Neuro-muscular Synapsis

Question 1

What is the Df of synapses?

Answer 1

• synapses: is morpho-functional formation for transferring excitation from one cell to another

Question 2

Structure of chemical neuro-muscular synapsis ?

Answer 2

Synapses consisted of three main elements:
1- presynaptic membrane
2- synaptic gap
3- postsynaptic membrane

Question 3

What is the all elements of synapses?

Answer 3

1-presynaptic membrane 
2-synaptic gap
3-postsynaptic membrane 
4-axon
5-synaptic patch 
6-vesicles
7-spread of excitation
8-Calcium channel
9-unpacked vesicles 
10-diffusion of a mediator to postsynaptic membrane 
11-connection of a mediator with receptor 
12- receptor and chemoexcited channel 
13- entry  of cations ( calcium and sodium )

Question 4

Explain the mechanism of synaptic transmission ?

Answer 4

-1-first the arrival of exterior irritant , for the synapses exterior irritant will be AP in form of local current coming by axon to presynaptic membrane these local current from axon open the calcium channel on the presynaptic membrane and the sodium channel also open because the exterior irritant

-2- calcium enters inside through the presynaptic membrane causing depolarisation inside the synaptic patch it’s essential for unpacking the mediator
In a neuro-muscular synapses acetylcholine (AH) its mediator after AH diffuses to the postsynaptic membrane , there its connect with a special receptor can connect only with a mediator and dont react to any other irritation, receptor on AH are called (cholinergic receptor (HER)
-3- due to intraction of ( HER) and AH channels on the postsynaptic membrane are opening , this channel called chemoexcited channel ( ChEC) through it sodium and calcium ions pass inside the postsynaptic membrane

And the result will be generation of an impulse ( depolarization) on a postsynaptic membrane

Question 5

Morphology of myelin sheath ?

Answer 5

-myelin sheath is formed from Schwann cell and contains a large amount of fat
, fat is dielectric not conductive of electrical current
- in the process of ontogensis at the place where its axon grows and develops together with axon grow not just extending in length but as if screwing into tissues ,
- thus myelin is winded on the axon and small areas of an axon free from myelin are formed : nodes of ranvier

Question 6

Law of conduct

Answer 6

1- on a myelinted nerve fiber local current are spread in salutatory way , from one node of ranvier to the next , thats why the speed of spread is high
2-isolation
3-Bilateralism : local current pass only from the body of neuron to synapses
4- law of anatomical and physiological integrity

Question 7

Comprative characterstic of excitation spreading along a synapsis and nerve fiber

Answer 7

• 1-
• Nerve fiber : high.
• comprative sign : speed
• synapsis : low ( synaptic delay )
• 2-
• Nerve fiber : high
• comprative sign : lability
• synapsis : low
• 3-
• Nerve fiber : low.
• comprative sign : fatiguability
• synapsis : high
• 4-
• Nerve fiber : can bilateral.
• comprative sign : direction
• synapsis : only one way

Question 8

Differences between chemoexcited chnnels and electroexcited channels

Answer 8

1- location :
- Chec : only on postsynaptic membrane 
-EEC : on any other membrane of excitable tissue 
2- irritation :
- Chec : only by a mediator 
-EEC : by any irritation 
3- ion transmission 
- Chec : able to pass any ion
-EEC : specific and only one type of ion which potassium