocrine glands • Contralateral reflex - starts on one side of body and travels to opposite side • Ipsilateral reflex - stimulus and response are on same side of body Reflex Arc 5 Components: • Sensory receptor—activated by stimulus • Sensory neuron—transports AP to gray matter of spinal cord or brain stem (cranial n.) and synapses with other neurons • • • Interneuron—sensory info integrated with info from other sensory neurons Motor Neuron—response is sent out via motor neuron Target organ—effector cell Stretch Reflex (tap knee) • Monosynaptic (1) reflex arc; ipsilateral reflex • Involves 1 sensory neuron and 1 motor neuron • Signals also sent to: • Antagonistic m (inhibitory) • Cerebellum/Cerebrum Withdrawal Reflex (toe pinch) • Also called flexor reflex; ipsilateral reflex • Several interneuron synapses • Several segments of spinal cord • Results in: • Contraction of muscles • Before cerebrum is aware • Inhibition of antagonist m Crossed Extensor Reflex • Contralateral reflex • Withdrawal reflex initiated • afferent sensory neuron synapses with interneurons • Causes contraction of opposite extensor muscles CNS Moderation of Reflexes • Upper CNS (brain) normally produces an inhibitory effect on the reflex arcs (muffled effect) • With injury, intact reflex arcs caudal to spinal cord trauma become hyperreflexive • Trauma to a portion of the reflex arc results in either hyporeflexive or absent reflexes