Types Of Muscles , Functions, And Common Conditions

Muscles

Question 1: What is the muscle?
Answer.

Muscle: The muscle is a contractile tissue (the muscle cells contain contractile proteins in their cytoplasm) that brings about the movements of the body. During contraction, the muscles shorten and convert the chemical energy into mechanical energy.

Question 2: What are the different types of muscles?
Answer. There are three types of muscles:

• Skeletal muscle
• Cardiac muscle
• Smooth muscle

Question 3: What are the properties of the muscles?
Answer. The properties of muscles are as follows:

• Irritability, i.e. they are sensitive to stimuli.
• Contractility, i.e. they contract in response to stimuli.
• Extensibility, i.e. they can stretch.
• Elasticity, i.e. they can assume a desired shape after being stretched.

Compare and contrast three types of muscles – skeletal, cardiac and smooth.

Comparison and Contrast Between Skeletal, Cardiac and Smooth Muscles

Classify the various types of muscles according to their shape and direction of their muscle fibres.

• When the direction of muscle fibres is parallel to each other, i.e. in line of pull
  • Strap muscles: These muscles are like long ribbons. Examples: Sternohyoid, sternothyroid and sartorius.
  • Fusiform muscles: These muscles are spindle shaped. Examples: Biceps femoris and biceps brachii.
  • Quadrilateral/quadrate muscles: These muscles are square shaped. Examples: Pronator quadratus and thyrohyoid.
  • Flat muscles: These muscles are in the form of thin sheets of fleshy fibres. Examples: Muscles of anterior abdominal wall such as external oblique, internal oblique, and transversus abdominis.
• When the direction of muscle fibres is oblique to line of pull
  • Triangular, e.g. temporalis and adductor longus.
  • Pennate (feather-like):
    • Unipennate, e.g. extensor digitorum longus, flexor pollicis longus, palmar and plantar interossei.
    • Bipennate, e.g. rectus femoris, dorsal interossei and flexor hallucis longus.

Read And Learn More: Selective Anatomy Notes And Question And Answers

• • • Multipennate, e.g. deltoid (acromial part) and subscapularis.
    • Circumpennate, e.g. tibialis anterior.
• When the direction of muscle fibres is circular, i.e. they are arranged circularly around the orifice, e.g. orbicularis oris and orbicularis oculi.
• When the muscle fibres are arranged in a twisted manner, e.g. trapezius, pectoralis major and latissimus dorsi.
• When the muscle fibres are arranged in two planes in different directions and cross, these are called cruciate muscles, e.g. masseter, sternocleidomastoid and adductor magnus.

Enumerate the parts of a typical skeletal muscle.

These are given in the following flowchart:

Question 4: What is the difference between the fleshy and tendinous parts of a muscle.
Answer.

Differences Between Fleshy and Tendinous Parts of a Muscle

Question 5: Write a short note on a tendon.
Answer.

Tendon :

• The tendon is silvery white, fibrous, cord-like part of the muscle, which connects the muscle to the bone. It is made up of parallel, dense, collagen fibres. The tendon transmits forces of muscular contraction to the bone. It is attached to the periosteum and through it to the cortical bone through Sharpey’s fibres.
• The fibres of tendon are twisted or plaited so that the force of muscle pull is distributed to all the points at the site of insertion.
• The tendon is extremely powerful; for example, a tendon with cross-sectional area of 1 square inch can support a weight up to 9700–18,000 pounds.

When tendon is subjected to sudden accidental traction at its insertional end, it may cause avulsion/fracture of the bone without being ruptured itself. This shows tremendous power of the tendon.

Question 6: What is ‘aponeurosis’?
Answer. The aponeurosis is a silvery white, flat fibrous sheet that connects the muscle to the bone or deep fascia. It is made up of densely arranged collagen fibres. The aponeurosis provides a wider area of muscular attachment.

Question 7: Classify muscles according to the force of their action.
Answer.

Classification Of Muscle

• Spurt muscles
• Shunt muscles

When muscle contracts, its force of contraction at the site of insertion is resolved into two components: (1) swing and (2) shunt. Swing component produces movement at the joint, while shunt component pulls the distal bone towards the joint.

If the site of insertion is close to the joint and the site of origin is away from the joint, when the muscle contracts, its swing becomes more powerful than shunt. These muscles are called spurt muscles, e.g. brachialis.

On the contrary, if the site of insertion is away from the joint and the site of origin is close to the joint, then shunt becomes more powerful than swing. Such muscles are called shunt muscles, e.g. brachioradialis.

Question 8: What are the types of muscles according to their action?
Answer. A single muscle or a group of muscles alone cannot produce a desired movement at a particular joint.

