coordination and response

• Accommodation


  The process by which the elastic lens changes its shape (with the aid of ciliary muscles and suspensory ligaments) to focus on near or distant objects
• Light is focused onto the retina
• Adrenal glands


  Endocrine glands located above the kidneys that produce adrenaline
• Adrenaline


  A hormone produced by the adrenal glands that is involved in the 'fight or flight response. It increases heart rate, breathing rate and widens the pupils. Adrenaline also increases blood glucose concentration.
• Antagonistic muscles


  Pairs of muscles that work in an opposing fashion e.g. circular and radial muscles
• Auxins


  A group of plant hormones that stimulate growth in shoot tips. They are involved in plant tropisms.
• Blind spot


  The area at the back of the eye where the optic nerve exits the eye. It lacks receptor cells so cannot detect an image.
• Central nervous system (CNS)


  The brain and spinal cord
• Ciliary muscle


  A ring of smooth muscle that controls the shape of the lens
• Circular muscles


  Muscles of the iris that are involved in the pupil reflex action. In bright light, the circular muscles contract to constrict the pupil. Less light enters the eye.
• Cone cells


  Cells found in the retina that are sensitive to high light intensity (bright light). There are three types of cone cells that can detect light of different colours.
• Cornea


  The transparent outer covering of the eye which refracts light entering the eye
• Dopamine


  A stimulant neurotransmitter which causes a short term 'high'
• Effector


  An organ, tissue, or cell that produces a response to a stimulus
• Endocrine glands


  Glands of the endocrine system that secrete hormones directly into the bloodstream
• Endocrine system


  A collection of glands that secrete hormones into the bloodstream
• Transmission of signals in the endocrine system

  • Slow
  • Long-lasting effects
• Fovea


  A region of the retina with a high density of cone cells
• Glucagon


  A hormone secreted by the pancreas when blood glucose concentration is too low, it causes the breakdown of glycogen to glucose in the liver
• Gravitropism


  A plant's growth response to gravity
• Hair erector muscles


  Tiny muscles found in the skin which contract causing hairs to stand erect
• Heroin


  An illegal drug that stimulates receptors at synapses in the brain, causing dopamine release
• Homeostasis


  The maintenance of a stable internal environment in the body (within set limits) despite fluctuations in internal and external conditions
• Hormone


  A cell signalling molecule produced by endocrine glands and released into the blood, it travels to a target organ and binds to receptors on effectors, initiating a response
• Hypothalamus


  A structure in the brain that contains the thermoregulatory centre, it coordinates information from the receptors and sends instructions to the effectors
• Insulin


  A hormone secreted by the pancreas when blood glucose concentration is too high, it causes liver and muscle cells to increase their uptake of glucose and the conversion of glucose to glycogen in the liver
• Involuntary action


  An action that does not involve conscious thought, also known as a reflex action
• Iris


  A pigmented ring of circular and radial muscles, it controls the size of the pupil to alter how much light enters the eye
• Lens


  The transparent structure at the front of the eye which refracts light, focusing it onto the retina, it is attached to a ring of ciliary muscle via suspensory ligaments
• Motor neurone


  A neurone that carries nerve impulses from the CNS to the effectors
• Negative feedback


  A corrective mechanism that allows only small shifts from a set point, reversing a change in conditions
• Negative plant tropism


  The growth of a plant away from a stimulus
• Nerve impulse


  An electrical signal that travels along neurones
• Neurotransmitter


  Chemicals that are used for communication between neurones and their target cells. Neurotransmitters are stored in synaptic vesicles in the presynaptic neurone and released into the synaptic cleft.
• Oestrogen


  A female sex hormone released by the ovaries that is involved in the development of the female secondary sexual characteristics. It also causes the growth and repair of the uterus lining during the menstrual cycle.
• Optic nerve


  A nerve at the back of the eye that transmits nerve impulses to the brain from the retina.
• Ovaries


  A pair of endocrine glands in females that secrete oestrogen into the bloodstream.
• Pancreas


  An endocrine gland situated behind the stomach that produces insulin.
• Peripheral nervous system


  Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.
• Phototropism


  A plant's growth response to light