AP BIOLOGY THE NERVOUS SYSTEM DIVISIONS OF THE

A. AUTONOMIC NERVOUS SYSTEM regulates the body’s automatic or involuntary functions motor neurons that conduct impulses from: central nervous system to cardiac muscle smooth muscle glandular epithelial tissue 3

AUTONOMIC NERVOUS SYSTEM 1. Composed of two divisions: Sympathetic Nervous System = flight or fight Anger fear Hate anxiety 2. Parasympathetic Nervous System = rest and digest sexual arousal Salivation lacrimation (tears) Urination digestion defecation 4

PARASYMPATHETIC AND SYMPATHETIC GROUPS Normally work antagonistically � Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis Many visceral effectors are doubly innervated � receive fibers from parasympathetic and sympathetic divisions � are influenced in opposite ways by the two divisions

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B. SOMATIC NERVOUS SYSTEM the voluntary control of body movements via skeletal muscles consists of efferent nerves responsible for stimulating muscle contraction including all the non sensory neurons connected with skeletal muscles and skin 7

GENERAL INFORMATION ABOUT THE NERVOUS SYSTEM 8

NEURONS Classification according to function: Sensory (afferent) neurons: conduct impulses to the spinal cord and brain Motor (efferent) neurons: conduct impulses away from brain and spinal cord to muscles and glands Interneurons: conduct impulses from sensory neurons to motor neurons 9

1. NEURONS – REVIEW! Consist of three main parts: dendrites 2. cell body of neuron 3. Axon 1. Dendrites conduct impulses to cell body of neuron Axons conduct impulses away from cell body of neuron 10

AXON DIFFERENCES 1. Myelinated axons: Myelin = white, fatty substance created by Schwann cells 2. Neurilemma = outer membrane of schwann cells responsible for regeneration of cut or injured axons Only in the PNS Nodes of Ranvier Unmyelinated axons: 11

2. GLIA (NEUROGLIA) Support cells, bringing the cells of nervous tissue together structurally and functionally Three main types of glial cells of the CNS: 1. Astrocytes — star-shaped cells that anchor small blood vessels to neurons Forms blood-brain-barrier 2. 3. Microglia — small cells that move in inflamed brain tissue carrying on phagocytosis (scavengers) Oligodendrocytes — form myelin sheaths on axons in the CNS Holds tissue together 12

GLIA Glioma – common brain tumor 13

NERVES Nerve = bundle of axons Tract — bundle of CNS axons White matter — tissue composed primarily of myelinated axons (nerves or tracts) Gray matter — tissue composed primarily of cell bodies and unmyelinated fibers 14

REFLEX ARCS Nerve impulses are conducted from receptors to effectors over neuron pathways One way conduction only results in a reflex (contraction by a muscle or secretion by a gland) Two-neuron arcs — consisting of sensory neurons synapsing in the spinal cord with motor neurons Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons 15

Know these terms: • receptor • sensory neuron • synapse • motor neuron • effector 16

ANATOMY OF REFLEX ARC Receptor – Located in tendons, skin, mucous membranes Beginning of dendrites of sensory neuron Sensory Neuron – Sends generated impulse to spinal cord Synapse – Microscope space between two neurons Motor Neuron – Carries impulse away from spinal cord to the effector Effector – Tissue that puts the impulse into effect 17

NERVE IMPULSES Self-propagating wave of electrical disturbance that travels along the surface of a neuron AKA – action potential Mechanism: A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron Inward movement of positive sodium ions leaves a slight excess of negative ions outside at a stimulated point; marks the beginning of a nerve impulse 18

ACTION POTENTIALS ARE ALL-ORNOTHING Only occurs if the stimulus causes enough sodium ions to enter the cell to change the membrane potential (depolarization) to a certain threshold level. If the depolarization is not great enough to reach the threshold, then an action potential (and hence an impulse) WILL NOT be produced.

