Nervous system

• What is a stimulus?

  A change in the environment to which an organism responds to.
• What is a response?

  A change in behaviour in response to a stimulus.
• What is the central nervous system (CNS) made of?

  The brain and the spinal cord.
• What makes up the nervous system?

  The brain and spinal cord (for the CNS) and trillions of nerve cells called neurones.
• What is the nervous system for?

  It is an organ system that allows allows your body to communicate, using electrical signals called impulses.

  
• What is a sense organ? Give an example.

  An organ that contains receptor cells to detect stimuli. E.g. eyes, ears, skin.
• How does the body create a response to a stimulus?

  Receptor cells in a sense organ detect a stimulus, they create impulses which usually travels to the brain. The brain then processes this information and can send impulses to other parts of the body to cause a response.
• What are different steps to get from a stimulus to a response for a reflex action?

  Stimulus ---> Sensory receptor ---> Sensory neurone ---> Relay neurone ---> Motor neurone ---> Effector ---> Response
• What is neurotransmission?


  The process by which nerves communicate with each other using impulses and it happens in the neurones.
• How have neurones adapted to carry impulses?

  They have long extensions called axons and an insulating covering called a myelin sheath.

  
• What are the different types of neurones?

  Sensory neurones, relay neurones and motor neurones.
• What is the function of a sensory neurone?

  To carry messages from the receptor cells to the CNS.
• What is the function of a relay neurone?


  To pass an impulse from one neurone to another.
• What is the function of a motor neurone?

  To carry messages from the CNS to a muscle or a gland (effector)
• What is a neurotransmitter?

  Chemicals that allow a message to be passed from one neurone across the synapse, to the next neurone.
• What is the path of an impulse along the sensory neurone?

  receptor cell - dendrite- dendron-cell body- axon- axon terminal.
• How have the dendrons and axons adapted to their function?

  1. long: fast neurotransmission over long distances

  2. surrounded by myelin sheath: insulates the neurone from neighbouring neurones, stopping the signal from losing energy. It also makes an impulse 'jump' along the cell between the gaps in the myelin and so speeds up neurotransmission.
• What is the myelin sheath?

  A fatty tissue layer that surrounds the dendrone and the axon.
• What is the function of a dendrite?

  It receives impulses from receptor cells and conducts nerve impulses towards the cell body.

  
• What is a synapse?

  A gap where two neurones meet.
• What's the difference between a reflex action and a normal action?

  Normal actions: the messages pass to the brain for processing.

  A reflex action: an automatic response is required so the message is not sent to the brain - it goes via the spine.
• What is a reflex action?

  When the neuronal pathways skip the brain and just go straight to the spine. This allows for very fast responses to danger that would damage the body if the action were delayed. E.g. pulling your hand away from a hot object, blinking when an object gets too close to your eyes.
• What are the different steps to get from a stimulus to a response for a reflex action?

  Stimulus ---> Sensory receptor ---> Sensory neurone ---> Relay neurone ---> Motor neurone----Effector ---> Response
• What happens when a brain coordinates a response to a stimulus?

  It sends impulses to the effectors that carry out these actions. Effectors can be glands or muscles (e.g. sweat glands)
• What are relay neurones?

  Short neurones found in the spinal cord that link sensory neurones to motor neurones. They also make up a lot of nerve tissue in the brain.
• What is a similarity between a motor neurone and a relay neurone?

  They both don't have a dendron and the dendrites are on the cell body.
• What happens when an impulse reaches an axon terminal?

  A neurotransmitter substance is released into the gap (or the synapse). This is detected by the next neurone, which creates a new impulse.
• Which neuronal pathways do reflexes use?

  Reflex arcs, which bypass the parts of the brain involved in processing information and so are quicker than responses that require processing.
• What do axon terminals do?

  Pass impulses to other neurones.