Nuerophysiology Flashcards
photo of axon
functional classifications of nuerons
-sensory
-motor
-internuerons
sensory nuerons general characteristics
-unipolar
-cell bodies grouped in sensory ganglia
-afferent fibers (processes) extend from sensory redeptors to CNS
types of sensory nuerons
-visceral and somatic
sensory receptors
-interoreceptors (internal systems, internal senses)
-exteroreceptors (complex senses, external environment)
-proprioreceptors (skeletal muscles)
motor nuerons
-CNS to effectors through efferent fibers
-somatic motor nuerons (SNS)
-visceral motor nuerons (ANS)
somatic motor nuerons of SNS
innervate skeltal muscles
visceral motir nuerons of ANS
-innervate all other peripheral effectors
-smooth and cardiac muscles
internuerons
-CNS mostly
-between sensory and motir nuerons
-distribution of sensiry info
-coordubation of motor activity
-higher functions such as memory, planning and learning
types of nueroglia in CNS and PNS
-astrocytes
-ependymal cells
-oligodendrocytes
-microglia
- sattelite cells
-schwann cells
astrocytes
-maintain BBB
-structural support
-regulate ion, nutrient, gas and dissolved gas concentration
-absorb and recycle nuerotransmitters
-form scar tissue after injury
-large cell bodies with many processes
ependymal cells
-line ventricles
-assits in producting cirucltating and monitoring CSF
-form epithelium that line central canal and ventricles
-produce and monitor CSF
-clilia help ciruclate CSF
oligodendrocytes
-myelinate CNS
-provide strucutral frameowork
-small cell bodies with few processes
microglia
-remove cell debris, wastes and pathogens by phagocytosis
-smallest and least numeroud
-have fine branchesd processes
-migrate through nervous tissue
internodes
-myelinated segments of axon
nodes
-also called nodes of ranvier
-lie between internodes where axons may vranch
satellite cells
-surround ganglia
-regulate intersitial fluid around nuerons in ganglia
schwann cells
-form myelin sheath or indented folds of plasma membrane around axons
-neurolemma is the outer surface of schwann cells
-myelinating schwan cells sheaths only one axon
-participate in repair process after injury
myelinated axon
resting membrane potential
-resting cell
-difference between positive and negative ions on either side of the membrane
-inside the cell is negative relative to outside the cell
-ICF is -70mV
graded potential
-temporary localized change in resting potential
-caused by stimulus
action potential
-electrical impulse
-produced by graded potential
-propagates along surface of axon to synapse
equilibrium potential
-membrane potential at which there is no net movement of a particular uon
-K+ = -90mV
-Na+ = +66mV
what is the plasma membrane highly permeable to
-K+
-this expalins the similarity of equilivirum potential for K+ and resting membrane potential
what is the resting membrane permeability very low to
-sodium
-Na+ has small effect on resting potential
three important concepts of resting membrane potential
-the extracellular fluid and intracellular fluid differ greatly in ionic composition
-cells have selectively permeable membranes
-membrane permeability varies by ion
difference in ion composition of intracellular and extracellular fluid
-extracellular fluid contains high concentrations of Na and Cl
-cytosol contains high concentrations of K+ and negatively charged proteins
passive ion channels
-leak channels
-always open
-permeability changed with conditions of cell
active ion channels
-gated ion channels
-open and close in response to stimuli
-at resting membrane potential most are closed
processes that produce resting membrane potential
-passive chemical gradients
-active Na/K+ pumps
-passive electrical gradients
-resting membrane potential
passive processes acting across cell membrane
-chemical gradients
-electrical gradients (cytosol is negative relative to ECF)
-electrochemical gradients
potassium ion gradients
sodium ion gradients
sodium potassium exchange pump
-powered by ATP
-ejects 3 Na+ for every 2K+ brought in
-balances positive forces of diffusion
-stabalize RMP at -70mV
types of active channels
-chemically gated ion channels
-voltage gates ion channels
-mechanically gated ion channels
chemically gates ion channels
-also called ligand gated ion channels
-open when they bind specific chemicals like ACh
-found on cell body and dendeties of nuerons
voltage gated ion channels
-respond to changed in membrane potential
-found in axons of nuerons and sarcolemma of skeletal and cardiac muscle cells
-activation gates opens when stimulated
-inactivatoon gate closes to stop ion movement
three possible states of voltage gated ion channels
