Exam II Study Guide Functional Anatomy and Physiology Chapter 11 Fundamentals of the Nervous System and Nervous Tissue Nervous system o Sensory input Integration Motor Output Sensory function input to sense changes in the internal and external environment through sensory receptors Afferent pathway begins in the peripheral and travels towards the central NS Integrative function to analyze sensory information store some aspects and make decisions regarding appropriate behaviors INTERNEURONS WILL NOT BE ON EXAM 2 Motor function output to respond to stimuli by initiating action Efferent pathway begins in the CNS and travels towards the o Nervous System Divisions Central and Peripheral peripheral Central NS consists of the brain and the spinal cord Peripheral NS consists of cranial and spinal nerves that contain both sensory and motor fiber connects CNS to muscles glands all sensory receptors Peripheral Nervous System o Sensory afferent Somatic fibers impulses from skin skeletal muscles and joints to the brain o Motor efferent o Motor Division Visceral fibers impusles from visceral organs to the brain Impulses from the CNS to effector organs Somatic Nervous System controls voluntary actions motor neurons that conduct impulses from CNS to skeletal muscles only Autonomic Nervous System WILL NOT BE ON EXAM 2 o Neurons Nerve Cells functional units cells of the nervous system have the capacity to produce action potentials electrical excitability Structure Dendrites and soma receptive or input regions of the neuron integral proteins act as receptors Neurotransmitter produced by the soma transmits neural impulse that travels along axon released from axon terminals by exocytosis transported by vesicle and received by the receptors in the soma and dendrites of postsynaptic neuron Functions of neurons convert stimuli into electric signals action potentials that travel to other neurons muscle tissue or glands Myelin Sheath Schwann cells myelinate wrap around axons in the PNS peripheral nervous system Whitish fatty segmented sheath around most long axons Functions to increase the speed of the nerve impulse Rate of impulse propagation is determined by o Axon diameter the larger the diameter the faster o the impulse o Presence of a myelin sheath myelination dramatically increases impulse speed Unmyelinated Axons Neurons without myelin SLOWER nerve impulse conduction than myelineted neurons 1 Anterior ventral horn cell 2 Peripheral nerve ventral and dorsal nerve roots 3 Neuromuscular junction 4 Muscle White and Gray Matter o White matter primarily myelinated axons less mass looks whiter o Gray matter neuronal cell bodies dendrites unmyelinated axons axon terminals darker part of brain towards the cortex more mass soma found in cortex The Action Potential membrane Types of Ion Channels o MOST IMPORTANT Ligand gated channels open and close in the response to a stimulus results in neuron excitability o Voltage gated channels respond to direct change in the membrane potential o Resting Membrane Potential electrical potential difference across the plasma Negative along inside of the cell membrane positive along the outside Potential energy difference at rest 70 mV Resting potential exists due the different concentrations of ions inside and outside the cell extracellular fluid OUTSIDE of cell rich in Na and Cl cytosol INSIDE of cell rich in K organic phosphates and amino acids Factors that contribute to resting membrane potential Different concentrations of ions inside and outside cell Membrane permeability differes for sodium and potassium K more permeability inward flow of sodium cant keep up with outward flow of K sodium potassium pump removes Na as fast as it diffuses leaks in Na K pump facilitated diffusion o Action Potential all or nothing electrical signal nerve impulse is a sequence of rapidly occurring events that decrease and eventually reverse membrane potential depolarizing phase and then restore it to the resting state repolarizing phase Voltage gated Na and K channels open in sequence If stimulus reaches threshold action potential is always the same Stronger stimulus will not cause a larger impulse o 1 Depolarization change from negative to positive charge due to sodium going into the cell producing an electrical change sodium diffuses using facilitated diffusion sodium concentration will always be greater on the outside o 2 Repolarization K channels open Na channels close K outflow returns membrane potential to 70 mV rest recovering the negative electrical charge o 3 Hyperpolarization 90 mV membrane potential too much K leaves the cell o Ionic Events Neurotransmitter binds to receptor integral protein and ion channel allowing Na to enter stimulating the cell Na diffusion Depolarization Na closes positivity caused by sodium will cause K opens Repolarization Hyperpolarization last phase of repolarization Axons of the Central Nervous System o Tracts bundle of neurons located in the CNS interconnect neurons in the spinal cord and brain Synapses the communication between neurons functional junction between neurons o Chemical one way information transfer from presynaptic to postsynaptic neuron Axodendritic from axon to dendrite Axosomatic from axon to cell body o Presynaptic sending and Postsynaptic receiving Neurons o Ca2 at axon terminal Voltage gated Ca2 channels open when action potential reaches end of the bulb Ca2 flows inward triggering release of neurotransmitter moves vesicles holding neurotransmitter to synaptic terminal membranes fuse neurotransmitter released through exocytosis into synaptic cleft Neurotransmitter crosses synaptic cleft binding to ligand gated receptors the more neurotransmitter released the greater the change in potential of the postsynaptic cell One way information transfer o Removal of neurotransmitter Neurotransmitter bound to a postsynaptic neuron 1 produces a continuous postsynaptic effect 2 must be removed from the receptor Removal of neurotransmitters occurs when they 3 are degraded by enzymes 4 diffuse from the synaptic cleft Diffusion move down concentration gradient Uptake by neurons Enzymatic degradation acetylcholinesterase Inhibitory Synapses o Inhibitory postsynaptic potential IPSP results from the opening of ligand gated CL or K channels causing the postsynaptic cell to become more negative or hyperpolarized meaning the postsynaptic cell is less likely to reach threshold and produce an action potential o Neurotransmitter binds to receptor at
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