47535007-Biology-sem1-chap10

8/22/2019 47535007-Biology-sem1-chap10

1/93

8/22/2019 47535007-Biology-sem1-chap10

2/93

CHAPTER 12NERVOUS SYSTEM

12.1 The nervous system

12.2 The transmission of impulse

12.3 The synapse

12.4 Neuromuscular junction

12.4.1 Structure of the neuromuscular junction

12.4.2 Structure of the skeletal muscle

12.4.3 The sliding-filament theory

12.4.4 Mechanism of the muscle contraction

12.4.5 The autonomic nervous system

12.5 Drug abuse

8/22/2019 47535007-Biology-sem1-chap10

3/93

OBJECTIVESAt the end of the lesson, students should be able to :

1) Build the organization chart of the humannervous system

2) Explain the rising of a resting potential inneurons

3) List down the characteristics of impulse

4) Explain the propagation of impulse along theaxon

8/22/2019 47535007-Biology-sem1-chap10

4/93

NERVOUS SYSTEM

To synchronize the activities of the inner bodyparts (by cooperating with the endocrine /

enzymatic systems) towards general balance.

Performs the three overlapping functions ofsensory input, integration & motor output.

Impulse is transmitted from one receptor to aneffector specifically.

8/22/2019 47535007-Biology-sem1-chap10

5/93

Sensory input

Brain & spinal cord

Motor input

Sensory receptor

EffectorPeripheral nervous

system (PNS)

Central nervous

system (CNS)

THE RELATIONSHIP BETWEEN THE SENSORY INPUT, INTEGRATION &

MOTOR OUTPUT

8/22/2019 47535007-Biology-sem1-chap10

6/93

ORGANIZATION

NERVOUS SYSTEM

CENTRALNERVOUS SYSTEM

PERIPHERALNERVOUS SYSTEM

BRAIN SPINAL CORD SENSORYMOTOR

(EFFERENT DIV)

SOMATIC

AUTONOMIC

PARASYMPATHETIC

SYMPATHETIC

8/22/2019 47535007-Biology-sem1-chap10

7/93

CENTRAL NERVOUS

SYSTEM

Comprises of :1) the brain

2) the spinal cord

8/22/2019 47535007-Biology-sem1-chap10

8/93

PERIPHERAL NERVOUS SYSTEM

consists of neurons that interconnect the brain to all partsof the body ;

a) the body muscle

b) the sensory organs

c) the organ built systems

the neurons are :

a) motor neurons somatic & autonomicb) sensory neurons

8/22/2019 47535007-Biology-sem1-chap10

9/93

MOTOR NEURONSSOMATIC

Controls thevoluntarily responseswhich involves the

skeletal muscles

AUTONOMIC

Regulates the internal environmentby controlling smooth & cardiacmuscles

Controls the involuntarily responsesof all the internal organs & glands

Actions are controlled in themedulla & hypothalamus

Consists ofsympathetic &parasympathetic division.

Both act on the same target but very

often antagonistic in the effect theybring.

8/22/2019 47535007-Biology-sem1-chap10

10/93

Neuronbasic unit of nervous system

8/22/2019 47535007-Biology-sem1-chap10

11/93

Neuron

Functions :

a) receive information from the inner/ outerenvironment ; and/or from other neurons.

b) integrates information received &produces the

appropriate output signals.

c) guiding the signals until it reaches the farend/terminal of a neuron.

d) sending signals to other nerve cells, glands or

muscles.

Comprises of plasma membrane

The selective permeability of the membrane ensures theinformation from the environment reaches the desired target

8/22/2019 47535007-Biology-sem1-chap10

12/93

RESTING POTENTIAL & THE GENERATION

OF THE ACTION POTENTIAL

8/22/2019 47535007-Biology-sem1-chap10

13/93

Unstimulated neuronmaintains a different chargecondition across the

membranes.

The different chargesdevelops a localizedelectrical gradient, which iscalled the resting potential.

The resting potentialdevelops when the charge ismore negative within thecell than from the outside

(which is more positive).

The voltage measuredacross the plasma membrane(the membrane potential) is

about -70 mV.

