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Muscle Histology
Assoc. Prof Dr. karim Al-Jashamy IMS 2009
Muscular TissueMuscle tissue is composed of cells which have the
ability to contract (shorten) and relax (lengthen).Muscle tissue is highly vascular zed and dense
tissue.Muscle tissue can not regenerate itself once it has
been destroyed.Muscle cells are called muscle fibers. There are three types of muscle tissues:
a. Striated or skeletal muscle
b. Cardiac muscle or myocardial tissue
c. Smooth or visceral muscle
Muscular Tissue Types Striated or skeletal muscle: This muscle is composed of
long, cylindrical, parallel fibers. There are bands or striations present which run across the
width of the fiber. These fibers are multinucleated (more than one nucleus present per cell).
This type of muscle tissue is under conscious or voluntary control.
This muscle has the greatest strength of contraction but tires most rapidly. It functions are locomotion and facial expressions.
Muscular Tissue Types Cardiac muscle: Cardiac muscle fibers are branched at the end
with striations present, usually only one nucleus is present per cell.
The branches of each fiber come into contact at specialized junctions called intercalated discs.
It is involuntarily controlled by the autonomic nervous system and hormones. Its contractions are short, but the muscle fibers are constantly contracting.
Its function is to create the pump which propels the blood throughout the body.
Muscular Tissue Types Smooth or visceral muscle: These cells are spindle-shaped
(tapered on the ends) and lack striations.
They have one nucleus present. They produce weaker contractions, however they contract for extended periods of time.
They are involuntarily controlled by the autonomic nervous system or hormones.
They are found in the digestive organs, arteries and veins, the trachea and bronchiole tubes, and the urogenital tract. Their contractions propels or moves substances or objects from one location to another.
Functions of muscle tissue Movement
Maintenance of
posture
Joint stabilization
Heat generation
Special functional characteristics of muscle
Contractility
Only one action: to shorten
Shortening generates pulling force
Excitability
Nerve fibers cause electrical impulse to travel
Extensibility
Stretch with contraction of an opposing muscle
Elasticity
Recoils passively after being stretched
Types of Muscle Tissue
Skeletal•Attach to and move skeleton
•40% of body weight
•Fibers = multinucleate cells (embryonic cells fuse)
•Cells with obvious striations
•Contractions are voluntary
Cardiac: only in the wall of
the heart
•Cells are striated
•Contractions are
involuntary (not
voluntary)
Smooth: walls of hollow organs
•Lack striations
•Contractions are involuntary (not voluntary)
Similarities…
Their cells are called fibers because they are elongated
Contraction depends on myofilaments
Actin
Myosin
Plasma membrane is called sarcolemma
Sarcos = flesh
Lemma = sheath
Skeletal muscle
Epimysium:
surrounds
whole muscle
Perimysium
is around
fascicle
Endomysium is around each
muscle fiber
Skeletal Muscle Each muscle: one nerve, one artery,
one vein Branch repeatedly
Attachments One bone to another Cross at least one movable joint Origin: the less movable attachment Insertion: is pulled toward the origin
Usually one bone moves while the other remains fixed
In muscles of the limb, origin lies proximal to the insertion (by convention)
Note: origin and insertion may switch depending on body position and movement produced
Attachments continuedMany muscles span two or more joints Called biarticular or multijoint muscles Cause movements at two joints
Direct or “fleshy” attachments Attachments so short that muscle appears to attach directly
to bone
Indirect: connective tissue extends well beyond the muscle (more common) Tendon: cordlike (most muscles have tendons) Aponeurosis: flat sheet Raised bone markings where tendons meet bones Tubercles, trochanters, crests, etc.
