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59 Cards in this Set

  • Front
  • Back

Muscle Tissue

A primary tissue type, divided into;


-skeletal muscle


-Cardiac muscle


-Smooth muscle

Skeletal muscles

-are attached to the skeletal system


-allow us to move


-The muscular system

The muscular system

-includes only skeletal muscles

Functions of skeletal muscles

-produce skeletal movement


-maintain body position


-support soft tissues


-guard openings


-maintain body temp.


-store nutrient reserves

Skeletal muscle structures

-muscle tissue(muscle cells or fibers)


-connective tissues


-nerves


-blood vessels

Muscles have three layers of connective tissues

-epimysium


-perimysium


-endomysium

Epimysium

–exterior collagen layer


–connected to deep fascia


–Separates muscle from surroundingtissues

Perimysium

–surrounds muscle fiber bundles(fascicles)

–contains blood vessel and nervesupply to fascicles

Endomysium

–surrounds individual muscle cells(muscle fibers)

–contains capillaries and nervefibers contacting muscle cells


–contains myosatellite cells (stem cells) that repairdamage

Muscle attachments


-endomysium, perimysium, and epimysium come together:

-at ends of muscles

-to form connective tissue attachment to bone matrix


-i.e, tendon(bundle) or aponeurosis(sheet)


Nerves

-skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system( brain and spinal cord)

Blood Vessels

Muscles have extensive vascular systems that


-supply large amounts of oxygen


-supply nutrients


-Carry away wastes

Skeletal Muscle Fibers

-are very long


-develop through fusion of mesodermal cells(myoblasts)


-become very large


-contain hundreds of nuclei

The sarcolemma

-The cell membrane of a muscle fiber(cell)


-Surrounds the sarcoplasm( cytoplasm of muscle fiber)


-A change in transmembrane potential begins contractions.



Transverse tubules (T tubules)

-transmit action potential through cell


-allow entire muscle fiber to contract simultaneously


-have the same properties as sarcolemma

Myofibrils

-lengthwise subdivisions within muscle fiber


-made up of bundles of protein filaments(myofilaments)


-Myofilaments are responsible for muscle contraction


-Types of myofilaments:


-thin filaments


-thick filaments

Thin filaments


-made of the protein actin

Thick filaments

-made of the protein myosin

sarcoplasmic reticulum(SR)

-a membranous structure surrounding each myofibril


-helps transmit action potential to myofibril


-similar in structure to smooth endoplasmic reticulum


-forms chambers(terminal cisternae) attached to T tubules

Triad

-is formed by one T tubule and two terminal cistern


-Cisternae:


-concentrate Ca2+(via ion pumps)


-release Ca2+ into sarcomeres to begin muscle contraction

Sarcomeres

-the contractile units of muscle


-structural units of myofibrils


-form visible patterns within myofibrils

Muscle striations

-a striped or striated pattern within myofibrils:


-alternating dark, thick filaments( A bands) and light, thin filaments( I bands)

Sacromeres

-M lines and Z lines



M line

-the center of the A band


-at midline of sacromere

Z lines

-the centers of the i bands


-at two ends of sarcomere

Sacromeres

-zone of overlap


-the H Band

Zone of overlap

-the densest, darkest area on a light micrograph


-where thick and thin filaments overlap

The H Band

-the area around the M line


-has thick filaments but no thin filaments

Sarcomeres


-Titin

-are strands of protein


-reach from tips of thick filaments to the z line


-stabilize the filaments

Sarcomere Funcion

-transverse tubules encircle the sarcomere near zones of overlap


-Ca2+ released by SR causes thin and thick filaments to interact

Muscle contraction

-is caused by interactions of thick and thin filaments


-structures of protein molecules determine interactions

Four thin filament proteins

-F-actin(Filamentous actin)


-Nebulin


-tropomyosin


-troponin

F-actin(Filamentous actin)

-is two twisted rows of globular G-actin


-the active sites on G-actin strands bind to myosin



Nebulin

- Holds F-actin strands together

Tropomyosin

-is a double strand


-prevents actin-myosin interaction



Troponin

-A globular protein


-binds tropomyosin to G-actin


-Controlled by Ca2+

Initiaing Contraction

-Ca2+ binds to receptor on troponin molecule


-Troponin-tropomyosin complex changes


-exposes active sit of F-actin

Thick filaments

-contain twisted myosin subunits


-contain titin strands that recoil after stretching


-the myosin molecule


-tail


-head

The myosin molecule:


-Tail

-binds to other myosin molecules

The myosin molecule:


-Head

-made of two globular protein subunits


-reaches the nearest thin filament

Myosin Action

-During contraction, myosin heads:


- Interact with actin filaments, forming cross-bridges


-Pivot, producing motion

Sliding filament theory

-thin filaments of sarcomere slide toward M line, alongside thick filaments


-the width of A zone stays the same


-Z lines move closer together

The process of contraction

-neutral stimulation of sarcolemma


-cisternae of SR release Ca2+

Neutral stimulation of sarcolemma

-causes excitation-contraction coupling



Cistern of SR release Ca2+

-which triggers interaction of thick and thin filaments


-consuming ATP and producing tension

The neuromuscular junction

-is the location of neural stimulation


-action potential (electrical signal)

Action potential (electrical signal)

-travels along nerve axon


-ends at synaptic terminal

Synaptic terminal

-realeases neurotransmitter(acetylcholine or ACh)


-into the synaptic cleft (gap between synaptic terminal and motor en plate)

The Neurotransmitter:


- Acetylcholine or ACh

-travels across the synaptic cleft


-binds to membrane receptors on sarcolemma (motor end plate)


-causes sodium-ion rush into sarcoplasm


-is quickly broken down by enzyme (acetylcholinesterase or AChE)

Action potential

-generated by increase in sodium ions in sarcolemma


-travels along the T tubules


-leads to excitation-contraction coupling

Excitation- contraction coupling

-action potential reaches a triad:


-realeasing Ca2+


-triggering contraction


-requires myosin heads to be in "cocked" position:


-loaded by ATP energy

Five steps of the contraction cycle

-exposure of active sites


-formation of cross-bridges


-pivoting of myosin heads


-detachment of cross-bridges


-reactivation of myosin

Fiber Shortening

-as sacromeres shorten, muscle pulls together, producing tension



Contraction Duration

-depends on:


-duration of neural stimulus


-number of free calcium ions in sarcoplasm


-availability of ATP

Relaxation

-Ca2+ concentrations fall


-Ca2+ detaches from troponin


-active sites are re-covered by tropomyosin


-sarcomeres remain contracted

Rigor Mortis

-a fixed muscular contraction after death


-cause when:


-ion pumps cease to function; ran out of ATP


-calcium builds up in the sarcoplasm

The Contraction Cycle

-Skeletal muscle fibers shorten as thin filaments slide between thick filaments


-Free Ca2+ in the sarcoplasm triggers contraction


-SR releases Ca2+ when a motor neuron stimulates the muscle fiber


-Contraction is an active process


-Relaxation and return to resting length are passive

The all-or-none principle

-as a whole, a muscle fiber either contracted or relaxed

Tension of a single muscle fiber

-Depends on:


-the number of pivoting cross-bridges


-the fibers resting length at the time of stimulation


-the frequency of stimulation