Use the diagram to label:

1. Sensory (afferent) neuron2. Motor (efferent) neuron3. CNS4. PNS5. 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

Medullary cone

Cauda equina

31 PAIR of spinal nerves

• 8 cervical• 12 thoracic• 5 lumbar• 5 sacral• 1 coccygeal

Spinal cord levelsSpinal nervesVertebral levels

T1

T1

T1

T1

T2

infant

adult

Meninges of the spinal cord

Dura mater (pink)

Pia mater

Arachnoid mater (blue)

Subarachnoidspace

Dura mater is continuous with epineurium of nerve fibers

Denticulate ligamentCoccygeal ligament

Dura mater andarachnoid

Pia mater

Subarachnoid space

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?

Spinal anesthesia & spinal tap

Epidural anesthesia

Anatomy of the spinal cord

Posterior (dorsal) sulcusPosterior (dorsal) horn

Central canal(CSF)

Anterior (ventral) horn Anterior (ventral) fissureFissure >> sulcus

Spinal nerve

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 PNSNucleus = 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?

A simple reflex arc

Sensory neuron

Motor neuron

Info processingin CNS

Information relayed to brain - slower

** Don’t need the brain to havea reflex **

The Stretch Reflex

Too much stretch, too fast

Contract muscles to protect them

Sensory or ascending tracts Motor or descending tracts

The spinal cord is very organized – anatomically & functionally

• Ipsilateral• Contralateral• Decussation

brain

midbrain

medulla

spinal cord

Midbrain

Medulla

Thalamus

3rd order neuron

2nd order neuron

1st order neuron

Ascending tract(Sensory info)

Decussation in medulla

L R

Fig. 14.4(TE Art)Somatosensory cortex

Gracile fasciculusBelow T6 (legs)

Cuneate fasciculusAbove T6 (arms)

Midbrain

Thalamus

Fine touch, proprioception, pressure

Spinothalamictract

Midbrain

Medulla

pain, heat, and cold

Ascending tract summary

R

Motor cortex

Midbrain

Medulla

Lateral corticospinal tractVentral corticospinal tract

Lower motor neurons

To skeletal muscles

Upper motor neurons

Descending tractsMotor info

Corticospinal tract

Upper motor neuronsSpastic paralysis

Lower motor neuronsFlaccid paralysis

Damage to motor neurons…..

Paralysis• loss of muscle function• causes?• para, quad, hemi – plegia

• flaccid = no reflexes• spastic = exaggerated reflexes no inhibitory control from UMN hyperreflexia

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

Upper motor neurons

Lower motor neurons

Diseases that damage motor neurons…..

Spinal nerves

31 PAIR of spinal nerves

8 cervical (C1 is different) 12 thoracic 5 lumbar 5 sacral 1 coccygeal

Vertebral level vs

spinal level

Dorsal root ganglionSpinal nerve anatomy

Thoracic cavity

Dorsal ramus

Ventral ramus

Spinal nerve

Thoracic cavitySpinal nerve = mixedRamus = mixed

1. dermatomes2. plexuses

Spinal Nerves

Each spinal nerve innervates 1 somiteSomite = 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 assess spinal nerve damage

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??Will he be paraplegic or quadriplegic?

Thoracic nerves (12 pairs)

Cervical plexus (C1 –C5)

Brachial plexus (C5–T1)

Lumbar plexus (L1–L4)

Sacral plexus (L4 –S4)

Sciaticnerve

sciatica

Nerve Plexuses:Ventral rami traveling together

No plexus in thoracic region

Fig. 14.13(TE Art)

C1

C2

C3

C4

C5

Phrenic nerve C3-C5

Cervical plexus• C1-C5• ventral rami• neck & shoulder• phrenic nerve

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 (upper or lower motor neuron lesion?)

Lower motor neuron lesion = flaccid paralysis

Brachial plexus damage

Thoracic nerves (12 pairs)

Cervical plexus (C1 –C5)

Brachial plexus (C5–T1)

Lumbar plexus (L1–L4)

Sacral plexus (L4 –S4)

Sciaticnerve

sciatica

Nerve Plexuses:Ventral rami traveling together

No plexus in thoracic region

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 – why?

• can be complete or incomplete

• flaccid paralysis immediately after injury (due to spinal shock)

• spastic paralysis after spinal shock subsides

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

Back to Frank…..