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Week 12
The Spinal Cord & PNS
What’s ahead
• Identify structures of the spinal cord
• Identify peripheral nerves
• Identify components of the reflex arc
Activity 1:
The Spinal Cord
The Spinal Cord
Cervical
enlargement
Cervical
spinal
nerves
Thoracic
spinal
nerves
Lumbar
enlargement
Conus
medullaris
Cauda
equina
Lumbar
spinal nerves
Sacral
spinal nerves
L2
L3
Conus Medullaris
L4
L5
Cauda Equina
(horse’s tail)
Lumbar Tap
T12
Cauda equina
Subarachnoid
space
L5
L4
L5
Spinal Cord Anatomy
Spinal meninges
Subarachnoid
space
Pia mater
Arachnoid mater
Dura mater
Spinal Cord Anatomy
Central canal
Posterior median sulcus
Anterior median fissure
Spinal Cord Anatomy
Gray matter
White matter
Dorsal horn
Posterior
funiculus
Lateral horn
Ventral horn
Lateral
funiculus
Gray
commisure
Anterior
funiculus
Pia mater
Arachnoid mater
Dura mater
Gray matter = Inside, cell bodies & unmyelinated fiber tracts
White matter = Outside, myelinated fiber tracts
Spinal Cord / Spinal Nerve Anatomy
Dorsal Root
Dorsal Root Ganglion
Spinal Nerve
Ventral Root
Spinal Cord / Spinal Nerve Anatomy
Dorsal root
Spinal
nerve
Dorsal root
ganglion
Dorsal
ramus
Ventral
ramus
to
Plexus
Ventral root
Posterior Spinal Cord
What
do
Posterior
you
median
suppose
sulcus
this is?
Denticulate
ligament
Dorsal root
Arachnoid
mater
Dorsal root
ganglion
Dura mater
What do
Ventral
youroot
suppose
this is?
How can you tell the Ventral side from the
Dorsal side?
PMS vs. AMF
Posterior Median Sulcus
AMF
Anterior Median Fissure
Cross sectional anatomy of the spinal cord
Gray Matter
A visual analogy
Dorsal horns
Sensory/inter neurons
Dorsal
horn
Ventral
horn
Ventral horns
motor neurons
?
Posterior 1amedian
sulcus
Dorsal
2a ? horn
Lateral
2b ?
horn
Vental
2c ? horn
1b ? fissure
Anterior median
Regional Differences
Cervical
Thoracic
Cervical
enlargement
Lateral
horn
Lumbar
enlargement
Lumbar
Sacral
Cross sectional anatomy of the spinal cord
White Matter
•fiber tracts for transmission of information
•ascending (sensory) tracts
•descending (motor) tracts
Posterior funiculus
Lateral funiculus
Anterior funiculus
Some fiber tracts in the different funiculi
Posterior funiculus:
•Faciculus cuneatus and gracilis
•Ascending sensory
Lateral funiculus
•Spinothalamic tract
•Ascending sensory
•Corticospinal tract
•Descending motor
Anterior funiculus
•Spinothalamic tract
•Ascending sensory
•Corticospinal tract
•Descending motor
Spinal cord c.s. microscopic view
Central
canal
Dorsal
root
Dorsal
root
ganglion
Gray
commissure
Ventral
root
Dura
mater
Dorsal root ganglion
Pseudounipolar neuron cell bodies
Identify the
structural
classification
of these
neurons
Physiology
Posterior
In 
Anterior
 Out
Dorsal root: afferent, sensory
Ventral root: efferent, motor
Dorsal ramus: mixed, motor and sensory
to trunk
Ventral ramus: mixed motor and sensory
form nerve plexi
Activity 2: Nerve Plexi & Peripheral Nerves
Ventral Rami  Plexus  Peripheral Nerve
There are
31 pairs
of
spinal nerves
&
4 nerve plexi
Cervical
Plexus
The phrenic
nerve innervates
the respiratory
diaphragm
“ C3,4,5 keeps the
diaphragm alive!
Brachial Plexus
Nerves Arising from Thoracic Ventral Rami
Lumbar Plexus
Sacral Plexus
Activity 3:
Human Reflex Physiology
Reflex Terminologies
Reflex: A rapid, predictable, involuntary motor response to a
stimulus that acts to return the body to homeostasis
Mediated by the spinal cord
Reflex Arc: The neural pathway a nerve impulse follows that
mediates a reflex
(from sensory receptor  effector organ)
Autonomic (Visceral) Reflex: Mediated through the ANS
Not subject to conscious control
Vasoconstriction/dilation, sweating, salivation,
digestion, heart rate, pupil dilation/constriction
Somatic Reflex: Involve stimulation of skeletal muscles by the
somatic division of the nervous system
Subject to conscious interference
Reflex Arc
(1) Receptor - reacts to stimulus
(2) Sensory Neurons - afferent impulses to CNS
(3) Integration centers - synapses in CNS
(4) Motor Neurons - efferent impulses from Integration
centers to effector
(5) Effector - muscle or glands
Classifications of Sensory Receptors
by Location
Exteroceptors*
Interoceptors
Proprioceptors*
Respond to stimuli arising
outside the body:
Touch
Pain
Detect stretch
Temperature
Pressure
Respond to stimuli
inside the body
(viscera, vessels)
Proprioceptors
Stretch Reflexes
Receptor =
Proprioceptor of
the muscle
Patellar Reflex
Receptor =
Proprioceptors of (?) muscle
Afferent Neuron =
Afferent fibers of (?) nerve
Integration Center =
?
Efferent Neuron =
Efferent fibers of (?) nerve
Effector=
(?) muscle
Patellar Reflex
Patellar Reflex
3 Tests
1. Simultaneous muscle activity
2. Mental distraction
3. Fatigue
Is the
response
greater
or less
than
baseline?
Pupillary Reflex
Contralateral?
– or -
Ipsilateral?
Lab Activity:
• Study Spinal Cord & Peripheral Nerves
• Perform Reflex experiments & analyze
On the Practical:
• Identify the structures of the Spinal Cord from
models and slides
• Identify the Peripheral Nerves and Nerve Plexi
from models
• Identify the components of the Reflex Arc