8/22/2019 47535007-Biology-sem1-chap10

14/93

RESTING POTENTIAL

The intracellular & extracellular fluid of a neuron contains allkinds of solutes; including ions (cations &anions)

The fluid within the neurons contains mostlypotassium ions (K+)& a lower concentration of sodium ions (Na+)

In contrast, the extracellular fluid contains a higher concentrationof sodium ions.

8/22/2019 47535007-Biology-sem1-chap10

15/93

In its unstimulated stage, the membrane of the neuron is highly

permeable to K+ ions which passively diffuse across the membrane

according to the concentration gradient (from the inside, out of themembrane)

A slow diffusion of Na+ ions occur across the membrane because the

permeability to these ions is lower than to the K

+

ions.

8/22/2019 47535007-Biology-sem1-chap10

16/93

These diffusions do not achieve an equilibrium since the

sodium-potassium pump transports these ions againsttheir concentration gradient.

This results in the resting potential condition or the

polarization stage.

8/22/2019 47535007-Biology-sem1-chap10

17/93

THE ACHIEVEMENT OF RESTING (POLARIZED) STAGE

8/22/2019 47535007-Biology-sem1-chap10

18/93

THE RISING OF ACTION POTENTIAL

The neuron is stimulated by

the change in theenvironment (inner / outer).

The electrical potential across

the membrane will change

form its resting stage; the

charge within the cell

becomes more positive

because :

the sodium-potassium pumpsstop functioning

Na+ ions rush into the cell,

changing the membrane

potential to a more positive

state

8/22/2019 47535007-Biology-sem1-chap10

19/93

The change in theelectrical potential iscalled depolarization.

If graded potentials sum to 55mv, a thresholdpotential is achieved. This

triggers an action potential(impulse).

At the peak of the actionpotential, the sodium-

potassium pumps continuefunctioning; theconductivity of the Na+

ions decreases while theconductivity of the K+

ions increases again

8/22/2019 47535007-Biology-sem1-chap10

20/93

The K+ ions diffuse

out passively from thecell; resulting a more

negative state within

the cell.

The neuron is said to

undergo repolarization

which ultimatelyreaches the resting

stage.

8/22/2019 47535007-Biology-sem1-chap10

21/93

CHANGES IN THE MEMBRANE POTENTIAL :

DEPOLARIZATION, ACTION POTENTIAL, REPOLARIZATION

8/22/2019 47535007-Biology-sem1-chap10

22/93

In the resting state, both the sodium channel

and potassium channel are closed, and the

membranes resting potential is maintained.

During the depolarizing phase, the action

potential is generated as activation gates of

the sodium channels open, and thepotassium channel remains closed.

8/22/2019 47535007-Biology-sem1-chap10

23/93

THE TRANSMISSION OFIMPULSE

8/22/2019 47535007-Biology-sem1-chap10

24/93

THE TRANSMISSION OF IMPULSE

Is an electrical phenomena

that occurs through thedendrite, dendron & theaxon.

Involves 2 important

phases :1) the resting stage

2) the action potential

The features of actionpotentials / impulse are :

1) stimulation

2) all-or-nothing event

3) refractory period

4) speed of conduction

8/22/2019 47535007-Biology-sem1-chap10

25/93

STIMULATION

There are 2 kinds of stimulation that affect the nerves:

1) common stimulation

- involves the stimulation of the receptor organs

- e.g light, sound, taste, smell

2) situational stimulation

- all the stimulation that are capable of depolarizing

the axons.

- e.g mechanical, chemical, heat, pressure, electrical

stimulations.

8/22/2019 47535007-Biology-sem1-chap10

26/93

ALL-OR-NOTHING EVENT

The size of a nerve impulse is not determined by the size of the

stimulation received.The action potential is triggered only if the depolarization of the

membrane is above the threshold level.

8/22/2019 47535007-Biology-sem1-chap10

27/93

Below the threshold level, the stimulation is not sufficient todepolarize the membrane & thus triggering the action potential.

If an action potential is achieved, a stronger intensity of astimulus wont increase the size of it.

