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Nervous system

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the master controlling and communicating system of the body

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functions of the nervous system

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sensory input-stimuli integration-interpretation motor output-response

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central nervous system CNS

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brain and spinal cord integration and comand center

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peripheral nervous system PNS

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anything other than the brain and spinal cord out on the edges carries messages to and from the spinal cord communicates to the brain whats going on inside and outside the body

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sensory (afferent) division of the PNS

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sensory afferent fibers-carry info to the brain and spinal cord (skin, skeletal muscles, joints) visceral afferent( one direction) fibers (viseral organs)

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motor (efferent) division of the PNS

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effector organs (brain sends its messages out to effector ogans via PNS) paired nerves that help regulate the body

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somatic nervous system (motor)

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conscious control of skeletal muscles

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autonomic nervous system (motor) ANS

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regulates smooth muscle cardiac muscle and glands

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sympathetic (ANS)

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active response to danger/scary adrenoline heart respitory elevated fight or flight gets everything kicked up

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parasympathetic (ANS)

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rest everything goes down

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the two principal cell types of the nervous system are

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neurons supporting cells

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neurons

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excitable cells that transmit electrical signals (depolarize throw action potential)

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supporting cells

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cells that surround and wrap neurons called neuroglia or glial cells don't throw AP structually and functionally important to cell

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supporting cells (CNS) astrocytes= star

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most abundant, versatile, and highly branched glial cells they cling to neurons, synaptic endings, and cover capillaries support and brace neurons (are soft tissue) anchor neurons to nutrient supplies guide migration of young neurons control the chemical enviroment

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blood brain barrier

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don't want the brain to come in direct contact or it will kill cells

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supporting cells (CNS) microglia

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small oval support cells with spiny processes phagocytes that moniter the health of neurons (mobile move around look for what doesn't belong)

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supporting cells (CNS) ependymal cells

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range in shape from squamous to columnar line the central cavities of the brain and spinal column circulate cerebral spinal fluid

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supporting cells (CNS) oligodendrocytes

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branched cells wrap CNS nerve fibers myelin sheath

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supporting cells (PNS) satellite cells

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surround neuron cell bodies

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support cells (PNS) schwann cells

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myelin sheath surround nerve fibers of the PNS

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neurons (nerve cells)

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structural units of the nervous system extreme longevity amitotic high metabolic rate

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nerve cell body

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contains the nucleus and a nucleolus is the major biosynthetic is the focal point for the outgrowth of neuronal processes has no centrioles (hence its amitotic nature) has well developed nissl bodies (rough ER) contains an axon hillock-cone-shaped area from which axons arise

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dendrites

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receive input graded potentials not action potentials unmyelinated

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axons

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axon hillock generate and transmit action potentials long axons are called nerve fibers axon collaterals=branch axon terminals branches 10,000 not unusual myelinated

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myelin sheath

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fatty (protein-lipoid) segmented sheath around most long axons

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myelin sheath functions to

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protect the axon electrically insulate fibers from one another increase the speed of nerve impulse transmission

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myelin sheath and neurilemma formation

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formed by schwann cells in the PNS

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schwann cell

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envelopes an axon in a trough encloses the axon with its plasma membrane has concentric layers of membrane that make up the mtelin sheath

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neurilemma

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remaining nucleus and cytoplasm of a schwann cell

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node of ranvier (neurofibral nodes)

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between adjacent schwann cells (1mm axon collaterals can emerge)

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node of ranvier (unmyekinated axons)

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schwann cells partially enclose 15 or more axons no coiling

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Axons of the CNS

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myelinated and unmyelinated fibers myelinated formed by oligodendrocytes (up to 60 axons) nodes of ranvier are widely spaced white matter (myelinated fibers) grey matter (nerve cell bodies and unmyelinated fibers)

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multipolar neurons

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many processes extend from cell body all are dendrites except for a single axon abundunt motor neurons bridge gaps

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bipolar

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two processes extend from the cell body one is a fused dendrite the other is a axon rare special sense organs ex eyes ears

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unipoloar

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one extension extends from cell body forms central and peripheral processes which comprise an axon

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neurophysiology

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sensative easy to stimulate

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action potentials

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electrical impulses carried along the length of axons always the same regardless of stimulis the unerlying functional feature of the nervous system

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electrical current and the body

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reflects the flow of ions rather than electrons (RMP)

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types of plasma membrane ion channels

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passive or leakage channels always open chemically gated channels -open with binding of a specific neurotransmitter (no ATP reguired flow down) voltage gated channels-open and close in response to membrane potential (constantly leak a little) mechanically gated channels-open and close in response to physical deformation of receptors (stretched, squashed)

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opperation of a chemically gated channel

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Na+ and K+ gated channels (NOT THE Na+ K+ PUMP) neurotransmitter regulated diffusion

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operation of a voltage-gated channel

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Na+channels voltage controlled when gate channels are open ions move quickly along their electrochemical gradients an electrical current created voltage changes across the membrane

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resting membrane potential (Vr)=RMP

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it is generated by different concentrations of Na+ K+ Cl- and protien anions (A-) -70mV ionic differences are the consequence of differential permeability of the neurilemma to Na+ an K+ operation of the sodium-potassium pump

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membrane potential signals

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used to recieve integrate and send information membrane potential changes are produced by changes in membrane permeability to ions alterations of ion concentrations across the membrane two types of signals (coming in short distances) graded potentials (further you are peters off pond ripple) usually incoming short distances-dendrites action potentials (all exactly the same strength) long distance axons

