Human Responses

Nervous system Endocrine System (hormones)

Organisms must be aware of what is happening around them,as this affects their survival chances.

The Nervous System

A nervous system allows an organism to detect and respond to stimuli in its internal or external environment.

e.g. a flash of light, a noise, increase in blood concentration.

A stimulus is any change in your internal or external environment

Co-ordination of an organism’s activities is carried out by the nervous system and the endocrine system.

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The nervous system relies on electrical signals, carried byspecialised cells [neurons], and is involved in fast responses.

The brain keeps a check on internal organs and activities, such as the level of carbon dioxide or water in the blood.

The central nervous system (CNS) is your brain and spinal cord.

The peripheral nervous system (PNS) is the nerves branching outfrom the CNS to all parts of the body. 3

NS ----- Co-ordination & Response

An impulse is an electrical message that is carried along aneuron.

A neuron is a specialised cell that carries electrical messages(impulses) around the body.

A stimulus is any change in your .....environment….

A receptor is a nerve cell that detects the stimulus

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The brain is composed of over 100 billion neurons, eachreceiving messages simultaneously from thousands of otherneurons.

The brain is protected by the skull bones, meninges (three membranes) and cerebrospinal fluid.

The Brain

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The cerebrum is our conscious brain, with different parts havingdifferent jobs to do – memory, emotion, learning….

The pituitary ‘[master] gland secretes hormones that stimulateother glands to release their hormones.

The hypothalmus controls homeostasis – osmoregulation

cerebrumhypothalamus

pituitary

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The cerebellum = co-ordination, movement, balance

The medulla oblongata co-ordinates involuntary, automatic processes — such as breathing, heartbeat.

cerebellumMedulla oblongata

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Conscious actionsA conscious action is one where the brain makes a considered response. Here’s what happens:

Stimulus Receptor Sensory Neuron Coordinator

Motor Neuron Effector Response

1) Receptors in your skin detect a stimulus

3) Here another sensory neuron carries the signal to the brain

4) The brain decides to move away the hand

5) This impulse is sent by MOTOR NEURONS to the hand muscles (the effectors) via the spinal chord…

2) The impulse is carried by SENSORY NEURONS to the spinal chord

6) Which then moves the hand away

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There are three types of Neuron :

Motor neuron –carries impulses from the CNS to muscles and glands.

Interneuron –connects sensory and motor neurons and so carries messages within the CNS.

Sensory neuron –carries messages from the sense organ to the central nervous system (CNS).

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Cell body

position

Cell body location within CNS or not

Direction of impulse

Where are the synaptic knobs?

Where are the synaptic knobs?

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Differences between Motor and Sensory Neuron

1.Direction of impulse – to or away from CNS2.Position of cell body – at start or along length3.Location of cell body - within CNS or outside CNS in ganglion

The cell body contains the nucleus and other organelles andproduces neurotransmitter chemicals.

The axon is a very long fibre that conducts impulses away from the cell body.

Neuron structure

A dendrite is a short fibre that receives impulse (information) and carries it towards the cell body.

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Many Schwann cells wrap their fatty cell membranes around an axon, forming a myelin sheath.

The myelin sheath insulates the neuron from electrical impulses flowing in other neurons.

Synaptic Knobs (containing neurotransmitter vesicles) – produce, store and release neurotransmitter chemicals e.g acetylcholine 16

LEARNING CHECK• Name the 5 main parts of the brain and one

function of each.

• How is the brain protected?

• What is meant by “conscious action”?

• What does the term “involuntary” mean?

• Distinguish between the cerebrum and the cerebellum.

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