8/22/2019 47535007-Biology-sem1-chap10

28/93

THE ALL-OR-NOTHING EVENT

8/22/2019 47535007-Biology-sem1-chap10

29/93

REFRACTORY PERIOD

Impulse travels one-way along theaxon from the excitable region to the

resting region next to it.

The previously active regionundergoes a recovery phase which is

known as the refractory period.

Two phases are involved in this very

short period of about 5-10ms :

1) absolute refractory period

2) relative refractory period

8/22/2019 47535007-Biology-sem1-chap10

30/93

Absolute refractory period

the previously active region

undergoes a recovery phaseduring which the axon cannotrespond to a depolarizationeven if the stimulus intensityis increased.

during this period the axonmembrane goes throughhiperpolarization; themembranes permeability toK+ ions increasesdramatically.

these ions diffuse out veryhighly making the chargewithin the neuron becomestoo negative.

8/22/2019 47535007-Biology-sem1-chap10

31/93

Relative refractory perioda phase following the

absolute refractoryperiod where a high-intensity stimulusmay produce adepolarization.

the axon membranereaching its normal

permeability state,

allowing the Na+

ionsinto the cell; thecharge within the cellslowly becomes lessnegative; nearing its

resting state.

8/22/2019 47535007-Biology-sem1-chap10

32/93

SPEED OF CONDUCTIONDepends on :

a) the presence ofmyelin

sheath

act as an electrical insulator

depolarization only occurs atthe nodes of Ranvier whereno myelin sheath is present.

local circuits are set up atthese points & current flowsacross the axon membranegenerating the next action

potential.

8/22/2019 47535007-Biology-sem1-chap10

33/93

in effect, the actionpotential jumps fromnode to node & passesalong the myelinatedaxon faster.

this type of conductionis called saltatory.

the conduction

velocities is increasedup to 50x as comparedto in the unmyelinatedaxon.

8/22/2019 47535007-Biology-sem1-chap10

34/93

b) The axon diameter

the bigger the diameter,the higher the velocity of

the propagated actionpotential.

the resistance is reducedwhen the diameter of the

axon is big

8/22/2019 47535007-Biology-sem1-chap10

35/93

THE SALTATORY CONDUCTION ALONG THE MYELINATED AXON

8/22/2019 47535007-Biology-sem1-chap10

36/93

GENERATION & PROPAGATION OF IMPULSE

The action potential is produced

locally in axon; the membrane is

depolarized at a specific area in the

axon.

The action potential flows along the

axon because it is self-propagated.

An action potential achieved at one

region of the membrane is sufficient to

depolarized a neighboring regionabove threshold because the

depolarized area has a different charge

from the inactive area next to it; thus a

local circuit is produced.

8/22/2019 47535007-Biology-sem1-chap10

37/93

The current flow from one

activated region to theinactivated area enables

depolarization to occur, thus

produces the action potential.

The continuous occurrence of

depolarization from one area

to the one next to it, ensures

the transmission of impulse

even in a great distance.

8/22/2019 47535007-Biology-sem1-chap10

38/93

THE PROPAGATION OF IMPULSE ALONG THE AXON

8/22/2019 47535007-Biology-sem1-chap10

39/93

SYNAPSE

8/22/2019 47535007-Biology-sem1-chap10

40/93

Objectives

At the end of the lesson, students should be able to:

Draw out and label a picture of a synapse

Explain the mechanism of the impulse transmissionacross the synapse

Compare the transmission of impulse across thesynapse with the transmission along the axon

8/22/2019 47535007-Biology-sem1-chap10

41/93

Synapse

An area of functional

between neurons for

transferring information.

Found between fineterminal branches (axon),

dendrites or cell body.

