Nervous system

Question 1

What is the structure of a nerve cell?

Answer 1

Soma (cell body)
Dendrites
Axon
Axon terminals

Question 2

What are afferent neurons?

Answer 2

Neurons that come from tissues/ organs

Cell body outside of CNS

Question 3

What are efferent neurons?

Answer 3

Neurons that come from CNS to effector organs

Cell body and dendrites within the CNS

Question 4

What is included in the reflex arc?

Answer 4

Sensory receptor - Sensory neuron - Relay neuron - Motor neuron (interneuron) - Effector

Question 5

What is an effector?

Answer 5

A muscle or gland that responds to motor impulses

Question 6

What is Acetylcholine and what does it do?

Answer 6

A neurotransmitter found in the brain and neuromuscular junctions.
Synthesised from choline
It acts as a chemical message .that is released by neurons and allows them to communicate with one another and other specialized cells
Broken down by the enzyme acetylcholinesterase.

Question 7

What is a neuromuscular junction?

Answer 7

A synapse between an axon and a muscle cell

Question 8

What is hyperpolarisation?

Answer 8

When the membrane is more negative than its resting value

Question 9

What is repolarisation?

Answer 9

When membrane potential is back at its resting value, Na+ channels are closed

Question 10

What is the refractory period?

Answer 10

The minimum amount of time after an action potential has occurred before another can happen.

Question 11

What is saltatory conduction?

Answer 11

When the impulse jumps along the nodes of ranvier. This occurs in myelinated neurons. It allows conduction of action potential to be faster the impulse is not going through axon walls.

Question 12

What can harm the myelin sheath? (Demyelination)

Answer 12

• Stroke
• Inflammation
• Immune disorders
• Nutritional deficiencies
• Metabolic disorders
• Excess drug and alcohol use

Question 13

What initiates action potential?

Answer 13

Outside the body stimulus e.g. touch

Inside the body stimulus e.g. change in concentration of carbon dioxide in the blood

Question 14

What is an excitatory neurotransmitter?

Answer 14

A neurotransmitter with stimulating effect
Increases chance of action potential
e.g. epinepherine

Question 15

What is an inhibitory neurotransmitter?

Answer 15

A neurotransmitter than inhibits neurones
Decreases likelihood of action potential
E.g. GABA, endorphins

Question 16

What are neuromodulators?

Answer 16

Neurotransmitters that effect a large number of neurons at one time and can influence other neurotransmitters
They don’t activate receptors of neurons but work with neurotransmitters to enhance their effect.

Question 17

How is an impulse passed through a synapse?

Answer 17

Chemical synapses

1. Action potential arrives at synaptic knob, causing calcium voltage gated channels to open.
2. Calcium flows into the synaptic knob and allows vesicles to fuse with the cell membrane releasing the neurotransmitters, via exocytosis, across the synaptic cleft
3. The neurotransmitters bind to the receptors on postsynaptic synapse
4. Sodium channels open so sodium diffuses in
5. Depolarisation occurs and action potential on post synaptic neurone is generated if threshold is reached

Question 18

What is the mechanism of Na-K ATPase pump

Answer 18

1. 3x Na bind to a transporter protein with high affinity
2. The binding activates enzyme activity of ATP
3. Phosphorylation occurs on the surface of the protein and ADP is released
4. This causes a conformational change exposing Na to the extracellular fluid
5. This then reduces the affinity for Na and Na is released
6. It now has a high affinity for K, 2 bind to the extracellular surface of the transporter protein
7. Dephosphorylation occurs
8. Transporter protein returns to its original shape
9. It now has a low affinity for K, so K is released into the intracellular fluid

Question 19

Describe resting potential

Answer 19

Inside the cell is more negatively charged than the outside.
There are more K in the cell and more Na outside the cell
Na-K atpase pump actively transports 3 sodium ions out for every 2 potassium in
Some K channels are open whilst Na channels are closed so K ions diffuse back out decreasing the potential further

Question 20

Describe how an action potential is generated

Answer 20

1. The cell is at resting state, all Na channels are closed, some K channels are open
2. A stimulus causes some Na channels to open and are released down their electrical and concentration gradient.
3. If the potential difference threshold of -55mv is reached more Na channels open causing a higher influx of Na ions
4. K ion channels open and leave the cell down its concentration gradient however is slowed by its electrical gradient
5. Once the potential difference of around 40mv is reached, Na ion channels close
6. K ions continue to leave bring the membrane down to its resting potential level. K is driven by both electrical and concentration gradients
7. Hyperpolarisation occurs as K channels are slow to close and the resting potential level is overshot as too many K ions diffuse out
8. K channels close and Na-K ATPase returns membrane to its resting potential

Question 21

What is saltatory conduction?

Answer 21

Instead of the current going through the axon walls, the myelin creates insulation which means that the currents has to jump along the nodes of ranvier. This causes the conduction of action potential to be much faster.

Question 22

What is the refractory period?

Answer 22

Minimum amount of time after an AP has occurred before another one can happen. The shorter the period the quicker the the frequency of the signal generated by the axon.
After this there is a relative refractory period which requires a larger signal to generate an action potential.
Absolute refractory period is when an action potential is reached no matter the size of the signal immediately after an action potential. Na channels closed.

Question 23

How can temperature effect conduction speed?

Answer 23

It can increase it if its up to 40’C as the ions diffuse faster
But too high and the enzymes denature and the speeds decreases

Question 24

Explain how acetylcholine is reabsorbed

Answer 24

1. Acetylcholinsterase hydrolyses acetylcholine into acetyl and choline, which then diffuse back into the presynaptic neuron.
2. Mitochondrial ATP recombines acetyl and choline into acetylcholine which is then stored in vesicles
3. Na channels close in postsynaptic neuron receptor sites now there is no longer acetylcholine

Question 25

How can drugs effect synapses?

Answer 25

They can cause stimulation of the nervous system by creating more action potentials in the post synaptic neurone:

• When the drug is the same shape as the neurotransmitter they can mimic their action at the receptor and activate them, causing an AP
• They can stimulate the release of neurotransmitter they then bind and activate receptors of the the PostNS
• They could inhibit enzymes which break down neurotransmitters so there are more to bind to the receptors and they stay there for longer

They can inhibit nervous system by causing fewer action potentials in the PostSN

• Block receptors so they cant be activated
• Inhibit release of neurotransmitters from preSN so fewer receptors are activated