Module 5: Muscular System

Electrical excitability

- ability to respond to certain stimuli by producing electrical signals called action potentials

Autorhythmic electrical signals

- arising in the muscular tissue itself, as in the heart’s pacemaker

Chemical stimuli

- neurotransmitters released by neurons, hormones distributed by the blood, or even
local changes in pH

Contractility

- ability of muscular tissue to contract forcefully when stimulated by an action potential

Extensibility

- ability to stretch without being damaged

Elasticity

- ability of muscular tissue to return to its original length and shape after contraction or
extension

SKELETAL MUSCLE

- consists of long cylindrical fibers with many peripherally located nuclei and striations

Hypodermis

- Connects the skin to the muscle fibers
- serves as an insulating layer that reduces heat loss, and protects muscles from
physical trauma

Fascia

- dense sheet or broad band of irregular connective tissue
- supports and surrounds muscles and other organs of the body
- holds muscles with similar functions together
- allows free movement of muscles, carries nerves, blood vessels, and lymphatic
vessels, and fills spaces between muscles

Epimysium

- Dense irregular connective tissue
- extend from the fascia to protect and strengthen skeletal muscle
- outermost layer, encircling the entire muscle

Perimysium

- Dense irregular connective tissue
- surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles

Endomysium

- thin sheath of areolar connective tissue
- Penetrates the interior of each fascicle
- Separates individual muscle fibers from one
another

Tendons

- cord of dense regular connective tissue and
parallel bundles of collagen fibers
- attach a muscle to the periosteum of a bone

Blood Vessels

* Supplies blood to the muscle fibers
* Bring in oxygen and nutrients and remove heat and the waste products of muscle metabolism

Somatic Motor Neurons

- Stimulate skeletal muscle to contract
- Acetylcholine

Sarcolemma

- The plasma membrane of a muscle cell

Transverse Tubules

- tiny invaginations of thesarcolemma
- ensures that an action potential excites all parts of the muscle fiber at essentially the same instant

Sarcoplasm

- cytoplasm of a muscle fiber
- glycogen – used for synthesis of ATP
myoglobin

Myofibrils

- Thread-like structures
- the contractile organelles of skeletal muscle
- causes the striations

Sarcoplasmic Reticulum

- fluid-filled system of membranous sacs
- encircles each myofibril
- stores calcium ions (relaxed)
- releases stored calcium ion (muscle contraction)

Filaments

- Smaller structures within myofibrils
- Consists of thin and thick filaments
- Do not extend on the entire length of muscle fiber

Sarcomeres

structure that compartmentalizes the thin and thick filaments

Z-Disc

narrow, plate-shaped regions of dense protein material which separates
one sarcomere from the next

A Band

the dark, middle part of the sarcomere that extends the entire length of the thick filaments and also includes those parts of the thin filaments that overlap with the thick filaments.

I Band

The lighter, less dense area of the sarcomere that contains the rest of the thin filaments but no thick filaments. A Z disc passes through the center of each I band.

H-Zone

A narrow region in the center of each A band that contains thick filaments but no thin filaments.

M line

A region in the center of
the H zone that contains proteins that hold the thick filaments together at the center of the
sarcomere.

Contractile proteins

- generate force during contraction
actin

myosin

located in the center and makes up the thick filament.
Regulatory proteins

Structural proteins

- keep the thick and thin filaments in the proper alignment
- give the myofibril elasticity and extensibility, and link the myofibrils to the sarcolemma and extracellular matrix

sliding filament mechanism

is a fundamental process that occurs in muscle
contraction.

CARDIAC MUSCLE TISSUE

- Composed of branched cylindrical fibers with one centrally located nuclei
- Has striations and intercalated discs that joins adjacent fibers
- principal tissue in the heart wall intercalated discs
- unique to cardiac muscle fiber
- irregular transverse thickenings of the sarcolemma

caveolae

small pouch like invaginations of
the plasma membrane that contain extracellular calcium ions

Origin

the attachment of a muscle’s tendon to the stationary bone

Insertion

the attachment of the muscle’s other tendon to the movable bone

Orbicularis oris

Closes and protrudes lips, as in kissing; compresses lips against teeth;
shapes lips during speech.

Zygomaticus major

Draws angle of mouth superiorly and laterally, as in smiling.

Zygomaticus minor

Raises (elevates) upper lip, exposing maxillary (upper) teeth.

Levator labii superioris

Raises upper lip.

Depressor labii inferioris

Depresses (lowers) lower lip.

Depressor anguli oris

Draws angle of mouth laterally and inferiorly, as in opening mouth.

Levator anguli oris

Skin of lower lip and orbicularis oris.

Buccinator

Orbicularis oris.

Risorius

Skin at angle of mouth.

Mentalis

Skin of chin.

Platysma

Mandible, muscle around angle of mouth, and skin of lower face.

Orbicularis oculi

Circular path around orbit.

Corrugator supercilia

Skin of eyebrow.

superior and inferior recti - move the eyeballs superiorly and inferiorly

lateral and medial recti

move the eyeballs laterally and medially

Superior b

moves the eyeballs inferiorly and laterally

Inferior Oblique

moves the eyeballs superiorly and laterally

Levator palpebrae superioris

does not move the eyeballs, it raises the upper eyelids, that is, opens the eyes

Masseter

Elevates mandible, as in closing mouth.

Temporalis

Elevates and retracts mandible.

Medial pterygoid

Elevates and protracts (protrudes) mandible and moves mandible from side to side.

