What is the complete three-neuron anatomical pathway of the oculosympathetic tract, and what triad of signs defines Horner Syndrome?

1st-order neuron: posterior hypothalamus descending ipsilaterally through brainstem to the ciliospinal center of Budge (C8–T2 intermediolateral cell column); 2nd-order (preganglionic) neuron: exits T1, ascends over the lung apex (vulnerable to Pancoast tumor) to synapse in the Superior Cervical Ganglion; 3rd-order (postganglionic) neuron: ascends along the internal carotid artery plexus (vulnerable to carotid dissection) into the orbit; injury causes ipsilateral Ptosis (superior tarsal/Müller muscle), Miosis (dilator pupillae), and Anhidrosis.

Which nerve and muscle are injured in classic Medial Winging of the Scapula, and what surgical procedure is a common cause?

Injury to the Long Thoracic Nerve (arising directly from roots C5, C6, and C7) paralyzes the serratus anterior muscle, causing the medial border of the scapula to protrude posteriorly when pushing against a wall and preventing arm abduction above 90 degrees; classically injured during axillary lymph node dissection / mastectomy.

Which nerve is injured in a Midshaft Fracture of the Humerus (radial groove) or 'Saturday Night Palsy', and what deficits result?

The Radial nerve (C5–T1, Posterior Cord), accompanied by the profunda brachii artery; injury causes 'wrist drop' (loss of wrist and finger extensors, brachioradialis, and supinator) and sensory loss over the posterior forearm and dorsal first web space (triceps extension is often spared in midshaft fractures because its branches arise proximally).

How do you clinically distinguish an Obturator Nerve injury from a Femoral Nerve injury after pelvic surgery or anterior/posterior hip trauma?

Obturator nerve (L2–L4, exits obturator canal) injury causes weakness of thigh ADDUCTION and sensory loss over the medial thigh; Femoral nerve (L2–L4, passes deep to inguinal ligament lateral to femoral artery) injury causes weakness of hip flexion and knee EXTENSION (buckling knee), loss of the patellar reflex, and sensory loss over the anterior thigh and medial leg (saphenous nerve).

What neurotransmitters and receptor subtypes are used at all autonomic ganglia, sympathetic postganglionic targets (including exceptions), and parasympathetic postganglionic targets?

All autonomic preganglionic fibers (both sympathetic and parasympathetic) release Acetylcholine (ACh) onto Nicotinic Nn (N2) ligand-gated ion channels on postganglionic neurons (and chromaffin cells of the adrenal medulla); Parasympathetic postganglionic fibers release ACh onto Muscarinic (M1–M5) GPCRs; Sympathetic postganglionic fibers release Norepinephrine onto Adrenergic (alpha-1, alpha-2, beta-1, beta-2, beta-3) GPCRs, EXCEPT eccrine sweat glands (which use ACh on M3 receptors) and renal vascular smooth muscle (dopamine D1).

How do you clinically distinguish a Proximal Median Nerve lesion (supracondylar humerus fracture) from Carpal Tunnel Syndrome (distal median nerve compression)?

Both cause thenar eminence atrophy ('ape hand' / loss of thumb opposition via the recurrent branch) and sensory loss over the palmar radial 3.5 digits; however, ONLY a proximal lesion paralyzes the forearm flexors (flexor digitorum superficialis and radial half of profundus), producing active 'Hand of Benediction' when attempting to make a fist (inability to flex digits 2 and 3) and loss of sensation over the central thenar palm (because the palmar cutaneous branch arises proximal to and travels superficial to the carpal tunnel). In contrast, a distal lesion produces a passive 'Median Claw' of digits 2 and 3 on finger extension due to paralysis of the lateral two lumbricals with intact FDP.

What is the 'Ulnar Paradox' regarding why a Distal Ulnar Nerve lesion at the wrist causes worse 'Ulnar Clawing' of digits 4 and 5 than a Proximal lesion at the elbow?

In a distal lesion (Guyon's canal), the medial two lumbricals are paralyzed (causing MCP hyperextension and IP flexion of digits 4 and 5) while the ulnar half of flexor digitorum profundus (FDP) remains intact and pulls the DIP joints into severe flexion; in a proximal elbow lesion, FDP is ALSO paralyzed, resulting in less pronounced clawing.

What is Anterior Interosseous Nerve (AIN) Syndrome, and how is it tested clinically?

Pure motor neuropathy of the anterior interosseous branch of the median nerve in the forearm, paralyzing flexor pollicis longus, flexor digitorum profundus (digits 2 and 3), and pronator quadratus without sensory loss; the patient cannot make the 'OK' sign (pincer grasp flattens instead of forming a circle).

