Muscular System

how many muscles in the human body

650

what is the main function of the muscular system

To generate force and movement in the body.

aponeuroses

Fibrous sheets that connect muscles to bones or other muscles, allowing for the transmission of force and providing stability and support; broad tendon sheaths

what is the basic unit of the muscle cell

sarcomere

Muscle Tone

The natural state of tension in muscles, even at rest

maintain posture, stabilize joints, and provide a base for movement.

regulated by the nervous system and influenced by factors like physical activity, age, and overall health.

_____ produced by muscle tone prevents muscle from weakening, allowing muscles to stabilize joints and maintain posture

tension

hypotonia

Abnormally low muscle tone, characterized by decreased resistance to passive movement and a floppy or limp appearance.

hypertonia

condition characterized by increased muscle tone or tension; excessive muscle tone

What are the two forms of hypertonia?

spasticity and rigidity

spasticity

type of stiffness related to uncontrolled reflexes

rigidity

stiffness of muscle not associated with reflexes

what are two types of skeletal muscle contractions.

isotonic and isometric

isotonic contractions

Muscle contractions where the muscle length changes while maintaining constant tension. These contractions are commonly seen during activities like weightlifting or carrying heavy objects.

what are two types of isotonic contractions

concentric and eccentric

concentric contractions

Muscle contractions where the muscle shortens as it generates force. It occurs when the force produced by the muscle is greater than the resistance.

example of concentric contraction

bicep muscle shortening as hand weight brought upward and angle of elbow decreases

Eccentric Contraction

muscle lengthens while generating force

It occurs when the external force applied to the muscle is greater than the force generated by the muscle itself

doesn’t produce adequate force to move load, but used for movement, balance, resisting movement

example of eccentric contraction

movement of bicep as it performs lowering portion of bicep curl

______ contraction brings arm upward, reducing angle of elbow while _____ contraction lowers arm, resisting gravity and increasing elbow angle slowly

concentric, eccentric

isometric contractions

muscle produces tension without changing length; do not produce movements or lift loads, maintain posture and joint stability

example of isometric contraction

ex. holding head in upright position to maintain stationary and not produce movement

epimysium

connective tissue that wraps around outer laryer of each muscle; allows muscle to contract and move powerfully while maintaining structural integrity; composed of thick layer of collagen fibers

Fascia

Connective tissue that surrounds muscles, organs, and other structures, providing support and protection. It helps to separate and compartmentalize different body parts, allowing them to move independently; plays a role in facilitating the transmission of forces and maintaining structural integrity.

a single muscle cell is called a ________

muscle fiber

each______ contains many long muscle fibers bound by the perimysium

fascicle

perimysium

contains collagen fibers and elastin fibers; middle layer of connective tissue that surrounds each fascicle

endomysium

connective tissue layer that encases individual muscle fibers; thinner than other two layers, contains areolar and reticular tissues to form loose delicate networks; contain small blood vessels and motor neurons to support and activate each muscle fiber

sarcolemma

plasma membrane of skeeltal muscle fiber; located just under endomysium; site of action potential conduction

sarcoplasm

cytoplasm of the muscle cell

muscular dystrophy

A progressive genetic disorder characterized by the weakening and degeneration of muscles. It leads to muscle wasting, loss of muscle control, and eventual disability.

what is most common type of muscular dystrophy

Duchenne muscular dystrophy

duchenne muscular dystrophy (DMD)

genetic disorder characterized by progressive muscle weakness and degeneration; primarily affects boys and is caused by a mutation in the dystrophin gene.

purpose of dystrophin

helps thin filaments of myofibrils bind to sarcolemma and maintains equal force transmission through muscle tissue; without sufficient amounts of this protein muscle contractions cause sarcolemma to tear

inheritance pattern of Duchenne Muscular Dystrophy

X-linked recessive

parallel muscles are arranged parallel to ______ axis of muscle

long

parallel muscles are

equidistant and run in the same direction

What type of muscle fiber organization do skeletal muscles follow?

