Axial skeleton Questions in English

(C) The correct answer is $C$. In the first two or three lumbar vertebrae,there is a small,unpaired,median process located on the ventral side of the centrum,which is known as the hypapophysis. This structure provides an additional site for muscle attachment.

(B) The rib has two articulation points on its vertebral end.
$1$. The head (capitulum) articulates with the body of the thoracic vertebrae.
$2$. The tuberculum articulates with the transverse process of the thoracic vertebrae.
Therefore,the part of the rib that articulates with the transverse process is the tuberculum.

(B) The human vertebral column consists of $33$ vertebrae in total during early development,which later fuse to form $26$ bones in adults.
The vertebral formula is represented as follows:
$1$. Cervical vertebrae $(C)$: $7$
$2$. Thoracic vertebrae $(T)$: $12$
$3$. Lumbar vertebrae $(L)$: $5$
$4$. Sacral vertebrae $(S)$: $5$ (fused into $1$ bone in adults)
$5$. Coccygeal vertebrae $(C)$: $3-5$ (fused into $1$ bone in adults)
Thus,the formula is $C_7 T_{12} L_5 S_5 C_{3-5} = 33-35$.

(B) Cancellous bone,also known as spongy or trabecular bone,is a porous type of bone tissue found at the ends of long bones and within the interior of vertebrae and flat bones.
It consists of a lattice-like network of bony plates called trabeculae,which provides structural support while keeping the bone lightweight.
Therefore,the correct term for cancellous bone is spongy bone.

(C) Prezygapophysis and postzygapophysis are articular processes found on the neural arches of vertebrae.
They interlock with each other to form zygapophyseal joints between adjacent vertebrae.
These joints provide stability to the vertebral column by preventing excessive or undue bending and restricting the displacement of adjacent vertebrae,thereby protecting the spinal cord.

(A) The $Hyoid$ bone is a $U$-shaped bone situated at the base of the buccal cavity. It is not articulated with any other bone but is suspended by ligaments from the temporal bones. It provides attachment for the muscles of the tongue and the floor of the mouth,hence it is commonly referred to as the tongue bone.

(D) The human rib cage consists of $12$ pairs of ribs.
Ribs $1$ to $7$ are called true ribs as they are attached directly to the sternum.
Ribs $8, 9,$ and $10$ are called false ribs (vertebrochondral ribs) as they join the $7^{th}$ rib instead of the sternum.
The last two pairs ($11^{th}$ and $12^{th}$) of ribs are not connected ventrally to the sternum at all and are therefore known as floating ribs.

(B) The long neck of a camel is primarily due to the presence of elongated bony structures or modifications in the cervical vertebrae,often described as bony plates or extensions between the vertebrae that provide structural support and length to the neck.

(D) $Sella \text{ turcica}$, also known as the 'Turkish saddle', is a saddle-shaped depression located in the $sphenoid$ bone of the human skull.
It is specifically situated in the $basi-sphenoid$ region.
This depression serves as the housing for the pituitary gland (hypophysis).

(C) The mammalian sternum (breastbone) is a flat bone located in the center of the chest.
It is composed of several segments known as sternebrae.
In most mammals,the sternum consists of $6$ sternebrae,a xiphisternum (the posterior segment),and a xiphoid cartilage (the cartilaginous tip at the end of the xiphisternum).
Therefore,the correct composition includes $6$ sternebrae,a xiphisternum,and a xiphoid cartilage.

(D) The $Foramen \ magnum$ is a large opening at the base of the skull through which the spinal cord passes.
It is located in the $Occipital \ bone$.
The $Occipital \ condyles$ are two protuberances on the $Occipital \ bone$ that articulate with the $Atlas$ (the first cervical vertebra,$C1$),allowing for the nodding movement of the head.
Therefore,both these structures are characteristic features of the $Occipital \ bone$.

(D) The $Atlas$ vertebra is the first cervical vertebra $(C1)$.
It is unique because it lacks a $centrum$ (body) and a $spinous$ process.
Instead,it consists of a bony ring with two lateral masses that support the skull.
It possesses well-developed $transverse$ processes for the attachment of muscles that rotate the head.

(D) The $Nucleus \ pulposus$ is the inner gelatinous core of the intervertebral disc.
It is derived from the embryonic notochord,which persists in the central portion of the intervertebral discs in mammals.
It acts as a shock absorber for the vertebral column.

(B) The cervical vertebrae are the bones located in the neck region of the vertebral column.
In almost all mammals,the number of cervical vertebrae is constant at $7$,regardless of the length of the neck.

