homeostasis

• your automatic control systems keep your internal environment stable using a mechanism called negative feedback
• the receptor of a negative feedback loop detects a stimulus
• In a negative feedback loop the coordination centre receives and processes this information and organises a response
• In a negative feedback loop the effector produces a response that counteracts the change and restores the optimum level
• The cells and enzymes need to work in specific conditions so homeostasis is needed to regulate temperatures or blood glucose levels or water levels
• Two examples of an effector - muscles and glands
• The synapse is the gap between two neurones
• The nerve signal is transferred by chemicals which diffuse across the synapse
• The chemicals that have been diffused across the synapse set off a new electrical signal in the next neurone
• Reflexes are automatic responses to stimuli that do not involve the conscious part of the brain
• A reflex arc is the passage of information from a receptor to an effector in a reflex
• An effector is a muscle or gland that responds to nervous impulses
• Pain receptor is stimulated, impulses travel along the sensory neurone , impulses are passed along a relay neurone via a synapse, impulses travel along a motor neurone via a synapse, impulses meets muscle and it contracts
• the cerebellum is responsible for muscle coordination and balance
• the medulla oblongata is responsible for unconscious activity like breathing and your heartbeat
• the cerebral cortex is at the front and is the bigger bit and is responsible for consciousness, memory and language
• scientists use a range of methods to study the brain - studying patients with brain damage, electrically stimulating the brain, doing an MRI scan
• The sclera is the tough supporting wall of the eye, like a cell wall for the eye
• the cornea is the transparent outer layer found at the front of the eye that refracts light
• the lens focuses light onto the retina
• the iris controls how much light enters the pupil by changing its diameter
• the shape of the lens is controlled by ciliary muscles and suspensory ligaments
• to look at nearer objects, the ciliary muscles contract, which slackens the suspensory ligaments and the lense becomes fat which increases the amount by which it refracts light
• to look at distant objects the ciliary muscles relax which allows the suspensory ligaments to tighten and makes the lense become thin so it refracts light by a smaller amount
• long sighted people (hyperopia) are unable to focus on near objects because the lense is the wrong shape or the eyeball is too short. This makes the image be formed behind the retina so glasses with convex lenses are used which refracts the light rays so they focus on the retina
• short sighted people (myopia) are unable to focus on distant objects because the lense is the wrong shape or the eyeball is too short. The image is formed in front of the retina so concave glasses are used to focus the light rays onto the retina
• The thermoregulatory system is in the brain
• Temperature receptors detect temperatures that are not optimal (37)
• The thermoregulatory system receives info from the temperature receptors and triggers the effectors
• effectors such as sweat glands produce a response and counteract the change
• when you are too hot, sweat is produced by the sweat glands and evaporates. The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin (vasodilation) which helps transfer energy to the environment.
• when you are too cold, the hairs stand up and create an insulating layer and no sweat is produced. Blood vessels supplying the skin capillaries constrict (vasoconstriction) and your muscles contract automatically (shivering) which needs respiration, which needs energy which warms the body.
• hormones are produced in the endocrine glands
• the pituitary gland is also known as the master gland
• the ovaries produce oestrogen
• the testes produce testosterone
• the thyroid produces thyroxin which regulates metabolism, heart rate and temperature
• the adrenal gland produces adrenaline
• the pancreas produces insulin to regulate glucose levels
• If a response is instantaneous and rapid then it is nervous, if it the response lasts for a long time and does not target a very specific area then it is hormonal