spine/peripheral nerve Flashcards
Which of the following nerves passes through the quadrangular space below the teres minor
The quadrangular space is lateral to the scapula and is defined by laterally by the humerus, medial by the triceps, rostrally by the teres minor and caudally by the teres major. The axillary nerve along with the circumflex artery exit caudal to the teres minor and rostral to the teres major, providing innervation to the deltoid. The suprascapular nerve originates from the upper trunk and passes across the posterior triangle of the neck providing innervation to the supraspinatus and infraspinatus. The thoracodorsal nerve originates from the posterior cord and provides innervation to the latissimus dorsi. The radial nerve innervates most of the upper extremity extensors and exits below the quadrangular space between the long and lateral heads of the triceps. The long thoracic nerve originates from roots C5, C6, and C7 traversing the chest to provide innervation of the serratus anterior muscle. Injury to the long thoracic nerve results in scapular winging.
For patients with post ACDF horners syndrome, what was injured and how?
The sympathetic plexus or trunk is located running on the longus colli muscle. In anterior cervical surgery, the sympathetic plexus is at risk of injury due to unintentional thermal injury from using monopolar electrocautery directly on the longus colli muscle, or from prolonged retraction inducing stretching of the fibers.
Thoracic pedicle morphology studies consistently show that the narrowest pedicle is most likely to be found at which of the following locations?
T5 as the transverse diameter of the thoracic pedicle decreases from T1 to its narrowest diameter between T4-6. From T7 -T12 the diameter of the thoracic pedicles progressively enlarge.
Each somatic muscle fiber is innervated by?
Each somatic muscle fiber is innervated by an alpha motor neuron which has a cell body in either the spinal cord or brain stem. A motor neuron and muscle fibers it innervates is called a motor unit. The number of fibers innervated by one motor neuron can vary. A smaller innervation number leads to finer motor control. Gamma motor neurons adjust the sensitivity of muscle spindle fibers
A 52-year-old man is brought to the emergency department after being involved in a motor vehicle collision. He has an L2 sensory level; muscle strength is 4/5 in the proximal lower extremities and 4-/5 in the distal lower extremities. X-ray films show a severe L2 fracture. Which of the following is the most likely ASIA Impairment Scale score (modified Frankel score) in this patient?
The patient here has sustained an ASIA D injury, where motor function is preserved below the neurological level, and more than half of the key muscles below the neurological level have a muscle strength of at least grade 3. An ASIA A injury is complete, an ASIA B injury is incomplete where sensory function is spared without motor function except for preservation of the sacral segments. An ASIA C injury has motor function preserved below the neurological level, and more than half of the key muscles below the neurological level have a muscle strength less than grade 3. ASIA E is normal strength.
A 50-year-old man is evaluated because of a two-week history of low back pain and sciatica on the right side. Straight-leg raising test is positive at 30 degrees and extensor hallucis longus strength on the right side is 4/5. Which of the following disc herniations is most likely?
L5 radiculopathy.
Far lateral and foraminal disc herniations are most likely to affect the exiting nerve root at that level while central and paracentral herniations most likely affect the traversing nerve root.
Vertebra plana (pancake VB) is classically associated with which spinal lesions?
eosinophilic granuloma otherwise known as Langerhan cell histiocytosis (LCH) or histiocytosis X, a proliferation of Langerhan cells and abundance of eosinophils, lymphocytes, and neutrophils. These cells produce prostaglandins which result in medullary bone resorption.
Hand-Schuller-Christian disease describes when the disease is chronic and disseminated in bone and viscera.
Letterer-Siwe describes a fatal form that occurs in young children.
Other causes of vertebrae plana can be identified from the mnemonic I MELT (infection, metastasis/myeloma, eosinophilic granuloma, lymphoma/leukemia, trauma/tuberculosis)
Most common level at which the vertebral artery enters the vertebral foramen on the cervical spine?
C6
Innervation of the median nerve:
The median nerve:
orginates from both the lateral and medial cords of the brachial plexus (C5-T1)
provides sensory innervation to the anterolateral surface of the hand and provides motor innervation to the following muscles – pronator teres, flexor carpi radialis, palmaris longus, and flexor digitorum superficialis, flexor pollicis longus and flexor digitorum profundus, pronator quadratus, opponens pollicis brevis, and flexor pollicis brevis, 1st and 2nd lumbricals.
Innervation of obturator nerve:
originates from L2, L3, and L4, providing sensory innervation to the medial thigh and motor innervation to the adductor longus, adductor brevis, adductor magnus, external obturator, and variably to the pectineus
How is pelvic incidence calculated?
Pelvic incidence is a fixed spinopelvic parameter.
It is calculated as the angle between the perpendicular line drawn from the center of the S1 endplate and the line that joins the center of the femoral heads to the center of the S1 endplate.
It is also defined by the formula: PI = PT + SS, (PI=pelvic incidence, PT=pelvic tilt, SS=sacral slope). Sacral slope and pelvic tilt can vary with retroversion of the pelvis, and lumbar lordosis changes with flexion and extension maneuvers.
Fractional scoliosis is a coronal plane parameter that is variable in the absence of spinal fusion.
A patient is diagnosed with left vestibular schwannoma and bilateral hypoglossal canal meningiomas. This patient most likely has which of the following genetic conditions?
neurofibromatosis type 2 (NF2) is diagnosed when one of the following criteria are met.
- Bilateral vestibular schwannoma (VS), diagnosed before age 70
- First-degree relative family history of NF2 and unilateral VS, diagnosed before age 70
- First-degree relative family history of NF2 or unilateral VS or 2 of: meningioma, cataract, schwannoma, cerebral calcification (if unilateral VS and > 2 nonintradermal schwannomas, needs negative LZTR1 genetic testing)
- Multiple meningiomas (2 or more) and 2 of: unilateral VS, cataract, ependymoma, schwannoma, cerebral calcification
- Constitutional or mosaic pathogenic NF2 gene mutation in blood or identical mutations in 2 distinct tumors.
Which muscles is innervated by the anterior interosseous nerve?
anterior interosseous nerve is a distal branch of the median nerve that originates at the level of the anterior forearm
It originates from the nerve roots C8 and T1
It intervates the flexor pollicis longus, flexor digitorum profundus, and the pronator quadratus.
Compression at the level of the forearm or parsonage turner syndrome are the most common pathologies producing varying degrees of weakness but without sensory deficit.
Duchennes muscular dystophy: inheritance, lab abnormalities, and symptoms?
x linked recessive
caused by decreased dystophin
Increased creatinine kinase, muscle fiber necrosis
atrophy of shoulder and pelvic gridle muscles, calf pseudohypertrophy, CHF, + gowers test Tx: prednisone
myotonic muscular dystophy: inheritance, lab abnormalities, and symptoms?
AD 19
CTG trinucleotide repeat
ring fibers, EMG: dive bomber frequency
face then extremity, MR, dysrythmias, cataracts, endocrinopathies
Tx: quinine, procainamide, and dilantin
Beckers muscular dystophy: inheritance, lab abnormalities, and symptoms?
x linked
decreased dystrophin
less severe than duchennes
Muscles of the tympanic cavity and their innervation:
Tensor tympani: CN5
stapedius: CN7
Muscles of mastication:
temporalis, masseter, medial pterygoid, lateral pterygoid (only one that opens the mouth)
innervation: CN5
Muscles of the tongue and innervation:
CN 12: genioglossus, hyoglossus, styloglossus
CN 10: palatoglossus
Muscles of the palate and innervation:
CN 5: tensor veli palatini
CN 10: levator veli palatini, palatoglossus, and palatopharyngeus
Muscles of the pharynx and innervation:
CN 9: stylopharyngeus
CN 10: salpingopharyngeus, superior, middle, and inferior pharyngeal constrictors
Muscles of the larynx and innervation:
all CN 10
cricothyroid from external branch of the superior laryngeal nerve but all others by recurrent laryngeal nerve
Brachial plexus subdivisions and level, innervation (branches) at each level:
Roots C5-T1:
- C5-8: longus colli and scalene muscles
- C5: dorsal scapular nerve -> rhomboids and levator scapula
- C5-7: long thoracic nerve –> serratus anterior
Trunks:
- upper: suprascapular nerve -> supra and infraspinatus
- middle: no branches (runs under the anterior scalene)
- lower: no branches (behind the subclavian artery)
cords:
- lateral: lateral pectoral nerve -> pectoral muscles
- posterior: upper/lower subscapular nerves -> teres major, subscapularis ; thoracodorsal nerve -> latissimus dorsi ; terminates as the axillary and radial nerves
- medial: medial pectoral nerve -> pectoral muscles; medial brachial cutaneous nerve -> arm; medial antebrachial cutaneous nerve -> forearm; terminates as median cutaneous and ulnar nerves
Nerves:
- musculocutaneous: coracobrachialis, biceps, and brachialis
- axillary: deltoid and teres minor
- radial: triceps, brachioradialis, extensor carpi radialis longus and brevis; continues as the posterior interosseous nerve (C7-8) -> supinator, externsor carpi ulnaris, extensor digitorum, extensor digiti minimi, abductor pollicus longus, extensor pollicus longus and brevis, and extensor indicis
- median:
- ulnar:
Which type of muscle has a longer depolarization and plateau phase?
cardiac muscle due to fast voltage-gated sodium channels, slow voltage-gated calcium channels, and potassium channels that do not open until the end of the plateau
what is the conduction velocity in small, unmyelinated fibers?
0.5m/s
What are the 5 types of sensory fibers and how are they organized/what do they transmit?
Ia (type A-alpha [Aα])—annulospiral endings of muscle spindles; largest (i.e., 17-μm diameter) and fastest (120 m/s).
Ib (Aα)—Golgi’s tendon organs; 16 μm in diameter.
II (type A-beta [Aβ] and A-gamma [Aγ])—flower-spray endings of muscle spindles and cutaneous tactile receptors; 8 μm in diameter.
III (type A-delta [Aδ])—temperature, crude touch, and pricking pain; 3 μm in diameter.
IV (type C)—unmyelinated fibers relaying pain, itch, temperature, and crude touch sensations; 0.5 to 2 μm in diameter.
What are the 3 types of motor nerve fibers?
Skeletal muscle—α-type A (myelinated; fastest fibers).
Muscle spindle—γ-type A (myelinated).
Sympathetic—type C (unmyelinated; slowest fibers).
What are the two types of anterior motor neurons?
α motor neurons—larger. They innervate skeletal muscle by sending α-type A fibers to large skeletal muscle fibers within the motor unit.
Gamma motor neurons—smaller. They are 50% less numerous and relay γ-type A fibers to the intrafusal fibers of the muscle spindle.
Describe muscle spindle organization, type of endings with attached fibers, and types of intrafusal fibers:
spindles lie parallel to fibers, composed of 3-12 intrafusal fibers attached to larger extrafusal fibers
detects length and velocity of change in length of the muscle
two sensory endings of the spindle: primary (type Ia fiber with 70-120m/s impulse relay) and secondary (type II flower spray, slower conduction)
Two types of intrafusal fibers:
-nuclear bag fibers: 1-3/spindle and innervated by primary endings
-nuclear chain: 3-9/spindle; smaller and innervated by primary and secondary endings
Primary motor cortex: cells?
brodmanns area 4. Bets cells are large pyramidal neurons found only in the primary motor cortex; they relay impulses at 70 m/s
Efferent fibers from the motor cortex to:
collateral fibers to the cortex (for lateral inhibition), caudate and putamen, red nucleus (rubrospinal fibers), reticular formation (reticulospinal, cerebellar fibers), vestibular system (vestibulospinal, cerebellar fibers), and inferior olive (olivocerebellar fibers)
Afferent fibers to the motor cortex from:
input from somatosensory systems (e.g., muscle spindles), visual cortex, auditory cortex, frontal cortex, contralateral motor cortex (via the corpus callosum), ventrobasal thalamus, ventrolateral (VL) and ventroanterior (VA) thalamus (with input from the cerebellum and basal ganglia), and intralaminar nuclei of the thalamus (which regulate the level of excitability)
descending motor pathway:
contains 1 million fibers (30% from area 4, 30% from premotor and supplementary motor cortices [area 6], and 40% from sensory fibers). 40% of the fibers are from the parietal lobe. Cells (Betz cells) arise from layer 5.
travels in the posterior limb of the internal capsule and down through the brainstem, forming the medullary pyramid
most fibers then cross and descend in the lateral corticospinal tract, terminate on interneurons (in cord gray matter, mostly Lamina VII), sensory relay neurons (in the dorsal horn), and anterior motor neurons
Some fibers, however, remain ipsilateral; these descend in the ventral corticospinal tract, ultimately crossing at lower levels within the spinal cord. These fibers are used for bilateral postural control, relaying impulses from the supplementary motor area
What is the appearance of SNAPs in nerve root avulsion? what does it look like if the lesion is distal to the DRG?
If lesion is proximal, there is still a normal SNAP but no sensation since the axon is attached to the cell body
if lesion is distal to cell body, the SNAP is abnormal
What does the nervi erigentes innervate?
parasympathetic supply to the pelvis and perineum
also called the pelvic splanchnic nerve; S2, 3, 4
cause and symptoms of meralgia paresthetica?
entrapment or injury of the lateral femoral cutaneous nerve causing pain and numbness in the anterolateral thigh
Wartenbergs sign is associated with which nerve injury?
Ulnar nerve
inability to adduct the little finger due to weakness of interossei secondary to ulnar n palsy. The little finger is abducted due to the unopposed action of extensor digiti minimi.
what is the membrana tectoria?
cranial extension of the PLL and connects C2 to clivus
The transverse ligament of atlas is anterior to it.
(There is another tectorial membrane in the inner ear and is involved with hearing)
which tract carries pain and temp from contralateral body?
lateral (neo) spinothalamic tract transmits pain and temperature from the contralateral body and is somatotopically organized with the legs laterally. The ventral (paleo) spinothalamic is involved in light touch.
Substance P is the main neurotransmitter in the:
substantia gelatinosa of Rolando (II) and is involved in pain sensation
All of the following tracts enter the cerebellum through the inferior cerebellar peduncle, except:
Ventral spinocerebellar (enters through the superior cerebral peduncle)
Dorsal spinocerebellar
Ventral external arcuate fibers
Dorsal external arcuate fibers
Olivocerebellar
which nerve courses through the achilles tendon and medial malleolus?
Tibial nerve
branch of sciatic nerve at a distal thigh level
How do the trigeminal nerve branches course through meckels cave?
What are the median nerve innervated hand muscles?
What are the ulnar nerve innervations of the hand muscles?