(C) vertebra with convexity on both the anterior and posterior surfaces is known as an $Amphicondylar$ or $Amphi-convex$ vertebra.
However,in standard biological classification,a vertebra that is flat on both ends is called $Acoelous$ or $Amphiplatyan$.
$Procoelous$ vertebrae have a concave anterior surface and a convex posterior surface.
$Amphicoelous$ vertebrae have concave surfaces on both ends.
Since the question describes a vertebra with convexity on both sides,it is technically an $Amphicondylar$ vertebra,which is a specific type of $Acoelous$ or modified structure depending on the classification system used. Given the options provided,$Acoelous$ is often used in broader contexts to describe non-concave surfaces,though $Amphiplatyan$ (flat) is more precise for $Acoelous$.

(D) . The $Pterygoid$ is a paired bone that forms part of the skull,specifically contributing to the lateral walls of the nasal cavity and the posterior roof of the mouth cavity.
$Atlas$ is the first cervical vertebra.
$Coracoid$ is a bone of the pectoral girdle.
$Arytenoid$ is a cartilage associated with the larynx.

(B) The correct answer is $B$.
In birds,the posterior thoracic,lumbar,sacral,and anterior caudal vertebrae are fused together to form a single structure known as the $Synsacrum$.
This structure provides rigidity to the skeleton,which is essential for flight and for supporting the weight of the body on the hind limbs.

(C) The vertebral column consists of $26$ serially arranged units called vertebrae.
These are categorized into different regions based on their location.
Cervical vertebrae are the first $7$ vertebrae located in the neck region.
Therefore,the correct option is $C$.

(C) The human vertebral column consists of $33$ vertebrae arranged in different regions.
These include $7$ cervical,$12$ thoracic,$5$ lumbar,$1$ sacral (fused),and $1$ coccygeal (fused) vertebrae.
Therefore,the number of lumbar vertebrae is $5$,which are located in the abdominal region.

(C) In human beings, there are $12$ pairs of ribs.
These are categorized as follows:
$1$. The first $7$ pairs are known as true ribs because they are attached directly to the sternum.
$2$. The $8^{th}$, $9^{th}$, and $10^{th}$ pairs are known as false (vertebrochondral) ribs because they do not attach directly to the sternum but join the $7^{th}$ rib.
$3$. The last $2$ pairs ($11^{th}$ and $12^{th}$) are known as floating ribs because they are not connected to the sternum at all.

(C) The axis vertebra is the second cervical vertebra. It is characterized by a prominent,tooth-like projection called the $Odontoid$ $process$ (or $dens$). This process fits into the atlas vertebra $(C1)$ and acts as a pivot for the rotation of the head. The $Odontoid$ $process$ is embryologically derived from the centrum of the atlas vertebra.

(A) The endoskeleton provides structural support,protection for internal organs,and serves as a site for muscle attachment,which facilitates locomotion.
It also contains bone marrow,which is responsible for the production of $RBCs$ (hematopoiesis).
While certain bones of the skull (like the ossicles in the middle ear) are involved in the process of hearing,the endoskeleton itself does not perform the function of sight.
Therefore,sight is not a function of the endoskeleton.

(A) In the human body,there are $12$ pairs of ribs.
The first seven pairs of ribs are known as true ribs because they are directly attached to the sternum via hyaline cartilage.
The $8^{th}$,$9^{th}$,and $10^{th}$ pairs of ribs do not articulate directly with the sternum but join the $7^{th}$ rib,and are called false ribs.
The last two pairs ($11^{th}$ and $12^{th}$) are not connected ventrally and are called floating ribs.

(C) The Haversian system (or osteon) is the fundamental functional unit of compact bone. It is a characteristic feature of the long bones of mammals,such as the femur,which provide structural support and facilitate the transport of nutrients and waste through the bone matrix.

(A) In birds,the skeletal system is highly adapted for flight. The pelvic girdle is fused to a specialized composite bone structure known as the $Synsacrum$.
This structure is formed by the fusion of the last thoracic vertebrae,all lumbar vertebrae,the sacral vertebrae,and the first few caudal vertebrae.
The $Synsacrum$ provides a rigid framework that supports the weight of the body and provides a stable attachment point for the pelvic girdle and the hind limbs,which is essential for bipedal locomotion and landing.

(B) The human skeletal system is primarily composed of bones and cartilages.
In an adult human,the skeleton consists of $206$ bones.

(C) In the human skeletal system, homologous or corresponding bones are often compared between the upper and lower limbs.
$1$. $Humerus$ (arm) corresponds to $Femur$ (thigh).
$2$. $Pectoral$ girdle corresponds to $Pelvic$ girdle.
$3$. $Carpals$ (wrist bones) correspond to $Tarsals$ (ankle bones).
$4$. $Atlas$ is the first cervical vertebra, while the $Coccyx$ is the terminal part of the vertebral column (tailbone). They do not serve corresponding functions or positions in the limbs or girdles, making them the correct choice.

