Neuroanatomy: Spinal Cord Tracks

Front 1

forebrain, midbrain, and hindbrain - what are the divisions and what major structures are present ineach?

Back 1

the forebrain is made of the telencephalon (cortex and CN 1) and diencephalon (CN2 and thamus, hypothalamus, third ventricle, pineal gland, subthalamus?

the midbrain (mesencephalon) has CN 3 and 4, as well as the aqueduct, the tegmentum and tectum (superior and inferior caniculi ). front of fourth ventricle.

the metencephalon (hindbrain) is the pons and cerebellum and back of 4th ventricle. includes pyramids and olives. Also, cranial nerves 5 through 7.

Front 2

blood supply: what are the major arteries coming to the brain and in what layer do they travel?

Back 2

2 pairs: identaical internal carotids and identical vertebrals (2 of each). Total of 4.

live in the subarachnoid space.

Front 3

what ascending tracts should we be generally familiar with and what do they detect?

Back 3

pain and temperature/light touch go through the spino-thalamic tract (divided into anterior and lateral...note that anterior does light touch and pressure, lateral does pain and temperature).

discriminitve touch (how many and where being touched) and propreceptive go through the white dorsal columns (cuneatus and gracilis).

spinocerebellar tract does unconscious information

Front 4

describe the progression of the spino-thalamic tract: spinal segment

Back 4

cell bodies in the DRG sense something, sends a process into the spinal cord.

enters the gelatinosa and can travel up a segment or two, but for our purposes, it synapses on a cell in the posterior horn and then DECUSATES over the anterior commisure and ascends in the contralateral spino-thalamic tract.

NOTE: the lower body parts are represented on the outside, the upper body on the inside...this is opposite of the dorsal columns where the lower body is medial

Front 5

spino thalamic tract ascending through cord into the brain - describe it.

Back 5

it stays fairly lateral in the cord, and maintains in a lateral position up through the medulla and pons. in the pons, it stays lateral and the ML system ends up immediately medial to it.

by the time it gets to the midbrain, it's above the ML system.

Ascends to the VPL (ventral posterio-lateral nucleus) in the thalamus, synapses, and becomes 3rd order destined for the cortex (post-central gyrus)

also remember

Front 6

Talk about the ML system at the level of the spinal segment and spine:

Back 6

the Medial leminiscus is equivelant to the posterior columns/gracilis/cuneatus.

it's going to transmit proprioceptive and discriminating senses.

its neuron is in the DRG - it has a process that goes directly into the white dorsal column OF THE SAME SIDE (no crossing in the spine! no synapsing either - so traveling in the spine are only 1st order neurons for this system). This is the fasiculitus gracilis and cuneatus.

Front 7

talk about the ML system higher than the spinal cord:

Back 7

the gracilis is present the whole way - the cuneatus is added after the mid-thoracic (need all those fibers from the fingers). Note that the gracilis is central, the cuneatus is lateral.

makes it up as far as the closed medulla where it synapses on the GRACILIS and CUNEATUS NUCELI. Now 2nd order neurons - first part called the internal acruate fibers, these DECUSATE (was ipsilateral, now contralteral).

Front 8

once you have your secondary fibers that have crossed over, then what happens with the ML system?

Back 8

once you get into the open medulla, you've crossed over to the other side. the fibers are now very medial and kinda shaped like a pyramid (very long and up/down).

once you hit the pons, THEY BECOME HORIZAONTAL and end up kinda high

in the midbrain, they end up kinda high and more vertical again.

Front 9

corticospinal tract - what brain regions must the signal travel through as it goes down?

Back 9

start in the cortex, go through subcortical white matter and through the internal capsule.

then through the cerebral peduncle and into the pons, then the medulla (pyramid, where 85% synapse/decusate and end up contralateral).

this whole tract is called the cortical-spinal tract.

Front 10

how does it travel in relation to the tegmentum? is damage felt ipsilaterally or contralaterally?

Back 10

goes BELOW the the tegmuntum - remember that the tegmnuntum is where most of the cranial nerves live, and we don't need tracts going right through them.

if it's damaged before decusation in the pyramids, it's felt contralaterally.

if it's damaged after, it's felt ipsilaterally.

Front 11

if looking at cross sections of the cortical-spinal tract, where is the CST seen generally?

Back 11

it stays pretty ventral (remember that it's going to synapse with ventral horn nuclei).

in the pons, it's fairly central (in the dark region in the middle)

in the open medulla, it's again most ventral (and dark). same in the open and closed medulla.

note that it crosses at the pyramids and ends up in the POSTERIOR FASICLE, kinda in the middle. so it starts ventral, ends up dorsal.

Front 12

where is the CST going?

Back 12

ends up synapsing in the anterior horn, giving off a short interneuron (this is the second-order - remember that it's FIRST ORDER ALL THE WAY DOWN THE SPINE), and then syapses again in the ventral horn and gives off the terminal 3rd order neuron to the body.

Front 13

talk about sense from the face - what are the different kinds and how are they transmitted?

Back 13

is kinda opposite to the body - pain and temperature travel for awhile as a 1st order neuron whereas discriminatory sense synapses immediately.

so: discriminitory sense - CN5 comes in and synapses immediately and travels up to the TrTT (trigeminothalamic tract) to the VPM to the cortex.

pain/temperature - this one's weird. 1st order comes in and DOESN'T immediately synapse - descends SPINAL TRACT OF V, which actually contains the nucleus the whole way. it goes DOWN INTO THE CERVICAL CORD

there it synapses on the CERVICAL NUCLEUS OF V, crosses oer, and ascends up the Trigeminothalamic tract to the VPM to form the 3rd order neuron going to the cortex.