📚 Question Bank

The condition shown above is Dupuytren's contracture. It is the contracture of the flat or broad sheet-like tendon known as the aponeurosis, which leads to flexion deformities of the fingers, especially the ring and little fingers.

The aponeurosis is a pearly-white sheet of fibrous tissue that replaces tendons in sheet-like muscles having wide areas of attachment. They are whitish-silvery in colour and shiny. It is similar to tendons in histology and are sparingly supplied with blood vessels and nerves.

Examples of aponeuroses include:

• Palmar aponeuroses on the palms of the hands
• Plantar aponeuroses on the plantar aspect of the foot
• Anterior abdominal aponeuroses superficial to the rectus abdominis muscles
• Anterior and posterior intercostal membranes between the ribs
• Scalp aponeuroses or galea aponeurotica in the scalp

Option A: The retinaculum is a strong, short, and broad fibrous band around the tendons which holds them in place.

Option B: The linear fibrous band formed by interdigitation of the tendinous or aponeurotic ends of the muscles is known as raphe.

Option D: Fascia is a generic term applied to sheaths, sheets or other dissectible masses of connective tissue that are large enough to be visible to the unaided eye.

All the other arteries except the posterior cerebral artery are end arteries.

Arteries whose terminal branches do not anastomose with branches from neighbouring arteries are called end arteries or terminal arteries. They can be of two types:

• Anatomic end arteries (or true end arteries) - do not have anastomoses. e.g., central artery of retina, internal auditory artery (labyrinthine artery of the internal ear).
• Functional end arteries - have anastomoses but they are insufficient to provide adequate blood supply when the main vessel is occluded. e.g., segmental arteries supplying the kidney.

Muscular arterioles contribute to the major part of peripheral resistance to blood flow.

The smallest arteries of the muscular type are called arterioles. They have a tunica media that is relatively thicker than the tunica adventitia. Arterioles cause the largest drop in blood pressure before the blood flows into the tissue capillary beds. They are densely innervated by sympathetic fibres. The contraction of arterioles is mainly regulated by local vasoactive and metabolic factors, but central mechanisms also play a role.

The following image shows a micrograph of a muscular arteriole:

Umbilical arteries carry deoxygenated blood from the heart to the placenta during the fetal period.

Arteries carry oxygenated blood away from the heart, with the exception of the pulmonary and umbilical arteries that carry deoxygenated blood.

Circulation through the anastomosis is called collateral circulation.

Precapillary or postcapillary communication between neighbouring vessels is called anastomoses. Anastomoses are of the following types:

• Arterial anastomoses are communications between the arteries or branches of arteries. e.g., palmar arch, plantar arch, the circle of Willis.
• Venous anastomoses are communications between the veins or tributaries of veins. e.g., dorsal venous arches of the hand and foot.
• Arteriovenous anastomosis (shunt) are communications between an artery and a vein. e.g., av shunts found in the skin of nose, lips, ears, mucosa of nose and intestines, and erectile tissue.

The image below is a graphical representation of superficial and deep palmar arch.

The vasa vasorum (Latin: vessels of the vessels) is a network of small blood vessels that supply tunica adventitia and the outer part of tunica media of large blood vessels.

Blood supply of arteries:

• Small arteries- The vessel wall gets nourishment by diffusion from the blood circulating in the vessel itself. When the vessel wall thickness is more than 1 mm, simple diffusion from the lumen becomes inadequate.
• Larger arteries- They have their own vascular supply within the adventitia called vasa vasorum. It supplies the adventitia and the outer part of the tunica media. The intima and the

inner part of the media of large vessels are nourished directly by diffusion from the luminal blood.

The given image shows a transverse section of the aorta showing vasa vasorum and the layers as follows:

• Tunica intima
• Tunica media
• Tunica adventitia
• Vasa vasorum

Fenestrated capillaries are absent in the lungs.

Fenestrated capillaries have gaps between endothelial cells. They are present in certain tissues that allow the passage of larger molecules such as the renal glomeruli, endocrine glands, intestinal mucosa, and pancreas.

Muscle contraction without a change in muscle length is known as isometric contraction. The lady is performing a plank exercise which is an isometric exercise to strengthen the abdominal muscles.

