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Anatomy Practice Questionssssssssss.pptx

The document discusses various clinical scenarios related to nerve injuries affecting shoulder and arm function, particularly focusing on the long thoracic, musculocutaneous, and axillary nerves. It examines symptoms such as scapular winging, elbow flexion weakness, and sensory loss related to specific nerve damages. Moreover, it provides details about anatomical relationships and implications of injuries sustained in different situations, such as motorcycle accidents and industrial incidents.

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Anatomy Practice Questions Dr Subodh K Yadav Associate Profeesor MBBS.MS.DMUD
• During a fight a man is stabbed in the lateral chest beneath the right arm. The wound does not enter the chest cavity. Physical examination reveals that the vertebral (medial) border of the patient's scapula projects posteriorly and is closer to the midline on the injured side. On return visit the patient complains that he cannot reach as far forward (such as to reach for a door knob) as he could before the injury. The nerve injured which caused these symptoms is which of the following? A) Axillary B) Long thoracic C) Musculocutaneous D) Radial E) suprascapular
• Long thoracicRemember--an injury to the long thoracic nerve denervates serratus anterior, meaning that there will be no muscle protracting the scapula and counteracting trapezius and the rhomboids, powerful retractors of the scapula. The long thoracic nerve is derived from the nerve roots of C5-7; this nerve is particularly vulnerable to iatrogenic injury during surgical procedures because it is located on the superficial side of serratus anterior. • The axillary nerve innervates teres minor and deltoid. It wraps around the surgical neck of the humerus and is endangered by fractures of the surgical neck. If the axillary nerve was damaged and deltoid was denervated, the patient would be unable to abduct his upper limb beyond 15 to 20 degrees. The musculocutaneous nerve innervates biceps brachi, coracobrachialis, and brachialis. If this nerve was disrupted, the patient would be unable to flex her or his forearm, and have weakened arm flexion. The radial nerve innervates extensors of the forearm and triceps brachi--if this nerve was injured, the patient would no longer be able to extend forearm, but only have slightly weakened arm extension (latissimus is the powerful extensor of the arm). Finally, the suprascapular nerve innervates supraspinatus--the muscle that initiates abduction. Damage to this nerve would prevent the patient from starting to abduct her or his arm.
• A man suffers a penetrating wound through the anterior axillary fold, with resulting damage to one of the main terminal branches of the brachial plexus. Among the effects is a significant weakening of flexion of the elbow. One or more other effects to be expected is/ are which of the following? A) Loss of cutaneous sensation on the tips of several fingers B) Only loss of cutaneous sensation on the anterolateral surface of the forearm C) Only weakening of flexion at the shoulder D) Weakening of flexion at the shoulder and loss of cutaneous sensation on the anterolateral surface of the arm E) Weakening of flexion at the shoulder and loss of cutaneous sensation on the anterolateral surface of the forearm
• Key-E • Weakening of flexion at the shoulder and loss of cutaneous sensation on the anterolateral surface of the forearm Flexion at the elbow is produced by biceps brachii and brachialis, and both of these muscles are innervated by the musculocutaneous nerve. So, you know that the musculocutaneous nerve was damaged. Beyond innervating the muscles that flex the forearm, the musculocutaneous nerve gives off the lateral antebrachial cutaneous nerve which provides sensory innervation to the anterolateral surface of the forearm. This means that the other symptom that would be present is a loss of cutaneous sensation on the anterolateral surface of the forearm. The biceps brachii and coracobrachialis muscles flex the arm, so you should have weakening of flexion at the shoulder - you would still have pectoralis major, a powerful arm flexor.
• A person sustains a left brachial plexus injury in an auto accident. After initial recovery the following is observed: 1) the diaphragm functions normally, 2) there is no winging of the scapula, 3) abduction cannot be initiated, but if the arm is helped through the first 45 degrees of abduction, the patient can fully abduct the arm. From this amount of information and your knowledge of the formation of the brachial plexus where would you expect the injury to be? a) Axillary nerve b) Posterior cord c) Roots of plexus d) Superior trunk e) Suprascapular nerve
• Key-E • suprascapular nerveLet's take the observations one by one to break down this question. If the diaphragm is functioning normally, you know that the phrenic nerve is probably uninjured, which means that the C5 root has not been damaged. Since the scapula is not winged, there was no damage to the long thoracic nerve or the C5-7 nerve roots. Finally, since the patient cannot initiate abduction of the arm, you know that the suprascapular nerve is injured and supraspinatus has been denervated. But, the patient can abduct the arm once it is lifted to 45 degrees, so the deltoid muscle and the axillary nerve must be intact.