2 types of synapsesa) electrical

b) chemical

8/22/2019 47535007-Biology-sem1-chap10

42/93

Structure of the chemical synapse

Commonly found in

vertebrates

Consist a bulbous

expansion of a nerve

terminal called synaptic

knob

8/22/2019 47535007-Biology-sem1-chap10

43/93

The membrane of the

synaptic knob is thickened

and form the presynapticmembrane

The thickened membrane

of the dendrite is termed

the postsynaptic membrane

The two membranes areseparated by a gap called

synaptic cleft (20nm)

8/22/2019 47535007-Biology-sem1-chap10

44/93

Structure of the chemical synapse

The cytoplasm of thesynaptic knotcontainsmitochondria,smooth

endoplasmicreticulum,microfilaments,andnumerous synapticvesicles

Each vesiclecontains a chemicalneurotransmitter

substance

8/22/2019 47535007-Biology-sem1-chap10

45/93

Two main neurotransmittersubstances are

a) acetylcholine

- secreted by parasympathetic

b) noradrenaline

- secreted by sympathetic

nerves

Protein channels are found onthe postsynaptic membrane andthey have receptors for theneurotransmitter substance

These channels allow themovement of ions into the

postsynaptic neurons

8/22/2019 47535007-Biology-sem1-chap10

46/93

Mechanism of synaptictransmission

M h i f i i i

8/22/2019 47535007-Biology-sem1-chap10

47/93

Mechanism of synaptic transmission

The arrival of nerve

impulses at thesynaptic knob

depolarizes the

presynaptic

membrane.

The permeability of

the membrane toCa2+ ions is

increased, and they

easily enter the knob.

8/22/2019 47535007-Biology-sem1-chap10

48/93

The entrance of those ions

causes the synaptic

vesicles to fuse with thepresynaptic membrane and

rupture; discharging their

contents into the synaptic

cleft.

The vesicles then return to

the cytoplasm where they

are refilled with

neurotransmitter

substance.

8/22/2019 47535007-Biology-sem1-chap10

49/93

The neurotransmitter

substance diffuses across the

synaptic cleft and attaches to

a specific receptor site on thepostsynaptic membrane;

causing the opening of the

protein channels.

Na+ ions enter thepostsynaptic neurons,

followed by the leaving of

K+ ions down their

respective concentration

gradient.

This leads to a depolarization

of the postsynaptic

membrane.

The depolari ation

8/22/2019 47535007-Biology-sem1-chap10

50/93

The depolarizationresponse is known as anexcitatory postsynapticpotential (EPSP)

Having produced a changein the permeability of the

postsynaptic membrane,the neurotransmittersubstance is thenhydrolyzed by a specificenzyme

acetylcholine ishydrolyzed byacetylcholinesterase

noradrenalin ishydrolyzed by

monoaminoxidase

8/22/2019 47535007-Biology-sem1-chap10

51/93

The depolarizing effect of the EPSP is additive, a phenomenon calledsummation:

two or more EPSP arising simultaneously at different regions on the sameneuron may produce collectively sufficient depolarization (spatialsummation).

rapid release of transmitter substance from several synaptic vesicles by thesame synaptic knob produces individual EPSP close together, they summate

and give rise to action potential in postsynaptic neuron (temporalsummation).

8/22/2019 47535007-Biology-sem1-chap10

52/93

Fig 12.11 : The relationship between EPSP with the achievement of action potential

The action potential produced is then transmitted along the postsynaptic axon by the

flow of an electric current.

The summation effect of EPSP delays the transmission of impulse in neurons; but it

ensures the flow of impulse is unidirectional.Because: the synaptic vesicles only exist in the presynaptic membrane side.

C i f i l t i i th d

8/22/2019 47535007-Biology-sem1-chap10

53/93

Comparison of impulse transmission : across the synapse and

along the axon

Synapse Axon1. Impulse is chemically transmitted. 1. Impulse is electrically transmitted.

2. Involves the neurotransmitter substances. 2. No neurotransmitter substances are

involved.

3. Impulse transmission is slower because :

-the neurotransmitter need to diffuse

across the synaptic cleft

-the summation of EPSP is needed to

reach the threshold level

3. Impulse transmission is very fast.

4. Involves the diffusion of Ca+ ions into

the synaptic knob to activate the vesicles.

4. Ca+ ions are not involved.

5. The diffusion of Na across the membrane

is needed.

5. The diffusion of Na across the membrane

is needed.

