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Nervous System
Anatomy & Physiology
| Question | Answer |
|---|---|
| three major steps of the nervous system | sensory input, integration, and motor output |
| sensory input | information is gathered by sensory receptor about internal and external changes, notice sensation (i.e. see water) |
| integration | interpretation of sensory input, perceive sensation (i.e. feel thirsty) |
| motor output | activation of effector organs (muscles and glands) to produce a response, respond to sensation (i.e. grab a glass for a drink) |
| central nervous system (CNS) | consists of the brain and spinal cord and is the integration and command center |
| peripheral nervous system (PNS) | paired spinal and cranial nerves carry messages to and from the CNS (includes nerves, ganglia and glial cells) |
| nerves | bundles of neuron processes |
| ganglia | clusters of neuron cell bodies |
| two function divisions | sensory (afferent) division and motor (efferent) division |
| components of sensory (afferent) division | composed of somatic afferent fibers and visceral afferent fibers |
| somatic afferent fibers | convey impulses from skin, skeletal muscles, and joints to the brain |
| visceral afferent fibers | convey impulses from visceral organs to the brain |
| afferent | going toward the brain (i.e. feeling cold... perceiving the sense) |
| motor (efferent) division | transmits impulses from the CNS to effector organs (going away from the brain) (i.e. kick someone... interpret sensation and respond) |
| visceral | unconscious |
| somatic (voluntary nervous system) | conscious control of skeletal muscles (i.e. move arms and legs) |
| autonomic (involuntary) nervous system (ANS) | visceral motor nerve fibers, regulates smooth muscle, cardiac muscles, and glands |
| two functional subdivisions of the ANS | sympathetic and parasympathetic |
| sympathetic | fight or flight - sensations are heightened (involuntary) |
| parasympathetic | rest and digest - body system focuses on one process (involuntary) |
| all sensory inputs go all the way to the ____ at some point | central nervous system (CNS) |
| two divisions of the motor division | autonomic nervous system and the somatic nervous system |
| nervous tissue is responsible for how the body... | perceives and responds to multiple sensations (controls multiple muscle movements and other movements without voluntary input (i.e. beating of the heart) |
| nervous system | controls and interprets all sensations and muscle movements, is the body's primary communication and control system, and integrates and regulates body function |
| nervous system activities | collects information, processes and evaluates information, and initiates responses to information |
| the nervous system as a collector of information | has receptors that detect stimuli (i.e. receptors on the skin detecting information about touch) |
| receptors | specialized nervous structures |
| stimuli | changes in external and internal environment |
| nervous system as it processes and evaluates information | does this to determine the response that is required |
| nervous system as it initiates responses to information | initiates a response via nerves to effectors (include muscle tissue and glands) (i.e. muscle contraction or change in glass secretion) |
| effectors | puts out a response to the stimuli |
| sensory nervous system | (aka afferent nervous system), responsible for receiving sensory information from receptors, transmits information to the CNS, is further divided into visceral and somatic sensory, |
| types of somatic sensory receptors | eyes, nose, tongue, ears, skin, and proprioreceptors |
| proprioreceptors | receptors detecting body position |
| somatic sensory | detects stimuli that we consciously perceive |
| visceral sensory | detects stimuli we do not consciously perceive |
| types of visceral sensory receptors | structures within blood vessels, structures within internal organs (i.e. detecting stretch of organ wall) |
| motor nervous system | (aka efferent nervous system), initiates and transmits motor output from CNS, transmits information to the effectors, and may be further divided into somatic and visceral parts |
| somatic motor | transmits motor output from CNS to voluntary skeletal muscles, effector is consciously controlled (i.e. pushing on the accelerator of a car with your foot) |
| autonomic motor | transmits output from CNS without conscious control, transmits to cardiac muscle, smooth muscle, glands (involuntary, i.e. release insulin after you eat) |
| two cell types in nervous system | neurons and glial cells |
| neurons | basic structural unit of the nervous system, excitable cells that transmit electrical signals |
| glial cells | nonexcitable cells that primarily support, nourish, and protect neurons and nerves |
| special characteristics of neurons | excitability, conductivity, secretion, and extreme longevity |
| excitability | responsive to stimulus |
| conductivity | electrical changes propagated along membrane |
| secretion | release neurotransmitters in response to electrical charges |
| extreme longevity | most formed before birth still present in advanced ages |
