Homeostasis and response

• Homeostasis


  homeostasis is 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 does homeostasis control

  blood glucose levels, body temperature, water levels
• Homeostasis control systems

  They are automatic and may involve nervous responses or chemical responses
• All control systems include

  Receptors, coordination centres and effectors
• Receptor


  Cells that detect a change in environment
• Coordination centres

  Recieve and process information from receptor cells
• Effectors

  muscles and glands; makes a response which controls the bodies optimum levels
• Function of nervous system

  Detect and make a response through effectors
• 3 neurones involved with the CNS

  Sensory, relay and motor neurone
• CNS consists of

  brain and spinal cord
• reflex arc

  Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.stimulus -> receptor -> coordinator -> effector -> response

  
• Synapse

  Gap between neurons, when the electrical impulse reaches the synapse it causes a release in chemicals (neurotransmitters) . This causes an electrical impulse to start in the next nerve

  
• Why do we need reflexes for

  Reflex actions are automatic and rapid; they do not involve the conscious part of the brain. helps stop getting severely injured
• What does the brain control

  Complex behaviour
• What is the brain made of

  Billions of interconnected neurones, it has different regions which carry out different functions.
• Function of cerebral cortex

  intelligence, memory, language and consciousness
• Function of hypothalamus

  Temperature control
• Function of pituitary gland

  Releasing chemical messengers called hormones
• Function of cerebellum

  Muscle activity and coordination
• Function of Medulla

  Heartbeat, digestion and movement
• Why is it difficult to investigate brain function, brain damage or brain diseases

  • protected by skull• structure is extremely complex• delicate and easy to damage
• How do scientists investigate brain function?

  Look at patients who suffer brain damage and see where damage has taken place electrically simulate different parts of the brain and look at the effects on the persons behaviour MRI scanning to see what parts of the brain are most active during different activities
• Cornea

  Clear area of sclera, it refracts light - bends as it enters the eye
• Lens


  Focuses light onto the retina
• Retina


  Contains light receptors cells
• Optic nerve


  Carries impulses between retina and brain
• Sclera


  White tough outer layer
• Pupil

  Small hole at the centre of the iris through which light enters the eye
• How does the eye change for near or far objects

  Lens changes shape, this is called accommodation
• To focus on near object the eye changes by

  cillary muscles contractsuspensory ligament loosenthe lens is thicker then refracts light rays strongly
• To focus on a distant object the eye

  the cillary muscles relaxthe suspensory ligaments are pulled tightthe lens is pulled thin and only slightly refracts light rays
• two common defects of the eye

  myopia (short sightedness) hyperopia (long sightedness)
• How are the defects treated

  glasses - spectacle lenses that refract the light rays so they focus on the retinanew technologies include hard and soft contact lenseslaser surgery to change the shape of the cornea and a replacement lens in the eye
• How does the eye change in bright or dim lights

  Muscles in the iris contract or relax making the pupil larger or smallercontract -> pupil larger relax -> pupil smaller this is a reflex action as this does not involve the conscious part of the brain
• Eye is a sense organ sensitive to


  The eye is a sense organ containing receptors sensitive to light intensity and colour
• What is body temperature monitored and controlled by

  the thermoregulatory centre in the brain.
• What does the thermoregulatory centre contain

  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 skin releases sweat from the sweat glands .
• If the body temperature is too low

  blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).
• How does vasodilation transfer energy to the surroundings

  With more warm blood in the skin, heat energy is lost by radiation from the skin