Learning Objectives How and why do organisms respond

Learning Objectives • How and why do organisms respond to changes in their environment? • Can you list what is required for a coordinated response? • What makes up the CNS? • Can you explain that receptors are used to generate impulses in neurones, resulting in a rapid response? • What is a reflex arc?

Responding to change • In order for living organisms to find food, avoid danger, find a mate they need to be able to respond to changes in their environment. • These changes are called.

Sense organs and receptors • Receptor cells are special cells adapted to detect stimuli. • They are found in our sense organs. Movement of sound waves Light Pressure/heat Chemical

Impulses • Information from these receptors passes as along nerve cells (neurones) to the brain. • The brain then coordinates the response. • Some responses are voluntary, some are automatic. • Some responses bypass the brain altogether, these are called reflex actions.

The structure of the nervous system • There are two parts: – The Central Nervous System (CNS) which consists of the brain and spinal cord. – The Peripheral Nervous System which is all the nerves that take information from our sense organs into the CNS and from the CNS out to effectors (muscles or glands).

Neurones • Neurones transmit impulses around the body. • Impulses travel at speeds of between 10 and 100 m/s carry impulses from the receptor to the brain. carry impulses from the brain to the effector.

Sensory neurone • Stimuli are picked up by sensory receptors and passed into the neurone.

Sensory neurone • Stimuli are picked up by sensory receptors and passed into the neurone. • This generates an impulse which travels along the neurone.

Sensory neurone • Stimuli are picked up by sensory receptors and passed into the neurone. Direction of impulse • This generates an impulse which travels along the neurone.

Sensory neurone • Stimuli are picked up by sensory receptors and passed into the neurone. Direction of impulse • This is then passed to the spinal cord or the brain to interpret the initial stimuli.

Sensory neurone • The neurone is surrounded by cells made of a substance called myelin. • This insulates the neurone. Myelin sheath

Sensory neurone • The dendron carries the impulse up to the cell body, it then becomes the axon. Cell body Dendron Axon all the other • The cell body contains the nucleus and components that a cell needs to function.

Sensory neurone Direction of impulse Cell body Junction with sensory receptor Dendron Myelin sheath Axon Junction with CNS

Motor neurone • A message is sent out from the brain down the dendrites. • The impulse travels down the axon. Dendron Dendrites Axon Cell body Myelin sheath Muscle

Motor neurone • The impulse arrives at a muscle (effector) causing it to contract. Direction of impulse Dendron Dendrites Axon Cell body Myelin sheath Muscle

Reflex Action • A reflex is a rapid, automatic response to a stimulus. • The action often protects the body. • The nerve pathway of a reflex is called the reflex arc.

Reflex Action • A reflex is a rapid, automatic response to a stimulus. • The action often protects the body. • The nerve pathway of a reflex is called the reflex arc. For example Iris constricting in bright

Reflex Action • A reflex is a rapid, automatic response to a stimulus. • The action often protects the body. • The nerve pathway of a reflex is called the reflex arc. For example Iris constricting in bright Touching something very hot

Reflex arc Sensory neurone Relay neurone Motor neurone Spinal cord

Reflex arc Spinal cord Sensory neurone Relay neurone Motor neurone The signal does not go up to the brain, but is processed in the spinal cord via a relay neurone.

Reflex arc Stimulus

Reflex arc Receptor Stimulus

Reflex arc Coordinator Receptor Stimulus

Reflex arc Coordinator Receptor Effector Stimulus

Reflex arc Response Coordinator Receptor Effector Stimulus

Reflex arc

Reflex arc Stimulus Receptor Sensory neurone Coordinator Motor neurone Effector Response

Reflex arc Stimulus Receptor Sensory neurone Coordinator Motor neurone Effector Response The candle

Reflex arc Stimulus The candle Receptor Temperature receptor in finger Sensory neurone Coordinator Motor neurone Effector Response

Reflex arc Stimulus The candle Receptor Temperature receptor in finger Sensory neurone Coordinator Motor neurone Effector Response Sensory neurone Relay neurone in spinal cord

Reflex arc Stimulus The candle Receptor Temperature receptor in finger Sensory neurone Coordinator Motor neurone Effector Response Sensory neurone Relay neurone in spinal cord Motor neurone Muscle in arm

Reflex arc Stimulus The candle Receptor Temperature receptor in finger Sensory neurone Coordinator Motor neurone Sensory neurone Relay neurone in spinal cord Motor neurone Effector Muscle in arm Response Arm moves away from candle

Coordinated response • A reflex is an example of an automatic coordinated response. • In a voluntary response the brain would be the coordinator not the spinal cord.