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deploarization

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the inside of the membrane becomes less negative or more positive

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repolarization

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the membrane returns to its RMP -70

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hyperolarization

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the inside of the membrane becomes more negative than the resting potential

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graded potentials (info flows in)

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short lived local changes in the membrane potential decrease in intensity with distance magnitude varies directly with the strength of the stimulis hence GRADED a little, a medium, a lot sufficiently strong graded potentials can initiate AP have to have a strong enough graded potential to communicate to the neuron to throw an action potential

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APs

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excitable membranes only in muscle fibers and neurons they do not decrease in strength over distance they are principle means of neural communication an action potential in the axon of a neuron is a nerve impulse 1. open up Na+ ion channels 2. close Na+ ion channels 3. open up K+ ion channels

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action potential resting state

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Na+ K+ channels are closed leakage accounts for small movements of Na+ and K+ each Na+ channels has two voltage regulated gates (activation and inactivation) K+ channels have one gate

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activation gates

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voltage sensative closed in the resting state

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inactivation gates

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open in the resting state

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action potential depolarization phase

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Na+ permeability increases membrane potential reverses Na+ gates are opened K+ gates are cloosed threshold- a critical level of depolarization (-55) at threshold depolarization becomes self-generating (sodium flows into cell opens quickly K opens slower)

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action potential repolarization phase

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Na+ inactivation gates close blocks inflow of Na+ membrane permeability to Na+ declines to resting levels as Na+ gates close voltage sensative K+ gates open K+ exits the cell and internal negativity of the resting neuron is restored (K+ stays open a little longer than it needs to (undershooting) becomes negative -90mv hyperpolarization)

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action potential hyperpolarization

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K+ gates remain open causing as excessive efflux of K+ undershoot the neuron is insensative to stimulis and depolarization during this time Na+ channels reset (activation gates close) Na+ K+ pump will reset ionic distribution (brings back up to -55mv RMP)

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threshold and action potential

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all or none phenomenon (+30mv) the CNS determines stimulus intensity by the frequency of impulse transmission greater the stimulis faster the AP are sent out the more it "hurts"

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absolute refactory period

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while generating an AP Na+ channels are open cannot respond to stimulis the absolute refactory period ensures that each action potential is sperate( can't blend enforces one-way transmission of nerve impulses

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relative refactory period

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following the absolute refractory period when sodium gates are closed potassium gates are open repolarization is occurring threshold level for AP is elevated strong stimuli

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saltatory conduction (jump faster)

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mylonated voltage-gated Na+ channels concentrated at nodes APs are triggered only at the nodes and jump from one node to the other 30x faster than continuous conduction (swiming) sensative areas have more nerve endings

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nerve fiber classification

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nerve fibers are classified according to diameter, degree of myelination, speed of conduction group A somatic sensory and motor nuerons big thick myelin 300 mph (voluntary almost instantaniously) group B and C ANS visceral motor and sensory neurons B-medium lightly myelinated 40mph C-small unmyelinated 2pmh (involuntary continous conduction) bigger/more myelinated=faster conduction

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synapses (all over the place)

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a junction that mediates information transfer from one neuron to another neuron to an effector cell (muscle or gland) presynaptic neuron (in neuron) postsynaptic neuron

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chemical synapses

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Ca2+ channels synaptic vesicles- neurotransmitters undirectional communication undirectional communication synaptic delay- time needed to do this (0.3-5.0 ms)

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postsynaptic potentials (excititory)

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neurotransmitter receptors mediate changes in membrane potential according to amount of nuerotransmitters released amount of time the neurotransmitter is bound to receptor the two types of postsynaptic potentials are EPSP excitatory postsynaptic potentials IPSP inhibitory postsynaptic potentials (Cl or K channels)

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excitatory postsynaptic potentials

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EPSP are graded potentials that can initiate an action potential in an axon chemically gated channels Na+ and k+ flow in opposite directions at the same time graded potential reaches axon hillock = AP

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inhibitory synapses and IPSP's

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IPSP's inhibit an AP induce hyperpolarization K+ Cl- driven farther from threshold

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summation

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a single EPSP cannot induce an AP EPSPs must summate to induce an AP temporal summation- presynaptic neurons transmit impulses in rapid fire order spatial summation postsynaptic neuron is stimulated by a large number of terminals at the same time IPSPs can also summate with EPSP canceling each other out

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common neurotransmitters

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acetylcholine ACh (acetylcholinesterase AChE) biogenic amines amino acids peptides endorphines novel messengers ATP and dissolved gases NO and CO pain sensation memory and learning cGMP

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biogenic amines

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broadly distributed in the brain play roles in emotional behaviors and our biological clock catecholamines- dopamine norepinephrine (NE) "feel good" indolamines- serotonin sleep appetite moods and histamine inflamation

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neural integration neuronal pools

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functional group of neurons that intergrate incoming information forward the processed information to its appropriate destination

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mutiple sclerosis

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an autoimmune disease that mainly affects young adults sypmtoms: visual disturbances, weakness, loss of muscle control, and urinary incontinence nerve fibers are severed and myelin sheaths in the CNS become nonfunctional scleroses shunting and short-circuiting of nerve impulses occurs

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multiple sclerosis treatment

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the advent of disease-modifying drugs including interferon beta-1a and -1b

Chapter 11 fundamentals of the nervous system and nervous tissue – Flashcards

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