Muscles can generate force through isotonic contraction or isometric contraction:

• Isotonic contraction involves maintaining constant tension as the muscle changes length. It can be concentric or eccentric.
• Concentric contraction involves shortening of the muscle. Example: biceps and brachialis contracting while lifting a weight by elbow flexion.
• Eccentric contraction involves lengthening of the muscle. Example: biceps and brachialis lengthening while lowering the weight by elbow extension.
• Isometric contraction involves force generation in the muscle while maintaining constant length.
• Example: Holding a crouched position or doing a wall-sit exercise.

Postural muscles predominantly contain Type I (slow-twitch) fibers that demonstrate slow, tonic contraction.

Muscle fibers belong to two main categories:

• Type I fibers (slow contracting or slow-twitch)
• Type II fibers (fast contracting or fast-twitch) - further subdivided to 2 types:
• Type IIA fibers
• Type IIX or IIB fibers

The following light micrograph shows fast-twitch fibers and myoglobin rich slow-twitch fibers:

Flexor carpi ulnaris is not a hybrid muscle as it is supplied by a single nerve (ulnar nerve).

A muscle supplied by two different nerves with different root values is called a composite or hybrid muscle. These muscles usually have more than one set of fibers and get their supply from different nerves for the different sets of fibers.

Examples of composite or hybrid muscles include:

• Brachialis
• Pectoralis major
• Iliopsoas
• Subscapularis
• Biceps femoris
• Adductor magnus
• Digastric
• Flexor pollicis brevis
• Flexor digitorum profundus
• Pectineus
• Opponens pollicis
• Trapezius

Mnemonic: BP IS BAD FOR FU™ POT

A small motor unit has 5-10 muscle fibers.

A motor unit (myone) is a single α motor neuron together with the muscle fibers supplied by it. The size of motor unit depends upon the precision of muscle control. Muscles that require fine control have fewer muscle fibers innervated by each neuron, muscles that participate in less controlled movements may have many fibers innervated by one neuron.

Motor units can be classified as follows:

• Small motor units (5–10 muscle fibers) are found in muscles of fine movements (such as extraocular muscles).
• Large motor units (100–2000 muscle fibers) are found in muscles of gross movements (such as proximal limb muscles).

Flower spray endings present in the muscle spindles are the secondary sensory nerve endings. The sensory nerve supply of muscle is as follows:

• Muscle spindles are supplied by thickly myelinated (IA) and thinly myelinated (II) afferents. The sensory nerve endings in the muscle spindle are of the following types:
• Primary sensory endings (type IA - Annulospiral endings) present in the central nuclear region of the intrafusal fibres.
• Secondary sensory endings (type II- Flower spray endings) present on either side of the nucleus of the intrafusal fibres.
• Golgi tendon organ is supplied by large, myelinated (IB) afferents.
• Connective tissue sheaths are supplied by fine, myelinated and unmyelinated axons that carry pain and other sensations.

Autonomic efferents supply the smooth muscle fibres of the blood vessels.

Every skeletal muscle is supplied by a motor nerve, which actually is a mixed nerve that contains motor and sensory fibres.

The motor supply of muscle contains the following efferents:

• Extrafusal muscle fibers are supplied by α-efferents that are large and myelinated.
• Intrafusal muscle fibers of muscle spindle are supplied by γ-efferents that are small and myelinated.
• Vascular smooth muscle fibers get autonomic efferents that are fine and unmyelinated.

Z disc or Krause's membrane is present in the middle of the I band of the myofibril.

Each myofibril has alternating dark (Anisotropic or A-band) and light (Isotropic or I-band) regions.

• A band
• The A-band contains both thick and thin filaments
• In the middle of the A-band, there is an H-band with only thick filaments
• In between the H-band, there is the dark M line
• I band
• The I-band contains only thin filaments
• In the middle of the I-band, there is a dark Z-disc or Krause's membrane
• The segment of the myofibril between two Z-discs is known as the sarcomere

The following photomicrograph of the skeletal muscle shows alternating dark and light regions with the Z-disc:

Skeletal muscles are multinucleated, while smooth muscles are uninucleated. There are three major muscle types in the human body:

• Skeletal muscle
• Smooth muscle
• Cardiac muscle

The incudostapedial joint is a ball and socket type of joint.

In ball and socket type of joints, the articular surfaces include a globular head (male surface) fitting into a cup-shaped socket (female surface). These joints are multi-axial and movements occur around a number of axes. Flexion, extension, abduction, adduction, medial rotation, lateral rotation, and circumduction, all occur quite freely. E.g., shoulder joint, hip joint,

talocalcaneonavicular joint, and incudostapedial joint.

Note: The other joint between the incus and malleus (incudomalleolar joint) is a saddle joint.

