wk 3. ch.20

Anatomy of the muscular system

• Skeletal muscles

> tendons and aponeurosis

• Deep fascial tissues

Physiology (functions of skeletal muscles)

Movement

•Posture maintenance

➢Posture: body positions maintained by muscle contractions

➢Ex: standing and sitting

➢Muscle tone (tonus): continuous/partial contraction of skeletal muscles

•Heat production

➢Thermogenesis: mechanism of body temperature maintenance

Posture

body positions maintained by muscle contractions

➢Ex: standing and sitting

Muscle tone (tonus)

continuous/partial contraction of skeletal muscles

•Heat production

Thermogenesis

mechanism of body temperature maintenance

Skeletal muscle

group of contractile tissues surrounded by connective tissue

➢Attached to bones

➢Can produce movement at joints

➢Organs of the muscular system

Muscle fibers

muscle cells and has properties of:

➢Excitability: ability to respond to stimulus

➢Contractility: ability to shorten

➢Extensibility: ability to lengthen or stretch

➢Elasticity: ability to return to precontraction after lengthening or stretching

Excitability

ability to respond to stimulus

Contractility

ability to shorten

Extensibility

ability to lengthen or stretch

Elasticity

ability to return to precontraction after lengthening or stretching

Fasciculi

groups of muscle fibers bundled together

➢Fascicle is singular

Muscle fiber anatomy

•Sarcolemma

~Motor end plates

~Receptors for acetylcholine

•Sarcoplasm

•Myofibrils

~sarcomeres

> thick filaments

> thin filaments

> I bands

> Z lines

> H zone

> A bands

• Sarcoplasmic Reticulum (SR)

~ transverse tubules (T tubules)

• Connective tissue

~ epimysium

~ perimysium

~ endomysium

~ tendons

~ aponeurosis

~ retinaculum

Sarcolemma

cell membrane

Motor end plate

folds in sarcolemma and has receptors for ACH

Acetylcholine (ACH)

neurotransmitter of muscle contraction

Sarcoplasm

intracellular fluid

➢Equivalent to cytoplasm in typical cells

Myofibrils

slender fibers with repeating compartments called sarcomeres

Sarcomeres

structural units of muscle contraction

Z Line

end of sarcomere

Filaments (myofilaments)

thin and thick strands within sarcomeres

➢Stacked in alternating, parallel rows

Thin filaments

actin, tropomyosin, troponin

➢Actin looks like a twisted double strand of beads; attaches to Z lines

Thick filaments: myosin

➢Chemically attracted to binding sites on actin

➢In center of sarcomere; does not attach to Z lines

➢Looks like golf clubs with shafts bundled together

➢Heads angle toward thin filaments

I bands

thin filaments and Z lines

H zone

center of sarcomere

➢Has only thick filaments

A bands

runs entire length of thick filaments

➢Includes H zone

Sarcoplasmic Reticulum (SR)

System of interconnected tubes

➢Surrounds myofibrils

•Stores/releases calcium

•Plays role in contraction

Transverse (T) tubules

indentations in SR

➢Called “transverse” because they extend transversely across the SR

➢Allows impulses to travel into the muscle fiber

Connective Tissues

Surround muscle fibers, anchor muscles to bones, stabilize their tendons

•Endomysium: around muscle/muscle group

•Perimysium: around fascicle

➢Allows for vascularization/innervation

•Epimysium: around muscle fibers in the fascicle

Tendons: dense bands of connective tissue

➢Attach muscles to bones

•Aponeurosis: broad/flat tendons

➢Tendons and aponeuroses serve same function

➢Differ only in shape

➢Tendons are cord-like; aponeuroses are flat

•Retinacula: bands of connective tissue

➢Around tendons to keep them in place

➢May function as pulleys for tendons

Endomysium

around muscle/muscle group

Perimysium

around fascicle

➢Allows for vascularization/innervation

Epimysium

around muscle fibers in the fascicle

Tendons

dense bands of connective tissue

➢Attach muscles to bones

Aponeurosis

broad/flat tendons

➢Tendons and aponeuroses serve same function

➢Differ only in shape

➢Tendons are cord-like; aponeuroses are flat

Retinacula

bands of connective tissue

➢Around tendons to keep them in place

➢May function as pulleys for tendons

Parts of a Skeletal Muscle

Belly: wide central portion

➢Contains sarcomeres

•Origin: attachment on less movable bone

➢Often more medial/proximal

•Insertion: attachment on more movable bone

➢Often more lateral/distal

➢Insertions move toward origins

➢Opposite can occur, called functional reversibility

Muscle belly

wide central portion

➢Contains sarcomeres

Origin

attachment on less movable bone

➢Often more medial/proximal

Insertion

attachment on more movable bone

➢Often more lateral/distal

➢Insertions move toward origins

➢Opposite can occur, called functional reversibility

functional reversibility

Origin and insertion reversed roles

Muscle contraction

development of tension in muscle fibers through cross bridging

➢Sliding filament model: schema describing muscle contraction

•Muscle fibers shorten or lengthen, then return to their precontraction state

Sliding filament model

schema describing muscle contraction

•Muscle fibers shorten or lengthen, then return to their precontraction state

Cross Bridging

Begins with excitation by a motor neuron

•Thick filaments cross and bridge gap between them and the thin filaments

•Thick filaments attach and slide the thin filaments toward the sarcomere’s center

