NERVES & MUSCLES PHYSIOLOGY - PowerPoint Presentation

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NERVES & MUSCLES PHYSIOLOGY

Lecture

5

Dr. Amar AL-

M

usawi

MD, PhD

Synaptic plasticity:

It is the changes in the synaptic functions as a result of the history of discharging at a synapse, i.e. synaptic conduction can be strengthened or weakened on the basic of past experience.

1. Short-term post-tetanic potentiation

(

due to

buildup of excess Ca

2+

ions in the presynaptic neuron

)

.

2. Long-term post-tetanic potentiation

(

due to the

buildup of excess Ca

2+

ions in the postsynaptic neuron)

.

3. Postsynaptic habituation

(due to decrease of the presynaptic neurotransmitter release as a result of inactivation of voltage-gated Ca

2+

channels at the terminal button membrane).

Animation

Drugs that affect transmission at the neuromuscular junction:

Drugs that stimulate the muscle fiber by

Ach-like action (agonists)

or

causing excessive release of Ach

Moderate dose

 Muscle spasm

Extreme dose  F

laccid paralysis

2. Drugs that stimulate the neuromuscular junction by

inactivating

acetylcholinestrase

:

 S

pastic paralysis

3. Drugs that

inhibit transmission

at the neuromuscular junction and cause paralysis of the muscles

Inhibit Ach synthesis,

Prevent filling (storage) of the vesicles with acetylcholine,

Inhibit exocytosis of the ACH-containing vesicles

Block vesicular release of Ach

Compete with acetylcholine for the receptor sites of the end-plate membrane

Properties of skeletal muscles

:

Excitability

.

Contractility

.

Conductivity

.

Tonicity

.

Animation

Figure 4.18 B: Myosin and actin filaments.