Unit III – The Muscular System - Anatomy Types and structure of muscles Muscle groups Alterations in disease Applications and implications in nursing Muscle: Muscle is a soft tissue and it is one of the 4 basic tissues, along with nervous tissue, epithelium, and connective tissue. Muscles helps in movement, support and protection of internal organs. Muscles can perform variety of functions Muscles tissue is made up of cells called “MYOCYTES” or muscle fibers. There are more than 600 muscles in the human body. A kind of elastic tissue makes up each muscle, which consists of thousands, or tens of thousands, of small muscle fibers. Types of Muscles: There are 3 main types of muscles Skeletal muscle Cardiac muscle Smooth muscle Skeletal muscle: These are having close relationship to the bone or skeleton, so called Skeletal muscles It present in limbs and related body parts & It form about 40% of body weight. Under microscope the skeletal muscles fibers shows prominent striations, so called “Striated Muscles” & It is also known as “Voluntary Muscles” (movements are under our control) Structure of Skeletal muscle: Muscle fibers shows transverse striations under light microscope so it is called “striated muscles” The nucleus is located peripherally. Each skeletal muscle is an organ that consists of numerous cells called muscle fibers. Each muscle fibers surrounded by “ Endomysium” Inside each skeletal muscle, muscle fibers are organized into bundles, called fascicles, each fascicle surrounded by perimysium. The whole muscle is covered by “epimysium” Each skeletal muscle has three layers: endomysium, perimysium and epimysium Muscle fibers: Muscle is composed of many long cylindrical-shaped elongated fibres called muscle fibers Length varies according to the size and shape of the muscles. The actual arrangement of the fibres depending on the function of the muscle. Each muscle fibers covered by a membrane is called the sarcolemma. The cytoplasm of a muscle fiber is called Sarcoplasm  In sarcoplasm there are many mitochondria and bundles of fine longitudinal thread like part is called “myofibrils” Microscopic structure of myofibrils: A myofibril (also known as a muscle fibril or sarcostyle) is a basic rod-like part of a muscle cell. Muscles are composed of tubular cells called myocytes, known as muscle fibres in striated muscle, and these cells in turn contain many chains of myofibrils. They are created during embryonic development in a process known as myogenesis. Under light microscope each myofibril consist of 2 bands: Light band or “I” Band and Dark band or “A” Band The alternating pattern of these bands results in the striated appearance of skeletal muscle. Light band or “I” Band: The I-bands (isotropic in polarized light) appear light in color. I band divided into 2 portions by a narrow dark line called “Z” line or “Z” Disc. This “Z” line is formed by protein which does not permit the light. The part in between 2 “Z” lines called “sarc

2. Unit III – The Muscular
System - Anatomy
Types and structure of muscles
Muscle groups
Alterations in disease
Applications and implications in nursing

3. Muscle:
• Muscle is a soft tissue and it is one of the 4 basic tissues, along
with nervous tissue, epithelium, and connective tissue.
• Muscles helps in movement, support and protection of internal
organs.
• Muscles can perform variety of functions
• Muscles tissue is made up of cells called “MYOCYTES” or muscle
fibers.
• There are more than 600 muscles in the human body. A kind of
elastic tissue makes up each muscle, which consists of thousands, or
tens of thousands, of small muscle fibers.

4. Types of Muscles: There are 3 main types of muscles
1. Skeletal muscle
2. Cardiac muscle
3. Smooth muscle
Skeletal muscle:
• These are having close relationship to the bone or skeleton, so called
Skeletal muscles
• It present in limbs and related body parts & It form about 40% of body
weight.
• Under microscope the skeletal muscles fibers shows prominent striations,
so called “Striated Muscles” & It is also known as “Voluntary
Muscles” (movements are under our control)

5. Structure of Skeletal muscle:
• Muscle fibers shows transverse striations under light microscope so it
is called “striated muscles”
• The nucleus is located peripherally.
• Each skeletal muscle is an organ that consists of numerous cells
called muscle fibers.
• Each muscle fibers surrounded by “ Endomysium”
• Inside each skeletal muscle, muscle fibers are organized into bundles,
called fascicles, each fascicle surrounded by perimysium.
• The whole muscle is covered by “epimysium”
• Each skeletal muscle has three layers: endomysium, perimysium and
epimysium

