Lecture 13: Spinal cord internal structures Flashcards by Michael Sokol

a bundle of axons within the CNS

Tract

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a bundle of axons within the PNS

Nerve

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Name the 5 spinal tracts. Which are ascending vs descending?

Ascending:
Dorsal-Column Medial Lemniscal System
Spinocerebellar Tract(s)
Spinothalamic Tract(s)/anterolateral system
Descending:
Corticospinal Tracts: “Pyramidal Tracts”
“Extrapyramidal” Tracts

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Which spinal tract is responsible for sensing pressure? Where is it located in the cord?

Dorsal-Column Medial Lemniscal (DCML) System
- sits in dorsal part of cord and passes through the medial lemniscus in the brainstem

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Which spinal tract is responsible for sending sensory info from the spinal cord to the cerebellum? Where is it located in the cord?

Spinocerebellar Tract(s)
Lateral - anterior and posterior

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Which spinal tract is responsible for pain? Where is it located in the cord?

Spinothalamic Tract(s)/anterolateral system - front/sides of cord

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Which spinal tract is responsible for motor function that we think about? Where is it located in the cord?

Corticospinal Tracts: “Pyramidal Tracts” - lateral/posterior of cord

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Which spinal tract is responsible for coordinating complex movements that we don’t think about? Where is it located in the cord?

Extrapyramidal” Tracts - front of the cord

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How is the grey matter in the cord divided?

Rexed’s Laminae: numbered back to front, 10 in total

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Lamina I

Lamina Marginalis
- Sharp Pain - fast pain
- Aδ Pain - myelinated nociceptors (a delta fibers)

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Laminae II & III

Substantia Gelatinosa - also sometimes lamina V
- Slow Pain
- C-Fibers - non-myelinated nociceptors

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Which lamina are mechanoreceptors?

Laminae I→ VI

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Lamina VII

Intermediolateral Nucleus
- Lateral Grey Horn

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Laminae VIII → IX

Lots of large motor neurons that hang out in the anterior horn of grey matter in the cord - descending

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_______ allows signals to cross to the other side of the cord in the grey matter, while _________ allows signals to cross to the other side of the cord in the white matter

Lamina X
Anterior white commissure

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_______ is responsible for sending info in the grey matter of the cord, while ______ is responsible for sending info in the white matter of the cord

Rexed laminae
Spinal tracts

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Efferent vs afferent

Afferent is sensory, going up to brain
Efferent is motor

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What are the two parts of the DCML pathway? Where are they located in the spinal cord?

Fasciculus Gracilis: Sensory signals from lower parts of the body - posterior/medial dorsal column
Fasciculus Cuneatus: Sensory signals from upper parts of the body - lateral dorsal column

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Describe the pathway through the brainstem for the DCML pathway

Pathway through brainstem: X-over at medulla (lower part of brainstem) → medial lemniscus (pons) → thalamus (ventrobasal complex) → internal capsule → parietal lobe (post-central gyrus/sensory cortex)

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What are the two pathways the DCML sensory info can take?

Grey matter of cord (lateral inhibition)
Up towards the brain in the dorsal columns

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What is the name of the parietal lobe, post-central gyrus - topographical layout?

Homunculus

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Which areas of the homunculus take up the most space? Describe where they are located

Hands (middle) and face (lateral)

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What are the 3 pathways of the corticospinal (pyramidal) tracts? How much motor function are they responsible for?

Primary - 80% - lateral
Secondary - 17% - anterior
Tertiary - 2-3% - lateral

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Describe the pathway the primary corticospinal (pyramidal) tract takes

Cortex (motor/frontal lobe) → Internal Capsule → Pyramids of Medulla (brainstem) → X-over (pyramidal decussation)→ Lateral Corticospinal Tracts (originated in motor cortex and descends through the spinal cord) → anterior horn of spinal cord - excites motor neuron associated with it

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Describe the pathway the secondary corticospinal (pyramidal) tract takes

Same as primary except x-over in the spinal cord at the level of the motor neuron it needs to talk to in the anterior horn Cortex (motor/frontal lobe) → Internal Capsule → Pyramids of Medulla (brainstem) → Lateral Corticospinal Tracts (originated in motor cortex and descends through the spinal cord) → anterior horn of spinal cord (x-over) - excites motor neuron associated with it

Describe the pathway the tertiary corticospinal (pyramidal) tract takes

Same as other pathways 1 and 2 except no cross over

Describe the location where the primary corticospinal (pyramidal) tract crosses over

Pyramidal decussation - cross-hatch pattern in the pyramids of the medulla Aligns with the anterior median fissure

What are the two main divisions of the spinothalamic tract? What is another name for this tract?

AKA Anterolateral - slow pain (anterior) and fast pain (lateral)

Differentiate between the myelination of the neurons in the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast: Nociceptors - free nerve endings; A delta fibers Slow: C fibers - unmyelinated

Differentiate between the neurotransmitters in the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast: glutamate Slow: substance P (main), CGRP (calcitonin G-related peptide), glutamate (less common, works slower than the glutamate in the fast pain pathway)

Differentiate between the localization of the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast: Detailed localization - sent through the thalamus to parietal lobe Slow: Poor localization - reticular formation (brainstem), not much makes it to the thalamus

Differentiate between the laminae of the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast: lamina I - Lamina Marginalis Slow: Laminae II & III (Substantia Gelatinosa), then V

Differentiate between the sites of x-over of the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Both x-over in the anterior white commissure

The slow pain pathway is more ______ than the fast pain pathway

Emotional

What are the sensors in the slow pain pathway?

