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SF1 Unit 1 Post Exam 1 > Spinal Cord Organization -Wilson > Flashcards

Spinal Cord Organization -Wilson Flashcards

1
Q

The spinal cord does not go all the way down the vertebral canal. Where does it stop and why?

A

L2

the growth of the nervous system is slower than the growth of the vertebral column

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2
Q

Below the spinal cord ending at L2, what occurs with the spinal nerves?

A

below the SC you you have spinal nerves that are leaving at lower levels to form the cauda equina

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3
Q

Spinal cord is not of a uniform thickness or diameter. What are the two enlargement and what are they composed of? Why do they exist?!

A

cervical enlargement: C5-T1
lumbar enlargement: L1-S4

These form the brachial and lumbosacral plexus which each innervate the upper and lower limb respectively.

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4
Q

The spinal cord derived from what embryological structure?

A

neural tube which occurs at Week 4

the neural tube has a lumen, that in the adult system will be filled with CSF and a neuroepithelium that will give rise to neurons and glial cells

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5
Q

The lumen of the neurotube will become the central canal of the cord and ventricles of the CNS (ventricular system) filled with CSF. The neuroepithelium surrounding the the lumen is made up of the alar and basal plate that will become what?

A

alar plate–> sensory neurons
basal plate–> motor neurons

there is a basic dorsal-ventral organization to the neurotube

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6
Q

The central canal can develop a cyst or syrinx. What is this condition termed?

A

syringomyelia

  • there is enlargment of the canal that will put pressure on axons that will be passing the canal
  • it will affect mainly the motor system but its initial affect will be sensory

(NOT BEING TESTED AT THIS MOMENT)

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7
Q

The neuroepithelium develops a segmental organization, how so?

A

neuroepithelium is composed of alar plate which becomes the sensory neurons and the basal plate which becomes the motor neurons

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8
Q

A somite is found at each vertebral level. The ectoderm give rise to what?

A

ectoderm–> skin and nervous system

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9
Q

The notochord serves as a primitive what?

A

primitive spinal cord

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10
Q

The presence of notochord induces the ectoderm to form what?

A

neural tube

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11
Q

The neural tube will induce the mesoderm that is laterally located to form what?

A

somite

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12
Q

What is the relationship of the neural tube compared to the relationship of the somites?

A

there is segmental organization AKA metamerism: repeating segments

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13
Q

Somites derived from the mesoderm become what?

A

sclerotome, dermatome, myotome

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14
Q

What does the sclerotome, dermatome, and myotome become respectively?

A
  • sclerotome (migrate medially): vertebra; bones that come out of the sclerotome show a segmental organization
  • dermatome: skin which is innervated by the sensory neurons
  • myotome: skeletal muscle which is innervated by the motor neurons; each somite is giving rise to different groups of skeletal muscle
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15
Q

A somite is associated with a specific segment of the spinal cord. What does this say about the organization of somites and spinal cord respectively?

A

because the somites have a segmental organization, the spinal cord has a segmental organization

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16
Q

At each vertebral level, each segment of the neural tube innervates the ______________of the somite associated with it.

A

dermatome/myotome

the neurotube has growth cones seeking for something to innervate

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17
Q

Dorsal half of the spinal cord is _______and ventral half of the spinal cord is _______.

A

dorsal-sensory

ventral-motor

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18
Q

General somatic ________goes to skeletal muscle and general somatic _________goes to skin.

A

GSE: efferent to skeletal muscle
GSA: afferent to skin

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19
Q

Describe the organization of sensory innervation.

A

Sensory innervation of the skin is segmented into dermatomes.

T5: nipples
T10: umbilicus

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20
Q

What is maintained and what is varied in the adult spinal cord from the embryological neural tube?

A

maintained:
- neuroepithelium–> gray matter
- central canal
- axons traveling on the periphery of neurotube–> white matter
- basal plate–>ventral horn
- alar plate–>dorsal horn

changed:
- lateral horn

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21
Q

Thoracic vertebral develop another horn named what and found at what spinal cord segments? They give rise to what?

A

lateral horn at T1-L2 which give rise to the sympathetic autonomic nervous system

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22
Q

What type of neurons are found in gray matter of the spinal cord and what are their functions?

A
  • motorneurons: innervates skeletal muscle and autonomic structures like glands and smooth muscle
  • interneurons: integration of sensory signals and development of reflexes; allow for complex circuit systems
  • projection neurons (sensory neurons): info from sensory neurons in the SC undergoes synapses to relay to higher levels in brain for processing (brainstem, thalamus, cortex)
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23
Q

What is the function of the ventral white commissure?