7. Muscle fibers:
Muscle is composed of many long cylindrical-shaped
elongated fibres called muscle fibers
Length varies according to the size and shape of the muscles.
The actual arrangement of the fibres depending on the function
of the muscle.
Each muscle fibers covered by a membrane is called the
sarcolemma.
The cytoplasm of a muscle fiber is called Sarcoplasm
In sarcoplasm there are many mitochondria and bundles of fine
longitudinal thread like part is called “myofibrils”

9. • Microscopic structure of myofibrils:
• A myofibril (also known as a muscle fibril or sarcostyle) is a basic
rod-like part of a muscle cell.
• Muscles are composed of tubular cells called myocytes, known as
muscle fibres in striated muscle, and these cells in turn contain many
chains of myofibrils.
• They are created during embryonic development in a process known
as myogenesis.
• Under light microscope each myofibril consist of 2 bands:
• Light band or “I” Band and Dark band or “A” Band
• The alternating pattern of these bands results in the striated appearance
of skeletal muscle.

11. Light band or “I” Band:
• The I-bands (isotropic in polarized light) appear light in color.
• I band divided into 2 portions by a narrow dark line called “Z”
line or “Z” Disc.
• This “Z” line is formed by protein which does not permit the light.
• The part in between 2 “Z” lines called “sarcomere”
Dark band or “A” Band:
• the A-bands (anisotropic in polarized light) appear dark in color.
• In the middle of “A” band there is a light area called “H” Zone.
• In the middle of “H” Zone a part is called “M” Line or “M” Band
which is formed by Myosin Protein.

12. Sarcomere: In “I” band, the part in between 2 “Z” lines called
“sarcomere”
• Sarcomere is the structural and functional units of muscle fibers.
• When a muscle is contract, the “Z” line move close together and length of
each sarcomere is decreased.

13. Contractile elements of muscle: Myofibrils are the contractile units of
muscle fibers.
• Myofibrils are composed of smaller structures called myofilaments.
• There are two main types of myofilaments: thick filaments & thin
filaments.
• Thick filaments are composed of the protein myosin & thin – actin protein
• Muscle contraction occurs due to the interaction between the Myosin and
Actin proteins.

14. Sarcoplasmic reticulum (SR):
• The sarcoplasmic reticulum (SR) is a membrane-bound structure found
within muscle cells that is similar to the smooth endoplasmic reticulum in
other cells.
• The main function of the SR is to store and regulate calcium level
• The sarcoplasmic reticulum is a network of tubules that extend
throughout muscle cells.
• Transverse tubules (T-tubules) which are extensions of the sarcoplasm that
travel into the centre of the cell.it pass at the junction between “A” & “I”
bands.
• The part of SR on both side of “T” tubules form a sac like dilatations called
“Terminal Cisternae” or “L” tubules.
• “L” tubules release and store calcium during muscle contraction & relaxation.
• 2 “L” tubules & 1 “T” tubule form a “triad” at A – I Junction.

16. Innervation of skeletal muscles:
• Meaning of innervation: the process of supplying nerve to the organ or
part or tissue
• Each skeletal muscle is supplied by one or more nerves contain both
sensory and motor nerves.
• After entering into muscle, the nerve divided into branches for supplying
muscle fibers.
• A motor neuron & the muscle fiber innervated by “motor unit”
• The number of muscle fibers in a motor unit differs depends on the
function of muscle.
• In a muscle which has to perform very precise movements, a motor units
has very few fibers (Ex – Extrinsic muscle of eye)
• But in limb muscle, a motor unit has many - 500 fibers bcz of heavy and
more movements.

18. •Neuromuscular junction (NMJ) or myoneural
junction is a chemical synapse between a motor
neuron and a muscle fiber.
•It allows the motor neuron to transmit a signal to the
muscle fiber, causing muscle contraction.
•End part of nerve is called “Axon terminal”
•When axon comes close to the muscle fiber it loses the
“myelin sheath”, so the axis cylinder is exposed.(naked
axon)
•The axon part of neuron contact with muscle fibers

19. •The axon terminal part of neuron expand like a bulb
called “motor end plate”
•The motor end plate enter inside the muscle fibers and
form a depression
•The membrane of the muscle fiber below the motor end
plate is called “post synaptic membrane”
•The membrane of the nerve ending called “pre synaptic
membrane”
•The space between “post synaptic membrane” and “pre
synaptic membrane” is called “synaptic cleft”

21. • Mechanism of Muscle contraction or Neuro muscular
transmission for muscle contraction:
• Definition: it is defined as the process of transferring the information
from motor nerve ending to the muscle fibers through NMJ.
• It is the mechanism by which the motor nerve impulses initiate muscle
contraction.
• A series of events takes place during this process.
• Resting membrane potential: The membrane potential of a neuron at
rest—that is, a neuron not currently receiving or sending messages is
negative, typically around -70 millivolts (mV), This is called the resting
membrane potential.
• Action potential: Action potentials (those electrical impulses that send
signals around your body) are nothing more than a temporary shift (from
negative to positive) in the neuron that stimulate the muscle to contract.