Where do preganglionic neurons of the Sympathetic (Thoracolumbar) versus Parasympathetic (Craniosacral) nervous system reside, and how do the lengths of their pre- and postganglionic fibers compare?

Sympathetic preganglionic neurons reside in the intermediolateral cell column of spinal segments T1–L2 (short preganglionic myelinated B fibers, paravertebral/prevertebral ganglia, long postganglionic unmyelinated C fibers); Parasympathetic preganglionic neurons reside in brainstem nuclei (CN III, VII, IX, X) and sacral segments S2–S4 (long preganglionic fibers, intramural/terminal ganglia near target organs, short postganglionic fibers).

Which nerve innervates the perineum and external urethral/anal sphincters, and what anatomical landmark is palpated transvaginally to perform its nerve block during childbirth?

The Pudendal nerve (S2–S4), which exits the greater sciatic foramen, hooks around the ISCHIAL SPINE and sacrospinous ligament, and re-enters the perineum via the lesser sciatic foramen (Alcock's canal); the ischial spine is the landmark for a pudendal nerve block.

What is Thoracic Outlet Syndrome, and what neurovascular structures are compressed in the interscalene triangle?

Compression of the Lower Trunk of the brachial plexus (C8–T1) and the Subclavian Artery between the anterior and middle scalene muscles and the first rib (or a cervical rib / Pancoast tumor), causing ulnar-distribution hand pain/paresthesias, intrinsic hand muscle atrophy, and diminished radial pulse on overhead arm elevation.

What nerve roots, mechanism, and clinical posture characterize Erb-Duchenne Palsy ('Waiter's Tip')?

Traction injury to the Upper Trunk (C5–C6 roots) of the brachial plexus (e.g., lateral neck traction during shoulder dystocia or fall onto shoulder), paralyzing the suprascapular, axillary, and musculocutaneous nerves; the arm hangs adducted and internally rotated with the elbow extended, forearm pronated, and wrist flexed ('waiter's tip'), with preserved hand grasp.

What are the clinical findings of a Superior Gluteal Nerve (L4–S1) injury versus an Inferior Gluteal Nerve (L5–S2) injury?

Superior Gluteal Nerve innervates gluteus medius, gluteus minimus, and tensor fasciae latae (hip abduction); injury (e.g., misplaced IM injection outside upper outer gluteal quadrant) causes a positive Trendelenburg sign (pelvis drops on the CONTRALATERAL unsupported side when standing on the affected leg). Inferior Gluteal Nerve innervates gluteus maximus (hip extension); injury causes difficulty rising from a seated position or climbing stairs.

Which nerve fibers are damaged first in Diabetic Peripheral Neuropathy, and why does it follow a 'stocking-glove' distribution?

Chronic hyperglycemia leads to sorbitol accumulation (via aldose reductase), oxidative stress, and endoneurial microangiopathy of the vasa nervorum, causing length-dependent axonal degeneration that affects the longest peripheral nerves in the feet first before ascending to the hands, with early loss of small unmyelinated/thinly myelinated fibers (burning pain, paresthesias) and large myelinated A-beta fibers (loss of vibration and ankle reflexes, predisposing to painless neuropathic plantar ulcers).

How does Complex Regional Pain Syndrome (CRPS) Type I differ from Type II, and what autonomic and trophic features characterize both?

CRPS Type I (reflex sympathetic dystrophy) occurs after minor trauma or immobilization WITHOUT a definable major peripheral nerve lesion, whereas CRPS Type II (causalgia) occurs after a documented peripheral nerve injury; both present with severe regional pain, hyperalgesia, and allodynia disproportionate to the inciting event, accompanied by local vasomotor/sudomotor instability (edema, temperature/color changes, abnormal sweating) and trophic skin/nail/bone changes (patchy osteopenia).

What are the five sequential anatomical subdivisions of the Brachial Plexus (C5–T1), and how are its Trunks and Cords named?

Roots (ventral rami C5–T1) -> Trunks (Superior C5–C6, Middle C7, Inferior C8–T1) -> Divisions (3 Anterior, 3 Posterior) -> Cords (Lateral, Posterior, Medial, named by their relationship to the second part of the axillary artery) -> Terminal Branches (Musculocutaneous, Axillary, Radial, Median, Ulnar).

How do you clinically and pathophysiologically distinguish Myasthenia Gravis (MG) from Lambert-Eaton Myasthenic Syndrome (LEMS) at the neuromuscular junction?