-closed but capable of opening
-open (activated)
-closed and incapable of opening (inactivated)
mechanically gated ion channels
-respond to membrane distortion
-found in sensory receptors that respond to touch, pressure or vibration
graded potential
-temporary, localized change in resting potential
-caused by a stimulus that often triggers cell functions
-exocytosis of glandular secretions
action potential
-brief, rapid large (100mV) change in membrane potential
-needed for nuerons to conduct impulse
-produced by graded potential
characteristics of a graded potential
-changes in membrane potential that cannot spread far from site of stimulation
-produced by any stimulus that opens gated channels
-membrane potential most changed at site of stimulation; effect decreases with distance
-effect spreads passively due to local currents
-graded changes may involve depolarization or hyperpolarization
-stron stimuli proce greater changes in membrane potential and affect a larger area
-often trigger specific cell function
-ACh causes graded potential at motor wnd plate of NMJ
local current
-sodium ions move parallel to plasma membrane producing local current which depolarizes nearby regions of plasma membrane (graded potential)
repolarization
when stimulus is removed membrane potential returns to normal
hyperpolarization
-results from opening potassium channels
-positive ions move out not into the cell (opposite effect of opening
-soidum channels)
-increases negativity of the RMP
-becomes more negative
where do action potentials begin
-initial segment
threshold of action potentials
–60- -55 mV
all or none principle
-any stimulus that changes membrane potential to threshold
-all action potentials are the same no matter how large the stimulus
-action potential is either triggered or not triggered
4 steps of an action potential
step 1: depolarization to threshold
step 2: activation of voltage gated sodium channels (Na rushes in and inner membrane surfaces change from negative to positive)
Step 3: inactivation of Na channels and activation of K+ channels (K+ moves out of cytosol)
step 4: return to resting membrane potential
what happens during return to RMP
refractory period
-from begininng of action potential to return to resting state
-during which the membrane will not respond normally to additonal stimuli
absolute refractory period
-all voltage gated sodium channels are already open or inactivated
-membrane cannot respond to further stimulation
relative refractory period
-begins when sodium channels regain resting condition
-continues until membrane potential stablizes
-only a strong stimulus can initiate another action potential
graph of refractory periods
what does depolarization result from
-influx of sodium
what does repolarization result from
-loss of K+
sodium-potassium exchange pump
-returns concentration to prestimulation levels
-maintains concentration gradients of Na+ and K+ over time
-use ATP for each exchange of two extracellular K+ for three intracellular Na+
propagation
-moved an action potential along an axon in a series
-2 types: continous propagation, saltatory propagation
continous propagation
-occurs in unmyelinated axons
-affects one segment of an axon at a time
-action potential develops at initial segment to 30mV, local current develops to depolarize segment to threshold, action potential occurs in seond segment, local current depolarizes next segment
saltatory propagation
-occurs in myelinated axons
-faster than continous
-myelin prevents continous propagation
-local current jumps from node to node
-depolarization occurs only at nodes
what affects the propagation most
- axon diameter
-the lower the resistance the fster the speed
types of axons based on diameter, myelination and propagation speed
type A, B, C
how are messages carried by nerves routed
-according to priority
-critical info through type A
type A fibers
-myelinated
-large diamter
-transmit info to and from CNS rapidly
type B fibers
-myelinated
-medium diamter
-transmit info at intermediate speeds
type C fibers
-unmyelinated
-small diameter
-transmit info slowly
types of chemical synapses
-NMJ - synapse between synapse and skeletal muscle cell
-NGJ - synapse between nueron and gladn cell
function of chemical synapses
-axon terminal releases NT that bind to postsynaptic plasma membrane that produces localized change in permeability and graded potentials
-action potental may or may not be generated in postsynaptic cell depending on amount of NT released and sensitivity of postsynaptic cell
where is ACh released at
-all NMJ
-many synapses in CNS
-all nueron to nueron synapses in PNS
