Neuronal communication

Question 1

Describe the structure of a sensory neurone.

Answer 1

• Cell body protruding.
• The cell body contains the nucleus, mitochondria and endoplasmic reticulum - all involved in neurotransmitter synthesis.
• The cell body has 2 extensions: the dendron carries signals from receptors towards the cell body. The impulses are carried away by the axon.
• Myelin sheath formed by Schwann cells. Electrical insulator, faster transmission.
• Nodes of Ranvier maintain the quick propagation of the electrical signal down the axon.

Question 2

Describe the structure of a motor neurone.

Answer 2

• Cell body has a number of short dendrites which transmit signals from sensory/relay neurones to the cell body.
• The cell body contains the nucleus, mitochondria and endoplasmic reticulum - all involved in neurotransmitter synthesis.
• Has one long axon which extends away from the cell body to effector.
• Myelin sheath formed by Schwann cells. Electrical insulator, faster transmission.
• Nodes of Ranvier maintain the quick propagation of the electrical signal down the axon.

Question 3

Describe the structure of a relay neurone.

Answer 3

• Relay neurones have multiple short axons and dendrons.
• Central cell body.

Question 4

What is the resting state?

Answer 4

What happens in a neurone when an impulse is not being transmitted.

Question 5

What are the relative charges inside and outside of the neurone’s membrane?

Answer 5

• Inside (cytoplasm): negative
• Outside of axon: positive

Membrane is polarised.

Question 6

What is the resting potential?

Answer 6

• The value of the charge difference across the polarised membrane.

Question 7

How is a resting potential produced?

Answer 7

• Most Na+ ion channels are closed, so the rate of fac. diff. of Na+ inwards is low.
• Most K+ ion channels are open, so the rate of fac. diff. of K+ outwards is high.
• The Na/K pump actively transports 3 Na+ out for every 2 K+ it transports in.
• The combination of these two things means there is a higher concentration of positive ions on the outside of the axon membrane than on the inside (a charge difference), a membrane potential has been established.

Question 8

What ions are present across the neurone membrane?

Answer 8

Na+ and K+

Question 9

What membrane protein allows the ions to move across the axon membrane?

Answer 9

• Sodium Potassium pump

Question 10

What does the sodium potassium pump do?

Answer 10

• Uses ATP to actively transport Na+ ions out and actively transport K+ ions into the axon. This means there is a higher concentration of potassium ions inside of the cell.

Question 11

How many potassium ions are transported in vs sodium ions transported out? What effect does this have?

Answer 11

• 3 Na+ in, 2 K+ out.
• The concentration of positive ions is therefore greater on the outside of the axon than the inside. Conc gradient.

Question 12

What does the sodium potassium pump create?

Answer 12

• electrochemical gradients for both K+ and Na+.

Question 13

How else can ions move through the membrane?

Answer 13

• Through the ion channels by facilitated diffusion.

Question 14

What are the different types of ion channels?

Answer 14

• Some open at specific voltages.
• Some randomly open and close.

Question 15

Why is there a low rate of diffusion of sodium ions into the axon?

Answer 15

• The sodium ion channels are mostly closed.

Question 16

Why is there a high rate of potassium ion diffusion out of the axon?

Answer 16

• Most of the K+ ion channels are open.
• This makes the inside of the membrane more negative compared to the outside.