The brain, the eye and body temperature control

Biology · Homeostasis and response. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

The brain is made of billions of connected neurones, and different regions do different jobs. Scientists map these regions by studying patients with brain damage, by electrically stimulating parts of the brain and by MRI scans. The brain is complex and delicate, so treatment carries a risk of damaging other areas.

The eye is a sense organ. The cornea and lens focus light onto the retina. Changing the shape of the lens to focus on near or distant objects is called accommodation.

Body temperature is controlled by the thermoregulatory centre in the brain. It has receptors for the temperature of the blood, and it receives impulses from temperature receptors in the skin.

Rules to remember

Cerebral cortex: consciousness, intelligence, memory, language. Cerebellum: muscle coordination and balance. Medulla: unconscious activities such as heartbeat and breathing.
Retina: receptor cells sensitive to light intensity and colour. Optic nerve: carries impulses to the brain. Sclera: tough outer layer. Iris: controls the size of the pupil (in bright light the circular muscles contract and the pupil gets smaller).
Near object: ciliary muscles contract → suspensory ligaments loosen → lens thicker, refracts light strongly.
Distant object: ciliary muscles relax → suspensory ligaments pulled tight → lens thinner, refracts light only slightly.
Myopia (short sight): light focuses in front of the retina; corrected with a concave lens. Hyperopia (long sight): light focuses behind the retina; corrected with a convex lens.
Other treatments for sight: contact lenses, laser eye surgery, a replacement lens in the eye.
Too hot: vasodilation and sweating. Too cold: vasoconstriction, sweating stops, shivering (muscles respire more and transfer energy).

Common mistake

Writing that blood vessels move nearer to or further from the skin surface. They do not move; they get wider (vasodilation) or narrower (vasoconstriction).

Worked example

A swimmer climbs out of cold water. Her skin looks pale and she starts to shiver. Explain both changes.

The thermoregulatory centre detects that the blood temperature has fallen.
Blood vessels supplying the skin capillaries constrict, so less blood flows near the surface. The skin looks pale and less energy is transferred to the surroundings.
Skeletal muscles contract and relax rapidly (shivering). This needs more respiration, which transfers energy and warms the body.

Answer: Pale skin is caused by vasoconstriction, which reduces energy loss. Shivering raises the rate of respiration in muscles, which warms the body.

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