| components of neurons | cell body, dendrites, and axon |
| cell body | enclosed by plasma membrane, contains cytoplasm surrounding a nucleus, neuron's control center, and conducts electrical signals to axon |
| dendrites | short processes branching off cell body, may have one or many, receive input and transmit it to cell body |
| the more dendrites | the more input possible |
| axon | longer process, emanating from cell body that makes contact with other neurons, muscle cells, or glands, and has three components |
| three components of the axon | axon hillcok, synaptic knobs, and synaptic vesicles |
| axon hillcock | first part of the axon, a triangular region |
| synaptic knobd | the expanded regions at the extreme tips of axons |
| synaptic vesicles | contained by the knobs and contain neurotransmitters |
| sensory neurons (afferent neurons) | neurons of the sensory nervous system that conduct input from somatic and visceral receptors, and the cell bodies are usually in posterior root ganglia outside the CNS |
| motor neurons (efferent neurons) | neurons of the motor nervous system, conduct motor output to somatic and visceral effectors, and most cell bodies are in the CNS |
| interneurons (association neurons) | entirely within the CNS, receive stimulation from many other neurons, receive process, and store information, "decide" how body responds to stimuli, and facilitates communication b/w sensory and motor neurons (99% of neurons) |
| two types of nerves | cranial nerves and spinal nerves |
| cranial nerves | (12) extend from brain |
| spinal nerves (27) | extend from spinal cord |
| synapse | where neurons functionally connected to neuron or effector, two types |
| two types of synapses | chemical and electrical |
| chemical synapse | most common, composed of presynaptic neuron, signal producer, composed of postsynaptic neuron, signal receptor, between axon & any portion of postsynaptic neuron (most commonly w/ a dendrite), & knob almost touches the postsynaptic neuron (synaptic cleft) |
| synaptic cleft | narrow fluid-filled gap of the chemical synapse |
| transmission at chemical synapse | neurotransmitter molecules released from synaptic knob, released from synaptic vesicles into cleft, diffusion of neurotransmitter across cleft, binding of some neurotransmitter to receptor, and synaptic delay |
| synaptic delay | time between neurotransmitter release and binding |
| electrical synapse | much less common, presynaptic and postsynaptic neuron physically bound together, gap junctions present, no delay in passing electrical signal, in limited regions of brain and eyes (in upper nervous system) |
| glial cells (neuroglia) | nonexcitable cells found in CNS and PNS, smaller and more numerous than neurons, physically protect and nourish neurons, critical for normal function at neural synapses |
| types of glial cells | astrocytes (CNS), microglia (CNS), ependymal cells (CNS), oligodendrocytes (CNS), satellite cells (PNS), and Schwann cells (PNS) |
| astrocytes | star-like shaped glial cells (form projections) that are the most abundant in the CNS, help form the blood-brain barrier, and regulate tissue fluid composition |
| blood-brain barrier | strictly controls substances entering brain nervous system nervous tissue from blood, protects neurons from toxins, and allows nutrients to pass |
| fluid composition | controls movement of substances between blood and interstitial fluid (i.e. regulate K+ concentration - need constant K+ level for neuron electrical activity |
| microglia | small cells with slender branches that are the least abundant of the CNS glial cells, phagocytic cells of the immune system (wander CNS and replicate in infection and engulf infectious agents and remove debris from dead or damaged tissue) |
| ependymal cells | line internal cavities of brain and spinal cord and serve in production of cerebrospinal fluid and cilia help to circulate CSF |
| cerebrospinal fluid | liquid that bathes external CNS and fills internal cavities |
| oligodendrocytes | large cells with slender extensions that form processes (myelin sheath) wrapping around portions of axons of different neurons and prevent passage of ions through axonal membrane and allow for faster potential propagation through CNS |
| satellite cells | arranged around neuronal cell bodies in a ganglion and regulate the exchange of nutrients and waste products (i.e. surrounding bodies of sensory neurons in a posterior root ganglion) |
| Schwann cells | ensheathes PNS axons to form myelin sheath and allows for faster action potential propagation |
| myelination | process by which part of an axon is wrapped in myelin |
| myelin | insulating covering around axon that consists of repeating layers of glial cell plasma membrane, has high proportion of lipids, gives glossy appearance and insulates axon |
| cells that complete myelination | Schwann cells (PNS) and oligodendrocytes (CNS) |
| myelin sheaths function | protect and insulate axon and increase speed of impulse transmission |
| nodes of Ranvier | gaps between myelin sheaths |
| resting membrane potential | membrane potential in a resting, excitable cell (-70 mV), relative difference in charge across membrane (more positive ions outside a neuron than in it at rest), measured with a voltmeter, & is created because of the plasma membrane permeability to ions |
