Response, synapses and reflexes (paper 2 homeostasis)

Stimuli

Stimuli

Changes in the environment

Single celled organism

Can just respond to its environment

Multicellular organisms

Need to communicate with each other before responding to its environment (nervous and hormonal communication systems)

The nervous system

• humans react to their surroundings

• co-ordinate their behaviour

what is the Central nervous system (CNS) and what does it do?

• a co-ordination centre

• receives information from the receptors and then co-ordinates a response (decides what to do with it)

• response is carried out by effectors

What does the CNS consist of?

• the brain

• the spinal cord

Receptors

• the cells that detect the stimuli

• taste, smell, sound

what’s the job of Sensory Neurones?

• carry information as electrical impulses

• from receptors to CNS

what’s the job of Motor Neurones?

carry electrical impulses from the CNS to the effectors

Effectors

• muscles and glands (muscles contract, glands secrete hormones)

• respond to nervous impulses

Example of nervous system acting (small bird vs cat)

1. cat stalking prey (this is the stimulus)

2. The receptors in birds eye are stimulated (sensory neurons carry the information via electrical impulses from the receptors to the CNS

3. CNS decides what to do

4. motor neurons carry electrical impulses from the CNS to the effectors which provide the response (birds muscles work to make sure bird fly’s away)

what do Neurones do?

transmit information very quickly to and from the brain

what are Synapses and what happens at a synapse?

• connect two neurones

• nerve signal is transferred by chemicals which diffuse (move) across the gap

• the chemicals set off new electrical signals in the next neurone

what are Reflexes?

• rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain, reducing the chance of injury

• eg. bright light, pupils get smaller so less light gets into the eye (stops eyes from becoming damaged)

what is Adrenaline?

hormone given off subconsciously

Reflex arc

the passage of information in a reflex (from receptor to effector)

Example of reflex arc

1. neurones in reflex go through spinal cord or unconscious part of your brain

2. when a stimulus is detected by receptors are sent along a sensory neurone to a relay neurone in the CNS

3. when impulses reach a synapse (sensory and relay) they trigger chemicals to be released so that motor neurones can carry impulses

4. impulses travel from the motor neurone to the effector (a muscle or a gland)

6. muscles contract

7. this happens quicker than normal responses because you don’t have to think about the response

what is reaction time?

The time it takes to respond to a stimulus

What factors can affect reaction time?

1. Age

2. Gender

3. Drugs

Caffeine

a drug that can speed up a person’s reaction time