Honors Anatomy & Physiology

Muscular SystemPart 1

Muscular Tissue

3 types:1. Skeletal

striated & voluntary

2. Cardiac striated & involuntary

3. Smooth Smooth & involuntary

Types of Muscle Tissue

most attached to bonestriations:

see light & dark bands under microscope

Skeletal Muscle Tissue

found only in walls of heart chambersheart has a pacemaker that initiates each

contractioncalled autorhymicitycontrolled by hormones &

neurotransmitters

Cardiac Muscle Tissue

in walls of hollow organsattached to hair folliclessome autorhythmic (wall of intestines)regulated by ANS motor neuron&

hormones

Smooth Muscle Tissue

1. producing body movementsmoving whole body or parts of body

Functions of Muscular Tissue (#4)

2. stabilizing body positionskeletal muscles stabilize joints &

halp maintain body positionspostural muscles hold sustained

contractions (holding head up all day)

Functions

3. storing & moving substances w/in bodystoring: 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 heatprocess called thermogenesismost 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 excitabilityability 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. contractilityability of muscle fibers to contract

forcefully when stimulated by an action potential

muscle fiber shortens & pulls on whatever it is attached toif force > resistance of object,

movement occurs

Properties

3. extensibilityability of muscle tissue to stretch

w/out being damagedsmooth muscle fibers are stretched

every time your stomach or bladder is really full

Properties

4. elasticityability 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 organs2 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 fibersex: muscle growth in newborn

hyperplasia: increase in # of muscle fibersex: growth hormone causes increase in

#s from childhood adultfibrosis: replacement of muscle by

fibrous scar tissuesatellite cells: stem cells in muscle

tissue; limited capacity

Muscle Histology Terms

Why Muscle Fibers are Multinucleated

sarcolemma: plasma membrane sarcoplasm: cytoplasmmyofibril: 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 areafilled with interstitial fluidensures action potentials excites all

parts of muscle fiber

Terms for Muscle Fiber Organelles

T Tubule

sarcoplasmic reticulum: (SR) endoplasmic reticulum that encircles individual myofibrilsdilated end sacs called terminal

cistern T tubule + 2 terminal cisterns = triadin relaxed muscle fiber SR stores

Ca++release of Ca++ triggers contraction

Terms for Muscle Fiber Organelles

Triad

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

Where is the actin?

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120104/bio_b.swf::Sarcomere%20Shortening

http://www.wiley.com/college/pratt/0471393878/student/animations/actin_myosin/actin_myosin.swf

http://brookscole.cengage.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html

Review to do @ home

http://bcs.whfreeman.com/thelifewire/content/chp47/4702001.html

http://www.sumanasinc.com/webcontent/animations/content/muscle.html

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

Muscle Contraction Animations

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 filament

4. detachment of myosin from actin ATP binds to myosin head & cross

bridges released

Contraction Cycle Steps

before

after

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 ACh2. activation of ACh receptors3. production of muscle action

potential4. 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

effect of ACh binding short because ACh is rapidly broken down by enzyme acetylcholinesterase (AChE)

Termination of ACh Activity

@ midpoint of muscle fiber:muscle action potential propagate

both ends of fiberallows simultaneous activation & so

contraction of all parts of muscle fiber

NMJ

South American plant derivativecauses 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 contractiontoxin one of most lethal chemicals knowncauses 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

http://www.youtube.com/watch?v=jKygojJgFQE

Contraction Animations to Try @ Home

same arrangement actin/myosin: striations

muscle fibers branched*intercalated discs: unique to cardiac

muscleautorhymicity alone: 75 bpmremains contracted 10-15 x’s longer than

skeletal muscle after 1 action potentialdue to prolonged delivery of Ca++ (SR +

interstitial fluidlarger & more #s of mitochondria

Cardiac Muscle Tissue

Cardiac Muscle Tissue

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

Smooth Muscle Tissue

Development of Musclefrom mesodermstarts ~4 wkscardiac 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 movementseen 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 +painmost often affect quadraceps femoristx‘d RICE (rest, ice, compression ie a

wrap, elevation)

Medical Terminology