Coordination and control flashcards

Topic 14: Coordination and control

Reflex arc (O Level)

Receptor → sensory neurone → relay neurone → motor neurone → effector (muscle or gland). A reflex action is a rapid and automatic response to a stimulus.

Events at a synapse (O Level)

An impulse arrives; neurotransmitter is released from vesicles into the gap; it diffuses across and binds with receptor proteins on the next neurone; an impulse is stimulated there. One way only: vesicles on one side, receptors on the other.

Functions of the cornea, lens, retina and fovea

Cornea: refracts light. Lens: focuses light onto the retina. Retina: light receptors, some sensitive to different colours. Fovea: greatest density of light receptors.

Pupil reflex in bright light

Circular muscles of the iris contract and radial muscles relax, so the pupil constricts and less light enters. (In dim light the reverse: radial contract, pupil dilates.)

Accommodation: focusing on a near object

Ciliary muscles contract, suspensory ligaments slacken, the lens becomes fatter and refracts light more. For a distant object: muscles relax, ligaments taut, lens thinner.

Hormones from the pituitary, pancreas and adrenal glands

Pituitary: FSH and LH. Pancreas: insulin and glucagon. Adrenal glands: adrenaline.

Effects of adrenaline

Released in fear, stress or excitement. It raises the blood glucose concentration and the heart rate, so more glucose and oxygen reach the muscles for respiration.

Negative feedback (O Level)

A change away from the set point triggers a response that returns the value towards the set point.

Responses to overheating (O Level)

Sweating: water evaporates, transferring heat away. Hair erector muscles relax, hairs lie flat. Vasodilation: skin arterioles widen, so more heat is lost by radiation. Coordinated by the hypothalamus.

Responses to getting too cold (O Level)

Shivering: respiration in contracting muscles releases heat. Hair erector muscles contract, hairs trap air. Vasoconstriction: skin arterioles narrow, so less heat is lost.

How blood glucose concentration is controlled

High: pancreas secretes insulin; the liver converts glucose to glycogen; level falls. Low: pancreas secretes glucagon; the liver converts glycogen to glucose; level rises.

Type 1 diabetes: signs and treatment

Signs: increased blood glucose concentration and glucose in the urine. Treatment: administration of insulin.