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| Question | Answer |
| B1d - The Nervous System | Receptors are groups of specialised cells. They can detect changes (stimuli) in the environment. Receptors are often located in the sense organs, such as the ear, eye and skin. |
| The Central Nervous System | The human central nervous system (CNS) consists of the brain and spinal cord. |
| Play Label the Eye Game. | |
| Functions of parts of the Eye | Cornea Front part of the tough outer coat, the sclera. It is convex and transparent. refracts light - bends it as it enters the eye Iris Pigmented - decides the colour of your eyes - so light cannot pass through. Its muscles contract and relax to alter the size of its central hole or pupil. controls how much light enters the pupil Lens Transparent, bi-convex, flexible disc behind the iris attached by the suspensory ligaments to the ciliary muscles. focuses light onto the retina Retina The lining of the back of eye containing two types of photoreceptor cells - rods - sensitive to dim light and black and white, cones - sensitive to colour. A small area called the fovea in the middle of the retina has many more cones than rods. contains the light receptors Optic nerve Bundle of sensory neurones at back of eye. carries impulses from the eye to the brain |
| Pathway of Light | Light passes through the eyeball to the retina. It is refracted (its rays are bent) by the cornea and lens, so that the light is brought to a focus on the retina. |
| Binocular/Monocular vision | Because our eyes sit side by side, each eye captures a slightly different view. This is called binocular vision. Most birds and lizards have monocular vision - their eyes are on each side of their head. |
| Focussing | To focus of distant objects, the ciliary muscles relax and the suspensory ligaments tighten so the lens has a less rounded shape. To focus on near objects, the ciliary muscles contract and the suspensory ligaments slacken, so the lens regains a more rounded shape due to its elasticity. |
| Short sighted | Someone with short-sightedness can see near objects clearly, but can't focus properly on distant objects. This is because the lens focuses the sharpest image in front of the retina, instead of on it. It can be corrected by placing a concave lens in front of the eye. |
| Long Sighted | Someone with long-sightedness can see distant objects clearly, but can't focus properly on near objects. This is because the lens focuses the sharpest image behind the retina, instead of on it. It is corrected by putting a convex lens in front of the eye. |
| The nervous system | Nerve impulses are mainly electrical and carried in nerve cells, or neurones. There are three different types of neurones, each with a slightly different function: - sensory neurones carry signals from receptors to the spinal cord and brain - relay neurones carry messages from one part of the CNS to another - motor neurones carry signals from the CNS to effectors. |
| Synapses | Where two neurones meet, there is a tiny gap called a synapse. Signals cross this gap using chemicals. One neurone releases the chemical into the gap. The chemical diffuses across the gap and makes the next neurone transmit an electrical signal. |
| Reflex Actions | Sometimes a very quick response is needed, one that does not need the involvement of the brain. This is a reflex action. stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector |
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