22. Process of Muscle Contraction
When action potential reaches the nerve terminal, the pre
synaptic membrane become highly permeable to Ca+
The large amount of Ca+ enter into synaptic cleft
This Ca+ causes release of Acetylcholine into Synaptic Cleft
The Acetylcholine binds with nicotinic receptors (present in Post
Synaptic membrane), which initiates the muscle contraction
Once action potential is over, Acetylcholine is destroyed by Enz
called “Acetyl cholinesterase”

23. Types of muscle contraction:
• Isotonic contractions: maintain constant force or tone in
the muscle as the muscle length changes.
Concentric contraction: In concentric contraction, muscle
tension is sufficient to overcome the load, and the muscle
shortens as it contracts.
Eccentric contraction: In eccentric contraction, the
tension generated is insufficient to overcome the external load on
the muscle and the muscle fibers lengthen as they contract.
• Isometric contractions: changes in force without
changing the length of the muscle

25. Muscle tone:
• It is defined as the tension in a muscle at rest. Muscle tone is the
amount of tension (or resistance to movement) in muscles.
• Our muscle tone helps us to hold our bodies upright when we are sitting
and standing to maintain posture.
• Changes in muscle tone are what enable us to move.
• Muscle tone also contributes to the control, speed and amount of
movement we can achieve.
• Muscles with high tone are not necessarily strong and muscles with low
tone are not necessarily weak.
• In general, low tone does increase flexibility and decrease strength(dance
& yoga) and high tone does decrease flexibility and increase
strength(athletes).

26. Maintenance of Muscle tone:
• In skeletal muscle: Neurogenic, due to continuous discharge of
impulses from neuron – brain.
• In cardiac muscle: Myogenic, muscle themselves control the tone not
under the control of brain.
• In smooth muscle: myogenic, depends upon the calcium level.
• Muscle tone abnormalities:
• Hypertonia: increased muscle tone
• Hypotonia: decreased muscle tone
• Muscle fatigue: it is decrease in muscle performance due to repeated
stimuli, when the stimuli are applied continuously, after some time the
muscle does not show any response to the stimulus.

27. Types of skeletal muscle fibers:
According to the speed of activity there are 2 types of skeletal muscle fibers,
1. Slow twitch or Type – I or Red muscle fibers ( Gastrocnemius)
2. Fast twitch or Type – II or White muscle fibers (Extra ocular & Hand)
• Difference between slow and fast twitch muscles:
Features Type - I Type - I
Myoglobin content Decreased Increased
Speed of response Slow Fast
Duration of contraction Long Short
Myosin activity Slow Fast
Ca pumping Moderate High

28. Function of skeletal muscles:
• Body movement (locomotion): skeletal muscles enable humans
to move and perform daily activities.
• They play an essential role in respiratory mechanism
• Help in maintaining posture and balance.
• They also protect the vital organs in the body.
• Involve in Communication (verbal and facial)
• Production of body heat (thermogenesis)
• Helping Chewing and swallowing
• Playing essential role in Formation and protection of joints
• Skeletal muscle Stores some nutrients

29. Cardiac muscle:
• Also called heart muscle or myocardium
• Cardiac muscle forms the contractile walls of the heart.
• The cells known as Cardiomyocytes, also appear
striated under the microscope. So called “striated”
muscles
• Cardiac muscle movements are not in our control so it is
called “involuntary” muscle.
• Cardiac muscle is responsible for the ability of the heart to
pump blood.

30. Structure of cardiac muscle:
• It is composed of individual cardiac muscle cells joined
together by intercalated discs.
• The cardiac muscle (myocardium) forms a thick middle layer
between the outer layer of the heart wall (the pericardium) and
the inner layer (the endocardium)
• Cardiac muscle cells are single cells typically with a single
centrally located nucleus.
• It consist of there are several sheets of cardiac muscle cells or
Cardiomyocytes
• Contraction of this muscle help the heart to contract & relax.

