5.1.3 - Neuronal Communication

Question 1

What is a stimulus?

Answer 1

A change in the internal or external environment

Question 2

What are the main 3 key features of a neurone?

Answer 2

Cell body, dendrons, axons

Question 3

What is the cell body?

Answer 3

Contains the nucleus surrounded by cytoplasm. Cytoplasm contains large amounts of endoplasmic reticulum and mitochondria which are involved in neurotransmitter production

Question 4

What are dendrons?

Answer 4

Short extensions which come from the cell body. They divide into smaller and smaller branches called dendrites. They are responsible for transmitting electrical impulses towards the cell body

Question 5

What are axons?

Answer 5

Elongated nerve fibres that transmit impulses away from the cell body

Question 6

What are the three types of neurones?

Answer 6

Sensory, relay, and motor

Question 7

Describe sensory neurones

Answer 7

Neurones that transmit impulses from a sensory receptor to a relay neurone, motor neurone, or the brain. They have one dendron, which carries the impulse to the cell body, and one axon, which carries the impulse away from the cell body

Question 8

Describe relay neurones

Answer 8

Neurones that transmit impulses between neurones

Question 9

Describe motor neurones

Answer 9

Neurones that transmit impulses from a relay neurone or sensory neurone to an effector. They have one long axon and many short dendrites

Question 10

What covers the axons of some neurones?

Answer 10

Myelin sheath, made of many layers of plasma membrane. They are produced by Schwann cells

Question 11

What is a mechanoreceptor?

Answer 11

A receptor that responds to pressure and movement

Question 12

What is a chemoreceptor?

Answer 12

A receptor that responds to chemicals

Question 13

What is a thermoreceptor?

Answer 13

A receptor that responds to heat

Question 14

What is a photoreceptor?

Answer 14

A receptor that responds to light

Question 15

How do receptors act as transducers?

Answer 15

They detect a range of different stimuli, before converting the stimulus into a nervous impulse, called a generator potential

Question 16

Describe the processes taking place at resting potential

Answer 16

Sodium-potassium pump is active, 3 Na+ pumped out for every 2 K+ pumped in. Most gated Na+ channels are closed, so few Na+ ions diffuse back into the axon, while many K+ channels are open, so lots of K+ ions diffuse out.

Question 17

What is depolarisation?

Answer 17

A change in potential difference from negative to positive

Question 18

What happens when a stimulus is detected?

Answer 18

Energy from stimulus triggers some Na+ ion channels to open, making membrane more permeable to Na+ ions. Na+ ions diffuse in, increasing the membrane potential

Question 19

What does the increase in charge cause?

Answer 19

More Na+ ion channels to open. This is positive feedback

Question 20

What happens when the potential difference reaches +40 mV?

Answer 20

Na+ ion channels close and K+ ion channels open.

Question 21

What happens once the K+ ion channels open?

Answer 21

K+ ions diffuse out of the axon, decreasing membrane potential. It becomes more negative than its resting state, which is known as hyperpolarisation

Question 22

What happens after hyperpolarisation?

Answer 22

K+ ion channels close. Sodium potassium pump is still active. Axon returns to membrane potential.

Question 23

What is meant by the all or nothing principle?

Answer 23

Nerve impulses are said to be all-or-nothing responses. A certain level of stimulus, a threshold value, always triggers a response.

Question 24

What are the two types of neurotransmitter?

Answer 24

Excitatory, which causes depolarisation of the postsynaptic neurone, and inhibitory, which causes hyperpolarisation of the postsynaptic neurone

Question 25

What happens during synaptic transmission?

Answer 25

Action potential reaches end of presynaptic neurone. Depolarisation of presynaptic neurone causes Ca+2 ion channels to open, so Ca+2 enters, causing secretory vesicles containing neurotransmitters to fuse with the presynaptic membrane. Exocytosis takes place. Neurotransmitters diffuse across the cleft, and bind with the receptor. This causes Na+ ion channels to open, so Na+ ions move into the postsynaptic neurone, so action potential starts

Question 26

What happens after the neurotransmitter has triggered an action potential in the postsynaptic neurone?

Answer 26

It is broken down and removed.

Question 27

What is spatial summation?

Answer 27

When a number of presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitters which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone

Question 28

What is temporal summation?

Answer 28

When a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period. This builds up in the synapse until the quantity is sufficient to trigger an action potential

Question 29

What are the roles of synapses?

Answer 29

They ensure impulses are unidirectional, they allow one stimulus to cause many responses, and they can allow many stimuli to cause one response