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37 Cards in this Set

  • Front
  • Back
Muscles
All our activities need muscles
Muscle cells are called myocytes
Myocytes are specialized to contract
When a muscle cell contracts, it shortens and pulls upon the structures to which it is attached
The puling force created is called tension and requires energy
Muscle

Types
Smooth
Cardiac
Skeletal - represents the majority of muscle in the body
Smooth Muscle
Spindle- shaped
Mononcleated
Non-striated, no sarcomeres or myofibrils
Involuntary
Found in GI tract, reproductive tract, blod vessels, and some ducts
No T-tubules
Thin filaments attach to dense bodies
Dense bodies anchor thin contractile proteins and allow thick and thin filaments to slide during contraction which results in shortening of the cell
Cardiac Muscle
Network of interconnectin gparallel fibers
Mononucleated
Striated
Involuntary
Has intercalated disks
Functional syncytium
Location: heart
Skeletal Muscle
Cylindrical shape
Multinucleated
Heavily striated
Voluntary
True syncytium
Location: skeletal system and diaphragm
Anatomy of Muscle and its attachments
Tendons - converging dense fibrous connective tissue which attaches muscle to bone
Aponeurosis - broad sheets of fibrous connective tissue that anchor muscle to bone
Tendon of origin - fixed attachment
Tendon of insertion - moves during contraction
Central region of the muscle is called the belly
Connective tissues associated with skeletal muscle
Called fascia
Epimysium
Perimysium
Endomysium
Muscle Structure
Endomysium wraps inidvidual muscle fibers
Perimyseium wraps bundles of fibers or fasicles
Epimysium and facia enclose the entire layer of muscle
Each muscle fiber has its own membrane a sarcolemma - analogous to a plasma membrane
Each muscle fiber is made up of myofibrils which are contractile proteins
Muscle Fibers
Extrafusil
Infusil
Extrafusil Fibers
These are large cells that are the working muscle fibers
May have a diameter up to 100 microns and a length equal to the entire muscle (12 inches)
During development groups of embryonic cells called myoblasts fuse forming multinucleated muscle fibers
Extrafusil Fibers
Each skeletal muscle is a true syncyitum and multinucleated
These nuclei direct the production of enzymes and proteins required for muscle contraction
Sarcolemma
Surrounds the muscle fiber
Penetrated by transverse tubules (T-tubules)
T-tubules run perpendicular to the long axis of the muscle
Each t-tubule is sandwiched by terminal cisterns that branch into L-tubules and sarcoplasmic reticulum
Sarcolemma
The T-tubule and cisterns create a triad that surround each myofibril
A stimulus is conducted from the sarcolemma through the cells by way of the T-tubules, cisterns L-tubules, and sarcoplasmic reticulum
Receptors release Ca++ when they become depolarized and take up Ca++ when they repolarize
Myofibrils
Threadlike structure
It is a contractile organelle
Each cell contains several hundred-thousand myofibrils
Myofilaments make up the myofibrils
Myofilaments are made up of the contractile proteins actin and myosin
Myofilaments

Actin
Thin filaments
G-actin molecules string together to form F-actin
F-actin filaments twist together and are anchored by Nebulin
Tropomyosin covers these strands too
Troponin is attached to the F-actin and tropomyosin and it regulates contraction
Myofilaments

Myosin
Thick filaments
Each thick filament is made up of 500 myosin molecules
Each myosin molecule is made up of a pair of myosin subunits twisted around each other
the tail binds to other myosin molecules in the thick filament
The heads attach by globular protein and interact with actin during a contraction - known as cross-bridges
Myosin is oriented with tails towards the M-line and heads away from it
M-line is a protein that secures the thick filament
Titin protein - extends through the filmanet and attaches to the Z-line
Myofibril Proteins
Contractile
Regulator
Structural & stabilizing
Myofibril Proteins

Contractile
Actin
Myosin
Myofibril Proteins

Regulator
Tropomyosin
Troponin
Myofibril Proteins

Structural & Stabilizing
Desmin or Skeletin
Nebulin
Actinin
Titin
Connectin
Dystrophin
Myofibril Proteins

Actin
F-actin filament is 2 chains of G-actin in a double helix
13 G-actin molecules per revolution
Attached to the G-actin is ADP which is the active site
G-actin contains ADP active site for myosin binding
F actin is 2 polymers of 300-400 G actin molecules
Myofibril Proteins

Myosin
Myosin filament is about 500 myosin molecules
Each molecule is a dimer - 2 polypeptide chains wound around each other
Each chain has a tail (light meromyosin) and a neck and head (heavy meromyosin)
Two heavy meromyosin heads per molecule which represent the functional portion of the molecule
Head and neck make up cross bridges
Neck is S2 region; head is S1 region
Contains sites for ATP and actin binding
Head has 2 functions: tug actin filaments inward and to act as an ATPase to furnish energy to the head region
Myofilament bridge is myomesin head, skelenin, and M-protein which is an isomer of creatine kinase
Regulator Proteins

Tropomyosin
Polymer
Length of 7 G-actin molecules
Multiple torpomyosin molecules extend to entire length of F actin helix
Loosely connected to F actin and cover the G actin active sites is a resting muscle fiber
Regulator Proteins

Troponin
Attached near the ends of the tropomyosin
Trimolecular with 3 subunits:
Tn-C high affinity for calcium
Tn-1 - affinity for actin
Tn-T affinity for tropomyosin
Structural and Stabilizing Proteins

Desmin or Skeletin
Crosslinks myofbrils
Structural and Stabilizing Proteins

Nebulin
Regulates length of actin filament
Extends entire length of F actin
Located in cleft between actin double helis
Stabilizes the molecules
Structural and Stabilizing Proteins

Actinin
Anchors F actin to Z line connectin
Structural and Stabilizing Proteins

Titin
Anchors myosin to to Z line, stabilizing it in center of sarcomere
Structural and Stabilizing Proteins

Connectin
Makes up Z line
Anchors other proteins in sarcomere
Structural and Stabilizing Proteins

Dystrophin
Anchors integral proteins to cytosol
Provides strength to membrane
Absence causes Duchenne's Musclar dystrophy
Sarcomere
Sarcomere means flesh part
Represent the repeating contractile units of a muscle cell
Each myofibril has thousands of sarcomeres
Each sarcomere has a resting length of 1.6 - 2.6 microns
Sarcomere is organized in bands based upon length and density of thick and thin filaments
Sarcomere
A band
I band
Z line
H band
Zone of overlap
Sarcomere

A band
Anisotropinc dark appearing band
Extends entire length of myosin
Sarcomere

I band
Isotropic light appearing band
Contains titn
Appears between the end of myosin and z line
Sarcomere

Z line
Represents boundaries between adjacent sarcomeres
Appear as striations running through the myofibrils of the muscle cell
Made up of proteins called connectin
Connectin connect filaments of adjacent sarcomeres
Sarcomere

H band
Region on either side of the M-line
Contains thick filaments, but no thin filaments
Distance from end of thin actin filament to M-line
Sarcomere

Zone of overlap
Each thin filament is surrounded by 3 thick filaments
Each thick filament is surrounded by 6 thin filaments