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By the end of this section, you will be able to:
  • Describe the layers of connective tissues packaging skeletal muscle
  • Explain how muscles work with tendons to move the body
  • Identify areas of the skeletal muscle fibers
  • Describe excitation-contraction coupling

The best-known feature of skeletal muscle is its ability to contract and cause movement. Skeletal muscles act not only to produce movement but also to stop movement, such as resisting gravity to maintain posture. Small, constant adjustments of the skeletal muscles are needed to hold a body upright or balanced in any position. Muscles also prevent excess movement of the bones and joints, maintaining skeletal stability and preventing skeletal structure damage or deformation. Joints can become misaligned or dislocated entirely by pulling on the associated bones; muscles work to keep joints stable. Skeletal muscles are located throughout the body at the openings of internal tracts to control the movement of various substances. These muscles allow functions, such as swallowing, urination, and defecation, to be under voluntary control. Skeletal muscles also protect internal organs (particularly abdominal and pelvic organs) by acting as an external barrier or shield to external trauma and by supporting the weight of the organs.

Skeletal muscles contribute to the maintenance of homeostasis in the body by generating heat. Muscle contraction requires energy, and when ATP is broken down, heat is produced. This heat is very noticeable during exercise, when sustained muscle movement causes body temperature to rise, and in cases of extreme cold, when shivering produces random skeletal muscle contractions to generate heat.

Each skeletal muscle is an organ that consists of various integrated tissues. These tissues include the skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Each skeletal muscle has three layers of connective tissue (called “mysia”) that enclose it and provide structure to the muscle as a whole, and also compartmentalize the muscle fibers within the muscle ( [link] ). Each muscle is wrapped in a sheath of dense, irregular connective tissue called the epimysium    , which allows a muscle to contract and move powerfully while maintaining its structural integrity. The epimysium also separates muscle from other tissues and organs in the area, allowing the muscle to move independently.

The three connective tissue layers

This figure shows the structure of muscle fibers. The top panel shows a skeleton muscle fiber, and a magnified view of the muscle fascicles are shown. The middle panel shows a magnified view of the muscle fascicles with the muscle fibers, perimysium and the endomysium. The bottom panel shows the structure of the muscle fiber with the sarcolemma highlighted.
Bundles of muscle fibers, called fascicles, are covered by the perimysium. Muscle fibers are covered by the endomysium.

Inside each skeletal muscle, muscle fibers are organized into individual bundles, each called a fascicle    , by a middle layer of connective tissue called the perimysium    . This fascicular organization is common in muscles of the limbs; it allows the nervous system to trigger a specific movement of a muscle by activating a subset of muscle fibers within a bundle, or fascicle of the muscle. Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer of collagen and reticular fibers called the endomysium    . The endomysium contains the extracellular fluid and nutrients to support the muscle fiber. These nutrients are supplied via blood to the muscle tissue.

