Ch48NervousSystem

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Ch 48: Nervous System
2016
Ch 48: Nervous System
From Topic 6.5
Nature of science: Cooperation and collaboration between groups of scientists—biologists are contributing to research into memory and
learning (4.3).
Essential idea: Neurons transmit the message, synapses modulate the message.
Understandings:
• Neurons transmit electrical impulses.
• The myelination of nerve fibres allows for saltatory conduction.
• Nerve impulses are action potentials propagated along the axons of neurons.
• Neurons pump sodium and potassium ions across their membranes to generate a resting potential.
• An action potential consists of depolarization and repolarization of the neuron.
• Propagation of nerve impulses is the result of local currents that cause each successive part of the axon to reach the threshold potential.
• A nerve impulse is only initiated if the threshold potential is reached.
• Synapses are junctions between neurons and between neurons and receptor or effector cells.
• When presynaptic neurons are depolarized they release a neurotransmitter into the synapse.
Guidance:
• The details of structure of different types of neuron are not needed.
• Only chemical synapses are required, not electrical, and they can simply be referred to as synapses.
Applications and skills:
• Application: Secretion and reabsorption of acetylcholine by neurons at synapses.
• Application: Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine
receptors.
• Skill: Analysis of oscilloscope traces showing resting potentials and action potentials.
• Skill: Analysis of oscilloscope traces showing resting potentials and action potentials.
Utilization:
• An understanding of the workings of neurotransmitters and synapses has led to the development of numerous pharmaceuticals for the
treatment of mental disorders.
Aim 8: The social effects of the abuse of psychoactive drugs could be considered, as could the use of the neurotoxin Botox for cosmetic
treatments.
Parts of the Nervous System
• Central nervous system (CNS)
– Brain and spinal cord
• Both contain fluid-filled spaces
which contain cerebrospinal fluid
(CSF).
– The central canal of the spinal
cord is continuous with the
ventricles of the brain.
– White matter is composed of bundles
of myelinated axons
– Gray matter consists of unmyelinated
axons, nuclei, and dendrites.
• Peripheral nervous system
(PNS)
– Everything outside the CNS.
Nervous System: https://www.youtube.com/watch?v=x4PPZCLnVkA
Peripheral Nervous System (PNS)
Neuron Anatomy
Neuron Anatomy
Membrane Potential
• Membrane Potential: a term used
to illustrate there is an electrical
potential difference between
the inside of the cell and the
surrounding extracellular fluid.
• -70 mV is the resting membrane
potential of a neuron, which means
that the inside of the cell is negative
compared to the outside.
Membrane Potential:
http://www.sumanasinc.com/webcontent/animations/content/electricalsignaling.html
Normal Levels
• Sodium-Potassium Pump: is used in establishing the membrane potential in
neurons
(1) it makes the [Na] high in the extracellular space and low in the intracellular space
(2) it makes the [K+] high in the intracellular space and low in the extracellular space
(3) it creates a negative voltage in the intracellular space compared to the extracellular
space.
Hyperpolarization
• Gated K+ channels open
 K+ diffuses out of the
cell  the membrane
potential becomes more
negative
Depolarization
• Gated Na+ channels open 
Na+ diffuses into the cell 
the membrane potential
becomes less negative
Action Potential
• Action Potential: All or Nothing
Depolarization
• If graded potentials sum to
 -55mV a threshold potential is
achieved.
• This triggers an action
potential.
• Axons only
Action Potential:
http://www.sumanasinc.com/webcontent/animations/content/action_potential.html
Action Potential w/ Graph:
http://bcs.whfreeman.com/thelifewire/content/chp44/4402002.html
Action Potential Diagram
• Step 1: Resting State.
Fig. 48.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Step 2: Threshold.
Fig. 48.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Step 3: Depolarization phase of the action
potential.
Fig. 48.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Step 4: Repolarizing phase of the action
potential.
Fig. 48.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Moving Potential
Saltatory Conduction
• In myelinated neurons, only unmyelinated regions of the
axon depolarize. Signal jumps from one node to the next,
making the impulse travel 100x faster than on a
unmyelinated neurons.
Khan Academy: https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/v/saltatory-conduction-neurons
Saltatory Conduction: http://wps.aw.com/bc_goodenough_boh_3/104/26721/6840613.cw/content/index.html
Fig. 48.11
Synapses
• Electrical Synapses.
– Action potentials travels directly from the
presynaptic to the postsynaptic cells via gap
junctions.
Chemical Synapses
• More common than electrical synapses.
• Postsynaptic chemically-gated channels exist
for ions such as Na+, K+, and Cl-.
• Depending on which gates open the postsynaptic
neuron can depolarize or hyperpolarize.
Fig. 48.12
Routes of Nerve Transmission

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