d. Superior frontal gyrus: Frontal eye field (8)
• Frontal eye field (8) is located at the middle frontal gyrus.

7) A physician orders a lumbar puncture (spinal tap) for his
43-year-old female patient in order to obtain a sample of cerebrospinal fl uid (CSF). He explains to her that this procedure will be done in the lower back, between the spinous processes of the L3 and L4 vertebrae. What is the best reason for performing the lumbar puncture at this location?

(A) The medullary cone ends at or above the L3 level
(B) The subarachnoid space ends at the L3 level
(C) The intervertebral foramina at L3-4 are large and easy to penetrate
(D) No vertebral venous plexuses exist below the L3 level
(E) The ligamenta fl ava are absent below the L3 level

The objective of a lumbar puncture is to enter (tap) the subarachnoid space and access the CSF. This procedure is performed using a long spinal needle. For several reasons, this procedure is best performed in the low lumbar region, between the spinous processes of the L3 and L4 (sometimes L4 and L5) vertebrae. The medullary cone (or conus medullaris) is the
tapered terminal end of the spinal cord. In adults, the medullary cone is normally located within the T12-L3 vertebral levels. Thus, penetrating the vertebral canal and subarachnoid
space below L3 is the “safe” place to go, in that the spinal needle
should not penetrate the spinal cord. Choice B (The subarachnoid space ends at the L3 level) is incorrect. The subarachnoid
space is the CSF-fi lled space between the arachnoid and pia
mater layers of the meninges. The dura-arachnoid layers line
the vertebral canal and end at the S2 level. The pia mater lines
the exterior surface of the neural tube and continues distally
to envelope the spinal nerve rootlets and roots. Because the
spinal cord ends at approximately the L1 level, there is a large
separation between the dura and arachnoid mater layers of the
meninges and the pia mater below L1. Thus, the subarachnoid
space is quite large below the medullary cone (conus medullaris), providing a signifi cant pool (the lumbar cistern) of CSF.
Choice C (The intervertebral foramina at L3-4 are large and
easy to penetrate) is incorrect. The intervertebral foramina in
the lumbar region are large openings; however, the lumbar
puncture does not occur at these locations. During a spinal tap, the spinal needle is inserted through an interlaminar space, on the posterior side of the vertebral column. These spaces are largest in the low lumbar spine, thus affording a relatively open path to the vertebral canal. Before a spinal tap
is administered, the patient is often bent forward into the fetal position by fl exing the spine, which expands the interlaminar spaces during the lumbar puncture. Choice D (No vertebral venous plexuses exist below the L3 level) is incorrect. The vertebral venous plexuses are an extensive network of valveless,
interconnecting vessels running the entire length of the vertebral column. The external vertebral venous plexus lies on the
anterior aspect of the vertebral column and the posterior side
of the vertebral arch. The internal vertebral venous plexus is
a major constituent of the epidural space within the vertebral
canal. A lumbar puncture must traverse both the external and
internal plexuses to reach the subarachnoid space. Choice E
(The ligamenta fl ava are absent below the L3 level) is incorrect. The ligamenta fl ava are short ligaments that connect the anterior sides of adjacent vertebral laminae along the entire length of the vertebral column. The spinal needle must pierce a ligamentum fl avum in order to enter the vertebral canal.

*Ans. B. Transverse process of lumbar vertebra and body of T12 vertebra*

The psoas major muscle is a muscle of the posterior abdominal wall. It has two slips of origin that enclose the lumbar plexus within it.

• *Option: A*. Greater trochanter of the femur gives origin to the vastus lateralis. Hence, it is the wrong answer.

• *Option: B*. Psoas major muscle superficial and deep origin sites owing to the presence of branches of the lumbar plexus embedded within it. The superficial part overlies the lumbar plexus and originates from the sides of the T12 and L1-L4 vertebrae along with the intervening intervertebral discs. The deep part originates from the transverse process of L1-L5. Hence, it is the correct answer.

• *Option: C*. The transverse process of the thoracic vertebra and body of the L1 vertebra doesn’t give rise to a specific muscle that has the lumbar plexus embedded within it. Hence, it is the wrong answer.

• *Option: D.* the lesser trochanter is the site of the insertion of the psoas major muscle. Hence, it is the wrong answer.

