L-19

Question 1

Name the 6 important features of the synapse:

Answer 1

• Pre-synaptic axon/nerve terminal
• synaptic cleft
• post-synaptic cell
• chemoreceptors in postsynaptic cell membrane
• V gated calcium channels in pre-synaptic nerve terminals
• synaptic vesicles containing neurotransmitter

Question 2

Explain how a chemical nerve-nerve synapse works:

Answer 2

The arrival of the action potential in the presynaptic axon terminal triggers the voltage gated calcium channels to open and the diffusion of calcium into the cell causes the neurotransmitter-containing vesicles to excrete the chemical through exocytosis. The neurotransmitter triggers chemically gated Na+ channels to open which causes a local/ graded potential in the postsynaptic neuron that may later become an action potential at the axon hillock.

Question 3

Explain how electrical synaptic transmission works:

Answer 3

In some cases the pre and post synaptic neurons sit very close together and are joined by a gap junction. In this case an electrical event/ AP in the presynaptic neuron with always cause an electrical even in the postsynaptic neuron with no chemical signal involvement. These synapses are relatively rare and provide no opportunity for signal modulation

Question 4

What does NMJ stand for

Answer 4

Neuro-muscular junction

Question 5

Explain the NMJ:

Answer 5

The NMJ is the synapse between the presynaptic neuron and the effector skeletal muscle fibre. When an action potential arrived at the axon terminals, vesicles holding ACh release their contents into the neuro-muscular synapse. The chemical binds to the chemically gated sodium channels and the entry of sodium depolarises the muscle cell and opens the voltage gates sodium channels and results in an action potential. At his spreads along the sarcolemma and down the t tubules and triggers the release of calcium ions from the sarcoplasmic reticulum, leading to a muscle contraction.

Question 6

Explain the differences between Nerve- nerve synapses and Nerve-muscle synapses regarding the size of the synapse:

Answer 6

The nerve-nerve synapses are tiny and each synapse may be one of thousands on the post-synaptic cell.
The nerve- muscle synapses are huge and each muscle fibre receives input from only one neuron at one site.

Question 7

Explain the differences between Nerve- nerve synapses and Nerve-muscle synapses regarding potential AP’s in the postsynaptic cell:

Answer 7

In nerve-nerve the pre- SN will rarely bring the Post SN to threshold
In the nerve musclle the AP in the pre SN will very likely bring the muscle fibre to threshold

Question 8

Explain the differences between Nerve- nerve synapses and Nerve-muscle synapses regarding types of inputs:

Answer 8

In Nerve-nerve the inputs may be excitatory or inhibitory (EPSP or IPSP)
In nerve muscle synapses there are only excitatory inputs (EPSP)

Question 9

Explain the differences between Nerve- nerve synapses and Nerve-muscle synapses regarding were AP starts in Post SN:

Answer 9

In nerve-nerve the AP may be formed in the axon hillock if depolarisation is strong enough
In nerve- muscle the AP is initiated at the Nerve-muscle junction