Human nervous system

• 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 central nervous system
  • the CNS coordinates an appropriate response and an electrical impulse is sent along motor neurons to the effector which carries out the response
• 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 an conscious input from the brain
• why are reflex actions important

  they 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 moves along a sensory neurone to the spinal cord

  • at a synapse between a sensory neurone and a relay neurone a chemical diffuses across the gap and stimulates a new impulse which passes along the relay neurone
  • the same process occurs at a synapse between a relay neurone and a motor neurone
  • at the effector an appropriate response is carried out
• what is the difference between a reflex pathway and a conscious pathway

  within a reflex pathway the coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain. in a conscious pathway the coordination centre is the conscious part of the brain
• What is the function of the cerebral cortex

  C- controls consciousnes, intelligence, memory and language

  
• What’s the function of the cerebellum?

  A-controls muscular coordination

  
• What’s the function of the medulla?

  B- controls unconscious activities e.g. 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?

  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 function and the structure of the retina?

  F- 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 function and structure of the optic nerve?

  G- the optic nerve connects the eye and the brain.

  it carries impulses to the brain so that an image can be visualised

  
• Describe the structure and function of the sclera

  H- the sclera is tough outer layer of the eye which protects its internal structures.

  
• Describe the structure and function of the cornea?

  A-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

  B-the iris is a muscle which controls the size of the pupil by contracting or relaxing.This allows the eye to adjust to bright and dim lighting.

  
• Describe the structure of the ciliary muscles and suspenders ligaments

  The ciliary muscles (C) and suspensions ligaments (E) hold the lens in place and control it’s shape

  
• Describe how the iris alters the size of the pupil in both bright and dim lighting

  • Bright light: circular muscles contract and radial muscles relax- makes pupil smaller to avoid retinal damage
  • Dim light: circular muscles relax and radial muscles contract-makes pupil larger so more light can enter the eye
• What is accommodation?

  It’s the alteration of the lens’ shape in order to focus on near or distant objects
• How does the eye focus on near objects?

  • Ciliary muscles contract
  • suspension ligaments loosen
  • lens becomes thicker and more curved- light rays are refracted strongly
• How does the eye focus on a far away object?

  • Ciliary muscles relax
  • suspensory ligaments tighten
  • lens becomes thinner- light rays are refracted weakly
• What is myopia?

  It’s short-sightedness which usually occurs when the lens of the eye is too curved which results in light focusing in front of the retina
• How can myopia be treated?

  Glasses with concave lenses which spreads out light rays so they can be focused on the retina
• What is hyperopia?

  its long-sightedness which usually occurs when the lens of the eye is too flat as a result light focused behind the retina
• How can hyperopia be treated?

  Glasses with convex lense which brings the light rays together so they can be focused on the retina
• What is laser eye surgery?

  It’s the use of lasers to fix visual defects in adults.

  to treat myopia the laser will reduce the thickness of the cornea so light is less strongly refracted.

  to try hyperopia the lasers alter the curvature of the cornea so that light is refracted correctly.
• How can replacement lenses be used to treat visual defects?

  A replacement lens can either implanted into the eye (along with the natural lens) or it may replace the natural lens altogether. Risks of lens replacement include retinal damage, cataracts and infections.
• Where is body temperature controlled in the body?

  The thermoregulatory centre in the hypothalamus of the brain.
• How is temperature monitored by the body?

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

  • Vasodilation- blood vessels near the surface of the skin dilate-more heat is radiated away.
  • sweating-evaporation of water takes away heat energy from the surface of the skin.
• What physiological changes occur when the body temperature is too low?

  • Vasoconstriction-blood vessels near the surface of the skin constrict-less heat radiated away.
  • shivering-respiration allows muscles to contract.it is exothermic process, so heat energy is released.
  • Sweating stops.