8/22/2019 47535007-Biology-sem1-chap10

54/93

NEUROMUSCULAR JUNCTION

8/22/2019 47535007-Biology-sem1-chap10

55/93

OBJECTIVES

At the end of the lesson, students should be able to:

draw out a label picture of a neuromuscular junction

completely explain the rising of end-plate potential

explain the fine structure of the skeletal muscle which

consists of myofibril, actin, myosin and sarcomere.

8/22/2019 47535007-Biology-sem1-chap10

56/93

STRUCTURE OF THE NEUROMUSCULAR JUNCTION

1. SPECIALIZED FORM OF SINAPSE FOUND BETWEENNERVE TERMINALS & MUSCLE FIBRES

2. THE CYTOPLASM OF THE MOTOR NEURONTERMINAL RELEASES ACETYLCHOLINE ONSTIMULATION

3. THE REGION WHERE THE THE AXON OF THE MOTORNEURON DIVIDES & FORM NON-MYELINATED

BRANCHES ON THE MEMBRANE CELL SURFACE ISCALLED THE THE MOTOR END- PLATE

4. POSTSYNAPTIC MEMBRANE (MUSCLE MEMBRANE )CALLED SARCOLEMMA HAS MANY FOLDS CALLEDJUNCTIONAL FOLDS

5. A LOCAL DEPOLARIZATION AT EACH MOTOR ENDPLATE PRODUCES END-PLATE POTENTIAL (EPP)

6. EPP IS SUFFICIENT TO LEAD TO A PROPAGATEDACTION POTENTIAL ALONG SARCOLEMMA DOWNINTO THE MUSCLE FIBRE VIA TRANSVERSE TUBULESYSTEM (T-SYSTEM)

8/22/2019 47535007-Biology-sem1-chap10

57/93

8/22/2019 47535007-Biology-sem1-chap10

58/93

STRUCTURE OF THE SKELETAL MUSCLE

8/22/2019 47535007-Biology-sem1-chap10

59/93

STRUCTURE OF THE SKELETAL MUSCLE

The major components are the

cylindrical muscle fibres; whichmeasure about 10 100 m in

diameter and 1 40 mm in

length

Within the muscle fibres are

numerous thin myofibrils

Each myofibril is composed of

two types of proteinaceousmyofilaments, actin (thin

filaments) and myosin (thick

filaments)

8/22/2019 47535007-Biology-sem1-chap10

60/93

The cytoplasm of the

myofibril is called

sarcoplasm and containsa network of internal

membranes termed the

sarcoplasmic reticulum

The skeletal muscle is

observed to be striated; a

regular alternation of light

and dark bands

The light and the dark

bands are called the I and

A bands respectively

The bands are due to the regular

8/22/2019 47535007-Biology-sem1-chap10

61/93

e b ds e due o e eguarrangement of actin andmyosin

Traversing the middle of each Iband is a dark line called the Zline

The section of a myofibril

between two Z line is called asarcomere; the functional unitof muscle contraction

In certain regions of thesarcomere, actin and myosinfilaments overlap

Myosin and actin filamentsconstitute the A band, whilstactin filament alone constitute