Resting state has slight + charge on outside and slight - on the inside Due to excess Na+ on outside of membrane When stimulated Na+ channels open - the opening and closing is a domino effect down the nerve cell

THE ACTION POTENTIAL SPIKES WHEN THRESHOLD IS REACHED

TYPES OF CONDUCTION Salutatory Conduction: If impulse encounters myelin it jumps around myelin faster Continuous Conduction: NO myelin slower

ANATOMY OF A SYNAPSE Presynaptic neuron Postsynaptic neuron Synaptic knob Neurotransmitter Synaptic cleft Receptors 24

THE SYNAPSE Chemical compounds released from axon terminals (of a presynaptic neuron) into a synaptic cleft Compounds then bind to specific receptor molecules in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane 25

NEUROTRANSMITTERS Acetylcholine – stimulates skeletal muscle contractions Norepinephrine – stress hormone involved in fight or flight response Serotonin Dopamine 26

THE CENTRAL NERVOUS SYSTEM 27

1. THE BRAIN 28

DIVISIONS OF THE BRAIN Brainstem Consists of three parts of brain: medulla oblongata pons midbrain Structure — white matter with bits of gray matter scattered through it Function — gray matter in the brainstem functions as reflex centers heartbeat, respirations, and blood vessel diameter Sensory tracts conduct impulses to the higher parts of the brain Motor tracts conduct from the higher parts of the brain to the spinal cord 29

DIVISIONS OF THE BRAIN Diencephalon = hypothalamus & thalamus 30

DIVISIONS OF THE BRAIN Hypothalamus Consists mainly of the: posterior pituitary gland pituitary stalk gray matter 1. 2. 3. Functions: Helps control the functioning of most internal organs Acts as the major center for controlling the ANS Controls hormone secretion by anterior and posterior pituitary glands indirectly helps control hormone secretion by most other endocrine glands Contains centers for controlling body temperature, appetite, wakefulness, and pleasure 31

DIVISIONS OF THE BRAIN Thalamus Dumbbell-shaped mass of gray matter in each cerebral hemisphere 1. 2. Functions: Relays sensory impulses to cerebral cortex sensory areas Produces the emotions of pleasantness or unpleasantness associated with sensations 32

DIVISIONS OF THE BRAIN Cerebellum Second largest part of the human brain Helps control muscle contractions to produce coordinated movements to maintain balance, move smoothly, and sustain normal postures 33

DIVISIONS OF THE BRAIN Cerebrum Largest part of the human brain Outer layer of gray matter = cerebral cortex made up of lobes composed mainly of dendrites and cell bodies of neurons Interior of the cerebrum composed mainly of white matter nerve fibers arranged in bundles called tracts Functions: mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements 34

2. SPINAL CORD 35

SPINAL CORD Outer part - white matter made up of many bundles of axons = tracts Interior - gray matter made up mainly of neuron dendrites and cell bodies Functions: center for all spinal cord reflexes sensory tracts conduct impulses to the brain motor tracts conduct impulses from the brain 36

Touch & pressure Muscle length Voluntary movements Muscle length Crude touch, pain & temp

COVERINGS AND FLUID SPACES OF THE BRAIN AND SPINAL CORD 1. Cranial bones and vertebrae 2. Cerebral and spinal meninges: : dura mater pia mater arachnoid mater 3. Fluid spaces: subarachnoid spaces of meninges central canal inside cord ventricles in brain 38

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PERIPHERAL NERVOUS SYSTEM 40

NERVE TYPES Cranial nerves: Twelve pairs — attached to undersurface of the brain Connect brain with the neck and structures in the thorax and abdomen Spinal nerves: Structure — contain dendrites of sensory neurons and axons of motor neurons Functions — conduct impulses necessary for sensations and voluntary movements 41

KNOW THESE CRANIAL NERVES! I – olfactory II – optic III – oculomotor IV – trochlear V – trigeminal VI – abducens VII – facial VIII – vestibulocochlear IX – glossopharyngeal X – vagus XI – accessory XII - hypoglossal 42

INTERESTING REVIEW: 43