Nervous system pt. V (RA)

Question 1

State how different factors affect the speed of transmission of action potential.

Answer 1

The diameter of the axon is directly proportional to speed.
The presence of myelin sheath increases the speed due to saltatory conduction.
Higher temperature allows faster transmission as diffusion rate of ions (local passive current) is increased.

Question 2

State how stimuli of different intensities are differentiated between.

Answer 2

By frequency of action potentials. The greater the strength of the stimulus, the more action potentials are initiated per unit time.

Question 3

Define synaptic transmission.

Answer 3

Synaptic transmission is the process by which one neuron communicates with another neuron or gland cell or muscle cell. It occurs at the synapse.

Question 4

Describe the movement of neurotransmitters.

Answer 4

At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters. Neurotransmitters bind to receptors on the postsynaptic cell. At neuromuscular junctions, neurotransmitters make muscle cells either contract or relax.

Question 5

Describe the process of synaptic transmission at the cholinergic synapse.

Answer 5

Neurotransmitters are manufactured by neurons and stored in vesicles at the axon terminals. An arriving action potential depolarizes the axon terminal membrane of a presynaptic neuron. Voltage-gated calcium ion channels are opened, and calcium ions enter the cytosol of the axon terminal. This results in the vesicles fusing with the pre-synaptic membrane. Neurotransmitter molecules are released into the synaptic cleft. Acetylcholine diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane. Cation (Na+) channels open, producing a graded depolarization due to Na+ inflow. Depolarization ends as acetylcholine is broken down into acetate and choline by acetylcholinesterase in the synaptic cleft. The axon terminal reabsorbs choline from the synaptic cleft and uses it to resynthesize acetylcholine. Post-synaptic membrane repolarizes.

Question 6

State the ways in which neurotransmitters can be inactivated by.

Answer 6

They can be inactivated by enzyme inactivation: degradation of enzymes or products being recycled or diffuse away from synaptic cleft.
Re-uptake by pre-synaptic transporters.
Diffusion away from synapse.