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PMU Anatomy > Anatomy of the Spinal Cord > Flashcards

Anatomy of the Spinal Cord Flashcards

1
Q

The Spinal Cord & its growth

A
  • The spinal cord is part of the central nervous system (CNS)
  • It is situated inside the vertebral canal of the vertebral column
  • During development, there’s a disproportion between spinal cord growth and vertebral column growth
  • The spinal cord finishes growing at the age of 4, while the vertebral column finishes growing at age 14-18. This is the reason why, in adults, the spinal cord occupies only the upper two thirds of the vertebral canal.
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2
Q

The spinal cord’s position - where it starts and where it ends

A
  • The spinal cord is a continuation of the brainstem
  • It extends from the foramen magnum at the base of the skull to the L1/L2 vertebra where it terminates as the conus medullaris (medullary cone)
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3
Q

Filum Terminale

A
  • A thin thread called filum terminale extends from the tip of the conus medullaris all the way to the 1st coccygeal vertebra (Co1) and anchors the spinal cord in place.
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4
Q

Segments of the spinal cord (spinal nerves)

A
  • cervical, thoracic, lumbar, sacral, and coccygeal
  • Each segment of the spinal cord provides several pairs of spinal nerves, which exit from vertebral canal through the intervertebral foramina
  • There are 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal pair of spinal nerves (a total of 31 pairs).
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5
Q

What are the longitudinal fissures of the SC?

A
  • anterior median fissure
  • anterolateral fissure
  • posterior median sulcus
  • posterolateral sulcus
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6
Q

What does grey matter have?

A
  • comprised of neuronal cell bodies
  • It shows anterior, lateral, and posterior horns.
  • lateral present in 1st thoracic to 2nd lumbar segments and from 2nd to 4th sacral segments
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7
Q

ant, post, lat. horns of grey matter

A
  • posterior horns contain interneurons
  • ant. horns contain interneurons as well as motor neurons
  • these cell bodies project their axons via the ventral roots of the SC to the skeletal muscle
  • amount of ventral grey matter at a given level of SC ~ amount of skeletal muscle innervated
  • lateral horn neurons are sympathetic motor neurons serving visceral organs
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8
Q

Grey commissure

A
  • connects the two symmetrical halves of the grey matter
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9
Q

What does white matter have?

A
  • White matter surrounds the gray matter and is made of myelinated axons
  • have afferent tracts - general somatosensory information - neuron is funicular neuron from post. gm
  • efferent tracts - conduct impulses to motor neurons in anterior grey horn
  • white matter divided into funiculi
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10
Q

Grey and white matter of spinal cord

A
  • The spinal cord consists of various regions of grey and white matter that in turn carry specific cell groups and nuclei depending on the vertebral level
  • This matter houses the ascending and descending tracts of the spinal cord

WHITE

  • anterior funiculus (white column)
  • posterior funiculus - fasciculus gracilis/cuneatus
  • lateral funiculus

GREY

  • anterior horn - motor
  • posterior horn - sensory
  • lateral horn - autonomic
  • grey commissure - anterior and posterior
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11
Q

Posterior grey horn

A
  • longer and narrower than anterior
  • two types of neurons - funicular (afferent which give rise to the ascending tracts of the white matter) and interneurons

3 cell groups - Zona spongiosa, Substantia gelatinosa and Nucleus proprius - receive general somatic afferents

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12
Q

Lateral grey horn

A
  • 3 nuclei
  • nucleus dorsalis - proprioception - post. spinocerebellar tract
  • intermediolateral nucleus - visceral motor nucleus - rise to preganglionic sympathetic fibers
  • intermediomedial nucleus - visceral sensory nucleus - rise to viescerosensory ascending pathways
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13
Q

Anterior grey horn

A
  • two types of motor (efferent) neurons, both cholinergic
  • large alpha motor neurons
  • small gamma motor neurons - form ventral roots of spinal nerves and reach skeletal muscle

collectively referred to as LMN - they receive input from neurons in the cerebral motor cortex UMN

Renshaw’s cells are closely related to alpha - provide a feed-back mechanism for alpha

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14
Q

Motor neurons that innervate proximal limbs are located where in the anterior grey horn?