-all NMJ and nueroglandular junctions in parasympathetic division of ANS
events at a cholinergic synapse
-action potential arrives at axon terminal and depolarizes membrane
-extracelllar calcium ions enter axon terminal and trigger exocytosis of ACh
-ACh binds to receptors on postsynaptic membrane and depolarize it
-ACh is removed from synaptic cleft by acetylcholinesterase (into acetate and choline)
calcium role in action potential
-in axon terminal, AP opens Ca@+ channels in synaptic knob
-Calcium causes release of NT from synaptic vessels to synaptic cleft
-NT diffuses across cleft and binds to receptor sites on sub-synaptic membrane
neurotransmitters
-chemical messengers contained within synaptic vesicle in axon terminal of presynaptic cell
-released into synaptic cleft
-affect receptors of postsynaptic membrane
-broken down by enzymes
-reabsorbed and reassembled by axon temrinal
excitatory NT
-cause depolarization of postysynaptic membrane
-promote action potentials
inhibitory NT
-hyperpolarization
-suppress action potential
major classes of NT
-biogenic amines
-AA
-nueropeptides
-dissolved gasses
nueromodulators
-rate of NT release
-response by postsynaptic cell
-effect are long term and slow to appear
-multiple steps involved
-intemrdiate compounds also involved
-affect presynaptic membrane, post synaptic membrane or both
-released along or with a nuerotransmitter
types of nueromodulators
-nueorpeptides
-opiods
-dissolved gasses
nueropeptides
-small peptide chains
-syntheized and released by axon terminal
opiods
-bind tos same receptors as opium and morphine
-CNS opiods: enkepahalins, endorphind, dynorphins
dissolved gasses
-important NT
-Nitric oxide
-carbon monoxide
effects that NT and NM may have on membrane potential
-may have a direct effect on membrane potential (opening or closing chemically gated ion channels)
-an indirect effect through G proteins
-an indirect effect via intracellular enzymes
indirect effect by second messengers
G protein links first messengers (NT) and second messengers (ions or molecules)
-G proteins include an enzyme that is activated when an extracellular compound binds
indirect effects by G proteins photo
indirect effects by intracellular enzymes
-lipid soluble gasses
-diffuse through lipid membranes
-bind to enzymes inside of brain cells
excitatory postysynaptic potential
-graded depolarization of postysynaptic membrane
inhibitory postsynaptic potential
-graded hyperpolarization of postysynaptic membrane
a nueron that recieves many IPSPs
-is inhibited from poridcuing another action potential
to trigger an action potential what needs to happen
-one EPSP is not enough
-EPSPs and IPSP combine though summation (temporal and spatial)
temporal summation
-occurs on a membrane that recieved two depolarizing stimuli fro the same source in rapid succession
-the effects of the second stimulus are added to those of the first
spatial summation
0two stimuli arrive at the same time but different locations, local currents spread the depolarizing effect and areas of overlap experience combined effects
a nueron becomes facilitated when:
-as EPSPs accumulate and raise membrane potential closer to threshold until a small stimulus can trigger an action potential
can nueromodulators and hormones change membrane sensitivity to nuerotransmitters
yes
information processing
-information may be converyed simply by the frequency of action potentials recieved
-holding membrane potential above threshold
-maximum rate of action potentials is reached when relative refractory period is eliminated
axoaxonic synapses
-synapses between axons of two nuerons
presynaptic inhibition vs presynaptic facilitation
-decreases the rate of NT release at presynaptic membrane vs increases rate of nuerotransmitter release at presynatic membrane
three groups of nueronal pools
-sensory nuerons
-motor nuerons
-internuerons (interpret, plan and coordinate signals coming in and out)
five patterns of nueral circuits in nueronal pools
-divergence
-convergence
-serial processing
-paralell processing
-reverberation
divergence
-spreads information from one nueron or nueronal pools to many
-especially common in sensory pathways
convergence
-several nuerons synapse on a single nuerons
-ex; conscious and subconscious control of the diaphragm in breathing- two nueronal pools synapse with the same motor nuerons
serial processing
-information moves along a single path, sequentially from one nueron or nueronal pool to the next
-ex: pain signals pass sequentially through 2 nueronal pools to reach conscious brain
parallel processing
-several nuerons/nueronal pools process the same information at the same time
