REVISION: COORDINATION

This figure shows a structure in the human nervous system. R is ​ (a)   while S is ​ (b)   . The receptors are on ​ (c)  

• synaptic vesicle
• synaptic cleft
• synapse
• chemical synapse
• ligand-gated ion channel

Describe the process at the synapse when action potential depolarizes the axon terminal.

• The high concentration of Ca²⁺ triggers the synaptic vesicles move and fuse with the presynaptic membrane.

• Neurotransmitter is released into the synaptic cleft by exocytosis.

• Neurotransmitter diffuses across the synaptic cleft towards postsynaptic membrane and bind to the protein receptor on the ligand-gated ion channels on the postsynaptic membrane.

• Ligand-gated ion channels open and Na⁺ ions diffuse through postsynaptic membrane that lead to the depolarization of the postsynaptic membrane.

• The depolarization of axon terminal causes the permeability of open Ca²⁺ voltage gated channel that trigger an influx of Ca²⁺ into synaptic knob.

This figure shows a mechanism of hormone action. State ONE example of hormone involved in this mechanism.

Match the followings.

• adenylyl cyclase

• First messenger

• Non-steroid hormone

• Identify D.

• protein kinase A

• Identify C.

Why cAMP acts as a second messenger in this mechanism? (You can choose more than one answer if suitable)

• The hormone is small.

• The hormone cannot diffuse through the membrane of the target cell.

• The hormone is insoluble in lipids.

• The hormone is lipids soluble.

Differentiate between gene activation and second messenger.

Groups:

(a) gene activation

,

(b) second messenger

• No production of a specific protein.

• Transcription and translation do not occur.

• Hormone cannot pass through the cell membrane.

• Transcription and translation occur.

• Hormone can pass through the cell membrane.

• Involves production of a specific protein.