Muscoskeletal 4: Muscle 1 Flashcards
List the functions of muscle
- Movement : movement of bones, transport of gut content, lymph transport (smooth), circulating blood (cardiac)
- Stability : stabilising joints with wide range of movement through active contraction (instead of ligaments articular capsule). + maintaining posture
- Communication: facial expression, body language, writing, speech
- Control of body openings and passages: sphincters in pupil, mouth (entry) + urethral, anal (smooth + skeletal) for exit
- Heat production: produces 85% of body heat which maintains body at 37 degrees for normal function
Compare the terms Origin, Insertion, Osteotendinous junction, Myotendinous junction, tendon and muscle belly to describe the general anatomy of skeletal muscle
The muscle belly is the organ which attaches to the bone by tendons.
The attachment that moves the least during muscle contraction is the origin (us.axial) whereas the attachment that moves the most during muscle contraction is the insertion (us. append)
On the two sides of the tendon are osteotendinous junction to the bone and myotendinous junction to the muscle. OTJ is much stronger (sharpeys fibres) than MTJ.
List the order of layers of skeletal muscle from Epimysium to myofibril
Epimysium, perimysium, fascicle, endomysium, myocyte, sarcolemma, sarcoplasm, myofibril
Describe the features of a myocyte - what makes it up
Multinucleated, has a sarcolemma that conducts AP well for uniform contraction. It has a sarcoplasm containing lipids, glycogen and myoglobin (O2 store) and many myofibrils
Describe the structure of a myofibril
They are made of contracting units called sarcomeres.
which are divided by Z discs
Describe the structure of a sarcomere
Dark A band in the middle and Light I bands on the outside. Z discs separate the I bands into half.
Describe the structure of Fascicle
A bundle of myocytes surrounded by endomysium: Loose irregular CT. With a basement membrane in between the sarcolemma and endomysium (secreted by both).
This contains lots or nerves and capillaries that supply the myocytes.
Describe the structure of muscle (organ)
A bundle of fascicles that are surrounded by perimysium (dense irregular). Then layer of epimysium that surrounds the perimysium, getting coarser and stronger as you get to the outside border of muscle.
Compare the CT of skeletal muscle and how are they arranged in muscle in to out
endo: loose irregular
peri + epi: dense irregular
Arranged in to out : endo, peri, epi but all blended together.
Where is the deep fascia found
It underlies the skin and subcutaneous tissue called superficial fascia.
It covers the epimysium of muscle but allows it to glide underneath,
- around bones it can blend with the periosteum or
-can be part of muscle tendon as an attachment for muscle.
Function of deep fascia
Often, it separates muscles with similar action or supplied with same nerves / bv into compartments by making these walls of deep fascia.
What is investing fascia
Deep fascia that are deeper walls or septa- a continuation of the lining that goes between muscles (intermuscular septa) or bones (interosseous membrane). Where investing fascia comes into contact with bone it fuses with the periosteum.
Compare hyperplasia vs hypertrophy.
Hyperplasia: when tissue/organ increases in size due to an increase of cell number. (skeletal muscle can’t)
Hypertrophy: increase in size due to increase in cell size but not
# of cells. This is due to increases in size of individual myocytes by increasing number of myofibrils.
What stimulates hypertrophy
Heavy resistance training - use to maximum fatigue and use of anabolic steroids.
How do anabolic steroids increase size of muscle
Anabolic steroids are variants of testosterone that overstimulate skeletal muscle and bone to increase protein synthesis. But it has other side effects like 2nd puberty.
What is atrophy and what causes it. compared to hypoplasia
When muscles decrease in size due to the reduction of myofibrils in the myocyte.
Caused by muscles not being stimulated by motor neurons. ie paralysed, sedentary due to other disease. reversable
Whereas hypoplasia is a reduction in the number of myocytes as a result of dying when no more myofibrils. hard to reverse.
What is the rate of loss of muscle mass as you age.
starts at 20 and accelerates after 50. It is replaced by fat and CT. It can be slowed/reversed by using muscle.
What are satellite cells (myoblasts) location, function.
Found outside sarcolemma but under basement membrane.
They are the only cells that can divide and fuse with each other and the myocytes to repair limited damage/ replace myocytes as they are created in embryonic stage so limited amount.
Why can’t skeletal muscle undergo hyperplasia
Myocytes are created by fusion of many myoblasts during embyronic stage of life and can’t divide mitotically because they have lots of nuclei and are big cells.
What are 4 functions of skeletal muscle connective tissue
- To provide organisation and scaffolding upon which the muscle is constructed
- To provide a medium for bv and nerves to gain access to myocytes
- To prevent excessive stretching and therefore damage to myocytes
- To distribute the forces generated by muscle fibre contraction.
How do Z lines move during sarcomere contraction
they move closer together as i band is shortening
How does myofibril cut in vivo still exert a pulling force on muscle tendons
The Z lines of adjacent myocytes are held together by structural proteins called desmins. This allows contractile force from sarcomere either side of the cut to be transmitted to neighbouring. sarcomeres.
How does an
entire myocyte cut in vivo still exert a pulling force on muscle tendons
The Z lines of outermost sarcomere is bound to the sarcolemma, basement membrane and endomysium by the Protein complex containing dystrophin. This allows the contracting forces either side of the cut to be transmitted to the surrounding endomysium–>myotendinous junction
