Nerve Organisation
• Central Nervous System (CNS): Made up of the brain and spinal cord
• Peripheral Nervous System (PNS) Made up of the pairs of nerves that originate from either the brain or the spinal chord
o Sensory Neurons: Carry nerve impulses from receptors  CNS
o Motor Neurons: Carry nerve impulses away from CNS  Effectors
• The motor Neuron system can be divided into:
o Voluntary Nervous system: Nerve impulses to body muscles is with conscious
o Autonomic Nervous system: Nerve impulses to glands, smooth muscles and cardiac muscles and is without conscious
Spinal Cord
• The spinal cord is a column of nervous tissue that runs along the back and lies inside the vertebral column for protection
• At regular intervals do pair of nerves separate off of the cord
Reflex Arc



Example: Heat



Heat from hot object



Temperature receptors in skin create nerve impulse to sensory neuron


Sensory Neuron

Passes nerve impulse to spinal cord


Intermediate Neuron

Links the sensory neurone to the motor neuron found in spinal cord


Motor Neuron

Carries nerve impulse from spinal cord to muscle in the upper arm



Muscle in upper arm, which is stimulated to contract



Hand is pulled away from hot object

Importance of the Reflex Arc
• The reflex arc is an involuntary response which allows for an instant reaction to a danger
• The reflex arc being involuntary frees up the brain to carry out more complex tasks
• The reflex arc does not have to be learnt and therefore is effective since birth
• The response is fast as the neurone pathway is short from spinal cord to receptor this is further increased by few synapses.