• An open arterial anastomosis in the shoulder occurs between the suprascapular artery and which other artery? a) Anterior circumflex humeral b) Circumflex scapular c) Dorsal scapular d) Thoracodorsal e) Transverse cervical
• Key-B circumflex scapular • The circumflex scapular artery, the dorsal scapular artery, and the suprascapular artery create arterial anastomoses around the scapula. This means that the scapula will be supplied with blood even if one of these arteries is ligated. Additionally, if the subclavian or axillary artery needs to be ligated, blood can flow from the dorsal scapular artery and suprascapular artery to the circumflex scapular artery. This effectively shunts blood from the first part of the subclavian artery to the third part of the axillary artery so that the upper limb will still receive blood. The connection between the suprascapular and circumflex scapular arteries is termed an open anastomosis because it is grossly visible, compared to the anastomosis with the dorsal scapular, which typically happens within small vessels.
• Following the above injury there would most likely be diminished cutaneous sensation over what part of the upper limb? a) the back of the shoulder b) the pectoral region c) the top of the shoulder and the lateral side of the arm d) the medial side of the arm and forearm e) the tip of the little finger Key-Cthe top of the shoulder and the lateral side of the arm The C5 and C6 dermatomes cover the top of the shoulder and lateral side of the arm. The T1 and C8 dermatomes cover the medial side of the arm, with C8 extending to the tip of the little finger. The back of the shoulder is covered by numerous dermatomes, including C6, C7, C8, and T1. Finally, the pectoral region is covered by T1, T2, and T3 dermatomes..
• A patient is found to have a melanoma (cancer arising in pigment cells) originating in the skin of the left forearm. After removal of the tumor from the forearm, all axillary lymph nodes lateral to the medial edge of the pectoralis minor muscle are removed. Which axillary lymph nodes would not be removed by this procedure? a) Apical b) Central c) Lateral d) Pectoral e) Subscapular Key-Aapical If all the lymph nodes lateral to the medial edge of pectoralis minor are removed, the central, lateral, pectoral and subscapular nodes will be removed. The central nodes are found directly under pectoralis minor, while the other three groups of nodes are lateral to the entire muscle. The apical nodes, which are medial to the medial edge of pectoralis minor, will not be removed.
• During a motorcycle accident, an 18-year-old male landed on the right lateral side of his rib cage with his right upper limb abducted. In the hospital he was found to have "winging" of the right scapula. Which nerve was likely damaged in the accident? a) Accessory b) Lateral pectoral c) Long thoracic d) Phrenic e) Vagus Key-C Long thoracic nerveAn injury to the long thoracic nerve denervates serratus anterior, meaning that there will be no muscle protracting the scapula and counteracting trapezius and the rhomboids, powerful retractors of the scapula. This means that the scapula will be winged backwards, which is this patient's main symptom. The long thoracic nerve is derived from the nerve roots of C5-7. This nerve is particularly vulnerable to iatrogenic injury during surgical procedures, such as mastectomies, because it is located on the superficial side of serratus anterior.
• During an industrial accident, a sheet metal worker lacerates the anterior surface of his wrist at the junction of his wrist and hand. Examination reveals no loss of hand function, but the skin on the thumb side of his palm is numb. Branches of which nerve must have been severed? a) Lateral antebrachial cutaneous b) Medial antebrachial cutaneous c) Median d) Radial e) Ulnar Key-C Median nerve The median nerve provides sensory innervation to the skin of the radial 3.5 fingers of the palm. So, the patient's loss of cutaneous sensation is suggestive of a median nerve injury. The location of the injury also implies that there has been an injury to the median nerve--this nerve enters the hand by crossing over the anterior side of the wrist.