| voltmeter | microelectrodes into neuron and interstitial fluid |
| depolarization and hyperpolarization | opening of chemically gated channels or voltage-gate channels that causes changes in ion flow across membrane and alters resting membrane potential |
| depolarization | inside of cell becomes more positive than RMP (i.e. from -70 mV to -60 mV), occurs when gated channels open and allow movement of Na+ into neurons causing inside of neuron to become more positive |
| hyperpolarization | inside of cell becomes more negative (i.e. from -70 mV to -80 mV), may result from opening of gated K+ channels (lose K+ ions) or Cl- channels (gain Cl- ions) |
| graded potential | local potentials, occur in the receptive segment of a neuron and result from opening of chemically gated channels temporarily allowing passage of small amount of specific ion establishing a local current |
| local current | ions moving parallel to plasma membrane, experiences resistance from contents of cytosol, and eventually becomes weaker and ceases |
| graded potentials (continued) | may cause de- or hyperpolarization (size and type depend on channel that opens & stimulus magnitude) (larger stimulus opening more chemically gated channels and flow of more ions) decreases in intensity with distance along the membrane and is short-lived |
| action potential | generated within the initial segment, propagated along axon, due to opening of voltage-gated channels |
| threshold value | minimum voltage change to open voltage-gated channel (-55 mV, +15 mV from RMP), any value below this is considered a subthreshold value |
| if threshold value reached | channels opens and membrane potential reversed, if Na+ channel opens, enters he neuron, makes inside relatively positive, flow of local current to adjacent areas and voltage-gated channels open in these areas and successively down the axon |
| if threshold value reached continued | followed by sequential opening of voltage-gated K+ channels, movement of K+ out of neuron returns membrane to RMP |
| action potentials | involve temporary reversal of polarity across plasma membrane (inside become relatively positive, followed by a return to RMP), are self-propagated (maintain intesity as move to synaptic knob), and obey "all or none law" |
| all or none law | if threshold reached, action potential propagated, if threshold not reached, not propagated, same intensity of response to values greater than threshold, similar to what occurs with a gun (pull trigger, fire and opposite) |
| postsynaptic potentials | graded potentials that occur in postsynaptic neurons, occur after release of neurotransmitter from presynaptic neuron, opening of gated channels after binding of neurotransmitters, results in small local potentials |
| postsynaptic neuron | able to bind many neurotransmitters at once, numerous postsynaptic potentials generated at once |
| type of graded potential formed depends on neurotransmitter | excitatory or inhibitory neurotransmitter |
| generation of EPSPs (step 1) | excitatory neurotransmitter crosses synaptic cleft (binds to receptor and opens a chemically gated cation channel) |
| generation of EPSPs (step 2) | more Na+ moves into neuron than K+ moves out |
| generation of EPSPs (step 3) | inside becomes slightly more positive (less negative state called excitatory postsynaptic potential (EPSP)) |
| generation of EPSPs (step 4) | local current of Na+ becomes weaker (decreases in intensity with distance traveled) |
| generation of EPSPs depend on | amount of neurotransmitter bound per unit time (degree of change in RMP), type of neurotransmitter released (more cation channels open, greater charge in the positive direction (i.e. from -70 mV to -65 mV) |
| generation of IPSPs (step 1) | inhibitory neurotransmitter crosses synaptic cleft (binds to chemically gate K+ channel or Cl- channel and depends on neurotransmitter and channels present) |
| generation of IPSPs (step 2) | if neurotransmitter binds K+ channel, K+ moves out of neuron/ if neurotransmitter binds Cl- channel, Cl- flows into neuron |
| generation of IPSPs (step 3) | inside of the cell becomes slightly more negative (more negative state termed inhibitory postsynaptic potential (IPSP) |
| generation of IPSPs (step 4) | local current of ions becomes weaker, decreases in intensity with distance traveled toward initial segment |
| summation | addition of graded postsynaptic potentials (IPSPs and EPSPs), occurs at the initial segment, determines if threshold membrane potential is reached, if threshold reached (voltage-gated channels open, action potential generated that travels along axon |
| summation continued | IPSPs negate effects of EPSPs, thousands of EPSPs required to reach threshold (must arrive at nearly the same time) |
| spatial summations | release of neurotransmitter from multiple presynaptic neurons, action potential initiated if enough EPSPs generated |
| temporal summation | repeated release of excitary neurotransmitter at same location, effects added if occur within small timeframe, action potential initiated if threshold reached |
Created by:
Nicolekr
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