Myasthenia Gravis (associated with thymoma/thymic hyperplasia): postsynaptic IgG autoantibodies against nicotinic ACh receptors (or MuSK/LRP4), causing fatigable ocular/bulbar weakness (ptosis, diplopia, dysphagia) that WORSENS with repetitive use/evening and improves with cooling (Ice Pack Test) and acetylcholinesterase inhibitors (pyridostigmine; avoid aminoglycosides, fluoroquinolones, macrolides, beta-blockers, and IV magnesium); LEMS (paraneoplastic with small cell lung cancer): presynaptic autoantibodies against P/Q-type voltage-gated Ca2+ channels, causing proximal limb weakness, autonomic dysfunction (dry mouth), and hyporeflexia that IMPROVES with repetitive contraction (treated with amifampridine [3,4-DAP]).

What are the Greater, Lesser, and Least Thoracic Splanchnic Nerves, and which prevertebral sympathetic ganglia do they innervate?

They are preganglionic sympathetic nerves that pass through the paravertebral sympathetic chain without synapsing and pierce the diaphragm: Greater Splanchnic (T5–T9) synapses in the Celiac ganglion (foregut); Lesser Splanchnic (T10–T11) synapses in the Superior Mesenteric and Aorticorenal ganglia (midgut); Least Splanchnic (T12) synapses in the Renal plexus (while Lumbar Splanchnics L1–L2 synapse in the Inferior Mesenteric ganglion for the hindgut).

What are the major nerves of the Lumbar Plexus (L1–L4) and their clinical roles in pelvic/inguinal surgery or trauma?

Iliohypogastric/Ilioinguinal (L1: abdominal wall/inguinal hernia injury), Genitofemoral (L1–L2: cremasteric reflex), Lateral Femoral Cutaneous (L2–L3: compressed under inguinal ligament in Meralgia Paresthetica causing anterolateral thigh burning/numbness without motor loss), Obturator (L2–L4: medial thigh sensation and hip adduction), and Femoral (L2–L4: hip flexion, knee extension, patellar reflex, and saphenous medial leg sensation).

Which nerve is compressed around the neck of the fibula (e.g., fibular neck fracture or tight leg cast), and what are its clinical features?

The Common Peroneal (Fibular) nerve (L4–S2); divides into the Deep Peroneal nerve (anterior compartment: loss of ankle dorsiflexion and toe extension causing 'foot drop' and steppage gait, plus sensory loss in the 1st dorsal web space) and Superficial Peroneal nerve (lateral compartment: loss of foot eversion and sensory loss over the anterolateral lower leg and dorsum of foot) — remember 'PED' (Peroneal Everts and Dorsiflexes).

What are the G-protein second-messenger pathways and primary physiological effects of M1, M2, and M3 muscarinic receptors?

M1 (Gq -> IP3/DAG): CNS cognition and enteric nervous system/gastric parietal cell acid secretion; M2 (Gi -> decreased cAMP and opening of GIRK K+ channels): decreased SA node heart rate and decreased AV node conduction velocity; M3 (Gq -> IP3/DAG): bronchoconstriction, increased GI peristalsis and exocrine gland secretions (salivation, lacrimation, sweating), bladder detrusor contraction, pupillary sphincter contraction (miosis), and ciliary muscle contraction (accommodation), plus endothelium-dependent NO vasodilation.

How do the Parasympathetic and Sympathetic nervous systems coordinate male sexual function ('Point and Shoot')?

Parasympathetic pelvic splanchnic nerves (S2–S4, 'Point') release nitric oxide (NO) and ACh, increasing cGMP to relax corpus cavernosum smooth muscle and cause vasodilation/erection; Sympathetic hypogastric nerves (T11–L2, 'Shoot') stimulate Alpha-1 receptors to contract the vas deferens, seminal vesicles, and internal urethral sphincter for emission, while somatic Pudendal nerves (S2–S4) contract the bulbospongiosus/ischiocavernosus muscles for expulsion/ejaculation.

Which peripheral nerve arises from the Lateral Cord of the brachial plexus, pierces the coracobrachialis muscle, and what deficits follow its injury?

The Musculocutaneous nerve (C5–C7); it innervates the biceps brachii, brachialis, and coracobrachialis (elbow flexion and forearm supination) and terminates as the lateral cutaneous nerve of the forearm; injury causes weak elbow flexion/supination, absent biceps reflex, and lateral forearm sensory loss.

How does the Autonomic Nervous System coordinate Urination (micturition) versus Urinary Storage across the detrusor muscle and urethral sphincters?

Urinary Storage (Sympathetic T11–L2 via hypogastric nerve): Beta-3 receptors relax the detrusor muscle while Alpha-1 receptors contract the internal urethral sphincter; Micturition/Voiding (Parasympathetic S2–S4 via pelvic splanchnic nerves): M3 receptors contract the detrusor muscle while somatic Pudendal nerve (S2–S4) nicotinic inhibition relaxes the external striated urethral sphincter.

Which nerve is injured in a fracture of the Medial Epicondyle of the Humerus or compression at Guyon's Canal (handlebar palsy), and what deficits result?

