Nervous system and spinal cord Flashcards
The diameter of a motor nerve fiber is?
A 20-50 micrometers
B 5-7 millimetres
C 10 millimetres
D 12-20 micrometres
D
Explanation
A nerve fibre consists of an axon, its neurolemma (i.e. Schwann cells with or without myelin), and surrounding endoneurial connective tissue Fibers are of differering size, with larger myelinated fibres conducting faster than smaller unmyelinated fibers.
Fibre types:
Myelinated:
Aα - somatic motor and proprioception, diameter 16µm, speed 100m/s Aß - touch, diameter 8µm, and speed 50m/s
Ay - motor to muscle spindles, diameter 4µm, speed 25m/s
Aδ - pain and temperature (fast pain or epicritic pain), diameter 4µm, speed 25m/s
B - preganglionic autonomic, diameter 2µm, speed ~12.5m/s
Unmyelinated:
C - pain and temperature (slow pain or protopathic pain), postganglionic sympathetic diameter 1µm, speed 2m/s
MEMORY AID: Aα is 16µm and 100m/s, and each successive fibre is approx half the diameter and half the speed of the one before it (other than Ay and Aδ which are the same). C fibres are unmyelinated and thus very slow (“C” for slow).
With respect to dermatomal nerve supply, which of the following is correct?
A T6 lies at level of the nipple
B The anterior axial line divides C6 and C7
C The umbilicus is supplied by T12
D C7 supplies the index finger
D
Explanation
The umbilicus is supplied by T10. The line of junction of two dermatomes supplied from discontinuous spinal levels is demarcated by an axial line. T4 lies at the level of the nipple
Extra:
Dermatomes have created some problems in the past. Anatomy TB don’t seem to always agree
Old prescribed TB
C7-middle fingers
New prescribed TB
C7-middle and ring fingers (or middle three fingers)and centre posterior aspect of the forearm.
The picture: Palmer aspect C7-middle and ring finger. Dorsum aspect C7-middle finger nad half of the index and ring fingers
C6-lateral forearm and thumb. Picture, palmer-thumb, dorsum-thumb and half of the index finger
Regarding myotomal supply, which of the following is correct?
A Opponens pollicis - C7/C8
B Elbow extension - C6/C7
C Plantar flexion - L4/5
D Shoulder abduction - C5/6
B
Explanation
Plantar flexion is S1/S2.
Shoulder abduction is C5.
Opponens policis is T1-mainly with a small C8 component
Please note that in the current prescribed textbook it is C6/C7 for elbow extension. However, in previous text books used for the primary, elbow extension is shown as C7/C8
Cell bodies for the motor supply of the trigeminal nerve lie in which of the following areas?
A In the hypothalamus
B In the pons
C In the cerebral cortex
D Posterior to the cerebral aqueduct
B
Explanation
The trigeminal nerve is the largest cranial nerve. The sensory root rises in the trigeminal (semilunar) ganglion that is at the apex of the petrous temporal bone. The motor neurons arrise in the upper pons. First 4 cranial nerve nuclei lie above the pons, second 4 lie in the pons, last 4 lie below the pons.
Cell bodies for the motor supply of the facial nerve lie in which of the following areas?
A Pons
B Floor of third ventricle
C Hypothalamus
D Midbrain
A
Explanation
The motor part of the facial nerve arises from the facial nerve nucleus in the pons while the sensory part arises from the nervus intermedius which emerges between the pons and the inferior cerebellar peduncle, near the vestibulocochlear nerve
Which of the following is a direct connection from the vestibular nucleus?
A Oculomotor nerve
B Medial longitudinal fasciculus
C Medial geniculate body
D Vestibulospinal tract
D
Explanation
The vestibulospinal tract is one of the descending spinal tracts of the ventromedial pathway. It originates from thevestibular nerve of the medulla, which conducts information from thevestibular labyrinth in the inner ear. Motion of fluid in the vestibular labyrinth activates hair cells that signal the vestibular labyrinth via the cranial nerve VIII
Regarding myotomes, which of the following statements is correct?