A

it serves as the communication between the 2 sides of the spinal cord
-if the canal gets larger this is the structure that is most vulnerable to pressure and to be impacted by syrinx

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24
Q

What are the types and two functions of interneurons?

A

Functions: excitatory or inhibitory

Types:

  • intrasegmental interneurons (renshaw cell) which are inhibitory
  • propriospinal interneurons
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25
Q

Compare Renshaw cells and propriospinal neurons.

A

-Renshaw cells AKA intrasegmental neurons are the smallest size of interneurons whose axons remains in a SINGLE spinal cord segment

  • propriospinal interneurons: form direct connections between cervical and lumbar spinal circuits; connects motor neuron pools;
  • short: can span 3-4 SC segments; unilateral; coordinate muscles around a joint
  • intermediate: coordinate the upper and lower limbs
  • long: coordinate the muscles that span the entire length of cord; bilateral
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26
Q

Intrasegmental interneurons stays within a single spinal cord segment.

A

FACTS!!

Intrasegmental interneuron= Renshaw cells

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27
Q

What are the functions of large alpha motor neurons?

A

innervate skeletal muscle

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28
Q

How were long propriospinal interneurons demonstrated to have very long axons that project bilaterally?

A
  • inject retrograde tracer (CTB)
  • take histological sections
  • label ipsilaterally proprioceptive neurons
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29
Q

How were short propriospinal intersegmental interneurons demonstrated?

A

-an electrode was stuck into one segment of the SC and given electrical shocks and then 2-4 segments below a recording was performed

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30
Q

What does medial and lateral motor pathways connect? What interneurons do they use?

A
  • medial motor system: connects the paraxial, intercostal skeletal muscle using the long propriospinal interneurons
  • lateral motor system: connects the lateral motor groups; coordinate the activity of the cervical and sacral region using the short propriospinal interneurons????
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31
Q

How are motor neurons to a particular muscle arranged?

A

motorneurons to each muscle form islands of cells called nuclei surrounded by a sea of interneurons
-usually a motor nucleus is found at 2 or 3 spinal cord segments

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32
Q

In cross section motor nuclei appear circular or ovoid but in 3D appear to form what?

A

cell columns

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33
Q

What is the proximal distal rule in regards to motor nuclei?

A
  • motor neurons located medially innervate paraaxial structures
  • motor neurons located laterally innervate distal structures
34
Q

What is the flexor extensor rule in regards to motor nuclei?

A
  • motor neurons located more ventrally in the ventral horn will be extensors
  • motor neurons located more distally in the ventral horn will be flexors
35
Q

Motor neurons are found in which rexed lamina?

A

rexed lamina IX (lamina 9)

-located laterally and close to the anterior median fissure all within the ventral horn

36
Q

Lamina IX is composed of individual islands or nuclei, so is not continuous. What are each of the islands?

A

Motor neurons going to different skeletal muscle.

37
Q

Rexed Lamina IX consists of what two distinct groups and what do they innervate?

A
  • medial group- innervates axial musculature

- lateral group: innervates appendiculare (relating to limbs) musculature

38
Q

Where are the lateral group of Rexed lamina IX most developed?

A

best developed where brachial and lumbosacral plexuses arise

39
Q

What does a large lateral group denote?

A

that you’re in a region where the limbs are; if not, maybe you’re in the thoracic region

40
Q

A lateral (descending) motor system controls the lateral motorneurons of lamina IX innervating appendicular musculature.

A

A medial (descending) motor system controls the medial motorneurons of lamina IX innervating axial musculature.

41
Q

Provide details for Rexed lamina VII

A
  • the intermediate zone, contains INTERNEURONS subserving REFLEX activity
  • contains intermediolateral cell column (this is where motor neuron sympathetic cells are found)–> gives rise to the lateral horn (only find this at T1 to L2) and Clarke’s column: part of the spinal cerebellar system for proprioceptive info up to the cerebellum
42
Q

Provide details for Rexed lamina VIII

A

-commissural and motor interneurons
The commissural fibers or transverse fibers are axons that connect the two hemispheres of the brain.
-modulate gamma motor neurons
-modulates muscle tone and movement (because they are involved in the muscle spindle)

43
Q

What are the four nuclear groups of the dorsal horn (GRAY matter)?

A

GRAY MATTER

  • marginal zone
  • substantia gelatinosa
  • nucleus proprius
  • intermediate zone

dorsolateral zone is WHITE matter

44
Q

What is a major pathway for the afferent system?

