Exercise 24 and 26: Spinal Cord, Spinal Nerve, Reflexes, and the
Autonomic Nervous System
1. Define the following terms, and identify them on a model with the gross
structures of the spinal cord (posterior view) [e.g. big open torso model
(T7 and T10); Somso model (M11)]:
a. Conus medullaris – cone shaped region along the 1st or 2nd vertebra
b. Cauda equina – collection of spinal nerves along the inferior end of the
vertebral canal
c. Filum terminale – fibrous extensions of the pia mater
d. Cervical enlargement
e. Lumbar enlargement
f. Sympathetic chain ganglia
g. Dorsal root ganglia and plexuses
2. Identify structures of the spinal cord on a model (e.g. M2, M3, M4: 3-D
models of the spinal cord cross section; Somso Model (M11))
a. Gray matter
i. Dorsal/posterior horns
ii. Ventral/anterior horns
iii. Lateral horn
iv. Gray commissure
v. Central canal
vi. Dorsal/posterior root
vii. Dorsal/posterior root ganglion
viii. Dorsal/posterior ramus
ix. Ventral/anterior root
x. Ventral/anterior ramus
xi. Rami communicantes (white ramus and gray ramus)
xii. Spinal nerves
b. White matter
i. Posterior white column/funiculus
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ii. Lateral white column/funiculus
iii. Anterior white column/funiculus
iv. Anterior median fissure
v. Posterior median sulcus
c. Meninges
i. Epidural space
ii. Dura mater
iii. Subdural space
iv. Arachnoid mater
v. Subarachnoid space
vi. Pia mater
3. Identify structures of the spinal cord on a histology slide
a. Anterior funiculus, lateral funiculus, and posterior funiculus
b. Dorsal horn, ventral horn, lateral horn
c. Gray commissure
d. Central canal lined by ependymal cells
e. Anterior median fissure
f. Posterior median sulcus
Spinal nerves and spinal nerve plexuses [e.g. Head & Neck Model-M9, hanging
skeletal/spinal cord model (MA); Somso Model (M11)]
1. Identify all 31 pairs of spinal nerves and indicate they are mixed (motor and
sensory) nerves: 1st – 7th pair emerge above the vertebra they are named
after, the rest emerge below the vertebra they are named after, except spinal
nerve C8 emerges between the 7th cervical and the 1st thoracic vertebrae
a. Cervical (C1-C8)
b. Thoracic (T1-T12)
c. Lumbar (L1-L5)
d. Sacral (S1-S5)
[S5 is missing on MA model]
e. Coccygeal (Co1)
[Co1 is missing on MA model]
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2. Identify the location of the following spinal nerves and plexuses on a model,
and give the function of each [e.g. “Nerve Man” model (M12); arm and leg
models; Somso model (M11)]
Spinal Nerves
Cervical Plexus
Phrenic nerve
Brachial Plexus
Function (Innervation)
Head, Neck and Diaphragm
Diaphragm, respiration
Arm muscles and skin
Axillary Nerve
Musculocutaneous
Nerve
Radial Nerve
Shoulder muscles and skin
Anterior upper arm muscles/ lateral
forearm skin
Posterior/lateral upper arm and
forearm muscles and skin
Anterior forearm muscles and skin
Medial forearm muscles and skin
Innervates lower limb
Median Nerve
Ulnar Nerve
Lumbar Plexus
Femoral
Obturator
(missing on M12)
Sacral Plexus
Sciatic Nerve
Tibial
Common Fibular
Location
Cervical
Cervical Plexus
Cervical
Enlargement
Brachial Plexus
Brachial Plexus
Brachial Plexus
Brachial Plexus
Brachial Plexus
Lumbar
Enlargement
Lower abdomen, anterior and medial Lumbar Plexus
thigh muscles and skin
Hip and medial thigh muscles and
Lumbar Plexus
skin
Lower Limb
Lower trunk, posterior thigh muscles Sacral Plexus
and skin
Branch of sciatic, posterior lower leg Sacral Plexus
and foot muscles and skin
Branch of sciatic, anterior and lateral Sacral Plexus
lower leg and foot muscles and skin
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Reflexes
Note: the terminology and activities concerning reflexes are based on both the current
lab manual by Wood (2013) as wells the former lab manual by Marieb and Mitchell
(2009). Terms and activities not found in the current lab manual are in red and are
optional.
1. Reflex Terminology:
a. List the components of a reflex arc; identify each component on a diagram or
model, and indicate the function of each.
b. Distinguish monosynaptic and polysynaptic reflexes.
c. Distinguish between an innate (inborn, basic) reflex from an acquired
(learned) reflex
d. Define the following terms with respect to reflexes: (see textbook and/or
outside reference)
1) spinal reflex
2) inhibition
3) reciprocal inhibition
4) reinforcement
2. Reflexes Activities
Perform the following reflexes with a partner. Describe the initiation and response of
the following reflexes and indicate the spinal and/or cranial nerves involved in each.
a. Somatic reflexes
1) Stretch reflexes (see current lab manual)
a) patellar “knee jerk”
b) Achilles “ankle jerk”
c) biceps reflex
d) triceps reflex
2) Cross-Extensor reflex (with the back of subject’s hand resting on a lab
bench, prick subject’s index finger with a pencil while subject’s eyes are
closed and observe response in both upper limbs)
3) Superficial cord reflexes
a) abdominal (see current lab manual)
b) plantar (Babinski’s) (stroke the plantar surface of bare foot with
the handle of a reflex hammer moving from heel to ball of
foot on lateral side, and then across to medial ball of foot.
Observe toes spread apart and extend upward (positive
response) or flex downward (negative response).
4) Cranial reflexes
a) corneal (with cotton fibers of a sterile cotton swab, touch the
surface of the eye and observe response)
b) gag (touch a tongue depressor on the back of the throat and
observe response)
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b. Autonomic reflexes
3) pupillary (in a darkened room, shine a pen light in one eye)
a) ipsillateral (look for pupil response in illuminated eye)
b) consensual (contralateral) (look for pupil response in opposite
eye while shielding opposite eye from light shown in other eye)
4) ciliospinal (gently stroke hair or pinch skin of subject’s neck, close to
hairline on the left side of the back of neck and watch for pupil
responses)
c. Acquired (learned) reflexes
Test the reaction time for catching a metric ruler between the thumb and index
finger. Have a partner hold the ruler vertically 3 cm above the participant’s hand
with the number 0 at the bottom. Compare the reaction time indicated by the
number grasped when the ruler is caught with full concentration versus mental
distraction (e.g. while subtracting 3 repeatedly from a large number: 100, 97, 94,
91, 88, etc).
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