The document discusses the muscular system, including the three types of muscles - skeletal, cardiac, and smooth muscles. It describes the microscopic anatomy of skeletal muscles and key functions such as muscle contraction. Some specific muscles are highlighted, like the masseter muscle for jaw closure. Effects of exercise like increased muscle size and strength are also summarized.

1. THE MUSCULAR SYSTEM

2. MUSCULAR SYSTEM_OBJECTIVES
By the end of the lesson, the student should be able to:
Describe the muscle and its functions
Mention and differentiate between the types of muscles
Explain the major events that occur during muscle fiber
contraction
Describe how exercise affects muscles
Explain how the locations of skeletal muscles help
produce movements and how muscles interact.

3. MUSCULAR SYSTEM
A system of muscles responsible for all types of body
movements.
They contract or shorten to stimulate movements and
hence, are regarded as the ‘machine’ of the body.
The prefixes ‘myo’ and ‘mys’ refer to muscle. For
example, cardiomyocyte - heart - muscle - cell.

4. TYPES OF MUSCLES
There are 3 basic muscle types:
Skeletal muscle
Cardiac muscle
Smooth muscle

5. SKELETAL MUSCLES
Skeletal muscles are striated (have visible banding)
They are subject to conscious control (vouluntary
movements)
Location: With the exception of some facial muscles
which attach to soft tissues (skin), all skeletal muscles
attach to bones directly by a tendon (or aponeurosis) or
indirectly to other connective tissue (cartilage).
Skeletal muscles create movement of bones and
facial skin by contractions

6. SKELETAL MUSCLES
Characteristics of skeletal muscle contraction include:
Voluntary regulation (only muscle type that is voluntary).
No rhythmic contraction
Has a rapid speed of contraction, with great force and tire
easily

7. COVERINGS OF SKELETAL MUSCLES
Endomysium - A thin connective tissue covering muscle
cell (fiber).
Perimysium - Coarser fibrous membrane covering
bundles of muscle fibers creating a fascicle. The fascicle
is a bundle of muscle fibers bound together by connective
tissue.
Epimysium - A tough fibrous connective tissue
surrounding many fascicles creating a skeletal muscle. It
is the outer covering of the entire skeletal muscle. It
blends into strong, cordlike tendons or into sheetlike
aponeurosis.

8. COVERINGS OF SKELETAL MUSCLES
Tendon - A cord of dense fibrous tissue attaching a muscle
to a bone.
 Tendons provide durability & conserve space.
 Tough collagenic fibers, can cross rough bony
projections (would tear muscles).
 Tendons have small size; therefore more tendons than
fleshy muscles can pass over a joint

9. SKELETAL MUSCLES

10. CARDIAC MUSCLES
Cardiac muscle cells are striated and involuntary i.e. do
not respond to conscious control.
Location: Only found in the walls of the heart.
Function: force movement of blood through heart
chambers to arteries.

11. CHARACTERISTICS OF CARDIAC MUSCLES
Contraction
1. Regulation: involuntary. Control of cardiac muscle
contraction is via heart “pacemaker” (for rhythmic
contractions), nervous system (for increased rate of
contractions for a short period) and the endocrine system
(hormones e.g. Epinephrine increases heart rate).
2. Speed: the speed of contraction of cardiac muscle is
slow and muscles do not tire easily
3. Rhythmic contractions

12. CHARACTERISTICS_CONT’D
Morphology
Cardiac muscles consist of branching chain of cells joined
together by intercalated discs. Cells are striated and
uninucleated (each cell has a single nucleus). Muscle
fibers are cushioned with soft connective tissue fibers
arranged in spiral or figure 8 shaped bundles which
enables heart activity to be closely coordinated.

13. SMOOTH MUSCLES
Location: Smooth muscles are found in walls of hollow
visceral organs including the stomach and the intestines,
urinary bladder, and respiratory passages. They are also
found in the walls of blood vessels.
Function: create movement of substances through a
tract or pathway.

14. CHARACTERISTICS OF SMOOTH MUSCLES
Contraction
Regulation: involuntary and control is via nervous system
(parasympathetic nervous system), endocrine system
(hormones e.g. Gastrin), chemicals (e.g. cholecystokinin),
and by mechanical stretching of the wall of the organ (e.g.
food in the stomach).
Speed: very slow & sustained. Smooth muscles do not
tire easily
Rhythmic contractions in some.

15. CHARACTERISTICS OF SMOOTH MUSCLES
Morphology
Smooth muscles consist of single cells that are fusiform in
shape (spindle shaped). Cells of smooth muscles are
nonstriated and uninucleated.
They are arranged in sheets or layers that run circularly
and longitudinally.
The layers alternatively contract & relax to;
change shape & size of organ
move substances through tract

16. FUNCTIONS OF MUSCLES
Producing movement
Maintaining posture (via skeletal muscles)
Stabilizing joints (pull of skeletal muscles on bones)
Generating heat - Heat is a byproduct of muscle activity.
75% of ATP energy creates heat (only 25% used to
contract muscle). In all the muscles account for about
85% of the total body heat.