Some sites showing animations of muscle contraction
http://entochem.tamu.edu/MuscleStrucContractswf/index.html
http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/muscles/muscles.html
Skeletal muscle
Fibers (each is one cell) have striations
Myofibrils are organelles of the cell: these are made up of filaments
Sarcomere Basic unit of contraction Myofibrils are long
rows of repeating sarcomeres
Boundaries: Z discs (or lines)
This big
cylinder is a
fiber: 1 cell -an organelle
Myofibrils
Made of three types of filaments (or myofilaments):
Thick (myosin)
Thin (actin)
Elastic (titin)
______actin
_____________myosintitin_____
Sliding Filament Model
__relaxed sarcomere__ _partly contracted_
fully contracted
“A” band constant
because it is
caused by
myosin, which
doesn’t change
length
Sarcomere
shortens because
actin pulled
towards its middle
by myosin cross
bridgesTitin resists overstretching
EM (electron microscope): parts of 2 myofibrils
Sarcoplasmic reticulum is smooth ER Tubules surround myofibrils
Cross-channels called “terminal cisternae”
Store Ca++ and release when muscle stimulated to contract
To thin filaments triggering sliding filament mechanism of contraction
T tubules are continuous with sarcolemma, therefore whole muscle (deep parts as well) contracts simultaneously
Neuromuscular Junction
Motor neurons innervate muscle
fibers
Motor end plate is where they
meet
Neurotransmitters are released
by nerve signal: this initiates
calcium ion release and muscle
contraction
Motor Unit: a motor neuron and all the muscle fibers it innervates (these all
contract together)
•Average is 150, but range is four to several hundred muscle fibers in a motor
unit
•The finer movement, the fewer muscle fibers /motor unit
•The fibers are spread throughout the muscle, so stimulation of a single motor
unit causes a weak contraction of the entire muscle
Types of skeletal muscle fibers
Fast, slow and intermediate
Whether or not they predominantly use oxygen to produce ATP (the energy molecule used in muscle contraction) Oxidative – aerobic (use oxygen) Glycolytic – make ATP by glycolysis (break down of sugars without
oxygen=anaerobic)
Fast fibers: “white fibers” – large, predominantly anaerobic, fatigue rapidly (rely on glycogen reserves); most of the skeletal muscle fibers are fast
Slow fibers: “red fibers” – half the diameter, 3X slower, but can continue contracting; aerobic, more mitochondria, myoglobin
Intermediate: in between
A skeletal muscle contracts when its motor units are stimulated
Amount of tension depends on1. the frequency of stimulation2. the number of motor units involved
Single, momentary contraction is called a muscle twitch
All or none principle: each muscle fiber either contracts completely or not at all
Amount of force: depends on how many motor units are activated
Muscle tone Even at rest, some motor units are active: tense the
muscle even though not causing movement: “resting tone”
Muscle hypertrophy Weight training (repeated intense workouts): increases
diameter and strength of “fast” muscle fibers by increasing production of Mitochondria Actin and myosin protein Myofilaments containing these contractile proteins The myofibril organelles these myofilaments form
Fibers enlarge (hypertrophy) as number and size of myofibrils increase[Muscle fibers (=muscle cells) don’t increase in number but increase in diameter producing large muscles]
Endurance training (aerobic): doesn’t produce hypertrophy
Muscle atrophy: loss of tone and mass from lack of stimulation Muscle becomes smaller and weaker
Note on terminology: in general, increased size is hypertrophy; increased number of cells is hyperplasia
Tendon Anatomy Very strong, stronger than muscle for size As strong as bone with a failing point similar to steel! Can transmit force through ability to glide Passive component of the musculotendinous unit in
light of their incredible influence on the foot.
Tendon Histology 30% Collagen, 2% Elastin,
68% Water Bulk is supplied by reticulin 70% Type I collagen
Ligament Histology 33% Composition: 90% Type I
collagen,
Elastin, Glycosaminoglycans.
67% Water
Anatomy of the Tendon Tropocollagen – the most basic molecular unit of
tendon
3 Coverings:
Endotenon- fascicles are surrounded by this areolarCT, contains BV, L, N, and FB.
Epitenon- Fascicles bound together by this 1-2 cell fibroblastic & synovial layer
Paratenon- loose areolar layer continuous with the epitenon & perimysium, straight.
Anatomy of the Tendon
Tendon/Synovial Sheath: acts like a pulley when tendon has an angled course.
Peritenon- term applied collectively to all CT structures associated with a tendon incl para-, meso-, epi-, and endotenon.
Tendon Anatomy
Tendon Anatomy
Tendon Circulation 3 Sources:
a) Small amount from the central blood vessels originating in the muscle.
b) Some from vessels of the bone and periosteum near the tendon’s insertion.
c) Majority comes from small vessels in the paratenon or through the mesotenon. If absent then carried thru the vincula. Synovial fluid also nourishes the tendon.
Tendon Sheath Anatomy
Tendon Innervation Afferent supply only Source in musculotendinous
junction and external local nerves.
Golgi tendon organs: monitor increases in tension rather than length.
Tendon Attachment to Bone Attach at 90° angles to bone
in 4 layers:
1. Tendon collagen fibers
2. Fibrocartilage
3. Bone
4. Sharpey’s fibers – originate in bone and end in perisoteum.