Muscular System 1

To be copied

• 3 types:1. Skeletal– striated & voluntary

2. Cardiac– striated & involuntary

3. Smooth – Smooth & involuntary

Types of Muscle Tissue

• most attached to bone• striations: – see light & dark bands under microscope

Skeletal Muscle Tissue

• found only in walls of heart chambers• heart has a pacemaker that initiates each contraction– called autorhymicity– controlled by hormones & neurotransmitters

Cardiac Muscle Tissue

• in walls of hollow organs• attached to hair follicles• some autorhythmic (wall of intestines)• regulated by ANS motor neuron& hormones

Smooth Muscle Tissue

• 1. producing body movements–moving whole body or parts of body

Functions of Muscular Tissue (#4)

• 2. stabilizing body position– skeletal muscles stabilize joints & halp

maintain body positions– postural muscles hold sustained contractions

(holding head up all day)

Functions

• 3. storing & moving substances w/in body– storing: accompanied by sustained

contractions of ringlike bands of smooth muscle called sphincters (hold material in organ)

– contraction/relaxation of smooth & cardiac muscle moves material thru bld vessels heart bld vessels

Functions

• 4. generating heat– process called thermogenesis–most of heat generated by muscle contraction

maintains normal body temp of 37°C– shivering: involuntary contraction of skeletal

muscle increases heat production

Functions

• 1. electrical excitability– ability to respond to certain stimuli by

producing electrical signals called action potentials

– 2 main types stimuli:1. autorhythmic electrical signals2. chemical stimuli (neurotransmitters) released

by neurons

Properties of Muscle Tissue (#4)

• 2. contractility– ability of muscle fibers to contract forcefully

when stimulated by an action potential–muscle fiber shortens & pulls on whatever it is

attached to• if force > resistance of object, movement occurs

Properties

• 3. extensibility– ability of muscle tissue to stretch w/out being

damaged– smooth muscle fibers are stretched every time

your stomach or bladder is really full

Properties

• 4. elasticity– ability of muscle tissue to return to original

length & shape after contraction or extension

Properties

• fascia: sheet or broad band of fibrous CT that supports & surrounds muscles or other organs– 2 layers: superficial & deep

CT Components

• 2. 3 layers of CT extend from deep fascia deeper into muscle tissue1. epimysium: outermost layer, encircles entire

muscle2. perimysium: surrounds groups of 10 – 100

muscle fibers = a fascicle3. endomysium: surrounds individual muscle

fibers

CT Components

• 3. tendon: extension of epimysium, perimysium, & endomysium beyond muscle that attaches the skeletal muscle to another structure (bone or another muscle)

CT Components

• hypertrophy: enlargement of existing muscle fibers– ex: muscle growth in newborn

• hyperplasia: increase in # of muscle fibers– ex: growth hormone causes increase in #s from

childhood adult• fibrosis: replacement of muscle by fibrous scar

tissue• satellite cells: stem cells in muscle tissue; limited

capacity

Muscle Histology Terms

Why Muscle Fibers are Multinucleated

• sarcolemma: plasma membrane • sarcoplasm: cytoplasm• myofibril: contractile organelles; thread-like

structures; each extends length of muscle fiber

Terms for Muscle Fiber Organelles

• T tubules: (transverse) invaginations of sarcolemma into sarcoplasma; increasing surface area– filled with interstitial fluid– ensures action potentials excites all parts of

muscle fiber

Terms for Muscle Fiber Organelles

• sarcoplasmic reticulum: (SR) endoplasmic reticulum that encircles individual myofibrils– dilated end sacs called terminal cistern – T tubule + 2 terminal cisterns = triad– in relaxed muscle fiber SR stores Ca++– release of Ca++ triggers contraction

Terms for Muscle Fiber Organelles

• 3 kinds proteins in myofibrils:1. contractile proteins– myosin make up thick filaments, golf-club shape

