Neuronal physiology

Question 1

Neurons are responsive to what and which location does it use

Answer 1

Neuron are responsive to the stimuli and electrical impulse is generated throughout whole axon

Question 2

Electrical Properties of cells are due to

Answer 2

1. Ionic Concentrations
2. Permeability of cell membrane to ions
   ( determined by ion channels)

Question 3

Important Ion in regards to charge differences

Answer 3

• 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

Question 4

ion channel types

Answer 4

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)

Question 5

What is RMP

Answer 5

a charge difference across cell membrane when it is at rest ( no stimuli)

Question 6

What helps establish RMP

Answer 6

1. NA/K pump ( against concentration gradient)
2. Negatively charged org
   3.more non gated K channels ( K is major determinant of RMP)

Question 7

What is membrane Potential

Answer 7

charge difference across membrane (-70mvp)

Question 8

how does NA/K pump establish RMP

Answer 8

• 3NA out and 2K in ( pumped against concentration gr)

1.which helps maintain concentration gradient of NA/K

2. contribute a little mV to RMP ( more + ions out than in) = more positive inside

Question 9

how is K the major determinant of RMP

Answer 9

1. K goes out more because of having more open channel (follow concentration gradient at rest)
2. making inside more negative , attracting Na due to -ve cell inside
3. until -70mv is reached, more K out than Na in
4. once at -70mv, equal in and out ( more pressure on Na) = net movement of 0

Question 10

Electrically Excitable cells location and purpose

Answer 10

ONLY in muscle and nerve cells and capable of moving away from RMP in response to a stimuli

Question 11

What happens when a neuron is stimulated

Answer 11

1. gated channels open
2. Mp changes = creating graded potential ( if thereshold is reached)
3. it will trigger Action potential

Question 12

What is Graded Potential (multipolar)

Answer 12

stimulus causes change in RMP(-70) by opening gated channels changing membrane permeability

Question 13

possible results of GP

Answer 13

1. more +ve than RMP = depolarization
   (-70mv -> -65)
2. more -ve than RMP = Hyperpolarization
   (-70 to -75)

Question 14

Characteristic of GP(multipolar)

Answer 14

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)

Question 15

What happens after GP

Answer 15

Repolarization - return to RMP

Question 16

GP -> Action Potential

Answer 16

1. GP is needed to intiate a action potential
2. only in depolarization or if stimuli is large enough can lead GP to AP

Question 17

Steps from GP to AP

Answer 17

1. depolarization or summating stimuli
2. GP reaches threshold
3. Action potential

Question 18

What is Action Potential

Answer 18

a nerve signal cause by a large change in MP that propagates along axon with no change in intensity

Question 19

all or none principle of AP

Answer 19

ALL: if threshold is reached, AP is produced

None: below threshold -> NO AP

Question 20

AP Propagation

Answer 20

To be able to act as an communication device

1. AP must be propagated along the axon entire length
2. depolarization during AP ( more +) and moves into adjacent membrane
3. new membrane reaches threshold due to more + in resulting in AP

Question 21

rate of propagation depends on

Answer 21

• 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

Question 22

Steps of Synaptic Transmission at Neuronal Junction

Answer 22

-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)

Question 23

Postsynaptic potentials ( PSP) can be

Answer 23

Excitatory or inhibitory
occurs on cell body or dendrites

Question 24

Excitatory PSP

Answer 24

GP => Depolarization due to opening of NA or CA channels or closing of K channels

often actylcholine or glutamate

Question 25

Inhibitory PSP

Answer 25

Gp => hyperpolarization due to opening of K or Cl channels (stops neuron from reaching AP) (gycine and gaba)

Question 26

Synaptic transmission at Neuromuscular Junction ( location)

Answer 26

1. junction between axon terminal of neuron and individual muscle fibre

Question 27

Steps for Synaptic transmission at neuromuscular junction

Answer 27

1. nt is released = always ACh 2.Na+ chemical gates open on muscle motor end plate causing GP (End Plate Potential) 3. EPP triggers AP on sacrolemma *(lots of ACh released:: always get an AP from an EPP)*

Question 28

Phases of AP

Answer 28

1. GP reaches threshold 2. Depolarization: NA+ Channels open up causing inside to be more + (+30mv)(+ve feedback) 3. Repolarization: NA channels inactivates causing K channels to open ( K move out = decrease RMP) 4. After-hyperpolarization: K slowly closes, N reactivated and can respond to stimuli 5. After K channels close MP returns to RMP

Question 29

Absolute Refractory period ( prevents AP Summation)

Answer 29

No AP can be generated whatsoever Na channels are either open or inactivated

Question 30

Relative Refractory period

Answer 30

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)