Nervous system and eye

• what is the iris?

  Coloured part of the eye
• what is the cornea?

  Outer transparent layer, bends/refracts light into the eye
• what is the retina?

  the light-sensitive inner surface of the eye, containing the receptor rods and cones
• what is the scelera?

  the visible, white, tougher outer coating of the eye
• what is the pupil?


  The hole in the centre where light enters
• what is the choroid?

  dark pigmented layer underneath sclera, stops light being reflected around inside the eye
• what is the optic nerve?

  Carries impulses from the receptors on the retina to the brain
• what is the fovea?

  the region of the retina with a high density of cones
• what is a rod?


  allows you to see in dim light, but can't differentiate colours
• what is a cone?


  only work well in very bright light that can respond to different wavelength of light: red blue and green
• what does the eye do when in bright light?

  1. The light receptors detect bright light

  2. The circular muscles in the iris contract

  3. The pupil is made smaller
• what does the eye do when in dark light?

  1. The radial muscles contract

  2. The pupil gets bigger so that more light can enter
• how does the eye focus on near objects?

  ~ The lens need to be fatter/ wider

  ~ the ciliary muscles contract which relax the suspensory ligaments

  ~ the more rounded lens enables light to focus more correctly on the retina
• how does the eye focus on distant objects?

  ~ the lens need to be thinner

  ~ the ciliary muscles relax which tighten the suspensory ligaments

  ~ the less rounded lens enable light to focus correctly on the retina
• what is the stimulus?


  a change in the environment
• what is the response?

  a reaction to change
• what is the receptor?


  the organ that detects change
• what is the effector?

  contraction of muscles causing the response, also can be a hormones release from a gland
• What is the central nervous system (CNS)?

  it contains the brain and spinal cord only and is the hub of the nervous system, PNS is attached to it
• what is the peripheral nervous system (PNS)?


  it consists of nerves attaches to the CNS and the receptor cells around the body, the messages from the receptors cells and taken to the CNS by the nerves using electrical impulses
• what is the axon?

  carries electrical impulse from a neurone. they are covered in sheath made fatty material called myelin which insulates the nerve cell and increases the speed of conductions
• what is the dendrites?


  they receive impulses from connecting neurones
• what is the sensory neurone?


  the first neurone involved in a reflex. takes information from the receptor to the CNS
• what is the relay neurone?


  the second neurone in a reflex and found inside the CNS, connecting the sensory neurone and the motor neurone
• what is the motor neurone?


  the third neurone that connects to a muscle or gland, known as the effector
• what is a reflex action?

  an involuntary and nearly instantaneous movement in response to a stimulus, that doesn't involve the conscious part of the brain
• what is a synapse?

  it is a junction between two neurones across which a chemical signal passes before stimulating a new electrical impulse
• what are the steps for the nerves moving across a synapse?

  1. Nerve impulse arrives at the synapse

  2. Chemical messenger (a neurotransmitter) is released into synapse

  3. Neurotransmitter diffuses across synapse

  4. Neurotransmitters binds with receptors on the membrane of the post synaptic neurone

  5. Binding of transmitter to receptor stimulates impulse in post synaptic neurone
• what happens when we detect a stimulus which causes a reflex?

  1. We detect a stimulus

  2. Pain receptors in the skin are stimulated

  3. A nerve impulse travels along the sensory neurone

  4. The nerve impulse enters the spinal cord

  5. The nerve impulse passes across a synapse into a relay neurone

  6. The nerve impulse passes into a motor neurone and travels along this out of the spinal cord

  7. When the nerve impulse reaches the effector, the muscle contracts/the gland releases a hormone which carries out a response
• What is a relfex arc?


  The nerve pathway of a reflex and the arc bit is the pathway that goes into the CNS and straight back out again in a structure (no brain involvement)
• Differences between endocrine and nervous system

  Endocrine slower, nervous faster response

  Endocrine lasts long term

  endocrine is chemical, nervous is electrical/ uses nerve cells

  nervous goes to target cells