Lec14 - The Nervous System.doc

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22 Apr 2012
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The Nervous System
Slide One – topics
Functions of the nervous system
oEarly experiments on nerves and axons were done on the giant axons of
squids / worms which were relatively easy to dissect and examine
Organization of the nervous system
Cells of the nervous system
Resting membrane potential
Action potential generation
Action potential propagation
Refractory periods
Synaptic transmission
Slide Two – functions of the nervous system
Beginning stimulus final effect
oReception
Receptors
Sensors
oTransmission
Nerves
Neurons
oIntegration
Ganglia
Brain
oResponse
Motor nerves
Effectors
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Cells sense things in the external or internal environment
o–e.g. light / movement / blood pressure / temperature / pH levels etc
Once sensed, causes a transmission to be sent into the central nervous system
via an afferent (sensory) pathway
Information arrives in central nervous system integrated by interneurons
(intermediates between the in / out signals)
Transmission of signal out of the central nervous system through an efferent
pathway to various organs / glands / muscles so that they elicit an appropriate
response
The nervous system that sends things in and out of the brain is called the
peripheral nervous system (PNS)
The spinal cord and the brain encompasses the central nervous system
Slide Threereception: sensory systems
To cause an effect, there must first be a sensory stimuli
Diverse array of sensory system
oUsed to monitor internal and external environments
oSome are complex but many are simple
Range from single cells to complex sense organs
Examples of stimulus receptors
oSent through a signal transduction pathway opening of ion channels
change in membrane potential
Chemical stimulus
Odour molecules in environment
Oxygen / Carbon Dioxide levels in blood
Pressure stimulus
Mechanical receptor
Pressing on body from outside
Blood Pressure being sent
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Lungs inflated and deflated
Light stimulus
Senses of light
Slide Four – reception and transmission
Two general ways to transmit senses to the brain
oSensing cells themselves can generate a signal directly to the brain
Depolarization (generator potential)
-i.e. increase in membrane potential
oElectrical charge that exists across the cell
membrane
oCell is negative on the inside relative to the outside
Depolarization refers to negative charge moving to the
positive direction
Activates a trigger zone leading to large changes in membrane
potentials (called action potentials) which are sent to the brain
oRelease of a neurochemical to a second cell which then releases signal
to brain
Stimulus is sensed
Depolarization (receptor potential) leads to neurotransmitter
release onto a second cell, which then generates action potential
in the trigger zone of that cell
Slide Five – integration: central nervous system
Central Nervous System (CNS) is the major integrating system
Brain has three major subdivisions
oMost primitive – hindbrain
Cerebellum
Pons
Medulla Oblongata
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