The Ulnar nerve (C8–T1, Medial Cord); causes paralysis of the interossei (loss of finger abduction/adduction), adductor pollicis (positive Froment sign), hypothenar muscles, and medial two lumbricals, plus sensory loss over the fifth digit and ulnar half of the fourth digit.

What is Guillain-Barré Syndrome (Acute Inflammatory Demyelinating Polyradiculoneuropathy), what infection precedes it in 30–40% of cases, and what is the classic CSF finding?

Autoimmune peripheral Schwann cell demyelination via molecular mimicry (anti-GM1/GD1a ganglioside antibodies), most commonly preceded by Campylobacter jejuni enteritis; presents with symmetric ASCENDING flaccid paralysis, areflexia, and potential diaphragmatic respiratory failure/autonomic instability; CSF shows 'albuminocytologic dissociation' (markedly elevated protein with normal white blood cell count), treated with IVIG or plasmapheresis (NOT corticosteroids).

How do you pharmacologically localize a Horner Syndrome lesion using Apraclonidine/Cocaine drops versus Hydroxyamphetamine drops?

Cocaine (blocks NE reuptake) fails to dilate a Horner pupil, and Apraclonidine (weak alpha-1 agonist) reverses miosis/ptosis via denervation supersensitivity, confirming Horner syndrome; Hydroxyamphetamine (triggers release of stored NE from 3rd-order nerve terminals) dilates the pupil if the lesion is 1st- or 2nd-order (intact 3rd-order neuron), but FAILS to dilate the pupil if the lesion is 3rd-order (postganglionic, e.g., internal carotid dissection).

Which nerve is injured in a popliteal fossa lesion or Tarsal Tunnel Syndrome behind the medial malleolus, and what deficits result?

The Tibial nerve (L4–S3); injury causes inability to plantarflex the ankle (cannot walk on tiptoes), loss of foot inversion (tibialis posterior), loss of toe flexion, absent Achilles reflex, and sensory loss over the sole of the foot — remember 'TIP' (Tibial Inverts and Plantarflexes).

Which nerve is injured in a fracture of the Surgical Neck of the Humerus or anterior shoulder dislocation, and what deficits result?

The Axillary nerve (C5–C6, Posterior Cord), accompanied by the posterior circumflex humeral artery; injury causes flattened deltoid contour, inability to abduct the shoulder from 15 to 90 degrees, weakness of teres minor, and sensory loss over the lateral proximal arm ('regimental badge' area).

What nerve roots, mechanism, and clinical findings characterize Klumpke Palsy?

Upward traction injury to the Lower Trunk (C8–T1 roots) of the brachial plexus (e.g., grabbing an overhead branch while falling or traction on an abducted arm during delivery), damaging the ulnar and median intrinsic hand fibers; causes 'total claw hand' (lumbrical and interossei paralysis) and frequently an ipsilateral Horner syndrome (T1 sympathetic root injury).

What is Charcot-Marie-Tooth Disease (Hereditary Motor and Sensory Neuropathy), and what are its classic physical examination findings?

Most commonly an autosomal dominant duplication of the PMP22 gene on chromosome 17p (CMT1A) causing defective peripheral myelin production and onion-bulb Schwann cell hypertrophy; presents in adolescence with symmetric distal muscle weakness and atrophy of the lower legs ('inverted champagne bottle' or 'stork legs'), bilateral foot drop, pes cavus (high-arched feet), hammertoes, and stocking-glove sensory loss.

What are the G-protein second-messenger pathways and primary physiological effects of Alpha-1, Alpha-2, Beta-1, and Beta-2 adrenergic receptors?

Alpha-1 (Gq -> IP3/DAG -> increased Ca2+): vascular smooth muscle vasoconstriction, pupillary dilator contraction (mydriasis), internal urethral/anal sphincter contraction; Alpha-2 (Gi -> decreased cAMP): presynaptic inhibition of NE release, decreased insulin release, CNS sympatholysis; Beta-1 (Gs -> increased cAMP): increased heart rate (chronotropy), contractility (inotropy), AV conduction (dromotropy), and renin release from JG cells; Beta-2 (Gs -> increased cAMP): bronchodilation, skeletal muscle vasodilation, uterine tocolysis, glycogenolysis, and ciliary epithelium aqueous humor production.

Neurology: Brachial & Lumbosacral Plexuses, Peripheral Neuropathies & Autonomic Nervous System

Clinical neurology and neuroanatomy of the brachial plexus (Erb and Klumpke palsies, winged scapula, axillary/radial/median/ulnar nerve lesions), lumbosacral plexus (femoral, obturator, gluteal, peroneal, tibial, pudendal nerves), Horner syndrome, autonomic receptors, and neuromuscular junction disorders.

