NBME 7 block 4 q 1 to 50 - maryam2009

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to add Q 46 C (Kaplan Bioch book page 193)

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47. C
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis major, its fibers being derived from C5, C6 and C7.
Path
It penetrates the Coracobrachialis muscle and passes obliquely between the Biceps brachii and the Brachialis, to the lateral side of the arm; a little above the elbow it pierces the deep fascia lateral to the tendon of the Biceps brachii and is continued into the forearm as the lateral cutaneous nerve of the forearm.
In its course through the arm it innervates the Coracobrachialis, Biceps brachii, and the greater part of the Brachialis.
• The branch to the Coracobrachialis is given off from the nerve close to its origin, and in some instances as a separate filament from the lateral cord of the plexus; it is derived from the seventh, cervical nerve.
• The branches to the Biceps brachii and Brachialis are given off after the musculocutaneous has pierced the Coracobrachialis; that supplying the Brachialis gives a filament to the elbow-joint.
• The nerve also sends a small branch to the bone, which enters the nutrient foramen with the accompanying artery.
Damage
Although rare, the musculocutaneous n. can be affected through compression due to hypertrophy or entrapment between the biceps aponeurosis & brachialis fascia or it may be injured through stretch as occurs in dislocations & sometimes in surgery.
Isolated injury, causes weakness of elbow flexion & supination of the forearm.
A discrete sensory disturbance is present on the radial side of the forearm.
The nerve is usually involved in an upper brachial plexus palsy
Injury can occur before entering the coracobrachialis due to dislocation or apparently due to stretch due to throwing injury
Heavy backpacks can cause damage to the upper trunk of the brachial plexus – dysfunction can be severe & prolonged with similar injury as occurs with Erb's palsy from breech deliveries. Early detection is important – the combination of time, avoidance of wearing a backpack, and strengthening of the shoulder muscles will probably be effective.
Distal to the coracobrachialis, the MC cause appears to be weight lifting – either through compression due to hypertrophy or entrapment between the biceps & brachialis, the nerve may lead to a painless loss of muscle strength in flexion & supination of the forearm. Initial treatment should include avoidance of biceps curls or other biceps exercises.
http://en.wikipedia.org/wiki/Musculocutaneous_nerve

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48. A
Coartation of the aorta: Infantil type ( preductal) aortic stenosis proximal to insertion of ductus arteriosus.
Adult type: ( postductal) stenosis is distal to ductus arteriosus.
Associated with notching ribs (due to collateral circulation), hypertension in upper extremities, weak pulses in lower extremities. Associated with Turner syndrome.

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48-A Symptoms may be absent with mild narrowings (coarctation). When present, they include: difficulty breathing, poor appetite or trouble feeding, failure to thrive. Later on, children may develop symptoms related to problems with blood flow and an enlarged heart. They may experience dizziness or shortness of breath, faint or near-fainting episodes, chest pain, abnormal tiredness or fatigue, headaches, or nosebleeds. They may have cold legs and feet or have pain in their legs with exercise (intermittent claudication) Wikipedia,
to add ;Clinical sings proximal to the constriction---- increased upper ext BP, dilatation of aorta and aorta valve ring (regurgitation) increased risk for developing an aorta dissection, increased cerebral blood flow (increased risk for berry aneurysm.
Clinical signs distal to the constriction; ----dicreased blood pressure in the lower extremity, leg claudication( pain in calf or bottocks when walking, dicreased renal blod flow with activates RAA system causing the phisiophathology of the hepertension

