-We have 2 parts in our nervous system:
The central nervous system (CNS) is the nerves in our brain and spinal chord. The peripheral nervous system (PNS) is a network of nerve cells in the rest of our body. -Our nervous system detects stimuli and allows us to react to them.
-Stimulus: a change, action or occurrence in the environment that can cause an organism to respond. Eg. Light, noise, pressure…
How do we detect stimuli?
-We have sensory organs that detect particular stimuli eg. Skin
What happens after we have detected a stimulus?
1. An impulse (electrical message) is sent from the sense organ receptors to our CNS. This impulse travels along a sensory neurone. 2. The CNS co-ordinates a response and sends an impulse to an effector (organ or gland) that brings about a response. This impulse travels along a motor neurone.
Are we always aware of our responses?
-Some actions are voluntary eg. Calling someone’s name; we are conscious we are doing them and we feel in control of these actions. -Other actions are involuntary eg. Digestion; we aren’t conscious of doing them and they continue even in our sleep.
-When we detect a stimulus our sense receptors send an impulse along sensory neurones. -Sensory neurones have branched dendrites and a long axon.
-The axon is insulated by a fatty material called a myelin sheath. It needs insulation because ‘electricity’ goes through it. -The cell body is found midway along the long axon.
-The direction of movement of the impulse is always from the sense organ to the CNS.
-The dendrites of a motor neuron are connected to the cell body at one end of the nerve cell (which is connected to the CNS) -The long axon (insulated too by myelin sheath) ends at muscle fibres to allow a response -The direction of movement is always from the CNS to the effector.
-They are fast and automatic
-They are defensive (protect your body)
-Reflex arc: the pathway of the nerve impulse, it must be as short as possible to allow a fast response.
The pupil reflex:
-The role of the pupil and the iris is to regulate the light entering the eye. -Two types of muscle are involved: circular and radial muscles
-In bright light the circular muscles contract and the radial muscles relax to constrict (narrow) the pupil; this lessens the amount of light entering the eye. -In dim light the circular muscles relax and the radial muscles contract to dilate (widen) the pupil; this maximises the amount of light entering the eye. -They therefore are an antagonistic pair of muscles.
-This is a reflex response
Structure of the eye:
Transparent, viscous liquid that maintains the shape of the eyeball Lens
Transparent, convex, flexible, jelly-like structure that refracts light to focus it. Iris
Coloured ring of circular and radial muscles that control the size of the pupil. Aqueous humour
Transparent, colourless, watery liquid in front of the lens that maintains the shape of the cornea. Conjunctiva
Transparent, sensitive layer on the surface of the cornea.
Transparent layer at the front of the eye that refracts the light entering to help focus it. Pupil
Hole in the centre of the iris that controls the amount of light reaching the retina. Suspensory ligament
Attaches the lens to the ciliary body so the lens is held in place. Ciliary body
Rind of muscle that controls the shape of the lens to allow focusing. Sclera
Tough, white layer that protects the eyeball
Part of the retina where the optic nerve goes through that lacks rods and cones. Optic nerve
Transmits electrical impulses from the retina to the brain.
Area of the retina containing...
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