Synaptic Transmission, Action potential etc.

Question 1

What is the purpose of the sympathetic nervous system?

Answer 1

Prepares the body for acute/stress responses (fight or flight system).

Question 2

Effects of the sympathetic nervous system

Answer 2

Increased heart rate, pupil size, and sweating
Constricting blood vessels to skin
Decreased gastric motility and salvation

Question 3

What is the purpose of the parasympathetic nervous system?

Answer 3

Prepares the body for restful situations.

Question 4

Effects of the Parasympathetic nervous system

Answer 4

Decreased heart rate and pupil size
Increased gastric motility and salvation

Question 5

In the sympathetic nervous system:
The pre ganglionic axon of the second neuron is __, and therefore the ganglion is _____ to the CNS

Answer 5

Short, Closer to

Question 6

In the parasympathetic nervous system:
The pre ganglionic axon of the second neuron is ____, and therefore the ganglion is _____ the CNS

Answer 6

Long, Further from

Question 7

What is a voltage gated ion channel?

Answer 7

An ion channel that opens when there is a change in voltage. It only allows through a specific ion.

Question 8

What is step 1 of an action potential?

Answer 8

Initial depolarisation. Gated sodium ion channels open, causing an influx of Na+ ions into the cell. Resulting in local depolarisation.

Question 9

What is step 2 of an action potential?

Answer 9

Rapid depolarisation. When enough local depolarisation occurs, it causes the threshold to be reached (-59mV) and the membrane permeability to sodium increases dramatically, causing rapid depolarisation to spread down the axon in a Mexican wave like fashion.

Question 10

What is step 3 of an action potential?

Answer 10

Repolarisation. Sodium channels close at minimum depolarisation (+30mV), voltage gated K+ channels open which let out K+, repolarising the cell.

Question 11

What is step 4 of an action potential?

Answer 11

Hyperpolaristion. K+ channels overshoot, and the membrane potential becomes more negative than RMP.

Question 12

What is step 5 of and action potential?

Answer 12

Resting membrane potential. RMP is restored by the Na+/K+ ATPase to around -70mV.

Question 13

What are the two types of refractory periods?

Answer 13

Absolute refractory periods
Relative refractory periods

Question 14

What are absolute refractory periods?

Answer 14

The time in which no another stimulus given to the neuron, no matter how strong, will not lead to another action potential.
The inactivation gates of the sodium channels lock shut for a time after they have opened, so no sodium will pass through. No sodium = No depolarisation = No action potential

Question 15

What are relative refractory periods?

Answer 15

The period of time after the absolute refractory period, when the activation gates are open again. During this time it is really hard to send an action potential because the cell is still hyperpolarised after sending an action potential, so hit will take even more positive ions than usual to reach the threshold potential.

Question 16

What are the three ways to enhance the speed of an action potential?

Answer 16

1. Size - bigger diameter = faster
2. Sheath - myelinated = faster, as it prevents the loss of ions.
3. Saltatory conduction - Nodes of ranvier allow the AP to jump from node to node down the nerve = faster

Question 17

What are the three key components of a synapse?

Answer 17

1. Presynaptic cell made of the axon terminal, vesicles, citoskeleton, mitochondria, and voltage gated Ca2+ channels.
2. Synaptic cleft (gap between cells)
3. Post-synaptic cell - neurotransmitter receptors and often a thin synaptic membrane.

Question 18

What is the process of synaptic transmission?

Answer 18

1. An action potential triggers the opening of voltage gated Ca2+ channels
2. Calcium ions then diffuse into the axon terminal causing the release of acetylcholine by exocytosis.
3. Ach diffuses across the synaptic cleft, binding to ligand gated channels causing depolarisation = excitatory postsynaptic potential. Enough EPSP’s will trigger an action potential in the post-synaptic cell (Temporal summation).
4. Acetylcholinesterase breaks down Ach with choline being reabsorbed from the synaptic cleft to make more Ach.

Question 19

What are excitatory post-synaptic potentials?

Answer 19

an excitatory postsynaptic potential is a postsynaptic potential that makes the postsynaptic neuron more likely to fire an action potential.

Question 20

What are inhibitory post synaptic potentials (IPSP’s)?

Answer 20

Is a kind of synaptic potential that makes a post-synaptic neuron less likely to cause an action potential.

Question 21

Temporal summation

Answer 21

series of subthreshold excitatory post-synaptic potentials in one excitatory fiber produce an AP in the postsynaptic cell.