Neuro7 Spinal Nerves and Spinal Cord

Question 1

Spinal nerves

Answer 1

There are 31 spinal nerves altogether: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal. Nerves C 1-C7 exit via intervertebral foramina above the corresponding vertebra. All other nerves exit below.

31 , just like 31 flavors! Vertebral disk herniation (nucleus pulposus herniates through annulus fibrosus) usually occurs between L5 and S1 .

Question 2

Spinal cord-lower extent

Answer 2

In adults, spinal cord extends to lower border of
Ll-L2; subarachnoid space extends to lower
border of S2. Lumbar puncture is usually
performed in L3-L4 or L4-L5 interspaces, at
level of cauda equina.

To keep the cord alive, keep the spinal needle
between L3 and L5.

Question 3

Spinal cord and associated tracts

Answer 3

Legs are Lateral in Lateralcorticospinal,
spinothalamic tracts.

Dorsal column is organized as you are, with
hands at sides. Arms outside, legs inside.

Question 4

Dorsal column medial lemniscal pathway (ascending

pressure, vibration, touch, and proprioceptive sensation)

Answer 4

1st Order Neuron:
Sensory nerve ending goes to cell body in dorsal root ganglion goes to enter spinal cord, ascends ipsilaterally in dorsal column

Synapse 1
Ipsilateral nucleus cuneatus or gracilis (medulla)

2nd-order neuron:
Decussates in medulla then ascends contralaterally in
medial lemniscus

Synapse 2:
VPL of thalamus

3rd-order neuron:
Sensory cortex

Question 5

Spinothalamic tract (ascending pain and temperature
sensation)

Answer 5

1 st-order neuron:
Sensory nerve ending (A-delta and C fibers) (cell
body in dorsal root ganglion) then enters spinal cord

Synapse 1:
Ipsilateral gray matter (spinal cord)

2nd-order neuron:
Decussates at anterior white commissure then ascends contralaterally

Synapse 2:
VPL of thalamus

3rd-order neuron:
Sensory cortex

Question 6

Lateral corticospinal tract (descending voluntary movement of contralateral limbs)

Answer 6

1 st-order neuron:
Upper motor neuron: cell body in Primary motor
cortex then descends ipsilaterally (through internal
capsule) until decussating at caudal medulla (pyramidal
decussation) then descends contralaterally

Synapse 1
Cell body of anterior horn (spinal cord)

2nd-order neuron:
Lower motor neuron: Leaves spinal cord

Synapse 2:
Neuromuscular junction

Question 7

Landmark dermatomes: C2, C3, C4, T4, T7, T10, L1, L4, S2, S3, S4

Answer 7

C2 -posterior half of a skull “cap.”
C3-high turtleneck shirt.
C4-low-collar shirt.
T4-at the nipple. T4 at the teat pore
T7 -at the xiphoid process.
TlO -at the umbilicus (important for early
appendicitis pain referral). T10 at the belly butTEN.
L1 -at the inguinal ligament. L1 is IL ( Inguinal Ligament) .
L4-includes the kneecaps. Down on L4s (all fours) .
S2, S3, 54- erection and sensation of penile and
anal zones. “S2, 3, 4 keep the penis off the floor.”

Diaphragm and gallbladder pain referred to the
right shoulder via the phrenic nerve.

Question 8

Clinical reflexes:
C5 nerve root.
C7 nerve root.
L4 nerve root.
S1 nerve root.

Answer 8

Biceps == C5 nerve root.
Triceps == C7 nerve root.
Patella == L4 nerve root.
Achilles == S1 nerve root.
Babinski-clorsiflexion of the big toe and fanning of other toes; sign of UMN lesion, but normal reflex in 1st year of life.

Reflexes count up in order:
S1, 2
L3, 4
C5, 6
C7, 8

Question 9

Primitive reflexes

Answer 9

l . Mora reflex-“hang on for life” reflexabduct/
extend limbs when startled, and then
draw together
2. Rooting reflex-movement of head toward
one side if cheek or mouth is stroked (nipple
seeking)
3. Sucking reflex-sucking response when roof
of mouth is touched
4. Palmar reflex: curling of the fingers if palm is stroked
5. Plantar reflex: dorsiflexion of the large toe and fanning of other toes with plantar stimulation
6. Babinski reflex-dorsiflexion of large toe and
fanning of other toes with plantar stimulation
7. Gallant reflex-stroking along one side of the
spine while newborn is in ventral suspension
(face clown) causes lateral flexion of lower
body toward stimulated side

Normally disappear within l st year of life. May
reemerge following frontal lobe lesion.

Question 10

CNs that lie medially at brain stem

Answer 10

III, VI, XII. 3 (x2) = 6 (x2) = 12 ( Motor = Medial).

Question 11

Pineal gland

Answer 11

melatonin secretion, circadian rhythms.

Question 12

Superior colliculi

Answer 12

conjugate vertical gaze center.

Your eyes are above your ears, and the superior colliculus (visual) is above the inferior colliculus (auditory).

Question 13

Inferior colliculi

Answer 13

auditory.

Question 14

Parinaud syndrome

Answer 14

paralysis of conjugate vertical gaze due to lesion in superior colliculi (e.g., pinealoma) .