B Nervous System

8/13/2019 B Nervous System

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Chapter 48:Nervous System


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Neurons and Supporting cells Organization of Nervous system

Diffuse nerve net-hydra

Brain in front

Central nervous system (CNS)- planarian

Ganglia (cluster of neurons)- in annelidsPeripheral nervous system (PNS)-connects CNS with

rest of body


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Information Processing

1. Sensory input- sensory neurons transmit externalstimuli or internal conditions to CNS

2. Integration- interneurons integrate (analyze andinterpret). Greatest complexity in neural circuits cells.

3. Motor output- leaves CNS via motor neurons thatcommunicate with effector cells (muscle or endocrinecells)


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Question 1

a. Arrange the following neurons in the

correct sequence for information flow

during the kneejerk reflex: interneuron,

sensory neuron, motor neuron.

b. Which of the neuron types is located

entirely within the CNS?


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Neuron Structure

dendrites

sensory neuron cell body

axon

cell body

interneuron

cellbody

motor neuron

dendrites

associative


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Neuron Structure

Dendrites- receive signals

Synapses- site of communication from

presynaptic cell to postsynaptic cell by

neurotransmitters

Axon- transmits the signal


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Question 2

Would severing a neurons axon stop the

neuron from receiving or from transmitting

information? Explain.


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Supporting cells

Astrocytes- structural support

Radial glia- form tracks

Oligodendrocytes (in CNS) and Schwann

cells (in PNS) form myelin sheaths around

axon

Similar to plastic protecting electric covers


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Question 3

What would be the most obvious structural

abnormality in the nervous system of a

mouse lacking oligodendrocytes?


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Action potentials are the signals that

conducted by axons

If gated channels, membrane potential willchange when open or closed

Hyperpolarization- increase in membrane

potential (inside is more neg)Ex. Opening of K+ channels

Depolarization- decrease in membranepotential (inside is less neg)Ex. Opening of Na+ channels


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Action potentials contd

Threshold- depolarization up to a certain

membrane voltage

Action potential-once reached amount of

stimulus has been reached; signal that

carry information along axons; very brief

Animation Link
http://outreach.mcb.harvard.edu/animations/actionpotential.swfhttp://outreach.mcb.harvard.edu/animations/actionpotential.swf


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Question 4

Draw the sketch below and label the

following: outside cell, inside cell. Show

where the concentrations of Na+ and K+

are highest.


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Conduction of Action Potentials

For an action potential to function long distances, it

regenerates itself as it moves along the axon, increasing

action potential as it moves down axons

What effects speed of transmission?

Diameter of axon

Myelin sheath


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Question 5

Arrange the following from lowest to

highest conduction speed: (a) myelinated,

smalldiameter axon; (b) myelinated,

largediameter axon; (c) unmyelinated,smalldiameter axon.


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Neurons communicate with other cells at

synapses

Two types of communication:1. Electrical synapses- gap junctions that allow electric

current to flow from one cell to another

2. Chemical synapses-most; release neurotransmitter

in a synaptic vesicle, it depolarizes the terminalmembrane and vesicles fuse with terminal

membrane, releasing neurotransmitters by

exocytosis. It can

then have a director indirect effect on

postsynaptic cell.

Online Link Mouse Party Link
http://learn.genetics.utah.edu/content/addiction/reward/neurontalk.htmlhttp://learn.genetics.utah.edu/content/addiction/drugs/mouse.htmlhttp://learn.genetics.utah.edu/content/addiction/drugs/mouse.htmlhttp://learn.genetics.utah.edu/content/addiction/reward/neurontalk.html


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Direct synaptic transmission

Neurotransmitter binds to channel (the

receptor), it opens and allows ions to

diffuse across the membrane

Result- postsynaptic potential (change in

membrane potential)

Excitatory postsynaptic potentials (EPSPs)

membrane potential brought down to thresholdInhibitiory postsynaptic potentials (IPSPs)

increase past threshold


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Indirect transmission

Neurotransmitter binds to a receptor that is

not part of the channel, activates a signal

transduction pathway

Slower onset but longer lasting than direct

transmission

Indirect Link
http://www.blackwellpublishing.com/matthews/neurotrans.htmlhttp://www.blackwellpublishing.com/matthews/neurotrans.html


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Types of neurotransmitters

Acetylcholine (Ach)- released at

neuromuscular junctions, exciting motor

cells; other times, can be an inhibitor

Biogenic amines- neurotransmitters from

aa

One group, catecholamines from aa tyrosine

include epinephrine and nonepinephrine(hormones); dopamine (brain-affect sleep,

mood, attention and learning)


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Types of neurotransmitters

Amino acids and peptides

Aa-most in brain

Peptides- short chains called neuropeptides

Gases- some neurons release gases

especially NO (nitric oxide) and CO

(carbon monoxide)

Aa-most in brain

Peptides- short chains called neuropeptides


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Question 6

A single postsynaptic neuron can be

affected by neurotransmitter molecules

released by many other neurons, some

releasing excitatory and some releasinginhibitory neurotransmitters. What will

determine whether an action potential is

generated in the postsynaptic neuron?


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Question 7

There are many different types of

neurotransmitters. Each neuron secretes

only onetype of neurotransmitter. Some

neurotransmitters hyperpolarize thepostsynaptic membrane. Are these

excitatory or inhibitory neurotransmitters?

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