homeostasis

• maintaining a stable internal environment
• the conditions inside your body need to be kept steady , even when the external environment changes . this is really important so your cells have the right conditions for enzyme action
• homeostasis is the regulation of internal conditions to maintain a stable internal environment in responses to changes in both internal and external conditions
• you have automatic control systems - nervous and hormonal communication that regulate your internal environment, they maintain body temperature , blood glucose and water content
• automatic control systems are made from three main components , receptors , coordination centres and effectors
• negative feedback

  receptor detects stimulus level too high or low

  coordination centre recieves and processes the information then organise a response

  effector produces a response which counteracts the change and restores the optimum level
• nervous system means that humans can react to their surroundings and coordinate their behaviour
• central nervous system

  vertebrate (animals with backbones) this consists of the brain and spinal cord only in mammals , the cns is connected to the body by sensory neurones and motor neurones
• sensory neurone

  the neurones that carry information as electrical impulse from the receptors to the CNS
• motor neurones

  the neurones that carry electrical impulses from the CNS to effecotrs
• effectors

  all your muscles and glands which respond to nervous impulses
• receptors are cells that detect stimuli
• effecotrs respond to nervous impulses and bring about a change

  muscles and glands are known as effectors - they respond in different ways . muscles contract whereas glands secrete hormones
• the connection between two neurones is called a synapse

  the nerve signal is transferred by chemicals which diffuse across it

  these chemicals then create new electrical signal in the next neurone
• reflexes are rapid and automatic , dont involve the conscious part of the brain - reduce the chance of being injured
• reflex arc

  1.stimulus is detected by receptors impulses sent along sensory neurone to relay neurone in the spinal cord

  2.when the impulses reach a synapse between relay and motor neurone , chemicals are released and cause impulses to be sent to the motor neurone

  3.impulses travel along motor neurone to effector

  4.effector produces a response (muscle contracts or glands secrete hormones)
• brain

  made up of billions of interconnected neurones

  in charge of running complex behaviours

  different regions carry out different functions
• cerebal cortex

  outer layer of the brain - controls consciousness , memory , intelligence and language
• cerebellum

  responsible for muscle coordination and balance
• medulla

  in the brain stem - top of spinal cord

  responsible for unconscious activities
• studying patients with brain damage

  small part of the brain is damaged you can moniter the effects it has on the person to tell what the damaged part of the brain does
• electrically stimulating the brain

  stimulated electrically by tiny electrodes in the tissues , by observing different parts you can get an idea of what those parts do
• mri scans

  magnetic resonance imaging scanner

  produces a detailed picture of the brains structures - you can see what areas of the brain is active when doing certain tasks
• consequences

  incredibly complex and delicate

  carries risks such as physical damage , increased problems

  hard to access because of skull

  hard to treat with medications
• sclera is the tough supporting wall of the eye
• cornea is the transparent outer layer found at the front of the eye . it refracts the light into the eye
• iris contains muscles that control the size of the pupil and how much light gets into the eye
• lens focuses the light onto the retina which contains light sensitive cells (sensitive to light rod and colours cones ) main parts of the cone cells in fovea
• shape of lens controlled by ciliary muscles and suspensory ligaments
• optice nerve carries impulses from receptors on the retina to the brain
• bright light

  circular muscles contract , radial muscles relax , pupil constricts
• dim light

  circular muscles relax , radial muscles contral , pupil dilates
• near objects

  ciliary muscles contract , suspensory ligament slacken

  lens is fat

  increase the amount it refracts light
• distant objects

  ciliary muscles relax , suspensory ligament pulled taut

  lens long and thin

  reducing the amount it refracts light
• the eye focuses on the retina by changing the shape of the lens - accommodation
• long sighted (hyperopia)

  blurry near objects

  eyeball too short lens doesnt bend light enough

  imgaes fall behind the retina

  fixed with convex lenses . so the lens can refract the light rays so the focus on the retina
• short sighted (myopia)

  ditant objects blurry

  eyeball too long , lens bend light too much

  images fall before the retina

  concave lenses to fix
• other fixes

  contact lenses , laser eye surgery , lens replacement surgery
• body has to balance the amount of energy lost and gained to keep core temperature constant

  thermoregulatory centre in the brain , contains receptors sensitive to the temperature of blood flowing through it

  receives impulses from the temperature receptors in the skin giving information about skin temperature
• temperature receptors detects core body temperature changing

  thermoregulatory centre acts as a coordination centre - receives information and triggers the effectors automatically

  effectros produce a response to counteract the change