parallel muscle fiber organization

central body of muscle

large mass of tissue located in middle of the muscle

aka the belly

circular muscles

aka sphincters, arranged around an opening in rings

orbicularis oris muscle

circular muscle around the mouth under lips

orbicularis oculi muscle

circular muscle surrounding each eye

convergent muscles

fascicles extend from broad fan-shaped area and converge on single attachment site where muscle interacts with tendon; can be stimulated in different, smaller areas

example of convergent muscle

pectoral muscle on chest

example of parallel muscle

bicep muscle

pennate muscle

feather-shaped, form different fascicle arrangements at angle to tendon; contracting this msucle pulls at an angle and can produce high tension but doesn’t move tendons very far

subtypes of pennate muscles

uni, bi, multi

unipennate muscle type

fascicles located on one side of the tendon

ex. extensor digitorum in forearm

bipennate muscle type

fascicles on both sides of the tendon

ex. rectus femoris in thigh

multipennate muscle type

tendon branches within pennate msucle

ex. deltoid muscle of shoulder

fusiform muscles

muscles that are spindle-shaped, with a thick belly and tapered ends; enable rapid and coordinated movements, such as running and jumping

example of fusiform muscles

biceps brachii or gastrocnemius

triangualr muscles

can be convergent or multipennate to create this muscle shape

ex. trapezius which extends from head down back and out the shoulder

5 types of muscle fiber organization

parallel, circular, convergent, pennate, fusiform (triangular as extra)

direct muscle attachment

The type of muscle attachment where the muscle fibers attach directly to the bone without any tendons or other connective tissues in between.

indirect muscle attachment

Type of muscle attachment where the muscle connects to the bone indirectly via a tendon or aponeurosis

aponeurosis

Sheet-like, fibrous connective tissue that attaches muscles to bones or other muscles. Provides strength and support, allowing for efficient transmission of muscle force.

tendon sheath

Structure surrounding a tendon, providing lubrication and reducing friction during movement.

example of direct muscle attachment

abdominal wall muscles attach directly onto brim of pelvis; temporalis muscle to skull

example of indirect muscle attachment

bicep attaching to humerus and radius and ulna via tendons

bursae

fluid filled sacs join tendons to reduce friction as tendon moves

bursitis

inflammation of bursae caused by overuse of joint or other mechanical stress which can result in pain and swelling

common in knees, elbows, shoulders

lever in muscular system

a rigid structure (like a bone) that rotates around a fixed point (joint) when muscles contract, allowing movement

each _____ is a lever and each ____ is a fulcrum, ______ supply the applied forces

bone, joint, muscles

first class levers

only few located in body, fulcrum located between force and load

example of first class levers

the head resting on the neck, with the neck muscles acting as the effort, the joint as the fulcrum, and the weight of the head as the load

second class levers

load located between applied force and fulcrum; force further from fulcrum than the load so you can move larger weight with less effort

example of second class levers

when standing on your toes, fulcrum is ball of foot, load is body weight, and effort comes from muscles in back of leg

third class levers

force applied between load and fulcrum; most common levers in body

example of third class levers

biceps brachii in arm, load is the hand, fulcrum is the elbow joint, and biceps brachii attaches between the fulcrum and load

skeletal muscles are arranged in ______ for balance and to work efficiently

pairs

antagonist muscle

opposes the action of the agonist muscle

synergists

minor muscle that improves efficiency of agonist muscle or major muscle

brevis muscle

short

longus muscle

long

lateralis

lateral side or away from midline

medialis

toward the midline

flexor muscle

decrease angle at joint

extensor muscle

increase angle at joint

abductor muscle

moves bone away from midline

adductor muscle

moves bone towards midline

when naming muscles, location of ____ always named first

origin

rectus muscle direction means

straight

latissimus

widest

longissimus

longest

magnus, major, vastus

large, larger, huge

what shape is deltoid

triangular

what shape is trapezius

trapezoidal

what shape is serratus

serrated

what shape is rhomboid

diamond-shaped

what shape is pectinate

comb-like

what shape is piriformis

pear-shaped

what shape is platys

flat

what shape is gracilis

slender

supinator

turns palm anteriorly

pronator

turns palm posteriorly

muscle hierarchy

actin/myosin →sarcomeres →myofibrils →myofibers →fascicles → muscle

titin

large structural proteins in muscle cells; forms an elastic filament; helpss align myosin proteins and allows muscle cell to maintain structural integrity by resisting extreme stretching

dystrophin

protein that helps bind actin to muscle cell membrane; insufficient production of this protein results in inability ot transfer force of organized actin-myosin contraction

thick filament composed of

myosin

thin filament composed of

actin