B10- Human Nervous System

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B10.1

B10.1- The Principles of Homeostasis

Homeostasis in Action

Internal environment: the conditions inside your body

Homeostasis: the regulation of internal conditions of cells to maintain optimum conditions for functioning, in response to internal and external changes

Homeostasis is important for maintaining optimal conditions for enzyme action and all cell function

Internal conditions that are controlled include:

body temperature

the water content of the body

blood glucose concentration

Working Together

Involves coordination and control

Organisms need to be aware of changes and respond accordingly

Automatic response systems include nervous responses in your nervous system and chemical responses in your hormone system

Demands of a control system

Receptors: detect changes (stimuli) in internal and external environment. May be part of the nervous or hormonal control systems of the body

Coordination centres: receive and process info sent from receptors. Send out signals and coordinate body response. Includes the brain, spinal cord and some organs e.g. the pancreas.

Effectors: muscles or glands that bring about response to received stimulus, which restore body conditions to optimum levels

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B10.2

B10.2- The structure and function of the human nervous system

The Nervous System

Receptor cells pick up stimuli and are similar to most animal cells, e.g. nucleus, cytoplasm and cell membrane.

They are usually found clustered together in special sense organs e.g. eyes and skin.

You may have different types of sensory receptor

How your nervous system works

When stimulus is detected, the information is sent as an electrical impulse that passes along neurones.

Neurones are usually found in bundles of hundreds/thousands of neurones, known as nerves.

Cells that carry impulses from sense organs to your CNS are sensory neurones.

The impulse travels along the neurone until it reaches the CNS

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

The brain (CNS) coordinates a response and sends this as an impulse along motor neurones to the rest of your body

These impulses are sent to make the right bits of your body (the effectors) respond

Effectors are muscles or glands. Muscles respond by contracting, glands respond by secreting chemical substances.

STIMULUS - RECEPTOR - [sensory neurones] - COORDINATION (CNS) - [motor neurones] - EFFECTOR

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B10.3

B10.3- Reflex actions

What are reflexes for?

They help to avoid danger (happen very fast) and some take care of basic bodily functions e.g. breathing

Reflexes are automatic and rapid; they do not involve the conscious part of your brain

How do reflexes work?

Relay neurones: connect a sensory neurone and a motor neurone, they are found in the CNS

- Reflex arc

Electrical impulse passes from:

stimuli - receptor - along sensory neurone - CNS - along a relay neurone (usually in spinal cord) - along motor neurone - effector organ (muscle or gland) - response

In a reflex arc, the impulse bypasses the conscious part of your brain so that the time between stimuli and action is as short as possible

Reflex arc in detail

Touching a hot object:

Skin receptor stimulated

electrical impulse from receptor passes along sensory neurone to CNS (here- the spinal cord)

impulse from sensory neurone arrives at synapse with a relay neurone, chemical is released.

chemical diffuses across synapse to relay neurone where it sets of a new impulse along the relay neurone

same thing happens when the impulse from the relay neurone meets the synapse with a motor neurone

impulse travels down from motor neurone to effector

effector organ is stimulated to respond. (here - muscle contracts, hand moves away)

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B10.4

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B10.5

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B10.6

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Summary Questions

B10.1