Anatomy and Embryology of Skeletal Muscle

Skeletal muscle cells fuse to form giant multinucleate cells with several nuclei located on the periphery that control a common cytoplasm - they form a syncitium.

What name is given to the primary site of force transmission at the muscle-tendon interface?

The myotendinous junction arises from the fusion of what structures? Check all that apply

Fill in the blanks to give the names of each classification of muscle according to its function. [blank_start]Flexor[blank_end] muscles bend a joint, decreasing its angle. [blank_start]Extensor[blank_end] muscles straighten a joint, increasing its angle. The [blank_start]prime mover[blank_end] or agonist muscle performs concentric contraction to bring about movement. The [blank_start]antagonist[blank_end] muscle opposes the action of the primer mover to return it to its normal position. The [blank_start]fixator[blank_end] muscle steadies the position produced by the prime mover by isometric contraction. The [blank_start]synergist[blank_end] muscle complements the action of the prime mover by performing the same contraction.

Blood vessels and nerves are embedded in the fascicles.

Fill in the blanks below to describe the structure of muscle based on the divisions by the different layers of connective tissue. The [blank_start]epimysium[blank_end] is the tough outermost layer surrounding the entire muscle. The [blank_start]perimysium[blank_end] surrounds bundles of muscle fibres to create fascicles. The [blank_start]endomysium[blank_end] surrounds each muscle fibre within the fascicles.

Label this image to show the general structure of a skeletal muscle.

Fill in the blanks below to describe the formation of skeletal muscle. 1. A single [blank_start]myoblast[blank_end] cell exists in a medium containing growth factor. 2. The cell [blank_start]proliferates[blank_end]. 3. Multiple cells fuse to form [blank_start]myotubes[blank_end]. 4. Myotubes gather to form [blank_start]myofibres[blank_end].

Muscle fibres are post-mitotic cells - myonuclei cannot re-enter the cell cycle and divide.

What type of cell exists on the surface of muscle fibres that divide in response to stimuli and differentiate into new myoblasts?

Satellite cells cannot self-renew.

What processes do we need satellite cells for? Check all that apply.

What is the most basic unit of skeletal muscle?

Label this image to give the structure of a sarcomere.

What does the speed of contraction of a muscle fibre depend on?

Which muscle fibre isoform is described as a white muscle fibre as it only contains a small amount of myoglobin?

Which muscle fibre isoform is described as a red muscle fibre as it contains a lot of myoglobin?

Type I slow muscle fibres are suited to [blank_start]long[blank_end]-term contraction for [blank_start]endurance[blank_end] work. They are red and contract with slow [blank_start]twitch[blank_end] velocity. They have a higher density of [blank_start]mitochondria[blank_end] so are better suited to aerobic respiration. They are therefore fatigue [blank_start]resistant[blank_end]. However, they produce [blank_start]less[blank_end] instantaneous force so are described as 'weak'. They store energy in the form of [blank_start]triglycerides[blank_end].

Type II muscle fibres are better suited to [blank_start]short[blank_end]-term contraction. They are [blank_start]white[blank_end] in colour due to a lack of myoglobin. They contract with [blank_start]fast[blank_end] twitch velocity and are more prone to aerobic respiration. They therefore fatigue easily, but produce more instantaneous force. They store energy in the form of ATP and creatine phosphate.

Type II muscle fibres are better suited to [blank_start]short[blank_end]-term contraction. They are [blank_start]white[blank_end] in colour due to a lack of myoglobin. They contract with [blank_start]fast[blank_end] twitch velocity and are more prone to [blank_start]anaerobic[blank_end] respiration. They therefore fatigue easily, but produce more [blank_start]instantaneous[blank_end] force. They store energy in the form of ATP and [blank_start]creatine phosphate[blank_end].

The Type IIa fast [blank_start]oxidative[blank_end] muscle fibres have higher concentrations of [blank_start]myoglobin[blank_end] and mitochondria. They are therefore the most resistant to [blank_start]fatigue[blank_end] of the Type II fibres and are used in [blank_start]long[blank_end] term anaerobic activities. Type IIb fast [blank_start]glycolytic[blank_end] muscle fibres have low concentrations of myoglobin and [blank_start]mitochondria[blank_end] so fatigue easily but contract [blank_start]quickly[blank_end] with high power. They are therefore used in short term [blank_start]anaerobic[blank_end] activities. Type IIx super-fast [blank_start]glycolytic[blank_end] muscle fibres have the lowest concentrations of muscle fibres so are very vulnerable to [blank_start]fatigue[blank_end]. They do, however, contract the fastest with the largest amount of [blank_start]power[blank_end].

Each muscle fibre receives innervation from one motor neuron.

What name is given to the group of muscle fibres from a single neuron innervating multiple fibres?

Larger motor units have greater degrees of control.

What is dystrophin?

Why are males more prone to muscular dystrophies (disorders of the dystrophin protein)?

What is the function of dystrophin?

The C-terminus of dystrophin binds to the [blank_start]dystrophin associated protein complex[blank_end] (DAPC) found at the [blank_start]sarcolemma[blank_end]. The N-terminus of dystorphin binds to filamentous [blank_start]actin[blank_end] in the cytoskeleton.

What disease is characterised by necrosis and fibrosis of the muscles causing later-stage walking, toe walking, Gower's manoeuvre often leading to death in 20s-30s?

The limb and trunk muscles are derived from embryonic structures known as [blank_start]somites[blank_end] - buds of the mesoderm. The [blank_start]somites[blank_end] are divided into sections which will give rise to different parts of the body. The [blank_start]dermomyotomes[blank_end] will give rise to the skeletal muscle, the satellite cells and the overlying dermis. The [blank_start]sclerotome[blank_end] will give rise to cartilage, joints and tendons. The [blank_start]myotome[blank_end] will form differentiated myocytes.

Muscle precursor cells that end up in medial locations will initially migrate into the limb bud periphery before moving back towards the midline to their final location.