11a important

• There are 5 steps in the response pathway:

  • Stimulus

  • Receptor

  • Co-ordinator

  • Effector

  • Response
• Receptors detect stimuli
• When a receptor is stimulated, it sends a signal (an electrical nerve impulse) along the nerve cells (called neurones) to the central nervous system
• Sensory neurones send electrical impulses from the receptor cell to the Central Nervous System
• The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones
• The motor neurone is the neurone that carries the electrical impulse from the CNS to the effector
• An effector is a muscle (contracts) or a gland (secretes/releases chemicals) that produces a response
• Communication of signals:

  • Neurones – transmit signals as electrical impulses; organised into neural pathways that ensure a stimulus is linked to a response.
  • Synapses – gaps between neurones where a CHEMICAL signal is transmitted across the gap.
• Co-ordinator – CNS processes the signals received from stimuli and initiates a response.
• Responding – EFFECTOR organs are MUSCLES or GLANDS that either contract to make a movement, or secrete/release a chemical.
• cerebral cortex – concerned with consciousness, intelligence, memory and language.
• cerebellum – concerned mainly with the coordination of muscular activity.
• medulla – concerned with unconscious activities such as heartbeat & breathing.
• Order of the reflex arc:

  1. Stimulus
  2. Receptor
  3. Sensory neurone
  4. Relay neurone to Spinal Cord/Brain
  5. Motor neurone
  6. Muscle (effector)
  7. Response
• What happens in the reflex arc when someone burns their hand on a candle?

  • stimulus / heat detected by temperature receptors in skin
  • impulses travel along sensory neurone to spinal cord / CNS
  • chemical transmission across synapse
  • via relay neurone
  • impulses to muscle / effector via motor neurone
  • muscle / effector contracts, moving the hand away
• Cornea- Refracts light as it enters the eye
• Iris - Controls how much light passes through the pupil
• Lens - Further refracts the light in order to focus it on the retina
• Retina - Detects the light stimulus and passes on signals to sensory neurones
• Optic nerve - Carries electrical impulses from the light receptor cells to

  the brain
• Sclera - Helps protect eye from injury
• What happens when light hits the retina?

  Retina receptor cells absorb light energy & send electrical impulses along sensory neurones to brain along the optic nerve.
• Ciliary muscle - Controls the shape of the lens
• Cornea - Forms the outer protective membrane of the eye and bends the light in towards the pupil
• Iris - Gives the eye its colour and controls the amount of light entering the eye
• Retina - Receives the pictures, by turning the light into nerve impulses
• Lens - Changes shape in order to focus the light on the retina
• Optic nerve - Carries the nerve impulses to the brain
• How do your eyes focus on a NEAR object?

  The ciliary muscles contract, the suspensory ligaments loosen, the lens is then thicker and refracts light rays strongly
• How do your eyes focus on a DISTANT object?

  The ciliary muscles relax, the suspensory ligaments are pulled tight, the lens is then pulled thin and only slightly refracts light rays
• Short sight is caused by one of the following:

  • The eyeball being elongated - so that the distance between the lens and the retina is too great.
  • The lens being too thick and curved - so that light is focused in front of the retina.
• Short-sightedness can be corrected by placing a concave (diverging) lens in front of the eye
• Long-sightedness is caused by one of the following:

  • the eyeball being too short - so the distance between the lens and retina is too small
  • a loss of elasticity in the lens - meaning it cannot become thick enough to focus (which is often age-related)
• the lens focuses light behind the retina instead of onto it. Long-sightedness is corrected by putting a convex (converging) lens in front of the eye