A A myotome is a muscle supplied by single peripheral nerve
B Knee is flexion is L3,4
C Foot inversion is L4, L5
D Shoulder adduction is C5
C
Explanation
The unilateral muscle mass receiving innervation from fibres conveyed by a single spinal nerve (from the anterior ramus division) is a myotome. Knee flexion is L5, S1. Shoulder adduction and medial rotation is C6, C7, C8
The myotome of the great toe extension is
A S1
B L5
C L4
D S2
B
Explanation
L4: tibialis anterior and posterior and inversion of the foot
L5: extensor hallucis longus and extension of the great toe
S1: gastrocnemius, plantarflexion of the foot, ankle jerk
S2: small muscles of the foot
Note: this appears to be an old question. In the current textbook- it appears that either L5, S1 or both myotomes are involved. The older textbook was more specific and reported L5 as the myotome. Internet sources also prefer L5
Which movement of the upper limb does not involve C6?
A Wrist extension
B Shoulder adduction
C Pronation
D Supination
C
Explanation
Pronation is C7, C8.
Supination = C6
Shoulder adduction and medial rotation C6, C7, C8.
Wrist flexion = C7
Note: Old textbook write: wrist extension is C6C7 and wrist flexion C6C7. The current textbook writes : wrist extension C6 and Wrist flexion C7
In which ganglion do the cell bodies of afferent taste fibres of the anterior two thirds of the tongue occur?
A Trigeminal
B Otic
C Submandibular
D Genicular
D
Explanation
For general sensation (touch and temperature) the mucosa of the anterior two thirds of the tongue is supplied by the lingual nerve, a branch of CN V3- cell bodies in the trigeminal ganglion
For special sensation (taste), this part of the tongue, except for the vallate papillae, is supplied by the chorda tympani nerve, a branch of CN VII- cell bodies in the geniculate ganglion of the facial nerve.
Which is the correct myotome for elbow extension?
A C7/C8
B C5/C6/C7
C C5/6
D C6/7
D
Explanation
Using the current textbook
C5/6= elbow flexion
C6= elbow extension, wrist extension, supination, arm adduction, medial rotation of the arm
C7=is incorporated into many myotomes/actions (medial rotation of elbow, adduction of arm, arm extension, elbow extension hand flexion, pronation, digital extension and flexion)
C5/C6/C7= do not occur together
C7/C8 = digital flexion and extension and pronation of the hand
Note: in different textbooks, elbow extension isC7C8
Regarding dermatomes which of the following statements is correct?
A A dermatome is separated from a discontinuous segment of the spinal cord by an axial line
B They overlap at axial lines
C They do not overlap in the chest
D A dermatome is the area of skin and muscle supplied by a single spinal nerve
A
Explanation
They overlap considerably on the trunk and the limbs except at axial lines.
Which of the following dermatomes supplies the little toe?
A L4
B S2
C L5
D S1
D
Explanation
L3= anterior and medial thigh and knee
L4= medial leg, medial ankle and side of foot
L5= lateral leg, dorsum of foot, medial sole, 1-3 toes
S1= lateral ankle, lateral side of dorsum and sole of foot, 4-5 toes (5th toe=little toe)
S2= Posterior leg, posterior thigh, buttocks and penis
Note: current sources say S1= 5th toe only, S3=penis and bulk of buttocks, S4=scrotum, and small medial part of buttocks (close to rectum)
Which of the following is the myotome responsible for knee extension?
A L3,4
B L4,5
C L2,3
D L5,S1
A
Explanation
L2, L3= Hip flexion
L4, L5= Hip extension
L5, S1=Knee flexion
L3, L4=Knee extension
L4, L5=Ankle dorsiflexion
S1,S2= Ankle plantarflexion
A Horner’s Syndrome can result from interruption of all of the following tracts/areas except?
A Post-ganglionic fibres entering the sympathetic trunk
B Superior cervical ganglion
C Lateral horn cells inT1 segmant of the cord
D Cavernous sinus
A
Explanation
The sympathetic path to the pupil is very long.
From cells in the hypothalamus, fibres run down through the brain stem and spinal cord to the lateral horn cells in the T1 segment of the cord. Preganglionic fibres enter the sympathetic trunk via the white rami communicantes of the T1 nerve and pass up to the superior cervical ganglion. From there the postganglionic fibres accompany the internal carotid artery into the skull and cavernous sinus, leaving the artery to join the opthalic nerve and become distributed to the eye by the nasocilliary and the long ciliary branches.
