International A Level Biology / Coordination in animals and plants
Nervous and hormonal coordination
Edexcel International A Level Biology (YBI11), chapter 24: Coordination in animals and plants, specification point 8.13, 8.10. Free lesson.
Read the revision notes · International A Level Biology past papers
Animals coordinate responses using the nervous system, hormones, or both together. Knowing how their signals differ, and how the peripheral nervous system is organised, helps explain how the body responds to everyday actions and threats.
How nervous and hormonal control differ
Both systems coordinate effectors, such as muscles and glands, but they send signals in different ways. A neurone is a nerve cell that carries impulses. At a synapse, there is a chemical step as a signal passes between cells. Hormones are chemical messengers released by glands into the blood. Their different routes explain why their effects differ. Nervous signals are impulses along neurones. They reach an effector in milliseconds, so the response is very fast. Hormones travel in the blood, so their responses are slower. Nervous responses are usually short-lived and localised to the…
How the peripheral nervous system is divided
The peripheral nervous system is made up of neurones outside the brain and spinal cord. Sensory neurones carry impulses in towards the central nervous system. Its motor side carries impulses out and divides according to the structures it controls. The somatic system is voluntary. Its motor neurones control skeletal muscles, so kicking a ball uses the somatic system. The autonomic system is involuntary. Its neurones go to cardiac muscle, smooth muscle and glands, not skeletal muscle. The autonomic system has two divisions: sympathetic and parasympathetic.
How sympathetic and parasympathetic control balance
The two autonomic divisions often act on the same organs in opposite ways. This is called an antagonistic effect. The organ's response depends on the balance between the two divisions. Sympathetic activity prepares the body for action, or fight or flight. It mostly releases noradrenaline at the effector. Parasympathetic activity supports rest and digestion. It releases acetylcholine, and many parasympathetic neurones run in the vagus nerve. At the eye, sympathetic impulses dilate the pupil, while parasympathetic impulses constrict it. At the heart, sympathetic impulses raise the…
How nerves and adrenaline work together in a fright
A threat can trigger nervous and hormonal coordination at the same time. Receptors detect the threat and send impulses to the brain. The hypothalamus sends impulses down the spinal cord, and sympathetic neurones carry them onwards. This gives the body a fast start. Some sympathetic impulses go directly to organs such as the heart and eyes. Heart rate rises and pupils dilate within a second. Other sympathetic neurones stimulate the adrenal medulla, the inner part of an adrenal gland, to release adrenaline into the blood. Adrenaline travels to target cells throughout the body. It binds…
How to compare the two systems in an answer
A comparison should put both systems in the same sentence. This makes the difference clear and helps you give a direct, complete answer. You can compare the route, speed, duration or spread of the response. For example: nervous coordination uses impulses along neurones, whereas hormonal coordination uses hormones carried in the blood. You can also compare speed and duration: nervous responses are faster and shorter-lived, while hormonal responses are slower and last longer.