The deformity shown is hallux valgus. This is caused due to an excessive lateral deviation at the first metatarsophalangeal joint. It is an example of an ellipsoid joint.

Ellipsoid joints have an oval, convex (male) surface fitting into an elliptical concave (female) surface. They show biaxial movements such as flexion-extension, and abduction–adduction. A combination of these movements results in circumduction. Movement on the third axis is prevented due to the general articular shape.

E.g., Wrist (radiocarpal) joint, atlanto-occipital joints, metacarpophalangeal joints, and metatarsophalangeal joints.

Forward and backward movement of the mandible that occurs at the temporomandibular joints are called as protraction and retraction, respectively. Protraction occurs when the lower jaw is pushed forward, while retraction pulls the lower jaw backward.

Protraction and retraction also occur in the scapula. During protraction, the scapula is moved laterally and anteriorly along the chest wall, such as during rowing movements. Retraction is bringing scapula back to the original position after protraction.

Option A: Opposition is the thumb movement that brings the tip of the thumb in contact with the tip of a finger. Returning the thumb to its anatomical position next to the index finger is called reposition.

Option B: Excursion is the side to side movement of the mandible.

Option D: Depression and elevation are downward and upward movements of the mandible (or scapula), respectively.

The styloid process is a sharp elevation of bone. Bony elevations can be sharp or rounded:

• Rounded or irregular elevations include a tubercle, tuberosity, epicondyle, malleolus, and trochanter.
• Sharp elevations of bones include styloid process, spine, cornu (horn), and hamulus (hook-like).

The joint marked in the above image is the costotransverse joint, which is a synovial type of joint. The various types of joints in the thoracic wall include:

Sternocostal joints: These are the joints between the costal cartilages of the first seven ribs and the sternum.

• The joint between the 1st costal cartilage and manubrium is a fibrocartilaginous joint

(synarthrosis).

• The joints between the 2nd to 7th costal cartilages and the sternum are synovial joints.

The interchondral joint between the costal cartilages of the 9th and 10th ribs is never synovial and is usually absent.

Type of Joint Synovial joint

Primary cartilaginous joint/S ynchondrosis

Secondary cartilaginous/Sym physes joint

Examples

Costovertebral jointCostotran verse jointInterchondral joint s

Costochondral joint

Manubriosternal and xiphiste rnal joints

The origin of the muscle is fixed, while the insertion moves during contraction.

Skeletal muscles exert their force on the bones through their tendon attachments and the force generated helps in generating movements or in maintaining posture.

The tibialis anterior muscle has oblique muscle fibers arranged in a circumpennate (radial) fashion and not parallel fibers. The muscle fibers start from the walls of osteofascial compartment in the leg and converge obliquely in a radial fashion on a central tendon.

The other muscles listed (sartorius, rectus abdominis, and sternohyoid) have parallel fibers.

The muscle marked X in the cadaveric image is the pectoralis major, which is a spiral muscle. Spiral muscles have fiber architecture as follows:

• The muscle fibers have a spiral or twisted arrangement. e.g., pectoralis major (sternocostal fibers) and latissimus dorsi that undergo a 180° twist between their medial and lateral attachments.
• The entire muscle takes a spiral course around a bone. e.g., supinator winds obliquely around the proximal radial shaft.

Cruciate is a type of spiral muscle where two or more planes of muscle fibers are arranged in differing directions. e.g., sternocleidomastoid, masseter and adductor magnus are all partially spiral and cruciate.

The trapezius muscle individually is a flat, triangular muscle that extends over the back of the neck and upper thorax. When paired together, they resemble a trapezium and hence the name.

Muscles with oblique fibers are further subclassified as follows:

• Triangular - They are triangular in shape.
• Pennate - They are feather-shaped. Based on their complexity, they can have the following subtypes:
• Unipennate - fascicles on one side of the tendon.
• Bipennate - fascicles on two sides of the tendon.
• Multipennate - central tendon branches into two or more branches within the muscle.
• Circumpennate (radial) - muscle fibers converge to a central tendon in a radial fashion.

A muscle with two bellies with an intervening tendon is called a digastric muscle. Examples include the digastric muscle (digastricus) that has anterior and posterior belly with an intermediate tendon and omohyoid that has superior and inferior belly with an intermediate tendon.

Diarthric muscles are those which extend over two joints. Biaxial is a term used for joints that have movements in 2 axes.

The following image shows an illustration of the anterior and posterior belly of the digastric muscle with an intervening tendon: