Nervous System

Nervous SystemNervous SystemNervous SystemNervous System Made up of nerve Made up of nerve

cells called cells called neurons neurons found in the:found in the:

BrainBrain

Spinal CordSpinal Cord

All of the nerve cells All of the nerve cells connected to all connected to all other parts of the other parts of the body body

Nervous SystemNervous SystemNervous SystemNervous System The nervous The nervous

system can be system can be divided into the:divided into the:– Central Nervous Central Nervous

SystemSystem – brain and – brain and spinal cordspinal cord

– Peripheral Nervous Peripheral Nervous SystemSystem – neurons – neurons outside the spinal outside the spinal cord/braincord/brain

PNSPNSPNSPNS

The PNS is made up of:The PNS is made up of:

– Sensory neurons (affector neurons) Sensory neurons (affector neurons) – detect – detect changes in the external and internal changes in the external and internal environment and sends information environment and sends information toto the the CNSCNS

– Motor neurons (effector neurons) Motor neurons (effector neurons) – send – send information information away fromaway from the CNS to muscles the CNS to muscles and other effector organsand other effector organs

PNSPNSPNSPNS The motor neurons of the The motor neurons of the

PNS can be further divided PNS can be further divided into 2 categories:into 2 categories:

Autonomic nervous Autonomic nervous system system – involuntary, – involuntary, transmits messages to transmits messages to internal organsinternal organs

cannot be consciously cannot be consciously controlled by thoughtscontrolled by thoughts

Somatic nervous Somatic nervous system system – voluntary, – voluntary, transmits messages to transmits messages to skeletal muscleskeletal muscle

can be consciously can be consciously controlledcontrolled

CNSCNSCNSCNS The CNS acts as the control centre The CNS acts as the control centre

of the entire nervous system:of the entire nervous system:

– It processes the information received It processes the information received by the sensory neurons in the PNS; by the sensory neurons in the PNS; and and

– sends messages back through motor sends messages back through motor neurons in the PNS to the effector neurons in the PNS to the effector organs, initiating a response.organs, initiating a response.

SummarySummarySummarySummaryNervous Nervous systemsystem

CNSCNS PNSPNS

SensorSensoryy

MotorMotor

AutonomiAutonomic c

SomaticSomatic

BrainBrainSpinal Spinal CordCord

VoluntaryVoluntary

InvoluntaryInvoluntary

Nerve cells, NeuronsNerve cells, NeuronsNerve cells, NeuronsNerve cells, Neurons These are the basic units of the These are the basic units of the

nervous systemnervous system There are 3 main types:There are 3 main types:

– SensorySensory (affector) (affector)– Motor (effector) (effector)– Interneurons Interneurons (connecting neurons)(connecting neurons)

When many neurons are When many neurons are connected together in a bundle, connected together in a bundle, they are called a nervethey are called a nerve

Typical motor neuronTypical motor neuronTypical motor neuronTypical motor neuron

Reflex arcReflex arcReflex arcReflex arc

NeuronsNeuronsNeuronsNeurons Neurons are able to pass Neurons are able to pass

messages onto other neurons and messages onto other neurons and cells by sending electrical cells by sending electrical impulses called impulses called action potentialsaction potentials

Electrical impulses are created by Electrical impulses are created by a rapid change in a rapid change in positive/negative charges across positive/negative charges across the membrane of the neuronthe membrane of the neuron

Electrical impulses are generated Electrical impulses are generated when a stimulus is detectedwhen a stimulus is detected

Action PotentialsAction PotentialsAction PotentialsAction Potentials There are 4 main phases in an There are 4 main phases in an

action potential:action potential:

1.1.Resting potentialResting potential – when neuron – when neuron is not active/stimulated - there is not active/stimulated - there is a difference in charge across is a difference in charge across membrane, called potential membrane, called potential More + outside membrane More + outside membrane

compared to insidecompared to inside

2.2. Depolarisation Depolarisation – when the neuron is – when the neuron is stimulated the potential reverses stimulated the potential reverses and this change in potential is and this change in potential is carried along the axon to the axon carried along the axon to the axon terminal, causing a signalling terminal, causing a signalling molecule called a molecule called a neurotransmitterneurotransmitter (within the secretory vesicles) to be (within the secretory vesicles) to be releasedreleased

• This neurotransmitter then diffuses This neurotransmitter then diffuses across a very short distance (called a across a very short distance (called a synapsesynapse) to the neighbouring ) to the neighbouring ((postsynapticpostsynaptic neuron, causing it to be neuron, causing it to be stimulatedstimulated

Action PotentialsAction PotentialsAction PotentialsAction Potentials

Action PotentialsAction PotentialsAction PotentialsAction Potentials3.3.RepolarisationRepolarisation – The potential – The potential

returns to resting statereturns to resting state More + outside membrane More + outside membrane

compared to insidecompared to inside

4.4.Refractory period Refractory period – For a brief – For a brief period after repolarisation, the period after repolarisation, the neuron cannot be stimulated neuron cannot be stimulated againagain

http://www.learner.org/channel/courses/http://www.learner.org/channel/courses/biology/archive/animations/hires/biology/archive/animations/hires/a_neuro1_h.htmla_neuro1_h.html

http://www.learner.org/channel/courses/biology/archive/animations/hires/a_neuro2_h.html

Resting potential

Depolarisation – stimulus reached threshold

Repolarisation

Na+ comes into neuron

K+ flows out of neuron

AnimationsAnimations

http://http://outreach.mcb.harvard.edu/outreach.mcb.harvard.edu/animations/actionpotential.swfanimations/actionpotential.swf

– Toxins and venoms produced by Toxins and venoms produced by animals such as snakes and animals such as snakes and spiders can cause paralysisspiders can cause paralysis

– This is because they can:This is because they can: interfere with the release of interfere with the release of

neurotransmitters neurotransmitters Prevent transmission of electrical Prevent transmission of electrical

impulses from travelling along the impulses from travelling along the axonaxon

Damage the presynaptic or post-Damage the presynaptic or post-synaptic membranessynaptic membranes

Toxins and venomToxins and venomToxins and venomToxins and venom