The human nervous system

• The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
• Information from receptors passes along cells (neurones) as impulses to the central nervous system, or CNS (the brain or the spinal cord). The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones
• stimulus- receptor- coordinator- effector- response/ There are three main types of neurone: sensory, motor and relay.
• Reflex actions are automatic and rapid; they do not involve the conscious part of the brain. An example of a simple reflex action is the pain withdrawal reflex. This can be explained in terms of a reflex arc.
• Sensory neurones carry impulses from receptors to the spinal cord and brain. Relay neurones carry impulses within the CNS. Motor neurones carry impulses from the CNS to effectors
• Where two neurones meet, there is a tiny gap called a synapse. Impulses cross this gap using chemicals
• Reaction times vary from person to person. Typical values range from 0.3s to 0.9s