4.16. Spinal cord and Long tracts

Question 1

Segments of the spinal cord (hint: based on where the spinal nerves emerge, npt the vertebral level)

2 enlargements in the spinal cord

Answer 1

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

2 enlargements: lumbar and cervical

Question 2

Spinal cord layers

CSF fills the ___ and the ___ canal

Answer 2

Dura mater

Arachnoid mater

Pia mater

Subarachnoid space; central canal

Question 3

what’s the lumbar cistern? what’s it filled with?

Answer 3

Lumbar cistern: enlargement of the subarachnoid space between vertebrae L2 and S2

Filled with CSF, the cauda equina, and filum terminale

Question 4

Spinal cord anatomy:

White mater

Gray mater components

Answer 4

white mater:

Dorsal/posterior column

Ventral/anterior column

Lateral column

gray mater:

Posterior horn

Lateral horn

Anterior horn

Question 5

general organization of gray mater

(which nuclei are located most dorsally, laterally, most ventrally)

At the thoracolumbar levels are ___ which house the sympathetic neurons

__ horns house motor neurons and their axons exit via the ventral roots

__ horns house sensory neurons and receive sensory fibers

Answer 5

Somatosensory nuclei located most dorsally (and visceral sensory nuclei right behind that)

Laterally – somatic motor nuclei

Most ventrally – autonomic efferent nuclei

Anterior horns

Posterior horns

Question 6

general organization of white mater

Answer 6

White matter – arranged in funiculi containing ascending and descending tracts (or fasciculi).

Anterior funiculi

Lateral funiculi

Posterior funiculi (a.k.a dorsal columns) made up of: Fasciculus cuneatus (cuneate fascicle), located laterally and Fasciculus gracilis (gracile fascicle), located medially

Question 7

For the sensory portion of the spinal cord, the primary sensory neurons are in the ___ ___ ___.

The neurons receive input from the periphery and send it to the ___ and ___ of the spinal cord.

The neurons bifurcate as they enter the spinal cord; there’s a branch that goes up to the medulla via the ___. The branch can either go up the ___ or the ___

What happens to the rest of the neurons past the dorsal column?

Answer 7

For the sensory portion of the spinal cord, the primary sensory neurons are in the dorsal root ganglion

The neurons receive input from the periphery and send it to the dorsal column and dorsal horn of the spinal cord

The neurons bifurcate as they enter the spinal cord; there’s a branch that goes up to the medulla via the dorsal columns (both the gracilis and the cuneate will get similar info); the branch can either go up the Fg or the Fc

The rest terminate in the dorsal horn

Question 8

which is lateral or medial, the FG or FC? why?

How can you tell which spinal level you’re on? (2 things)

Answer 8

The FC is added to the already existing FG, which is why its more lateral and the FG is more medial

There’s more gray mater going up the spinal cord because at each level, axons and fiber tracts are being picked up on their way to the brain; likewise, there are pathways coming down and terminating at each level as they go down, hence there’s more white mater caudally

Higher up, you can see both the fasciculus gracilis and cuneatus; below the cervical level (or at the thoracic level), you only have fasciculus gracilis

Lower levels: the FG starts to decrease in proportion, while there’s more white mater

Question 9

DRG afferent types

function/characteristics of each (myelinated vs unmyelinated; large vs small diameter etc)

Answer 9

Group 1/alpha: very fast conducting; large diameter, and myelinated; Proprioceptors of skeletal muscle

Group 2/beta: medium size and myelinated; they’re the mechanoreceptors of skin (convey tactile information)

Group 3 or 4/A-delta or C: thin myelinated or unmyelinated; they both convey mainly pain information and temperature. A-delta is faster than C, C is the slowest. The delta fibers are for the sharp pain, and the C fibers are for long lasting dull pain

Question 10

dermatome definition

what happens if a given nerve succumbs to a viral infection?

Answer 10

An area of skin that is supplied by a single spinal nerve is called a dermatome

Viral infection of a given nerve can also manifest as a reaction restricted to the particular dermatome of that nerve, e.g., as can be seen with shingles.

Question 11

Rexed’s spinal gray nuclei (name them)

Answer 11

Substantia gelatinosa (apparently these layers/nuclei look gelatinous on histo): related to pain information

Nucleus propius: somatic sensory/tactile information

Dorsal nucleus aka Posterior thoracic nucleus/Column of Clarke

Intermediolateral nucleus: has sympathetic neurons

Motor neurons in the ventral horn: lateral and ventral groups

Question 12

Function of the following:

substantia gelatinosa

nucleus propius

dorsal nucleus

intermediolateral nucleus

Answer 12

Substantia gelatinosa (apparently these layers/nuclei look gelatinous on histo): related to pain information

Nucleus propius: somatic sensory/tactile information

Dorsal nucleus aka Posterior thoracic nucleus/Column of Clarke - he didn’t talk about I don’t think

Intermediolateral nucleus: has sympathetic neurons

Question 13

terminal distribution of sensory afferents

(basically, where do the following fibers terminate?)