➢This shortens I bands and H zones, and pulls Z lines together

•The neuromuscular junction facilities excitation

Neuromuscular Junction

Motor neuron: presynaptic structure that transmits impulses to muscle fibers

➢Acetylcholine (ACH): neurotransmitter of contraction  

•Synaptic gap (synapse): space between motor neuron and motor end plate

•Motor end plate: folded sections of sarcolemma

➢Contains receptor sites for ACH

Acetylcholine (ACH)

neurotransmitter of contraction

Synaptic gap (synapse)

space between motor neuron and motor end plate

Motor end plate

folded sections of sarcolemma

➢Contains receptor sites for ACH

Excitation of the Motor End Plate

Binding of ACH to receptors on motor end plate causes excitation of muscle fiber

•Impulse travels through T tubules into the SR

➢SR releases calcium

➢Calcium enters the sarcoplasm containing sarcomeres

Contraction

Troponin and tropomyosin slide off to expose binding sites on actin

➢This allow cross bridging

•Myosin heads attaches to actin and slides it toward the center of the sarcomere

➢Called the power stroke

•If ATP is present, myosin heads detach, toggle back, reattach to repeat power stroke

•Power strokes will continue if Ca is present

Power stroke

•Myosin heads attaches to actin and slides it toward the center of the sarcomere

•If ATP is present, myosin heads detach, toggle back, reattach to repeat power stroke

•Power strokes will continue if Ca is present

Relaxation

Released calcium is pumped back into SR

•Troponin/tropomyosin slide back

➢This covers binding sites on actin

•Myosin heads return to precontraction state

•Muscle is now at rest

Motor unit

single motor neuron and all muscle fibers it innervates

➢Motor neuron may connect to anywhere between 2 and 2000 muscle fibers

All-or-none law

when a muscle fiber receives a stimulus to contract, it will contract to its fullest ability or not contract at all

➢True for motor units, NOT entire muscle

Recruitment

Process of motor unit activation based on units needed to perform an action

➢If more strength is needed, more units are recruited

Energy Sources for Contraction

Main sources: adenosine triphosphate, glucose, and oxygen

Adenosine triphosphate (ATP)

➢Cell’s energy molecule

➢Produced by mitochondria

Glucose

used to produce ATP

Myoglobin

respiratory pigment

➢Stores oxygen

 

Muscle fatigue

decline in ability of muscles to generate force

➢Occurs when muscles run out of ATP, glucose, or oxygen

Delayed-onset muscle soreness

temporary muscle damage/inflammation after physical activity

Types of Contractions

•Isotonic: muscle length changes; involves movement

➢Dynamic contractions

➢Concentric: muscle shortens

➢Eccentric: muscle lengthens

•Isometric: muscle length remains the same; no movement occurs

➢Static contractions

Isotonic

muscle length changes; involves movement

➢Dynamic contractions

➢Concentric: muscle shortens

➢Eccentric: muscle lengthens

Isometric

muscle length remains the same; no movement occurs

➢Static contractions

Types of Muscle Fibers

Muscles/muscle fibers can be classified:

➢Structurally by amount of myoglobin, mitochondria, and blood vessels

•Type 1 and type 2

➢Functionally by rate of contraction and fatigue

•Slow twitch and fast twitch

Type 1 (Red/Slow Twitch)

Has large amounts of mitochondria, myoglobin, and blood capillaries

➢Red muscle: characteristics makes them appear red

➢Greater capacity for slow or sustained contraction and take longer to fatigue

➢Most postural or core muscles are type 1

Type 2 (White/Fast Twitch)

•Fewer mitochondria, myoglobin, and blood capillaries

➢White muscle: characteristics makes them appear lighter in color

➢More suited for movement, contracts faster, for shorter periods of time, and fatigues more quickly

➢Most phasic or dynamic muscles are type 2.

