Describe the role of the human nervous system.
The human nervous system enables humans to react to their surroundings and to coordinate their behaviour.
What is the central nervous system?
The central nervous system comprises of:
- the brain
- the spinal cord
How is information from receptors passed through the nervous system?
The information is passed through the nervous system as electrical impulses.
Describe the pathway through the nervous system, starting at the receptor.
The pathway is as follows:
stimulus --> Receptor --> Coordinator --> Effector --> Response
What is the role of receptors?
Receptors detect a change in the environment.
What is the role of an effector?
An effector brings about a response. Effectors can be muscles (eg hand muscles contracting to move a hand away from a hot plate) or glands secreting hormones (eg the pancreas releasing insulin)
What is the role of a sensory neurone?
A sensory neurone carries signals from the receptors to the spinal cord or brain.
What is the role of a relay neurone?
A relay neurone carries messages from one part of the CNS to another
What is the role of a motor neurone?
Motor neurones carry signals from the CNS to effectors.
What is a reflex action?
A reflex action is automatic and rapid. It does not involve the conscious part of the brain.
How are electrical impulses carried between neurones?
Between neurones are junctions called synapses. electrical impulses are converted in to chemical signals as neurotransmitter. The neurotransmitter diffuses across the synapse where it is the converted back in to an electrical impulse.
Describe the role and structure of the brain.
The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.
What is the role of the cerebral cortex?
The cerebral cortex is concerned with:
What is the role of the cerebellum?
The cerebellum controls muscular activity and balance.
What is the role of the medulla?
The medulla controls unconscious activities such as controlling heartbeat, breathing and the movements of the gut.
Explain why it is difficult to investigate and treat brain disorders.
Many of the process that take place in the brain involve many different neurones in different areas. There is also a range of different chemicals released in the synapses.
Drugs do not always reach the brain through the membranes that surround it.
Surgery is difficult because the brain is not fully understood and it is easy to cause unintended damage.
Explain how neuroscientists have been able to map the regions of the brain with particular functions.
Neuroscientists have been able to study patients with brain damage. They have also been able to eectrically stimulate different parts of the brain and use MRI scanning techniques.
What is the role of the retina?
The retina is a light sensitive layer that contains receptors which are sensitive to light intensity and colour.
Describe the structure and role of the optic nerve?
The optic nerve is a bundle of sensory neurones at back of eye. It carries impulses from the eye to the brain.
Describe the structure and function of the sclera.
The sclera is the white outer layer of the eye. It is relatively strong and tough so the eyeball does not get damaged.
Describe the structure and function of the cornea.
The cornea is a transparent area at the front of the eyeball. It is convex and transparent. The cornea refracts light - bends it as it enters the eye.
Describe the structure and function of the iris.
The iris is 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 which controls how much light enters the pupil.
Describe the structure and function of the ciliary muscles.
The ciliary muscles change the shape of the lens so that the image always comes to a sharp focus on the retina.
Describe the structure and function of the lens.
The lens is a ransparent, bi-convex, flexible disc behind the iris attached by the suspensory ligaments to the ciliary muscles.
The lens focuses light onto the retina.
Describe the function of the suspensory ligaments.
The suspensory ligament
What is accomodation?
Accomodation is the process of changing the shape of the lens to focus on near or distant objects.
Explain what happens to the ciliary muscles, suspensory ligaments and the lens in order to focus on a near object.
In order to focus on a near object:
- the ciliary muscles contract
- the suspensory ligaments loosen
- the lens becomes thicker and refracts light rays strongly.
Explain what happens to the ciliary muscles, suspensory ligaments and the lens in order to focus on a distant object.
In order to focus on a near object:
- the ciliary muscles relax
- the suspensory ligaments tighten
- the lens becomes thinner and only slightly refracts light rays.
What is myopia?
Myopia is also known as short sightedness. People with myopia can see close objects with clear focus but distant objects look blurred.
This may be a result of a lens that is too curved or a long eyeball. The light is focused infront of the retina.
What is hyperopia?
Hyperopia is also known as long-sightedness. People with hyperopia can focus clearly on distant objects but close objects appear blurred.
This may be a result of a lens that is too flat and thin or a short eyeball. This means that the lens cannot refract the light rays stongly enough and light is focused behind the retina.