• The nerve which passes through the quadrangular space of the posterior shoulder innervates which muscle? a) Deltoid b) Infraspinatus c) Subscapularis d) Supraspinatus e) Teres major Key-A Deltoid The quadrangular space is bounded medially by the tendon of the long head of the triceps, laterally by the humerus, superiorly by teres minor, and inferiorly by teres major. The posterior circumflex humeral artery and the axillary nerve traverse this space. The axillary nerve innervates 2 muscles: deltoid and teres minor. So, deltoid is the answer!
• The surgeon next encounters a large (about 2 cm in diameter) horizontally running vein, fortunately intact, which is also retracted downward. This exposes the damaged artery. He knows that the cords of the brachial plexus are closely associated with this artery, so he carefully retracts one found superolateral and one found inferomedial to the artery and then proceeds to repair the artery itself and close the wound. The large artery that severed was which of the following? a) Axillary b) Brachial c) Radial d) Subscapular e) Suprascapular
• Key-A axillary • The axillary artery is the continuation of the subclavian artery lateral to the first rib. The cords of the brachial plexus are wrapped around the axillary arteries, so this should be a clue that the axillary artery is the one that was severed. The brachial artery is an extension of the axillary artery distal to teres major. Although these two arteries are continuous, the cords of the brachial plexus are not associated with the brachial artery.
• Neurological testing of a patient reveals no cutaneous sensation on the tip of the index finger. Such a finding would indicate injury to some portion of which nerve? a) Axillary b) Median c) Musculocutaneous d) Radial e) Ulnar Key-B median nerve The median nerve provides cutaneous sensation to the palmar face of the radial side of the hand, continuing through the first 3.5 fingers. It also innervates the tips of these fingers and their nail beds on the dorsal side of the hand. So, a lack of sensory innervation at the tip of the index finger means that the median nerve is damaged.
• You are attending an axillary lymph node dissection in a patient with a melanoma in the upper limb. The surgeon says, "We are going to sample the level II lymph nodes posterior to the pectoralis minor muscle." Having excelled in anatomy, you realize that she is referring to the anatomical nodes known as which of the following? a) apical axillary nodes b) central axillary nodes c) lateral axillary nodes d) lateral pectoral nodes e) subscapular axillary nodes
Key-Bcentral lymph nodes The central lymph nodes are defined as the group of lymph nodes situated deep to the pectoralis minor at the base of the axilla. The central nodes receive lymph from the lateral, subscapular and pectoral lymph nodes. The lateral nodes are found on the lateral wall of the axilla; the subscapular nodes are found on the posterior wall of the axilla; the pectoral nodes are found on the anterior wall of the axilla. These groups of lymph nodes are lateral to pectoralis minor. The apical lymph nodes are medial to the medial border of the pectoralis minor, so they would not be found under pectoralis minor.
• In a patient with Erb-Duchenne palsy, a nerve arising from the superior trunk of the brachial plexus is nonfunctional. This nerve is which of the following? a) Suprascapular b) Dorsal scapular c) Long thoracic d) Lateral pectoral e) Medial pectoral
Key- A Suprascapular Remember -- Erb-Duchenne palsy is the avulsion of the C5 and C6 roots of the brachial plexus. The suprascapular nerve comes from the superior trunk of the brachial plexus to innervate supraspinatus and infraspinatus. Since the superior trunk is made entirely from the C5 and C6 nerve roots, it makes sense that the suprascapular nerve would be damaged in Erb-Duchenne palsy. The dorsal scapular nerve comes off of the C5 root to innervate levator scapulae and the rhomboids. This nerve would also be damaged in a case of Erb-Duchenne palsy, but it is not coming off of the superior trunk. (Remember: the question specified the superior trunk!) The long thoracic nerve comes off the roots of C5, C6, and C7 to innervate serratus anterior. This nerve would be affected by Erb-Duchenne palsy, but it's not from the superior trunk. Finally, the lateral and medial pectoral nerves come off the lateral and medial cords of the brachial plexus, respectively. Lateral pectoral nerve would be affected in Erb's palsy, but not medial pectoral.
• The axillary nerve arises directly from which part of the brachial plexus? a) inferior trunk b) lateral cord c) medial cord d) middle trunk e) posterior cord Key-Eposterior cord The axillary nerve and radial nerve are both terminal branches from the posterior cord. There are no nerves from the inferior trunk. The lateral cord gives off the musculocutaneous nerve and contributes a branch to the median nerve. The medial cord of the brachial plexus terminates with the ulnar nerve and a branch to the median nerve; it also gives off the medial pectoral nerve, the medial cutaneous nerve of the arm, and the medial cutaneous nerve of the forarm. The middle trunk of the brachial plexus has no direct branches. There is no superior cord of the brachial plexus--only a superior trunk!
• While putting metal panels on the roof of a barn, one of the panels slips out of the hands of the man on the roof. During an attempt to catch the panel, a worker below is struck by its sharp edge. The panel hits across the anterior surface of his right arm at midlength and the impact severs all of the tissue to the bone. When examined in the emergency room it is noted that the patient can only weakly flex his elbow and the lateral side of his forearm is numb. In addition to the muscles, which nerve is injured? a) Axillary b) Median c) Musculocutaneous d) radial e) ulnar
Key-B Median nerve The brachial artery runs down the medial side of the arm, near the basilic vein and the median nerve. This artery is a continuation of the axillary artery distal to the teres major. The deep brachial artery is a branch of the brachial artery which runs with the radial nerve in the radial groove of the humerus. The radial and ulnar arteries are branches of the brachial artery which run down the ulnar and radial sides of the forearm.
• In a case of Erb's palsy, where roots C5 and C6 of the brachial plexus are avulsed (torn out) which muscle is paralyzed? a) Latissimus dorsi b) Pectoralis minor c) Supraspinatus d) Trapezius e) Triceps brachii
• Key-C Supraspinatus • The C5 and C6 roots make the superior trunk of the brachial plexus. So, all the muscles innervated by nerves from the superior trunk of the brachial plexus will be denervated following the avulsion. Supraspinatus is innervated by the suprascapular nerve, which comes off of the superior trunk of the brachial plexus. This means that avulsing the C5 and C6 nerve roots would denervate supraspinatus and paralyze that muscle.
• If the second part of the axillary artery was interrupted, collateral blood flow could pass from branches of the thyrocervical trunk into which artery? a) Anterior humeral circumflex b) Circumflex scapular c) Deep brachial d) Posterior humeral circumflex e) Thoracoacromial
• Key-B Circumflex scapular • One branch of the thyrocervical trunk is the suprascapular artery. This artery contributes to the scapular anastamosis with the dorsal scapular artery and the circumflex scapular artery. The circumflex scapular artery is a branch of the subscapular artery, which comes from the third part of the axillary artery. So, blood could flow from the suprascapular artery, through the scapular anastamosis, into the circumflex scapular artery, travel retrograde through the circumflex scapular artery and the subscapular artery, and reach the third part of the axillary artery. This would bypass any problems in the second part of the axillary artery.
• While riding a bike, a patient fell against a tree and fractured the shaft of the humerus at midlength. What nerve may be injured because of its close proximity to the injury? a) Ulnar b) Radial c) Axillary d) Medial antebrachial cutaneous e) Median
Key-B Radial The radial nerve and the deep brachial vessels spiral around the shaft of the humerus in the radial groove. If the humerus is fractured, the radial nerve and the deep brachial vessels may be injured, since these structures are closely associated with the shaft of the humerus. The ulnar nerve passes posterior to the medial epicondyle of the humerus--a fracture to this epicondyle may injure the ulnar nerve. The axillary nerve wraps around the surgical head of the humerus— a fracture near the surgical head may endanger the axillary nerve. The medial antebrachial cutaneous nerve and the median nerve travel superficially with the basilic vein and the brachial artery in a neurovascular bundle. These nerves are not going to be injured by a fracture of the humerus.
• Supination of the hand and forearm would be diminished by loss of radial nerve function. But one very powerful supinator would remain intact and unaffected, namely: a) Brachialis b) Brachioradialis c) Biceps brachii d) Flexor carpi radialis e) Supinator
Key-C biceps brachii Biceps brachii supinates the arm, but it is not innervated by the radial nerve--instead, it is innervated by the musculocutaneous nerve. So, it would not be affected by a radial nerve injury. Brachialis is also innervated by the musculocutaneous nerve, but it is only involved with flexing the forearm--it is not a supinator. Brachioradialis flexes the elbow and assists in pronation and supination--it is innervated by the radial nerve and would be paralyzed after a radial nerve injury. Flexor carpi radialis is a flexor, not a supinator--it is innervated by the median nerve. Finally, supinator is innervated by the deep radial nerve.
