Module 1.1 Structure & organisation of skeletal muscle Flashcards
Explain the structure of muscle
A muscle consists of hundreds to thousands of muscle cells, plus connective tissue wrappings, blood vessels, and nerve fibres. Connective tissue wrappings are covered externally by the epimysium.
What components of the muscle cell are responsible for force generation?
Bundles of contractile proteins called myofibrils
Explain myofibrils
They are the force generating component of the muscle fibre, which are composed of two contractile protein filaments (myofilaments) called actin and myosin. The interaction of the thin actin myofilaments and thick myosin filaments provide the basis for force production.
What are sarcomeres?
Individual segments of the myofibrils are called sarcomeres. They contain:
Z lines - structural proteins that mark the edges of the sarcomere
A band - the darker area containing the thick myosin filaments
I band - the lighter area containing the thin actin filaments (this alternating light and dark bands give the muscle fibre its striated appearance)
H zone - the area in the middle of the sarcomere with only myosin that doesn’t overlap with actin
What are the functions of organelles in muscle fibres?
They are essential for muscle contraction, storage of DNA, expression and synthesis of new proteins (ribosomes), transport systems across the cell membrane (sarcolemma), and energy generation (mitochondria).
What are the two specific structures in skeletal muscle that are important for force generation?
Sarcoplasmic reticulum - network of membranes that store and release calcium (Ca2+).
Transverse (T)-tubules - tubes that are extensions of the sarcolemma that pass all the way through the width of the muscle fibres
What is the other known name for the sarcoplasmic reticulum and t-tubules when they meet?
The triad
Explain the neuromuscular junction (there are three points)
- important component of muscle contraction and is the site at which the peripheral nerve meets the surface of the muscle fibre
- provide the link between the signal from the CNS and the initiation of muscle contraction
Explain the neuromuscular junction (there are three points)
- important component of muscle contraction and is the site at which the peripheral nerve meets the surface of the muscle fibre
- provide the link between the signal from the CNS and the initiation of muscle contraction
Explain the step by step process for sending an electrical signal from the CNS down a motor neuron to stimulate muscle fibres.
- an electrical signal travels from the CNS and down the motor neuron e.g. the top motor neuron
- motor neuron will stimulate the muscle fibres that it is in contact with (and only those in contact) to contract
- if a signal travels down the other motor neuron then only the other fibres will contract
- for all muscle fibres to contract, then an electrical signal must travel down both motor neurons
What is a motor unit comprised of?
A single motor neuron and all the muscle fibres that it connects with via the neuromuscular junction
What is often referred to as the smallest anatomical force producing unit within a skeletal muscle?
The sarcomere; it is intracellular, and it is the collection of sarcomeres that makes up the largest myofibrils, which organise the sarcomeres within cells.
What gives skeletal muscle cells (fibres) an alternating light and dark banded appearance across its length when viewed under a microscope?
The alternating overlap of the thick myosin and thin actin contractile proteins.
What is the classic definition of a “motor unit” within skeletal muscle?
A somatic alpha-motoneuron and all of the muscle fibres that it innervates
In general, how many somatic alpha-motoneurons innervate the length of a single skeletal muscle fibre?
1, and always 1! Any more signals from other neurons will produce an uncoordinated contraction.