the I band

The centre of the A band is lighter

8/22/2019 47535007-Biology-sem1-chap10

62/93

The centre of the A band is lighter

than its other regions because it

constitutes only the filament

myosin, and is called the H band

The H band is bisected by a dark

line, the M line; which joins

adjacent myosin filaments together

at a point halfway along their length

Running transversely across the

fibre and between fibrils is a system

of tubules known as the T system

The T system is in contact with the

surface of the sarcolemma

8/22/2019 47535007-Biology-sem1-chap10

63/93

At certain points the T tubules

pass between the pairs of

vesicles which are components

of the sarcoplasmic reticulum

The vesicles are involved in the

uptake and release of Ca2+ ions

which controls the contractile

behaviour of the muscle fibre

MECHANISM OF MUSCLE CONTRACTION

8/22/2019 47535007-Biology-sem1-chap10

64/93

MECHANISM OF MUSCLE CONTRACTION

AT REST, TROPOMYOSIN BLOCKS THEMYOSIN ATTACHMENT TO ACTIN

UPON STIMULATION BY NERVEIMPULSE, Ca2+ IONS ARE RELEASEDINTO THE SARCOPLASM

THE IONS BIND TO THE TROPONINCOMPLEX

TROPONIN COMPLEX CHANGES ITSCONFORMATION

NOW THE MYOSIN BINDING SITESARE EXPOSED

MYOSIN HEADS ATTACHED TO THEACTIN FILAMENT

CROSS BRIDGES ARE FORMED

MUSCLE CONTRACTS

8/22/2019 47535007-Biology-sem1-chap10

65/93

IN SOME MUSCLES Ca2+ ALSOSTIMULATES THE MYOSINATPASE ACTIVITY.

THE ATPASE HYDROLIZES THEATP & CHANGE THE MYOSINHEAD TO A HIGH ENERGYCONFIGURATION.

THIS ALLOWS THE FORMATIONOF CROSS BRIDGES.

WHEN THE EXCITATION OF THESARCOMERES CEASES, Ca2+ ARE

PUMPED BACK INTO THEVESICLES.

SARCOMERES RELAXES

8/22/2019 47535007-Biology-sem1-chap10

66/93

THE MECHANISM OF MUSCLE CONTRACTION

8/22/2019 47535007-Biology-sem1-chap10

67/93

The Sliding Filament Theory

The Sliding Filament Theory

8/22/2019 47535007-Biology-sem1-chap10

68/93

The Sliding Filament TheoryProposed by Huxley and

Hanson in 1954.

They suggested that the muscle

contracts when the thin filament

(actin) and the thick filament

(myosin) slide past each other.

During contraction the actin

filament move inwards towards

the centre of the sarcomere,making it (the sarcomere)looks

shorter without changing the

length of the A band.

8/22/2019 47535007-Biology-sem1-chap10

69/93

The myosin head is the centre ofbioenergetic reactions that powermuscle contraction.

The high energy configurationheads of the myosin filamentoperate like a hook attaching tothe specific sites on actin in a

particular way to form crossbridges.

The high energy configurationstate is achieved when the ATP

molecules bound to the headsbeen hydrolyzed into ADP andinorganic phosphate, andreleasing high energy used tochange the configuration.

8/22/2019 47535007-Biology-sem1-chap10

70/93

The myosin heads then

change their relative

configuration such that the

actin molecules are pulled

further into the A band.

After the process is

completed, the myosin

heads, bound to another

ATP molecules, detachfrom the actin.

8/22/2019 47535007-Biology-sem1-chap10

71/93

They then split the new ATP

molecules to revert to the high

energy configuration and attach to

another sites further along the actinfilament.

The cross bridge

attachment/detachment cycles

could be repeated many timesdepending on the speed of

shortening.

The pulling of the actin filament

repeatedly towards the centre isunidirectional in a mechanism

called the ratchet mechanism.

8/22/2019 47535007-Biology-sem1-chap10

72/93

AUTONOMIC

NERVOUS SYSTEM

8/22/2019 47535007-Biology-sem1-chap10

73/93

OBJECTIVES

At the end of the lesson, students should be

able to :

Explain the structure and the functions of the

sympathetic and parasympathetic systems

Compare both the sympathetic and the

parasympathetic system

MAMALIAN AUTONOMIC NERVOUS SYSTEM (ANS)

8/22/2019 47535007-Biology-sem1-chap10

74/93

( )

A part of peripheral nervous system controlling the involuntaryactivities of internal environment ;eg: heart rate, peristalsis, sweating

Consist of motor neuron passing to the smooth muscles of internalorgan and cardiac muscle

Most activities of ANS is integrated locally within the spinal cord orbrain by visceral reflexes

ANS composed 2 types of neurons :

Preganglionic neuron (mylienated) emerges from CNS

Postganglionic neuron (unmylienated) leading the effectors

8/22/2019 47535007-Biology-sem1-chap10

75/93

2 division of ANS :

Symphatetic nervous system

Parasymphatetic nervous system

The two systems differ primarily in the structural

organization of their neurons

SYMPATHETIC NERVOUS SYSTEM (SNS)

