13.2 Neurones

Question 1

What is the role of the nervous system?

Answer 1

To direct changes in the internal and external environment

These changes are known as stimuli

Question 2

What is the nervous system made up of?

Answer 2

Billions of neurones

Question 3

What is the role of neurones?

Answer 3

To transmit electrical impulses around the body so the organism can respond to changes in the internal + external environment

Question 4

What does the cell body of a neurone contain?

Answer 4

• Cell body contains the nucleus which is surrounded by the cytoplasm
• In the cytoplasm, there are large amounts of endoplasmic reticulum + mitochondria, which are involved in the production of neurotransmitters

Question 5

What are neurotransmitters?

Answer 5

Chemicals used to pass signals from one neurone to the next

Question 6

What are dendrons?

Answer 6

• Short extensions which come from the cell body

- These divide into smaller and smaller branches known as dendrites

Question 7

What is the role of dendrites?

Answer 7

Transmit electrical impulses towards the cell body

Question 8

What are axons?

Answer 8

Singular, elongated nerve fibres that transmit impulses away from the cell body

• Axons are very long
• Axons are cylindrical in shape, consisting of a narrow region of cytoplasm surrounded by a plasma membrane

Question 9

What are the 3 groups of neurones?

Answer 9

Sensory neurones
Relay neurones
Motor neurones

Question 10

What are sensory neurones?

Answer 10

Transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain

• They have one dendron, which carries the impulse to the cell body
• They have 1 axon, which carries the impulse away from the cell body

Question 11

What are relay neurones?

Answer 11

Transmit impulses between neurones
- They have many short axons and dendrons

For example:
Between sensory neurones and motor neurones

Question 12

What are motor neurones?

Answer 12

Transmit impulses from a relay/sensory neurone to an effector, such as a muscle or gland.
- They have one long axon and many short dendrites

Question 13

What is the electrical impulse pathway?

Answer 13

Receptor→Sensory Neurone→Relay Neurone→Motor Neurone→Effector Cell

Question 14

What are some neurons covered in?

Answer 14

Myelin sheath

Question 15

What is myelin sheath made from?

Answer 15

Many layers of plasma membrane

Question 16

What do Shwann cells do?

Answer 16

Produce layers of membrane by growing around the axon several times

• Each time the Shwann cells grow around the axon, a double layer of phospholipid bilayer is laid down
• When Shwann cells stop growing, there are around 20 layers of membrane around the axon

Question 17

What is the role of myelin sheath?

Answer 17

Acts as an insulating layer + allows myelinated neurones to transmit electrical impulse at a much faster speed than unmyelinated neurones

Question 18

How fast can myelinated neurones transmit impulses versus unmyelinated neurones?

Answer 18

Myelinated neurones transmit impulses at 100m/s

Non-myelinated neurones transmit impulses at 1m/s

Question 19

What is the node of Ranvier?

Answer 19

A gap between each Shwann cell, 2-3 microns

Question 20

What is the role of the node of Ranvier?

Answer 20

To create gaps in the myelin sheath, every 1-3mm in humans

Question 21

What is the role of the myelin sheath?

Answer 21

To act as an electrical insulator

Question 22

What happens in myelinated neurones?

Answer 22

Electrical impulse jumps from one node to the next as it travels along the neurone
- This allows the impulse to be transmitted much faster

Question 23

What happens in non-myelinated neruones?

Answer 23

Electrical impulse doesn’t jump, it transmits continuously along the nerve fibre so is much slower