21.1 (a), (b)

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:

21 0 COORDINATION

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21.1 Nervous System 2

21.2 Mechanism of muscle contraction 2

21.3 Hormones in mammals 1

21.4 Hormones in plants 1

Chapter 21 : Coordination (6 hrs)

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21.1 Nervous System 2

21.2 Mechanism of muscle contraction 2

21.3 Hormones in mammals 1

21.4 Hormones in plants 1


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a) State the organization of nervous

systemb) Explain the generation of action

potential, transmission &

characteristics of nerve impulse along

an axon

21.1 : Nervous System


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c) Describe the structure of synapse and

explain the mechanism of impulsetransmission across synapses

d) Compare the transmission of impulse at

the synapse and along the axon

e) Explain the mechanism of action of

drugs on the nervous system



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At the end of the lesson, you should beable to :

o State the organization of the nervoussystem

o Explain the generation of action



an axon



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OVERVIEW OF COORDIN TION

Involves :

Nervous System

Endocrine system

Nervous system involves neurons which isspecialized to transmit impulse very fast

(few milliseconds) directly to specific site

Endocrine system involves gland which is

relatively slower may takes minutes, hours

to produce hormones & carried it along

blood vessels before it reaches target

organs

Learning outcomes

21.1: State the organization of the nervous system

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Nervous System

Learning outcomes


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Regulatory System

Involve 3 components :

Sensory input (PNS)1

2

3

Integration (CNS)

Motor output (PNS)

Nervous System

Learning outcomes


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NERVOUS SYSTEM

Brain Spinal cordSensory

(afferent) division

Sympathetic

division

Parasympathetic

division

Autonomic (involuntary)nervous system

Somatic(voluntary)

Central Nervous System (CNS) Peripheral Nervous System (PNS)

Motor(efferent) division

Organization of Nervous System

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MOTOR NEURONS

SOMATICControls the voluntaryresponsesInvolves ~ skeletalmuscles

AUTONOMIC

Controls the involuntary

response (internal organs &

glands)

Control smooth & cardiacmuscles

Actions are controlled in the

medulla & hypothalamus

Consists of sympathetic &parasympathetic division.

Both act on the same target

but very often antagonistic

Learning outcomes


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Somatic Vs Autonomic Nervous System

Learning outcomes


L i

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Learning outcomes


L i t

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UTONOMIC NERVOUS SYSTEM

Autonomic nervous system has 2

division

Sympathetic & parasympatheticnervous system

Both division differ in terms of neuron

structure & action They act in opposite (antagonist) way

Learning outcomes


L i t

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Sympathetic NervousSystem

Learning outcomes


L i t

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ParasympatheticNervous System

Learning outcomes


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1. Origin ofneuron

2. Position ofganglion

3. Length offibres

Differences between Sympathetic & Parasympathetic

Features Sympathetic

Originate from thoracic& lumbar regions of CNS

Short preganglionicLong postganglionic

Parasympathetic

Originate from cranial &sacral regions of CNS

Closer to spinal cord Closer to effector

Long preganglionicShort postganglionic

5. Degree ofbranching

Postganglionic fibers arehighly branched

Postganglionic fibersbranches are minimal

4. Distribution

of fibers

Preganglionic fibers are

widely spread

Preganglionic fibers are

restricted

6. Area ofinfluence

Effects are widespread& longer

Effects are localized &short

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7. Transmittersubstance

8. Generaleffect

Features Sympathetic

Norepinephrine isreleased at effector

Parasympathetic

Acetylcholine is releasedat effector

Conserve & store energyDominant during restPrepare body for stress,emergencies & danger

Differences between Sympathetic & Parasympathetic

Learning outcomes

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Learning outcomes


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a) State the organization of nervous

systemb) Explain the generation of action



an axon



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Learning outcomes 21.1 b) Explain the generation of action potential, transmission and

characteristics of nerve impulse along an axon

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THE TRANSMISSION OF NERVE IMPULSE

Its an electrical phenomenon that occurs

through the dendrite, dendron & the axon.



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THE TRANSMISSION OF IMPULSE

Involves 2 important phases :1) the resting potential

2) the action potential



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1) RESTING POTENTIAL

In unstimulated neuron, Na-K pumpisactive

3 Na+is pumped to the outside of the

axon, 2 K+is pumped into the axon



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[Na+] is higher on the

outside

[K+] is higher in the inside

Axon membrane is more

permeable to K+than Na+



Voltage-gated channel ions

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K+diffuses out from the axon through ungated

K+channel/passive transport

Less Na+ion diffuses into the axon

These diffusion cannot reach equilibrium

because the Na-K gradient is maintainedby Na-

K pump



Voltage-

gated

ion channel

Ungated

channel

ions

Na-Kpump

L i t 21 1 b) E l i th ti f ti t ti l t i i d

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In axoplasm, [anions] because anions cannot

diffuse out due to their large size

Causing the charges within the axon becomes

relatively ve

Voltage-gated channels of Na & K by this time

were closed



Learning o tcomes 21 1 b) E plain the generation of action potential transmission and

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So, membrane is in resting potential

Since the membrane is negatively

charged during resting potential,

membrane is in polarization stage



L i t 21 1 b) E l i th ti f ti t ti l t i i d

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2) ACTION POTENTIAL A stimulus opens some Na channels &

causes Na-K pump to stop functioning

Na+ inflow through those channelsdepolarizes the membrane

Causing the charges within the axon

becomes slightly relatively positive

The change in the electrical potential is

called depolarization



Learning o tcomes 21 1 b) E plain the generation of action potential transmission and

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2) ACTION POTENTIAL If the depolarization does not reach a

certain critical value, the stimulated

neuron will not generate impulse / action

potential (ignored) The critical valueis called threshold level



Learning outcomes 21 1 b) Explain the generation of action potential transmission and

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If graded potentials sum to55mV, athreshold potential is achieved. This

triggers an action potential (impulse).




