chapter 6: muscular system

Chapter 6: Muscular System

Anatomy & PhysiologyKasprowicz

The essential function of muscle is contraction – making it responsible for

almost all body movement.

Types of Muscle

Types of Muscle1) Skeletal2) Cardiac3) Smooth

General Muscle Characteristics

• muscle cells are elongated = muscle fibers (smooth, skeletal)• contain myofilaments (ability to contract)• terminology: myo-, mys- = muscle sarco- = flesh

Skeletal Muscle

1) Very large, multinucleated cells2) Striated (visible stripes or banding

pattern)3) Voluntary (conscious) control; can

be reflexive too4) muscle fibers (cells) are bundled

together by strong connective tissues

exert great force, but tire easily

Connective Tissues in Skeletal Muscle

Deep fascia

Connective Tissues in Skeletal Muscles

· Endomysium – around single muscle fiber

· Perimysium – around a fascicle (bundle) of fibers

· Epimysium – covers the entire skeletal muscle

· Deep Fascia – on the outside of the epimysium

Connective Tissues in Skeletal Muscle


· tendon – dense connective tissue attaching muscle to bone (cord-like)

· aponeuroses – attach muscles indirectly to bone,cartilages or connective tissue coverings (sheet-like)

· Epimysium blends into a connective tissue attachment


Aponeurosis of the external oblique


Refer to pg. 272 in your textbook

Smooth Muscle

1) Spindle-shaped cells with one nucleus

2) no striations3) Involuntary (no conscious

control)4) Found in hollow visceral organs5) Have small amount of

endomysium

Smooth Muscle

6) slow, sustained, tireless movement

7) often layers in opposite directions

Smooth Muscle: Stomach Wall

Cardiac Muscle

1) Branching cells with one nucleus connected by intercalated discs2) Striated3) Involuntary (no conscious

control)4) small amounts of endomysium

Cardiac Muscle

5) Cardiac fibers are arranged in spiral or 8-

shaped bundles

Muscle Functions

1) Producing movement2) Maintaining posture3) Stabilizing joints4) Support soft tissues5) Generating heat6) Guard entrances and exits

Muscle Functions

Skeletal Muscle Fiber (Cell) Formation

Microscopic Anatomy of Muscle

· Cells are multinucleate· Nuclei are just beneath the sarcolemma

(1) sarcolemma - specialized plasma membrane of muscle cells


(2) Cytoplasm filled with myofibrils

myofibrils – perfectly aligned, ribbon- like organelles; give muscle fiber its striped appearance



A closer look at the myofibrilLight (I) bands Dark (A) bands



Banding Pattern: Light (I) bands contain the Z discDark (A) bands contain the H zoneM line - holds adjacent filaments together; center of H zone


An even closer look at the myofibril…(3) Sarcomere - contractile unit of the myofibril - Z disc to Z disc


An even closer look at the myofibril…(3) Sarcomere


Zooming in on the sarcomere…(4) Myofilaments - special proteins that cause muscle to contract

Two Types: a) myosin (thick filament) b) actin (thin filament)


Two Types: a) myosin (thick filament)

protein with heads that form cross bridges b/t thick & thin filaments during muscle contraction

Contain ATPase enzymes


Two Types: b) actin (thin filament)

Made of the contractile protein actin & some other regulatory proteins


Zooming in around the H zone….


(5) Sarcoplasmic reticulum (SR) specialized smooth ER surrounding each myofibril stores calcium which is released when muscle is stimulated to contract


Sarcoplasmic reticulum (SR)

Let’s put this all together….

Microscopic Organization of Muscle: Level 1 (refer to Fig. 10-6, pg. 278)


Microscopic Organization of Muscle: Level 2

Skeletal Muscle Activity: Initiating the Contraction

Special Functional Properties of Muscle

· Irritability – ability to receive and respond to a stimulus

(a property shared with neurons)

· Contractility – ability to shorten when an adequate stimulus is received

Skeletal muscles must bestimulated by a nerve to contract (motor neuron).

