Sensory, Relay, Motor neurons

• Sensory neurons are found in receptors (eyes, ears, tongue and skin) and carry nerve impulses to the spinal cord and the brain (PNS to CNS). When these nerve impulses reach the brain they are translated into 'sensations' (vision, hearing, taste and touch). Some neurons stop at the spinal cord, allowing quick reflex actions.

  
• Relay Neuron - Connects sensory neurons to other relay/motor neurons. It is found in the brain and spinal cord and carries information from one sensory neuron to another motor neuron to communicate.
• Motor neurons are found in the CNS (connect CNS to effectors) and control muscle movements. When motor neurons are stimulated they release neurotransmitters that bind to the receptors on muscles to trigger a response, which lead to movement.
• The dendrites are typically connected to the cell body, which is often referred to as the 'control centre' of the neuron as it contains the nucleus. The dendrite receives signals from other neurons or sensory receptor cells.
• The axon is a long slender fibre that carries nerve impulses, in the form of an electrical signal (action potential), away from the cell body toward the axon terminals, where the neuron ends.
• Most axons (except relay neurons) are surrounded by a myelin sheath which insulates the axon so that the electrical impulses travel faster along the axon.
• The axon terminal connects neurons to other neurons using synaptic gap (or directly to organs) through synaptic transmission.
• Synapses are junctions between two neurones, or between a neurone and an effector organ such as a muscle or gland.
• Neurotransmitter molecules diffuse across the gap at the synapse into the cleft and then bind to specific receptors on the postsynaptic membrane.
• Neurons are the basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.
• When neuron in resting state the inside of the cell is negatively charged.
• When neuron activated by stimulus, inside of cell becomes positively charged for split second causing action potential to occur. This creates an electrical impulse that travels down axon towards end of neuron.
• Neurons structure

  A) Receptor cell

  B) Myelin sheath

  C) Axon

  D) Cell body

  E) Dendrite

  F) Pre-synaptic terminal

  G) Neurofibril (Node of Ranvier)

  
• Distinguish a difference between a sensory neuron and relay neuron


  Sensory neurons have long dendrites and short axons, whereas relay neurons have short dendrites and short axons.