Lab 10
Anatomy of Spinal Cord and
Spinal Nerves, Reflexes, and
Reaction Time and Learning
Joseph R. Schiller, Ph.D., James F. Thompson, Ph.D., and Gilbert Pitts, Ph.D.
Lab 10 Activities
1. Identify spinal cord structures on microslides
2. Identify spinal cord structures on models and charts,
3.
4.
5.
including the protective coverings
Identify major nerve plexuses on nerve tree model
(cervical, brachial, lumbar, + sacral)
Elicit somatic, superficial, and autonomic reflexes in
members of your lab group to learn about the various
kinds of reflexes (stretch reflex, Babinski, pupillary +
ciliospinal)
Biopac Lesson 11 – Reaction Time and Learning:
understand a basic difference in reflexes versus
learning
Structure of the Spinal Cord
•
•
•
•
Gray Matter: deep “H” shaped region
White Matter: peripheral (myelinated) fiber tracts
Protective coverings: bone, meninges, related tissues
related structures: spinal nerve roots, spinal nerves, dorsal root
ganglia
Functional Map of Gray Matter
• Posterior (dorsal) (gray) horns: sensory axonal endings synapse
with interneurons
• Anterior (ventral) (gray) horns: somatic motor neuron cell bodies
• Lateral (gray) horns: visceral = autonomic motor neuron cell
bodies
Spinal Cord with Dorsal Root
Spinal Cord, c.s., silver stain, 40x
• Silver stain produces sharp contrast between white and gray
•
matter
Note the meninges and a dorsal root ganglion are also
present
Spinal Cord, c.s., Masson, 40x
• This slide also provides
•
•
•
•
good contrast
Posterior/dorsal horn
Gray commissure
Central canal
Anterior/ventral horn
Spinal Cord, c.s., Thoracic, 40x
• Gray commissure
• Lateral horn
Lining of the Central Canal
• Ependymal cells
• in central canal
Sensory Neurons of Dorsal Root
Dorsal Root, Sensory Neurons
Dorsal Root, Sensory Neurons
Dorsal Root, Sensory Neurons with Satellite
Cells
31 Pairs of
Spinal Nerves
• All are mixed (m/s) nerves
• Thousands of fibers per
•
spinal nerve
Each pair serves a
particular region of the
body, but overlaps some
with the region supplied by
the spinal nerve above and
below it (redundancy)
Spinal Nerve Anatomy
• Formed from
•
junction of dorsal
and ventral roots
Divide into:


dorsal ramus supplies posterior
body trunk
ventral ramus supplies the rest
of body trunk and
the limbs
Spinal Nerve Branches into
Dorsal and Ventral Rami
Branches of Ventral Ramus
• Rami Comminicantes (autonomic system:
supplies viscera)


White ramus communicans (to sympathetic chain)
Gray ramus communicans (from sympathetic
chain)
• Intercostal nerve (somatic motor and
somatosensory supply to muscle and skin)

Cutaneous branches (supply skin)
Dermatomes
• Areas of skin
•
innervated by the
cutaneous
branches of each
pair of spinal
nerves
Each pair also
provides some
service to the
region of the spinal
nerve above and
the spinal nerve
below
(redundancy)
Reflexes
•
•
•
•
•
A rapid, predictable, automatic response to a stimulus
Unlearned, unpremeditated, and involuntary
One is aware of somatic reflexes only after they occur
A homeostatic mechanism (feedback path)
Two fundamental types:


Somatic – effector is skeletal muscle
Autonomic (visceral) – effector is smooth muscle, cardiac
muscle, or glands

Generally not consciously perceived
Components of a Reflex Arc
1) Receptor - dendrites or other sensory structures respond to changes
2)
3)
4)
5)
in the internal or external environment
Sensory neuron - conducts from a receptor to axon terminals
Integrating center (region within the CNS)
 Simple - monosynaptic (2 cells only: sensory and motor neurons)
 Complex – polysynaptic (> 2 cells: interneurons involved)
Motor neuron - impulses from integrating center to effector
Effector - body part (muscle or gland) which responds to the motor
nerve impulse
Stretch Reflexes
• Receptor - muscle
spindles



Mechanoreceptors
which respond to
stretching
Stimulus: stretch, causes
increased nerve impulses
to the spinal cord
Response: muscle
contraction which
reduces stretching of the
muscle spindle and
decreased nerve
impulses to spinal cord
Stretch Reflexes
• Remember, if a
•
muscle is being
stretched, its
antagonist is
contracting
This sensory
proprioception
information
contributes to
maintaining
proper muscle
tone
Patellar
Reflex
•
•
•
•
Monosynaptic
Ipsilateral (same side)
Segmental (at one level of the spinal cord)
Reciprocal component – polysynaptic, inhibition of
the antagonist
Golgi (Deep) Tendon Reflex
• Receptor: Golgi tendon organ



Mechanoreceptor that responds to
muscle tension (via the tendon)
Stimulus: increased tension
(increased nerve impulses to
spinal cord)
Response: muscle relaxes
(decreased nerve impulses to
spinal cord)
 Inhibits the agonist
 Reciprocal path: activates
the antagonist
• Polysynaptic, ipsilateral, and
segmental
Flexor Reflex
• A pull on the limb,
•
•
•
extending it, will trigger
the reflex
Also a painful stimulus
– a burn, pin prick, toe
stub, etc.
F-R causes an
automatic withdrawal
from the (dangerous)
stimulus
Polysynaptic, ipsilateral,
and segmental
Classifying Reflexes
• Reflexes are classified according to:



Number of synapses in path: mono- versus polysynaptic
Location of receptor versus effector: ipsi- versus
contralteral
Level of receptor versus effector: segmental (at same
level) versus intersegmental (at different levels)
• Patellar (stretch) reflex: monosynaptic, ipsilateral,
segmental
• Golgi Tendon Reflex: polysynaptic, ipsilateral,
segmental
Crossed Extensor Reflex
• Flexion of a body part is often balanced by extension of the
same body part on the opposite side of the body
• Polysynaptic
• Contralateral
• Segmental
Reflexes to Observe in Lab
• Patellar or Knee Jerk Reflex
• Ankle Jerk Reflex
• Plantar (Babinski) Reflex – sole of the foot
• Abdominal Reflex – if dressed appropriately
• Pupillary Reflex
• Ciliospinal Reflex
Biopac Lesson 11
• Reaction Time and Learning

Note: change font size to 9 before printing collected data
• Learning requires the ability to connect one event
(symbol, stimulus, pattern) with another
• Reflexes do not

This lesson involves two different types of events:
 Random:
cannot be predicted and connected
 Regularly repeated: can be learned and anticipated
segment 1
segment 2
segment 3
segment 4
 Reformat
Follow the onscreen instructions to collect five segments of data. Reformat the
lesson-file name-day/date-time lines into a single line. Print your data journal
with font size set to 8). You do not have to print the graph. Use the first four
data segments to answer the questions from your lab guide on p. 10-21.
Lab 9 Written Homework
to Turn in Next Week
• Answer the questions and fill out the Table on
p. 10-21
• Answer the questions on p. 10-23
• Attach your Biopac Data Journal
• Put your name, your instructor’s name, day
and time of your lab on all three pages
End Lab 10 Presentation