A

more medial

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15
Q

Motor neurons that innervate the extensor muscles are located where in the anterior grey horn?

A

more posterior

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16
Q

Motor neurons that innervate more distal musculature are located where in the anterior grey horn?

A

more lateral

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17
Q

What do the ascending and descending tracts do?

A

govern movement, the senses and autonomic functions.

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18
Q

Posterior white column

A
  • 2 ascending tracts
  • fasciculus cuneatus - laterally
  • fasciculus gracilis - medially
  • convey general somatic info for proprioception and discriminative touch
  • also has fasciculus interfascicularis
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19
Q

Lateral White Column

A
  • ascending and descending tracts
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20
Q

Ascending tracts of lateral white column

A
  • posterior spinocerebellar tract - nucleus dorsalis, unconscious properioception

- anterior ST - post. grey horn neurons, unconscious proprioception from lower limbs

  • spinothalamic tract - nucleus proprius - conveys general somatic afferent information for pain and temp to thalamus

- spinotectal tract - originates from nucleus proprius - spinovisual reflexes

- spinooilivary tract - olivary n,

  • spinoreticular tract - processing pain
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21
Q

Descending pathways of the lateral white column

A
  • lateral corticospinal tract - major motor tract, rapid, precise voluntary movements
  • rubrospinal tract - nucleus ruber, not well developed

- medullary reticulospinal tract - RF, descends

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22
Q

Anterior White column

A
  • contaisn descending tracts only
  • anterior corticospinal tract - terminated at LMN
  • tectospinal tract - reflex movements
  • pontine reticulospinal tract - muscle tone, reflexes and voluntary movements
  • vestibulospinal tracts - m. and l.
  • interstitiospinal tract - motor reflexes
  • descending autonomic pathways
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23
Q

Sacral region of spinal cord

A

The sacral region of the spinal cord is round in shape and consists of white matter, the anterior grey column and the posterior grey column.

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24
Q

White matter of sacral region of spinal cord

A

The white matter is only a small amount comprising of only the fasciculus gracilis, without the fasciculus cuneatus.

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25
Q

Enlargements in the spinal cord

A

the spinal cord shows two well defined enlargements to accommodate for innervation of the upper and lower limbs: one at the cervical level (upper limbs, C5-T1), and one at the lumbosacral level (lower limbs, L1-L4).

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26
Q

Cross section of spinal cord

A
  • The spinal cord is made of gray and white matter just like other parts of the CNS
  • It shows four surfaces: anterior, posterior, and two lateral. They feature fissures (anterior) and sulci (anterolateral, posterolateral, and posterior).
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27
Q

Spinal Meninges

A
  • The spinal cord and spinal nerve roots are wrapped within three layers called meninges
  • The outermost is the dura mater, underneath it is the arachnoid mater, and the deepest is the pia mater
  • Dura mater has two layers (periosteal and meningeal), between which is the epidural space
  • Between the arachnoid and pia mater is the subarachnoid space, it is filled with cerebrospinal fluid.
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28
Q

Epidural anaesthesia

A

Epidural administration is a medical route of administration in which a drug such as epidural analgesia and epidural anaesthesia or contrast agent is injected into the epidural space around the spinal cord.

29
Q

Lumbar Puncture

A
  • a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing
  • The main reason for a lumbar puncture is to help diagnose diseases of the central nervous system, including the brain and spine
30
Q

Where does lumbar puncture occur?

