Ahs 131 Lecture Week Muscles

Front 1

Muscles

Back 1

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

Front 2

Muscle

Types

Back 2

Smooth
Cardiac
Skeletal - represents the majority of muscle in the body

Front 3

Smooth Muscle

Back 3

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

Front 4

Cardiac Muscle

Back 4

Network of interconnectin gparallel fibers
Mononucleated
Striated
Involuntary
Has intercalated disks
Functional syncytium
Location: heart

Front 5

Skeletal Muscle

Back 5

Cylindrical shape
Multinucleated
Heavily striated
Voluntary
True syncytium
Location: skeletal system and diaphragm

Front 6

Anatomy of Muscle and its attachments

Back 6

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

Front 7

Connective tissues associated with skeletal muscle

Back 7

Called fascia
Epimysium
Perimysium
Endomysium

Front 8

Muscle Structure

Back 8

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

Front 9

Muscle Fibers

Back 9

Extrafusil
Infusil

Front 10

Extrafusil Fibers

Back 10

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

Front 11

Extrafusil Fibers

Back 11

Each skeletal muscle is a true syncyitum and multinucleated
These nuclei direct the production of enzymes and proteins required for muscle contraction

Front 12

Sarcolemma

Back 12

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

Front 13

Sarcolemma

Back 13

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

Front 14

Myofibrils

Back 14

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

Front 15

Myofilaments

Actin

Back 15

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

Front 16

Myofilaments

Myosin

Back 16

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

Front 17

Myofibril Proteins

Back 17

Contractile
Regulator
Structural & stabilizing

Front 18

Myofibril Proteins

Contractile

Back 18

Actin
Myosin

Front 19

Myofibril Proteins

Regulator

Back 19

Tropomyosin
Troponin

Front 20

Myofibril Proteins

Structural & Stabilizing

Back 20

Desmin or Skeletin
Nebulin
Actinin
Titin
Connectin
Dystrophin

Front 21

Myofibril Proteins

Actin

Back 21

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

Front 22

Myofibril Proteins

Myosin

Back 22

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

Front 23

Regulator Proteins

Tropomyosin

Back 23

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

Front 24

Regulator Proteins

Troponin

Back 24

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

Front 25

Structural and Stabilizing Proteins

Desmin or Skeletin

Back 25

Crosslinks myofbrils

Front 26

Structural and Stabilizing Proteins

Nebulin

Back 26

Regulates length of actin filament
Extends entire length of F actin
Located in cleft between actin double helis
Stabilizes the molecules

Front 27

Structural and Stabilizing Proteins

Actinin

Back 27

Anchors F actin to Z line connectin

Front 28

Structural and Stabilizing Proteins

Titin

Back 28

Anchors myosin to to Z line, stabilizing it in center of sarcomere

Front 29

Structural and Stabilizing Proteins

Connectin

Back 29

Makes up Z line
Anchors other proteins in sarcomere

Front 30

Structural and Stabilizing Proteins

Dystrophin

Back 30

Anchors integral proteins to cytosol
Provides strength to membrane
Absence causes Duchenne's Musclar dystrophy

Front 31

Sarcomere

Back 31

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

Front 32

Sarcomere

Back 32

A band
I band
Z line
H band
Zone of overlap

Front 33

Sarcomere

A band

Back 33

Anisotropinc dark appearing band
Extends entire length of myosin

Front 34

Sarcomere

I band

Back 34

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

Front 35

Sarcomere

Z line

Back 35

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

Front 36

Sarcomere

H band

Back 36

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

Front 37

Sarcomere

Zone of overlap

Back 37

Each thin filament is surrounded by 3 thick filaments
Each thick filament is surrounded by 6 thin filaments