Chapter 12 Study Guide
Chapter 12 Study Guide MCB 244
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This 12 page Study Guide was uploaded by Jessica Logner on Sunday April 3, 2016. The Study Guide belongs to MCB 244 at University of Illinois at Urbana-Champaign taught by Dr, Chester Brown in Fall 2015. Since its upload, it has received 40 views. For similar materials see Human Anatomy and Physiology I in Biology at University of Illinois at Urbana-Champaign.
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Date Created: 04/03/16
MCB 244: Chapter 12 Nervous System all neural tissue in body and specialized organs Neurons cells that send and receive signals perform all communication, info processing and control functions basic functional unit of nervous system "workhorses" neuroglia (glial cells) cells that protect and support neurons preserve physical and biochemical structure of neural tissue essential to the survival of neurons "nursemaids" comprise half the volume of the nervous system outnumber neurons many types of neuroglia in CNS and PNS CNS brain and spinal cord functions are to process and coordinate: sensory data from inside and outside the body control activities of peripheral organs (skeletal muscle) = motor command higher functions of brain: intelligence. memory, learning and emotion PNS neural tissue outside PNS functions: deliver sensory info to CNS carry motor commands to peripheral tissue and systems Divisions of PNS Efferent carries motor commands, from CNS to PNS and effectors (muscles, glands) divided into SNS and ANS Afferent carries sensory information, from PNS to CNS Receptors division of PNS input detect changes or respond to stimuli neurons and specialized cells complex sensory organs (ears, eyes) Effectors division of PNS output respond to efferent signals cells and organs Somatic Nervous system division of efferent controls skeletal muscle contractions voluntary and involuntary (reflexes) Autonomic Nervous System division of efferent controls subconscious actions: contraction of smooth muscles and cardiac muscle and glandular secretions sympathetic division: stimulating effect parasympathetic: relaxing effect Neuron Morphology anaxonic more than 2 processes, all dendrites bipolar 2 processes separated by cell body unipolar single elongated process with cell body to side multipolar more than 2 processes, a single, long axon with many short, branched dendrites (MOST COMMON IN CNS) FIGURE 12. 4 Organelles of Cell Body large nucleus and nucleolus perikaryon (cytoplasm) mitochondria (produce energy) RER and ribosomes (produce NT's) Cytoskeleton Nissl Bodies Dendrites Cytoskeleton neurofilaments and neurotubules (in place of microfilaments and micrtoubules) neurofibrils: bundles of neurofilaments that provide support for dendrites and axon Nissl Bodies dense areas of RER and ribosomes make neural tissue appear gray (gray matter) Dendrites highly branched dendritic spines: many fine processes receive info from other neurons 8090% of neuron surface area Structure of Axon axon hillock thick section of cell body, attaches to initial segment axon long process that carries electrical signals (AP) to target (via synaptic endings), structure critical to neuron functioning axoplasm cytoplasm of axon, contains neurotubules/fibrils, enzymes, organelles axolemma specialized cell membrane, covers axoplasm collaterals branches of a single axon telodendria fine extensions of distal axon synaptic terminals ends of telodendria Synaptic Cleft small gap that separates the presynaptic membrane and postsynaptic membrane presynaptic cell cell that sends message postsynaptic cell cell that receives message Synaptic Knob expanded area of axon of presynaptic neuron contains synaptic vesicles of NT's Neurotransmitters NT's chemical messengers released at presynaptic membrane affect receptors of postsynaptic membrane broken down by enzymes reassembled at synaptic knob Neuroglia in PNS satellite cells schwann cells Neuroglia in CNS Ependymal cells astrocytes oligodendrocytes microglia Ependymal cells form epithelium called ependyma line central canal of spinal cord and ventricles of brain secrete cerebrospinal fluid (CSF) have cilia or microvili that circulate CSF monitor CSF contain stem cells for repair Astrocytes maintain bloodbrain barrier (isolates CNS) create 3D framework for CNS repair damaged neural tissue guide neuron development control interstitial environment Oligodendrocytes processes contact other neuron cell bodies wrap around axons to form myelin sheaths Myelination: increases speed of AP's myelin insulates myelinated axons makes nerves appear white (white matter) internodes: myelinated segments of axon nodes: gaps b/w internodes, where axons may branch Microglia migrate through neural tissue clean up cellular debris, waste products, and pathogens (phagocytic cells) Schwann cells neurilemmocytes form myelin sheath (neurilemma) around peripheral axons one schwann cells sheaths one segment of axon many shcwann cells sheath entire axon diptheria causes damage to schwann cells Satellite Cells amphicytes surround ganglia regulate environment around neuron 5 major membrane processes in neural activity Resting potential transmembrane potential of resting cell Graded potentials temporary, localized change in resting potential Action potential electrical impulse, produced by graded potential, propogates along surface of axon to synapse Synaptic Activity releases NT's at presynaptic membrane, produces graded potentials in post synaptic membrane Info processing response (integration of stimuli) of postsynaptic cell Transmembrane potential exists across PM b/c cytosol and extracellular fluid have different chemical/ionic components Ion movements and electrical signals all PM's of nerves and muscles produce electrical signals via ion movements (currents) across them ion movements occur to reduce the potential (charge) difference or concentration gradient difference ion