Organisms Respond To Changes In Their Environment: - A Reflex Arc

- Reflex Arc -

The nervous system has two main devisions:

1. Central Nervous System = made up of the spinal cord and the brain ~ (CNS)
2. Peripheral Nervous System = made up nerves branching from either the brain or the spinal cord. ~ (PNS) 

Peripheral System the divides into subdivisions: 

1. Sensory neurons = carries electrical impulses AWAY from receptors TO CNS 
2. Motor neurons = carries nerve impulses AWAY from CNS TO effectors 

Motor neurons are sub-divided into:

1. Voluntary nervous system = carries nerve impulses to body muscle // conscious control = voluntary 
2. Autonomic nervous system = carries nerve impulses to glands // smooth muscle & cardiac muscle under subconscious control = involuntary. 

This is a summary of the nervous organisation. ↑

Spinal Cord

This is summarised in the picture // no need for additional information the spinal cord for the specification is pretty simple. 

Reflex Arc 

Involuntary response to a sensory stimulus = Reflex Arc.

For example, withdrawal reflex // a spinal reflex 

Spinal reflex has 7 main stages:

Stimulus > Receptor > Sensory Neurone > Coordinator > Motor Neurone > Effector > Response  

An example of this would be if you was to touch a hot surface -

Stimulus = heat from the surface

Receptor = temperature receptors on the skin generates a nerve impulse in sensory neurone

Sensory Neurone = passes impulse to spinal cord

Coordinator // Intermediate neruone = links sensory to motor neruone in spinal cord

Motor Neurone = carries the impulse from spinal cord to the muscle in the upper arm

Effector = muscle in the upper arm is stimulated to move

Response = pulling your hand away from the hot surface