• Quiz #3 available today at 3pm
until Monday at 11pm
Use the diagram to label:
1. Sensory (afferent) neuron
2. Motor (efferent) neuron
3. CNS
4. PNS
5. Interneuron
Spinal cord and spinal nerves
• spinal cord anatomy
• spinal meninges
• where to put that needle
• spinal cord terminology
• spinal nerves
• ascending and descending tracts
• where do spinal nerves go?
• dermatomes
• nerves plexuses
• cervical plexus
• brachial plexus
• simple reflexes
• anatomy of spinal cord injuries
31 PAIR of spinal nerves
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
Medullary cone
Cauda equina
infant
adult
Meninges of the spinal cord
Dura mater (pink)
Pia mater
Subarachnoid
space
Arachnoid mater (blue)
Dura mater is continuous with epineurium of nerve fibers
Denticulate ligament
Coccygeal ligament
1. From which space is a spinal tap taken from?
2. Into which space is spinal anesthetic injected?
3. Into which space is an epidural anesthetic injected?
Dura mater and
arachnoid
Pia mater
Subarachnoid space
Spinal tap or spinal anesthesia
Epidural anesthesia
Anatomy of the spinal cord
Posterior (dorsal) sulcus
Posterior (dorsal) horn
Central canal
(CSF)
Spinal nerve
Anterior (ventral) horn
Anterior (ventral) fissure
Fissure >> sulcus
Nerve roots
Gray and White Matter
• White matter = myelinated nerve fibers
• Gray matter = nerve cell bodies, dendrites, neuroglia
& unmyelinated axons
Nerve Fiber = nerve process (axon or dendrite)
Nerve = bundle of nerve fibers in PNS (mixed)
Tract = bundle of nerve fibers in the CNS (mixed)
Ganglion = cluster of neuronal cell bodies in PNS
Nucleus = cluster of neuronal cell bodies in the CNS
1. Label anterior and posterior.
2. Label a nerve root and a spinal nerve.
3. What is in the central canal?
4. Label the posterior (dorsal) horn.
5. What is it composed of?
Sensory or ascending tracts
Motor or descending tracts
The spinal cord is very organized – anatomically & functionally
brain
midbrain
medulla
• Ipsilateral
• Contralateral
• Decussation
spinal cord
Ascending tract
(Sensory info)
3rd order neuron
Thalamus
Midbrain
2nd order neuron
Medulla
1st order neuron
Decussation in medulla
Somatosensory cortex
Fig. 14.4(TE Art)
Thalamus
Midbrain
Midbrain
Gracile fasciculus
Below T6 (legs)
Medulla
Cuneate fasciculus
Above T6 (arms)
Fine touch, proprioception, pressure
Spinothalamic
tract
pain, heat, and cold
Ascending tract summary
Descending tracts
Motor info
Corticospinal tract
Motor cortex
Upper motor neurons
Midbrain
Medulla
Lateral corticospinal tract
Ventral corticospinal tract
Lower motor neurons
To skeletal muscles
Damage to motor neurons…..
Paralysis
• loss of muscle function
• causes?
• para, quad, hemi - plegia
Upper motor neurons
Spastic paralysis
Amyotrophic Lateral Sclerosis
• degeneration of upper and lower motor neurons
• paralysis of voluntary muscles
• Lou Gehrig 1903-1941 & Stephen Hawking 1942-
Poliomyelitis
• degeneration of lower motor neurons
• occurs in ventral horn
• caused by polio virus
Lower motor neurons
Flaccid paralysis
Spinal nerves
31 PAIR of spinal nerves
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
Vertebral level
vs
spinal level
Spinal nerve anatomy
Dorsal root ganglion
Dorsal ramus
Ventral ramus
Thoracic cavity
Intercostal
nerve
Spinal Nerves
1. dermatomes
2. plexuses
3. reflexes
Each spinal nerve innervates 1 somite
Somite = skin, muscles, bones
Dermatome
– area of skin supplied by the
sensory nerve fibers of one
spinal nerve
– Characteristic pattern
– No dermatome for C1
(motor only)
– Use dermatomes to access
spinal nerve damage
Cervical plexus (C1 –C5)
Nerve Plexuses:
Ventral rami traveling
together
Brachial plexus (C5–T1)
Thoracic nerves (12 pairs)
No plexus in thoracic region
Lumbar plexus (L1–L4)
Sacral plexus (L4 –S4)
Sciatic
nerve
sciatica
Fig. 14.13(TE Art)
C1
C2
C3
C4
C5
Cervical plexus
• C1-C5
• ventral rami
• neck & shoulder
• phrenic nerve
Phrenic nerve C3-C5
Phrenic nerve
• C3-5
• motor to diaphragm
• skeletal muscles
Brachial plexus
• C5-T1
• ventral rami
• arm & shoulder
• Brachial plexus passes deep to the clavicle
• Damage to brachial plexus
Brachial plexus damage
Lower motor neuron lesion = flaccid paralysis
A simple reflex arc
Information relayed
to brain - slower
Sensory neuron
Info processing
in CNS
Motor neuron
** Don’t need the brain to have
a reflex **
The Stretch Reflex
Too much stretch, too fast
Contract muscles to protect them
You are an EMT
- Frank dove into shallow end
- you evaluate him and find:
- his neck hurts
- he can breath well on his own
- he can’t feel or move his legs
- he can’t feel his pinky
- he can feel his thumb
Where is his injury??
Spinal cord injuries (SCI)
• SCI’s are damage to the spinal
cord (vs vertebral column)
• damage occurs from severing,
stretching or compression
• result in loss of motor & sensory
function below injury site
• can be complete or incomplete
• flaccid paralysis immediately after
injury (due to spinal shock)
• spastic paralysis after spinal shock
subsides
Back to Frank…..
1. Can he breath on his own?
2. Will he be able to move/feel his
legs? His arms?
3. Upper or lower motor neuron
lesion?
4. What kind of paralysis will Frank
have?
- during spinal shock = flaccid
paralysis, no reflexes
- after spinal shock = spastic
paralysis, uncontrolled reflexes