Control and Coordination in Mammals

2026 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Describe the features of the endocrine system with reference to the hormones ADH, glucagon and insulin
  2. Compare the features of the nervous system and the endocrine system
  3. Describe the structure and function of a sensory neurone and a motor neurone and state that intermediate neurones connect sensory neurones and motor neurones
  4. Outline the role of sensory receptor cells in detecting stimuli and stimulating the transmission of impulses in sensory neurones
  5. Describe the sequence of events that results in an action potential in a sensory neurone, using a chemoreceptor cell in a human taste bud as an example
  6. Describe and explain changes to the membrane potential of neurones, including: how the resting potential is maintained; the events that occur during an action potential; how the resting potential is restored during the refractory period
  7. Describe and explain the rapid transmission of an impulse in a myelinated neurone with reference to saltatory conduction
  8. Explain the importance of the refractory period in determining the frequency of impulses
  9. Describe the structure of a cholinergic synapse and explain how it functions, including the role of calcium ions
  10. Describe the roles of neuromuscular junctions, the T-tubule system and sarcoplasmic reticulum in stimulating contraction in striated muscle
  11. Describe the ultrastructure of striated muscle with reference to sarcomere structure using electron micrographs and diagrams
  12. Explain the sliding filament model of muscular contraction including the roles of troponin, tropomyosin, calcium ions and ATP

The Endocrine System

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What is the Endocrine System?

The endocrine system is a communication system in your body that uses chemical messengers called hormones. A hormone is a chemical substance produced by a special type of organ called an endocrine gland and carried around the body in the blood.

Think of hormones like letters sent through the postal system. The endocrine gland is like the post office that sends out the letter, the blood is like the delivery van, and the target cells are like the houses that receive the letters.

Key Features of the Endocrine System

Endocrine glands are groups of cells that make and release hormones. These glands have a very good blood supply because they need to get hormones into the bloodstream quickly so they can travel to wherever they are needed in the body.

Major endocrine glands include:

  • Pituitary gland (at the base of the brain)
  • Thyroid gland (produces thyroxine)
  • Adrenal glands (produce adrenaline)
  • Pancreas (produces insulin and glucagon)
  • Testes (produce testosterone in males)
  • Ovaries (produce oestrogen in females)

How Hormones Work

Hormones travel in the blood plasma (the liquid part of blood) to reach all parts of the body. However, they only affect certain cells called target cells. Target cells have special receptor proteins on their surface or inside them that match the shape of specific hormones, like a lock and key.

If a cell does not have the right receptor for a particular hormone, that hormone will have no effect on it. This is why hormones can be highly specific in their action.

Two Types of Hormones

1. Peptide Hormones (water-soluble)

Hormones like insulin, glucagon, and ADH (antidiuretic hormone) are made of amino acids (small proteins). Because they dissolve in water but not in fat, they cannot pass through cell membranes (which are made of fat-like substances).

These hormones bind to receptors on the outside of target cells (on the cell surface membrane). When they bind, they activate messenger molecules inside the cell that carry out the hormone's instructions.

2. Steroid Hormones (lipid-soluble)

Hormones like testosterone, oestrogen, and progesterone are made from lipids (fats). Because they are fat-soluble, they can pass directly through cell membranes.

These hormones bind to receptors inside the cell (in the cytoplasm or nucleus) and directly affect what happens inside the cell.

Three Important Hormones to Know

ADH (Antidiuretic Hormone)

  • Produced by the pituitary gland
  • Target organ: kidneys
  • Function: controls how much water the kidneys reabsorb, helping to regulate water balance in the body

Glucagon

  • Produced by the pancreas
  • Target organ: mainly the liver
  • Function: raises blood glucose levels when they are too low by causing the liver to break down stored glycogen into glucose

Insulin

  • Produced by the pancreas
  • Target organs: liver, muscles, and other body cells
  • Function: lowers blood glucose levels when they are too high by causing cells to take up glucose from the blood

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