The Nervous SystemThe Nervous System

OR…OR…

Why you are able to poke yourself Why you are able to poke yourself in the eye.in the eye.

Functions of the Nervous Functions of the Nervous SystemSystem

Receives sensory information from internal and external environment

Processes information and transmits it around the body.

Organises a coordinated response to information

Structure of the Nervous SystemStructure of the Nervous System

The Central Nervous SystemThe Central Nervous System

Brain – protected by the cranium.

Spinal cord – protected by the vertebra

The Peripheral Nervous SystemThe Peripheral Nervous System

Consists of all of the nervous system Consists of all of the nervous system apart from the brain and spinal cord.apart from the brain and spinal cord.

Divided into:Divided into:

1.1. Somatic Nervous SystemSomatic Nervous System

2.2. Autonomic Nervous SystemAutonomic Nervous System

Somatic Nervous SystemSomatic Nervous System

Voluntary movement.Voluntary movement.

Conveys sensory messages from the Conveys sensory messages from the sense organs to the CNS…..ANDsense organs to the CNS…..AND

Conveys motor messages from the CNS Conveys motor messages from the CNS to the muscles and glands.to the muscles and glands.

Autonomic Nervous SystemAutonomic Nervous System

Involuntary movement.Involuntary movement.

Regulates internal environment.Regulates internal environment.

Controls functioning of the heart, Controls functioning of the heart, intestines and other organs.intestines and other organs.

Divided into Divided into SympatheticSympathetic and and ParasympatheticParasympathetic Nervous System. Nervous System.

Nerve CellsNerve Cells

Basic units of the Basic units of the

nervous system.nervous system.

Also known asAlso known as

neurons.neurons.

4 basic parts to4 basic parts to

a neuron.a neuron.

NeuronsNeurons

1.1. Dendrites = Receive messages from Dendrites = Receive messages from other neurons.other neurons.

2.2. Soma/Cell body = Accepts impulse Soma/Cell body = Accepts impulse travelling from the dendrites.travelling from the dendrites.

3.3. Axon = Impulses travel from the soma Axon = Impulses travel from the soma and are carried along this thin fibre.and are carried along this thin fibre.

4.4. Axon terminals = Branches at the end of Axon terminals = Branches at the end of the axon that link with the dendrites of the axon that link with the dendrites of other neurons.other neurons.

NeuronsNeurons

Neurons do not touch each other.Neurons do not touch each other.

Instead a chemical, called a Instead a chemical, called a neurotransmitterneurotransmitter, is released from the , is released from the axon terminals into a gap called a axon terminals into a gap called a synapsesynapse..

The chemical is then picked up by the The chemical is then picked up by the dendrites of the next neuron.dendrites of the next neuron.

i.e. nerve impulses are i.e. nerve impulses are electrochemicalelectrochemical..

Myelin SheathMyelin Sheath

Fatty layer that protects axon, and conducts Fatty layer that protects axon, and conducts messages faster.messages faster.

Gaps in myelin is called nodes of Ranvier.Gaps in myelin is called nodes of Ranvier.

Match the terms with their definitionsMatch the terms with their definitionsTermTerm DefinitionDefinition

NeuronNeuron a. A fatty layer coating some axons.a. A fatty layer coating some axons.

AxonAxon b. The main cell body of a neuron.b. The main cell body of a neuron.

SomaSoma c. Fibre that carries information away from c. Fibre that carries information away from the cell body of a neuron.the cell body of a neuron.

DendriteDendrite d. A bundle of neuron fibres.d. A bundle of neuron fibres.

MyelinMyelin e. Branching fibre at the end of an axon.e. Branching fibre at the end of an axon.

NerveNerve f. Carries chemical message across the f. Carries chemical message across the synapse.synapse.

SynapseSynapse g. An individual nerve cell.g. An individual nerve cell.

Axon terminalAxon terminal h. Microscopic space between two neurons.h. Microscopic space between two neurons.

NTNT i. A neuron fibre that receives incoming i. A neuron fibre that receives incoming messagesmessages

True or False?True or False?

1.1. A neuron and a nerve are structurally the same A neuron and a nerve are structurally the same thing.thing.

2.2. An axon is about 0.1mm long.An axon is about 0.1mm long.3.3. The transmission of a message within a The transmission of a message within a

neuron is electrochemical.neuron is electrochemical.4.4. The release of NT’s occurs at the axon.The release of NT’s occurs at the axon.5.5. Axons are coated with myelin in order to Axons are coated with myelin in order to

protect them from damage.protect them from damage.6.6. A synapse is a gap between the axon terminal A synapse is a gap between the axon terminal

of one neuron and an adjacent neuron.of one neuron and an adjacent neuron.

Activity: Making a NeuronActivity: Making a Neuron

1.1. Use pipe cleaners to construct a model Use pipe cleaners to construct a model of a neuron.of a neuron.

2.2. Label the main parts of a neuron and Label the main parts of a neuron and state the function of each.state the function of each.

3.3. Indicate the direction of the nerve Indicate the direction of the nerve impulse.impulse.

Sensory (Afferent) NeuronSensory (Afferent) Neuron

Detect changes in the external or internal Detect changes in the external or internal environment and transmit that information environment and transmit that information to the CNS, via the PNS.to the CNS, via the PNS.

