B1 - The Eye and the Nervous System Flashcards
How does the eye generally work?
It contains light receptors that change light into electrical impulses, which travel along the optic nerve to the brain.
Describe the functions of the : cornea, iris, lens, retina, optic nerve.
Cornea - refracts light into the eye
Iris - control how much light enters the eye
Lens - focuses light onto the retina
Retina - contains receptors that turn light into electrical impulses
Optic nerve - carry these impulses to the brain
What is binocular and monocular vision? What are the pros and cons?
Binocular = both eyes facing forwards and focussing on the same thing. Can focus well and judge distance accurately BUT not very wide field of view.
Monocular = eyes on each side of the head. Wide field of view BUT can’t judge distance well.
How do you judge distance? What is accommodation?
Your brain compares the images from each eye. If the images are similar the brain knows you are looking at something at a distance.
Humans can’t focus on both near and far things at the same time and so the lens has to change shape, which is called accommodation.
Describe the accommodation of the ciliary muscles, suspensory ligaments and lens for close viewing and for distant viewing.
Close viewing :
ciliary muscle = contracted
suspensory ligaments = slacken
lens = rounded, fat shape
Distant viewing :
ciliary muscle = relaxed
suspensory ligaments = taut
lens = flatter, thinner shape
What is the problem with the eye ball in short sightedness and how is it corrected?
The eyeball is too long so the light rays meet in front of the retina so the final image is blurred.
To fix this you need diverging lens which bend the light rays outwards before they enter the eye, making them meet on the retina.
What is the problem with long sightedness and how is it corrected?
The eyeball is too short so the light rays do not meet on the retina so the image is blurred.
To correct it you need converging lens which bend the light rays inwards before they enter the eye so the meet on the retina.
What are the two main parts to the nervous system?
- The central nervous system - the brain and the spinal cord
- The peripheral nervous system - nerves taking information from sense organs into the CNS, and from the CNS to effectors ( muscle or glands)
Explain how voluntary responses happen.
Receptor cells are special cells adapted to decree stimuli. Information from the receptors passes as electrical impulses along nerve cells called neurones to the brain. The brain then co ordinates the response.
What is a reflex action?
A reflex which doesn’t involve the brain, but the spinal cord. It is fast, automatic and protective.
What is the reflex action pathway? Mnemonic?
Some rabbits make elephants roar
Sensory neurone > relay neurone > motor neurone > effector > response
How are neurones adapted to their function ?
- They are long
- Insulating sheath to prevent impulses leaking away
- Branched endings so they can communicate with other neurones
How do impulses cross a synapse?
Gaps between neurones are called synapses and electrical nerve impulses cannot cross these. Instead, chemicals called neurotransmitters released by one neurone diffuse across the synapse and cause an impulse to be fired in the next neurone.
What is an effector?
They are gland or muscles that carry out a response. A muscle responds by contracting and a gland responds by secreting chemical substances.