A
  • The cerebrospinal fluid can be accessed most safely below the first or second lumbar vertebrae (L1 or L2)
  • the spinal cord terminates (conus medullaris)
  • Nerves continue down the spine below this, but in a loose bundle of nerve fibers called the cauda equina
  • There is lower risk with inserting a needle into the spine at the level of the cauda equina because these loose fibers move out of the way of the needle without being damaged.
31
Q

Spinal anaesthesia

A
  • is a form of neuraxial regional anaesthesia involving the injection of a local anaesthetic or opioid into the subarachnoid space, generally through a fine needle, usually 9 cm long
32
Q

Describe the denticulate ligament

A
  • denticulate ligaments are bilateral triangular lateral extensions of pia mater that anchor the spinal cord to the dura mater
  • They are formed by pia mater of the spinal cord
33
Q

Cordotomy

A
  • a surgical procedure that disables selected pain-conducting tracts in the spinal cord, in order to achieve loss of pain and temperature perception
  • Denticulate ligaments are important for locating spinal pathways
34
Q

Image of meninges of SC

A
35
Q

Arterial Blood supply of SC

A
  • supplied by branches of the vertebral and segmental arteries
  • vertebral artery gives rise to anterior and posterior spinal arteries
  • segmental arteries (e.g. deep cervical, ascending cervical, and posterior intercostal) give rise to 31 pairs of radicular arterial branches
  • they supply the roots of the spinal nerves
36
Q

Venous blood supply of SC

A
  • artery-similar named veins accompany arteries - ant/post. spinal veins drain into radicular veins
  • these empty into internal/external vertebral venous plexus
  • this network eventually empties into the vertebral (neck) and segmental (trunk) veins
37
Q

Dorsal root ganglion

A
  • afferent sensory fibers carrying info from peripheral receptors form the dorsal roots of the SC
  • the somata of these sensory fibers are found in an enlargement known as dorsal root ganglion
  • dorsal and ventral roots fuse to form spinal nerves
38
Q

Image of positions on spinal cord

A
39
Q

Longitudinal arrangement of SC

A

fibers (white matter) - white column

cell groups (grey) - grey column

40
Q

Transverse arrangement of SC

A
  • afferent and efferent fibers
  • crossing fibers
41
Q

Somatotopical arrangement

A
42
Q

SC Rexed Laminae

A
  • The Rexed laminae represent a system of organizing the neurons of the spinal cord

  • There are ten Rexed laminae and they roughly follow a topographic organization
  • lower numbers being towards the back of the spinal cord (ie: posterior)
  • higher numbers being towards the front
  • Rexed laminae are not strictly organized based on anatomical location, but are actually based on the types, and functions, of the neurons in each laminae
43
Q

Where is 1-6 Laminae of Rexed located

A

posterior horn of grey matter

44
Q

Where is 7, 8-9 and 10 laminae located

A

7 - intermediate zone

8-9 - anterior horn

10 - gray commissure

45
Q

Ascending tracts

A
  • convey information from periphery to the brain
  • modality, receptor, primary/secondary/tertiary neurons, termination
46
Q

Modality of ascending tracts

A

touch

pain

temp

kinesthesia

47
Q

Receptors of ascending tracts

A
  • exteroceptor
  • interoceptor
  • proprioceptor
48
Q

neurons of ascending tracts

A

primary - dorsal root ganglion

secondary - spinal cord, brain stem

tertiary - thalamus (ventrobasal nuclear complex)

49
Q

termination of ascending tracts

A

cerebral cortex

cerebellar cortex

brain stem

50
Q

Examples of ascending tracts

A
51
Q

Posterior white column - medial lemniscal pathway

A
  • ascending
  • lemniscal decussation
  • first-order neurons form the ascending tracts of the gracile fasciculus, and the cuneate fasciculus which synapse on the second-order neurons in the gracile nucleus and the cuneate nucleus known together as the dorsal column nuclei
  • axons from these neurons ascend as the internal arcuate fibers; the fibers cross over at the sensory decussation and form the medial lemniscus which connects with thalamus
  • ipsilateral loss of discriminiative touch sensation and conscious proprioception below level of lesion
52
Q

Spinothalamic tract

A
  • ascending
  • decussation at anterior white commissure
  • posterior root
  • contralateral loss of pain and temp sensation below level of lesion
53
Q