• A worker doing repetitive lifting develops an inflammation in the tendon of origin of the extensor carpi radialis brevis muscle, commonly called "tennis elbow". The focal point of pain would most likely be near which palpable bony landmark? a) Coronoid process of ulna b) Lateral epicondyle of humerus c) Lateral supracondylar ridge of humerus d) Medial epicondyle of humerus e) Medial supracondylar ridge of humerus Key-B lateral epicondyle of the humerus The extensor carpi radialis brevis muscle originates from the common extensor tendon off the lateral epicondyle of the humerus. So, an injury to this tendon would result in pain near the lateral epicondyle. Tennis elbow is due to the repetitive use of superficial extensor muscles of the forearm-- the pain is often felt at the lateral epicondyle and it radiates down the posterior surface of the forearm. None of the other bony landmarks are associated with the common extensor tendon, although the medial epicondyle is the origin of the common flexor tendon.
• In an attempt to commit suicide by slashing the ventral side of the wrist, the two tendons of the flexor digitorum superficialis located most superficially were completely severed. What movement would be affected? a) Flexion of the MP and IP joints of the thumb b) Flexion of the PIP joints of digits 2 and 5 c) Flexion of the PIP joints of digits 3 and 4 d) Flexion of the DIP joints of digits 2 and 5 e) Flexion of the DIP joints of digits 3 and 4
Key-Cflexion of the PIP joints of digits 3 and 4 When cutting the ventral side of the wrist, the first tendons cut would be the tendons of flexor digitorum superficialis. These tendons help flex the metacarpophalangeal and proximal interphalangeal joints, but not the distal interphalangeal joints. Flexor digitorum profundus (which has deeper tendons) is responsible for flexing the distal interphalangeal joints. The tendons of flexor digitorum superficialis are arranged in a packet with two superficial tendons and two deeper tendons. The tendons that go to fingers 3 and 4 are superficial, while the ones to finger 2 and 5 are underneath. So, the tendons to fingers 3 and 4 will be cut, impairing flexion of the proximal interphalangeal joints of digits 3 and 4.
• While going up for a rebound, a basketball player jams her middle finger against the ball. She experiences severe pain and the trainer notes that she can no longer extend the distal phalanx of the finger. The injury has avulsed (torn away from the bone) which structure from her distal phalanx to produce this condition? a) extensor carpi radialis brevis tendon b) extensor carpi radialis longus tendon c) extensor digiti minimi tendon d) extensor expansion e) extensor indicis tendon
• Key-D extensor expansions • The extensor expansions are the expanded distal ends of the extensor tendons which wrap around the heads of the metacarpals and the bases of the proximal phalanges and insert on the bases of the middle and distal phalanges. These extensor expansions hold the extensor tendon in the middle of the digit and provide a place for the lumbricals and interossei to attach. If an extensor expansion was torn, the extensor tendon would not be held in place and a lumbrical would be torn from its attachment. This would impair extension at the joint.
• The tendons on the dorsal side of the wrist are held in place by a thickening of the antebrachial fascia called which of the following? a) bicipital aponeurosis b) extensor expansion c) extensor retinaculum d) interosseous membrane e) palmar carpal ligament
Key-C extensor retinaculum The extensor compartment is on the dorsal surface of the arm. The tendons of the muscles from this compartment pass onto the dorsal side of the wrist by crossing under the extensor retinaculum. The bicipital aponeurosis is the membranous band that runs from the biceps tendon across the cubital fossa and merges with the antebrachial fascia over the forearm flexor muscles. An extensor expansion wraps around the head of a metacarpal and the base of the proximal phalanx to hold the extensor tendon in place on the digit. The interosseous membrane connects the radius to the ulna, and the palmar carpal ligament is a thickening of the antebrachial fascia over the palmar surface of the wrist. The palmaris longus and ulnar neurovascular bundle pass deep to the palmar carpal ligament, and the flexor retinaculum lies deeper and more distal, forming the carpal tunnel.