31. Cardiac muscle

32. Contraction of Cardiac muscle:
 It consist Specialized modified Cardiomyocytes known as pacemaker
cells.
 Cardiac pacemaker cells carry the impulses that are responsible for the
beating of the heart.
 They are distributed throughout the heart and are responsible for
generating and conducting electrical impulses to contract and relax. .
• The pacemaker cells control heart rate and determine how fast the
heart pumps blood.
• Cardiac muscle also contains specialized cells known as Purkinje
fibers for the rapid conduction of electrical signals.
 They contract on their own intrinsic rhythms without any external
stimulation.

34. Features Skeletal muscles Cardiac muscle
Myofibrils Yes Yes
Striations Yes Yes
Capillary network Yes Yes
Actin & Myosin Yes Yes
A & I band Yes Yes
Similarities between skeletal and cardiac muscle:

35. Difference between skeletal and cardiac muscle:
Features Skeletal muscles Cardiac muscle
Location: Bone Heart
Nucleus Peripheral Central
Cell type: Multi nucleated Uninucleated
Shape of cells: Bundles Branched
Intercalated disc No Yes
Control: Voluntary Involuntary
Contraction: Neurogenic contraction Conductive system
Length : Longer Short
Function: Movements Pumping of blood

36. Function of Cardiac muscle
Rapid, involuntary contraction and relaxation of the cardiac
muscle are vital for pumping blood throughout the
cardiovascular system.
It maintain Bp within blood vessels

37. Smooth muscle:
• Smooth muscle is responsible for involuntary movements
in the internal organs.
• Smooth muscle is an involuntary non-striated muscle, so-
called because it has no sarcomeres and therefore
no striations.
• It is divided into two subgroups, single-unit and multiunit
smooth muscle.
• It forms the contractile parts of the digestive, urinary, and
reproductive systems as well as the airways and arteries.

38. Smooth Muscle Structure:
• Spindle shaped cells, Single nucleus and no visible striations
• This is because smooth muscle cells are organized in a different
way than other muscle cells & It can tense and relax.
• There are no myofibrils present but much of the cytoplasm is taken
up by the proteins of myosin and actin.

39. Arrangement of smooth muscles:
• Smooth muscle fibers may be arranged in different way.
• In some organ (Intestine), S.M arranged in the form of 2
layers: inner - circular & outer - longitudinal.
• In Ureters, inner - longitudinal & outer - circular
• In urinary bladder - 3 layers; inner: longitudinal,
middle: circular & outer: longitudinal.
• In uterus arranged in layer not differ from each others.
• In some tubes (bile duct) arranged as “Sphincter”
• In skin & some parts S.M occurs in the form of narrow
bands.

40. Contraction of smooth muscle:
• Smooth muscle contraction is caused by the sliding
of myosin and actin filaments (a sliding filament
mechanism) over each other.
• Smooth muscle-containing tissue needs to be stretched
often, so elasticity is an important attribute of smooth
muscle.
• Single-unit smooth muscle consists of multiple cells
connected through connexins (gap junction protein) that
can become stimulated in a synchronous pattern from
only one synaptic input.

41. •Connexins allow for cell-to-cell communication between
groups of single-unit smooth muscle cells.
•This intercellular communication allows ions and
molecules to diffuse between cells giving rise to calcium
waves.
•This unique property of single-unit smooth muscle allows
for synchronous contraction to occur.
•Multi-unit smooth muscle, each smooth-muscle cell
receives its own synaptic input, allowing for the multi-unit
smooth muscle to have much finer control to contract.

42. Location of smooth muscle:
• Smooth muscle is found in:
• In the walls of hollow organs, including the stomach, intestine,
bladder and uterus,
• In the walls of passageways, such as blood, and lymph vessels,
• In the tracts of the respiratory, urinary, and
reproductive systems.
• In the eyes, the ciliary muscle, a type of smooth muscle, dilate
and contract the iris and alter the shape of the lens.
• In the skin, smooth muscle cells such as those of the arrector
pili cause hair to stand erect in response to cold temperature
or fear.

43. Functions of Smooth Muscle:
• Gastrointestinal tract - propulsion of the food bolus
• Cardiovascular - regulation of blood flow and pressure
• Renal - regulation of urine flow
• Genital - contractions during pregnancy, propulsion of sperm
• Respiratory tract - regulation of breathing
• Integument - raises hair with erector pili muscle
• Sensory - dilation & constriction of the pupil, changing lens shape
• Reproductive functions