homeostasis and response

• homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for functions in response to internal and external changes
• in the human body:

  • blood glucose concentration
  • body temperture
  • water levels
• these are automatic control systems that may involve nervous responses or chemical responses
• all control systems include:

  • receptors which detect stimuli
  • coordination centres
  • effectors, muscles or glands
• stimuli : a change in the environment that causes a response in an organism
• coordination centres : receive and process information from receptors

  • brain
  • spinal cord
  • pancreas
• effectors, muscles and glands bring about receptors which restore optimum levels
• neurons:

  • have long axon fibres so they can carry messages up and down the body over long distances
• the nervous system enables humans to react to their surroundings and to coordinate their behaviours
• 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
• reflex arc controls reflexes
• reflex arc does not involve the brain as reflexes do not involve the conscious part of the bran
• reflexes are rapid and automatic
• synapses in a reflex arc ensure that impulses only travel in one direction
• receptor --> sensory neurone --> motor neurone --> effector
• receptor: a cell that detects a stimulus and responds to it
• sensory neurone: carries impulses from receptors to the CNS
• relay neurone: in the CNS there is a synapse and a relay neurone takes it through the CNS
• motor neurone: the impulses then move from the CNS to the effector
• effector: muscle or gland that responds to a stimulus and produces a response
• examples of reflex arc:

  • knee- jerk
  • hot object
• the brain control complex behaviours.
• the brain is made of billions of interconnected neurones and has different regions that carry out different functions
• cerebral cortex is the outer layer of the brain and is responsible for conscious thought and memory
• the cerebellum controls movement, balance and the coordination of muscles
• medulla is involved in unconscious control of heart rate and breathing
• the hypothalamus is involved in homeostasis it helps maintain body temperature and produce hormones that control the pituitary gland.
• pituitary gland produces important hormones
• the complexity and delicacy of the brain makes investigating and treating brain disorders very difficult
• what have neuroscientists discovered while studying patients with brain damage?

  they can electrically stimulate different parts of the brain and using MRI scans to map out different regions of the brain
• the eye is a sense organ that detects light
• the light receptor cells in the back of the eyes are called rod and cone cells
• stimuli the receptor cells of the eyes sensitive to :

  • colour
  • light intensity
• muscles in the eye:

  • radial muscles
  • circular muscles
• cornea: transparent lens that refracts light as it enter the eye
• iris: controls how much light enters the pupil to ensure the optimum amount of light enters the eye
• lens: transparent disc that can change shape to focus light onto the retina