Note: Neurons

The Structure of a Neuron
- have specialized cell structures that enable them to transmit nerve impulses
- four common features amongst neurons:

• Dendrites:
  - short branching terminals that receive nerve impulses from other neurons or sensory receptors, and relay the impulse to the cell body
  - numerous and highly branched (increases surface area available to receive information
• Cell Body:
  - processes input from dendrites
  - contains the nucleus and is the site of the cell's metabolic reactions
  - if the input is big enough, the cell body relays it to the axon in which it conducts the impulse away from the cell body to receptors or dendrites of neighboring cells (by releasing a chemical signal)
• Axon:
  - conducts the impulse away from the cell body
  - terminal end of axon branches into many fibers
  - sends chemical signals to the receptors or dendrites of neighboring cells to communicate with nearby neurons, glands, and muscles
  - some axons are enclosed in myelin sheath which gives it a shiny white appearance (myelin sheath: fatty, insulating layer composed of Shwann cells, protects myelinated axons and speeds up the rate of nerve impulse transmission)
• Branching Ends

Classifying Neurons

- three main types of neurons (sensory neurons, integration neurons, motor neurons) form the basic impulse transmission pathway of the entire nervous system

• Sensory Input:
  - sensory receptors receive stimuli and form a nerve impulse
  - transmit impulses from the sensory receptors to the central nervous system (brain and spinal cord)
• Integration:
  - process and integrate incoming sensory information, and relay outgoing motor information
  - found within the central nervous system
  - link between the sensory and motor neurons
• Motor Output:
  - transmit information from the central nervous system to effectors (muscles, glands, organs that respond to impulses from motor neurons)

The Reflex Arc

- reflexes: involuntary responses to certain stimuli
- reflex arc: simple connections of neurons that explain reflective behavior
- reflex arcs and withdrawal reflexes usually involve only three neurons to transmit messages (rapid)
- moves directly to and from the brain or spinal cord before the brain centres involved with the voluntary control have time to process the sensory information (don't feel the pain immediately but very shortly after when your brain processes it)