Homeostasis and response

• Enzymes and cells need very stable conditions to work
• 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
• the automatic control system includes hormones and the nervous system
• receptor cells detect a change in stimulus and pass the info onto the coordinator
• the coordinators are the brain and the spinal chord
• coordinators receive and process info from the sensory receptors and send it to the effector
• an effector is a muscle or a gland that responds to a stimulus
• the central nervous system consists of the brain and spinal chord
• the peripheral nervous system consists of the nerves branching off the CNS
• Reflex arc 


  . Stimulus detected by receptor

  . Electrical impulse pass from receptor along a sensory neurone to a coordinator

  . The synapse at the end of the sensory neurone release neurotransmitters which trigger the impulse in the relay neurone

  . the synapse at the relay neurone also release neurotransmitters which trigger the response in the motor neurone

  .the impulse passes down the motor neurone to an effector
• reflexes require no decision making which makes it fast and automatic
• the cerebellum controls balance and coordinates movements
• the medulla controls heart and breathing rate
• the cerebral cortex controls language, memory and consciousness
• the hypothalamus produces the hormone that regulates the body
• the pituitary gland secretes hormone that controls growth, metabolism, sexual maturity and blood pressure
• the brain is hard to treat as it is tricky to access due to the skull, it has a complex structure and it is delicate
• Ways to investigate the brain

  . investigate patients with brain damage

  . electrical stimulation

  . MRI scans
• the eye is a sense organ that contains receptors that detect light intensity and colour
• the cornea is a transparent layer which light passes through and focuses on the retina
• the iris is the coloured part of the eye with an pupil which it controls depending on light intensity
• the lens changes shape to focus light onto the retina (accommodation )
• the retina contains receptor cells to see light intensity and colour and sends impulses down the optic nerve to the brain
• the sclera is the tough outer structure that protects the eye
• the ciliary muscles and the suspensory ligaments allow us to focus on near and distant objects