Postural Muscles

involved in maintaining an upright posture

➢Ex: spinal and calf muscles

Phasic muscles

responsible for movement

➢Ex: glutes and shoulder muscles

Classifying Muscles

•Muscles can be classified by their

➢Shape

➢Actions they provide

➢Number of joints they cross

➢Lever system used to produce movement

Classifying Muscles by Levers

➢Load: weight of body/object to be moved

➢Pull: effort or muscle contraction needed to move the bone or lever

➢Fulcrum: joint

•Lever systems organized by the arangments of the load, pull, and fulcrum

Class 1-3

•Class 1: fulcrum/joint positioned between load and pull or muscle (L-F-P)

➢Ex: seesaw or scissors

•Class 2: pull/muscle at one end, load in middle, fulcrum/joint at other end (P-L-F)

➢Ex: wheelbarrow

•Class 3: load at one end, pull/muslc in middle, fulcrum/joint at other end (L-P-F)

➢Ex: shovel

➢Most common arrangement

Load (lever system)

weight of body/object to be moved

Pull (lever system)

effort or muscle contraction needed to move the bone or lever

Fulcrum (lever system)

joint

Class 1 (lever system)

fulcrum/joint positioned between load and pull or muscle (L-F-P)

➢Ex: seesaw or scissors

Class 2 (lever system)

pull/muscle at one end, load in middle, fulcrum/joint at other end (P-L-F)

➢Ex: wheelbarrow

Class 3 (lever system)

load at one end, pull/muslc in middle, fulcrum/joint at other end (L-P-F)

➢Ex: shovel

➢Most common arrangement

Classifying Muscles by Shape

•Muscles can be classified by shape

➢Ex: parallel, convergent, spiral, circular, pennate

•Some muscles fall into several categories

➢Ex: pectoralis major in chest can be convergent or spiral

Parallel/fusiform

fibers parallel and pull in one direction

➢Most are this type

➢Fusiform: spindle shaped, tapered ends, with larger central region or belly

•Ex: biceps brachii

➢Nonfusiform: more rectangular shaped with constant diameter

•Ex: rectus abdominis

Fusiform

spindle shaped, tapered ends, with larger central region or belly

•Ex: biceps brachii

Nonfusiform

more rectangular shaped with constant diameter

•Ex: rectus abdominis

Convergent

fibers join at one end and spread out at other end; fanlike

➢Allows for more movement

➢Often has triangular shape

➢Ex: pectoralis major

spiral

twist between points of attachment

➢Ex: latissimus, levator scapulae

Circular

rounded fiber arrangement

➢Cause an opening to become smaller

➢Ex: orbicularis oris, orbicularis oculi

Pennate

•Fibers emerge diagonally from one or more central tendons

➢Unipennate: muscle fibers on same side of tendon

➢Bipennate: muscles fibers on both sides of tendon

➢Multipennate: muscles have several tendons within the muscle with fibers running diagonally between them

Unipennate

muscle fibers on same side of tendon

Bipennate

muscles fibers on both sides of tendon

Multipennate

muscles have several tendons within the muscle with fibers running diagonally between them

Classifying Muscles by Action

•Prime movers/agonists: muscles causing the desired action

•Synergists: assist prime movers

➢Performs same movement at the same time

•Fixators/stabilizers: stabilize joints or maintains posture

•Antagonists: lengthen while prime movers and their synergists perform desired action

Prime movers/agonists

muscles causing the desired action

Synergists

assist prime movers

➢Performs same movement at the same time

Fixators/stabilizers

stabilize joints or maintains posture

Antagonists

lengthen while prime movers and their synergists perform desired action

Classifying Muscle by
Number of Joints Crossed

•When a muscle crosses a joint, it acts on the joint to create movement

➢Uniarticular: crosses one joint

➢Biarticular: crosses two joints

➢Multiarticular: crosses three or more joints

Uniarticular

crosses one joint

Biarticular

crosses two joints

Multiarticular

crosses three or more joints

Muscular Pathologies

•Fibromyalgia syndrome

•Headaches

➢Tension, migraine, and cluster headaches

•Myofascial pain syndrome

•Plantar fasciitis

•Shin splints (medial tibial stress syndrome)

•Strain

•Tendinopathies

➢Tendonitis, tendinosis, tenosynovitis, and epicondylitis

•Rotator cuff tears and impingement syndrome

•Torticollis

•Whiplash-associated disorders

Fibromyalgia syndrome (FMS)

a chronic condition characterized by widespread pain and joint stiffness, restless sleep, and chronic fatigue. "Widespread" is defined as pain. on both sides of the body, and above and below the waist Individuals with FMS also experience headaches, lack of concentration, bowel dysfunction, temporomandibular dis-orders, and mood problems ranging from anxiety to depression.

Headaches

pain or discomfort in the face, head, or neck.

Primary headaches are not caused by an underlying condition, disorder, or pathology.

Tension headaches, migraine headaches, and cluster headaches are primary headaches.

Tension (headache)

the most common type and usually has a band-like or bilateral pattern with non-throbbing pain ranging from mild to moderate.

pain may occur frequently and does not worsen during routine daily activities such as bending over or walking upstairs.