5.1 - The Nervous System

• What is homeostasis?

  The regulation of the conditions inside your body to maintain a stable internal environment, in response to changes in both internal and external conditions.
• What is stimulus?

  A change in you environment that you might need to respond to. For example: light, sound, touch, etc.
• What are the 3 main components of the automatic control system?

  Receptors, coordination centre, effectors.
• What happens when there is a stimulus?

  Receptors detect the stimulus when the level is too high/low. Send the information to the coordination centre. Coordination centre processes information and organises a response from the effectors. Effectors respond to counteract the change.
• What is negative feedback?

  The mechanism that restores the optimum level of a body condition.
• What are receptors?

  Cells that detect stimuli.
• What is the central nervous system (CNS)?

  Where all the information from the receptors is sent, and where reflexes and actions are coordinated.
• What does the CNS contain?

  Brain, spinal cord, relay neurone. Connected by the sensory and motor neurones.
• What are effectors?

  Muscles or glands which responds to electrical impulses and bring about a response to a stimulus.
• How do muscles respond to nervous impulses?

  Contract
• How to glands respond to nervous impulses?

  Secrete chemical substances called hormones.
• What does a sensory neurone do?

  Carry information as electrical impulses from the receptors in the sense organs to the CNS.
• What does the relay neurone do?

  Carry electrical impulses from sensory neurones to motor neurones. They are found in the CNS.
• What does the motor neurone do?

  Carry electrical impulses from the CNS to the effectors.
• Summary of information transmission:

  Stimulus, receptors, sensory neurone, relay neurone (CNS), motor neurone, effector, response.
• What happens when a nerve impulse reaches a synapse?

  Chemicals diffuse across the gap and set off new electrical signal in the next neurone.
• What is a reflex arc?

  The passage of information in a reflex (from receptor to effector).
• What is the order of operations in a reflex arc?


  Stimulus, receptor, sensory neurone, relay neurone, motor neurone, effector, response.
• What is reaction time and what affects it?


  The time taken to respond to a stimulus and can be affected by factors such as: age, gender or drugs.
• How can you measure reaction time?

  Using a computer game or calculating the speed somebody can catch a ruler.
• What are the 3 areas of the brain?

  Cerebral cortex, medulla and cerebellum
• What is the function of the cerebral cortex?

  Outer wrinkly layer of the brain. Responsible for things like consciousness, intelligence, memory and language.
• What is the function of the medulla?

  Base of the brain, at the top of the spinal cord. Controls unconcious activities.
• What is the function of the cerebellum?

  Found in the back of the brain. Responsible for muscle coordination.
• How do you study people with brain damage?

  If a small part of the brain is damaged, the effect it has on the patient tells a lot about what the damaged part of the brain does.
• How and why would you electrically stimulate the brain?

  Pushing a tiny electrode into the tissue and giving it a small zap of electricity. By observing what stimulating different parts of the brain does, it's possible to get an idea of what those parts do.
• What are MRI scans used for?

  Scientists use it to find out what areas of the brain are active when people are doing things like listening to music or trying to recall memory.
• What is the sclera?

  The tough, supporting wall of the eye.
• What is the cornea and it's function?

  The transparent outer layer found at the front of the eye. It refracts light into the eye.
• What is the pupil?

  The hole in the centre of the eye, through which light enters.
• What is the iris and its function?

  The coloured part of the eye. Contains muscle that allow it to control the diameter of the pupil and therefore how much light enters the eye.
• What is the retina?

  Layer at the back of the eye that contains two types of light receptor cells. One sensitive to colour and the other sensitive to light intensity.
• What is the function of the lens?

  Focuses the light onto the retina
• What is the function of the ciliary muscles and suspensory ligaments?

  Controls the shape of the lens.
• What is the function of the optic nerve?

  Carries impulses from the receptors on the retina to the brain.
• How does the eye react to bright light?

  Light receptors detect bright light and a reflex is triggered to make the pupils smaller. The circular muscles (in the iris) contract and the radial muscles relax. Reducing the amount of light that can enter the eye.
• How does the eye react to dim light?

  The radial muscles contract and the circular muscles relax, making the pupil wider. Allowing more light to enter the eye.
• Describe accommodation to near objects:

  The ciliary muscles contract, so the suspensory ligaments relax. The lens becomes fat (more curved), increasing the amount by which it refracts light.
• Describe the accommodation to distant objects:

  The ciliary muscles relax, so the suspensory ligaments pull tight. The lens becomes thin (less curved), so it refracts light by a smaller amount.
• How do you correct hyperopia?

  Use glasses with a convex lens (a lens which curves outwards), this refracts the light more so it focuses on the retina