Neuronal physiology Flashcards
Neurons are responsive to what and which location does it use
Neuron are responsive to the stimuli and electrical impulse is generated throughout whole axon
Electrical Properties of cells are due to
- Ionic Concentrations
- Permeability of cell membrane to ions
( determined by ion channels)
Important Ion in regards to charge differences
- Na/K : maintains NA/K pump
- Ca2 : due to various transporters in cell
- Cl: repelled by -org ( higher outside than in)
- Negative Org: stay inside cell
ion channel types
Non- gated: always open and more K gates causing K to cross more at rest ( helps establish RMP)
Gated: opens in response to stimuli
(voltage, chemical,thermal and mechanical)
What is RMP
a charge difference across cell membrane when it is at rest ( no stimuli)
What helps establish RMP
- NA/K pump ( against concentration gradient)
- Negatively charged org
3.more non gated K channels ( K is major determinant of RMP)
What is membrane Potential
charge difference across membrane (-70mvp)
how does NA/K pump establish RMP
- 3NA out and 2K in ( pumped against concentration gr)
1.which helps maintain concentration gradient of NA/K
- contribute a little mV to RMP ( more + ions out than in) = more positive inside
how is K the major determinant of RMP
- K goes out more because of having more open channel (follow concentration gradient at rest)
- making inside more negative , attracting Na due to -ve cell inside
- until -70mv is reached, more K out than Na in
- once at -70mv, equal in and out ( more pressure on Na) = net movement of 0
Electrically Excitable cells location and purpose
ONLY in muscle and nerve cells and capable of moving away from RMP in response to a stimuli
What happens when a neuron is stimulated
- gated channels open
- Mp changes = creating graded potential ( if thereshold is reached)
- it will trigger Action potential
What is Graded Potential (multipolar)
stimulus causes change in RMP(-70) by opening gated channels changing membrane permeability
possible results of GP
- more +ve than RMP = depolarization
(-70mv -> -65) - more -ve than RMP = Hyperpolarization
(-70 to -75)
Characteristic of GP(multipolar)
1, ions move passively = current flow
2. short distance signals = die quickly
3. magnitude and distance traveled varies on the strength of stimuli
4. can summate (multiple stimuli added up creating GP)
What happens after GP
Repolarization - return to RMP
GP -> Action Potential
- GP is needed to intiate a action potential
- only in depolarization or if stimuli is large enough can lead GP to AP
Steps from GP to AP
- depolarization or summating stimuli
- GP reaches threshold
- Action potential
What is Action Potential
a nerve signal cause by a large change in MP that propagates along axon with no change in intensity
all or none principle of AP
ALL: if threshold is reached, AP is produced
None: below threshold -> NO AP
AP Propagation
To be able to act as an communication device
- AP must be propagated along the axon entire length
- depolarization during AP ( more +) and moves into adjacent membrane
- new membrane reaches threshold due to more + in resulting in AP
rate of propagation depends on
- Diameter of Axon: larger diameter, the faster
- Myelination:
(unmylinated = continous making it slower)
(myelinated = AP occurs on ranvier, group out so AP can jump to the next = faster) - Fiber types:
Type A: large diameter, mylinated, faster propagation(130m), sensory neurons and motor neurons to skeletal muscles
-Type C: small diameter, unmyelinated, slow propagation (0.5m), Autonomic NS and pain fibers
Steps of Synaptic Transmission at Neuronal Junction
-AP arrives at axon terminal ( synaptic end bulb)
-Ca++ voltage gates open due to AP and enter inside
- rise in Ca triggers Exocytosis of nt containing vesicles
- nt diffuses across synaptic cleft, bind to specific receptors on postsynaptic membrane
( receptors = chemically gated opens in response to nt) - gates ion channels open - in and out of ion in postsynapthic membrane creating GP called postsynapthic potential (PSP)
Postsynaptic potentials ( PSP) can be
Excitatory or inhibitory
occurs on cell body or dendrites
Excitatory PSP
GP => Depolarization due to opening of NA or CA channels or closing of K channels
often actylcholine or glutamate
Inhibitory PSP
Gp => hyperpolarization due to opening of K or Cl channels
(stops neuron from reaching AP)
(gycine and gaba)
Synaptic transmission at Neuromuscular Junction ( location)
- junction between axon terminal of neuron and individual muscle fibre
Steps for Synaptic transmission at neuromuscular junction
- nt is released = always ACh
2.Na+ chemical gates open on muscle motor end plate causing GP (End Plate Potential)
- EPP triggers AP on sacrolemma
(lots of ACh released:: always get an AP from an EPP)
Phases of AP
- GP reaches threshold
- Depolarization: NA+ Channels open up causing inside to be more + (+30mv)(+ve feedback)
- Repolarization: NA channels inactivates causing K channels to open ( K move out = decrease RMP)
- After-hyperpolarization: K slowly closes, N reactivated and can respond to stimuli
- After K channels close MP returns to RMP
Absolute Refractory period ( prevents AP Summation)
No AP can be generated whatsoever
Na channels are either open or inactivated
Relative Refractory period
where AP can be generated but only when stimuli is greater than normal
Na channels are reactivated when MP passes RMP ( can be opened if threshold reached)
