Chapter 10 COORDINATION Part 1

. CHAPTER 10: COORDINATION_SB025_MINMOHD2022

CHAPTER 10 : COORDINATION

10.1 – Nervous system
10.2 – Mechanism of muscle contraction
10.3 – Hormones in mammals
10.4 – Photoperiodism in plants
10.1 : NERVOUS SYSTEM

FUNTIONS of Nervous System
To synchronize the activities of the inner body parts (by cooperating with the endocrine /
enzymatic systems) towards general balance.
Performs the three overlapping functions of sensory input, integration & motor output.
Impulse is transmitted from one receptor to an effector specifically.
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PERIPHERAL NERVOUS SYSTEM

— Can be divided into: 1 Sensory 2 Sensory neuron

◦ S.ensory Neurone receptor

– Conducts impulses from Ganglion
receptors to the CNS
4 Motor 3
– Informs the CNS of the state of
the body interior and exterior neuron Interneuron

◦ M. otor Neurone Effector
muscles
– Conducts impulses from CNS to
effectors (muscles/glands) CNS

PNS

Label the Neuron structures. 2
1

3
4

General function of a neuron.

Comprises of plasma membrane

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

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What is the FUNCTION of the structure in neuron label 1 – 4.
1. Receive information from the inner/ outer environment ; and/or from other neurons.
2. Integrates information received & produces the appropriate output signals.
3. Guiding the signals until it reaches the far end/terminal of a neuron.
4. Sending signals to other nerve cells, glands or muscles.
Roles of Symphathetic and parasympathetic

• control the smooth and cardiac muscles, gastrointestinal organs, cardiovascular, excretory
and endocrine system

• Works involuntarily

Sympathethic nervous system works oppositely from parasympathethic nervous system
Examples of their opposite activity.

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HOW do Neuron works?

# RESTING potential
# ACTION potential

WHAT is RESTING POTENTIAL?

Resting = that NO CURRENT is flowing across the membrane.
Potential = a separation of charge. In this case the separation is across the membrane.

The resting potential develops when the charge is more negative within the cell
than from the outside (which is more positive).

Cations.
l K+ the principal intracellular cation.
l Na+ is the principal extracellular
cation.

Anions. Too large to diffuse out.
l Proteins, amino acids, sulfate, and
phosphate are the principal
intracellular anions.
l Cl– is principal extracellular anion.

Resting potential in the axon
= The fluid within the neurons contains mostly potassium ions (K+) & a lower concentration of

sodium ions (Na+)

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

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OUTSIDE /extracellular fluid
Higher Na+ ions concentration
Lower K+ ions concentration

INSIDE /intracellular
Higher K+ ions concentration
Lower Na+ ions concentration

RESTING POTENTIAL maintain by …………. Active transport
– Sodium-potassium pumps

OUTSIDE OF CELLK+ NaN+ a+ Na+ K+ Na+ Na+
Na+ Na+Na+ Na+
Na+ Na+ Na+
Na+
channel
Na+ - K+
Plasma K+ pump
membrane

Protein Na+ K+ K+ K+
K+ K+ channel K+
INSIDE OF CELL
K+ K+ K+
K+ K+

Passive transport (diffusion)

– Passive ions channels (Na+ and K+)

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SHOW the charge (- / +) inside and outside of the axon membrane for RESTING POTENTIAL

intracellular

Outside/extracellular
Neuron membrane is highly permeable to K+ ions, permeability increases
Passively diffuse out according to the concentration gradient
A slow diffusion of Na+ ions occur across the membrane because the permeability to these
ions is lower than to the K+ ions.
The meaning of

Polarised = The inside of the axon is negatively charged , and positively charged on the outside.

SUMMARY
• During resting potential:
• Sodium-potassium pump
• Pump Na+ out and K+ in actively
• Passive ions channels
• Allows more K+ out than Na+ in passively
• Voltage-gated ions channels CLOSED

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ACTION POTENTIAL

What is action potential?
Action potentials are how electrical messages are transmitted within a neuron.
(other names include impulse, fire, spike)
Action potential

Where does Action Potential arise?
• At the trigger zone- the junction of the axon hillock and the initial segment.
• Then propagates along the axon to the axon terminals.