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Action potential : A rapid voltage change which

has a self-propagating effect that produces an

impulse//an electrical signal resulting from

depolarization of the plasma membrane in a

neuron or muscle cell.




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An action potential is an all-or-none event

because it occurs or it does not

A stimulus that is strong enough to depolarize

the membrane to the threshold level results in

the transmission of an impulse along the axon




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GENERATION OF ACTION POTENTIAL

If depolarisation reaches threshold level, all

voltage-gated Nachannels open

Causes inflow/influx of Na+into the axon

Sudden increase of Na

+

causes the chargewithin the axon to become positively charged

This is called as rising phase of the action

potential




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GENERATION OF ACTION POTENTIAL

When depolarizationreaches maximum

level, most voltage-

gated Na channel

become inactivated& voltage-gated K

channel starts to

open

Axon becomes less

permeable to Na+

but more permeable

to K+




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This allowing rapid outflow/efflux of K+out

of the axon; resulting a negative statewithin the cell again

The neuron is said to undergo

repolarization which ultimately reaches the

resting stage.




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Since the voltage-gated K channel close slowly,

excess K+moves out from the axon

Causes the inner part of the axon becomes more

negatively chargedthan during resting potential

This condition is known as

hyperpolarisation/undershoot

Resting potential is preserved by reactivation of

Na-K pump



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Fig. 48.11

Generation of Action Potentials


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A recovery phase for axon that had just

transmit impulse

Refractory Period

2 phases

Absoluterefractory

period

Relativerefractory

period




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Cannotgenerate new action potential

Even if the intensity of the stimulus is high

Axon membrane undergoes hyperpolarization

Outflow of K+ causes the charge within axonbecomes too negative

Absolute Refractory Period

Importance

Prevent impulse from moving backward Limit the frequency of impulse that can pass

along an axon




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Cangenerate new action potential

If the intensity of the stimulus is high

Relative Refractory Period

Importance

Prevent impulse from moving backward Limit the frequency of impulse that can pass

along an axon

Charge within the cell slowly becomes less -ve;

nearing its resting state Resting potential is restored by Na-K pump the

cell



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(A) TRANSMISSION OF ACTION

POTENTIAL IN MYELINATED NEURON



Structure of a myelinated neurone


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(A) TRANSMISSION OF ACTION

POTENTIAL IN MYELINATED NEURON

ea g outco es b) p a t e ge e at o o act o pote t a , t a s ss o a d


Saltatory conduction


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In myelinated axons, voltage-gated Na

channels are restricted to gaps in the myelinsheath called nodes of Ranvier

The extracellular fluid is in contact with the

axon membrane only at the nodes

(A) TRANSMISSION OF ACTION POTENTIAL IN

MYELINATED NEURON

g ) p g p ,



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As a result, action potential are notgenerated

in the regions between the nodes

The inward current produced during therising phase of the action potential at a node

travels all the way to the next node, where it

depolarizes the membrane & generates the

action potential


MYELINATED NEURON

g ) p g p ,



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The time consuming process of opening &

closing of ion channels occurs at only a

limited number of positions along the axon.

This mechanism for action potential

propagation is called saltatory conduction

because the action potential appears tojump

along the axon from node to node


MYELINATED NEURON

g ) p g p ,



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(B) TRANSMISSION OF ACTION POTENTIAL IN

UNMYELINATED NEURON

g ) p g p


Conduction

of an

action potential


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1. An action potential is generated as Na+flows inward across the membrane at

one location.


UNMYELINATED NEURON

g ) p g p



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2. The depolarization of the action potential

spreads to the next region of the membrane,

reinitiating the action potential there.

To the left of this region, the membrane is

polarizing as K+flows outward.


UNMYELINATED NEURON



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3. The depolarization-repolarization process is

repeated in the next region of the membrane.In this way, local currents of ions across the

plasma membrane cause the action potential

to be propagated along the length of the axon.


UNMYELINATED NEURON



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Characteristics of Nerve Impulse AlongAn Axon

Speed of impulse transmission depends on :

1

1 Presence of myelin sheath

2 Diameter of axon



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Act as electrical insulator

Depolarization only occurs at node of Ranvier

Local circuit are formed here

1. Myelin Sheath



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Impulse jumps from node to node along the

myelinated neuron in saltatory conduction

Speed up the transmission of impulse

1. Myelin Sheath



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2. Diameter Of Axon

The bigger the diameter, the higher the

velocityof the transmission of impulse.

The resistance is reduced (eg :

arthropods, annelids)


Documents

21.1 (a), (b)