Stimuli and Responses

• The nervous system is made up of the central nervous system (CNS) and peripheral nervous system (PNS).
• Central Nervous System (CNS) is made up of the brain and spinal cord while the Peripheral Nervous System (PNS) is made up of the cranial nerves and spinal nerves
• Functions of the Human Nervous System

  1. Detects Stimuli 2. Interprets impulses 3. Produces appropriate responses 4. Sends information in the form of impulses
• Voluntary actions are conscious actions and conducted under one’s will. All voluntary actions are carried out by the brain
• Involuntary actions are actions that occur immediately without conscious control or prior thoughts
• There are two types of involuntary actions, one involving the medulla oblongata and the other involving the spinal cord
• Involuntary actions involving Medulla Oblongata : breathing, peristalsis, heartbeat and secretion of saliva
• Involuntary actions involving spinal cord (reflex actions) : Withdrawing hand when accidentally touching a hot object, withdrawing foot when accidentally stepping on a sharp object, sneezing when dust enters nose
• Eye Lens is a transparent and elastic lens which focuses light onto the retina
• Cones have three different pigments to distinguish red, green and blue colours
• Iris is the coloured part of the eye which controls the size of the pupil
• Pupil is the opening in the centre of the iris which controls the quantity of light that enters the eye
• Suspensory ligaments are strong fibres which hold the eye lens in position
• Aqueous humour is a transparent fluid which focuses light into the eye and maintains the shape of the eye
• Vitreous humour is a transparent jelly-like substance which helps maintain the shape of the eyeball and focuses light on the retina
• Choroid is a black layer that prevents reflection of light in the eye and supplies oxygen and nutrients to the eye
• Retina is a layer containing photoreceptors which detect light and produces nerve impulses
• Yellow spot is part of the retina which is most sensitive to light as is has many photoreceptors
• Ciliary muscle is a muscle that changes the thickness of the eye lens through contractions and relaxations
• Blind spot is part of the retina which is not sensitive to light as there are no photoreceptors and an exit point for all optic nerve fibres
• Sclera is 


  a strong layer which maintains the shape of the eye and protects it
• Conjunctiva is 


  a transparent membrane which protects the front part of the sclera
• Optic nerve is


  nerve fibres which carry nerve impulses from the retina to the brain to be interpreted
• Rod cells


  are sensitive to different light intensities including faint light but are not sensitive to the colours of light
• Outer ear


  Ear lobe and ear canal
• Middle ear


  Ear drum, oval window, ossicles and eustachian tube
• Inner ear


  Cochlea, semicircular canal, auditory nerve
• Ear lobe


  Collects and directs sound waves into the ear canal
• Ear canal


  Directs sound waves to the ear drum
• Ear drum


  Thin membrane which vibrates according to the frequency of the sound waves received and transfers the vibrations to the ossicles
• Ossicle


  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 air pressure on both sides of the eardrum
• Cochlea


  Detects and converts sound vibrations into nerve impulses
• Semicircular canal


  Detects the position of the head and help to balance the body
• Auditory nerve


  Sends nerve impulses from the cochlea to the brain to be interpreted