Gated Ion Channels

• Voltage-gated ion channels are found in axons & open or close when the membrane
potential changes.

• Voltage-Gated K+ Channels
• Voltage-Gated Na+ Channels

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The rising of action potential

The electrical potential across
the membrane will change form
it’s resting stage; the charge
within the cell becomes more
positive because :

- Na+ ions rush into the cell,
changing the membrane
potential to a more positive
state

Depolarization = Sodium ions rush into the cell, and the interior of the cell becomes more positive.

> -55 mV

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INITIATION OF ACTION POTENTIAL

CHANGES IN THE MEMBRANE POTENTIAL :
DEPOLARIZATION, ACTION POTENTIAL, REPOLARIZATION

__ __ __ __
++ ++ ++ ++

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STEP
Description
1. Resting state Both the sodium and potassium voltage gated channels
are closed and the membrane’s resting potential is
2. Threshold maintained.

A stimulus opens some Na+ channels, if the Na+ influx
achieves threshold potential, then additional Na+ gates
open, triggering an action potential.
• Membrane potential becomes slightly positive
• Voltage-gated potassium channels remain closed

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3. Depolarization of the action When threshold level is reached, action potential is
potential triggered

Activation gates of the sodium channels are open, but the
potassium cannels remain closed.

Sodium ions rush into the cell, and the interior of the cell
becomes more positive.

4. Repolarization of the action Þ Triggers more Na+ gated channels to open
potential Þ Becomes more positive (+40mV)
Sodium gated channels closed, potassium gated channels

open.

Potassium ions leave the cell and the loss of positive
charge causing the inside of the cell become more
negative than the outside.

Þ K+ diffuse out of the cell
Þ Down their electrochemical gradient
Þ Restoring negative charge inside of the cell

5. Undershoot/hyperpolarization • Voltage-gated potassium ion channels begin to close slowly
• An excess of K+ ions leave the axon

• Inside of the membrane becomes more negative
• Below -70 mV
• Undershoot/hyperpolarization

¡ Undershoot/Hyperpolarization
• Gated Na+ channels are closed
• Gated K+ channels remain open (and begin to close
slowly )
• K+ diffuses out of the cell
• the membrane potential becomes more negative.

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THE CHARACTERISTICS OF IMPULSE/ACTION POTENTIAL ALONG AXON.

1. Stimulation
2. All or nothing event
3. Refractory period
4. Speed of conduction

1. STIMULATION (i) Common stimulation
- involves the stimulation of the receptor organs
- e.g light, sound, taste, smell

(ii) Situational stimulation
- all the stimulation that are capable of
depolarizing the axons.

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

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2. 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.

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

If an action potential is achieved, a stronger
intensity of a stimulus won’t increase the size of
it.

3. REFRACTORY PERIOD Absolute refractory =

• Impulse ‘travels’ one-way along the axon — The previously active region undergoes a
from the excitable region to the resting recovery phase during which the axon cannot
region next to it. respond to a depolarization even if the stimulus
intensity is increased.
• The previously active region undergoes a
recovery phase which is known as the — During this period the axon membrane goes
refractory period. through hyperpolarization; the membrane’s
permeability to K+ ions increases dramatically.
• Two phases are involved in this very short
period of about 5-10ms : — These ions diffuse out very highly making the
charge within the neuron becomes too negative.
o absolute refractory period
o relative refractory period Relative refractory=

— A phase following the absolute refractory period
where a high-intensity stimulus may produce a
depolarization.

— The axon membrane reaching its normal
permeability state, allowing the Na+ ions into the

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cell; the charge within the cell slowly becomes
less negative; nearing its resting state.
— Regeneration of “new” action potentials only
after refractory period
— Forward direction only

4. SPEED of CONDUCTION Depends on

(i) The presence of myelin sheath

•act as an electrical insulator
•depolarization only occurs at the nodes of Ranvier

where no myelin sheath is present.
•local circuits are set up at these points & current

flows across the axon membrane generating the
next action potential.
•in effect, the action potential ‘jumps’ from node to
node & passes along the myelinated axon faster.
• this type of conduction is called saltatory.
• the conduction velocities is increased up to 50x as
compared to in the unmyelinated axon.