Quick Review of Neurons & Synapses

Nerve Stimulus to Muscle

Motor unit: One neuron & the muscle cells stimulatedby that neuron


Neuromuscular junctions the neuron & muscle fibers do NOT touch

separated by a gap called the synaptic cleft which is filled w/ interstitial fluid


Neuromuscular junctions

Transmission of Nerve Impulse to Muscle

Neurotransmitterschemical released by neurons used to “carry” the impulse across the synaptic cleft

Acetylcholine (ACh) is the neurotransmitter used at the neuromuscular junction of skeletal muscle


Steps in Impulse Transmission· ACh is released by the pre-synaptic

axon terminal of the motor neuron · ACh crosses the synaptic cleft &

attaches to receptors on the sarcolemma

· Sarcolemma becomes permeable to sodium (Na+)


Steps in Impulse TransmissionSodium floods into the cell generating an

action potential (electrical current)· Once started, muscle contraction cannot

be stopped !! · ACh is broken down by the enzyme

acetylcholinesterase This prevents continued contraction of the

muscle cell in the absence of additional nerve impulses.


Steps in Impulse Transmission When an action potential sweeps along the sarcolemma and a muscle cell is excited, calcium ions are released from the sarcoplasmic reticulum


Steps in Impulse Transmission

The flood of Ca+ ions is the final trigger for the contraction of the muscle

Skeletal Muscle Activity: Sliding Filament Theory of

Muscle Contraction

Mechanism of Muscle Contraction

Sliding Filament Theory: Overview · Myosin heads form cross bridges with binding sites on actin

· Myosin heads detach & then bind to the next site on actin

Resting Sarcomere

Sarcomere Contracts


Sliding Filament Theory: Overview · This action continues, causing the myosin & actin to slide past each other

Sarcomere Contracts

Resting Sarcomere


Sliding Filament Theory: Overview

Collective shortening of

the muscle cell

sarcomeres =

muscle contraction

Sarcomere Contracts

Resting Sarcomere

The Contraction Cycle : The Nitty Gritty

Step 1: Ca+ ions released from the SR attach to the troponin- tropomyosin complex

Binding sites on the actin filament are exposed


Step 1:


Step 2: myosin heads attach to actin binding sites, forming cross bridges

ATP was required to prep the myosin head (ATP ADP + P)


Step 2:


Step 3: ADP + P released from myosin head

myosin head flexes/pivots = “power stroke”


Step 3:


Step 4: ATP binds to myosin head, causing it to detach from the actin filament


Step 5: myosin head re-energized (ATP ADP + P)

Step 6: Ca+ ions pumped back into the SR troponin-tropomyosin complex moves back to its original position

Muscle Contraction Animations

http://www.mhhe.com/biosci/bio_animations/09_MH_MuscleContraction_Web/index.htmlMuscle Contraction 3-D Animation

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html

Action Potentials & Muscle Contraction

https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__breakdown_of_atp_and_crossbridge_movement_during_muscle_contraction.html

Break Down of ATP & Cross Bridge Attachmenthttps://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

Sarcomere Contraction

http://www.mhhe.com/biosci/bio_animations/09_MH_MuscleContraction_Web/index.html

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html




https://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html

Contraction of the Whole Muscle

The “all-or-none” response of muscle contraction refers to the muscle cell, NOT the whole muscle

Whole muscle reacts with a graded response (different degrees of shortening)


Graded responses are produced in 2 ways:

1)Change the frequency of stimulation

2)Change the # of muscle cells stimulated/time - more activated muscle cells stronger FORCE of contraction


Muscle Twitch – 1 stimulus; single, brief, jerky contraction1

Changing Stimulation Frequency


Wave Summation– frequency of stimulus increases; less time to relax; contraction strength “summed”

2



Incomplete Tetanus – frequency of stimulation increases even more

3



Tetanus – frequency of stimulation very rapid; no evidence of relaxation; smooth, sustained contraction

4


Energy for Muscle Contraction

· Initially, muscles used stored ATP for energy· ATP is hydrolyzed into ADP + P· Only 4-6 seconds worth of ATP is stored

by muscles· After this, other metabolic pathways

must be used to produce ATP


Pathway 1: Direct Phosphorylation· Muscle cells contain creatine phosphate (CP)

·CP is a high-energy molecule that transfers energy to ADP, regenerating ATP

· CP supplies are exhausted in about 20 seconds


Pathway 1: Direct

Phosphorylation


Pathway 2: Anaerobic Respiration (a.k.a. lactic acid fermentation)

· breaks down glucose without oxygen· Glucose is broken down to pyruvic acid; 2 ATP are produced