Motor (Effector) NeuronMotor (Effector) Neuron

Carry impulses away from the CNS to muscle Carry impulses away from the CNS to muscle cells or glands and cause a response.cells or glands and cause a response.

Interneuron (Relay Neuron)Interneuron (Relay Neuron)

Link sensoryLink sensory

and effectorand effector

neurons.neurons.

Normally foundNormally found

in CNSin CNS

(particularly PNS)(particularly PNS)

S-A-M-ESensory = Afferent + Motor = Efferent

Reflex ArcsReflex Arcs

Reflex ArcsReflex Arcs

Putting it all together…Putting it all together…

Create a flowchart to illustrate:Create a flowchart to illustrate:

1.1. How sensory information is transmitted How sensory information is transmitted from the PNS to the CNS.from the PNS to the CNS.

2.2. How motor information is transmitted How motor information is transmitted from the CNS to the PNS.from the CNS to the PNS.

The Nerve ImpulseThe Nerve Impulse

Ions are electrically charged chemical Ions are electrically charged chemical molecules, e.g. Kmolecules, e.g. K++, Na, Na++, Cl, Cl-- etc. etc.

In and around a neuron there will be In and around a neuron there will be positive and negative ions.positive and negative ions.

When a neuron is resting it has a negative When a neuron is resting it has a negative charge. charge.

This is known as its resting potential.This is known as its resting potential.

The neuron is said the be The neuron is said the be polarisedpolarised..

The Resting NeuronThe Resting Neuron

The Action PotentialThe Action Potential

Along the axon membrane there are Along the axon membrane there are numerous ion channels.numerous ion channels.

Normally these channels are blocked, but Normally these channels are blocked, but if a neuron is sufficiently stimulated the ion if a neuron is sufficiently stimulated the ion channels open and positive ions rush in.channels open and positive ions rush in.

The neuron becomes positively charged The neuron becomes positively charged and an and an action potentialaction potential is been is been generated.generated.

The Action PotentialThe Action Potential

An action potential is a very rapid change in An action potential is a very rapid change in polarity. polarity.

The neuron moves from the resting potential to The neuron moves from the resting potential to some positive value in a few milliseconds. some positive value in a few milliseconds.

The Action PotentialThe Action Potential

If a nerve cell is stimulated past the If a nerve cell is stimulated past the threshold (about -30mV in humans) ion threshold (about -30mV in humans) ion channels open and positive ions rush into channels open and positive ions rush into the axon.the axon.

This causes a region of the axon to have This causes a region of the axon to have a more positive charge.a more positive charge.

This is called This is called depolarisationdepolarisation. .

The Action PotentialThe Action Potential

Soon after the positively charged ions are Soon after the positively charged ions are pushed back outside.pushed back outside.

The neuron moves back to its resting The neuron moves back to its resting potential.potential.

This is known as This is known as repolarisationrepolarisation..

The ion channels are only located at the The ion channels are only located at the nodes of Ranvier.nodes of Ranvier.

The action potential jumps from node to The action potential jumps from node to node.node.

The Action PotentialThe Action Potential

Once an action potential has occurred Once an action potential has occurred there is a period when the neuron is there is a period when the neuron is unable to conduct another nerve impulse.unable to conduct another nerve impulse.

This is known as the This is known as the refractory period.refractory period.

This ensures that the nerve impulse This ensures that the nerve impulse moves in one direction along the axon.moves in one direction along the axon.

     

All-or-None LawAll-or-None Law

Action potentials occur maximally or not at Action potentials occur maximally or not at all. all.

I.e. There is no such thing as a partial or I.e. There is no such thing as a partial or weak action potential. weak action potential.

Either the threshold potential is reached Either the threshold potential is reached and an action potential occurs, or it isn't and an action potential occurs, or it isn't reached and no action potential occurs. reached and no action potential occurs.

Bridging the GapBridging the Gap

The axon ends with many small swellings The axon ends with many small swellings called axon terminals.called axon terminals.

The small gap or space between the axon The small gap or space between the axon of one neuron and the dendrites or cell of one neuron and the dendrites or cell body of the next neuron is called the body of the next neuron is called the synapse synapse or or synaptic gapsynaptic gap. . 

A nerve impulse cannot go backward A nerve impulse cannot go backward across a synapse.across a synapse.

Bridging the GapBridging the Gap

The axon terminals contain tiny vesicles The axon terminals contain tiny vesicles filled with chemicals known as filled with chemicals known as neurotransmitters.neurotransmitters.When an impulse reaches the axon When an impulse reaches the axon terminal, NT’s are released into the terminal, NT’s are released into the synaptic gap.synaptic gap.The NT moves through the synapse and The NT moves through the synapse and bind to receptor molecules on the post-bind to receptor molecules on the post-synaptic neuron.synaptic neuron.

Bridging the GapBridging the Gap

Bridging the GapBridging the Gap

NT’s attach only to specific receptors.NT’s attach only to specific receptors.

NT’s may excite or inhibit the next neuron.NT’s may excite or inhibit the next neuron.

If the neuron receives enough excitatory If the neuron receives enough excitatory messages an action potential is messages an action potential is generated.generated.

Any leftover NT’s are rapidly removed or Any leftover NT’s are rapidly removed or destroyed.destroyed.

SYNAPTIC CLEFT OR GAPSYNAPTIC CLEFT OR GAP