A/alpha

A/beta

A/delta

C

Answer 13

A/alpha fibers terminate at lamina 6, 7 and 9, where the motor neurons are. They bring sensory information to that region and are partly involved in spinal cord reflexes

A/beta fibers terminate at lamina 3, 4, 5 and 6 (also called the proper nucleus), and bring in tactile information from skin

A/delta fibers terminate at lamina 1 (substantia gelatinosa)

C fibers terminate at lamina 2 (substantia gelatinosa)

(Superficial lamina of the dorsal horn will be related to pain)

Question 14

difference between upper and lower motor neurons

location of UMN and LMN

Answer 14

UMN don’t directly interact w/ muscles whereas the LMNs do

Upper motor neurons are located for e.g. in the precentral gyrus or at bulbar levels if they have something to do with the spinal cord

Lower motor neurons are directly connected with muscles; in the spinal cord, they live in the ventral horn, and they also reside in the brainstem (those innervate eye muscles or facial nucleus)

Question 15

why wouldn’t the forehead and eye area be affected if you had an upper motor neuron lesion vs a lower motor neuron lesion?

Answer 15

The reason why the forehead and eyes area is unaffected is b/c one side of the brain will basically help out to keep that area innervated

Facial nucleus receives inputs from the motor cortex (corticobulbar fibers). Dorsal parts of the facial nucleus which innervates the forehead and eyelids receives bilateral cortical inputs whereas the ventral parts of the facial nucleus which innervates the facial muscles below the eyes receive input only from the contralateral motor cortex.

Question 16

ascending pathways

Answer 16

Dorsal column lemniscal pathway

Spinothalamic pathway

Spinocerebellar pathway (3 subdivisions)

Spinoreticular tract

Spinomesencephalic tract

Question 17

functions of dorsal column lemniscal pathway

Answer 17

responsible for touch, texture, pressure, vibration, position info.

Question 18

functions of spinothalamic pathway

facial component of this pathway + function

Answer 18

responsible for temperature, pain, crude touch info

facial component – spinal trigeminal thalamic tract (that’s the pain component of the face)

Question 19

functions of spinal cerebellar pathway

Answer 19

responsible for proprioception, touch, texture, pressure + vibration; convey info from the spinal cord to the cerebellum

Question 20

subdivisions of spinocerebellar pathway

(1 comes from accessory cuneate nucleus;

1 comes from the Dorsal nucleus;

1 is the opposite of dorsal and comes from laminae 6 and 7)

Answer 20

cuneocerebellar pathway

dorsal spinocerebellar pathway

ventral spinocerebellar pathway

Question 21

descending pathways

hint: (they all end in -spinal. One is red, one doesn’t respond to tects, one is vestibule)

where do these tracts initially comes from?

Answer 21

Corticospinal tract (responsible for motor info. Consists of lateral CST and anterior CST)

Rubrospinal (red nucleus to spinal cord)

Tectospinal (superior colliculus to spinal cord)

Vestibulospinal (vestibular nuclei to spinal cord)

Reticulospinal (reticular formation to spinal cord)

Question 22

3 major somatosensory ascending pathways

Answer 22

dorsal column lemniscal pathway

spinothalamic pathway

trigeminal pathway

Question 23

dorsal column lemniscal pathway

Answer 23

DRG >> Dorsal column nuclei >> internal arcuate fibers (after crossing midline) >> medial lemniscus >> VPL >> 4th layer of postcentral gyrus

Question 24

Lissauer’s tract

Answer 24

C fiber (pain fibers) axons coming into the spinal cord branch right before entering the dorsal horn and they travel up and down. They synapse in lamina 1 and 2 of the dorsal horn (substantia gelatinosa)

Question 25

spinothalamic pathway

Answer 25

DRG >> dorsal horn of the spinal cord >> (cross spinal cord to the other side; form spinothalamic tract) >> VPL >> thalamus >> Si and limbic cortex

Question 26

components of spinothalamic tract (plus functions)

Answer 26

Lateral spinothalamic component carries most of the pain information (plus temp)

Anterior component carries some crude touch information (plus light touch)