5.1.3 neuronal comminucation

Question 1

What are the key types of receptors?

Answer 1

Mechanoreceptor-pressure
Chemoreceptor-chemical
Thermoreceptor-temperature
Photoreceptor-light

Question 2

What is a transducer?

Answer 2

A transducer transduce the external energy of the stimulus into the code of the nerve impulse.

Question 3

What is the Pacinian corpuscle?

Answer 3

Pacinian corpuscles are sensory neurones that detect mechanical pressure.

Question 4

What is the gross structure of a neurone?

Answer 4

-cell body: contains nucleus and large amount of endoplasmic reticulum and mitochondria (involved in the production of neurotransmitters).
-Dendrons: short extensions from the cell body, divide into smaller extensions called dendrites. Responsible for transmitting electrical impulses towards the cell body.
-Axons: singular, elongated nerve fibres transmitting impulses away from cell body.

Question 5

What are the three types of neurones?

Answer 5

-Sensory neurone.
-Relay neurone.
-Motor neurone.

Question 6

What is the structure of a Sensory neurone?

Answer 6

They have one dendron and one axon, the cell body is in the middle of the neurone.
They also have myelin sheath and node of Ranvier.

Question 7

What is the structure of a Relay neurone?

Answer 7

They have many short axons and dendrons coming off the cell body.

Question 8

What is the structure of a Motor neurone?

Answer 8

One long axon and many short dendrites. The cell body is on the end and also has a myelin sheath and node of Ranvier.

Question 9

What is the usual pathway for an electrical impulse?

Answer 9

Receptor->Sensory neurone->Relay neurone->Motor neurone->Effector cell.

Question 10

What is the structure of the myelin sheath?

Answer 10

Myelin sheath is made of layers of plasma membrane.
Schwann cells produce layers of membrane by growing around the axon.

Question 11

What is the function of the myelin sheath?

Answer 11

Myelin sheath acts as an insulating layer, and allows myelinated neurones to conduct the electrical impulse at a faster speed.

Question 12

What is node of Ranvier?

Answer 12

Node of Ranvier is a gap between each Schwann cell, creates gaps in myelin sheath.

Question 13

What is the function of node of Ranvier?

Answer 13

Allows electrical impulse to ‘jump’ from one node to another=>allows impulse to be transmitted faster.

Question 14

How does a Pacinian corpuscle convert mechanical pressure into a nervous impulse?

Answer 14

1. In its normal state, the stretch-mediated sodium ion channels in the sensory neurone’s membrane are too narrow to allow sodium ion to pass through.
2. When pressure is applied to the Pacinian corpuscle, the corpuscle changes shape, causing the membrane surrounding its neurone to stretch.
3. When the membrane stretches, the sodium ion channels widen, sodium ions can now diffuse into the neurone.
4. The influx of sodium ions changes the potential of the membrane-it becomes depolarised, results in a generator potential.
5. The generator potential creates an action potential that passes along the sensory neurone.

Question 15

What is a resting potential?

Answer 15

The potential difference across a neurone when it is not transmitting an impulse.

Question 16

What causes the creation of a resting potential?

Answer 16

1. Sodium ions are actively transported out of the axon and potassium ions are actively transported into the axon by a sodium-potassium pump. Three Sodium ions pumped out for every two potassium ions pumped in.
2. As a result there are more sodium ions outside the membrane. Therefore sodium ions diffuse back into the axon down its electrochemical gradient, whereas potassium ions diffuse out the axon.
3. However, most of the gated sodium ion channels are closed, whereas the potassium ion channels are open. There are more positively charged ions outside the axon rather than in.

Question 17

What happens during an action potential?

Answer 17

1. Neurone has a resting potential, some potassium ion channels open but sodium voltage-gated channels closed.
2. Energy of the stimulus triggers some sodium voltage-gated channels to open, making the membrane more permeable to sodium ions.
3. The change in charge causes more sodium ion channels to open allowing more sodium ions to diffuse across axon (positive feedback).
4. When the action potential reaches +40 mV the voltage-gated sodium ion channels close, and potassium voltage-gated channels open.
5. Potassium ions diffuse out the axon, reduces the charge.
6. Initially lots of potassium ions diffuse out and the inside of the axon becomes more negative than resting state (hyperpolarisation).
7. Voltage-gated potassium channels close, sodium-potassium pump causes sodium ions to move out the cell and potassium ions in (repolarised).