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

Step

Stage

Example: Heat

1

Stimulus

Heat from hot object

2

Receptor

Temperature receptors in skin create nerve impulse to sensory neuron

3

Sensory Neuron

Passes nerve impulse to spinal cord

4

Intermediate Neuron

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

5

Motor Neuron

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

6

Effector

Muscle in upper arm, which is stimulated to contract

7

Response

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.