8/22/2019 47535007-Biology-sem1-chap10

76/93

SYMPATHETIC NERVOUS SYSTEM (SNS)

Neurons are originated from spinal cord( the thoracic + lumbarregion)

Synapses + cell bodies of postganglionic neurons in the trunk regionare situated in ganglia close to spinal cord

Adjacent segmental symphatetic ganglia on each side of spinal cordare linked together by the sympathetic nerve tract

They form chain of symphatetic ganglia running alongside the spinalcord

Its preganglionic neurons are shorter than postganglionic neurons

The chemical transmitter substance released at postganglionic effectorsynapses in noradrenalin (Ad)

8/22/2019 47535007-Biology-sem1-chap10

77/93

The effect s spread to all part of the body and

takes time to decease

The symphatetic nervous system is especially

dominant under stress or at time danger

Eg.of its effects :Dilates pupil

Increase amplitude and rate of heart beatIncrease ventilation rate

Constricts arterioles to gut and smooth muscle

PARASYMPHATETIC NERVOUS SYSTEM (PNS)

8/22/2019 47535007-Biology-sem1-chap10

78/93

PARASYMPHATETIC NERVOUS SYSTEM (PNS)

Neurons originated from the cranial and the sacral region of the CNS

The ganglia of PNS situated close to or within the effector organ

Its preganglionic neurons longer than its postganglionic neurons

Chemical transmitter substance secreted at the postganglionic

synapses is AceKoa

Its effect locally and short

PNS controls the routine activities of the body at rest ; a compensationfor the symphatetic effect

Eg :decrease the amplitude + rate of heart beat,ventilation rate

Maintains steady muscle tone in atrioles to gut,smooth muscle,brain and skeletal

muscle

Diff b h i & h i

8/22/2019 47535007-Biology-sem1-chap10

79/93

Differences between symphatetic & parasymphatetic nervous system

Feature Symphatetic Parasymphatetic

Origin of neuron Emerges from thoracic and

lumbar regions of CNS

Emerges from cranial +

sacral regions of CNS

Position of ganglion Close to spinal cord Close to effector

Length of fibres Short preganglionic , long

postganglionic fibers

Long preganglionic

fibers,short postganlionic

fibers

Numbers of fibers Numerous postganglionic fibres Few ganglionic fibers

Distribution of fibers Preganglionic fibers innervate a

wide area

Preganglionic fibers

innervate a restricted region

Area of influence Effect difuse Effect localized

8/22/2019 47535007-Biology-sem1-chap10

80/93

Feature Symphatetic Parasymphatetic

Transmitter substance Noradrenalin released ateffector

AceKoa released ateffector

General effects Increase metabolite

Lowers sensory threshold

Restores sensory

threshold to normal level

Decrease metabolite level

Overall effect Excitatory homeostatic

effects

Inhibitory homeostatic

effect

Condition when active Dominant duringdanger,stress + activity

Dominant during rest

Controls routine body

activities

8/22/2019 47535007-Biology-sem1-chap10

81/93

DRUG ABUSE

8/22/2019 47535007-Biology-sem1-chap10

82/93

OBJECTIVES

At the end of the lesson the students should be able to :

Give the definition of drugs

List and give explanations of the 5 types of drugs

Explain the effect of cocaine on the synapses andneuromuscular junction

DRUGS

8/22/2019 47535007-Biology-sem1-chap10

83/93

DRUGSDefinition

Any chemical substance that alters the physiological state of a living organisms

Also known as psychoactive substance which could lead to addiction ifabused

giving harmful effect to mental & physical activities

Addiction

Chemically dependent on drugs resulting from the body tolerancemore dosage is needed to get the same effect

Individual is said to be addicted when the drugs has taken over the importantrole in his biochemical reaction

Most drugs interfere with the impulse transmission by : Changing

Hindering synthesis the neurotransmitter substance

Releasing and absorbing

8/22/2019 47535007-Biology-sem1-chap10

84/93

TYPES OF DRUGS

DEPRESSANTSTIMULANT

HALLUCINOGEN

ANTI-DEPRESSANT

INHALANT

STIMULANT

8/22/2019 47535007-Biology-sem1-chap10

85/93

STIMULANT

Small dosage - activities of CNS (feeling more energetic)