Level: advanced
Languages: en → en
Cards: 32
Markdown: Neurology: Brachial & Lumbosacral Plexuses, Peripheral Neuropathies & Autonomic Nervous System (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What is the complete three-neuron anatomical pathway of the oculosympathetic tract, and what triad of signs defines Horner Syndrome?	1st-order neuron: posterior hypothalamus descending ipsilaterally through brainstem to the ciliospinal center of Budge (C8–T2 intermediolateral cell column); 2nd-order (preganglionic) neuron: exits T1, ascends over the lung apex (vulnerable to Pancoast tumor) to synapse in the Superior Cervical Ganglion; 3rd-order (postganglionic) neuron: ascends along the internal carotid artery plexus (vulnerable to carotid dissection) into the orbit; injury causes ipsilateral Ptosis (superior tarsal/Müller muscle), Miosis (dilator pupillae), and Anhidrosis.
2	Which nerve and muscle are injured in classic Medial Winging of the Scapula, and what surgical procedure is a common cause?	Injury to the Long Thoracic Nerve (arising directly from roots C5, C6, and C7) paralyzes the serratus anterior muscle, causing the medial border of the scapula to protrude posteriorly when pushing against a wall and preventing arm abduction above 90 degrees; classically injured during axillary lymph node dissection / mastectomy.
3	Which nerve is injured in a Midshaft Fracture of the Humerus (radial groove) or 'Saturday Night Palsy', and what deficits result?	The Radial nerve (C5–T1, Posterior Cord), accompanied by the profunda brachii artery; injury causes 'wrist drop' (loss of wrist and finger extensors, brachioradialis, and supinator) and sensory loss over the posterior forearm and dorsal first web space (triceps extension is often spared in midshaft fractures because its branches arise proximally).
4	How do you clinically distinguish an Obturator Nerve injury from a Femoral Nerve injury after pelvic surgery or anterior/posterior hip trauma?	Obturator nerve (L2–L4, exits obturator canal) injury causes weakness of thigh ADDUCTION and sensory loss over the medial thigh; Femoral nerve (L2–L4, passes deep to inguinal ligament lateral to femoral artery) injury causes weakness of hip flexion and knee EXTENSION (buckling knee), loss of the patellar reflex, and sensory loss over the anterior thigh and medial leg (saphenous nerve).
5	What neurotransmitters and receptor subtypes are used at all autonomic ganglia, sympathetic postganglionic targets (including exceptions), and parasympathetic postganglionic targets?	All autonomic preganglionic fibers (both sympathetic and parasympathetic) release Acetylcholine (ACh) onto Nicotinic Nn (N2) ligand-gated ion channels on postganglionic neurons (and chromaffin cells of the adrenal medulla); Parasympathetic postganglionic fibers release ACh onto Muscarinic (M1–M5) GPCRs; Sympathetic postganglionic fibers release Norepinephrine onto Adrenergic (alpha-1, alpha-2, beta-1, beta-2, beta-3) GPCRs, EXCEPT eccrine sweat glands (which use ACh on M3 receptors) and renal vascular smooth muscle (dopamine D1).
6	How do you clinically distinguish a Proximal Median Nerve lesion (supracondylar humerus fracture) from Carpal Tunnel Syndrome (distal median nerve compression)?	Both cause thenar eminence atrophy ('ape hand' / loss of thumb opposition via the recurrent branch) and sensory loss over the palmar radial 3.5 digits; however, ONLY a proximal lesion paralyzes the forearm flexors (flexor digitorum superficialis and radial half of profundus), producing active 'Hand of Benediction' when attempting to make a fist (inability to flex digits 2 and 3) and loss of sensation over the central thenar palm (because the palmar cutaneous branch arises proximal to and travels superficial to the carpal tunnel). In contrast, a distal lesion produces a passive 'Median Claw' of digits 2 and 3 on finger extension due to paralysis of the lateral two lumbricals with intact FDP.
7	What is the 'Ulnar Paradox' regarding why a Distal Ulnar Nerve lesion at the wrist causes worse 'Ulnar Clawing' of digits 4 and 5 than a Proximal lesion at the elbow?	In a distal lesion (Guyon's canal), the medial two lumbricals are paralyzed (causing MCP hyperextension and IP flexion of digits 4 and 5) while the ulnar half of flexor digitorum profundus (FDP) remains intact and pulls the DIP joints into severe flexion; in a proximal elbow lesion, FDP is ALSO paralyzed, resulting in less pronounced clawing.
