Coordination and response (copy)

Stimulus

A change in an organism’s internal or external environment

Which two systems do organisms use to respond to stimuli?

The nervous system and the endocrine system

Describe the pathway for a coordinated response

• The receptors (cells found in sense organs) detect a stimulus

• The receptors, acting as transducers, convert the stimulus energy into electrical energy

• The electrical impulse travels down a sensory neurone to the coordination centre/CNS/brain+spinal cord

• The electrical impulse is processed by the spinal cord and brain

• The electrical impulse travels from the CNS down a motor neurone to an effector (gland or muscle) which carries out a response

Central nervous system (CNS)

Brain + spinal cord

Peripheral nervous system (PNS)

Neurones (nerve cells)

What are nerves, and what do they do?

Long structures that consist of many nerve cells (neurones). They connect the CNS to the sense organs.

What are neurones, and what do they do?

Nerve cells. Electrical impulses travel through them.

Three types of neurones

Sensory, relay, motor

What is a synapse?

The junction between two neurones

What happens at a synapse?

• The electrical impulse reaches the end of the pre-synaptic neurone

• This triggers the nerve-ending of the neurone to release neurotransmitters (chemical messengers), from vesicles, into the synaptic cleft

• The neurotransmitters diffuse across the synaptic cleft, and bind with receptor molecules on the post-synaptic neurone

• The receptor molecules (complementary to a specific neurotransmitter) stimulate an electrical impulse to travel down the post-synaptic neurone

• The neurotransmitters are then broken down by enzymes (to prevent continued stimulation of the post-synaptic neurone), and are sent back to the pre-synaptic neurone

Direction of travel across a synapse

One direction only; pre-synaptic to post-synaptic neurone

If a drug can bind to a neurotransmitter receptor, what is the effect?

It can trigger electrical impulses in different regions of the brain

The reflex arc that takes place when a person touches a hot object

• The pain receptors in the skin detect the stimulus (the high temperature)

• The receptors convert the stimulus energy (thermal) into electrical energy

• The electrical impulse travels down a sensory neurone, to the spinal cord, where it travels down a relay neurone, via a synapse

• The electrical impulse then travels down a motor neurone, to an effector (in this case, muscles, which contract to move the person, or their finger, away from the hot object)

What is a receptor?

A cell in a sense organ that detects a stimulus

Difference between a normal response and a reflex action

• A normal response is conscious (uses impulses from the brain to stimulate a response), whereas a reflex action is unconscious (the electrical impulse does not reach the brain, so no impulse is sent from the brain)

• Reflex actions are faster, as they are used to protect the organism from harm

• Reflex actions are innate, and not learnt

Difference between a reflex action and an involuntary action

• An involuntary action is controlled by the brain; a reflex action does not involve the brain (but does involve the spinal cord)

• An involuntary action does not involve a stimulus; a reflex action is a response to a potentially harmful stimulus, that protects the organism from harm

• Reflex actions are generally quicker