Any particular movement of a joint is brought about by a group of muscles, while the whole range of any movement is brought about by the smooth coordinated actions of different groups of muscles. These groups of muscles are as follows:

• Prime movers (agonists): These are the muscles that initiate and bring about a desired movement. They are responsible for the specific movements. Examples: Biceps brachii and brachialis are prime movers to cause flexion at elbow joint.
• Antagonists: These are the muscles that have opposite action to that of prime movers, i.e. they oppose prime movers or initiate and maintain a movement converse to that produced by agonists. Examples: Triceps brachii, which acts as antagonist during flexion of the elbow joint but helps in smooth flexion of the elbow joint by gradually relaxing itself.
• Fixators: These are the muscles that stabilize the proximal joint/joints of a limb to provide a fixed base for the agonist muscle (prime mover) to act on a distal joint to bring about a desired movement.
• Synergists: These muscles help the prime movers in bringing out the desired movement. They eliminate the undesired actions at proximal joint when the prime movers cross two or more joints. Examples: While making a tight fist, extensors of the wrist act as synergists to long flexor tendons.

Question 9: Write a short note on the nerve supply of a skeletal muscle.
Answer. The nerves supplying skeletal muscles are somatic nerves and consist of three functional components.

Nerve Supply Of Motor fibres: They enter the individual muscle fibres at a point called motor end plate/neuromuscular junction. The nerve fibres are of following two types:

• Alpha motor fibres arising from alpha motor neurons of anterior horn cells and supply the extrafusal muscle fibres.
• Gamma motor fibres arising from gamma motor neurons of anterior horn cells and supply the intrafusal muscle fibres of muscle spindle (sensory end organ of skeletal muscle).

Nerve Supply Of Sensory fibres:

• Myelinated fibres: They are distributed to muscle spindles, tendon and fascia of the muscle and carry exteroceptive and proprioceptive sensations. The fibres carrying pain sensations are free nerve endings around the muscle fibres, while the fibres carrying sensation of tension and degree of contraction, end in special sense organs called Golgi tendon organs.
• Nonmyelinated fibres: Distribution of these fibres is not known as yet.

Autonomic fibres: These fibres innervate the smooth muscle of the blood vessels present within the muscle. These fibres thus regulate the amount of blood flow in the muscle.

Question 10: Write a short note on motor unit.
Answer. It is a functional unit of muscle. It consists of a single alpha motor neuron and all the muscle fibres which it innervates.

About 150 muscle fibres are innervated by a single alpha motor neuron. The motor units are of two types: large and small.

The large motor units supply large number of muscle fibres, i.e. 2000–3000. These units supply muscles responsible for coarse but powerful actions, e.g. gluteus maximus, gastrocnemius and deltoid.

The small motor units supply small number of muscle fibres, i.e. 10–20. These units supply muscles responsible for fine and precise movements, e.g. muscles causing eye movements, finger movements and vocal cord movements.

Question 11: Write a short note on neuromuscular junction (or motor end plate).
Answer.

It is a junction between the nerve terminal and cell membrane (sarcolemma) of a muscle fibre. At neuromuscular junction, the axon loses its myelin sheath and breaks up into number of branches to supply the individual muscle fibres. Each branch becomes distended to form synaptic knob .

which contains large number of vesicles containing acetylcholine. The muscle fibre at this site also becomes specialized into a sole plate . Here the muscle membrane, i.e. sarcolemma, is thrown into folds and contain receptors for acetylcholine.

The narrow space between the two plates – the synaptic cleft – is filled by a chemical substance called acetylcholine (a neurotransmitter). At the time of passage of impulse, the acetylcholine is broken down by an enzyme called acetylcholinesterase.

Question 12: Define a synovial bursa and mention its types.
Answer.

The synovial bursa (bursa = purse) is a closed sac of synovial membrane filled with a capillary film of a synovial fluid. The bursae are supported by an irregular connective tissue. They reduce friction between two mobile units to permit free movements.

Types Of Synovial Bursa

According to the location, the synovial bursae are classified into the following types:

• Subcutaneous, between skin and bone, e.g. prepatellar bursa and subcutaneous infrapatellar bursa.
• Submuscular, between muscle and bone, e.g. bursa deep to medial head of gastrocnemius.
• Subtendinous, between tendon and bone, e.g. trochanteric bursa of gluteus medius.
• Subfascial, between fascia and bone.
• Interligamentous, between ligaments.

Question 13: What are adventitious bursae?
Answer. Adventitious Bursae:

The adventitious bursae develop in the subcutaneous tissue over bony prominences where the skin is subjected to pressure and friction. Examples:

• Tailor’s ankle: A bursa develops over lateral malleolus in tailors who sit in cross-legged position while at work, thus bringing lateral malleolus in contact with the table leading to pressure and friction.
• Weaver’s bottom: A bursa develops between gluteus maximus and gluteal tuberosity in weavers who sit for prolonged periods for weaving the cloth.
• Porter’s shoulder: A bursa develops over clavicle in porters who hang heavy luggage on their shoulders.