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Skeletal Muscles

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Anas Sohail

on 30 July 2015

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Transcript of Skeletal Muscles

Skeletal Muscles
Functions of Skeletal Muscle
Produce movement of the skeleton

Maintain posture and body position

Support soft tissues

Guard entrances and exits

Maintain body temperature
Muscles are connected to bones by tendons
Essentially involuntary
Connective Tissue


Voluntary Skeletal Muscle Movement:

Because each muscle fiber is innervated, we have control over muscle contraction.
By: Anas Sohail, Chandni Agarwalla, Jagroop Johal, Sasha Ramcharan, Shivani Shah & Vishaldeep Singh
Anatomy of Skeletal Muscles
AKA muscle cells
Longer than it is wide
Multinucleated so that large proteins do not have to wait and DNA information can be transmitted faster
Anatomy Cont'd
Membrane of the muscle
Myofibrils are the tubes within (striations are present)
Different bands will be found: with short bands and wide bands
Individual units are called sarcomere
Consists of:
Which is attached to myosin by titan
Holds the A-band and I-band
Corresponds with both myosin (two heads) and actin filaments
Only corresponds with the actin filaments.
Muscle Contraction
Action potential travels along the membrane, and down the T-tubules

The sarcoplasmic reticulum gets triggered to release calcium which attaches to troponin

Troponin is attached to the actin filaments

Tropomyosin gets moved and the myosin can start using ATP to help with the contraction

Myosin stays in one place whereas the actin filaments are going to be pulled together
Pathophysiology of Skeletal Muscle
Diseases of Muscular System

No specific doctor for treatment of muscular diseases and disorders
Rheumatologists, orthopedists and neurologists may all treat conditions that affect the muscles
Common Primary Muscular Disorders
Inflammatory myopathies:
Polymyositis: characterized by inflammation and progressive weakening of the skeletal muscles
Dermatomyositis: polymyositis accompanied by a skin rash
Body myositis: characterized by progressive muscle weakness and wasting

Other common disorders are, muscular dystrophies, and metabolic muscle disorders
Common Primary Muscular Disorders Cont'd
Neuromuscular disorders
Myasthenia gravis characterized by varying degrees of weakness of the skeletal muscles
Amyotrophic lateral sclerosis, or ALS Motor neuron disorders affect the nerve cells that supply muscles. Commonly known as Lou Gehrig's disease.
Most common sign of muscle disorder is weakness
Other symptoms include:
Abnormal fatigue with activity
Muscle spasms
Neuromuscular disorders affecting the eyes or mouth can cause:

Drooping eyelids
Double vision
Slurred speech
Difficulty swallowing
Sometimes, difficulty breathing
EMG (Electromyography):
Often used to diagnose muscular disorders
Identifies the causes of nerve and muscle disorders by stimulating nerves and recording the responses
Nerve or muscle biopsies are rarely needed.


Steroids and other medications help reduce spasms and cramping
Milder forms of chemotherapy can also help treat many muscular disorders
Histology of Skeletal Muscles
Very long tubular cells called muscle fibres
Contain many peripherally placed nuclei
Contain several hundreds of small nuclei with 1 or 2 nucleoli located just beneath the plasma membrane
Show characteristics of cross-striations (striated muscle)
Innervated by the somatic (voluntary) nervous system
Skeletal Muscle Development

Occurs through fusion of embryonic cells called myoblasts
These cells may contribute to growth and repair of skeletal muscle

Myofilaments –> Myofibrils –> Muscle Fiber

Cross-sectional image of skeletal muscle:- nuclei at the edges of the fibers
3 types of connective tissue sheaths:

- "overcoat" of dense irregular connective tissue that surrounds the whole muscle
- bundle together into fascicles
- surrounds each muscle fibre
Do you recall the layers of Skeletal Muscle connective tissues?

There are dark A bands and light I bands in longitudinal sections of muscle fibers
The fibers are multinucleated and the nuclei are located in a peripheral location in the fibers
Sarcomere is the contractile element of the muscle fiber
Histology Features:
Isometric - contracts without change in length
Isotonic - contracts with shortening in length
Steps That End a Contraction:

Action potential generation ceases as ACh is broken down by acetylcholinesterase (AChE)

Sarcoplasmic reticulum reabsorbs calcium ions, and the concentration of calcium ions in the sarcoplasm declines

When calcium ion concentrations approach normal resting levels, the troponin and tropomysin molecules return to their normal positions. This change re-covers the active sites and prevents further cross-bridge interaction

Without cross-bridge interactions, further sliding cannot take place and the contraction will end

Muscle relaxation occurs, and the muscle returns passively to its resting length
Thanks for listening!
Skeletal muscle stained with H&E (hematoxylin and eosin)
Shows several fascicles surrounded by perimysium.
Uniform size and shape, with nuclei located at the periphery of the cell
Cytoplasm is fairly uniformly distributed
Mosaic pattern

A Look Under the Microscope
High power of the same H&E stain shows normal appearance of sarcoplasm and a peripherally placed nucleus
Myofibers are separated by thin endomysial connective tissue
Capillaries, normally indistinct, can be found at the corners between myofibers

Shows the basal lamina of blood vessels such that the PAS stain also provides information about vascular structure

Highlights degenerating or necrotic fibers
High Power
H&E stain
Myofibers in longitudinal section forming an array of fibers lined up in parallel
Striations produced by the sacromeres
Indiction of myofiber necrosis is loss of these striations

Periodic acid-Schiff (PAS) stain
High-power view of PAS stain shows carbohydrates thus highlighting:
Commonly used and most useful for evaluating glycogen storage disease.

Skeletal muscle fibres:
Looks striped or "striated" –
Contain alternating light and dark bands (striations)
Packed into regular parallel bundles
The anatomical arrangement of skeletal, or striated muscle fascicles creates four types of skeletal muscles on the basis of fiber arrangements:
Ex. Biceps brachii, sartorius, etc.
Ex. Pectoralis major
Ex. Extensor digitorm (unipennate), rectus femoris (bipennate), deltoid (multipennate)
Sphincter (AKA circular)
Ex. Orbicularis Oris
Skeletal Muscle Classification
Not ALL muscle fibers are the same!!
Skeletal muscle fibres contract at different speeds depending on:
Ability to split ATP
The way they produce ATP
How quickly they get tired
Slow Twitch (also called Type I):

Contains many capillaries
Has many mitochondria
Has lots of myoglobin (the oxygen transporting and storage protein of the muscle)
Carries more oxygen
Doesn’t get tired easily (can sustain aerobic activity)
Contracts slowly
Found in large numbers in the postural muscles of the neck
Type IIa:
Is aerobic like slow twitch muscle
Is rich in capillaries
Looks red

Type IIx:
Has fewer mitochondria and less myoglobin
Can contract more quickly than Type IIa
Can contract with more force than aerobic muscle
Can sustain only short, anaerobic bursts of activity before muscle contraction
Becomes painful (Lactic acid)
Is the fastest muscle type in humans

Type IIb:
Is anaerobic white muscle
Is even less dense in mitochondria and myoglobin
Can contract even more quickly
Is the major fast muscle type in small animals like rodents or rabbits (which explains why their meat is so pale)
Fast twitch (also called Type II):
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