movements are due to movements of Na+ and K+ 3 Requirements for TMP 1. Concentration gradient (Na+,K+) 2. ion movement across selectively permeable channels 3. maintenance of a separation of charge diff across membrane (at rest potential is about 70mV) Na+ high in extracellular fluid low in intracellular fluid K+ high in intracellular fluid low in extracellular fluid Determinants of Ion Movement chemical gradients driven by diffusion, Na+ and K+ electrical gradients separate charges of positive and negative ions, results in potential difference at resting membrane potential, an electrical gradient opposes the chemical gradient for K+ the net electrochemical gradient tends to drive K+ out of cell at resting membrane potential, the electrical and chemical gradient combine to force Na+ into cell for sodium: net influx of sodium ions at rest for potassium: net efflux of potassium ions at rest Determinants of Ion Movement (Active) Sodiumpotassium ATPase exchange pump powered by ATP Carries 3 Na+ out and 2 K+ in balances passive forces of diffusion maintains resting potential (70 mv) electrogenic pump Equilibrium potentials K+: 90mV Na+: +66 mV Resting Membrane Potential PM is highly permeable to K+ (70mV is relatively close to equilibrium potential of K+ which is 90mv) Electrochemical gradient for Na+ is large, but the membrane's permeability to these ions is low thus, Na+ has a small effect on the RMP (which is why the RMP is slightly less negative than 90mv) Change in TMP changes occur in response to changes in membrane permeability results from opening or closing membrane channels Sodium and Potassium Channels Either passive or active passive channels (leak): are always open permeability changes with conditions active channels (gated): open and close in response to stimuli at resting potential, most gated channels are closed 3 conditions of gated channels: closed but capable of opening open (activated) closed, not capable of opening (inactivated) 3 Classes of Gated Channels Chemically gated channels Voltage gated channels mechanically gated channels Chemically Gated Channels open in presence of specific chemicals (ACh) at a binding site found on neuron cell body and dendrites Voltage Gated Channels respond to changes in TMP have activation gates (open) and inactivation gates (closed) characteristic of excitable membrane found in neural axons, skeletal muscle sarcolemma, and cardiac muscle Mechanically Gated Channels respond to membrane distortion found in sensory receptors (touch,pressure,vibration) graded potentials also called local potentials changes in TMP cannot spread far from site of stimulation any stimulus that opens a gated channel(produces a graded potential) potential is proportional to the stimulus Production of Graded Potential resting membrane exposed to chemical sodium channel opens sodium ions enter the cell TMP rises local depolarization occurs Types of Graded Potentials Depolarization shift in TMP towards 0 mV Repolarization when the stimulus is removed, TMP returns to normal Hyperpolarization increasing the negativity of the resting potential, result of opening a potassium channel, opposite effect of opening a sodium channel Location of Graded Potentials cell dendrites or cell bodies trigger specific cell function ex: exocytosis of glandular secretions motor end plate releases ACh into synaptic cleft Location of AP axon Properties of Action Potentials propogated changes in TMP along axon affect an entire excitable membrane link graded potentials at cell body with motor end plate actions obey all or none principle, 4 Steps in Generation of AP 1. Depolarization to Threshold 2. Activation of Na+ channels 3. Inactivation of Na+ channels, activation of K+ channels 4. Return to normal permeability Depolarization to threshold due to graded potentials initial suprathreshold stimulus graded depolarization of axon hillock large enough to change RMP(70mv) to threshold level of voltage gated sodium channels (b/w 60mV and 50 mV) Activation of Na+ channels (voltage gated) rapid depolarization Na+ ions rush into cytoplasm Inactivation of Na+ channels, activation of K+ channels at +30 mV inactivation gates close (Na+ channel inactivation) K+ channels open Repolarization begins Return to normal permeability K+ channels begin to close (when membrane reaches normal resting potential, 70mV) K+ channels finish closing membrane is hyperpolarized to 90mV TMP returns to resting level AP is over Refractory Periods the time period from beginning of an AP to return to resting state during which membrane will not respond normally to additional stimuli Absolute Refractory Period sodium channels open or inactivated no AP possible Relative Refractory Period membrane potential almost normal very large stimulus can initiate AP Review Slide 57 ch, 12 pt. 1 Propogation moves AP generated in axon hillock along entire length of axon a series of repeated actions, not passive flow 2 methods of propogation continuous: unmyelinated axons saltatory: myelinated axons Continuous Propogation AP's along unmyelinated axons 1. AP develops at initial segment, the membrane at this site depolarizes to +30mV 2. a local current produces a graded depolarization that brings the axolemma at the next node to threshold 3. process repeats down length of axon Saltatory Propogation AP along myelinated axon faster and uses less energy than continuous Myelin insulates axon, prevents continuous propogation local current "jumps" from node to node depolarization only occurs at nodes Classification of Neurons 3 groups of fibers classified based on diameter, myelination and speed of AP's type A type B type C Type A myelinated large diameter high speed carry rapid info to/from CNS position, balance, touch, motor impulses Type B myelinated medium diameter medium speed carry intermediate signals sensory info, peripheral effectors Type C unmyelinated small diameter slow speed carry slower info involuntary muscle, gland contro