The document discusses the neuromuscular junction and muscle contraction physiology. It defines the neuromuscular junction as the connection between motor neurons and muscle fibers that initiates muscle contraction. The structure and function of the neuromuscular junction is described, including the roles of acetylcholine, receptors, and acetylcholinesterase. The sliding filament model of muscle contraction is introduced. Different muscle fiber types, properties of muscle tissue, and the sarcomere as the contractile unit are defined.

1. Neuromuscular Junction (NMJ)
&
Physiology of Muscle Contraction
Dr. Pandian M
Assistant Professor
Dept. of Physiology
ZMCH, Dahod.

2. Definition & Structure
• DEFINITION
Neuromuscular (or myoneural) junction is the
junction between motor nerve and skeletal
muscle fiber by which the motor nerve
impulses initiate muscle contraction

3. Structure
Longitudinal section of neuromuscular junction

5. Structure
1. Skeletal muscle fibers are innervated by the motor
nerve fibers.
2. Each nerve fiber (axon) divides into many terminal
branches.
3. Each terminal branch innervates one muscle fiber
through the neuromuscular junction.
4. Axon terminal contains mitochondria and
synaptic vesicles.
5. This synaptic vesicles contains neurotransmetter
substance, acetylcholine (Ach).

6. Structure of neuromuscular junction

7. Synaptic Cleft
a. Membrane of the nerve ending is called the
presynaptic membrane.
b. Membrane of the muscle fiber is called
postsynaptic membrane. Here the receptors
are present its called nicotinic acetylcholine
receptors.
c. Space between these two membranes is
called synaptic cleft.
d. Synaptic cleft contains basal lamina
e. An enzyme called acetylcholinesterase
(AchE) is attached to basal lamina

8. Events of Neuromuscular Transmission
A series of events take place in the neuromuscular
junction.
The events are:
1. Release of acetylcholine
2. Action of acetylcholine
3. Development of endplate potential
4. Development of miniature endplate potential
5. Destruction of acetylcholine.

9. Function of Neuromuscular Junction

11. Significance of Endplate Potential
• Endplate potential is non-propagative. But it causes
the development of action potential in the muscle
fiber.

13. NEUROMUSCULAR BLOCKERS
1. Neuromuscular blockers are the drugs, which
prevent transmission of impulses from nerve
fiber to the muscle fiber through the
neuromuscular junctions.
2. These drugs are used widely during surgery and
trauma care.
3. Neuromuscular blockers used during anesthesia
relax the skeletal muscles and
4. induce paralysis so that surgery can be
conducted with less complication.

14. Following are important neuromuscular blockers,
which are commonly used in clinics and research.
1. Curare
• Curare prevents the neuromuscular transmission
by combining with acetylcholine receptors.
2. Bungarotoxin
• Bungarotoxin is a toxin from the venom of deadly
snakes. It affects the neuromuscular transmission
by blocking the acetylcholine receptors.
3. Succinylcholine and Carbamylcholine
4. Botulinum Toxin

15. Physiology of Muscle Contraction

16. Muscular System Functions
• Body movement
• Maintenance of posture
• Respiration
• Production of body heat
• Communication
• Constriction of organs and vessels
• Heart beat

17. Muscle Tissue Types
• Skeletal
– Attached to bones
– Nuclei multiple and peripherally located
– Striated, Voluntary and involuntary (reflexes)
• Smooth
– Walls of hollow organs, blood vessels, eye, glands, skin
– Single nucleus centrally located
– Not striated, involuntary, gap junctions in visceral smooth
• Cardiac
– Heart
– Single nucleus centrally located
– Striations, involuntary, intercalated disks

18. Properties of Muscle
• Excitability: capacity of muscle to respond to
a stimulus
• Contractility: ability of a muscle to shorten
and generate pulling force
• Extensibility: muscle can be stretched back to
its original length
• Elasticity: ability of muscle to recoil to
original resting length after stretched

19. Organization II:

21. SARCOMERE
Definition
Sarcomere is defined as the structural and functional
unit of a skeletal muscle. It is also called the basic
contractile unit of the muscle.

22. Types of Muscle Contractions
• Isometric: No change in length but tension increases
– Postural muscles of body
• Isotonic: Change in length but tension constant
• Muscle tone: Constant tension by muscles for long
periods of time

24. Cross-bridge formation:

25. Sarcomere Shortening

26. Sliding filament model :

27. Sliding
mechanism

29. Excitation
contraction
coupling

30. Events for muscle relaxation

31. Red (slow) muscle Pale (fast) muscle
Myoglobin content is high. So, it
is red
Myoglobin content is less. So, it
is pale
Blood vessels are more extensive Blood vessels are less extensive
Contraction is less powerful Contraction is more powerful
Fatigue occurs slowly Fatigue occurs quickly
Mitochondria are more in
number
Mitochondria are less in
number

32. Cardiac muscle

33. Smooth Muscle
• Characteristics
– Not striated
– Dense bodies instead
of Z disks as in skeletal
muscle
• Have noncontractile
intermediate filaments
– Ca2+ required to
initiate contractions
• Types
– Visceral or unitary
• Function as a unit
– Multiunit
• Cells or groups of cells
act as independent
units

34. Unstripped or smooth or involuntary muscle

35. Unstripped or involuntary muscle
• Present in –
1. Walls of hollow tubular & saccular
viscera,
2. Ducts of exocrine glands
3. Blood vessels
4. Tracheobronchial tree
5. Stroma of solid organs
6. Iris
7. Cilliary body
8. Arrectores pilorum
9. Sweat glands of skin

36. Features of skeletal, cardiac and smooth muscle fibers
Features Skeletal muscle Cardiac muscle Smooth muscle
Location In association
with bones
In the heart In the visceral
organs
Sarcomere Present Present Absent
Fatigue Possible Not possible Not possible
Action Voluntary
action
Involuntary
action
Involuntary
action
Nerve supply Somatic nerves Autonomic
nerves
Autonomic
nerves
Speed of
contraction
Fast Intermediate Slow
Number of
nucleus
More than one One One