9] Synovial joints allow free movement between their bony
elements. They are classifi ed into multiple subtypes according to the shape of the articulating surfaces and/or the degree of movement allowed. Which of the following synovial joint types permits multiaxial movement?
(A) Pivot
(B) Ball and socket
(C) Condyloid
(D) Saddle
(E) Hinge

Multiaxial movement occurs
through several (more than two) axes or planes. In ball and socket joints, the rounded head of on bone moves in the concave socket of the other bone, such as the hip and shoulder (glenohumeral) joints. These highly mobile joints permit fl exion-extension,abduction-adduction, medial and lateral rotation,
and other more subtle motions. Choice A (Pivot) is incorrect.
In pivot joints (e.g., the median atlanto-axial joint between the
atlas [C1] and the dens of the axis [C2]; the proximal radioulnar
joint between the head of the radius and the proximal end of
the ulna), a rounded process of one bone fi ts into a relatively
shallow socket of the other bone and is held in place by a strong
ligament. Pivot joints allow only rotation about a single axis,
and these movements are uniaxial or single planar. Choice C
(Condyloid) is incorrect. In condyloid joints, the rounded (con-
dylar) end of one bone moves in the shallow concave end of the other bone, such as the metacarpophalangeal joints. Move-
ment is biaxial (through two planes); however, one movement
typically is dominant. Some authors make a case that condyloid
joints may be multiaxial, depending on the degree of movement
argued for in the third plane. Choice D (Saddle) is incorrect. In
saddle joints, the ends of the articulating bones are both con-
cave and form a saddle-like junction. The movement here is
biaxial (through two planes). The carpometacarpal joint located
at the base of the thumb is a prime example. Choice E (Hinge)
is incorrect. In hinge joints, the rounded end of one bone fi ts
into the concave end of the other. The lateral sides of the joint
are reinforced with strong collateral ligaments so that move-
ment is essentially limited to a hinge-like, uniaxial plane. The
humeroulnar (elbow) joint is a hinge joint.

10)A man exhibits anhydrosis (lack of sweating) and erythema (fl ushing) on his chest due to loss of sympathetic innervation. A thorough neurological analysis reveals dysfunction of presynaptic (preganglionic) sympathetic nerve cell bodies. Which of the following sites is most likely damaged in this patient?

Presynaptic sympathetic neurons originate in the pronounced lateral gray horn of the spinal cord, from spinal segments T1-L2 (or L3). Thus, the sympathetic division is described as having a thoracolumbar outfl ow. It is the sympathetic nerve fi bers that are damaged in this patient, leading to the anhydrosis and erythema. Choice A (Brainstem) is incorrect. Nuclei-housing presynaptic parasympathetic neurons are associated with four cranial nerve outfl ow tracts in the brainstem: Oculomotor nerve (CN III); Facial nerve (CN VII); Glossopharyngeal nerve (CN IX); Vagus nerve (CN X). Because parasympathetic fi bers emerge from both cranial and sacral levels of the central nervous system, this division is described as having a craniosacral outfl ow. Choice C (Sympathetic chain ganglia) is incorrect. The sympathetic chain ganglia, strung along the lateral sides of the vertebral column, contain the cell bodies of postsynaptic sympathetic neurons. These neurons project axons to the head and neck, body wall and limbs, and thoracic viscera. Choice D (Prevertebral ganglia) is incorrect. Prevertebral (preaortic) ganglia are located along the anterior aspect of the vertebral column and house mainly the cell bodies of postsynaptic sympathetic neurons. These cells project their axons to the abdominopelvic viscera and the external genitalia. Choice E (Dorsal root ganglia) is incorrect. Dorsal root (spinal) ganglia, located on each dorsal root of a spinal nerve, contain the cell bodies of general sensory (general somatic afferent; GSA) and visceral sensory (general visceral afferent; GVA) neurons. The axonal processes of these pseudounipolar cells originate as sensory receptors in the periphery and project to the dorsal grey horn in the spinal cord.

