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Biology · The Nervous System

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The whole chapter on two pages. Print it on A4 — they are already landscape — or cover a box and see how much of it you can say from memory.

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Biology · OCR Paper 1

The Nervous System

Neurones and the Nervous System

The nervous system uses neurones to carry electrical impulses from receptors, through the central nervous system, to effectors.

  • Neurone A nerve cell that carries electrical impulses.
  • Stimulus A change in the surroundings that can be detected.
  • Receptor A cell that detects a stimulus and starts an impulse.
A flow chart from stimulus to receptor to central nervous system to effector to response.
Impulses travel from the receptor to the central nervous system, and then to an effector.

Receptors and effectors

  • Receptors Detect a stimulus; Change it into an electrical impulse; Found in sense organs such as the eye and skin
  • Effectors Carry out the response; Muscles contract and glands release chemicals; Receive impulses from motor neurones

Reflex Arcs

A reflex arc is a short pathway from a receptor, along a sensory neurone, a relay neurone and a motor neurone, to an effector.

  • Reflex action A rapid, automatic response that protects the body.
  • Reflex arc The pathway of neurones involved in a reflex action.
  • Relay neurone A neurone in the central nervous system that links a sensory and a motor neurone.
A reflex arc from a pin on a finger, along a sensory neurone to the spinal cord, through a relay neurone, and out along a motor neurone to a muscle.
In a reflex arc the impulse passes from receptor to sensory neurone, relay neurone, motor neurone and effector.

Reflex and voluntary actions

  • Reflex action Very fast; Automatic, without thinking; The pathway goes through the spinal cord
  • Voluntary action Slower; You choose to do it; The pathway goes through the brain

Investigating reaction time

  • Set up A partner holds a ruler vertically so that the zero mark is…
  • Drop Your partner lets go without warning.
  • Measure Read the distance on the ruler at the top of your thumb.
  • Repeat Repeat at least three times and calculate a mean.
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Biology · OCR Paper 1

The Nervous System continued

The Eye (Separate only)

The cornea and the lens focus light on the retina, the iris controls how much light enters.

  • Cornea The transparent front of the eye that refracts light.
  • Iris The ring of muscle that controls the size of the pupil.
  • Pupil The hole in the iris through which light enters.
The eye in cross-section with the cornea, iris, pupil, lens, ciliary body, suspensory ligaments, retina and optic nerve labelled.
Light is bent by the cornea and the lens, and forms an image on the retina.

Near and distant objects

  • Looking at a near object Ciliary muscles contract; Suspensory ligaments slacken; Lens becomes thicker and more curved
  • Looking at a distant object Ciliary muscles relax; Suspensory ligaments are pulled tight; Lens becomes thinner and less curved

The Brain (Separate only)

The brain is divided into regions with different functions.

  • Cerebrum The largest part of the brain, which controls thought, memory, language and voluntary movement.
  • Cerebellum The part of the brain that coordinates movement and balance.
  • Medulla The part of the brain that controls the heart rate and breathing.
A cross-section of the brain with the cerebrum, cerebellum, medulla, hypothalamus and pituitary gland labelled.
Each region of the brain has its own job.

What each region controls

  • Thinking and movement Cerebrum: conscious thought, memory, language, voluntary movement; Cerebellum: coordination of movement and balance
  • Keeping the body going Medulla: heart rate and breathing; Hypothalamus: body temperature and water balance; Pituitary gland: releases hormones