Anatomy of the Spinal Cord

Question 1

The Spinal Cord & its growth

Answer 1

• 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.

Question 2

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

Answer 2

• 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)

Question 3

Filum Terminale

Answer 3

• 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.

Question 4

Segments of the spinal cord (spinal nerves)

Answer 4

• 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).

Question 5

What are the longitudinal fissures of the SC?

Answer 5

• anterior median fissure
• anterolateral fissure
• posterior median sulcus
• posterolateral sulcus

Question 6

What does grey matter have?

Answer 6

• 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

Question 7

ant, post, lat. horns of grey matter

Answer 7

• 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

Question 8

Grey commissure

Answer 8

• connects the two symmetrical halves of the grey matter

Question 9

What does white matter have?

Answer 9

• 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

Question 10

Grey and white matter of spinal cord

Answer 10

• 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

Question 11

Posterior grey horn

Answer 11

• 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

Question 12

Lateral grey horn

Answer 12

• 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

Question 13

Anterior grey horn

Answer 13

• 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

Question 14

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

Answer 14

more medial

Question 15

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

Answer 15

more posterior

Question 16

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

Answer 16

more lateral

Question 17

What do the ascending and descending tracts do?

Answer 17

govern movement, the senses and autonomic functions.

Question 18

Posterior white column

Answer 18

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

Question 19

Lateral White Column

Answer 19

• ascending and descending tracts

Question 20

Ascending tracts of lateral white column

Answer 20

• 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

Question 21

Descending pathways of the lateral white column

Answer 21

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

- medullary reticulospinal tract - RF, descends

Question 22

Anterior White column

Answer 22

• 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

Question 23

Sacral region of spinal cord

Answer 23

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.

Question 24

White matter of sacral region of spinal cord

Answer 24

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

Question 25

Enlargements in the spinal cord

Answer 25

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).

Question 26

Cross section of spinal cord

Answer 26

- 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).

Question 27

Spinal Meninges

Answer 27

- 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.

Question 28

Epidural anaesthesia

Answer 28

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.

Question 29

Lumbar Puncture

Answer 29

- 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

Question 30

Where does lumbar puncture occur?

Answer 30

- 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.

Question 31

Spinal anaesthesia

Answer 31

- 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

Question 32

Describe the denticulate ligament

Answer 32

- 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

Question 33

Cordotomy

Answer 33

- 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

Question 34

Image of meninges of SC

Answer 34

Question 35

Arterial Blood supply of SC

Answer 35

- 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

Question 36

Venous blood supply of SC

Answer 36

- 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

Question 37

Dorsal root ganglion

Answer 37

- 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

Question 38

Image of positions on spinal cord

Answer 38

Question 39

Longitudinal arrangement of SC

Answer 39

fibers (white matter) - white column cell groups (grey) - grey column

Question 40

Transverse arrangement of SC

Answer 40

- afferent and efferent fibers - crossing fibers

Question 41

Somatotopical arrangement

Answer 41

Question 42

SC Rexed Laminae

Answer 42

- The Rexed laminae represent a system of organizing the neurons of the spinal cord ## Footnote - 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

Question 43

Where is 1-6 Laminae of Rexed located

Answer 43

posterior horn of grey matter

Question 44

Where is 7, 8-9 and 10 laminae located

Answer 44

7 - intermediate zone 8-9 - anterior horn 10 - gray commissure

Question 45

Ascending tracts

Answer 45

- convey information from periphery to the brain - modality, receptor, primary/secondary/tertiary neurons, termination

Question 46

Modality of ascending tracts

Answer 46

touch pain temp kinesthesia

Question 47

Receptors of ascending tracts

Answer 47

- exteroceptor - interoceptor - proprioceptor

Question 48

neurons of ascending tracts

Answer 48

primary - dorsal root ganglion secondary - spinal cord, brain stem tertiary - thalamus (ventrobasal nuclear complex)

Question 49

termination of ascending tracts

Answer 49

cerebral cortex cerebellar cortex brain stem

Question 50

Examples of ascending tracts

Question 51

Posterior white column - medial lemniscal pathway

Answer 51

- 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

Question 52

Spinothalamic tract

Answer 52

- ascending - decussation at anterior white commissure - posterior root - contralateral loss of pain and temp sensation below level of lesion

Question 53

Descending tracts

Answer 53

- 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

Question 54

Corticospinal tract

Answer 54

- 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

Question 55

Describe Spinal Nerves

Answer 55

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

Question 56

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

Answer 56

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

Question 57

Root sizes in spinal nerves

Answer 57

- short and horizontal in cervical and thoracic - longer and more horizontal in sacral and lumbar

Question 58

Rami communicantes

Answer 58

- 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

Question 59

Reflex arc

Answer 59

- rapid, predictable motor response to a stimulus - unlearned and involuntary

Question 60

components of reflex arc

Answer 60

- 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

Question 61

Reflexes

Answer 61

- 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

Question 62

Monosynaptic reflex

Answer 62

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.

Question 63

Polysynaptic reflex

Answer 63

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

Question 64

Poliomyelitis (infantile paralysis)

Answer 64

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

Question 65

Aymotrophic lateral sclerosis (ALS)

Answer 65

- 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

Question 66

Brown-sequard syndrome

Answer 66

- 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.

Question 67

4 Symptoms of Brown-Sequard syndrome

Answer 67

- 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)