Neurones

What are the key features of mammalian neurones?

• Cell body.

• Dendrons.

• Axons.

What is the cell body?

It is the part of the neurone that contains the nucleus surrounded by cytoplasm, within which there are also large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters.

What are dendrons?

These are short extensions which come from the cell body. These extensions divide into smaller and smaller branches known as dendrites.

What are dendrites responsible for?

Transmitting electrical impulses towards the cell body.

What are axons?

These are singular, elongated nerve fibres that transmit impulses away from the cell body.

What are the three types of neurone?

• Sensory neurones.

• Relay neurones.

• Motor neurones.

What is the role of the sensory neurones?

They transit impulses from a sensory receptor cell to a relay neurone, motor neurone, or the brain.

What is the general structure of sensory neurones?

They have one dendron, which carries the impulse to the cell body and one axon, which caries the impulse away from the cell body.

What is the role of relay neurones?

They transmit nerve impulses between neurones.

What is the general structure of relay neurones?

They have many short axons and dendrons.

What is the role of motor neurones?

They transmit nerve impulses from a relay or sensory neurone to an effector, such as a muscle or a gland.

What is the general structure of motor neurones?

They have one long axon and many short dendrites.

What is the pathway of most electrical impulses?

Receptor —> sensory neurone  —> relay neurone —> motor neurone —> effector cell.

What are the axons of some neurones covered in?

A myelin sheath, made of many layers of plasma membrane.

What is the role of Schwann cells?

They produce the membrane layers by growing around the axon many times.

What does the myelin sheath act as?

An insulating layer and allows these myelinated neurones to conduct the electrical impulse at a much faster speed than unmyleinated neurones.

What is present between each adjacent Schwann cell?

A small gap, known as a node of Ranvier. This creates gaps in the myelin sheath.

In myelinated neurones, what do the nodes of Ranvier allow?

The electrical impulse to ‘jump‘ from one node to the other as it travels along the neurone, allowing the impulse to be transmitted much faster.

How does the electrical impulse travel in non-myelinated neurones?

Continuously.