Questions & Answers

how to identify tissues cells under a microscope
Carla Reply
any advice on how to identify tissue cells under a microscope?
Carla
What is homeostasis
Haji Reply
ability of living organisms to adjust it internal environment to maintain a stable equilibrium
famuyiwa
how to identify tissues cells under a microscope
Carla
what is the anatomy
aamina Reply
anatomy is the branch of science concerned with the bodily structure of humans animals and other living organisms, especially as revealed by dissection and the separation of parts.
Misikir
what are silhouettes
Magret Reply
is dis Medical term?
Preity
yes
Magret
but I don't know what it means
Magret
silhouette outline of a figure. The sharpness of the silhouette is a function of the shape, size and density of the object. This is most marked in radiography. basketball-shaped silhouette the enlarged cardiac outline seen in the dorsal-ventral view of the thorax in a dog with chronic pericardial
Callisto
Homeostasis
Haji
it's the first stage of wound healing that involves vasoconstriction platelet plug formation and blood clotting
famuyiwa
Levels of complexity
julie
sorry that was fast hemostasis
famuyiwa
Kkkk
julie
Anti there is homeostasis and haemostasis
julie
yes , homeostasis is the abiltity of a living organism to adjust it environment to maintain a stable equilibrium
famuyiwa
Thank you Alice, how about Haemostasis?
Christina
why are postsynaptic ganglionic neurons unmyelinated
Callie Reply
Postganglionic motor neurons are unmyelinated because the lack myelin sheath. The myelin sheath on the peripheral nervous system is composed of Schwann cells wrapped around the axon inside the endoneurium.
Carmelo
they lack*
Carmelo
Postganglionic (and preganglionic) motor neurons belong to the division of the autonomic nervous system. In contrast, the somatic nervous system contains only one long thick myelinated somatic presynaptic motor neuron.
Carmelo
anatomy defination in urdu
Atif Reply
human body largest organ.....
jasveer Reply
liver
JOY
liver
Lem
Skin
amen
lungs
Zamiir
liver and skin
Marina
skin
brian
by mass is liver but externally is de skin
Kumsah
all answers Are correct
brian
no
Rehman
liver is the largest gland of the body but skin is the largest organ of the body
Rehman
so please what is the answer now
Marina
afcous skin.because difference between Gland and organ
Safiya
Only the skin
Williams
The largest organ is the skin and the liver is a gland
Williams
skin is the largest organ of the body
Denis
liver
julie
it's the skin
trinna
skin 100%
Mallikharjun
largest organ- liver largest system- Skin
Shahriar
largest organ is skin because it covers the rest of the organs
Syed
liver right answers
nisha
liver
Justine
skin
Areej
liver is largest gland
Areej
skin is largest organ liver is largest gland femur is largest bone thyroid gland is largest endocrine gland seratus muscle is largest muscle
Tanveer
sciatic nerve is largest nerve
Tanveer
portal vein is largest vein
Tanveer
GIT is largest tube in body
Tanveer
explain about cerebrum cereblum and pons medulla
Tanveer
Nervous system anotomy and physiology
Tanveer
skin is the human body's largest organ
Kimbley
@Tanveer, the cerebrum consists of the cerebral cortex, corpus callosum, hippocampus, and basal ganglia. The cerebellum is located inferior to the occipital lobe. The pons and medulla are part of the lower brainstem.
Carmelo
The cerebral cortex are divided into 4 lobes and control functions such as: thinking, learning, speech, sensory perception, motor functions, hearing and vision, etc. The cerebral cortex is mainly present only in mammals due to evolution. The hippocampus plays a main role in memory formation.
Carmelo
The cerebellum works together with the motor cortex and other parts of the brain to coordinate and fine tune muscular activity. The pons and medulla control autonomic functions such as: sleep, respiration, swallowing, vomiting, heart rate, vasomotor control and more other things.
Carmelo
skin hai friend
Tilak
what is the biliary tract
famuyiwa
The biliary tract involves the liver, gallbladder, and bile duct. Certain liver cells (hepatocytes) synthesize bile salts derived from cholesterol in response to Secretin hormone. The gallbladder stores the bile. Gallbladder releases bile to the bile duct in response to Cholecystokinin hormone.
Carmelo
The role of bile is to emulsify fats so that they can be easily broken down and absorbed by the enterocytes into the lacteal vessels.
Carmelo
what is the difference between negative feedback loop and positive feedback loop
famuyiwa
what is cholesterol
Kay
unsaturated fats
famuyiwa
so what is the main purpose of anomaly
Kay
Cholesterol is a waxy substance your body uses to protect nerves, make cell tissues, and produce certain hormones.
Favour
