PHSL - 215
Graded Potential & Action Potential
Neuron
Nerve Conduction in Myelinated & Unmyelinated Nerve Fiber
Synapse
Neuromuscular Junction
1

is local (small) change in the membrane potential.
e.g. : 1- motor end plate potential
2- EPSP
3- IPSP
,
.
2

4.
5.
1.
2.
3.
Stimulus does not reach threshold level.
Stimulus causes local change in membrane potential e.g. -70 to -60mv
It dies down over short distance.
Can be summated.
Does not obey all or none law.
3.
4.
5.
1.
2.
Stimulus reaches threshold level therefore causes AP.
Stimulus causes depolarization to threshold level.
It is propagated.
Can not be summated .
Obeys all or none law.
3

Q4. Draw diagram of AP of Neuron. Show depolarization, repolarization and hyper polarization phase and give the cause of each phase.
4

Q5. Nerve fiber can be stimulated easily, when it is at RMP or at hyper polarization stage. Give reason for your answer.
At RMP because it wont need more stimulation to reach the threshold . More over, hyper polarization would be more –ve and needs stronger stimulus to reach the threshold
Q6. What is absolute refractory period?


Absolute Refractory= (none responding) Period
It is that period of action potential during which no new action potential can be initiated even by strong stimulus.
Q7. What is relative refractory period?


Relative Refractory period
It is that period during which second action potential can be produced by very strong stimulus .
5

Q8. Draw AP and show absolute and relative refractory period?
Total depolarization phase
+1\3 rd of the repolarization phase
Last2\3rd of the repolarization phase
6

7

Continuous or Contiguous conduction saltatory Conduction occurs in UNMYELINATED nerve fibers.
Slower-walkingoccurs in MYELINATED nerve fibers
Faster-jumping-
8

Q12. What is myelin sheath?
a thick layer composed of lipids covering the Axon (Nerve fiber) produced by (peripheral nerve= Schwann cells)
(central nerve= oligodendrocytes).
Q13. What is node of Ranvier?
Gaps between the myelin sheath
Q14. What factors affect nerve conduction?
1) Diameter of the nerve fiber
2) Axon (Nerve fiber) is Myelinated or Unmyelinated
3) Temperature
Q15. What is synapse?
JUNCTION BETWEEN TWO NEURON
9

Q16. Draw the diagram of chemical synapse
10

11

Q17. What is excitatory post synaptic potential (EPSP)
Q18. What is inhibitory post synaptic potential (IPSP)
EPSPs and IPSPs are graded potential [local]. They can be summated [added].
EPSP= excitation =depolarization always!!
Definition: depolarization graded potential in the post synapse or-post synaptic membrane.
IPSP= hyper polarization graded potential that occurs in post synapse or –post synaptic membrane.
Q19. What is neuromuscular junction?
junction between Motor neuron and Skeletal muscle fiber. They are linked chemically.
12

13

Q20. What is a neurotransmitter at neuromuscular junction?
acetylcholine
Q21. How acetylcholine is destroyed?
acetylcholinesterase It is located in the Motor end plate (Muscle membrane).
Q22. What is myasthenia gravis?
disease of Neuromuscular junction.
Q23. What is the treatment of myasthenia gravis?
Drug such as Neostigmine that inhibits enzyme AChE
(Acetylcholinestrase) is given. This drug prolongs the action of acetylcholine at neuromuscular junction.
14

Q1. Abeer, a medical student, had a tooth ache. She went to the dentist and the dentist advised her “filling” in a cavity in tooth. The dentist injected a local anesthetic in the nerve pathway which carries the nerve impulses from the area of tooth. Due to injection, Abeer did not feel any pain during the drilling and filling procedure.
Information – local anesthetic block voltage gated Na+ channels.
Explain how this action of local anesthetic prevents the transmission of pain impulses to the brain?
(Reference – See page 131 in ‘Human Physiology’ by Lauralee Sherwood)
15

16