11) A 20-year-old woman is surprised to discover that she is pregnant. Following a review of her menstrual history and sexual activity, her physician determines that she is in the 4th week of pregnancy. Which of the following best describes the condition of the embryo at this time?
(A) Gastrulation is complete, resulting in two germ layers
(B) The embryo is entering a period of relative resistance to teratogenic substances
(C) Neurulation is nearly complete (D) Somites have not yet formed
(E) The trophoblast is present, but the syncytiotrophoblast has not yet formed

11)Neurulation (the process of formation of the neural tube) begins late in week 3 with formation of the neural groove and neural folds. However, most of the process, including formation and completion of the neural tube, occurs during week 4. Additional major events during this week include much of somite differentiation, the appearance of the pharyngeal (branchial) apparatus, and the appearance of the upper limb bud. Choice A (Gastrulation is complete, resulting in two germ layers) is incorrect. Gastrulation is the process of formation of the trilaminar germ disc, that is, establishing the three germ layers: ectoderm, endoderm, and mesoderm. Gastrulation is the defi ning characteristic of week 3 of development. Remember “threes”: three germ layers in week 3. Choice B (The embryo is entering a period of relative resistance to teratogenic substances) is incorrect. Weeks 3 to 8 constitute the embryonic period of development, which is the period of organogenesis during which the three germ layers form all tissues and organs. By the end of week 8, the main organ systems are formed and the major external body features are established. This is also regarded as the sensitive period of development because the organ primordia are very sensitive to teratogenic agents. As a result, most gross structural organ defects are induced during this time. Choice D (Somites have not yet formed) is incorrect. Somite formation is normally well underway during the 4th week. Segmentation of the paraxial mesoderm into somitomeres and somites begins late in week 3, with 4 to 7 pairs of somites formed at the cranial end of the embryo at day 21. New somites are added in a craniocaudal sequence at a rate of about 3 pairs per day. There are typically 26 to 29 pairs by the end of week 4, increasing to 42 to 44 pairs at the end of week 5. Because somites appear at a very specifi c rate, their number can be used to determine the age of the embryo with great accuracy during weeks 3 to 5. Choice E (The trophoblast is present, but the syncytiotrophoblast has not yet formed) is incorrect. Differentiation of the trophoblast (the outer cell mass of the blastocyst) into cytotrophoblast and syncytiotrophoblast areas occurs early in week 2. These layers form the fetal component of the placenta and thus are critical to full implantation. At the same time, the embryoblast (the inner cell mass of the blastocyst) differentiates into the bilaminar germ disc, consisting of the epiblast and hypoblast.

12) A child is born at home without diffi culty. Two weeks later, the mother takes the infant to her doctor, reporting that he “turns blue” when he cries. Physical examination reveals the infant is cyanotic and has a distinct systolic heart murmur. The physician suspects the baby has a tetralogy of Fallot (TOF). Which of the following conditions is a component of this syndrome?

An abnormally narrowed right ventricular outfl ow tract (pulmonary infundibular stenosis) is one of the four components of TOF. This syndrome is the most common malformation complex resulting from unequal division of the conus cordis and truncus arteriosus by the spiraling conotruncal septum. This septum contributes signifi cantly to the formation of the ventricular outfl ow tracts and the proximal parts of the aorta and pulmonary trunk. Anterior displacement of the developing conotruncal septum results in a narrow right ventricular outfl ow (pulmonary infundibular stenosis), plus an overriding aorta, ventricular septal defect (VSD), and hypertrophied right ventricle. The four classic characteristics of TOF are pictured in the given fi gure. Children with TOF are typically cyanotic due to the mixing of right and left side blood through the VSD and the overriding aorta. Also, the systolic heart murmur is typical due to the VSD. Choice A (Transposition of the great vessels) is incorrect. Failure of the conotruncal septum to follow its normal spiral course results in transposition of the great vessels. When the septum runs directly downward through the conotruncal region instead of spiraling, the aorta originates from the right ventricle and the pulmonary trunk arises from the left ventricle. Choice B (Hypertrophy of the left ventricle) is incorrect. In TOF, the combination of backpressure from the infundibular stenosis and systemic pressure needs from the overriding aorta and VSD results in hypertrophy of the right ventricle. Choice C (Interatrial septal defect) is incorrect. The conotruncal septum contributes to the formation of the upper (membranous) part of the interventricular septum. Thus, malformation of the conus septum commonly results in a membranous VSD, not an atrial septal defect. Choice E (Aortic valvular atresia) is incorrect. In this condition, the valvular orifi ce into the aorta is absent, and the aorta and left side chambers are underdeveloped. In TOF, the conotruncal septum is displaced, resulting in an open, overriding aorta

13)A young boy who was driving motorcycle at a high speed collided with a tree and was thrown on his right shoulder. Though there was no fracture, his right arm was medially rotated and forearm pronated. The following facts concerning this patient are correct, EXCEPT: