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The sarcomere is the functional unit of the muscle fiber. The sarcomere itself is bundled within the myofibril that runs the entire length of the muscle fiber and attaches to the sarcolemma at its end. As myofibrils contract, the entire muscle cell contracts. Because myofibrils are only approximately 1.2 μ m in diameter, hundreds to thousands (each with thousands of sarcomeres) can be found inside one muscle fiber. Each sarcomere is approximately 2 μ m in length with a three-dimensional cylinder-like arrangement and is bordered by structures called Z-discs (also called Z-lines, because pictures are two-dimensional), to which the actin myofilaments are anchored ( [link] ). Because the actin and its troponin-tropomyosin complex (projecting from the Z-discs toward the center of the sarcomere) form strands that are thinner than the myosin, it is called the thin filament    of the sarcomere. Likewise, because the myosin strands and their multiple heads (projecting from the center of the sarcomere, toward but not all to way to, the Z-discs) have more mass and are thicker, they are called the thick filament    of the sarcomere.

The sarcomere

This figure shows the structure of thick and thin filaments. On the top of the image a sarcomere is shown with the H zone, Z line and M lines labeled. To the right of the bottom panel, the structure of the thick filament is shown in detail. To the left of the bottom panel, the structure of a thin filament is shown in detail.
The sarcomere, the region from one Z-line to the next Z-line, is the functional unit of a skeletal muscle fiber.

The neuromuscular junction

Another specialization of the skeletal muscle is the site where a motor neuron’s terminal meets the muscle fiber—called the neuromuscular junction (NMJ)    . This is where the muscle fiber first responds to signaling by the motor neuron. Every skeletal muscle fiber in every skeletal muscle is innervated by a motor neuron at the NMJ. Excitation signals from the neuron are the only way to functionally activate the fiber to contract.

Every skeletal muscle fiber is supplied by a motor neuron at the NMJ. Watch this video to learn more about what happens at the NMJ. (a) What is the definition of a motor unit? (b) What is the structural and functional difference between a large motor unit and a small motor unit? (c) Can you give an example of each? (d) Why is the neurotransmitter acetylcholine degraded after binding to its receptor?

Excitation-contraction coupling

All living cells have membrane potentials, or electrical gradients across their membranes. The inside of the membrane is usually around -60 to -90 mV, relative to the outside. This is referred to as a cell’s membrane potential. Neurons and muscle cells can use their membrane potentials to generate electrical signals. They do this by controlling the movement of charged particles, called ions, across their membranes to create electrical currents. This is achieved by opening and closing specialized proteins in the membrane called ion channels. Although the currents generated by ions moving through these channel proteins are very small, they form the basis of both neural signaling and muscle contraction.

Both neurons and skeletal muscle cells are electrically excitable, meaning that they are able to generate action potentials. An action potential is a special type of electrical signal that can travel along a cell membrane as a wave. This allows a signal to be transmitted quickly and faithfully over long distances.

Questions & Answers

list types epithelial tissue
Sangu Reply
explain how hormonal control aids in homeostasis regarding fluids and electrolytes, internal organs, clinical application, edema electrolyte imbalance?
Hensheal Reply
someone to help me explain those
parathyroid hormone : Calcium uptake, H+ and PO-4 wasting thyroid hormone, cortisol for temperature regulation by acting on B.V
also renin
why retro abdominal region called flank?
it is just Anatomical terminology
meaning side of body b/w rib cage and hip bone
list down all the hormones secreted by adrenal gland
Odong Reply
adrenaline hormones
The amount of blood pumped by the left ventricle of the heart in one contraction.
Javid Reply
how we can calculate the cardiac output
and how do we calculate the strock valume
stroke volume is not all the blood contained in the left ventricle; normally, only about two-thirds of the blood in the ventricle is expelled with each beat.
Cardiac output 5.5 l S. V 68.75 ml H. R 80bpm
If we consider SV 70, end systolic vol is about 15% of total(approx always) out of a total of 80-85 ml only 70ml is pumped per systole
what is macrophages?and its function
Sajjad Reply
macrophages they are white blood cells that engulf dead cells in the body
what is power stroke?
no idea
what is the stroke volume of heart?
If an autoimmune disorder targets the alpha cells, production of which hormone would be directly affected?
Samantha Reply
what is a muscle?
Gideon Reply
A band or bundle of fibrous tissue in a human or animal body that has the ability to contract, producing movement in or maintaining the position of parts of the body
what's endolphthamities and panophthalmities?
fluid around the brain
louise Reply
what ?
cerebro spinal fluid
The brain and spinal cord are surrounded by a clear fluid called cerebrospinal fluid (CSF). This fluid is produced and stored in cavities in the brain called ventricles. It circulatesaround the brain, moving from ventricle to ventricle. ... Hydrocephalus is a condition in which there is too much CSF
what is hydrocphalus
aminul Reply
Google krlena na madarchod yha maa chudwa rha ha sabko notification bhjke
when cerebrospinal fluid produce în the brain, i.e. brain ventricles, is to abundent in the brain and is not trăind out of the brain. as a consequence this lichid pute mechanical pressure oñ the brain and it pushes the cerebrum tissue. as a consequence this pressure on the neuronscan cause neurologi
cal disfunctions, for example clinical headache
. It is posible to drainout the fluid through a device dalles shunt,as i remember.
but where are also home medicinsfor decreasing the production of cerebrospin.fluid etc
there are some medicines that can decrease the production of csf
a neurologist advice is needed
i wrote some medicines NOT home medicines. it is a serious condition and specialized medical advice is needed. of course also general medical knowledge may be helpful, but not enough, a specialist is neede
if anyone help me in physiology
Radika Reply
i am BSN student of first year which book is best for physiology
i am BSN student of first year which book is best for physiology
ross and wilson anotomy and physiology
it's 1 book for anotomy and physiology it's best for bs nursing
yes Ross and wilson physiology is better for study
I'm also the student of bs nursing
I study guiton and hall &ganong
I'm also midwif help me be the best book for midwif
what ia the function of indocrine system
salam all friend
help me with this question; explain at least five emergency acute pain found in fundamental emergency medicine
Fascial compartment of forearm
what's a tissue?
Mwape Reply
a group of cells with the same function
tissue is a group of cells that perform the same functions.
explain a bit about a tissue
A tissue is made up of cells that are similar in shape and perform the same function, for instance brain cells form up a brain tissue. Whereas a group of tissues that perform the same function form an organ... so in this case the brain which is the organ is formed as a result of brain tissues.
what is gross anatomy
the branch of anatomy that deals with the structure of organs and tissues that are visible to the naked eye.
1.To know how the structures functions. 2.To easily identify the micro structures and the macro structures. 3.To be able to explain that anatomy is the study of the structures and physiology is the study of how the structures functions
Abban Reply
Describe the two classes of hormones (3 with subclasses) and how they affect their target cells.
Shalaeha Reply
what is control centre
Gohil Reply
Angie The larger air passage of the lung is
Angie Reply

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