Nervous Tissue and Physiology II: Lecture 19 Flashcards
voltage
measure of potential energy by separate electrical charges
current
flow of charge from one point to another
resistance
hindrance to flow of electrical charge
relationship between current, voltage, and resistance
greater voltage = greater current
less resistance = greater current
Na+/K+ pump
3 Na+ out, 2 K+ in
more positive ions moving out than in on average
K/Na leak channels
both Na+ and K+ diffuse through leak channels down concentration gradients
many more K leak channels than Na leak channels
neuron resting membrane potential
-70 mV
difference in charge between inside and outside of neuron at rest
polarized neuron membrane
outside pos charged
inside neg charged
neuron cell cytosol ionic composition
lower conc of Na+
higher conc of K+
neuron extracellular fluid ionic compostion
cations balanced out by Cl- ions
neural plasma membrane permeability
K+ diffuse out of the cell more easily than Na+
allows internal portion of the cell to become more negative
graded potential
incoming signals over a short distance
action potential
long distance signaling
depolarization
decrease in membrane potential
inside becomes less negative
hyperpolarization
increase in membrane potential
inside becomes more negative
graded depolarization
sodium ions (+) enter the cell
graded hyper-polarization
chloride ions (-) enter the cell
basis of neural signaling
converting local potentials to action potentials is the basis of neural signaling
graded potential v action potential
graded: magnitude varies with signal strength
action: do not decay with distance, excitable membranes
action potential generation
resting state: all gated Na+ and K+ channels closed
depolarization: Na+ channels open, reach threshold level, self generating
repolarization: Na+ channels are inactivating, K+ channels open
hyperpolarization: K+ channels remain open and Na+ channels reset
action potential threshold
must reach -55 mV
all or nothing; reached and does not happen
propagation
spreads from point of origin
frequency of AP
frequency of AP determines the stimulus intensity
AP refractory period
neurons cannot respond until the Na+ channels reset
elevated threshold level
saltatory conduction
myelinated axons, jumps from node to node
continuous conduction
unmyelinated, every section of axolemma must propagate action potential, slows conduction speed
conduction velocity facors
axon diameter, degree of myelination
fiber group a
largest diameter
thick myelin sheath
somatic sensory and motor fibers
300+ mph
fiber group b
intermediate diameter
light myelin sheath
ANS
30 mph
fiber group c
smallest diameter
non-myelinated
ANS
2 mph
AP trigger zone
axon hillock
AP summary
- large concentration of voltage-gated Na+ channels in axon hillock
- local potential arrives, voltage-gated Na+ channels open and start pos feedback loop, massive depolarization
- Na channels inactivated, K channels activated
- Na channels return to resting state, K channels slowly close
- after brief hyperpolarization, both channels return to resting state
synapses
junction that mediates information transfer from one neuron to the next
presynaptic neuron
transmitting the signal
postsynaptic neuron
receiving the signal
axodendritic neurons
synapses between axon endings and dendrites
axosomatic synapses
synapses between cell body and axon
synaptic transmission
transfer of chemical or electrical signals between neurons at synapse
fundamental process for most functions of nervous system
chemical synapses
make up majority of synapses in nervous system, allow for release of neurotransmitters
synaptic vesicles
filled with chemical messengers
transmit signals from presynaptic to postsynaptic neurons at chemical synapse
synaptic cleft
small ECF-filled space
separates presynaptic and postsynaptic neurons in chemical synapses
prevents direct stimulation
axon terminal
contain synaptic vesicles containing neurotransmitter
receptor region
located on cell body or dendrites
reuptake
taken in by astrocytes of presynaptic terminal
degradation
broken down by enzymes
diffusion
moves away from receptors
synapse delay
signal must wait for chemicals to diffuse
slowest/ rate-limited step
chemical synapse info transfer summary
-action potential arrives at terminal
-voltage-gated Ca2+ channels open and calcium enters axon terminal
-Ca2+ entry causes release of neurotransmitter via exocytosis
-neurotransmitter diffuses across synaptic cleft and binds to receptors
-binding opens ion channels creating a graded potential (local or action)
-neurotransmitter effects terminated
-delay
excitatory synapses
binding of neurotransmitter opens chemically gated ion channels
excitatory postsynaptic potentials occur
inhibitory synapses
reduces the ability to produce an AP
-allows Cl- to move into cell
inhibitory postsynaptic potentials
postsynaptic potentials
local potentials in membranes of postsynaptic neuron
excitatory- membrane potential of postsynaptic neuron moves closer to threshold (EPSP)
inhibitory- membrane potential of postsynaptic neuron moves farther away from threshold (IPSP)
integration
summations, synaptic potentiation, presynaptic inhibition
summation
temporal: presynaptic neurons send impulses rapidly
spatial: large stimulation event
facilitated: partially depolarized, more easily excited
synaptic potentiation
-repeated or continuous use enhances synapse’s ability to be excited
presynaptic inhibition
-one neuron can inhibit the impulse of another
neurotransmitter
-chemical substance produced by the neurons
-causes the transfer of the impulse to another nerve fiber, a muscle fiber, or some other target structure
neurotransmitter function
excitatory- depolarization
inhibitory- hyperpolarization
direct-open ion channels
indirect- secondary messenger systems
neurotransmitter receptors
channel-linked: ligand-gated ion channels
G-protein linked receptors: indirect and slow, activate secondary messenger systems
catecholamines
-dopamine
-norepinephrine
-epinephrine
indolamines
-serotonin
-histamine
amino acids
-glutamate
-aspartate
-glycine
-gamma aminobutyric acid (GABA)
peptides
neuropeptides
-substance P
-endorphins
-gut-brain peptides
purines
-ATP
-adenosine
gases and lipids
-gasotransmitters
-endocannabinoids
-tetrahydrocannabinol (THC)
acetylcholine
in neuromuscular junction
within brain and spinal cord and within autonomic nervous system
norepinephrine
(noradrenalin) influences heart rate, blood pressure, and digestion; in CNS regulates sleep/wake cycle, attention, and feeding behaviors
epinephrine
(adrenalin) similar functions as norepinephrine, more widely used as hormone by endocrine system
dopamine
movement coordination, emotion and motivation
serotonin
mood regulation, emotions, attention, feeding behaviors
histamine
regulation of arousal and attention
glutamate
most important excitatory neurotransmitter in CNS; opens channels that allow flow of both Na and Cl ions, generate EPSPs in postsynaptic neuron
Glycine/GABA
major inhibitory, induce IPSPs; hyperpolarize axolemma
substance P
pain and temperature
opioids
include endorphins, enkephalins, and dynorphins;
all elicit pain relief; nervous system depressants
neuropeptide Y
feeding behaviors; may mediate hunger or feeling full
black widow neurotoxin
toxin causes massive release of neurotransmitter; causes repetitive stimulation of postsynaptic neuron
symptoms: muscle hyperexcitability, sweating, nausea and vomiting, and difficulty breathing
bark scorpion neurotoxin
most lethal; venom prevents postsynaptic sodium channels from closing; membrane remains polarized; continues to fire action potentials
neuronal pools
functioning groups of neurons
stimuli highest at center of pool
serial processing
step by step transmission of impulse
reflexes/reflex arcs
parallel processing
segregated input
simultaneous input to different pathways
types of circuits
patterns of connection
divergent, convergent, reverberating, parallel after-discharge