Lateral pterygoid

Protracts mandible, depresses mandible as in opening mouth and
moves mandible from side to side.

Extrinsic tongue muscles

originate outside the tongue and insert into it, they move the
entire tongue in various directions, such as anteriorly posteriorly, and laterally.

genioglossus

pulls the tongue downward and forward

styloglossus

pulls the tongue upward and backward

hyoglossus

pulls the tongue downward and flattens it

palatoglossus

raises the back portion of the tongue

Intrinsic tongue muscles

originate and insert within the tongue, these muscles alter the
shape of the tongue rather than moving the entire tongue.

suprahyoid muscles

located superior to the hyoid bone

digastric

elevates the hyoid bone and larynx (voice box) during swallowing and speech and depresses the mandible

stylohyoid

elevates and draws the hyoid bone posteriorly, thus elongating the floor of the oral cavity during swallowing

mylohyoid

elevates the hyoid bone and helps press the tongue against the roof of the
oral cavity during swallowing to move food from the oral cavity into the throat

geniohyoid

elevates and draws the hyoid bone anteriorly to shorten the floor of the oral
cavity and to widen the throat to receive food that is being swallowed, it also depresses
the mandible

infrahyoid muscles

named for their position inferior to the hyoid bone

omohyoid

- depress the hyoid bone

sternohyoid

- depress the hyoid bone

sternothyroid

- depresses the thyroid cartilage of the larynx

thyrohyoid

elevates thyroid cartilage and
depresses the hyoid bone

Sternocleidomastoid

Acting together (bilaterally), flex cervical portion of vertebral column, flex head, and elevate sternum during forced inhalation; acting singly (unilaterally), laterally rotate and flex head to side opposite contracting muscle. The posterior fibers of the muscle can assist in extension of the head.

Semispinalis capitis

Acting together, extend head; acting singly, rotate head to side
opposite contracting muscle.

Splenius capitis

Acting together, extend head; acting singly, laterally flex and rotate head to same side as contracting muscle.

Longissimus capitis

Acting together, extend head; acting singly, laterally flex and rotate head to same side as contracting muscle.

Rectus abdominis

Flexes vertebral column,
especially lumbar portion, and compresses
abdomen to aid in defecation, urination, forced exhalation, and childbirth.

External oblique

- Acting together (bilaterally), compress abdomen and flex vertebral column; acting singly (unilaterally), laterally flex vertebral column, especially lumbar portion, and rotate vertebral column.

Internal oblique

- Acting together, compress
abdomen and flex vertebral column; acting singly, laterally flex vertebral column, especially lumbar portion, and rotate vertebral column.

Transversus abdominis

- Compresses abdomen.
Quadratus lumborum

Diaphragm

- Contraction of the diaphragm
causes it to flatten and increases the vertical
dimension of the thoracic cavity, resulting in
inhalation; relaxation of the diaphragm causes it to move superiorly and decreases the vertical dimension of the thoracic cavity, resulting in exhalation.

External intercostals

Contraction elevates the ribs and increases the anteroposterior and lateral dimensions of the thoracic cavity, resulting in inhalation; relaxation depresses the ribs and decreases the anteroposterior and lateral dimensions of the thoracic cavity, resulting in exhalation.

Internal intercostals

Contraction draws
adjacent ribs together to further decrease the
anteroposterior and lateral dimensions of the
thoracic cavity during forced exhalation.

Levator ani

Supports and maintains position of pelvic viscera; resists increase in intra-abdominal pressure during forced exhalation,
coughing, vomiting, urination, and defecation; constricts anus, urethra, and vagina.

Ischiococcygeus

Supports and maintains position of pelvic viscera; resists increase in intra- abdominal pressure during forced exhalation, coughing, vomiting, urination, and
defecation; and pulls coccyx anteriorly following defecation or childbirth.
Superficial transverse perineal

Bulbospongiosus

- Helps expel urine during urination, helps propel semen along urethra, assists in erection of the penis in male; constricts vaginal orifice and assists in erection of clitoris in female.

Ischiocavernosus

- Maintains
erection of penis in male and clitoris in female by decreasing venous drainage.

Deep transverse perineal

- Helps expel last drops of urine and semen in male.

External urethral sphincter

- Helps expel last drops of urine and semen in male and urine in
female.

Compressor urethrae

- Serves as an accessory sphincter of the urethra.

Sphincter urethrovaginalis

- Serves as an accessory sphincter of the urethra and facilitates closing of the vagina.

External anal sphincter

- Keeps anal canal and anus closed.

Subclavius

- Depresses and moves clavicle anteriorly and helps stabilize pectoral girdle.

Pectoralis minor

- Abducts scapula and rotates it downward; elevates third through fifth ribs during forced inhalation when scapula is fixed.

Serratus anterior

- Abducts scapula and rotates it upward; elevates ribs when scapula is stabilized; known as “boxer’s muscle” because it is important in horizontal arm movements such as punching and pushing.

Trapezius

- Superior fibers upward rotate
scapula; middle fibers adduct scapula; inferior
fibers depress and upward rotate scapula;
superior and inferior fibers together rotate scapula upward; stabilizes scapula.

Levator scapulae

- Elevates scapula and rotates it downward.

Rhomboid major

- Elevates and adducts
scapula and rotates it downward; stabilizes
scapula.

Rhomboid minor

- Elevates and adducts
scapula and rotates it downward; stabilizes
scapula