Homeostasis and Response- Biology

• The hypothalamus detects change
• The lens refracts light further to enter the retina
• The iris controls how much light enters the eye
• The cornea refracts light as it enters the eye
• The sclera is a tough white outer layer of the eye that protects it from injury
• The retina contains light receptors
• The optic nerve carries electrical impulses between the eye and the brain
• To look at near objects, the ciliary muscles contract and the suspensory ligaments relax. The lens becomes more fat and curved which increases the amount of light that enters the eye
• To look at distant objects, the suspensory ligaments contract and the ciliary muscles relax. The lens becomes thinner and less curved. This refracts light by a smaller amount
• When you are long-sighted (hyperopia), the lens could be too weak which is linked to aging. Or the eyeball is too short or the cornea is too curved. These mean that the light falls behind the retina
• To fix hyperopia, convex lenses are used which are rounder and this converges the light rays before they enter the eye
• When you are short-sighted (myopia), the eyeball is too long or the cornea is too sharply curved. This means that when the eye tried to produce an image it falls short of the retina
• To fix myopia, concave lenses are used which diverges the light rays before they reach or enter the eye. They are more rectangular
• Cerebral cortex is the front and back of the brain responsible for memory, intelligence and consciousness
• The medulla controls unconscious activities such as breathing, heart rate, and blood pressure.
• The cerebellum controls muscle coordination and is the bit at the back
• Central Nervous System (CNS) is the brain and spinal cord. Connected to body by sensory neurones and motor neurones
• Sensory Neurones carry messages as electrical impulses from receptors to the CNS
• Motor Neurones carry electrical impulses from CNS to effectors
• Effectors are all muscles and glands which respond to CNS
• Receptors detect stimuli and can form large parts of complex organs such as the eye
• Effectors respond to the impulses and bring change. Glands secret hormones and muscles contract or relax
• Reflex action is when there is no conscious thought involved, it happens automatically
• Reflex Arc: stimulus, receptor, sensory neuron, CNS, motor neurone, effector, response.
• Synapses are the connection between two neurones. Nerve signals are transferred by chemicals that diffuse across the gap. Chemicals trigger electrical impulse in the next neurone
• Reflexes prevent injury or harm. Don't involve conscious part of the brain. Passage of info in a reflex is called a reflex arc
• Endocrine system is made of glands that secrete hormones into the blood stream. Blood carries hormones to the target organ where it produces an effect. Target organ has receptor cells on the cell membrane that picks up hormones and triggers a response.
• glucose is absorbed by villi and pancreas detects change. Pancreas releases insulin which converts glucose to glycogen.
• If blood glucose is too low, pancreas detects change and releases glucagon. Glycogen in muscles and liver is converted back into glucose and goes back into the bloodstream
• The nervous system enables humans to react to their surroundings and to coordinate their behaviour.
• Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques. The complexity and delicacy of the brain makes investigating and treating brain disorders very difficult.
• The eye is a sense organ containing receptors sensitive to light intensity and colour
• To focus on a near object, the ciliary muscles contract, the suspensory ligaments loosen, the lens is then thicker and refracts light rays strongly.
• To focus on a distant object, the ciliary muscles relax, the suspensory ligaments are pulled tight, the lens is then pulled thin and only slightly refracts light rays.
• Body temperature is monitored and controlled by the thermoregulatory centre in the brain. The thermoregulatory centre contains receptors sensitive to the temperature of the blood. The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre.
• If the body temperature is too high, blood vessels dilate (vasodilation) and sweat is produced from the sweat glands. Both these mechanisms cause a transfer of energy from the skin to the environment.
• If the body temperature is too low, blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver)
• The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer.
• The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.
• In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk factor for Type 2 diabetes