The human nervous system

HomeostasisThe human nervous systemReaction time required practicalThe human brainThe human eyeControl of body temperatureThe endocrine systemControl of blood glucose concentrationControl of nitrogen and water levelsHormones in human reproductionControl of fertility and treatment of infertilityAdrenaline, thyroxine and negative feedbackPlant hormonesGrowth of seedlings required practical

The nervous system enables humans to react to their surroundings and coordinate their behaviour.

The nervous system is made up of specialised cells called neurones, which transmit electrical impulses. These neurones are connected in a vast network that includes:

Receptors: These are cells that detect stimuli, such as light, sound, or temperature.
Sensory neurones: These carry impulses from receptors to the central nervous system (CNS).
Relay neurones: These connect sensory neurones to motor neurones within the CNS. The CNS processes information from receptors and coordinates a response.
Motor neurones: These carry impulses from the CNS to effectors.
Effectors: These are muscles or glands that respond to impulses, producing a movement or releasing a hormone.

Synapses are the junctions between neurones and other cells (either receptors, other neurones or effectors). The transmission of a signal across the synapse is slower than the impulse along the neurone, but the structures in the synapse ensure the impulse can only travel in the correct direction.

The CNS is made up of the brain and spinal cord.

Some responses are complex and need to be coordinated through many thousands or millions of relay neurones in the CNS.

Reflex actions are automatic and rapid; they do not involve the conscious part of the brain and only invole one relay neurone. The pathway of a reflex action is called a reflex arc.

Stimulus > Receptor > Sensory neurone > Relay neurone > Motor neurone > Effector > Response

Reflex actions are essential for your survival. They protect you from harm by allowing you to react quickly to danger. Examples of reflex actions include pulling your hand away from a hot surface, the pupil in your eye getting smaller when you look at a bright light, and coughing and sneezing.

Reaction time is the time it takes for you to respond to a stimulus. It can be measured using various methods, such as:

Ruler drop test: A ruler is dropped between someone's fingers, and their reaction time is calculated based on how far it falls before they catch it.
Computer-based tests: These use visual or auditory stimuli to measure reaction time.

Reaction times can be presented in numerical form (e.g. 0.25 seconds) or graphical form (e.g., a bar chart or line graph). By analysing data on reaction times, scientists can learn more about how the nervous system functions.

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