(ii) Axon diameter

• the bigger the diameter, the higher the velocity of
the propagated action potential.

• the resistance is reduced when the diameter of
the axon is big

(iii) Temperature
• Axons propagate action potentials at lower speeds

when cooled

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. CHAPTER 10: COORDINATION_SB025_MINMOHD2022

THE SYNAPSE

2 types of synapses

a) ELECTRICAL SYNAPSE- Action potentials travels directly from the presynaptic to
the postsynaptic cells via gap junctions.

b) CHEMICAL SYNAPSE-

More common than electrical synapses.
n Postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl-.
n Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize.

Structure of synapse

Presynaptic neuron Impulses are transmitted from
Postsynaptic neuron Presynaptic neuron to postsynaptic
neuron

Synaptic knob

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Synaptic cleft • A gap between the presynaptic neuron and the postsynaptic
Synaptic knob neuron

Presynaptic neuron • About 20nm-50nm width
Postsynaptic neuron
• Enlargement of the terminal end of the axon
• Contains:

Þ Synaptic vesicles - contains neurotransmitter-
acetylcholine or Noradrenaline/norepinephrine

Þ Mitochondria – provide ATP/energy

A nerve cell that carries a nerve impulse towards a synapse

A nerve cell that carries a nerve impulse away from a synapse/
to an effector cell that responds to the impulse at the synapse

• Ligand-gated channels
• Found on the postsynaptic membrane
• Have receptors for the neurotransmitter
• Allow the movement of ions into the postsynaptic
neurons

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TWO main neurotransmitter

acetylcholine noradrenaline
- secreted by parasympathetic - secreted by sympathetic nerves

PROTEIN channels Protein channels/ligand gated are found on the postsynaptic membrane and
@ligand gated they have receptors for the neurotransmitter substance

Function:
- allow the movement of ions into the postsynaptic neurons

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MECHANISM OF SYNAPTIC TRANSMISSION

STEP 1.
-The arrival of nerve impulses at the synaptic knob depolarizes the presynaptic membrane.
STEP 2.
-The permeability of the membrane to Ca2+ ions is increased, and they easily enter the knob.
-The entrance of Ca2+ ions causes the synaptic vesicles to fuse with the presynaptic
membrane and rupture; discharging their contents (neurotransmitter/Acetylcholine) into
the synaptic cleft by exocytosis.
-The vesicles then return to the cytoplasm where they are refilled with neurotransmitter
substance.

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STEP 3
- Neurotransmitter diffuse across synaptic cleft and bind to receptors of gated Na+ channel
on postsynaptic membrane
Causes the gated Na+ channel to open

STEP 4
- Na+ diffuse into postsynaptic cell and leads to the depolarization of postsynaptic
membrane
- Neurotransmitter is then degraded by specific enzymes. (refer diagram above)

STEP 5
- The neurotransmitter acetylcholine is broken down in the synaptic cleft into acetate and
choline by the enzyme acetylcholinesterase and recycled for future use.

The differences of impulse transmission : Across the Synapse and along the Axon

SYNAPSE AXON

1. 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 : 3. Impulse transmission is very fast.
-the neurotransmitter need to diffuse across
the synaptic cleft

4. Involves the diffusion of Ca+ ions into the 4.Ca+ ions are not involved.
synaptic knob to activate the vesicles.

5. The diffusion of Na+ across the membrane is 5.The diffusion of Na+ across the membrane is
needed. needed.

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DRUGS

Definition of drugs :
Any chemical substance that alters the physiological state of a living organisms
Also known as psychoactive substance which could lead to addiction
if abused : giving harmful effect to mental & physical activities

n Addiction - Chemically dependent on drugs resulting from the body tolerance – more
dosage is needed to get the same effect

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

n Most drugs interfere with the impulse transmission by :
• Changing
• Hindering synthesis the neurotransmitter substance
• Releasing and absorbing

COCAINE - Cocaine effects the brain’s limbic system (the body’s “plesure centre”), its blocks the

reabsorption of dopamine (neurotransmitter substance) back into the presynapse membranes
What is dopamine ???
Many areas of the brain produce dopamine. It is produced in the ventral tegmental
area (VTA in the image above) of the midbrain, the substantia nigra pars compacta,
and the arcuate nucleus of the hypothalamus.

n Dopamine is a neurotransmitter that helps control the brain's reward and pleasure centers.
n Dysfunctions of the dopamine system contribute to Parkinson’s disease, schizophrenia, restless legs

syndrome, and attention-deficit hyperactivity disorder (ADHD).
n Schizophrenia is characterized by high striatum dopamine, but abnormally low prefrontal dopamine

activity.

