Homeostasis
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What is homeostasis?
The regulation of conditions inside the body to maintain a stable internal environment so the body can respond to conditions.
Explain negative feedback. (4 steps)
• Receptor detects a stimuli is too high/ low • The coordination centre organizes a response to raise/ lower it • Effector produces a response which counteracts the stimuli • The response carries on until the level changes too much and the opposite problem occurs, meaning the negative feedback reverses
Name 2 types of effector
• Muscles • Glands
How do synapses work? (3 steps)
• The electrical nerve signal transforms into a chemical message in the pre-synaptic neurone • Neurotransmitters diffuse across the synaptic cleft • A new electrical signal is set off in the post-synaptic neurone
What is a reflex action?
Automatic responses which don’t involve the conscious part of the brain
State the 7 parts of a reflex action.
Stimuli, Receptor, Sensory neurone, Relay neurone in the CNS, Motor neurone, Effector, Response.
• Where is the cerebral cortex? • What does it do?
• Near the front at the top • Consciousness, memory, language
• Where is the medulla? • What does it do?
• Near the spinal cord • Unconscious activities
• Where is the cerebellum • What does it do?
• At the back • Muscle co-ordination
State 3 ways the brain can be studied.
• Studying patients with brain damage • Electrically stimulating certain parts • MRI scans
State 2 risks of brain investigation.
• Physical damage to the brain • Increased problems with its function
What does the sclera do?
Acts as a tough, supportive outer wall
What does the cornea do?
The thin outer layer of the eye which refracts light as it enters
What does the iris do?
Controls the diameter of the pupil, controlling the amount of light that enters the eye
What does the lens do?
Focuses light onto the retina
What happens to eye in bright light?
• Circular muscles in the iris contract • Radial muscles relax • To contract the pupil
What happens to the eye in dim light?
• Circular muscles in the iris relax • Radial muscles contract • To dialate the pupil.
State how the eye responds to near objects.
• Ciliary muscles contract, suspensory ligaments relax • Lens becomes more fat • Light is refracted more
State how the eye responds to far objects.
• Ciliary muscles relax, while suspensory ligaments contract • The lens goes thin • Light is refracted less
How does myopia (short-sightedness) occur?
Light is refracted too much and and objects are brought into focus in front of the retina.
How does hyperopia (long-sightedness) occur?
Light is not refracted enough and the object comes into focus behind the retina.
How is myopia combatted?
Concave lens
How is hyperopia combatted?
Convex lens
State 3 other options for combatting eye problems other than glasses.
• Contact lenses • Laser eye surgery • Replacement lens surgery