Muscle Histology Flashcards
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
What are the main types of muscle cells?
Skeletal or voluntary (aka striatal muscle)
Cardiac
Smooth or involuntary
What are not seen directly as muscle cells but have the capacity to produce force?
Myoepithelial cells
Myofibroblasts
Pericytes
Where are myoepithelial cells found?
In some glands
Where are myofibroblasts found?
Dermis of the skin
What are pericytes associated with?
Capillaries
contract to create flow in capillaries
How is muscle tissue formed?
Formed from muscle cells and associated connective tissue and forms the bulk of muscles
What do muscles contain?
Blood vessels Nerves Lymphatics Connective tissue Specialized sense organs
Percentage of skeletal muscle in the body?
40%
What are the main characteristics of skeletal muscle?
Striated
Unbranched
Multinucleate (forms a syncytium- single cell that contains multiple nuclei)
Where is the nuclei located in skeletal muscle?
At the periphery of the fibre, just under the cell membrane
What is the cell membrane called in a muscle cell?
Sarcolemma
Where do muscles develop from?
Myotubes
What is the mesenchyme?
Early tissue found in the embryo
How do muscles form?
Within the mesenchyme of mesoderm
Cells align, lose their cell membranes that separate them
Forms multinucleate myotubes
How are skeletal muscles organised?
Grouped into bundles called fascicles, muscle typically contains several
What are the three layers of connective tissue that are associated with muscles?
Epimysium
Perimysium
Endomysium
What is the function of Epimysium?
Surrounds the muscle as a whole
What is the function of perimysium?
Surrounds a single fascicle
What is the function of endomysium?
Surrounds a single muscle fibre
Is a muscle an organ?
yes
What does each fasicle compose of?
Contains many muscle fibres -> many myofibrils -> many sarcomeres placed end to end
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