-ex: step on a bee, signals spread through several nueronal pools so you can shift your weight, lift your foot, yell in pain at about the same time
reverberation
-collateral branches of neurons extend back and continue stimulating presynaptic nuerons
-forms positive feedback loop, continues until synapti fatigue or inhibition occurs
-may maintain consciousness, breathing and muscle coordination
4 ways to classify reflexes
-development
-response
-complexity of nueral circuit
-site of info processing
innate reflexes
-basic nueral reflexes formed before birth
-genetically programmed
-withdrawl, chewing visual tracking
acquired reflexes
-rapid, autonmatic learned motor patterns
-reptition enhances then
somatic reflex
-control skeletal muscle contractions
-superficial reflex in skin and mucous membrane
-stretch of deep tendon reflexes
-immediate impoertan in emergencies
visceral reflex
-control amooth muscle, cardiac muscle or glands
monosynaptic reflex
-single synapse
-sensory nueron synapses directly with motor nueron
-fast response
polysynaptic reflex
-at least one internueron between sensory nueron and motor nueron
-slower response; delay increase with # of synapses involved
-intersegmental reflex arcs
intersegmental reflex arcs
-many spinal cord segments interact and produce variable response
spinal reflexes
-aitomatic response to change in environment
-intergration processing center for spinal reflexes if gray matter of spinal cord
cranial reflexes
-processing occurs in the brain
-somatic or visceral reflexes and involve sensory and moror fibers of cranial nerves
nueral reflexes
-different types of nueral reflexes are all rapid; automatic responses to specific stimuli allin an effor to protect and maintain homeostasis
-basic building blocks of nueral function
-specific reflex produces the same motor response each time
five components of reflex arc
-sensory receptors
-sensory nueron
-information processing
-motor nueron
monosynaptic reflex steps
-stimulus = muscle stretching
-2 distortion of receptor sends action potential through sensory nueron
-sensory nueron synapses with motor nuerons in spinal cord
-motor nueron send signals to motor units; triggers reflexive contraction of stretched muscle
polysynaptic reflex
-more complicated than monosynaptic reflexes
-internuerons can control multiple muscle groups
-produce either EPSPs IPSP stimulating some muscles and inhibiting others
examples of polysynaptic reflex
-tendon reflex
-withdrawl reflex
-crossed extensor reflex
postural reflex
-include both stretch reflexes and also complex polysynaptic reflexes
-maintain normal upright posture
-involve multiple muscle groups
-maintain firm muscle tone
-extremely sensitive receptors allow constant find adjstments to be made as needed
tendon reflex
-prevents skeletal muscles from developing too much tension and tearing and breaking
-sensory receptors are golgi tendon organs
-stimulated when collagen fibers are overstretches
-stimulate inhibitory internuerons in Sc
-more muscle tension leads to more muscle inhibition
withdrawl reflex
-spinal reflex
-move body part away from stimulus
-strength and extent of response depends on intensity and location of stimulus
reciporical inhibition
-for flexor refle to work , stretch reflex of antogonistic muscles must be inhibited by internuerons in spinal cord
ipsilateral vs contralateral reflex arcs
-ipsilateral - occurs on same side of body as stimulus
-contralateral 0 occur on side opposite of stimulus
crossed extensor reflexes
-coordinated with flexor reflex
-maintain by reverberating circuits
-step on something sharp, lift foot and shift weigh happen simultaneously
five general characteristics of polysynaptic reflexes
-involve pools of internuerons
-involve more than one spinal segment
-involve reciporical inhibition
-have reverberating circuits
-several reflexes may cooperate
brain altering spinal reflexes
-integration and control of spinal reflexes - reflex are automatic but processing centers in brain can facilitate or inhibit spinal reflex motor patterns
-brain can also activate reflex motor pattersn through descending pathways
reinforcement of spinal reflexes
-higher center adjust sensitivity of reflexes by stimulating excitatory or inhibitory internuerons in brainstem or spinal cord
-when excitatory synapses are chronically stimulated, postsynaptic nuerons can be in general facilitation
-this reinforcement enhances spinal reflexes
-inhibition of spinal reflexes
-higher center inhibit spinal reflexes by stimulating inhibitory nuerons, creatins IPSPs at reflex motor arc and suppressing postsynaptic nuerons thus inhibiting reflex