8	What is Anterior Interosseous Nerve (AIN) Syndrome, and how is it tested clinically?	Pure motor neuropathy of the anterior interosseous branch of the median nerve in the forearm, paralyzing flexor pollicis longus, flexor digitorum profundus (digits 2 and 3), and pronator quadratus without sensory loss; the patient cannot make the 'OK' sign (pincer grasp flattens instead of forming a circle).
9	Where do preganglionic neurons of the Sympathetic (Thoracolumbar) versus Parasympathetic (Craniosacral) nervous system reside, and how do the lengths of their pre- and postganglionic fibers compare?	Sympathetic preganglionic neurons reside in the intermediolateral cell column of spinal segments T1–L2 (short preganglionic myelinated B fibers, paravertebral/prevertebral ganglia, long postganglionic unmyelinated C fibers); Parasympathetic preganglionic neurons reside in brainstem nuclei (CN III, VII, IX, X) and sacral segments S2–S4 (long preganglionic fibers, intramural/terminal ganglia near target organs, short postganglionic fibers).
10	Which nerve innervates the perineum and external urethral/anal sphincters, and what anatomical landmark is palpated transvaginally to perform its nerve block during childbirth?	The Pudendal nerve (S2–S4), which exits the greater sciatic foramen, hooks around the ISCHIAL SPINE and sacrospinous ligament, and re-enters the perineum via the lesser sciatic foramen (Alcock's canal); the ischial spine is the landmark for a pudendal nerve block.
11	What is Thoracic Outlet Syndrome, and what neurovascular structures are compressed in the interscalene triangle?	Compression of the Lower Trunk of the brachial plexus (C8–T1) and the Subclavian Artery between the anterior and middle scalene muscles and the first rib (or a cervical rib / Pancoast tumor), causing ulnar-distribution hand pain/paresthesias, intrinsic hand muscle atrophy, and diminished radial pulse on overhead arm elevation.
12	What nerve roots, mechanism, and clinical posture characterize Erb-Duchenne Palsy ('Waiter's Tip')?	Traction injury to the Upper Trunk (C5–C6 roots) of the brachial plexus (e.g., lateral neck traction during shoulder dystocia or fall onto shoulder), paralyzing the suprascapular, axillary, and musculocutaneous nerves; the arm hangs adducted and internally rotated with the elbow extended, forearm pronated, and wrist flexed ('waiter's tip'), with preserved hand grasp.
13	What are the clinical findings of a Superior Gluteal Nerve (L4–S1) injury versus an Inferior Gluteal Nerve (L5–S2) injury?	Superior Gluteal Nerve innervates gluteus medius, gluteus minimus, and tensor fasciae latae (hip abduction); injury (e.g., misplaced IM injection outside upper outer gluteal quadrant) causes a positive Trendelenburg sign (pelvis drops on the CONTRALATERAL unsupported side when standing on the affected leg). Inferior Gluteal Nerve innervates gluteus maximus (hip extension); injury causes difficulty rising from a seated position or climbing stairs.
14	Which nerve fibers are damaged first in Diabetic Peripheral Neuropathy, and why does it follow a 'stocking-glove' distribution?	Chronic hyperglycemia leads to sorbitol accumulation (via aldose reductase), oxidative stress, and endoneurial microangiopathy of the vasa nervorum, causing length-dependent axonal degeneration that affects the longest peripheral nerves in the feet first before ascending to the hands, with early loss of small unmyelinated/thinly myelinated fibers (burning pain, paresthesias) and large myelinated A-beta fibers (loss of vibration and ankle reflexes, predisposing to painless neuropathic plantar ulcers).
15	How does Complex Regional Pain Syndrome (CRPS) Type I differ from Type II, and what autonomic and trophic features characterize both?	CRPS Type I (reflex sympathetic dystrophy) occurs after minor trauma or immobilization WITHOUT a definable major peripheral nerve lesion, whereas CRPS Type II (causalgia) occurs after a documented peripheral nerve injury; both present with severe regional pain, hyperalgesia, and allodynia disproportionate to the inciting event, accompanied by local vasomotor/sudomotor instability (edema, temperature/color changes, abnormal sweating) and trophic skin/nail/bone changes (patchy osteopenia).
16	What are the five sequential anatomical subdivisions of the Brachial Plexus (C5–T1), and how are its Trunks and Cords named?	Roots (ventral rami C5–T1) -> Trunks (Superior C5–C6, Middle C7, Inferior C8–T1) -> Divisions (3 Anterior, 3 Posterior) -> Cords (Lateral, Posterior, Medial, named by their relationship to the second part of the axillary artery) -> Terminal Branches (Musculocutaneous, Axillary, Radial, Median, Ulnar).