17. Functional Characteristics of Muscles
Excitability (or Irritability): ability to receive and respond to
stimuli
Contractility: ability to shorten forcibly
Extensibility: ability to be stretched or extended beyond
resting length
Elasticity: ability to resume resting length after stretching

18. MICROSCOPIC ANATOMY OF THE SKELETAL MUSCLE
Skeletal muscles are made of single individual cells
known as the myofiber (muscle cell).
Myofibrils: Contractile elements of muscle cells; each
cell consists of thousands of myofibrils.
Sarcomere: Smallest contractile unit of a fiber

19. PARTS OF A MYOFIBER
Sarcolemma- muscle cell plasma membrane.
Sarcoplasm: cytoplasm of muscle cell with large
amounts of glycogen and myoglobin
Myoglobin: red pigmented oxygen-binding protein
Sarcoplasmic reticulum: Endoplasmic reticulum of
muscle cell and stores calcium for contraction.
T (transverse) – tubules: Continuations of the
sarcolemma invaginating into fiber. Located at A and I
band junction and encircle sarcomere. Conduct nerve
impulses to interior of muscle fiber.

20. ASSIGNMENT
Stimulation and contraction of skeletal muscles
Types of muscle contraction: isometric, isotonic, etc.
Body movements: flexion, extension, etc.

21. EFFECTS OF EXERCISE ON MUSCLES
Results of increased muscle use include;
 Increase in muscle size
 Increase in muscle strength
 Increase in muscle efficiency
 Muscle becomes more fatigue resistant

22. FUNCTIONS OF SOME MUSCLES
Buccinator- holds food between teeth during chewing,
considered a “chewing” & facial muscle; also flattens the
cheek
Masseter- prime mover of jaw closure
Origin- zygomatic process of temporal bone & maxilla
Insertion- mandible
Action- closes jaw by elevating the mandible
Temporalis- fan shaped muscle covering temporal bone
 Origin- temporal lines of skull

23. FUNCTIONS OF SOME MUSCLES
Zygomaticus - “smiling” muscle
Frontalis - covers the frontal bone
Origin- cranial aponeurosis
Insertion- skin of eyebrows
Action- raises eyebrows, wrinkles forehead; forms the
horizontal frown crease on the forehead
Orbicularis Oculi- fibers run in circles around eyes
Origin- frontal bone & maxilla inserts to medial side of orbit
(tissue around eye)
Action- closes eye; squinting, blinking, & winking the eyes

24. FUNCTIONS OF SOME MUSCLES
Orbicularis Oris - circular muscles of lips
Origin- maxilla & mandible
Insertion- skin & muscle around lips
Action- closes, compresses & protrudes lips “kissing muscle”
Platysma - single sheetlike muscle that covers anterior
lateral neck.
Action- pull corners of mouth inferiorly (downward sag of
mouth), tenses skin of neck & depresses mandible.
Sternocleidomastoid - paired muscles (one on each
side of the neck) “prayer muscle”

25. FUNCTIONS OF SOME MUSCLES
The sternocleidomastoid muscle is two headed (sternum &
clavicle).
Origin - sternum & clavicle
Action - prime mover of head flexion (when the 2 pairs contract
together), single muscle contraction: head is rotated toward
opposite side.
Trapezius - most superficial posterior neck muscle
Action- depends on active region and state of other muscles,
extends neck and head, antagonist of sternocleidomastoids,
may elevate, adduct, depress, or rotated scapula, elevate
clavicle hyperextend neck to “look at the sky”, elevate & or pull
back shoulder “shrugging”.

26. Muscles of the trunk
Intercostal Muscles
 Action: external intercostals elevate rib cage during inspiration,
Internal intercostals: depress rib cage during expiration
Diaphragm - “breathing muscle”.
action - flattens to enlarge chest cavity for inhalation
Pectoralis Major- anterior large fan-shaped muscle
covering the upper chest, forms anterior axilla wall
Action- adducts, flexes & medial rotation of humerus at
shoulder joint, prime mover for shoulder flexion and adduction

27. Developmental Aspects of the Muscular System
Embryonic Development: Maturation of Muscle Control
 Cephalic to caudal direction.
 Proximal to distal direction- gross motor skills first and fine
motor skills last
Aging Effects:
 Hypertrophy- increase in connective tissue
 Atrophy- decrease in muscle tissue
 Muscles become stringier, more sinewy
 There is also decrease in muscle strength