science f3 chap1-3

• Voluntary actions


  Conscious actions and conducted under one's will
• Involuntary actions


  Actions that occur immediately without conscious control or prior thoughts
• Voluntary actions controlled by


  • Brain
  • Medulla oblongata

  
• Involuntary actions controlled by

  • Spinal cord (Reflex actions)
• Voluntary actions


  • Reading
  • Writing
  • Speaking
  • Eating
• Involuntary actions


  • Heartbeat
  • Breathing
  • Peristalsis
  • Secretion of saliva
• Involuntary actions (reflex actions)


  • Withdrawing hand when accidentally touches a hot object
  • Withdrawing foot when accidentally steps on a sharp object
  • Sneezing when dust enters the nose
• Pathway for voluntary actions

  1. Stimulus (phone rings)

  2. Affector (receptor) in ear

  3. Nerve impulse

  4. Brain

  5. Nerve impulse

  6. Effector (muscle or gland)

  7. Response (touch phone)
• Pathway for involuntary actions (reflex actions)

  1. Stimulus (touch hot object)

  2. Affector (receptor) in skin

  3. Nerve impulse

  4. Spinal Cord

  5. Nerve impulse

  6. Effector (muscle or gland)

  7. Response (move hand)
• Importance of the Network of Human Nervous System in Daily Life

  • Controls and coordinates the organs and parts of the body to carry out body processes
  • If damaged → causes a person to become temporarily, partially or completely paralysed
  • Nerves (muscle in leg) damaged → difficulty in moving leg
• Parts of the eye

  • Cornea
  • Aqueous humour
  • Pupil
  • Eye lens
  • Vitreous humour
  • Retina
  • Optic nerves
  • Conjunctiva
  • Sclera
  • Iris
  • Suspensory ligaments
  • Ciliary muscle
  • Choroid
  • Blind spot
  • Yellow spot

  
• Cornea


  Transparent layer which refracts and focuses light onto the retina
• Aqueous humour


  Transparent fluid which maintains the shape of the eyeball and focuses light into the eye
• Pupil


  Opening in the centre of the iris which controls the quantity of light entering the eye
• Eye lens


  Transparent and elastic convex lens which focuses light onto the retina

  
• Vitreous humour


  Transparent jelly-like substance which maintains the shape of the eyeball and focuses light onto the retina
• Retina


  • Layer containing photoreceptors which detects light and produces nerve impulses
  • Rod cells: Sensitive to different light intensities including faint light
  • Cone cells: Sensitive to Red, green and blue lights under bright conditions
• Optic nerves


  Nerve fibres which carry nerve impulses from the retina to the brain to be interpreted
• Conjunctiva


  Transparent membrane that protects the front part of the sclera
• Sclera


  Strong layer that maintains the shape of the eye and protects it

  
• Iris


  The coloured part of the eye which controls the size of the pupil

  
• Suspensory ligaments


  Strong fibres which hold the eye lens in its position

  
• Ciliary muscle


  Muscle that changes the thickness of the eye lens through contractions & relaxations
• Choroid


  Black layer that prevents reflection of light in the eye and supplies oxygen and nutrients to the eye
• Blind spot


  Part of the retina which is not sensitive to light as there are no photoreceptors and an exit point of optic nerve fibres
• Yellow spot


  Part of the retina which is most sensitive to light as it has many photoreceptors
• Mechanism of Sight


  1. Light rays enter the eye through the cornea, aqueous humour, eye lens and vitreous humour before reaching the retina. These parts focus the light rays from the object onto the retina

  2. The object appears smaller and inverted

  3. The light rays stimulate photoreceptors to produce nerve impulses that are sent to the brain. The brain interprets the nerve impulses

  4. The smaller inverted image on the retina will then appear upright

  
• Functions of the Human Nervous System

  • Detects stimuli
  • Sends information in the form of impulses
  • Interprets impulses
  • Produces appropriate responses

  
• Parts of the ear

  • Earlobe
  • Ear canal
  • Eardrum
  • Ossicles
  • Oval window
  • Eustachian tube
  • Cochlea
  • Auditory nerve
  • Semicircular canals

  
• Earlobe


  Collects and directs sound waves into the ear canal

  
• Ear canal


  Directs sound waves to the eardrum

  
• Eardrum


  Vibrates according to the frequency of the sound waves received and transfers the vibrations to the ossicles

  
• Ossicles


  Amplify sound vibrations and transfer them to the oval window
• Oval window


  Collects and transfers sound vibrations from the ossicles to the cochlea
• Eustachian tube


  Balances the air pressure on both sides of the eardrum
• Cochlea


  Detects and converts sound vibrations into nerve impulses
• Auditory nerve


  Sends nerve impulses from the cochlea to the brain to be interpreted
• Semicircular canals


  Detect the position of the head and help to balance the body
• Mechanism of Hearing


  Source of sound → Earlobe → Ear canal → Eardrum → Ossicles bones → Oval window → Cochlea → Auditory nerve → Brain → Sounds is interpreted

  
• Sensory cells for smell

  • Tiny and covered with a layer of mucous
  • Chemical substances in the air will dissolve in mucous and stimulate the cells to produce nerve impulses
  • Nerve impulses are sent to the brain to be interpreted to determine the type of smell