17	How do you clinically and pathophysiologically distinguish Myasthenia Gravis (MG) from Lambert-Eaton Myasthenic Syndrome (LEMS) at the neuromuscular junction?	Myasthenia Gravis (associated with thymoma/thymic hyperplasia): postsynaptic IgG autoantibodies against nicotinic ACh receptors (or MuSK/LRP4), causing fatigable ocular/bulbar weakness (ptosis, diplopia, dysphagia) that WORSENS with repetitive use/evening and improves with cooling (Ice Pack Test) and acetylcholinesterase inhibitors (pyridostigmine; avoid aminoglycosides, fluoroquinolones, macrolides, beta-blockers, and IV magnesium); LEMS (paraneoplastic with small cell lung cancer): presynaptic autoantibodies against P/Q-type voltage-gated Ca2+ channels, causing proximal limb weakness, autonomic dysfunction (dry mouth), and hyporeflexia that IMPROVES with repetitive contraction (treated with amifampridine [3,4-DAP]).
18	What are the Greater, Lesser, and Least Thoracic Splanchnic Nerves, and which prevertebral sympathetic ganglia do they innervate?	They are preganglionic sympathetic nerves that pass through the paravertebral sympathetic chain without synapsing and pierce the diaphragm: Greater Splanchnic (T5–T9) synapses in the Celiac ganglion (foregut); Lesser Splanchnic (T10–T11) synapses in the Superior Mesenteric and Aorticorenal ganglia (midgut); Least Splanchnic (T12) synapses in the Renal plexus (while Lumbar Splanchnics L1–L2 synapse in the Inferior Mesenteric ganglion for the hindgut).
19	What are the major nerves of the Lumbar Plexus (L1–L4) and their clinical roles in pelvic/inguinal surgery or trauma?	Iliohypogastric/Ilioinguinal (L1: abdominal wall/inguinal hernia injury), Genitofemoral (L1–L2: cremasteric reflex), Lateral Femoral Cutaneous (L2–L3: compressed under inguinal ligament in Meralgia Paresthetica causing anterolateral thigh burning/numbness without motor loss), Obturator (L2–L4: medial thigh sensation and hip adduction), and Femoral (L2–L4: hip flexion, knee extension, patellar reflex, and saphenous medial leg sensation).
20	Which nerve is compressed around the neck of the fibula (e.g., fibular neck fracture or tight leg cast), and what are its clinical features?	The Common Peroneal (Fibular) nerve (L4–S2); divides into the Deep Peroneal nerve (anterior compartment: loss of ankle dorsiflexion and toe extension causing 'foot drop' and steppage gait, plus sensory loss in the 1st dorsal web space) and Superficial Peroneal nerve (lateral compartment: loss of foot eversion and sensory loss over the anterolateral lower leg and dorsum of foot) — remember 'PED' (Peroneal Everts and Dorsiflexes).
21	What are the G-protein second-messenger pathways and primary physiological effects of M1, M2, and M3 muscarinic receptors?	M1 (Gq -> IP3/DAG): CNS cognition and enteric nervous system/gastric parietal cell acid secretion; M2 (Gi -> decreased cAMP and opening of GIRK K+ channels): decreased SA node heart rate and decreased AV node conduction velocity; M3 (Gq -> IP3/DAG): bronchoconstriction, increased GI peristalsis and exocrine gland secretions (salivation, lacrimation, sweating), bladder detrusor contraction, pupillary sphincter contraction (miosis), and ciliary muscle contraction (accommodation), plus endothelium-dependent NO vasodilation.
22	How do the Parasympathetic and Sympathetic nervous systems coordinate male sexual function ('Point and Shoot')?	Parasympathetic pelvic splanchnic nerves (S2–S4, 'Point') release nitric oxide (NO) and ACh, increasing cGMP to relax corpus cavernosum smooth muscle and cause vasodilation/erection; Sympathetic hypogastric nerves (T11–L2, 'Shoot') stimulate Alpha-1 receptors to contract the vas deferens, seminal vesicles, and internal urethral sphincter for emission, while somatic Pudendal nerves (S2–S4) contract the bulbospongiosus/ischiocavernosus muscles for expulsion/ejaculation.
23	Which peripheral nerve arises from the Lateral Cord of the brachial plexus, pierces the coracobrachialis muscle, and what deficits follow its injury?	The Musculocutaneous nerve (C5–C7); it innervates the biceps brachii, brachialis, and coracobrachialis (elbow flexion and forearm supination) and terminates as the lateral cutaneous nerve of the forearm; injury causes weak elbow flexion/supination, absent biceps reflex, and lateral forearm sensory loss.
24	How does the Autonomic Nervous System coordinate Urination (micturition) versus Urinary Storage across the detrusor muscle and urethral sphincters?	Urinary Storage (Sympathetic T11–L2 via hypogastric nerve): Beta-3 receptors relax the detrusor muscle while Alpha-1 receptors contract the internal urethral sphincter; Micturition/Voiding (Parasympathetic S2–S4 via pelvic splanchnic nerves): M3 receptors contract the detrusor muscle while somatic Pudendal nerve (S2–S4) nicotinic inhibition relaxes the external striated urethral sphincter.
25	Which nerve is injured in a fracture of the Medial Epicondyle of the Humerus or compression at Guyon's Canal (handlebar palsy), and what deficits result?	The Ulnar nerve (C8–T1, Medial Cord); causes paralysis of the interossei (loss of finger abduction/adduction), adductor pollicis (positive Froment sign), hypothenar muscles, and medial two lumbricals, plus sensory loss over the fifth digit and ulnar half of the fourth digit.
26	What is Guillain-Barré Syndrome (Acute Inflammatory Demyelinating Polyradiculoneuropathy), what infection precedes it in 30–40% of cases, and what is the classic CSF finding?	Autoimmune peripheral Schwann cell demyelination via molecular mimicry (anti-GM1/GD1a ganglioside antibodies), most commonly preceded by Campylobacter jejuni enteritis; presents with symmetric ASCENDING flaccid paralysis, areflexia, and potential diaphragmatic respiratory failure/autonomic instability; CSF shows 'albuminocytologic dissociation' (markedly elevated protein with normal white blood cell count), treated with IVIG or plasmapheresis (NOT corticosteroids).
27	How do you pharmacologically localize a Horner Syndrome lesion using Apraclonidine/Cocaine drops versus Hydroxyamphetamine drops?	Cocaine (blocks NE reuptake) fails to dilate a Horner pupil, and Apraclonidine (weak alpha-1 agonist) reverses miosis/ptosis via denervation supersensitivity, confirming Horner syndrome; Hydroxyamphetamine (triggers release of stored NE from 3rd-order nerve terminals) dilates the pupil if the lesion is 1st- or 2nd-order (intact 3rd-order neuron), but FAILS to dilate the pupil if the lesion is 3rd-order (postganglionic, e.g., internal carotid dissection).
28	Which nerve is injured in a popliteal fossa lesion or Tarsal Tunnel Syndrome behind the medial malleolus, and what deficits result?	The Tibial nerve (L4–S3); injury causes inability to plantarflex the ankle (cannot walk on tiptoes), loss of foot inversion (tibialis posterior), loss of toe flexion, absent Achilles reflex, and sensory loss over the sole of the foot — remember 'TIP' (Tibial Inverts and Plantarflexes).
29	Which nerve is injured in a fracture of the Surgical Neck of the Humerus or anterior shoulder dislocation, and what deficits result?	The Axillary nerve (C5–C6, Posterior Cord), accompanied by the posterior circumflex humeral artery; injury causes flattened deltoid contour, inability to abduct the shoulder from 15 to 90 degrees, weakness of teres minor, and sensory loss over the lateral proximal arm ('regimental badge' area).
30	What nerve roots, mechanism, and clinical findings characterize Klumpke Palsy?	Upward traction injury to the Lower Trunk (C8–T1 roots) of the brachial plexus (e.g., grabbing an overhead branch while falling or traction on an abducted arm during delivery), damaging the ulnar and median intrinsic hand fibers; causes 'total claw hand' (lumbrical and interossei paralysis) and frequently an ipsilateral Horner syndrome (T1 sympathetic root injury).
31	What is Charcot-Marie-Tooth Disease (Hereditary Motor and Sensory Neuropathy), and what are its classic physical examination findings?	Most commonly an autosomal dominant duplication of the PMP22 gene on chromosome 17p (CMT1A) causing defective peripheral myelin production and onion-bulb Schwann cell hypertrophy; presents in adolescence with symmetric distal muscle weakness and atrophy of the lower legs ('inverted champagne bottle' or 'stork legs'), bilateral foot drop, pes cavus (high-arched feet), hammertoes, and stocking-glove sensory loss.
32	What are the G-protein second-messenger pathways and primary physiological effects of Alpha-1, Alpha-2, Beta-1, and Beta-2 adrenergic receptors?	Alpha-1 (Gq -> IP3/DAG -> increased Ca2+): vascular smooth muscle vasoconstriction, pupillary dilator contraction (mydriasis), internal urethral/anal sphincter contraction; Alpha-2 (Gi -> decreased cAMP): presynaptic inhibition of NE release, decreased insulin release, CNS sympatholysis; Beta-1 (Gs -> increased cAMP): increased heart rate (chronotropy), contractility (inotropy), AV conduction (dromotropy), and renin release from JG cells; Beta-2 (Gs -> increased cAMP): bronchodilation, skeletal muscle vasodilation, uterine tocolysis, glycogenolysis, and ciliary epithelium aqueous humor production.