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Anatomy & Physiology

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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  


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