· Pyruvic acid lactic acid


Pathway 2: Anaerobic Respiration

(lactic acid fermentation)


Pathway 2: Anaerobic Respiration · This reaction is not as efficient,

but it is fast· Huge amounts of glucose are needed· Lactic acid produces muscle fatigue

· Duration: 30-60 seconds


Pathway 3: Aerobic Respiration · Series of metabolic pathways that occur in the mitochondria & require oxygen

· Glucose is broken down to carbon dioxide and water releasing energy

· This is a slower reaction that requires continuous oxygen

· High energy pay-off: 36 ATP


Pathway 3: Aerobic Respiration

Muscle Fatigue & Oxygen Debt

· When a muscle is fatigued, it is unable to contract

· The common reason for muscle fatigue is oxygen debt· Oxygen must be “repaid” to tissue to remove

oxygen debt· Oxygen is required to get rid of accumulated

lactic acid· Increasing acidity (from lactic acid) and lack

of ATP causes the muscle to contract less

Types of Muscle Contraction

Isotonic Muscle Contraction· The myofilaments slide past each other muscle shortens movement occurs

Examples: bending knee, rotating the arms, smiling

Types of Muscle Contraction

Isometric Muscle Contraction muscle is not able to shorten muscle tension keeps increasingExamples:lifting a 1000 lb. object alone; pushing against an object thatdoesn‘t move

Muscle Tone

state of continuous partial contractions

Different fibers contract at different times to provide muscle tone

muscle remains firm, healthy & ready for action

Increasing muscle tone increases metabolic energy used, even at rest

Muscle Tone

Muscle Tone

If the nerve supply to a muscle isdestroyed, the muscle is nolonger stimulated in this manner,and it loses tone and becomesparalyzed. Soon after, it becomesflaccid (soft and flabby) andbegins to atrophy (waste away).

Muscle Tone

Effects of Exercise

“use it or lose it” Aerobic (Endurance) Exercise Examples: jogging, biking, swimming stronger, more flexible muscles w/ greater resistance to fatigue

Effects of Exercise

Aerobic (Endurance) Exercise Physiological Effects 1) increased blood supply to muscles 2) more mitochondria 3) increased metabolism 4) keeps bones strong 5) improves neuromuscular coordination

Effects of Exercise

“use it or lose it” Resistance (Isometric) Exercise Examples: weight training increased muscle size and strength

Effects of Exercise

Aerobic (Endurance) Exercise Physiological Effects 1) increased # of myofilaments increased size of muscle fibers 2) more connective tissue 3) keeps bone strong

“Golden Rules” of Skeletal Muscle Activity

1) All (almost ) skeletal muscle cross a least one joint

2) Most of a skeletal muscle lies proximal to the joint crossed

3) All skeletal muscles have at least 2 attachments: the origin and the insertion

4) Skeletal muscles can only PULL (create tension)

5) When a muscle contracts, the insertion moves toward the origin

Types of Body Movements

· Movement occurs when a muscle contracts and moves an attached bone

· Muscles are attached to at least two points· Origin – attachment to a immoveable bone· Insertion – attachment to an movable bone


When a skeletal musclecontracts, its insertionmoves toward its origin

Body Movements: Muscle Interactions

· prime mover – muscle primarily responsible for a certain movementExample: biceps, hamstrings(a.k.a. agonist)

· Antagonist – muscle that opposes or reverses a prime mover· Triceps when biceps flexes; quads

when hamstrings flex

Prime Mover – bicepsAntagonist – triceps

Prime Mover – triceps Antagonist – biceps

Body Movements: Muscle Interactions

· Synergist – muscle that aids a prime mover in a movement and helps prevent rotationExample: finger flexor muscles brachioradiulus & brachialis in

the forelimb


1) Flexion decreases angle of joint, bringing

2 bones closer together common in hinge, ball & socket joints

2) Extension increases the angle of a joint,

moving the bones apart hyperextension >180° angle

Flexion & Extension

Hyperextension

Flexion & Extension


3) Rotation movement of a bone around its

longitudinal axis common in ball & socket joints atlas (C1) around the axis (C2)

Rotation


4) Abduction movement of a limb away from the

medial plane also used to refer to fanning of finger or toes

5) Adduction movement of a limb toward the

midline

Abduction & Adduction


6) Circumduction proximal end is stationary; distal

end moves in a circle limb moves in a cone shape common in ball & socket joint combo of flexion, extension, abduction & adduction

