5.2

• What is the function of the nervous system?


  The nervous system allows the body to react to its surroundings and coordinate an appropriate response.
• How does a stimulus lead to a response being carried out by the body?


  • Stimulus is converted into an electrical impulse by the receptors.
  • The electrical impulse passes along sensory neurones to the CNS.
  • The CNS coordinates an appropriate response.
  • An electrical impulse is sent along motor neurones to the effector.
• What sequence of events describes how the nervous system works?

  • Stimulus → receptor → coordinator → effector → response
• What is a reflex action?


  A reflex action is an automatic and rapid response which does not involve any conscious input from the brain.
• Why are reflex actions important?


  Reflex actions aid survival by preventing harm to the body.
• Describe how a reflex action occurs via a reflex arc.


  • The stimulus is detected by a receptor.
  • An electrical impulse passes along a sensory neurone to the spinal cord.
  • At a synapse, a chemical stimulates a new impulse in the relay neurone.
  • The same process occurs at a synapse between the relay neurone and motor neurone.
  • At the effector, an appropriate response is carried out.
• What is the difference between a reflex pathway and a conscious pathway?


  In a reflex pathway, the coordination centre is a relay neurone in the spinal cord; in a conscious pathway, it is in the conscious part of the brain.
• What is the function of the cerebral cortex?


  The cerebral cortex controls consciousness, intelligence, memory, and language.
• What is the function of the cerebellum?


  The cerebellum controls muscular coordination.
• What is the function of the medulla?


  The medulla controls unconscious activities such as breathing and heart rate.
• Why is the investigation and treatment of the brain difficult?


  • The brain is a complex and delicate organ.
  • The brain is easily damaged and destroyed.
  • Certain membranes prevent drugs from reaching the brain.
  • The exact function of each part of the brain is not known.
• What methods are used by scientists to determine brain function?


  • Studying patients with brain damage
  • Electrical stimulation of the brain
  • MRI scans
• What stimuli are the receptors of the eye sensitive to?


  Receptors of the eye are sensitive to light intensity and colour.
• What are the two main functions of structures found within the eye?


  • Focusing on near or distant objects (accommodation).
  • Adaptation to dim light.
• Describe the structure and function of the retina.


  • The retina is a light-sensitive layer found at the back of the eye.
  • Light stimulates the retinal cells, resulting in impulses being sent to the brain.
• Describe the structure and function of the optic nerve.


  • The optic nerve connects the eye and the brain.
  • It carries impulses to the brain so that an image can be visualized.
• Describe the structure and function of the sclera.


  • The sclera is the tough outer layer of the eye.
  • It protects the internal structures of the eye.
• Describe the structure and function of the cornea.


  • The cornea is the curved transparent layer at the front of the eye.
  • It lets light into the eye and allows light to be focused onto the retina.
• Describe the structure and function of the iris.


  • The iris is a muscle that controls the size of the pupil.
  • It adjusts the eye to bright and dim lighting by contracting or relaxing.
• Describe the structure and function of the ciliary muscles and suspensory ligaments.


  • The ciliary muscles and suspensory ligaments hold the lens in place.
  • They control the shape of the lens.
• Describe how the iris alters the size of the pupil in both bright and dim light.


  • In bright light, the iris contracts to reduce pupil size.
  • In dim light, the iris relaxes to increase pupil size.
• What is the structure of the iris?


  The iris is a muscle.
• What is the function of the iris?


  The iris controls the size of the pupil by contracting or relaxing.
• How does the iris help the eye adjust to lighting conditions?


  It allows the eye to adjust to bright and dim lighting.
• What do the ciliary muscles and suspensory ligaments do?


  They hold the lens in place and control its shape.
• How does the iris alter the size of the pupil in bright and dim light?


  • Bright light: circular muscles contract, radial muscles relax, making pupil smaller.
  • Dim light: circular muscles relax, radial muscles contract, making pupil larger.
• What is accommodation in the context of the eye?

  Accommodation is the alteration of the lens’ shape to focus on near or distant objects.
• How does the eye focus on a nearby object?

  • Ciliary muscles contract.
  • Suspensory ligaments loosen.
  • Lens becomes thicker and more curved, refracting light rays strongly.
• How does the eye focus on a far away object?

  • Ciliary muscles relax.
  • Suspensory ligaments tighten.
  • Lens becomes thinner, refracting light rays weakly.
• What is myopia?


  Myopia is short-sightedness that occurs when the lens is too curved.
• How is myopia treated?


  Myopia can be treated using glasses with a concave lens.
• What is hyperopia?


  Hyperopia is long-sightedness that occurs when the lens is too flat.
• How is hyperopia treated?


  Hyperopia can be treated using glasses with a convex lens.
• What are the two types of contact lenses?

  • Hard: rigid material, long-lasting, must be kept sterile.
  • Soft: flexible material, shorter lifespan, more comfortable.
• What is laser eye surgery?


  Laser eye surgery uses lasers to fix visual defects in adults.
• How does laser eye surgery treat myopia and hyperopia?


  • Myopia: lasers reduce the thickness of the cornea.
  • Hyperopia: lasers alter the curvature of the cornea.
• How can replacement lenses be used to treat visual defects?


  • Implanted into the eye along with the natural lens.
  • Replace the natural lens altogether.
  • Risks include retinal damage, cataracts, and infections.
• Where is body temperature controlled in the body?

  Body temperature is controlled by the thermoregulatory centre in the hypothalamus.
• How is temperature monitored by the body?

  • Thermoregulatory centre has receptors sensitive to blood temperature.
  • Skin has receptors sensitive to skin temperature, sending impulses to the thermoregulatory centre.
• What physiological changes occur when body temperature is too high?

  • Vasodilation: blood vessels dilate, more heat radiated away.
  • Sweating: evaporation of water takes away heat energy.