Neurons

• Motor Neuron- Parts

  Dendrites -> Cell Body -> Myelin Sheath ->Axon<- Myelin Sheath <- Neurofibril node

  
• Relay Neuron- Parts

  Dendrite -> Cell Body -> Axon -> Pre-Synaptic terminal
• Sensory Neuron- Parts

  Receptor cell -> Myelin sheath -> Axon <- Myelin sheath -> Cell Body

  
• Motor Neuron

  - Found in the central nervous system

  - Control muscle movements. When the motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement.
• Sensory Neuron

  - Found in receptors such as eyes, ears, tongue and skin.

  - Carry the nerve impulses to the spinal cord and brain. When these nerve impulses reach the brain, they are translated into ' sensations ', such as vision, hearing, taste and touch.

  - However, not all sensory neurons reach the brain, as some neurons stop at the spinal cord, allowing for quick reflex actions.
• Relay Neuron

  - Found between sensory input and motor output/response.

  - Relay neurons are found in the brain and spinal cord and allow sensory and motor neurons to communicate.
• The process of synaptic transmission

  Synaptic transmission involves impulses crossing a space between an axon terminal and the

  adjacent neuron (the synaptic cleft) chemically.
• Stages of synaptic transmission

  1. Electrical impulses (action potentials) reach the presynaptic terminal.

  2. Action potentials trigger release of neurotransmitters (e.g. serotonin) from synaptic vesicles.

  3. Neurotransmitters diffuse across the synapse.

  4. Neurotransmitters combine with receptors on the postsynaptic membrane.

  5. Stimulation of postsynaptic receptors by neurotransmitters result in either excitation (depolarisation) or inhibition (hyperpolarisation) of the postsynaptic membrane.
• Features of synaptic transmission

  Information can only travel in one direction at a synapse. Because:

  · The synaptic vesicles containing the neurotransmitter are only released from the presynaptic membrane.

  · The receptors for the neurotransmitters are only present on the postsynaptic membrane.

  · It is the binding of the neurotransmitter to the receptor which enables the signal to be passed on.

  · Diffusion of the neurotransmitters mean they can only go from high to low concentration, so can only travel from the presynaptic to the postsynaptic membrane.