(B) In the vertebral column,the articulation between adjacent vertebrae is facilitated by specialized processes called zygapophyses.
Specifically,the $post-zygapophyses$ (inferior articular processes) of the anterior (front) vertebra articulate with the $pre-zygapophyses$ (superior articular processes) of the posterior (behind) vertebra.
In this arrangement,the $post-zygapophyses$ of the vertebra in front fit over the $pre-zygapophyses$ of the vertebra behind,providing stability and restricting excessive movement while allowing for flexibility.

(A) The central shaft of a long bone is called the $Diaphysis$.
The expanded ends of a long bone are known as $Epiphysis$.
$Hypapophysis$ refers to a ventral process on a vertebra,and $Zygapophysis$ refers to the articular processes of a vertebra.
Therefore,the correct answer is $A$.

(A) The primary function of the skeleton in vertebrates is to provide structural support to the body against gravity.
While certain bones (like the ear ossicles in mammals) are involved in hearing and the hyoid bone plays a role in sound production,the fundamental and defining function of the skeletal system as a whole is to provide a rigid framework for support,protection of internal organs,and attachment for muscles to facilitate movement.

(A) The $Humerus$ bone in humans features a $supratrochlear$ $foramen$ located at the base of the $olecranon$ $fossa$.
This $foramen$ allows for the passage of the $brachial$ $artery$ and the $median$ $nerve$.
Therefore,the presence of this specific $foramen$ is a characteristic feature of the $Humerus$.

(A) When a bone is kept in a $10\%$ $KOH$ (potassium hydroxide) solution for $3$ days,the bone itself remains unaffected because the mineralized matrix (calcium salts) is resistant to the alkaline solution. However,the surrounding muscles,fat,and connective tissues are dissolved by the $KOH$,which is a strong base. This process is often used in laboratory settings to clean bones for skeletal preparation.

(A) Red bone marrow is the site of hematopoiesis (blood cell formation).
In adults,it is primarily found in the spongy (cancellous) bone tissue located at the epiphyses or the tips of long bones,such as the $humerus$ and $femur$,as well as in flat bones like the sternum and ribs.
The shaft of long bones (diaphysis) typically contains yellow bone marrow,which is primarily composed of adipose tissue.

(C) The synsacrum is a composite bone formed by the fusion of several vertebrae in birds (fowl).
It consists of approximately $16$ fused vertebrae,which include the last thoracic,all lumbar,all sacral,and the first few caudal vertebrae.
This structure provides rigid support to the pelvic girdle and the ilia bones,which is essential for the bird's locomotion and weight-bearing during flight and walking.

(B) The transverse ligament is a strong band that extends across the ring of the $Atlas$ (the first cervical vertebra).
It divides the neural foramen of the $Atlas$ into two parts:
$1$. $A$ smaller anterior part called the odontoid fossa,which accommodates the $odontoid$ $process$ $(dens)$ of the $Axis$ vertebra.
$2$. $A$ larger posterior part,which serves as the vertebral foramen for the passage of the spinal cord.

(A) . $Zygapophysis$ are paired processes that provide articular surfaces for the attachment of vertebrae to each other. They also prevent the dislocation of the vertebrae.

(D) The neural arch of a vertebra typically gives rise to several processes.
$1$. The $\text{Neural spine}$ (or $\text{Spinous process}$) is the median, backwardly projecting process that arises from the dorsal part of the neural arch.
$2$. $\text{Hypapophysis}$ is a ventral process found in some vertebrae.
$3$. $\text{Metapophysis}$ and $\text{Anapophysis}$ are additional processes found in certain mammals for muscle attachment.
$4$. $\text{Post-zygapophysis}$ is a paired process for articulation with the succeeding vertebra.
Therefore, the backwardly projecting process is the $\text{Neural spine}$.

(A) The epiphyseal plate,also known as the epiphyseal disc or growth plate,is a layer of hyaline cartilage located between the diaphysis (shaft) and the epiphysis (end) of long bones.
During the period of growth,the chondrocytes in this plate undergo rapid division and ossification,which leads to the lengthening of the bone.
Therefore,epiphyseal discs are primarily responsible for bone elongation.

(D) In human beings $(Man)$,there are $12$ pairs of cranial nerves and $12$ pairs of ribs.
Specifically,humans possess $12$ pairs of ribs (true,false,and floating ribs) and $12$ pairs of cranial nerves that emerge from the brain.
In contrast,frogs have $10$ pairs of cranial nerves,and fish have $10$ pairs of cranial nerves.