Damage to the above fibres can interrupt this pathway.
Thus vascular lesions of the cortex or brainstem and damage to the sympathetic trunk by a cervical rib, carcinoma of the lung, thyroid or oesophagus may give rise to Horner’s syndrome.
Extra:
In a series of 450 patients with Horner syndrome, 270 (65%) were found to have an identifiable cause.21 Of the patients with a detectible aetiology, 13% had a central lesion, 44% had a preganglionic lesion, and 43% had a postganglionic lesion.
Which of the following nerves is a branch of the medial cord of the brachial plexus?
A Lower subscapular
B Dorsal scapular
C Medial pectoral
D Lateral pectoral
C
Explanation
The lateral pectoral nerve is a branch of the lateral cord. The dorsal scapular nerve (which supplies the rhomboids and levator scapulae) belongs to the C5 root. The lower subscapular nerve is a branch of the posterior cord. The medial pectoral nerve arises from the medial cord C8 T1 behind the first part of the axillary artery.
Regarding the Brachial plexus, which of the following statements is incorrect?
A Cords enter the axilla above the first part of the axillary artery
B Branches of the cords surround the third part of axillary artery
C Divisions form behind the clavicle and enter the anterior triangle
D Cords embrace the 2nd part of the axillary artery
C
Explanation
The 5 roots lie behind the scalenus anterior muscle and emerge between it and scalenus medius to form the trunks which cross the lower part of the posterior triangle of the neck. Each of the three trunks divides into an anterior and a posterior division behind the clavicle. Here, at the outer border of the first rib, the upper two anterior divisions unite to form the lateral cord, the anterior division of the lower trunk runs on as the medial cord, while all three posterior divisions unite to form the posterior cord. These three cords enter the axilla above the first part of the axillary artery, approach and embrace its second part, and give off their branches around its third part.
Thus the roots are between the scalenus muscles, trunks in the posterior triangle, divisions behind the clavicle, and the cords in axilla.
The information about the axillary artery comes from Last’s anatomy. I know it is an older textbook. I have also left the question as is.
The first part of the axillary artery and the cords of the brachial plexus are enclosed within the axillary sheath, which is projected down from the prevertebral fascia in the neck. The lateral and posterior cords are superolateral, and the medial cord posterior, to the artery.
The second part of the artery has the three cords of the plexus lateral, posterior and medial to it, as their names indicate.
The third part has the branches from the cords of the brachial plexus, having in general the same relation to the artery as their parent cords. The medial root of the median nerve crosses in front of the artery to join the lateral root and form the nerve lateral to the artery,
From the current TB
The brachial plexus is formed by the union of the anterior rami of the last four cervical (C5-C8) and the first thoracic (T1) nerve, which constitute the roots of the brachial plexus.
The roots of the plexus usually pass through the gap between the anterior and the middle scalene muscles with the subclavian artery. In the inferior part of the neck, the roots of the brachial plexus unite to form three trunks. A superior, middle and inferior trunk. Each trunk of the brachial plexus divides into anterior and posterior divisions as the plexus passes through the cervico-axillary canal posterior to the clavicle. Anterior divisions of the trunks supply anterior (flexor) compartments of the upper limb and posterior divisions of the trunks supply (extensor) compartments. The division of the trunks form three cords of the brachial plexus. Anterior divisions of the superior and middle trunks untie to form the lateral cord. Anterior division of the inferior trunk continues as the medial cord. Posterior divisions of all three trunks unite to form the posterior cord. The cords bear relationship to the second part of the axillary artery that is indicated by their names. The lateral cord is lateral to the axillary artery etc, The products of the plexus formation are multisegmental , peripheral nerves. The brachial plexus is divided into supraclavicular and infraclavicular parts.
Regarding the brachial plexus, which of the following statements is correct?