Cholesterol is a type of lipid and it is a nonpolar molecule. The molecule is mainly composed of hydrocarbon chains. Cholesterol is synthesized in the smooth endoplasmic reticulum in eukaryotic cells, and is the main building block material for steroids, Vit D, and bile salts.
Carmelo
Negative feedback loop reverses any change back to its set point. For ex, when your internal body temperature rises above 98.6 F, your hypothalamus triggers your dermal blood vessels to dilate and activate sweat glands through sympathetic motor nerves so you can sweat and cool off back to 98.6 F.
Carmelo
Positive feedback loop amplifies a change. For ex, during labor, oxytocin is released continuously in a positive feedback loop from the posterior pituitary gland to stimulate contraction of the myometrium so the baby can come out.
Carmelo
define homeostasis and explain it's importants
Adusei Reply
define the important life processes of humans
Adusei
how the bone marrow transplantation is done?
Tanveer
what is homeostasis
julie Reply
internal temperature of body
Sanket
Homeostasis is the internal constancy in which your body tries to maintain for optimal cellular functioning. For example, your body tries to maintain an internal body temperature of about 98.6F for optimal functioning of your body.
Carmelo
If a prolonged lost of homeostasis occurs, death of the organism will be the outcome.
Carmelo
Another example of homeostasis is that your body tries to maintain a specific blood sugar level, so that your cells can undergo constant cellular respiration and keep you alive.
Carmelo
homeostasis is the fairly constant internal changes of an environment (your internal environment).The temperature of a body must be kept between the range of 37.5°c
raphael
which tissue is more sensitive
Rit Reply
to what?
Lari
myasthenia gravis?
Selva
Myasthenia gravis is an autoimmune disease in which your own antibodies (produced by plasma cells) attack and inhibit nicotinic receptors at the neuromuscular junction.
Carmelo
As a result, acetylcholine will not bind to nicotinic receptors and now action potential is produced on the sarcolema. If no AP is produce, then there is no contraction of the muscle. For a long period of time, this will result in atrophy and muscle weakness.
Carmelo
and no action potential*
Carmelo
explain types of hypertension
Juli Reply
What is bulbar paralysis?
Roshni Reply
how can make penis larger
Marwat Reply
what is the stimuli initiates the control of erythropoiesis?
Ok Reply
oxygen
Liyungu
Erythropoietin, a hormone synthesized and released by the kidneys stimulate erythropoiesis in red bone marrow. When an Individual loses blood (hemorrhage) and the concentration of RBCs or oxygen decreases, erythropoitein will be released.
Carmelo
how lymph is from
Hafsa Reply
Lymph is essentially interstitial fluid that ends up in the lymphatic vessels that didn't go back into the venules. Lymph is composed of the same components as your blood plasma which contains water, solutes, oxygen, CO2, foreign particles such as toxins, bacteria and viruses.
Carmelo
what is the cause of twins
Clarus
The cause of identical twins is when a single fertilized egg undergo mitosis (splits in two) . As a result, both eggs now have the same genetic information, therefore producing two identical twins.
Carmelo
Different twins (fraternal) occurs when two different eggs are ovulated and two different sperm fertilize each egg. As a result, fraternal twins are not genetically identical and can even be opposite sex.
Carmelo
Fraternal twins occurs when two different eggs are ovulated and two different sperm fertilize each egg. As a result, fraternal twins are not genetically identical and can even be opposite sex.
Carmelo
If two eggs are ovulated during ovulation, and two different sperms fertilize each egg then fraternal twins will occur. Fraternal twins are not generically identical and can even be opposite sex.
Carmelo
Fraternal twins occurs when two different eggs are ovulated and two different sperm fertilize each egg. As a result, fraternal twins are not genetically identical and can even be opposite sex.
Carmelo
how structure and function relate to each other?
Garmai
This is a very important rule in Anatomy and Physiology. The structure of a cell, tissue, or organ will tell you a lot about it's function.
Carmelo
For example, simple columnar cells (enterocytes) in the villus present in the duodenum of the small intestine contain microvilli. Microvilli are finger like projections of the cell membrane (produce by the cytoskeleton)that increase the surface area for absorption of nutrients into the enterocytes.
Carmelo
The main role of these enterocytes is to absorb. Therefore, having Microvilli as a structure relates to its function.
Carmelo
@ Carmelo thanks for the answer.
Garmai
welcome
Carmelo
what is the difference between negative feedback loop and positive feedback loop
famuyiwa

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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