Structure of Muscles Flashcards
What is the name of the usually fixed point where the muscle attached and is this proximal or distal?
The origin
It is proximal
What is the name of the usually moveable attachment of the muscle and is this proximal or distal?
Insertion
It is distal
What exists between the origin and the insertion of a muscle?
The muscle belly
Skeletal Muscle fibres are mononucleated. T/F?
False
What is the name for a bundle of muscle fibres bound together by collagenous supporting tissue?
Fassicles
What is the name of the connective tissue which surrounds individual muscle fibres?
The endomysium
What is the name of the connective tissue which surrounds each fascicle?
The perimyosium
What is the name of the connective tissue which surrounds the whole muscle mast?
Epimysium
What is the role of the perimysium?
To protect the fascicles from damage. It also contains blood vessels and nerves the nourish the muscle fibres
Muscles which have small fascicles and a large proportion of perimysium are most likely involved in what kind of movement?
Fine, highly controlled movement (e.g. Movement of the fingers)
What binds skeletal muscle directly to the skeleton?
Tendons
What binds skeletal muscle indirectly to the skeleton?
Aponeurosis
Where are the nuclei of muscle fibres?
At the periphery
What is the name of the plasma membrane of muscle cells?
Sarcolemma
What is the name of the organelle of a muscle fibre which is analogous to the endoplasmic reticulum of other cells?
The sarcoplasmic reticulum
Where is calcium stored in muscle fibres?
The terminal cisternae of the sarcoplasmic reticulum
Large amounts of glycogen and myoglobin exist in the sarcoplasm. What is their role in a muscle fibre?
Glycogen - provides energy during muscle contraction by conversion to glucose for respiration
Myoglobin - acts as an oxygen store
Each muscle fibre is composed of bundles of…?
Myofibrils
What are the two main components of the myofibril?
The thin filament (mostly actin)
The thick filament (mostly myosin)
What is the structure of myosin?
Myosin has two large heavy chains and four small light polypeptide chains. They combine to form two globular heads (of both heavy and light chains) and a long tail of the two intertwined heavy chains. The two heads stick out to the sides to form cross-bridges
What are the two binding sites of the myosin molecule for?
The ATP binding site is to bind ATP and can also act as an ATP-ase
The other binding site is to bind to the thin filament
What is the role of tropomyosin?
It sits on the actin element of the thin filament and stops myosin from binding to it.
What is to role of troponin?
Troponin holds tropomyosin in its blocking position on the actin element of the thin filament.
What is the structure of tropomyosin?
It is a long rod-shaped molecule comprised of two intertwined polypeptides and is about seven actin monomers long
What is the structure of troponin?
It is a small globular protein and has three subunits:
TnI - inhibitory
TnT - tropomyosin binding
TnC - calcium binding
What is the structure of actin?
Actin is made up of monomers (G actin) which polymerise (forming F actin) and is made up of to intertwined helical strands
What is the role of the protein nebulin?
It is sheath-like and covers actin to help anchor the filaments to the Z line
What is the role of dystophin?
It is a structural protein which links actin to the sarcolemma, helping to transmit tension from the filaments to the tendon of the muscle. It helps reinforce the strength of the sarcolemma
In a microscopic view of a muscle fibre what does the A band represent?
The A band is a dark wide bind showing the thick filaments which reside in the middle of the sarcomere
What is the Z line of the sarcomere?
One end of each thin filament is anchored to a network of interconnected proteins known as the Z line. Thin filaments from to adjacent cells are anchored to the two sides of the Z line. The Z line marks the boundary of the sarcomere.
What is the name of the structural protein which makes up the Z line?
Alpha actinin
In a microscopic view of a muscle fibre what does the I band represent?
The I band lies between the ends of adjacent A bands and shows the thin filaments which do not overlap with the thick filaments
What is the M line?
The M line is in the middle of the sarcomere and joins to two halves of the thick filament
What protein is the M line composed of?
Myomesin
What is the name of the elastic protein which extends from the Z line to the M line and is linked to the M line proteins and the thick filaments?
Tintin
In a microscopic view of a muscle fibre what does the H band represent?
The H band is a narrow, light band in the centre of the A band which shows the space between opposing ends of the two sets of thin filaments.
What structure lies directly between and is intimately related to adjacent segments of the sarcoplamsic reticulum?
Transverse(T)-tubules
What structure exists in the area where the A and I bands meet?
T-tubules
What does a motor unit consist of?
A somatic motor neuron with all of the muscle fibres that it innervates
What does motor recruitment refer to?
The number of motor units activated during a contraction
The overall muscle movement produced depends on the recruitment of…?
Different sized motor units
Different strengths of motor unit
Quantity of motor units
All the muscle fibres of one motor unit are of the same fibre type. T/F?
True
