Neurons
Neurons
- Responsible for the detection of stimulus, relay of impulse and stimulation of response.
- Allow for rapid changes in an organisms internal and external environment.
- Dendrites: Connect to the synaptic knob of the previous neuron, allowing an impulse to be received.
- Dendron: Long nerve fibre extension leading to the cell body.
- Cell Body: Contains nucleus, mitochondria, endoplasmic reticulum and neurotransmitters.
- Axon: Long nerve fibre extension from the cell body through which impulses are transferred. Surrounded by a plasma membrane.
- Myelin Sheath: Myelinated tissue which insulates the nerve fibre helping the impulse travel more quickly.
- Nodes of Ranvier: Gaps in the myelin sheath which only allow depolarisation to occur at distanced intervals, speeding up transmission.
- Synaptic Knob: Neurotransmitters are released from here into the synaptic cleft when action potential stimulates an influx of calcium ions.
Types of Neurons
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Myelinated Neurons
- Schwann cells produce multiple plasma membrane layers which wrap around the axon and dendron, causing it to become myelinated.
- Each time the schwann cell grows, two phospholipid bilayers are laid.
- Above 20 membrane layers is enough to successfully insulate the axon or dendron.
- Myelinated neurons transmit impulses 100x faster than non-myelinated neurons can.
- Between each schwann cell is a gap, called a node of ranvier, which occur every 1-3nm. This causes the impulse to 'jump' along the neuron, as depolarisation can only occur at these gap.
- This causes transmission speed to increase.
- A neurological condition affecting 100,000 people in the UK.
- Mainly diagnosed between ages of 20 -40.
- Affects nerves in the brain and spinal cord, causing problems with movement, balance and vision.
- Caused by thinning/loss of myelin sheath as a result of an autoimmune response. Advanced MS can cause the breakdown of axons.
- Causes are unknown, but thought to be a combination of genetic factors and a viral infection.