Skeletal Muscle

Front 1

The 3 Types of Muscle

Back 1

Skeletal, Cardiac, and Smooth

Front 2

Striations

Back 2

alternating dark and light bands

Front 3

How are muscles classified (3)?

Back 3

1) Location (skeletal vs cardiac vs smooth), 2) Histology (striated vs non-striated), 3) Mode of control (voluntary vs unvoluntary)

Front 4

Classification of skeletal muscle; Function?

Back 4

CLASSIFICATION – Skeletal, striated, Voluntary; FUNCTION – move bones and structures; Attach primarily to bone but some to skin, deep fascia, and other muscles

Front 5

Classification of cardiac muscle; Function?

Back 5

CLASSIFICATION – Cardiac, Striated, Involuntary; FUNCTION – From walls of heart

Front 6

Classification of smooth muscle; Function?

Back 6

CLASSIFICATION - Smooth, Non-striated, Involuntary; FUNCTION – Form part of walls of vessels and hollow organs (ex: intestines, stomach, blood vessels)

Front 7

Skeletal Muscle

Back 7

Generates force through contraction; 40-50% of body weight

Front 8

3 Functions of Skeletal Muscle

Back 8

Motion, Posture, Generation of body heat (generates 85% of our body heat)

Front 9

4 Characteristics of Skeletal Muscle

Back 9

1) Excitability – Can generate electrical pulses to be transmitted along a membrane; 2) Contractility – Shortening muscle fibers to generate force; 3) Extensibility – can STRETCH without damage; 4) Elasticity – Can RETURN TO ORIGINAL SHAPE after contraction or extension

Front 10

Opposing pairs of muscles

Back 10

Sometimes muscles are in pairs such that one contract while the other relaxes

Front 11

Sarcolemma

Back 11

Plasma membrane of muscle fiber (cell)

Front 12

Sarcoplasma

Back 12

Cytoplasm of muscle cell

Front 13

Nucleus of Skeletal Muscle

Back 13

Multinucleated and located peripherally

Front 14

Sarcoplasmic reticulum (SR)

Back 14

Stores intracellular Calcium and releases it during periods of contraction (similar to smooth endoplasmic reticulum)

Front 15

Terminal cistern/cisternae of sarcoplasmic reticulum

Back 15

dilated ring-like channel portion of SR

Front 16

Transverse tubules (T-tubules)

Back 16

Invagination of sarcolemma that opens to outside of muscle fiber Runs transversely through fiber and perpendicular to SR; Helps conduct electric impulses into the cell; *SR runs up long axis of muscle fiber

Front 17

Triad

Back 17

Where T-tubules and Terminal Cisternae of SR meet (at both opposite ends of SR); Important for muscle contraction

Front 18

Myofibrils

Back 18

Consist of MYOFILAMENTS; Myofibrils are thousands of tube-shaped CONTRACTILE STRUCTURES running longitudinally in a muscle cell

Front 19

Two Types of Myofilament and protein composition

Back 19

1) Thin filament (Actin) and 2) Thick filament (Myosin)

Front 20

What are the striations along the myofibril – appearance and type of myofilament of each? (5)

Back 20

1) I bands –Light (less dense) and composed of THIN MYOFILAMENT ONLY; 2) z disc – dark line bisecting I band, 3) A band – dark band (dense) representing whole length of thick myofilament; SIDES OF A BAND ARE DARK WHERE THICK AND THIN MYOFILAMENTS OVERLAP , 4) H zone - Narrow, lighter midsection of A band made of THICK MYOFILAMENT ONLY, 5) M LINE – Line bisecting H zone, where adjacent thick filaments are suspended and linked via accessory proteins

Front 21

Sarcomere

Back 21

Smallest contractile unit of a muscle fiber (There are many sarcomeres in a myofibril); REGION BETWEEN 2 SUCCESSVIE z DISCS (An A band flanked by HALF AN I BAND on each side)

Front 22

Organization within muscle fibers

Back 22

Myofilaments make up sarcomeres which make up myofibrils, which make up muscle fibers

Front 23

What are the 3 structural proteins of sarcomeres?

Back 23

1) Titin – large, linear elastic protein that help connect the thick myofilaments to the z disc; 2) alpha- Actinin – rod-shaped protein in z disc that holds thin myofilament in place by binding thin myofilament in parallel arrays, 3) Nebulin – long, NON-ELASTIC proteins that wrap around entire length of thin myofilament (2nebulin molecules per each thin myofilament) to further anchor it in z disc

Front 24

What happens when muscles relax?

Back 24

Thick myofilaments DO NOT extend the entire length of sarcomere and thin myofilaments on either side of z disc DO NOT meet at midline

Front 25

What happens when muscles contract (3)?

