nervous system and the eye

• what is sensitivity?

  it is the ability to respond to a stimulus
• what are the components of the human nervous system and what is their function ?

  • brain, spinal cord and nerves
  • they serve to co-ordinate and regulate bodily functions
• where can neurones be found ?

  in the nervous tissue
• what are the 3 main types of neurone ?

  relay, sensory and motor neurone
• what is the function of the sensory neurone ?

  transmits nerve impulses from the sense organs or receptors to the central nervous system
• what is the function of the relay neurone?

  transmits nerve impulses from the sensory neurone to the motor neurone, and are found within the central nervous system
• what is the function of the motor neurone ?

  transmits nerve impulses from the central nervous system to the effectors
• how are nerve impulses transmitted from one neurone to another ?

  nerve impulses are transmitted across a synapse by chemicals released by the neurones
• what neurone is this ?

  motor

  
• what neurone is this ?

  sensory

  
• what neurone is this ?

  relay

  
• what is the pathway of nerve impulses ?

  receptor in the skin -> sensory neurone -> relay neurone in the spinal cord -> brain
• what is a voluntary actions ?

  it is a deliberate action carried out under conscious control
• what is the pathway of nerve impulses for a voluntary action ?

  brain -> relay neurone in the spinal cord -> motor neurone -> effector
• what is a reflex action ?

  it is an immediate response to a specific stimulus without conscious control
• how can reflex action be classified ?

  cranial and spinal reflexes
• what is cranial reflexes ?

  they are controlled by the brain but not the conscious will and usually occur in the head region
• what is spinal reflexes ?

  they are controlled by the spinal cord
• describe how an involuntary actions is produced when a hand comes in contact with a hot surface

  1. the heat stimulates the nerve endings in the skin and nerve impulses are produced
  2. the sensory neurones transmits the nerve impulses to the spinal cord
  3. the nerve impulses are transmitted first across a synapse to the relay neurone, then across another synapse to the motor neurone in the form of chemicals
  4. the motors neurone transmits the nerve impulses from the spinal cord to the effector
  5. the bicep muscle then contracts and causes the hand to withdraw from the hot object
• what is a reflex arc ?

  it is the shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action
• what are the difference between endocrine and nervous control ?

  • EC involves hormones as signals while NC involves nerve impulses as signals
  • Hormones are transported by the blood while nerve impulses are transmitted by neurones
  • EC responses may be short- lived (eg. adrenaline) or long- lived (eg. growth) while NC responses are short- lived
  • EC is always involuntary while NC may be voluntary or involuntary
  • EC may affect more than one target organ while NC is usually localised
• what are the external structures of the eye ?

  • sclera
  • eyelashes
  • conjunctiva
  • tear gland
  • eyelids
  • iris
  • pupil
• what is the function of the sclera ?

  protects the eyeball from mechanical damage
• what is the function of the conjunctiva ?

  it secretes mucus to help keep the front of the eyeball moist
• what is the function of eyelashes ?

  to help shield the eye from dust particles
• what is the function of the tear gland ?

  secretes tears that:

  • wash away dust particles
  • keep the cornea moist for atmospheric oxygen to dissolve to diffuse into the cornea
  • lubricate the conjunctiva, helping to reduce friction when the eyelids move
• what is the function of the eyelids ?

  • protect the cornea from mechanical damage
  • partly closed (squinting) to prevent too much light from entering the eyelid and damaging the retina
  • blinking to spread tears over the cornea and conjunctiva
  • blinking wipes dust particles off the cornea
• what is the function of the iris ?

  • controls the size of the pupil and hence the amount of light entering the eye
• what is the function of the pupil ?

  is a hole in the centre of the iris, allowing light to enter the eye
• what are the internal structures of the eye ?

  • retina
  • lens
  • blind spot
  • optic nerve
  • fovea
  • vitreous chamber
  • choroid
  • ciliary body
  • suspensory ligament
  • cornea
  • aqueous chamber
• what is the retina ?

  • innermost layer of the eyeball
  • contains light- sensitive cells (photoreceptors)
  • these cells are connected to the nerve endings from the optic nerve
• what is the blind spot ?

  • where the optic nerve leaves the eye
  • does not contain any photoreceptors
  • object is not visible if the image falls here
• what is the lens ?

  • transparent, circular and biconvex
  • elastic to change its shape or thickness to focus light onto the retina
• what is the optic nerve ?

  transmits nerve impulses to the brain when the photoreceptors in the retina are stimulated
• what is the fovea ?

  • small depression in the retina
  • where images are normally focused
  • enables a person to have detailed colour vision in bright light
• what is the vitreous chamber ?

  • filled with vitreous humour
  • keeps the eyeball firm and helps to refract light onto the retina
• what is the choroid ?

  • middle layer of the eyeball between the sclera and the retina
  • it is pigmented black to prevent internal reflection of light
  • contains blood vessels that bring oxygen and nutrients to the eyeball and remove metabolic waste products
• what is the ciliary body ?

  contains ciliary muscles that control the curvature or thickness of the lens
• what is the cornea ?

  • layer continuous with the sclera
  • refracts or bends light rays into the eye
• what is the aqueous chamber ?

  • space between lens and cornea
  • filled with aqueous humour that keeps the front of the eyeball firm and helps to refract light into the pupil