Human Nervous System

• Brain


  • contained within the skull which protects it
• Spinal Chord


  • the spinal chord runs down the back of the body
  • passes through the vertebral column which protects it
  • spinal nerves, which are composed of bundles of nerve fibres, connect the spinal cord to various parts of the body
• Reflex Arc


  • the shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action
  • Receptor -> Sensory Neurone -> Relay Neurone -> Motor neurone -> Effector
• Nervous system


  • regulates bodily functions and activities and how we react to the surroundings
  • consists of the brain, spinal chord, spinal nerves and sense organs
• Sense organs


  • detect changes in the environment
  • receive stimuli through the receptors found in them
  • inform the central nervous system of any change in the surroundings and produce nerve impulses
  • the nerve impulses are transmitted to the central nervous system by the nerves
• Central Nervous system


  • consists of the brain and spinal chord
• Peripheral nervous system


  • consist of the cranial nerves, spinal nerves and sense organs
• Voluntary actions 


  • activities that are controlled consciously
  • controlled by the brain
• Involuntary actions


  • activities that are not controlled consciously
  • does not require a stimulus (e.g. blinking)
  • controlled by the brain
• Sensory Neurone


  • A sensory neurone transmits nerve impulses from the receptors to the central nervous system
  • Circular cell body
  • One long nerve fibre between receptor and cell body
  • One short nerve fibre between cell body and CNS

  
• Relay Neurone


  • transmits nerve impulses from the sensory neurone to the motor neurone within the central nervous system.

  
• Motor Neurone


  • motor neurone transmits nerve impulses from the central nervous system to the effectors.
  • Irregular-shaped cell body
  • One long nerve fibre between cell body and effector

  
• Synapse


  • A synapse is the junction between two neurones
  • The neurones release chemicals that help transmit nerve impulses across the synapse
• Reflex Action


  • A reflex action is an immediate response to a specific stimulus without conscious control
  • Cranial reflexes are controlled by the brain
  • Spinal reflexes are controlled by the spinal cord
  • The brain and spinal cord are reflex centres.
• Endocrine control


  • involves hormones which are transported by blood
  • usually slow responses
  • responses may be short-lived
  • always involuntary
  • may affect more than 1 target organ
• Nervous Control


  • involved nerve impulses as signals
  • nerve impulses are transmitted by neurones
  • usually quick responses
  • responses are short-lived
  • may be voluntary or involuntary
  • usually localised