A

dorsolateral zone (white matter)

as the dorsal root comes into the dorsal horn they split into several axons (info from this dorsal root is affecting many segments of the spinal cord)

45
Q

What is the significance of the marginal zone and substantia gelatinosa?

A

they are two parts in the spinal cord where nociception are located

46
Q

What is the nucleus proprius?

A

receives sensory info from other modalities besides pain: vibration, touch (fine touch)

47
Q

Marginal zone, nucleus proprius, and substantia gelatinosa correspond to which rexed laminas?

A

Marginal zone: I
substantia gelatinosa: II
nucleus proprius: III, IV, V

48
Q

What is white matter?

A

myelinated axons

49
Q

Like a nerve, white matter is composed of myelinated axons, only.

What is the major difference between nerves and the CNS tract?

A
  • in the CNS there is NO connective tissue

- PNS has epimysium, endomysium, perimysium which are all connective tissue that allow for regeneration of damaged axons

50
Q

The white matter of the cord is organized into what 3 funiculi?

A
  • posterior funiculus: located in between the posterior lateral sulci (place where your dorsal root is coming off)
  • lateral funiculus: in betwen the anterior and posterior lateral sulci; dorsolateral funiculus, anterolateral funiculus

-anterior funiculus

51
Q

The white matter of CNS is organized into ascending and descending tracts. What occurs with damage to these tracts?

A
  • loss of motor function= descending tract

- loss of sensory function= ascending tract

52
Q

IMPORTANT!!!

What are the three long tracts that are critical for a medical student to master? What are their functions?

A
  • (lateral) spinothalamic tract: pain, temperature, crude touch–>anterolateral funiculus
  • dorsal columns: fine touch, proprioception–>dorsal funiculus
  • corticospinal tract: voluntary movements–> posterolateral funiculus and has an anterior part for controlling the body trunk (axial musculature)
53
Q

What are characteristics of cervical thoracic, lumbar, and sacral spinal cord?

A

cervical: large ventral horn: large motor neurons going to the upper limb; a lot of white matter
thoracic: lateral horn
lumbar: more white matter than sacral (sensory axons from both lumbar and sacral tracts)
sacral: large ventral horn to innervate lower limb; small amount of white matter as they are only coming from the sacrum

54
Q

Why does the amount of white matter decrease at lower levels of spinal cord?

A

In lower segments of the spinal cord, there is less white matter because there are fewer axons traveling to and from the brain.

55
Q

What is in the dorsal horn?

A

-dorsal HORN is the site where sensory information from the periphery is first modified before being transmitted to higher centres. It contains interneurons and the cells of origin of ascending (sensory) tracts.

in the dorsal ROOT: are afferent (sensory) fibers passing from the spinal nerve to the spinal cord.

in the dorsal root GANGLION: where the cells bodies of these fibers are located

56
Q

AXONS HAVE DIFFERENT SIZES!!

A

nerve fibers are classified according to diameter, degree of myelination, and speed of conduction

57
Q

What is the correlation between afferent axon diameter and function?

A
  • larger diameter like the A-alpha will be involved in proprioception (regulating stretch reflexes); will be heavily myelinated conducting impulses FAST; spindles and golgi tendon; size 12-20 um; conduction velocity 70-120 m/s
  • A-beta are myelinated and for mechanoreceptors; size 5-12 um; more slowly conducting with velocity 30-70m/s
  • A-delta have less myelin for nociception, cold, touch and with size 2-5 um; conduction velocity of 12-30 m/s
  • C have are unmyelinated and for nociception, temperature, some mechanoreption, reflex response; in dorsal root; size is 0.4-1.2um; conduction velocity 0.5-2
58
Q

What are other terms for Ia, Ib, II, III, and IV sensory nerve fibers?

A

Ia, Ib= A-alpha
II= A-beta
III= A-delta
IV= C

59
Q

Axons entering in the dorsal root divide into two divisions according to axon diameters. What are the two division and what type of sensory nerve fibers do they make up?

A

Medial division: A-alpha and A-beta (run most medially coming into the SC); largest axons Ia, Ib

Lateral division: A-delta and C; smaller axons; run more laterally

60
Q

Sensory neurons are what type of neurons?

A

pseudounipolar neurons

61
Q

Which Rexed lamina are for nociception?

A

I and II

62
Q

Which Rexed lamina are for integration and relay of sensory information?

A

lamina I-V (located in the dorsal horn)

63
Q

Which Rexed lamina are for movement execution?

