the nervous system

• the nervous system allows humans to react to their surroundings and coordinate their behaviour
• a sensory neurone is a nerve cell that carries signals as electrical impulses from receptors in the sense organ to the central nervous system
• a relay neurone is a nerve cell found in the central nervous system that carries an electrical impulse from the sensory neurone to the motor neurone
• a motor neurone is a nerve cell that carries an electrical signal from the central nervous system to the effector (muscle that contracts or gland that secretes a hormone)
• reflex arc:

  • stimulus -> receptor in sense organ -> sensory neurone -> relay neurone -> motor neurone -> effector
• reflex actions are rapid and automatic, and they do not involve the conscious part of the brain
• the synapse is the gap between two neurones
• in the synapse, the electrical impulses are converted into a chemical signal (chemical neurotransmitter) which diffuses across the synapse. There are receptor cells at the start of the new neurone which detects the chemical neurotransmitter, and converts it back into an electrical signal
• reflexes are important because:

  • they prevent injury, as they are rapid and automatic