Back 25

1) z discs are brought closer together as thin myofilament slides past thick myofilament towards the center so they overlap more (THICK AND THIN FILAMENTS DO NOT CHANGE LENGTH; JUST SLIDE); 2) I band width shortens, 3) H zone disappears (width shortens), 4) A bands move closer together but don’t change length

Front 26

Structure of Myosin (protein of thick myofilament)

Back 26

2 identical heavy chains and 2 PAIRS of light chains (4 light chains total); Heavy chain resembles 2 golf clubs with heads outward and the chains wrap around each other in alpha-helix

Front 27

Light chains

Back 27

Hidden by heads of myosin; 2 types: one of each type of light chain is associated with each S1

Front 28

How can the heavy chain of myosin be cleaved?

Back 28

Trypsin can cleave it into HMM (Heavy Meromysin) and LMM (Light Meromysin)

Front 29

Structure and function of LMM

Back 29

Rod-like tail consists of 2 rod-like polypeptide chains wrapped around each other; FUNCTION – proper assembly of molecule into bipolar thick myofilament

Front 30

Structure of HMM

Back 30

contains 2 globular heads and a short portion of 2 polypeptide chains

Front 31

How can HMM be further cleaved?

Back 31

Papain can cleave it into the globular domains S1 (subfragment 1) and S2 (subfragment 2; a short, helical,rod-like segment)

Front 32

Function of S1

Back 32

Binds ATP and functions in formation of cross bridges between thick and thin filaments

Front 33

How are myosin heads lined up?

Back 33

Paralell but staggered so heads can be 60 degrees relating to neighboring HMM and associate with thin filaments

Front 34

What is the major component of thin filaments?

Back 34

F-Actin

Front 35

G-Actin

Back 35

A polymer of F-actin (two F-actin strands wrapped in helix) that give myofilament a distinct polarity (PLUS end – bound to z disc by alpha-Actinin; MINUS end – extends toward center of sarcomere)

Front 36

Function of G-Actin

Back 36

Contains active site where head region of myosin binds

Front 37

Tropomyosin

Back 37

Occupy shallow groove of actin molecules to mask the active site of actin by partially overlapping them; EACH TROPOMYOSIN MOLECULE IS BOUND TO A TROPONIN MOLECULE

Front 38

The 3 Globular proteins of Troponin? Functions?

Back 38

1) Troponin T – binds entire troponin molecule to tropomyosin; holds tropomyosin to actin; 2) Troponin I - Binds actin, preventing interaction between actin and myosin SO THAT MUSCLES CAN’T CONTRACT; 3) Troponin C – has great affinity for Calcium for a conformational change that uncovers blocked active site again so S1 of myosin can bind actin TO RESUME CONTRACTION

Front 39

6 Steps of Sliding Filament Theory

Back 39

1) ATP binds myosin head to activate it; 2) Calcium binding to troponin shifts Tropomysin to expose active site for myosin head; 3) ATP bound to myosin head hydrolyzes to ADP + Phosphate ion and Myosin and Actin form a cross-bridge; 4) Phosphate ion is released and myosin head cocks to begin contraction; 5) ADP releases from myosin head, leading to POWER STROKE, where myosin head pulls actin toward the center of the sarcomere; 6) ATP binds myosin head once again, causing the head to release its bind on action to no relax the muscle

Front 40

How is muscle contraction initiated?

Back 40

Nervous system: Impulse is transmitted from motor neurons to skeletal muscle fiber via the neuromuscular junction

Front 41

Neuromuscular Junction (3 parts)

Back 41

Composed of 1) Axon terminal of motor neuron, 2) Synaptic cleft, 3) Muscle cell membrane (Post-synaptic membrane)

Front 42

What is found in the axon terminal?

Back 42

Mitochondrua, SER, and hundres of thousands of synaptic vesicles containing neurotransmitter Acetylcholine

Front 43

Junctional folds

Back 43

Secondary synaptic clefts within the synaptic cleft

Front 44

How does excitation of muscle cells lead to deliberation of Calcium (7 Steps)?

Back 44

EXCITATION-CONTRACTION COUPLING: 1) Nerve impulses travelling along nerve axon DEPOLARIzE the membrane of axon terminal; 2) Voltage-gated Calcium channel in presynaptic terminals open; 3) Influx of CALCIUM into axon terminal causes FUSION of synaptic vesicles and presynaptic membrane, leading to RELEASE OF ACETYLCHOLINE; 4) Acetylcholine diffuses across synaptic cleft, and bins to post-synaptic Acetylcholine receptors on muscle cell membrane; 5) Acetylcholine receptor activation leads to depolarization of sarcolemma and generation of ACTION POTENTIAL; 6) Action potential is propagated along the sarcolemma and down the T-tubules, triggering release of Calcium from terminal cisternae of sarcoplasmic reticulum (SR); 7) Calcium released from SR initiate the process of muscle contraction

Front 45

How do the T-tubules play a role?

Back 45

Special proteins of T-tubules act as a gate of the SR; When membranes depolarized, proteins undergo confromaional change, thy open the channel for Calcium to flow out; Channels close upon repoalrization