Form 3 Science Chapter 1:Stimuli and Responses

• The structure of the human nervous system consists of two systems.
• The central nervous system consists of the brain and the spinal cord.

  The peripheral nervous system consists of the cranial nerves and the spinal nerves.
• The peripheral nervous system consists of 12 pairs of cranial nerves connecting the brain to the sensory and internal organs.
• The human nervous system is an important control system in body coordination. It is made up of the brain, spinal cord, cranial nerves and spinal nerves.
• The human nervous system controls sight, thinking, body movement ,organs ,parts of the body and also controls and coordinates organ functions in the body and maintains a balanced internal environment through a process called homeostasis.
• The human nervous system functions to detect stimuli, send information in the form of impulses, interprets impulses and produces appropriate responses.
• The responses of the human body to stimuli can be divided into voluntary actions and involuntary actions.
• Voluntary actions are conscious actions and conducted under one's will.
• All voluntary actions are controlled by the brain.
• Involuntary actions can be classified into two. 
• Examples of involuntary actions involving medulla oblongata are heartbeat, breathing, peristalsis and secretion of saliva.
• Importance: The network of the human nervous system controls and coordinates the organs and parts of the body to carry out processes in the body such as breathing and body movements.
• Importance:A damaged nervous system normally causes a person to become temporarily, partially or completely paralysed.
• The constant changes human face in surroundings are called stimuli.
• Humans uses their five sensory organs, eyes, ears , nose, skin and tongue to detect stimuli.
• The skin has the largest sensory organs. It is also the first line of defence against pathogens.
• Eyes(sense of sight), Ears(sense of hearing), nose(sense of smell),tounge(sense of taste), skin(sense of touch).
• Examples of stimuli include light, sound and chemical substances.
• If it's a more serious problem, the person might have to depend on machines to carry out their physiological processes such as breathing or heart beating.
• Examples of involuntary actions involving spinal cord(reflex actions) are withdrawing hand when it accidentally touches a hot object, withdrawing foot when it accidentally steps on a sharp object and sneezing when dust enters the nose.
• Involuntary actions involving medulla oblongata and involving spinal cord(reflex actions).
• Examples of voluntary actions include reading,writing, speaking,eating,drinking,walking, running and exercising.
• Involuntary actions are actions that occur immediately without conscious control or prior thoughts.
• 31 pairs of spinal nerves connecting the spinal cord to the skeletal muscles.
• The human nervous system consists of central nervous system and peripheral nervous system.
• Ciliary muscle is a muscle that changes the thickness of the eye lens through contractions and relaxations.
• Eye lens is a transparent and elastic convex lens which focuses light onto the retina.
• Sclera is a strong layer that maintains the shape of the eye and protects it.
• 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 detects light and produces nerve impulses.
• Yellow spot is a part of the retina which is most sensitive to light as it has many photoreceptors.
• Optic nerves are nerve fibres which carry nerve impulses from the retina to the brain to be interpreted.
• Blind spot is a part of the retina which is not sensitive to light as there are no photoreceptors and is an exit point for all optic nerve fibres.
• Vitreous humour is a transparent jelly-like substance which maintains the shape of the eyeball and focuses light onto the retina.
• Conjunctiva is a transparent membrane which protects the front part of the sclera.
• Aqueous humour is a transparent fluid which maintains the shape of the eyeball and focuses light into the eye.
• Pupil is the opening in the centre of the iris which controls the quantity of Iight entering the eye.
• Iris is the coloured part of the eye which controls the size of the pupil.
• Cornea is the transparent Iayer which refracts and focuses light onto the retina.
• Suspensory ligaments are the strong fibres which holds the eye lens in its position.