• After suffering a gunshot wound to the forearm, it was determined that the posterior interosseous nerve was severed. What function was lost? a) Sensory from the wrist joint b) Motor to brachioradialis c) Motor to the extensor carpi radialis longus d) Parasympathetic to the dorsum of the forearm e) Motor to the flexor digitorum superficialis
Key-ASensory to the wrist joint The posterior interosseous nerve is the sensory continuation of the deep radial nerve, distal to its motor branches for the extensor muscles. It reaches the wrist joint and carpal bones for proprioceptive sense from these structures. Brachioradialis and extensor carpi radialis longus are innervated by the radial nerve, and extensor carpi radialis brevis is innervated by the deep radial nerve. Flexor digitorum superficialis is innervated by the median nerve. There are no parasympathetic nerves in the limbs or body wall.
• If the musculocutaneous nerve is severed at its origin from the brachial plexus, flexion at the elbow is greatly weakened but not abolished. What muscle remains operative and can contribute to flexion? a) Brachialis b) Brachioradialis c) Coracobrachialis d) Long head of biceps brachii e) Short head of biceps brachii
Key-B Brachioradialis Brachioradialis is a muscle innervated by the radial nerve--it flexes the elbow and assists in pronating and supinating the arm. Brachialis, coracobrachialis, and both heads of biceps brachii are all muscles which flex the arm and/or forearm, but they are all innervated by the musculocutaneous nerve. These muscles would be denervated if the musculocutaneous nerve was severed at its origin from the brachial plexus.
• After falling on the ice, it was determined that a patient had a Colles' fracture. Care must be taken to relieve tension on the broken distal end of the radius created by the pull of which muscle? a) Extensor carpi ulnaris b) Brachioradialis c) Extensor carpi radialis longus d) Pronator quadratus e) Extensor carpi radialis brevis
• Key-B brachioradialis • The Colles' fracture is a fracture to the distal end of the radius. It usually occurs when someone tries to catch themselves from falling on an outstretched arm. So, you need to look in the answer choices for a muscle that inserts on the distal end of the radius. Brachioradialis inserts on the lateral side of the base of the styloid process of the radius, so this muscle could pull the broken piece of the radius out of place. This is why a cast over a Colles' fracture needs to extend up to the elbow--brachioradialis needs to be immobilized!
• An infant was diagnosed as having hydrocephalus. It was determined that there was a blockage in the ventricular system of the baby's brain between the third and fourth ventricles. The blockage therefore must have involved which of the following? a) Central canal b) Cerebral aqueduct c) Foramen of Luschka (lateral foramen) d) Foramen of Magendie (medial foramen) e) Interventricular foramen Key-B cerebral aqueduct The cerebral aqueduct is the part of the ventricular system that carries cerebrospinal fluid from the third ventricle to the fourth ventricle. So, this must be the part of the ventricular system that was blocked. The central canal is the space where CSF flows through the spinal cord. It is continuous with the 4th ventricle. The foramina of Luschka (lateral aperatures) and foramen of Magendie (median aperature) are small foramina in the 4th ventricle that allow the CSF to leave the ventricular system and enter the subarachnoid space. The interventricular foramina are passages from the lateral ventricles that allow the CSF to enter the 3rd ventricle.
• An 84-year old woman suffers a stroke, with paralysis on the right side of her body. Neurological tests show that the intracerebral hemorrhage has interrupted the blood supply to the posterior part of the frontal, the parietal and medial portions of the temporal lobes of the left cerebral hemisphere. Which vessel was involved? a) Anterior cerebral artery b) Great cerebral vein c) Middle cerebral artery d) Middle meningeal artery e) Posterior cerebral artery
Key- c Middle cerebral artery The middle cerebral artery supplies blood to most of the lateral surface of cerebral hemispheres, and the temporal pole, including the frontal, parietal, and medial portions of the temporal lobes. So, the specific damage to the temporal lobe suggests that the middle cerebral artery was disrupted. The other arteries listed do not distribute to the same territory. The anterior cerebral artery supplies the medial and superior surfaces of the brain, including the frontal pole. The posterior cerebral artery supplies the inferior surface of the brain and the occipital pole. Strokes occur in arteries, not veins, so that's one reason why the great cerebral vein is not correct. Veins also drain regions of blood--they don't supply blood to areas. The middle meningeal artery supplies blood to the dura mater and the cranial vault bones--it does not supply blood to the brain.
