Neurones

Question 1

What is the structure of a neurone?

Answer 1

• Cell body (aka the soma) - has the nucleus in a cytoplasm. Many ER & mitochondria which produce neurotransmitters
  
  • Neurotransmitters are chemicals which communicate across a synapse between adjacent neurones or a neurone and muscle cell
• Dendrons - short extensions travelling towards the cell body. The extensions further divide into dendrites
  
  • responsible for transmitting electrical impulses to the cell body
• Axons - Singular elongated nerve fibres, they transmit impulses away from the cell body
  
  • cylindrical shape with a narrow region of cytoplasm surrounded by plasma membrane

Question 2

What is the structure and function of a sensory neurone?

Answer 2

• Transmits action potentials from sensory receptors to CNS, relay or motor neurone
• Has myelin sheath
• Has cell body positioned outside the CNS in a ganglion (a swelling of nerve cell bodies)
• Has one dendron (carries impulse towards cell body)
• Has one axon (carries impulse away from cell body)
• Ends with a synaptic knob

Question 3

What is the structure and function of a motor neurone?

Answer 3

• Transmits action potentials from CNS to effectors
• Has myelin sheath
• Has cell body positioned in CNS
• Has many dendrites but no dendron
• Has one long axon
• Ends with a motor end plate

Question 4

What is the structure and function of a relay neurone?

Answer 4

• Transmits action potentials between sensory and motor neurones
• Positioned within CNS
• Non-myelinated
• Has dendrites but no dendron
• Most have short axons some have longer ones
• Ends with synaptic knob

Question 5

What is a myelin sheath and how does it form?

Answer 5

Myelin Sheath: Membrane rich lipid which surrounds the axon of some neurones speeding up impulse transmission

Myelin sheath is made of multiple layers of plasma membrane growing around axons.

Schwann cells are responsible for producing the layers of membrane

Each time they grow a phospholipid bilayer is deposited. When the Schwann cells stop growing, the myelin sheath (20+ layers) insulates the neurones allowing for electrical impulse to be conducted faster.

Question 6

What are the properties of Schwann Cells?

Answer 6

Between each adjacent Schwann cell there is a gap called the node of Ranvier (it’s uninsulated) - creating a gap in the myelin sheath.

This gap allows for saltatory conduction - where electrical impulses jump from one node to another which is much faster than in non-myelinated neurones where the impulse in continually transmitted along the axon.