Muscle Histology Flashcards by Katie Angell

How is force produced in muscle fibres?

Force is produced by the movement of actin fibres over myosin fibres, with the aid of a number of accessory proteins. ATP is used as an energy source

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What are the main types of muscle cells?

Skeletal or voluntary (aka striatal muscle)
Cardiac
Smooth or involuntary

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What are not seen directly as muscle cells but have the capacity to produce force?

Myoepithelial cells
Myofibroblasts
Pericytes

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Where are myoepithelial cells found?

In some glands

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Where are myofibroblasts found?

Dermis of the skin

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What are pericytes associated with?

Capillaries

contract to create flow in capillaries

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How is muscle tissue formed?

Formed from muscle cells and associated connective tissue and forms the bulk of muscles

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What do muscles contain?

Blood vessels
Nerves
Lymphatics
Connective tissue
Specialized sense organs

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Percentage of skeletal muscle in the body?

40%

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What are the main characteristics of skeletal muscle?

Striated
Unbranched
Multinucleate (forms a syncytium- single cell that contains multiple nuclei)

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Where is the nuclei located in skeletal muscle?

At the periphery of the fibre, just under the cell membrane

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What is the cell membrane called in a muscle cell?

Sarcolemma

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Where do muscles develop from?

Myotubes

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What is the mesenchyme?

Early tissue found in the embryo

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How do muscles form?

Within the mesenchyme of mesoderm
Cells align, lose their cell membranes that separate them
Forms multinucleate myotubes

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How are skeletal muscles organised?

Grouped into bundles called fascicles, muscle typically contains several

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What are the three layers of connective tissue that are associated with muscles?

Epimysium
Perimysium
Endomysium

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What is the function of Epimysium?

Surrounds the muscle as a whole

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What is the function of perimysium?

Surrounds a single fascicle

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What is the function of endomysium?

Surrounds a single muscle fibre

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Is a muscle an organ?

yes

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What does each fasicle compose of?

Contains many muscle fibres -> many myofibrils -> many sarcomeres placed end to end

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Describe sarcomeres

‘unit of contraction’
They are the smallest contractile elements in the striated muscle cell
100-1000s are placed end-to-end to form myofibril
12-100s are packed into muscle fibre like cigarettes in a pack

When fully contracted how do actin and myosin look in a sarcomere?

The actin filaments fully overlap the myosin. There is no Z-line

What lines represent the anchor for actin and myosin?

Z-line - actin | M-line - myosin

How do muscle fibres contract?

The motor unit

Describe the motor unit

The motor neuron and all of the muscle fibres that it innervates - 1 motor neuron and many muscle fibres

What is the result of fewer muscles fibres to one motor unit? An example of where these muscles may be located

Finer control of movement The eyes

What does the motor neuron end with?

Synapse called the motor end plate

What is a neuromuscular joint?

Where motor axons terminate at a motor end-plate and action potentials arriving in the axon cause release of acetylcholine and initiate an action potential in the sarcolemma

How does action potential allow the muscle to all contract simultaneously?

Sweeps across the epimysium and enters through pores called t-tubules (transverse tubules)

What are t-tubules?

Exrtend from the sarcolemma into the cell, ramifying and surrounding each myofibril roughly at the A-I junction of each sarcomere

What is released following the action potential?

Calcium (Ca++) - contracts sarcomere

Along with t-tubules what two tubes are side by side to it?

Specialised smooth ER called the sarcoplasmic reticulum

What is the combination of t-tubules and sarcoplasmic reticulum called?

Triad

What is the end point of the sarcoplasmic reticulum called?

Terminal cisternae of the sarcoplasmic reticulum

What is the name of the junction where muscles are attached to the collagen part of the tendon?

The Myotendinous junction

Why is it hard for tendons to heal when damaged?

There is a low supply of blood

What are fibroblasts of the tendon called?

Tendinocytes

How do skeletal muscles feedback to the central nervous system?

Series of muscle cells encapsulated in muscle spindles

What do muscle spindles contain?

Intrafusal fibres (long, tapered) - Innervated by sensory nerves and motor fibres

What are normal contractile muscles fibres that make up the large majority of a muscle called?

Extrafusal muscle fibres

Why are cardiac muscles also classed as striated cells?

They have striations | However, less prominent

What do cardiac muscles form?

Forms the major part of the walls of the heart chambers and origins of the great vessels

Are cardiac muscles longer or shorter than skeletal muscle?

Much shorter

How many nuclei does a cardiac mucle contain? Where is it located?

usually a singular nucleus, however, sometimes 2 | Located near the centre of the fibre

What are intercalated discs in cardiac muscles for?

Pass across the fibres at irregular intervals | These are the sites of end-to-end attachments between adjacent cells

What flows through the gap junctions in a cardiac muscle?

No nerves that allows muscles in heart to move therefore, electrical signal is issued from specialised cells in the Sinoatrial node in the right atrium. This depolarization is spread across these muscle cells as a wave through the gap junctions between the muscle cells

Why is there many mitochondrion spread across cardiac muscles?

Aerobic metabolism dependant tissue (If there is a shortage of oxygen these cells will die and will turn into scar tissue which then means the heart is weaker and cant pump blood around the body at a sufficient rate)

How do cardiac muscles contract?

Have an intrinsic rythmic contraction Gap junctions allow for synchronization of contraction between cells Rythm is dependant on the autonomic nervous sytem

What is another name for cardiac muscles?

Cardiac myocytes

Do muscle cells have regenerative capacity?

They contain population of myoblasts called satellite cells on surface of sarcolemma After damage they are activated however they compete with scar tissue and often "lose" meaning after muscle is killed, new muscle is not regenerated

Why is smooth muscle called smooth muscle?

Does not have striations

Why is smooth muscle also called involuntary and visceral?

It is not under concious control | It is prodominantly found in organs

Where is smooth muscle often found?

Found in the walls of tubes- gut, respiratory tract, blood vessels and the uterus Also iris of the eye

What is the stimulus for smooth muscle cells to contract?

Can arrive from nerve fibres of the autonomic nervous system Can also be from hormones

How are actin and myson arranged in a smooth muscle cell? | What occurs from this placement

They converge on dense bodies within the cytoplasm and focal densities at the periphery of the cell Transverse force of contraction