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49-D the patient had and epidural hematoma, first lost the consciusness and then get back in ER, dilated pupil in the right secondary to the compression of the uncus and squeeze the III nerve oculomotor affecting the parasympatetic input to the right eye, cause of the dilatation.
to add: Epidural hematoma (EDH) is a rapidly accumulating hematoma between the dura mater and the cranium. These patients have a history of head trauma with loss of consciousness, then a lucid period, followed by loss of consciousness. Clinical onset occurs over minutes to hours. Many of these injuries are associated with lacerations of the middle meningeal artery. A "lenticular", or convex, lens-shaped extracerebral hemorrhage will likely be visible on a CT scan of the head. Although death is a potential complication, the prognosis is good when this injury is recognized and treated. http://www.reference.com/browse/uncal
to add:In uncal herniation, a common subtype of transtentorial herniation, the innermost part of the temporal lobe, the uncus, can be squeezed so much that it goes by the tentorium and puts pressure on the brainstem, most notably the midbrain.[5] The tentorium is a structure within the skull formed by the meningeal layer of the dura mater. Tissue may be stripped from the cerebral cortex in a process called decortication.[6]

The uncus can squeeze the third cranial nerve, which may affect the parasympathetic input to the eye on the side of the affected nerve, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should. Pupillary dilation often precedes the somatic motor effects of cranial nerve III compression, which present as deviation of the eye to a "down and out" position due to loss of innervation to all ocular motility muscles except for the lateral rectus (innervated by cranial nerve VI) and the superior oblique (innervated by cranial nerve IV). The symptoms occur in this order because the parasympathetic fibers surround the motor fibers of CNIII and are hence compressed first.

Compression of the ipsilateral posterior cerebral artery will result in ischemia of the ipsilateral primary visual cortex and contralateral visual field deficits in both eyes (contralateral homonymous hemianopsia (Wikiped

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49. D
In uncal herniation, a common subtype of transtentorial herniation, the innermost part of the temporal lobe, the uncus, can be squeezed so much that it goes by the tentorium and puts pressure on the brainstem, most notably the midbrain.[5] The tentorium is a structure within the skull formed by the meningeal layer of the dura mater. Tissue may be stripped from the cerebral cortex in a process called decortication.[6]
The uncus can squeeze the third cranial nerve, which may affect the parasympathetic input to the eye on the side of the affected nerve, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should. Pupillary dilation often precedes the somatic motor effects of cranial nerve III compression, which present as deviation of the eye to a "down and out" position due to loss of innervation to all ocular motility muscles except for the lateral rectus (innervated by cranial nerve VI) and the superior oblique (innervated by cranial nerve IV). The symptoms occur in this order because the parasympathetic fibers surround the motor fibers of CNIII and are hence compressed first.
Compression of the ipsilateral posterior cerebral artery will result in ischemia of the ipsilateral primary visual cortex and contralateral visual field deficits in both eyes (contralateral homonymous hemianopsia).
Another important finding is a false localizing sign, the so called Kernohan's notch, which results from compression of the contralateral cerebral crus containing descending corticospinal and some corticobulbar tract fibers. This leads to ipsilateral (same side as herniation) hemiparesis. Since the corticospinal tract predominately innervates flexor muscles, extension of the leg may also be seen. With increasing pressure and progression of the hernia there will be distortion of the brainstem leading to Duret hemorrhages (tearing of small vessels in the parenchyma) in the median and paramedian zones of the mesencephalon and pons. The rupture of these vessels leads to linear or flamed shaped hemorrhages. The disrupted brainstem can lead to decorticate posture, respiratory center depression and death. Other possibilities resulting from brain stem distortion include lethargy, slow heart rate, and pupil dilation.[6] Uncal herniation may advance to central herniation.[4]
A complication of an uncal herniation is a Duret hemorrhage. This results in the midbrain and pons being compressed, possibly causing damage to the reticular formation. If untreated, death will ensue.
http://en.wikipedia.org/wiki/Brain_herniation

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hi dna 23 thanks for your add Qs 48

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Hi god99 thanks for your time and your post, I really appreciated,
thanks to maryam, sash11 and captianjack too.

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50. C

Δ G < 0 Thermodynamically spontaneous ( energy released often irreversible)
Δ G > 0 Thermodynamically nonspontaneous ( energy required)
Δ G˚ = 0 energy involved under standarizer conditions
(Kaplan Bioch. Book page 122)

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Thanks to
Maryam
dna23
captainjack
sash11
step1success
firstaid1984
God bless us and give everybody 99