Nervous System & Neurons

• 2 main parts of the nervous system

  • central
  • peripheral
• central nervous system

  brain and spinal cord
• peripheral nervous system

  nerves throughout the body
• autonomic nervous system

  regulates involuntary bodily processes
• somatic nervous system

  controls voluntary movements
• sympathetic nervous system

  responds to threat by increasing heart rate and breathing rate etc - fight or flight
• parasympathetic nervous system

  slows other processes and promotes digestion - rest and digest
• neurons

  specialised cells that send electrical impulses to and from the central nervous system
• dendrites

  receive signals from other neurons and sensory receptors
• cell body

  receives information from the dendrites
• axon

  information from cell body is transmitted along this as an electrical impulse
• Schwann cells

  insulates the axon
• myelin sheath

  series of Schwann cells
• nodes of ranvier

  separates the myelin sheath
• 3 types of neurons

  sensory

  motor

  relay
• sensory neurons

  carry nerve impulses from sensory receptors to the brain and spinal cord, found in eyes, ears, tongue and skin
• motor neurons

  control movement, balance and coordination
• relay neurons

  allow sensory and motor neurons to communicate with each other within the brain or spinal cord
• transmission within a neuron

  electrical
• transmission between neurons

  chemical
• process of synaptic transmission

  • the action potential arrives at the end of the pre-synaptic neuron
  • the synaptic vesicles release neurotransmitters which diffuse across the synapse
  • the neurotransmitter is received by receptor sites in the dendrites of the next neuron
  • re-uptake occurs for unused neurotransmitters
• excitatory neurotransmitters

  increase the likelihood of a signal being sent
• inhibitory neurotransmitters

  reduce the likelihood of a signal being sent