A Pectoralis major is the only muscle that can test all roots
B Injury proximal to the trunks will not affect the supraspinatus nor infraspinatus muscles
C Erb’s palsy results in a medially rotated arm with elbow flexion
D Ulnar nerve palsy results in weakness of the interossei and numbness over the radial part of the hand
A
Explanation
Erb’s palsy results in a medially rotated arm with the elbow in extension. The nerve supply to supra and infraspinatous comes from the trunks and will be affected if the injury to the BP is at the level of the trunks or proximal to them. Ulnar nerve injury will give weakness to the ulnar part of the hand
Which of the following lies outside the blood-brain barrier?
A Temporal lobe
B Posterior pituitary
C Thalamus
D Cerebellar vermis
B
A patient is unable to look down when his right eye is abducted. Which muscle is affected?
A Inferior rectus
B Superior rectus
C Superior oblique
D Inferior oblique
A
Explanation
The superior and inferior recti are tested in abduction. The inferior rectus normally depresses, adducts and laterally rotates the eye, The oblique muscles are tested in adduction.
Extra:
This question is testing eye movements when the eye is abducted: if the gaze is directed laterally. Abducted by the lateral rectus so that the line of gaze coincides with the plane of the Sr and IR. The SR produces elevation only and IR produces depression only (and is likewise solely responsible).
If the gaze is directed medially-adducted by the medial recuts so that the line of gaze coincides with the plane of the inserting tendons of the SO and IO. The SO produces depression only (and is solely responsible for the movement) and the IO produces elevation only (and is likewise solely responsible).
Protrusion of the jaw is a function of which cranial nerve?
A CN X
B CN IX
C CN V
D CN VII
C
Explanation
TMJ movements are produced chiefly by the muscles of mastication. These four muscles (temporal, masseter, and medial and lateral pterygoid muscles) develop from the mesoderm of the embryonic first pharyngeal arch; consequently, they are all innervated by the nerve of that arch, the (motor root of the) mandibular nerve (CN V3).
A patient is unable to remove a food bolus from their cheek. Which nerve is likely damaged?
A Hypoglossal
B Facial
C Trigeminal
D Vagus
B
Explanation
If the injury weakens or paralyses the buccinator and orbicularis oris, food will accumulate in the oral vestibule during chewing, usually requiring continual removal with a finger. When the sphincters or dilators of the mouth are affected, displacement of the mouth (drooping of its corner) is produced by contraction of the unopposed contralateral facial muscles and gravity, resulting in food and saliva dribbling out of the side of the mouth. Weakened lip muscles affect speech because of an impaired ability to produce labial sounds. Affected persons cannot whistle or blow wind instruments
The hypoglossal nerve is responsible for motor supply to intrinsic and extrinsic muscles of the tongue (except palatoglossus)
Why do patients receiving epidural anaesthesia develop headache less frequently than with spinal anaesthesia?
A The epidural space ends at the foramen magnum
B The dura mater is impermeable at the level of an epidural
C The arachnoid does not extend to the level at which an epidural is undertaken
D Fibrillar meshwork surrounding the dura mater absorbs epidural substance
A
Explanation
With epidural anaesthesia, headache does not occur because the vertebral epidural space is not continuous with the cranial epidural space. The epidural space runs the length of the vertebral canal, terminating superiorly at the foramen magnum and laterally at the IV foramina.
Epidural block occurs by administering anaesthetic agent into the epidural space at the L3-L4 level. The epidural space does not continue into the cranial cavity, so the anaesthetic agent cannot ascend beyond the foramen magnum.
Spinal anaesthesia, anaesthetic agent introduced into the spinal subarachnoid space. This can allow the agent to circulate into the cerebral subarachnoid space in the cranial cavity when the patient lies flat following the delivery. Consequently, a severe “spinal headache” is a potential complication with spinal anaesthesia that cannot occur with epidural anaesthesia.
Extra:
“with epidural anaesthesia, no ‘Spinal headache’ occurs because the the vertebral epidural space is not continuous with the cranial epidural space”
With spinal anaesthesia “ because the anaesthetic agent is heavier than CSF, it remains in the inferior spinal subarachnoid space while the patient is inclined. The anesthetic agent circulates into cerebral subarachnoid space in the cranial cavity when the patient lies flat following the delivery. A severe headache is common in spinal anaesthesia
This headache is different to a headache due to a spinal leak from a spinal block due to the piercing of the arachnoid mater.