Circumduction

Special Body Movements

1) Dorsiflexion (point toes up towards shin) & Plantar Flexion (pointing the toes)


2) Inversion (turn sole of foot medially) & Eversion (turn sole of foot laterally)


3) Supination & Pronation movements of the radius around

the ulna supination: palm forward; radius &

ulna are parallel (anatomical position); thumb lateral

pronation: palm facing back; radius crosses ulna; thumb medial


3) Supination & Pronation


4) Opposition movement of thumb across palm

to touch fingertips

Elevation & Depression

Protraction & Retraction

Naming Skeletal Muscles

1) Direction of muscle fibers in reference to an imaginary line

(midline of body, long axis of limb) ie. Rectus (fibers parallel to line)

Oblique (fibers at a slant to line)


2) Relative Size

Longus = longLongissimus = longestTeres = long and roundBrevis = shortMagnus = largeMajor = largerMaximus = largestMinor = smallMinimus = smallest


3) Location of the Muscle in reference to the associated bone ie. temporalis (temporal bone)

frontalis (frontal bone)


4) Number of origins ie. biceps, triceps, quadriceps

5) Location of the muscle’s origin and insertion

ie. Sternocleidomastoid muscle


6) Shape of the muscle ie. Deltoid (triangular)

7) Action of the muscle ie. adductor muscle, extensor muscle

Head & Neck Muscles

Head and Neck Muscles

Facial Muscles • Frontalis raises eyebrows and wrinkles the forehead

• Orbicularis Oculi close, squint, blink and wink the eyes

• Orbicularis Oris closes the mouth and protrudes the lips; the “kissing” muscle


• Buccinator

flattens the cheek (whistling or playing a trumpet); also a chewing muscle

• Zygomaticus “smiling” muscle; raises the corners of the mouth upward


Chewing Muscles

• Buccinator• Masseter closes the jaw by elevating the mandible (prime mover)

• Temporalis helps masseter close the jaw (synergist)

Frontalis

Orbicularis oculi

ZygomaticusOrbicularis

oris

Buccinator

Masseter

Temporalis

Frontalis

Orbicularis oculi

Orbicularis oris

Zygomaticus Buccinator

Temporalis

Masseter

Frontalis

Zygomaticus

Orbicularis oris

Orbicularisoculi

Buccinator

Temporalis

Masseter


Neck Muscles • Platysma pulls down corners of the mouth, downward sag of the mouth

• Sternocleidomastoid two-headed muscle; flex your neck (bowing of head); tilt head to side

Frontalis

Orbicularis oculi

ZygomaticusOrbicularis

oris

Buccinator

Masseter

Temporalis

PlatysmaSternocleido-mastoid

Frontalis

Orbicularis oculi

Orbicularis oris

ZygomaticusBuccinator

Temporalis

Masseter

SternocleidomastoidPlastysma

Frontalis

Zygomaticus

Orbicularis oris

Orbicularisoculi

Buccinator

Temporalis

Masseter

Sternocleido-mastoid

platysma

Trunk Muscles

Trunk Muscles • move the vertebral column (mostly posterior, anti-gravity muscles)

• anterior thorax muscles (move ribs, head & arms)

• muscles of the abdominal wall (help move vertebral column & form the “girdle” holding internal organs in place)

Trunk Muscles

Anterior Muscles: Thorax • Pectoralis Major - fan-shaped muscle - origin: sternum, pectoral girdle, ribs - insertion: humerus - adduct & flex the arm

Pectoralis major

Pectoralis minor

Trunk Muscles

Anterior Muscles: Thorax • Intercostal Muscles - deep muscles between the ribs - aid in breathing (external – inhale, internal – forcible exhale)

External intercostals

Internalintercostals

Trunk Muscles

Anterior Muscles: Abdominal Girdle • Rectus abdominus - pubis to rib cage - flex the vertebral column - compression of abdominal contents

Trunk Muscles

Anterior Muscles: Abdominal Girdle • External Oblique - lateral walls of abdomen - origin: ribs insertion: illium - flex the vertebral column, rotate/bend trunk

Trunk Muscles

Anterior Muscles: Abdominal Girdle • Internal Oblique - origin: iliac crest insertion: ribs - function same as external oblique