(C) The vertebral column in vertebrates develops from the embryonic notochord. During development,the notochord provides structural support and serves as a scaffold around which the vertebrae form.

(C) Bones are primarily composed of a mineral matrix that provides strength and rigidity. The most abundant elements found in the bone matrix are Calcium $(Ca)$ and Phosphorus $(P)$. These elements combine to form hydroxyapatite crystals,which are the main inorganic component of bone tissue. Therefore,the correct option is $C$.

(C) The second cervical vertebra in mammals is known as the $Axis$ vertebra.
It is characterized by a prominent,peg-like projection called the $Odontoid$ $process$ (or $dens$).
This process fits into the $Atlas$ (first cervical vertebra) and acts as a pivot for the rotation of the head.

(A) $1$. The first vertebra is the $Atlas$, which articulates with the occipital condyles of the skull. This is a correct statement.
$2$. The $11^{th}$ and $12^{th}$ pairs of ribs are called floating ribs because they are not connected ventrally to the sternum. The $9^{th}$ and $10^{th}$ pairs are false ribs (vertebrochondral ribs). Thus, option $B$ is incorrect.
$3$. The glenoid cavity articulates with the head of the humerus (arm bone), not the thigh bone. The thigh bone (femur) articulates with the acetabulum. Thus, option $C$ is incorrect.
$4$. The bones of the skull are joined by sutures, which are a type of fibrous joint. However, the parietal and temporal bones are specifically joined by the squamous suture. While fibrous joints are present, the statement in $A$ is the most standard anatomical fact regarding the axial skeleton.

(A) In humans,there are $12$ pairs of ribs.
$1.$ The first $7$ pairs are called true ribs (vertebrosternal ribs) because they are attached directly to the sternum via hyaline cartilage.
$2.$ The $8^{th}, 9^{th}$ and $10^{th}$ pairs of ribs do not articulate directly with the sternum but join the $7^{th}$ rib with the help of hyaline cartilage. These are known as vertebrochondral or false ribs.
$3.$ The $11^{th}$ and $12^{th}$ pairs are not connected ventrally and are therefore called floating ribs.
Thus,the $8^{th}, 9^{th}$ and $10^{th}$ ribs are the vertebrochondral ribs.

(C) The human vertebral column consists of $33$ vertebrae.
Among these, the lumbar vertebrae are the largest and heaviest because they support the weight of the upper body and provide stability.
$A$ (Atlas) and $B$ (Axis) are cervical vertebrae, which are smaller.
$D$ (Thoracic vertebrae) are intermediate in size compared to cervical and lumbar vertebrae.
Therefore, the lumbar vertebra is the heaviest.

(C) The coccyx,commonly known as the tailbone,is a small,triangular bone located at the very base of the vertebral column. It is formed by the fusion of four coccygeal vertebrae. Therefore,it is a part of the vertebral column.

(C) In the human skeletal system,the rib cage consists of $12$ pairs of ribs.
Out of these,the first $7$ pairs are called true ribs,the $8th, 9th,$ and $10th$ pairs are called false (vertebrochondral) ribs,and the last $2$ pairs ($11th$ and $12th$) are called floating ribs because they are not attached to the sternum.
Therefore,the total number of floating ribs is $2$ pairs,which equals $4$ ribs.
Option $A$ is incorrect as there are more than $3$ types of diabetes.
Option $B$ is incorrect as there are $7$ cervical vertebrae in humans.
Option $D$ is incorrect as there are $20$ standard amino acids involved in protein synthesis.

(C) The axis vertebra is the $2^{nd}$ cervical vertebra $(C_2)$.
It is characterized by a strong,tooth-like projection called the odontoid process or dens,which extends superiorly from the body of the vertebra.
This process acts as a pivot around which the atlas $(C_1)$ rotates,allowing for the side-to-side movement of the head.

(B) In the human body,the skeletal and nervous systems have specific counts:
$1$. Cranial nerves: There are $12$ pairs of cranial nerves,not $10$.
$2$. Floating ribs: The $11^{th}$ and $12^{th}$ pairs of ribs are not connected to the sternum and are called floating ribs. Thus,there are $2$ pairs of floating ribs.
$3$. Clavicles: There is only $1$ pair of clavicles (collar bones) in the human body.
$4$. Salivary glands: There are $3$ pairs of major salivary glands (parotid,submandibular,and sublingual).
Therefore,the correct pair is floating ribs - $2$ pairs.

(C) In the human skeletal system,there are $12$ pairs of ribs,which makes a total of $24$ ribs.
These ribs are classified into three types: true ribs ($1-7$ pairs),false ribs ($8-10$ pairs),and floating ribs ($11-12$ pairs).
Therefore,the total number of ribs is $12 \times 2 = 24$.