Neurons

• Neurons

  The nervous system carries messages from one part of the body to another using individual nerve cells known as neurons.

  Neurons transmit nerve impulses in the form of electrical signals
• Stuctue and function of neuron

  They transmit signals electrically and chemically to allow communication.

  Vary in size, can be a millimetre up to a metre long. But all have the same basic structure
• Motor neurons

  Connect the CNS to muscles and glands

  They have short dendrites and long cons
• Sensory neurons

  Cary messages such as sight, sound and sensations from the PNS to the CNS.

  They have long dendrites and short axons
• Relay neurons

  Connect sensory neurons to motor neurons or to other relay neurons.

  They make up 97% of the CNS

  They have short dendrites and short axons
• Structure of neuron

  
• Soma - cell body of neuron which includes and contains the genetic material of the cell
• Dendrites - branch like structures of a neuron which carry nerve impulses to the cell body
• Axon - carries impulses away from the neuron cell body and down the length of the neuron
• Myelin Sheath - this is a fatty later that protects the icon and speeds up electrical transmission of the impulse
• Nodes of Ranvier - these are gaps in the myelin sheath which speed up transmission by forcing it to jump across the axon
• Terminal buttons - these communicate with the next neuron in the chain across the synapse
• A neuron is a nerve cell and there are 100 billion of them in the human nervous system
• Neurons transmit electrically and chemically to allow communication in the nervous system
• Neurons vary in size they can be a millimetre up to a metre long but all share the same basic structure
• Reflex arc

  Example if we touch something hot

  Sensory neuron detects the heat and sends a signal to the relay neuron in the CNS which in turn sends a signal to the motor neuron to move our hand away.
• Reflex arc diagram

  
• When a neuron is in a resting state, the inside of the cell is negative charged compared to the outside. When a neuron is activated by a stimulus, the inside of the cell becomes positively charged causing an action potential to occur

  This creates an impulse that travels down the axon
• Neurons do not directly touch and they communicate with each other through the release of neurotransmitters at the nerve endings
• Neurotransmitters - chemical messengers that communicate information throughout our brain and body.

  They relay signals between neurons.
• There are two kinds of neurotransmitters - inhibitory and excitatory
• Excitatory neurotransmitters

  These increase the chance of adjacent neurone firing
• Inhibitory neurotransmitters

  These decrease the chance of adjacent neurons from firing
• The post synaptic neuron will receive inputs from many additional neurons including both excitatory and inhibitory.

  The excitatory and inhibitory influences are summed and if the net effect is inhibitory the neuron will be less likely to fire
• Inhibitory neurotransmitter examples

  • GABA
  • Serotonin
• Excitatory neurotransmitter examples:

  • Dopamine
  • Noradrenaline