Human Responses 2

Nervous system Compared to Endocrine System (hormones)

Spinal Cord

Reflex action

SYNPASE

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Synapse—region where two neurons come into close contact.

Synaptic cleft—the gap between two neurons, bridged by chemicals (neurotransmitters).

Neurotransmitter—chemical released across a synaptic cleft tocarry a signal from one neuron to another e.g. acetylcholine

SYNAPSE

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Sequence of events

1. Impulse moves along neuron as ions move in/out of neuron

2. impulse arrives at synpatic knob

3. Neurotransmitter vesicles move to edge of syn.knob

4. Neurotransmitter chemical released

SYNAPSE

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4. Neurotransmitter chemical crosses synaptic cleft by diffusion

5. Neurotransmitter chemical lands on receptors on next neuron

6. Impulse sent along next neuron

7. The neurotransmitter chemical is then inactivated by enzymes &reabsorbed by presynaptic neuron – makes new neurotranmitter chemical to clear receptor sites for next impulse

SYNAPSE

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LEARNING CHECK• Distinguish between synapse and synaptic

cleft.

• What are neurotransmitter chemicals?

• What are neurotransmitter vesicles?

• What would happen if there were no gaps between neurons?

• What is the refractory period and why does it occur?

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Spinal chord structure

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31 pairs of Spinal nerves

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Bone

Different view

The spinal cord is well protected by the vertebrae, meninges (three membranes) and cerebrospinal fluid.

Meninges not shown - they are wrapped around here

It transmits impulses to and from the brain and controls many reflex actions.

10This diagram not needed

A cross-section through the spinal cord shows a small central canal, filled with cerebrospinal fluid, surrounded by an area of grey matter, shaped somewhat like the letter H.

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Learn this diagramwell

Outside the grey matter, the spinal cord consists of white matter (containing mostly axons) – white due to myelin -fatty.

Grey matter contains cell bodies and dendrites(regions of a neuron that have no white myelin covering).

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In humans, 31 pairs of spinal nerves branch off from the spinal cord.

The dorsal root ganglion is a swelling that consists of the cell bodies of the sensory neurons.

Each spinal nerve has a dorsal root and a ventral root.

The dorsal root consists of nerve fibres carrying information into the spinal cord from the senses.

13hint – Dorsal / sensory/swelling

The ventral root consists of nerve fibres carrying information out from the spinal cord, to the muscles and glands.

The cell bodies of the motor neurons are positioned within the grey matter of the cord.

The spinal cord transmits impulses to and from the brain and controls many reflex actions.

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hint - Move out

Reflex action

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Go to video clip OF REFLEX ACTION.

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A reflex action is a quick, automatic response to a particular stimulus.

Interneuron

REFLEX ACTION --- The Reflex Arc

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Suppose you touch a hot flame…..

Pain Receptors detect the heat and send an impulse along the sensory neuron Which enters the dorsal root to the GREY matter of spinal cord

Interneuron

REFLEX ACTION --- The Reflex Arc

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In the spinal cord, the sensory neuron synapses with the interneuron and this synapses with the motor neuron, An impulse is sent along the motor neuron, out the ventral root into muscles that respond by contracting and pulling your hand from the flame. Only now does the brain become aware of what has happened

Interneuron

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The response is called a reflex action, as it does not involve conscious control, and is FAST predictable and automatic.

Many of the activities of the body, such as breathing and keeping our balance, are regulated by reflex actions.

This response saves the body from injury.

Interneuron

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SUMMARY OF PATHWAY OF REFLEX ACTION.

Pain receptor (skin) sensory neuron IN Through dorsal root and dorsal root ganglion TO Grey matter of spinal cord synpases with interneuron Synpases with motor neuron Impulse OUT via ventral root Muscle to carry out response (move hand or foot etc)Brain becomes aware of what has happened

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Go to video clip OF REFLEX ACTION.

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Nervous System Disorder

It is caused by the brain reducing the normal amount of dopamine that it makes.

Parkinson’s disease is a nervous system disorder, normally seen in older people, in which muscles become rigid and movement is slow and difficult, with persistent tremors [shaking].

There is at present no means of preventing it, but giving L-dopa (which the body changes into dopamine) can relieve the symptoms in many patients.

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LEARNING CHECK• How is the spinal cord protected?

• Distinguish between grey and white matter.

• Distinguish between dorsal and ventral root

• What is meant by reflex action?

• Give some examples of reflex action>

• What is an interneuron?

• Distinguish between cell bodies and ganglions.

• Give cause treatment symptoms of parkinson’s disease 24

Comparison of the endocrine and nervous systems - 1

Target organReceived by

BloodCarried by

GlandCells involved

Cells throughout the body

Message sent to

Chemical (Hormone)

Message

Endocrine

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Comparison of the endocrine and nervous systems - 1

Endocrine Nervous

Cells involved Gland Sense receptor

Message Chemical (Hormone)

Electrical(Impulse)

Carried by Blood Nerve cell

Message sent to Cells throughout the body

A specific cell or tissue

Received by Target organ Effector (muscle or gland) 26

Endocrine Nervous

Speed of transmission

Usually slow Rapid

Effects Can be widespread Localised usually

Duration long-lasting (hours)

Usually brief (seconds)

Comparison of the endocrine and nervous systems -- 2

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LEARNING CHECK• Co-ordination of an organism’s activities is

carried out by what 2 body systems?

• Distinguish between the CNS and PNS.

• What is a neuron?

• What is an impulse?

• List the main differences between the endocrine and nervous systems.

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