Neural Electrophysiology Flashcards
What are the 2 types of electrical signals from the neuron?
- propagated action potential that can travel long distances
- local grated potential that do not spread from their site of formation
Define propagated action potential.
can travel long distances
Define local grated potential.
do not spread from their site of formation
What is the potential difference?
- separation of charge ( negative from positive)
- measured in volts
In living things charges come from what?
ions separated by membranes; they can move through channels in membranes
Potential difference in living things is measured in____.
millivolts (mV)
What are the 2 types of ion channels?
- Passive (aka leakage) channels that ions move freely through
- Active (aka gated) channels that require energy
What are some characteristics of leakage channels?
- open randomly
- cells generally contain more K channels than Na channels
What are some characteristics of gated channels?
- can be open or closed (we can control them)
- there are 3 types
a. voltage-gated channels
b. ligand-gated channel
c. mechanically-gated channel
What are voltage gated channels?
- a gated channel that opens or closes due to voltage change
What are ligand-gated channels?
- gated channels that open or close based on chemical stimuli
What are mechanically-gated channels?
- gated channels that open by mechanical stimulation
What is resting membrane potential?
- potential differnce measured acroos the cell membrane of an unstimulated (resting) nerve cell
- normally -60 to -70 mV
What is resting membrane potential?
- result of different composition of ICF (k and protiens) compared to ECF (Na and Cl)
What is determined by the relative permeability of membrane to Na and P?
Membrane potential
What are graded potentials?
small local deviations from resting membrane potential
What are 2 types of graded potential?
hyperpolarized (when membrane potential becomes more negative)
depolarized ( when membrane potential becomes more positive
When something is hyper polarized is is more ______.
negative
When something is depolarized it is more_______.
positive
What is an action potential?
(aka nerve impulse)
- brief, transient, local period of membrane depolarization
- membrane potential changes from -70mV to +30 mV and back again
What are the phases of an action potential?
- depolarization
- repolarization
- hyperpolarization
Depolarization is when….
resting membrane potential become more positive
Repolarization is when….
return of depolarization membrane potential to ward resting membrane potential
After- Hyperpolerization is when ….
there is a movement of resting membrane potential away from 0
- eg. -70 > -85 mV
- extra potassium leaks out of the cell causing the voltage to drop to -85mV
What is the threshold potential?
- -55mV
- the point at which a local potential becomes a self-propagating action potential
What is the all or nothing phenomenon?
- if the threshold potential is exceeded, an action potential is generated
- if the threshold potential is NOT exceeded, NO action potential is generated
- all action potentials are identical
What is the refractory period?
time following the onset of an action potential when it is impossible or difficult to produce a second one
(NO action potential during the ABSOLUTE REFRACTORY period; at the top of the curve on the graph)
What are some charactersitics of sodium gates?
- voltage-gated channels have 2 gates (activation gate, and inactivation gate (when closed it will not respond to stimuli)
- In a resting neuron the inactivation gate i open and the activation gate is closed
- depolarizaton opens activation gates, then closes in activation gates
When the cell is resting the inside is more ____ and the outside is more_____.
- inside is more negative
- outside is more positive
What are the 4 stages of changes in ion flow through voltage gated channels during the depolarization, and repolarization of an action potential
- Resting state- voltage gated Na and K channels are closed
- Depolarization- the depolarization to threshold -55mV, opens sodium channels and sodium rushes into the cell
- Repolarization- K channels finally open so K leaves the cell, and Na inactivation gated channels close
- Repolarization phase continues- outflow of K restores resting membrane potential, Na channel inactivation gates reopen and K channels close(p.469)
What happens to the voltage gated channels during resting state?
The K and Na channels remain closed
What happens to the voltage gated channels during depolarization?
the depolarization to threshold -55mV, opens sodium channels and sodium rushes into the cell
What happens to the voltage gated channels during repolarization?
K channels finally open so K leaves the cell, and Na inactivation gated channels close
What happens to the voltage gated channels during repolarization continuation?
outflow of K restores resting membrane potential, Na channel inactivation gates reopen and K channels close(p.469)
Summerize the chemical events of the action potential.
- Na gates open and Na enters the cell
- Na gates close & Na is trapped
- K gates open & K leaves the cell
- K gates close and the Na pump restores resting membrane potential
Define propagated action potential.
action potential that is transmitted along the length of an axon (aka nerve impulse)
What are the 2 types of propagation?
- continuous conduction (goes through action potential at each section in non myelinated neurons, slow)
- saltatory conduction (goes through action potential at each node of Ranvier, fast)
Define Continuous conduction.
step-by-step depolarization of each portion of the length of the axolemma; occurs in unmyelinated neurons
Define Saltatory Conduction.
occurs in myelinated fibres; depolarization happens only at the nodes of Ranvier where there are more sodium channels; between the nodes the current diffuses through ECF and ICF
What makes the action potential travel faster?
- longer diameter axons
- myelinated axons
Describe A fibres largest (130m/sec)
they are militated SOMATIC sensory fibres, motor fibres to skeletal muscle;
Largest and fastest
Describe B fibres medium (15m/sec)
myelinated VISCERAL sensory fibres, autonomic preganglionic fibres
Describe C fibres smallest (2m/sec)
UNMYELINATED sensory fibres, AUTONOMIC motor fibres
List the steps to synaptic transmission.
- action potential arrives
- Ca enters axon terminal, triggers the release of neurotransmitters to the synaptic cleft
- vesicles migrate to presynaptic membrane, neurotransmitters are released and diffuse across the synaptic cleft
- neurotransmitters bind to ligand-gated receptor sites on post synaptic neuron
- sodium enters post synaptic cell
- pstsynaptic membrane depolarize to threshold
- action potential occurs inthe post synaptic neuron
What happens to neurotransmitters after the next AP is triggered?
- enzyme breaks them off the receptor site
- then they either
a. get reabsorbed (reuptake)
or b. inactivate by an enzyme (degradation
or c. diffuse away
The neurotransmitters can either be ____ or ____.
excitatory or inhibitory
What are excitatory postsynaptic potentials (aka EPSP’s)?
produced by neurotransmitters at the postsynaptic membrane (OPEN Na CHANNELS) causing post synaptic cell to be MORE likely to reach threshold
What are inhibitory postsynaptic potentials
produced by neurotransmitters at the postsynaptic membrane (OPEN Cl & K CHANNELS) causing post synaptic cell to be LESS likely to reach threshold
Define Spatial summation.
summation of effect of neurotransmitters released from SEVERAL END BULBS ONTO ONE NEURON
Define Temporal summation.
summerization of effect of neurotransmitters released from TWO OR MORE FIRINGS of the SAME END BULB in RAPID succession ONTO SECOND NEURON
What are the 2 main categories of neurotransmitters?
- small-molecule
- neuropeptides
What are the 5 types of small neurotransmitters?
- ACETYCHOLINE (AcH); released from either CNS or PNS and is mainly inhibitory except at NMJ; inactivated by AchE
- AMINO ACIDS; ex. GABA-inhibitory neuro transmitter for 1/3 of the brain synapses; glutamate- released by nearly all excitatory neurons in the brain.
- BIOGENIC AMINES; (aka catecholamines) ex. tyrosine derivatives (norepinephrine-regulates mood, dreaming, and wakefulness; dopamine- regulated skeletal muscle tone; seritonin- regulates mood, body temp, and sleep)
- ATP and OTHER PURINES
- NITRIC OXIDE
Desrcibe neuropeptides.
- numerous and widespread in CNS and PNS
- have excitatory and inhibitory action
- some also act as hormones (ex. angiotensin2 and CCK)
