CBG 31 Flashcards
where is action potential initiated in neuron?
spike initiation/ near axon hollcock
neuroglial cells?
modulating the rate of nerve signal propagation, modulating synaptic action by controlling the uptake of neurotransmitters, providing a scaffold for some aspects of neural development. Also recovery help
what is the mylein sheath an outgrowth of?
type of glial cell
schwann cells
Supply the myelin for the peripheral nervous system.
what do dendrites receive?
presynaptic terminal signals and dendrites determine if action potential arises
what is multiple sclerosis?
loss of co ordinated muscle activity due to myelin sheath loss
are there voltage gated ion channels along myelinated fibers?
NO. Myelinated fibers lack voltage-gated ion channels (approximately 25 μm/m2) along the myelinated internodes, exposing them only at the nodes of Ranvier.
is it easier for vertebrates to repair neurones than low vertebrates such as salamanders?
no. vice-versa
what carries information?
electrical action potentials alternating with chemical synaptic signals
what are relay neurones also known as?
interneurones
what are examples of external and internal stimuli?
light and limb position
soma?
cell body of neurones
where is neurotransmitter secretion?
axon terminals
what are 2 main effector organs?
muscles (contraction)
Glands (secretion)
what needs to be recahed for an action potential to be generated?
threshold potential
depolarisation?
more positive, inward current of Na+
what channels are always open at rest?
leaky potassium K+ out
are there 2 types of potassium channels?
yes leaky and voltage-gated that open in response to depolarisation
what is reploarizing?
membrane potential is rapidly returning to the resting potential, activation of voltage gated potassium channels are at max and number of open Na+ channels is dramatically reduced
what is the repolaristation beyong the resting membrane voltage called?
hyperpolariastion. occurs because most v-g potassium channels are still open.
what happens during the recovery phase?
membrane potential returns to steady state and occurs as the delayed voltage gated potassium channels that were opened during the action potential now close. Membrane potential is determined by other channels normally open at resting potential
what is the threshold?
-40mV = activation
conductance?
how much charge is generated
is it positive or negative feedback in neurones?
POSITIVE.usually i biological systems this is a negative thing but here it is advantageous as allows system to work as quickly as possible
if threshold reached,Na+ channels open, Na+ enters, bigger membrane depolarisation.
Positive feedback of Na+ entry
Vm
voltage of membrane
ENa
equilibrium of Na so +40
Erev
resting voltage of membrane -70
Ek
equlibrium of potassium
-100
ECl
equilib Cl -60
what are gNa and gK ?
gNa and gK are both functions of time and membrane potential.
when gNa is hig hwhat does the membrane potential approach?
Na equilibrium of +40
what 3 things define things as voltage gated ion channels?
sensitive to membrane voltage
selective to ions
inactivation
what 4 different classes of VGIC can you name?
Na+,K+,Ca2+,Cl-
what are vgic made up of domain wise? which one is modulatory?
several Beta subunits VGSCB involved in modulatory roles
Alpha subunit VGSCa 4 transmembrane domain 240 kda and family of 9 gene products in vertebrates Nav1.1,Nav1.9
expressed in variety of cell types-cardiac muscle, neurones (Brain and PNS), skeletal muscle, smooth muscle). (ii) Called Nav1.1, Nav1.2 etc
where are alphas subunits thought to be arranged around?
central pole
where is the voltage sensor thought to be?
segment 4
how are Voltage-gated Na+ and Ca2+ channels similar
both are composed of alpha-subunits containing four-transmembrane domains (I-IV)
each domain with six transmembrane segments.
-several smaller proteins associated with the a-subunit (beta-subunits only for Na+ channels)
whilst Ca2+ channels have b, g, and d subunits).
how many nm across is the lipid bilayer?
5NM
how many v per cm for a 50mV pd?
100,00V per cm
what direction does AP travel in?
left to right
why is transmission unidirectional?
a patch of newly depolarized membrane cannot initially be reactivated
what amino acids are in segment 4?
Positively charged amino acids (arginine + lysine)
how does the
The action potential generated at the axon hillock propagates as a wave along the axon.The currents flowing inwards at a point on the axon during an action potential spread out along the axon, and depolarize the adjacent sections of its membrane. If sufficiently strong, this depolarization provokes an action potential at the neighboring membrane patches.
Once an action potential has occurred at a patch of membrane, the membrane patch needs time to recover( refractory period - time required for the voltage-activated sodium channels to recover from inactivation). There are many types of voltage-activated potassium channels in neurons, some of them inactivate fast and some of them inactivate slowly or don’t. Variability guarantees that there will be always an available source of current for repolarization, even if some of the potassium channels are inactivated. However all activated sodium channels inactivate within several millisecond during strong depolarization, thus making following depolarization impossible until a substantial fraction of sodium channels have returned to their closed state. Although it limits the frequency of firing,the absolute refractory period ensures that the action potential moves in only one direction along an axon.The currents flowing in due to an action potential spread out in both directions along the axon.
what is antidromic conduction?
opposite way of conduction. Very rare.
However, if a laboratory axon is stimulated in its middle, both halves of the axon are “fresh”, i.e., unfired; then two action potentials will be generated, one traveling towards the axon hillock and the other traveling towards the synaptic knobs.
