chapter 20 - coordination in mammals (part 2)

7/30/2019 Chapter 20 - Coordination in Mammals (Part 2)

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CHAPTER 20

COORDINATION

20.1 Nervous System


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Central NervousSystem (CNS)

Central NervousSystem (CNS)

Brain

Brain Spinal Cord

Spinal Cord

Peripheral NervousSystem (PNS)

Peripheral NervousSystem (PNS)

SensoryNeurons

SensoryNeurons

Motor Neurons

Motor Neurons

Somatic NervousSystem

Somatic NervousSystem

Autonomic NervousSystem

Autonomic NervousSystem

Sympathetic

Division

Sympathetic

Division

Parasympathetic

Division

Parasympathetic

Division

The Nervous System

The Nervous System

THE

ORGANIZATION OF

THE NERVOUSSYSTEM

PREVIOUS LECTURE


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PREVIOUS LECTURE

Objective:(b) Explain the general role of the sympathetic and parasympathetic nervous system.


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OBJECTIVES

(a)Describe the organization of the nervous

system.

(b)Explain the general role of the sympathetic

and parasympathetic nervous system.

(a)Explain the generation of action potential,transmission and characteristic of nerve

impulse along an axon.


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Does the stimulus travel one- way or

down the neuron in two directions?

Objective:

(c) Explain the generation of action potential, transmission and characteristic of nerveimpulse along an axon.


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Objective:


How is an action potential related to

the transmission of nerve impulse

along an axon?


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A stimulus alters the permeability of a portion of

the plasma membrane

Ions pass through the plasma membrane

Changing the membranes voltage

Causes a nerve signal to be generated

Action Potential

Objective:

(c) Explain the generation of action potential, transmission and characteristic of nerve



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Na+/K+ pumps and passive ion channels stop

operating

Only the voltage-gated ion channels are

operating

Objective:




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Action potential involves:

Depolarization

Repolarization

Hyperpolarization

Objective:




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An action potential is generated when the

voltage reaches a certain critical point

Threshold level

> -55 mV

Objective:



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A stimulus opens some

gated Na+ channels

Na+ ions rush slowly into the

axon down their

electrochemical gradient

Membrane potential

becomes slightly positive

Voltage-gated K+ channels

remain close

Depolarization

Resting

PotentialObjective:



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When threshold level is

reached, action

potential is triggered

Objective:



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Positive feedbackObjective:


Na+ gated channels are

sensitive to voltage

changes

Triggers more Na+ gatedchannels to open

Becomes more positive

(+40mV)


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Reversal in polarity to

+40mV cause the Na+

gated channel to close Membrane becomes

impermeable to Na+

Repolarization

Objective:



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K+ gatedchannels open

K+ diffuse out of the cell

Down their

electrochemicalgradient

Restoring negative

charge inside of the cell

Objective:



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K+ gated channels begins

to close slowly

An excess of K+ ions leavethe axon

Inside of the membrane

becomes more negative

Below -70 mV

Hyperpolarization

Objective:



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Within few miliseconds,

K+ gated channels close

Resting potential of

-70mV is reestablishedby:

Na+/K+ pumps

Passive ion channels

Objective:

http://c/Documents%20and%20Settings/kmpk/Desktop/coordination/D:/10.Coordination/Animation/nerve%20impulse.swf


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Figure 28.4

Resting state: voltage gated Na+

and K+ channels closed; resting

potential is maintained.

1

2

3

4

A stimulus opens some Na+

channels; if threshold is reached,

action potential is triggered.

Additional Na+ channels open,

K+ channels are closed; interior of

cell becomes more positive.

5 The K+ channels close

relatively slowly, causing

a brief undershoot.

Na+ channels close and

inactivate. K+ channels

open, and K+ rushes

out; interior of cell more

negative than outside.

