13.2 Neurones Flashcards
What is the role of the nervous system?
To direct changes in the internal and external environment
These changes are known as stimuli
What is the nervous system made up of?
Billions of neurones
What is the role of neurones?
To transmit electrical impulses around the body so the organism can respond to changes in the internal + external environment
What does the cell body of a neurone contain?
- 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
What are neurotransmitters?
Chemicals used to pass signals from one neurone to the next
What are dendrons?
- Short extensions which come from the cell body
- These divide into smaller and smaller branches known as dendrites
What is the role of dendrites?
Transmit electrical impulses towards the cell body
What are axons?
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
What are the 3 groups of neurones?
Sensory neurones
Relay neurones
Motor neurones
What are sensory neurones?
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
What are relay neurones?
Transmit impulses between neurones
- They have many short axons and dendrons
For example:
Between sensory neurones and motor neurones
What are motor neurones?
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
What is the electrical impulse pathway?
Receptor→Sensory Neurone→Relay Neurone→Motor Neurone→Effector Cell
What are some neurons covered in?
Myelin sheath
What is myelin sheath made from?
Many layers of plasma membrane
What do Shwann cells do?
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
What is the role of myelin sheath?
Acts as an insulating layer + allows myelinated neurones to transmit electrical impulse at a much faster speed than unmyelinated neurones
How fast can myelinated neurones transmit impulses versus unmyelinated neurones?
Myelinated neurones transmit impulses at 100m/s
Non-myelinated neurones transmit impulses at 1m/s
What is the node of Ranvier?
A gap between each Shwann cell, 2-3 microns
What is the role of the node of Ranvier?
To create gaps in the myelin sheath, every 1-3mm in humans
What is the role of the myelin sheath?
To act as an electrical insulator
What happens in myelinated neurones?
Electrical impulse jumps from one node to the next as it travels along the neurone
- This allows the impulse to be transmitted much faster
What happens in non-myelinated neruones?
Electrical impulse doesn’t jump, it transmits continuously along the nerve fibre so is much slower
