C10 Flashcards
What is homeostasis?
The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function, in response to internal and external changes.
What is homeostasis important for ?
Homeostasis is important for maintaining optimal conditions for enzyme action and all cell functions.
What does homeostasis control?
In the human body, homeostasis controls the blood glucose concentration, body temperature and water levels.
Control systems
The automatic control systems include nervous responses in your nervous system and chemical responses in your hormone system.
Receptors
cells that detect changes in the internal or external environment, known as stimuli.
Coordination centres
Areas that receive and process the information from the receptors. They send signals and coordinate the response of the body. They include the brain, spinal cord and the pancreas.
Effectors
Muscles or glands that respond to the stimulus that’s been received. These responses restore conditions in the body to the optimum levels.
Nervous system
The nervous system uses electrical impulses to enable you to react quickly to your surroundings and coordinate your behaviour.
Impulses
Impulses from receptors pass along sensory neurons to the brain or spinal cord. The brain coordinates a response and impulses are sent along motor neurons from the brain to the effector organs.
Effector functions
Your muscles respond to the arrival of impulses by contracting. Your glands respond by releasing chemical substances.
E.g - salivary glands produce and release extra saliva when you smell food
- Pancreas releases insulin when your blood sugar levels go up after a meal.
Nervous system order
stimulus
receptor
coordinator
effector
What are reflexes for ?
They help you avoid danger or harm because they happen so fast. Reflexes are automatic and rapid - they do not involve the conscious part of your brain.
Neurones
Simple reflex actions involve three types of neurone.
- sensory neurones
- motor neurones
- relay neurones: these connect a sensory neurone and a motor neurone.
How do reflexes work?
An electrical impulse passes from the receptor along the sensory neurone to the CNS. It then passes along a relay neurone and straight back to the motor neurone. From there the impulse arrives at the effector organ.
How do synapses work?
Your neurones are not joined up directly to each other. There are junctions between them called synapses which form gaps between the neurones. The electrical impulse has to cross this. The diffusion of the chemical across the synapse is slower than the electrical impulse in the neurones, so its possible to cross the gap.
The structure of the brain
cerebral cortex - is concerned with consciousness, intelligence, memory and language.
cerebellum - is concerned with coordinating muscular activity and balance.
medulla - is concerned with unconscious activities, such as controlling the heartbeat, the movements of the gut and breathing
MIR
Scientists map regions of the brain to their functions by studying patients with brain damage, by electrically stimulating different areas of the brain.
cornea
where light refracts into the eye
lens
focuses light rays onto the retina
pupil
hole in the centre of the iris that allows light to pass through
iris
has sets of muscles that control the size of the pupil and the amount of light reaching the retina
retina
where light sensitive receptor cells are found
optic nerve
carries impulses from the retina to the brain
ciliary body
secretes fluid that supports the front of the eye
suspensory ligaments
change the shape of the lens to focus light rays on the retina
ciliary muscle
changes the shape of the lens to focus light rays on the retina
colour blindness
a defect that affects the cones
cones
receptor cells in the retina that perceive colour
rods
receptor cells in the retina that perceive black and white and allow us to see in the dark
energy conversion by receptor cells
receptor cells convert light energy into the electrical energy of a nerve impulses
seeing in the dark
the radial muscles contract and the pupil becomes larger to allow more light in
seeing in light
the circular muscles contract and the pupil becomes smaller to allow less light in
refraction
the bending of light rays as they travel from one medium to another
focusing an image
first the cornea refracts light rays towards the lens then the lens refracts the light ray even more then an image is focused on the retina and the optic nerve carries impulses from the retina to the brain
focusing long distance objects
the light rays are almost parallel so the lens doesn’t have to do much
focusing short distance objects
because the light rays diverge the lens changes shape and becomes thicker
accommodation
the ability of the eye to change shape
accommodation of near objects
first the ciliary muscles contract then the suspensory ligaments loosen the lens gets thicker and the light rays are refracted strongly
accommodation of distant objects
first the ciliary muscles relax then the suspensory ligaments contract the lens gets thinner and the light rays are refracted less strongly
short-sightedness (myopia)
when a person can see objects at short distances but not at long distances because either the eyeball is too long for the strength of the lens or the cornea is too sharply curved. this can be fixed by a concave lens
long-sightedness (hyperopia)
when a person can see objects at long distances but not at short distances because either the eyeball is too short or the cornea is not curved enough. this can be fixed by a convex lens
eye technologies
contact lens correct refractive error. they are permeable to allow oxygen to reach the cornea
laser eye surgery corrects the shape of the cornea
