Unit 4 - Spinal Cord

Spinal/skull foramen labeling

• Cowboy R.O.S.:

  • Foramen rotundum

  • Foramen ovale

  • Foramen spinosum

• Foramen magnum: where spinal cord exits

Divisions of the Nervous System

• Peripheral Nervous System (PNS)

  • 31 pairs of spinal nerves

  • 12 pairs of cranial nerves

  • Sensory (incoming):

    • Monitor environment via cells that respond to stimuli

    • Afferent (arrive) nerve cells transmit info to receptor in the CNS

    • Touch skin → PNS → CNS

  • Motor (outgoing):

    • Activation or inhibition of effectors (muscles, glands, organs) - later divide into somatic & autonomic NS

    • Efferent (exit) nerve cells connect the CNS to effectors

  • S.A.M.E. → Sensory - Afferent/Arrive; Motor - Efferent/Exit

Motor & Sensory neuron visuals

• Motor: sends signals from CNS to effectors

• Sensory: sends signals from effectors to CNS

Spinal cord

• Serves as communication b/w the brain & PNS

• Reflex center

• Extends from the foramen magnum to approximately the L1 or L2 vertebrae level

Spinal cord gross anatomy

• Conus medullaris = Distal tapered end of spinal cord

• Cauda equina = Collection of spinal nerve roots that extend inferior to spinal cord → also called “Horse’s tail”

• Filum terminale = Extension of pia mater from the conus medullaris, anchoring to the posterior surface of the coccyx

Distal spinal cord

• Conus medullaris

• Cauda equina

• Filum terminale

2 major enlargements

1. Cervical enlargement

• C5-T1

• Brachial plexus → upper limb

2. Lumbosacral enlargement

• L1-S3

• → lower limb

Spinal cord protected by…

1. Bones

2. Meninges

3. CSF

Spinal cord meninges

• Pia Mater

• Arachnoid Mater

• Dura Mater

  • **Only meningeal layer b/c periosteal layer is absent in the vertebral column!

Meningeal Space

1. Epidural (extradural) space

• Actual space; filled w/ epidural fat & venous plexus

2. Subdural space

• Potential space

3. Subarachnoid space

• Actual space; location of CSF

Epidural

T10-L1

Spinal nerve roots

Spinal tap

L3-L4

L4-L5

Review of White vs. Gray matter

• Gray matter: cell bodies, interneurons, motor neurons

• White matter: myelinated axons, connecting grey matter

Anatomy of Spinal Nerves - visual

Motor/efferent

Sensory/afferent

Interneurons

Summary: the typical spinal nerve

Motor/efferent:

• Ventral horn (gray matter)

  • Lower motor neuron cells bodies

• Ventral roots

  • Lower motor axons

Sensory/afferent:

• Dorsal root ganglion

  • Sensory neuron cells bodies

• Dorsal roots

  • Sensory axons

• Dorsal horn (gray matter)

  • Sensory axons, interneurons

Mixed:

• Spinal nerve

  • Mixed motor & sensory axons

• Ventral rami

  • Motor & sensory axons to muscles & skin of anterior trunk & limbs

• Dorsal rami

  • Motor & sensory axons to muscles & skin of the back

Cross-section of spinal cord

• Cell bodies of motor neurons = located in ventral horn

  • Axons of motor neurons exit spinal cord through ventral root → spinal nerve → ventral OR dorsal ramus → through named nerves to effector

• Cells bodies of sensory neurons = located in dorsal root ganglia

  • Axons of sensory neurons enter through dorsal OR ventral ramus → spinal nerve → dorsal root → synapse with interneuron in dorsal horn

• White matter of spinal cord consists largely of organized myelinated axons organized into tracts or fasciculi

What type of signal would be interrupted here?

Motor - efferent

What type of signal would be interrupted here?

Mixed