• Infections may spread from the nasal cavity to the meninges along the olfactory nerves, as its fibers pass from the mucosa of the nasal cavity to the olfactory bulb via which of the following? a) Cribriform plate of the ethmoid b) Crista galli c) Foramen caecum d) Superior orbital fissure
Key-Acribriform plate of the ethmoid. The olfactory nerve exits the skull through the cribriform plate of the ethmoid bone--an infection in the nasal cavity may be carried to the olfactory bulb by the nerves that are passing through the cribriform plate. The crista galli is a ridge on the ethmoid bone between the two sides of the cribriform plate; it provides an anchor for the falx cerebri. Foramen cecum is a small hole in the frontal bone near the anterior end of the crista galli--it transmits an emissary vein. Finally, the superior orbital fissure is a hole in the sphenoid bone that transmits many cranial nerves: the oculomotor nerve (CN III), the trochlear nerve (CN IV), the ophthalmic division of the trigeminal nerve (CN V1) and the abducens nerve (CN VI) all pass through the superior orbital fissure.
• A patient who has sustained a fracture to the middle cranial fossa following a fall from a height, might have any of these nerves injured EXCEPT: a) Trigeminal b) Oculomotor c) Abducens d) Trochlear e) Hypoglossal
Key-E hypoglossal The middle cranial fossa is the part of the skull that supports the temporal lobes of the brain. It is made of the greater wings of the sphenoid and squamous part of the temporal bones laterally and the petrous part of the temporal bones posteriorly. Several cranial nerves enter foramina in the middle cranial fossa; all of these nerves might have been damaged in the fall. The trigeminal nerve (CN V) has three divisions that all leave through spaces in the middle cranial fossa. V1, the ophthalmic division, exits through the superior orbital fissure; V2, the maxillary division, leaves through foramen rotundum; V3, the mandibular division, leaves through foramen ovale. The oculomotor nerve (CN III) crosses through the superior orbital fissure, along with abducens (CN VI), the trochlear nerve (CN IV) and the ophthalmic division of the trigeminal nerve (CN V1). So, all of these nerves might have been damaged in the fall. The hypoglossal nerve, however, leaves the base of the skull by passing through the hypoglossal canal, which is in the occipital bone and the posterior cranial fossa. It is not likely that this nerve was injured in the fall.
• In a fall from a horse, a rider sustains a severe neck injury at the C6 level. In addition to crushing the spinal cord, the left transverse process of the C6 vertebra is fractured. What artery is endangered? a) Common carotid b) Costocervical c) Inferior thyroid d) Internal carotid e) Vertebral
Key-EVertebral The paired vertebral arteries travel through the transverse foramina of the C1-C6 vertebrae. So, since the C6 vertebra was damaged, the vertebral artery could also be ruptured. The other arteries are not closely related with the vertebrae. The common carotid arteries come off the brachiocephalic trunk on the right side and the aortic arch on the left side, giving off many arteries that supply the head and neck. The costocervical trunk is a branch of the subclavian artery that supplies the deep neck and the first 2 intercostal spaces. The inferior thyroid artery is a branch of the thyrocervical trunk that supplies the thyroid. Finally, the internal carotid artery is a branch of the common carotid that joins the circle of Willis and supplies the brain.
• A 35-year-old man was admitted to the hospital complaining of double vision (diplopia), inability to see close objects, and blurred vision in the right eye. A vertebrobasilar angiogram revealed an aneurysm of the superior cerebellar artery close to its origin on the right side. The doctor attributed the symptoms to the compression of an adjacent cranial nerve by the aneurysm. The compressed nerve is which of the following? a) Abducens (CN VI) b) Oculomotor (CN III) c) Optic (CN II) d) Trigeminal (CN V) e) Trochlear (CN IV)
• Key-BOculomotor (CN III) • Given the patient's symptoms, it seems that some nerve involving vision and the ability to control the eye has been injured. Now, you need to think about which nerve might be damaged by an aneurysm of the superior cerebellar artery. The oculomotor nerve, which innervates the superior rectus, medial rectus, inferior rectus, and inferior oblique muscles, passes between the posterior cerebral artery and the superior cerebellar artery. It could be injured if there was enlargement of or damage to either of these vessels. None of the other cranial nerves are in the right position to be injured from an aneurysm of the superior cerebellar artery.
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