A

lamina VII-IX

64
Q

What is the dorsolateral zone of Lissauer?

A

dorsal root entry zone for lateral division
-not in the gray matter but in the white matter

  • it is where the small diameter sensory axons can come in and go to different SC levels
  • mostly for pain (nociception)
  • lateral part of the dorsal root “entry zone”
  • descend and ascend to terminate at several other spinal cord levels
65
Q

Afferents enter the Zone of Lissauer, ascend and descend giving off collaterals that synapse at several spinal cord levels. Why is this clinically significant?

A

these primarily deal with small diameter sensory axons which deal with nociception

  • this is clinically important when patient loses the ability to sense pain
  • have to recognize that the zone of Lissauer; these sensory axons are going to higher levels synapsing before the info is relayed to the brain stem
66
Q

C fibers or IV comes from which division of the dorsal root to enter which rexed lamina?

A

lateral division of dorsal root to go to Rexed lamina I and II (synapsing in the marginal zone and substantia gelatinous)

  • unmyelinated sensory (pain) axons
  • slow conducting
  • slow pain (dull pain, warmth)
67
Q

Rexed lamina I and II is for what sensory innervation?

A

nociception and thermoreceptors

68
Q

A-delta or III come from which division of the dorsal root to enter which rexed lamina?

A

lateral division of the dorsal root to go to Rexed lamina I, IV, and V which there is a lot of sensory integration or where pain is integrated with other sensory modalities such as vibration, proprioception, and V is also the area where you have projection neurons

-sharp (fast) pain, cold

69
Q

A-beta or II come from which division of the dorsal root to enter which rexed lamina?

A

medial division of dorsal root to Rexed lamina III, IV, V VII, X (nucleus proprius)

  • large, myelinated axons for mechanoreception
  • these axons come in and go into the ascending dorsal funiculus as well(this will be info that will ascend up to brainstem and eventually reach the cortex telling us about what is going on in skin about fine touch, vibration, proprioception)
70
Q

A-alpha or Ia/Ib come from which division of the dorsal root to enter which rexed lamina?

A

medial division of dorsal root to Rexed lamina IX (in ventral horn), VII, VIII (motor integration: connects different motor interneurons involving synaptic reflexive activity)

  • largest, myelinated axons for proprioception
  • coming from muscle spindle and golgi tendon
  • involved in the somatic reflexes
  • are going straight up to medulla or cortex into the dorsal funiculus
  • monosynaptic with motor neurons
71
Q

What are the 3 major arteries that supply the SC with blood?

A
  • 2 posterior spinal arteries: supply the dorsal funiculi and dorsal horn
  • 1 anterior spinal artery in the anterior median fissure supplies everything else
72
Q

If you have obstruction of one of the posterior spinal arteries, what occurs?

A

they lose a lot of SENSORY info particularly in the dorsal funiculi which sends information coming from the Ia and II large myelinated axons

73
Q

If an individual has a stroke affecting the anterior spinal artery, what occurs?

A

patient will get BILATERAL symptoms of both MOTOR and SENSORY symptoms

74
Q

Where do the anterior and posterior spinal arteries come from?

A

the spinal arteries begin as branches of the vertebral artery

75
Q

At different levels, there will be reinforcement branches (intercostal, abdominal, etc.) of arteries going through the intervertebral foramen joining the spinal arteries.

A

The spinal arteries are reinforced by medullary (radicular) arteries from different spinal levels of the aorta.

Spinal arteries because they follow spinal nerve

76
Q

What is the great anterior segmental medullary artery of (Adamkiewicz)?

A

it is a medullary artery at the level of T10 on the left side that supplies the lumbosacral enlargement

-this is the main anastomosis supplying blood to the lower SC

77
Q

If the great anterior segmental meduallary artery is obstructed or surgeon clamps off the artery by mistake, what happens?

A

the distal part of the SC (lumbosacral enlargement) is deprived of blood development of PARAPLEGIA

78
Q

At each vertebral level, the aorta gives off segmental arteries (i.e. intercostal and lumbar arteries).

A

this is idea of metamerism (giving blood to each segment)

-gives off spinal branches that transverse the intervertebral foramen

79
Q

Spinal arteries give off anterior and posterior segmental medullary (radicular) branches.

A

FACTS!!

spinal arteries are the anterior and posterior spinal arteries

80
Q

What is the dorsolateral fasciculus?

A

Zone of Lissauer where the lateral division of the dorsal root enters into the dorsal horn

SF1 Unit 1 Post Exam 1 (14 decks)

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