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COCAINE : THE MECHANISM OF ACTION

Wihtout cocaine With cocaine

reuptake transporter Cocaine (drug)
act to remove blocks the
dopamine from the reuptake
synapse. transporter

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Results of blockage :
n dopamine stays in synaptic clefts and continually bind to the receptors in postsynaptic
membrane
n Depolarization occurs repeatedly which result in continuous impulse transmission
n More dopamine accumulates in the synapse, resulting in feelings of intense pleasure, increase
energy and feeling of power

Neuron responds:
reducing the number of dopamine receptor in postsynaptic membranes
Thus, more and more drug is needed for the addict to experience the pleasurable effects.

Addiction build, cocaine addicts find that their pleasure centres can’t function at all without
the stimulation of drugs
The drug’s effect wear off and the addicts begins to suffer deep depression
When drug again introduced into the body, the mood of depression swings to euphoria
Then, if the person stops using cocaine, there is not enough dopamine in the synapses,
the person experiences the opposite of pleasure--depression, fatigue, and low mood.

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10.2 Mechanism of muscle contraction

Synapse between motor neuron and the muscle fiber/ muscle cell.
i.e. the synapse occurs between the
“synaptic terminal” of the motor neuron and
“motor end plate” of muscle fiber.

Muscle tissue consists of several bundles of
muscle fibres

àone muscle fibre consist of groups of
myofibrils that have repetitive unit called
sarcomere

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Neuromuscular junction = Between synaptic terminal of motor neuron and motor end plate of muscle fiber
Composed of three parts:
Þ Synaptic terminal
Þ Motor End Plate
Þ Synaptic cleft

Structure of neuromuscular junction

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NEUROMUSCULAR JUNCTION: STRUCTURE

• The sarcolemma of the muscle fibre is extensively folded forming the motor end plate.
• each folded part on the motor end plate is called : junctional folds
• Synaptic terminal of motor neuron is enclosed by motor end plate
• The sarcolemma and the synaptic terminal of motor neuron are separated by the synaptic

cleft.
• There are ion channels on the sarcolemma
• The synaptic vesicles in the axon contain neurotransmitter.

NEUROMUSCULAR JUNCTION:
HOW IMPULSE TRANSMISSION OCCUR in neuromuscular junction???
1. Arrival of action potential at synaptic terminal
increase the permeability of presynaptic
membrane to Ca2+
¯
2. Ca2+ diffuse into synaptic terminal and
stimulates exocytosis of synaptic vesicles
¯
3. Synaptic vesicle release acetylcholine into
synaptic cleft through exocytosis
¯
4. The acetylcholine diffuse across synaptic cleft
and bindto specific receptor sites on gated Na+
channels on the sarcolemma
¯
5. Gated Na+ channels open and Na+ diffuse into
postsynaptic membrane to depolarize the motor
end plate
- action potential is generated when the
influx of Na+exceed the threshold level
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6. Action potential is transmitted along the
sarcolemma and move down the T-tubule
(transverse tubule ) of the muscle

¯
7. Action potential increases the permeability of

sarcoplasmic reticulum to Ca2+
¯

8. Ca2+ diffuse into sarcoplasm down
concentration gradient
¯

9. A specific enzyme will degrade the Neurotransmitter
- neurotransmitter unbind from the receptor
on gated Na+ channels
- results in, the closing of gated Na+ channels
- resting potential restored
Triggering action potentian in the muscle fibre
(to be continued in muscle
contraction)

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What happen NEXT ???
- At the sarcomere ??

MECHANISM OF MUSCLE CONTRACTION
BASED ON SLIDING FILAMENT THEORY.