Descending tracts

A
  • carry information from brain to periphery
  • lateral pathway - voluntary movement of distal muscles, direct cortical control
  • ventromedial pathway - pose and antigravitational movements, indirect cortical (stem) control
  • from brainstem - ventromedial and dorolateral
54
Q

Corticospinal tract

A
  • a white matter motor pathway starting at the cerebral cortex that terminates on lower motor neurons and interneurons in the spinal cord, controlling movements of the limbs and trunk
  • pyramidal decussation
  • ipsilateral UMN syndrome at the level of lesion
55
Q

Describe Spinal Nerves

A

31 nerves

  • connecting spinal cord and various body regiond
  • each connects to the SC by 2 roots - dorsal and ventral
  • each root forms a series of rootlets that attach along the whole length of the spinal cord segment
  • ventral roots are motor
  • dorsal roots are sensory
  • 2 roots join to form spinal nerve prior to leaving the vertebral column
56
Q

After emerging from intravertebral foramen, what does the spinal nerve divide into?

A

dorsal ramus, ventral ramus and meningeal branch that recurs to supply the meninges and associated blood vessels

57
Q

Root sizes in spinal nerves

A
  • short and horizontal in cervical and thoracic
  • longer and more horizontal in sacral and lumbar
58
Q

Rami communicantes

A
  • each ramus is mixed
  • joined to the base of the ventral rami of spinal nerves in thoracic region are the rami communicantes
  • these are sympathetic fibers that we will deal with shortly
  • dorsal rami supply the posterior body trunk whereas the thicker ventral rami supply the rest of the body trunk and the limbs
59
Q

Reflex arc

A
  • rapid, predictable motor response to a stimulus
  • unlearned and involuntary
60
Q

components of reflex arc

A
  • receptor - site of stimulus
  • sensory neuron - transmits afferent info to CNS
  • integration center - 1 or more interneurons
  • motor neuron - transmits efferent signals to effector
  • effector - muscle or gland
61
Q

Reflexes

A
  • reflexes involving skeletal muscles and somatic motor neurons are somatic
  • reflexes controlled by autonomic neurons are autonomic
  • reflexes may be inborn or learned
  • monosynaptic or polysynaptic
62
Q

Monosynaptic reflex

A

Monosynaptic reflexes play out with only two neurons participating in the reflex arc, one sensory and one motor

  • The first-order neuron (sensory) is in the spinal ganglion, while the second-order neuron (motor) is in the anterior horn of the spinal cord)
  • The sensory neuron gathers impulses from the muscle and sends this information to the motor neuron which innervates the same muscle. The motor neuron then causes contraction of the innervated muscle. An example of a monosynaptic reflex is the stretch reflex.
63
Q

Polysynaptic reflex

A

Polysynaptic reflexes on the other hand have multiple neurons participating

  • Besides one sensory and one motor neuron, there are also one or more interneurons between them making this communication indirect
  • They are more complex than monosynaptic reflexes as they involve muscle groups instead of a single muscle. An example is the withdrawal reflex
64
Q

Poliomyelitis (infantile paralysis)

A
  • viral infection of lower motor neuron
  • LMN syndrome at the level of lesion

motor syndrome

65
Q

Aymotrophic lateral sclerosis (ALS)

A
  • combined LMN and UMN lesion
  • LMN syndrome at the level of lesion
  • UMN syndrome below the level of lesion
  • Lou Gehrig’s disease in USA
66
Q

Brown-sequard syndrome

A
  • caused by damage to one half of the spinal cord, i.e. hemisection of the spinal cord resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion.
67
Q

4 Symptoms of Brown-Sequard syndrome

A
  • ipsilateral UMN syndrome below the level of lesion
  • ipsilateral LMN syndrome at the level of lesion
  • ipsilateral loss of discriminative touch sensation and conscious proprioception below the level of lesion (post. white column lesion)
  • contralateral loss of pain and temp sensation below the level of lesion (spinothalamic tract lesion)
68
Q
A
69
Q
A

PMU Anatomy (19 decks)

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