Homeostasis

• The body uses negative feedback to regulate body temperature, blood glucose concentration, and water balance.
• Homeostatic mechanisms are controlled by the nervous system or endocrine glands.
• receptor: detects a stimulus
• coordination centre: receives and processes information from receptors and sends out signals to effectors
• effector: an organ or cell that acts in response to a stimulus
• an effector is a muscle or a gland
• homeostasis: the regulation of the internal conditions of your body to maintain optimum conditions for enzyme activity
• central nervous system (CNS) - brain and spinal cord
• sensory neurone: carries electrical impulses from the receptors to the CNS
• effectors respond to nervous impulses and bring about a change in the body
• muscles contract in response to a nervous impulse
• glands secrete hormones
• synapse: the gap between neurones that allows the transmission of nerve impulses
• the nerve signal is transferred by chemicals which diffuse across the gap
• reflexes: rapid, automatic responses to certain stimuli that dont involve the conscious part of the brain
• the passage of information in a reflex (from receptor to effector) is called a reflex arc
• neurones in reflex arcs go through the spinal cord or an unconcious part of the brain
• relay neurone: a neurone that connects sensory neurones to motor neurones
• the brain is in charge of all complex behaviours and is the control centre of the body
• cerebral cortex: outer layer of brain, responsible for conscious thought, memory, language and intelligence
• medulla: the part of the brain that controls unconscious activities like; heart rate and breathing
• cerebellum: controls muscle coordination, balance, and posture
• studying patients with brain damage: if a small part is damaged the effect it has on the patient can tell us what that area controlls
• electrically stimulating: pushing tiny electrodes into the tissue and giving it a small zap of electricity . by observing, it can give us an idea on what it does
• MRI scans: produces detailed images of the brain and we can find out what areas are active when people are doing things
• electrical stimulation: for example, can reduce muscle tremors in patients with Parkinson's disease
• investigations carry risks of of physical damage to brain or increased problems
• sclera: tough and supporting wall of the eye (white part)
• Cornea: transparent layer of the eye that refracts light to focus it on the retina
• iris: contains muscles that allow it to control the diameter of the pupil and how much light enters the eye
• Lens: focuses the light onto the retina
• retina: the light-sensitive layer at the back of the eye that contains receptors for light and colour
• shape of the lens is controlled by sensory ligaments and ciliary muscles
• optic nerve: carries impulses from the retina to the brain
• when light receptors detect a bright light, a reflex is triggered that makes the pupils smaller. circular muscles contract and radial muscles relax
• dim light: radial muscles contract and circular muscles relax making pupils wider
• too look at near objects: 1)ciliary muscles contract and suspensory ligaments relax

  2) lens becomes fat

  3) increases the amount of refracted light
• look at distant objects: 1) ciliary muscles relax and sensory ligaments pull tight

  2) lens becomes thin

  3) refracts light by a smaller amount
• long sighted people are unable to focus on near objects
• hyperopia: farsightedness, the light rays focus behind the retina