Biology - paper 2

• Homeostasis is maintaining a stable internal environment
• Control systems are made from receptor cells, coordination centres and effectors
• Homeostasis


  Maintaining a stable internal environment
• Homeostasis


  • Responds to changes in both internal & external conditions
  • Automatic control systems are made of receptors cells, coordination centres and effectors
• The nervous system detects and reacts to stimuli
• Stimulus -> receptor - sensory neurone -> relay neurone -> motor neurone -> effector -> response
• Muscles contract
• Glands secrete hormones
• Central nervous system is made up of the brain and spinal cord.
• The brain and spinal cord are connected to the body by sensory and motor neurones.
• Sensory neurones carry electrical impulses from receptors to CNS
• Motor neurones carry electrical impulses from CNS to effectors
• Effector are muscles or glands that respond to impulses
• Synapses connect neurones and the nerve signal is transferred by chemicals that diffuse across the gaps
• Reflexes are rapid, automatic responses to stimuli that do not involve the brain - reduce chance of injury
• The brain is part of the central nervous system
• The brain is made of billions of neurones
• The cerebral cortex is the outer layer of the brain and is responsible for conscious thought and memory
• The medulla oblongata is the part of the brain stem that controls the heart rate and blood pressure (unconscious activities)
• The cerebellum is responsible for muscle coordination, balance, and posture.
• The spinal cord is a bundle of nerves that connects the brain to the body.
• Studying patients with brain damage can help us understand how the brain works and how it is damaged
• However studying brain damage can be invasive as the brain is delicate
• MRI scans produce a detailed picture of the brain’s structure and function.
• The eye is made up of 9 key components
• The suspensory ligaments control the shape of the lens
• The retina contains receptor cells that are sensitive to light intensity and colour
• The optic nerve is the nerve that carries impulses from the retina’s receptor cells to the brain
• The sclera is the white part of the eye and is the outer layer of the eye.
• The ciliary muscles are the muscles that control the shape of the lens.
• The lens focuses light on the retina
• The pupil is the opening of the eye that allows light to enter the eye.
• The cornea is the transparent layer at the front of the eye that refracts light.
• The iris is the colored part of the eye that controls the size of the pupil.
• When exposed to bright light the circular muscles contract and the radial muscles relax and the pupil becomes smaller
• When exposed to dim light the radial muscles contract and the circular muscles relax and the pupil widens
• When focusing on near objects, the ciliary muscles contract and the suspensory ligaments relax - the lens becomes fat which increases the amount of refracted light
• When focusing on far objects the ciliary muscles relax and the suspensory ligaments contract - the lens becomes thinner so a smaller amount of light is refracted
• Long sightedness means that the light rays are focused behind the retina, so the image is blurred - the eyeball is too short
• Longsightedness can also be called hyperopia