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STRUCTURE OF SARCOMERE

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Label the structure of a Sarcomere

Sarcomere

Thin filament = actin

Thick filament = myosin

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I band – consist A band –constitute M line – centered
only actin filament myosin and actin of sarcomere
filaments overlaps

H zone -constitutes only Z line-
the myosin attachment of
thin filament
/centered of I
band

ACTIN (Thin filament) Consists of three types of protein:

a. Actin-

- Consist of 2 helical strands of actin
molecules intertwined with 2
accessory proteins
o Tropomyosin
o Troponin

b. Tropomyosin –

- Long thin strand
- Fits in the groove of the actin strands
- Covers the binding sites of myosin

heads

c. Troponin- attached to the tropomyosin
threads

- Positioned at regular intervals along
tropomyosin

- Has Ca2+ ion binding sites

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MYOSIN (Thick filament) - Consist of myosin protein molecules
- Lie parallel to each other
ACTIVATION OF ACTIN - Structure:

o Head
§ 2 globular structures
§ Extend away from the body

- of the myosin filament

§ At rest (not contracting),
§ ATP bound to the myosin
- Myosin has an adenosine triphosphatase
(ATPase)
o An enzyme that splits ATP forming
ADP and inorganic phosphate(Pi)
- Attach to specific sites on actin
o Operate like a ‘hook’ (cross bridge)

1.At rest, tropomyosin blocks the myosin attachment
to actin.

2. Upon stimulation by nerve impulse, Ca2+ are
released by sacroplasmic reticulum

3. The Ca2+ bind to the troponin complex ,troponin
change its conformation

troponin change its conformation
4. Tropomyosin move slidely & changes its
conformation

5. Myosin binding sites are exposed

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IMPULSE TRANSMISSION AT THE NEURO MUSCULAR JUNCTION

Mechanism of impulse transmission at
neuromuscular junction

Step 3
• Action potential is

propagated along
plasma membrane
and dow n T tubules

STEP 1 - Upon the arrival of an __action potential__ at the axon terminal,
- calcium channels _open___
- __Ca2+____ions flow from the extracellular fluid into the motor neurons.

STEP 2 - This cause neurotransmitter-containing vesicles to fuse to the motor neuron's
cell membrane and release ___acetylcholine_____ into the _postsynaptic
membrane__.

- This initiates an ___action potential___ in the muscle cell membrane.

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STEP 3 - ______Action potential__________ arrives at neuromuscular junction.
- The action potential propagated along the __sarcolemma_____, spread to

the T tubule, the sarcoplasmic reticulum causing voltage gated calcium
channel to open.

- Ca2+ diffuse into ____sarcoplasm_______.

STEP 4 - The Ca2+ bind to ____troponin______ molecules.

SLIDING FILAMENT THEORY

1

Thin filament

AT P

AT P 2

5 T hick
T hin fila m e nt m ove s filament
tow ard center of sarcomere.
Actin M yosin-
binding sites

Low -e ne rgy ADP H igh-e ne rgy
c onfigura t ion Pi c onfigura t ion

ADP C r o s s -b r i d g e 3
Pi
ADP P i
4

STEP 1

Myosin head is bound to ATP & is in low energy configuration

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Myosin head hydrolyzes ATP to ADP & inorganic phosphate & is
STEP 2 in high –energy configuration

STEP 3 Myosin head binds to actin, forming cross-bridge
STEP 4
STEP 5 Releasing ADP & inorganic phosphate, myosin returns to low-
energy configuration, sliding the thin filament

Binding of a new ATP releases / detach myosin head from actin &
new cycle begins.

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Mechanism of muscle contraction

During muscle relaxation….

The position of thick
filament /myosin remain
unchanged
The thin filament /actin
slides out to the original
position.
The muscle reverts to its
original size/relaxes.

-the actin filament move inwards towards the centre of the sarcomere making the
sarcomere SHORTEN

During muscle contraction….

The position and of thick
filament /myosin
remains unchanged
Thin filament /actin
slides in ,past one
another
Myofibril becomes
shorter & thicker

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What happen to the sarcomere
when the muscle contract?

i) Z lines:
-come close together as the
sarcomere shorten.

ii) M lines:
- do not change.
iii) H zone:
- shorten.
iv) I band:
-shorten.
v) A band:
-do not change in length.

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