High dosage/prolong consumption lead to depression

Eg :

1. Caffeine prevents the hydrolyses of neurotransmitter substances continuous depolarization occurs at the postsynapse membrane

Small dosage stimulates the cerebrum cortex-increase alertness

High dosage influence medulla oblongata interfering motor andintellectual coordination

2. Nicotine mimics the effect of AceKoa on receptor and stimulates thesensory receptors

- short term use change in heart beat rate and blood pressure

3. Amphetamines and cocaine

Block the reabsorption of neurotransmitters from the postsynapsesmembrane continuous depolarization of the postsynapsemembranes in long period

DEPRESSANT

8/22/2019 47535007-Biology-sem1-chap10

86/93

SS N

Lowering activities in CNS lowering body activities as a

whole

Eg : Barbiturates

Gives different based on dosage consumed

Low dosage

stimulate synaptic activities, so persons would in state of euphoria/excited

High dosage

synaptic action is hindered ( a feeling of depression is experienced by the

individual)

HALLUCINOGEN

8/22/2019 47535007-Biology-sem1-chap10

87/93

HALLUCINOGEN

Change the perception of the senses especially sight and

hearing

Some acts by imitating/inhibiting the action ofneurotransmitter substance

Most involve in causing disorientation and hallucinating not fatal

Eg: LSD (Lysergic acid diethylamide) Marijuana

ANTI-DEPRESSANT

8/22/2019 47535007-Biology-sem1-chap10

88/93

(TRANQUILIZERS)

Use as pain killer & to lessen anxiety

Mimic the action ofendorphin and enkephalins which areneuromodulators that assist the action of the neurotransmittersubstances

Endorphin + enkephalins inhibit the transmission of pain signals to brain

Eg :Narcotics ( heroin, morphine)

Prolong consumption of narcotics increase the receptors for enkephalins bind to the receptor used

by enkephalins therefore, pain signals are prevented fromreaching brain

P l i f i

8/22/2019 47535007-Biology-sem1-chap10

89/93

Prolong consumption of narcotics

increase the receptors for enkephalins bind to thereceptor used by enkephalins therefore, pain signals

are prevented from reaching brain

High dosage needed when body becomes tolerant tothe drug

When drug withdrawn from body pain pathwayneurons become extremely sensitive

Because number of enkephalins receptor has beenincreased, more receptors are left unbound by

enkephalins and pain impulses are not blocked

The withdrawing addict experiences greater pain thannormal until the number of receptors reaches its

preaddiction level

INHALANT

8/22/2019 47535007-Biology-sem1-chap10

90/93

INHALANT

Drugs that taken by means of inhaling

Eg:

Organics solvent

Ether

Chloroform

Organic based adhesive substance

Causes :

Hallucination

Higher heart beat rate

Anaesthetize condition

A near fainted feelings

COCAINE :

8/22/2019 47535007-Biology-sem1-chap10

91/93

THE MECHANISM OF ACTION

As stimulant, cocaine effects the brains limbicsystem (the bodys pleasure centre) by imitatinga neuromodulator that blocks the reabsorption ofdopamine (neurotransmitter substance) back into

the presynapse membranes

Result of blockage

dopamine stays in synaptic clefts and continually binds tothe receptors in postsynaptic membrane

Depolarization occurs repeatedly which result incontinuous impulse transmission causes????????

Causes :

8/22/2019 47535007-Biology-sem1-chap10

92/93

intense pleasure, increase energy and feeling of power

Neuron respond to continual stimulation by reducing thenumber of dopamine receptor in postsynaptic membranes

Thus, more and more drug is needed for the addict toexperience the pleasurable effects that the dopamine bindingelicits

Addiction build, cocaine addicts find that their pleasure centrescant function at all without the stimulation of drugs

The drugs effect wear off and the addicts begins to suffer deepdepression

When drug again introduced into the body, the mood ofdepression swings to euphoria (intense feeling of happinessand pleasant excitement)

8/22/2019 47535007-Biology-sem1-chap10

93/93

Thats all for this topic