Neuron

interior

Actionpotential

Thresholdpotential

Resting potential

1

2

3

4

5

Na+

Na+

Na+

Na+

1 Return to resting state.

1

Neuron

interior

K+

K+

Objective:

http://c/Documents%20and%20Settings/kmpk/Desktop/coordination/D:/10.Coordination/Animation/nerve%20impulse.swf


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Characteristics of Nerve Impulse

Size of a nerve impulse is not determined by the sizeof the stimulation received

Action potential is triggered only if the depolarizationof the membrane is above the threshold level

All-or-none event

Objective:



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Below the threshold level,

Stimulation is not sufficient to depolarize the membrane

Action potential is not triggered

If an action potential is achieved,

A stronger intensity of a stimulus wont increase the size

of it


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Below threshold level

- No action potential triggered

Above threshold level

- Action potential triggered


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Can be divided into 2:

Absolute refractory period

During the milisecond or so in which it is depolarized,

Axon cannot transmit another action potential nomatter how great the stimulus is

The brief recovery phase after the

response of a neuron during which it cannot

respond to another stimulus

The Refractory Period.

Objective:



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The period when the majority of sodium channels

remain in the inactive state (closed)

Depolarization and Repolarization

Objective:



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Relative refractory period

The axon can transmit impulses but with higher

threshold level

During this period the axon membrane goes through

hyperpolarization

The membranes permeability to K+

ions increasesdramatically

Objective:



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These ions diffuse out very highly

The charge within the neuron becomes too negative

Membrane is at a lower threshold

Require a greater stimulus to cause action potentials to

fire.

Objective:



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Analogy

Imagine.In the toilet.

When you pull the handle,water floods the bowl.

Takes a coupleof seconds and

you cannot stop

it in the middle.

Objective:

(c) Explain the generation of action

potential, transmission and

characteristic of nerve impulse alongan axon.


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Once the bowl empties, the flush is complete.

The upper tank is empty.

Objective:

(c) Explain the generation of action potential,

transmission and characteristic of nerve impulsealong an axon.


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If you try pulling the handle at this point, nothing

happens (absolute refractory).

Wait for the upper tank to begin refilling. You can now flush again, but the intensity of the flushes

increases as the upper tank refills (relative refractory)

Objective:



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Depends on:

The presence of myelin sheath

The diameter of axon

Speed of Conduction

Presence of myelin sheath

Diameter of axon

Objective:



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Act as an electrical insulator

Myelinated neurones conduct action potential faster

than non-myelinated neurones

Presence of myelin sheath

Objective:

http://c/Documents%20and%20Settings/kmpk/Desktop/coordination/D:/10.Coordination/Animation/actionp.swf


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Depolarization only occurs at the nodes of Ranvier

No myelin sheath is present Ions gated channel present

The action potential will jump from one node of

Ranvier to another

Saltatory ConductionObjective:



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The larger the diameter, the faster the speed of

action potential transmission

Diameter of axon

Objective:


T f N I l


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Transmission of Nerve Impulse

Along The Axon

Action potential is produced locally in the axon

Depolarization occurs at a specific area

Once an action potential is generated,

Will be propagated along the axons nerve impulse

Objective:



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During depolarization,

The affected area of the membrane is more positive

The adjacent area is still at resting potential

Difference in potentials between active and resting

membrane regions

Causes Na+ ions to flow between them

Local current

Objective:



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The flow of Na+ ions into the adjacent region

Induces the opening of Na+ gated channels in the

adjacent area

Permitting Na+ ions to enter the adjacent regionGenerating new action potential

The process is repeated until the end of the axon

Objective:



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- Influx of Na+ ions exceeds threshold level

- Initiates an action potential

- Depolarisation of the membrane cause

a local current

- Local current stimulates the adjacentregion causing depolarization

- Initiating a 2nd action potential

- At the site of the 1st action potential,

the membrane is repolarizing

-The local current at one region therefore

induces a new action potential in the

next region

- Keeps moving in a forward direction


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LECTURE REVIEW.

Action potential

involves:

Depolarization

Repolarization

Hyperpolarization
http://c/Documents%20and%20Settings/kmpk/Desktop/coordination/D:/10.Coordination/Animation/channel2.swf


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LECTUREREV

IEW

.


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o Does the stimulus travel one- way or down the

neuron in two directions?

o Which part receives the stimuli? (The synapse,

dendrites, cell body, or axon)

o Which is covered by a myelin sheath ?

o What is the purpose of the myelin sheath?

LECTURE REVIEW.


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LECTURE REVIEW.


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NEXT LECTURE
http://c/Documents%20and%20Settings/kmpk/Desktop/coordination/D:/10.Coordination/Animation/synapse.swf