13.2 Neurones

Question 1

Neurones

Answer 1

The NS is responsible for detecting changes in the internal and external environment. These changes are called a stimulus. The information is then processed and an appropriate response is triggered.

Role of neurones = to transmit electrical impulses around the body.

Question 2

What’s the Structure of a neurone

Answer 2

Cell body - contains the nucleus surrounded by cytoplasm. Within the cytoplasm there are large amounts of ER and mitochondria which produce neurotransmitters.

Dendrons - short extensions which come from cell body. Divide into smaller branches called dendrites; transmit impulses TOWARDS cell body.

Axons - singular, elongated nerve fibres that transmit impulses AWAY from body. Can be very long and the fibre is cylindrically shaped consisting of a very narrow region of cytoplasm surrounded by a plasma membrane.

Question 3

What are the 3 Types of neurone

Answer 3

Can be divided based on their function
Sensory -> transmit impulses from receptors to relay neurones, motor neurones or the brain. Have 1 dendron, 1 axon.

Relay -> transmits between impulses. Have short axons and dendrons.

Motor -> transmit from relay or sensory to an effector. Have one long axon and many short dendrites.

Question 4

What is the order of a Sensory Arc

Answer 4

Receptor -> sensory -> relay -> motor -> effector cell

Question 5

What are Myelinated neurones

Answer 5

Axons of some neurones are covered in a myelin sheath, made of many layers of plasma membrane.
Schwann cells produce these layers of membrane by growing around the axon many times.

The myelin sheath acts as an insulating layer and allows the myelinated neurones to conduct the electrical impulse at a much faster speed. (Transmit up to 100m/s compared to 1m/s)

Question 6

What are Myelin sheaths

Answer 6

Each Schwann cell has a small gap between the them and the next one, called the node of Ranvier (2-3 micrometers). This creates small gaps in the myelin sheath.

In myelinated neurones, the impulse ‘jumps’ from one node to another; this allows the impulse to be transmitted much faster.

Question 7

What are the features of a sensory receptors

Answer 7

1. specific to a single type of stimulus

2. act as a transducer - convert stimulus into impulse

Question 8

What are the 4 main types of sensory receptor

Answer 8

1 mechanoreceptor - pressure/movement - Pacinian corpuscle - skin

2. chemoreceptor - chemicals - olfactory receptor - nose
3. thermoreceptor - heat - end-bulbs of Krause - tongue
4. photoreceptors - light - cone cell - eye