• Transversus abdominis - deepest muscle in abdomen - fibers run horizontally - compresses the abdominal contents

Trunk Muscles

Posterior Muscles • Trapezius - kite-shaped muscle - origin: occipital bone to last thoracic vertebrae insertion: scapula & clavicle - head extension & movement of scapula

Trunk Muscles

Posterior Muscles • Latissimus Dorsi - 2 large, flat muscles in the lower back - origin: lower spine & ilium insertion: proximal end of humerus - arm extension & adduction (“power stroke”)

Trunk Muscles

Posterior Muscles • Erector Spinae - prime mover of back extension (keep your body “erect”); control bending at the waist - paired; deep in the back - span vertebral column

Trunk Muscles

Posterior Muscles • Qudratus lumborum - posterior abdominal wall - flex spine laterally, extend vertebral column - origin: iliac crest insertion: upper lumbar vertebrae

Trunk Muscles

Posterior Muscles • Deltoids - triangular muscle forming shoulder - origin: spine of scapula to clavicle insertion: proximal humerus - prime mover of arm abduction

Muscles of the Upper Limb

• The anterior arm muscles cause elbow

flexion strongest: brachialis biceps brachii “weakest”: brachioradialis

• posterior arm: triceps brachii


Anterior Arm Muscles • Biceps brachii - origin: 2 heads in pectoral girdle insertion: radius - prime mover of forearm flexion & supination


Anterior Arm Muscles • Brachialis - origin: humerus insertion: ulna - forearm flexion

• Brachioradialis - origin: humerus insertion: distal forearm


Posterior Arm Muscles • Triceps brachii - origin: 3 heads in pectoral girdle insertion: olecranon process of ulna - prime mover of elbow extension - biceps brachii antagonist

Muscles of the Lower Limb

• cause movement of hip, knee &

foot joints• some of the largest, strongest muscles in the body• specialized for walking & balance• many of the muscles cross 2 joints and can cause movement at both


Muscles that Move the Hip Joint • Gluteus Maximus - forms most of the flesh of the buttock - origin: sacrum & illiac insertion: femur & iliotibial tract - hip extensor (important when climbing and jumping)


Muscles that Move the Hip Joint • Gluteus Medius - beneath gluteus maximus - hip abductor; steadies pelvis when walking

• Iliopsoas (two, fused muscles) - prime mover of hip flexion; keeps upper body from falling backward when standing


Muscles that Move the Hip Joint • Adductor Muscles - group of muscles; medial thigh - adduct, or press, thighs together - origin: pelvis insertion: femur - tend to get flabby

Iliopsoas

Adductor muscles

AnteriorView

Posterior View

Gluteus medius

Gluteus maximus

Adductor magnusIliotibial tract


Muscles that Move the Knee Joint • Hamstring Group - group of muscles; posterior thigh - biceps femoris, semimembranosus, semitendinosus - origin: ischium insertion: tibia - prime movers of thigh extension & knee flexion


Muscles that Move the Knee Joint • Sartorius - thin, strap-like, relatively weak flexor - most superficial thigh muscle - synergist in sitting “criss cross applesauce”


Muscles that Move the Knee Joint • Quadriceps Group - group of muscles; anterior thigh - rectus femoris & 3 vastus muscles - origin: pelvis & thigh insertion: tibia via patellar ligament - prime movers of knee extension; hip flexion

Iliopsoas

Iliopsoas

Adductor muscles

AnteriorView

SartoriusRectus femorisVastus lateralis

Vastus medialis

QUADS

Posterior View


Muscles that Move the Ankle & Foot • Tibialis Anterior - superficial muscle of anterior leg (shin) - origin: tibia insertion: tarsals - dorsiflex & invert the foot

• Fibularis Muscles - plantar flexion and eversion - origin: fibula insertion: metatarsals


Muscles that Move the Ankle & Foot • Gastrocnemius - forms curved calf; 2 parts - origin: femur insertion: heel using Achille’s tendon - prime mover of plantar flexion


Muscles that Move the Ankle & Foot • Soleus - deep to gastrocnemius - origin: tibia & fibula (no effect on knee) insertion: heel using Achille’s tendon - plantar flexion

AnteriorView

PosteriorView

chapter 6: muscular system

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