(myosin head)– actin thin filaments

2. regulatory proteins– tropomyosin & troponin: both in thin filaments

3. structural proteins– ~12 different ones function in alignment,

stability, elasticity, & extensibility of myofibrils

Muscle Proteins

1. ATP hydrolysis– ATP attached to myosin head

2. attachment of myosin head to actin to form cross bridges

3. power stroke– cross bridges rotate center slides thin

filament past thick filament4. detachment of myosin from actin– ATP binds to myosin head & cross bridges

released

Contraction Cycle Steps

• somatic motor neurons innervate muscle fibers to contract

Neuromuscular Junction (NMJ)

• synapse: functional junction between 2 neurons or between a neuron & an effector (muscle or gland); may be electrical or chemical

• 1st side of synapse: end of axon of motor neuron called synaptic end bulb

• then synaptic cleft (the space)• lastly, motor end plate: part of sarcolemma

that has receptors for neurotransmitter acetylcholine (ACh)

NMJ

• 1. release of ACh• 2. activation of ACh receptors• 3. production of muscle action potential• 4. termination of ACh activity

Steps in Nerve Action Potential Muscle Action Potential

• ACh stored in vesicles in synaptic end bulb• action potential travels down axon reaches

synaptic end bulb induces exocytosis of neurotransmitter from synaptic vesicles

• ACh diffuses across synaptic cleft toward motor end plate

Release of ACh

• 2 molecules of ACh bind to ACh receptors embedded in sarcolemma opens ion channel allows Na+ diffuse across membrane

Activation of ACh receptors

• inflow Na+ makes inside of muscle fiber more + charged

• this change in membrane potential triggers a muscle action potential propagates along sarcolemma T tubules

• this causes SR to release Ca++ sarcoplasm contraction

Production of Muscle Action Potential

• @ midpoint of muscle fiber:–muscle action potential propagate both ends

of fiber– allows simultaneous activation & so

contraction of all parts of muscle fiber

NMJ

• South American plant derivative• causes paralysis by binding to & blocking ACh

receptors on motor end plates• curare-like drugs used in general anesthesia to

relax skeletal muscles

Curare

• disease caused by Clostridium botulinum toxin that blocks exocytosis of synaptic vesicles so no ACh released so no muscle contraction– toxin one of most lethal chemicals known– causes death by paralyzing skeletal muscles:

breathing stops when diaphragm & intercostal muscles stop contracting

Botulism

• “equal tension”• force of contraction developed by muscle

remains almost constant while muscle changes its length

• used for body movements & for moving objects

• 2 types:1. concentric isotonic contraction2. eccentric isotonic contraction

Isotonic Contractions

• when tension generated is enough to overcome resistance of object being moved …muscle shortens & pulls on another structure (tendon) ….producing movement that reduces angle at a joint

Concentric Isotonic Contraction

• tension exerted by the muscle resists movement of the load (whatever was lifted up) slowing the lengthening process

Eccentric Isotonic Contraction

• tension generated by the muscle is < tension needed to overcome resistance of the object

• muscle does not change its length

Isometric Contraction

• same arrangement actin/myosin: striations• muscle fibers branched• *intercalated discs: unique to cardiac muscle• autorhymicity alone: 75 bpm• remains contracted 10-15 x’s longer than

skeletal muscle after 1 action potential– due to prolonged delivery of Ca++ (SR +

interstitial fluid– larger & more #s of mitochondria

Cardiac Muscle Tissue

• +thick & thin filaments but no T tubules & less SR so no striations

Smooth Muscle Tissue

Development of Muscle

• from mesoderm• starts ~4 wks• cardiac muscle forms

tubes bends & folds to form heart

• spasm: sudden involuntary contraction of a single muscle is a large group of muscles

Medical Terminology

• tic: an involuntary twitching by muscles that are normally under voluntary control

Medical Terminology

• tremor: rhythmic, involuntary, purposeless contraction that produces a quivering or shaking movement

Medical Terminology

• fasiculation: involuntary, brief twitch that is visible under the skin; occurring irregularly & not ass’c with movement– seen in MS or ALS

Medical Terminology

• fibrillation: spontaneous contraction of single muscle fiber that is not visible under skin but can be recorded by EMG (electromyograph) – signals destruction of motor neurons

Medical Terminology

• muscle strain: tearing of muscle due to forceful impact + bleeding +pain–most often affect quadraceps femoris– tx‘d RICE (rest, ice, compression ie a wrap,

elevation)

Medical Terminology