- Thermoreceptors/heat - Vibration/Irritant Sensors: Tickle and Itch

What are the other names for the fast and slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast - “Neospinothalamic Tract” - newer, more sophisticated Slow - “Paleospinothalamic Tract” - paleo = old

Differentiate between the site of termination of the fast vs slow pain pathways of the Spinothalamic/Anterolateral Tracts

Fast: Ascends to thalamus, Ventrobasal Complex (w/DCML sensory info) & Posterior Nuclear Group Slow: Reticular Nuclei: Medulla, Pons, Mesencephalon

Name the 4 extrapyramidal tracts

Vestibulospinal, Olivospinal, Reticulospinal, Rubrospinal

Which extrapyramidal tract is responsible for balance?

Vestibulospinal: Eye fixation, muscle orientation during acceleration

Which extrapyramidal tract is responsible for cerebellar output to coordinate movement?

Olivospinal

Which extrapyramidal tract is responsible for the maintenance of muscle tone?

Reticulospinal

Which extrapyramidal tract is responsible for the modulation of voluntary movement?

Rubrospinal - similar to cerebellum tracts, in charge of monitoring and adjusting voluntary movements

What are the 3 parts of the Descending Pain Suppression System or Descending Inhibitory Complex (DIC)?

Periventricular & Periaqueductal Grey Raphe Nucleus Dorsal Spinal Cord Complex

Where does the first neuron of the DIC begin from?

Either the Periventricular nuclei or the periaqueducatal grey

What does the first neuron of the DIC release? Into where?

Releases enkephalins when excited in the middle of the pons (raphe magnus nucleus (RMN) → excites second-order descending neuron (raphe nucleus)

What neurotransmitter does the raphe nucleus release? What structure does it release into?

Serotonin into the white matter before the dorsal horn

Which neurotransmitters does the dorsal spinal cord complex release? What structure does it release into?

Serotonin & Enkephalin Enkephalin is released to enkephalin receptors located on nociceptors and the next neuron in the ascending pain pathway

Enkephalin is an _______ neurotransmitter in the cord

inhibitory

_______ is the morphine analog of the endogenous opiate system

Enkephalin

Dorsal Spinal Cord Complex releases enkephalins into the _____ matter of the spinal cord

grey

Why do patients in need of dialysis have more pain?

increased H+, K+

What can increase the pain sensation?

ACh, K+, H+, PGs, 5-HT, histamines (inflammation), bradykinins, ischemia

Why are SSRIs and TCAs of use for chronic pain?

SSRIs - inhibit reuptake of 5-HT → more 5-HT in synapse → 3rd order inhibitory neuron TCAs - increase 5-HT in the synapse and have the side effect of drowsiness, can help chronic pain patients sleep better

________ a neural process that reduces the activity of neighboring neurons when one neuron is excited

Lateral inhibition - Pressure signal can inhibit pain signal (injury to hand - grab hand and squeeze - suppresses pain) - acupuncture

How far does lateral inhibition work?

Doesn’t go further than dorsal horn in cord

What are the types of glutamate recepotors?

1. Ionotropic: AMPA-R, NDMA-R, kainate 2. Metabotropic - GPCRs + ion channels

______ is the main neurotransmitter for the pain system

Glutamate

Glutamate is always ______

excitatory

The primary glutamate receptor is the ______ receptor

AMPA

The NMDA receptor is ____ and _____ than AMPA

slower and bigger

The AMPA receptor allows ____ into the cell

Na+

The NMDA receptor allows ____ into the cell

Ca++ (mostly) and Na+

What is the NMDA receptor blocked by? How is it removed?

Intracellular Mg++ at rest → depolarization pushes Mg++ out of the way

NMDA-R are added as we _____

Grow - don’t have a lot when born

Things that can block NMDA-R

EtOH, lead, ketamine (doesn’t work on AMPA-R), nitrous, tramadol (not great a great narcotic, more of an SSRI and inhibits NMDA-R but not AMPA-R)

Chronic pain causes______ population of pain receptors

higher - NMDA and AMPA

Where in the cerebellum do the spinocerebellar tracts end?

anterior - superior cerebellar peduncle posterior - inferior cerebellar peduncle

What is the difference between anterior and posterior spinocerebellar tracts?

- Anterior (ventral) - sends synaptic activity occurring in the anterior horn to cerebellum (superior cerebellar peduncle) - Posterior (dorsal) - sends information about tendons (golgi tendon reflex) and muscle spindle (stretch sensors in skeletal muscles) to lower parts of cerebellum (inferior cerebellar peduncle)

______ pain is connective tissue pain from peritoneum, pleura, or pericardium

parietal

_____ pain is internal organ pain via autonomic nerve bundles

visceral

parietal pain is ______ localized, while visceral pain is _____ localized

highly; poorly

parietal pain has type ____ fibers, while visceral pain has type ___ fibers

A; C

Name two organs that don't have pain sensors

brain and liver

________ pain is pain felt in a part of the body that is fairly remote from the tissue causing the pain.

Referred

Name two examples of referred pain

- heart pain radiates down L arm - kidneys - lower back

Dual pain =

parietal + visceral pain

Why does the L arm have pain for heart ischemia?

Because L side of heart more prone to ischemia than R

How does a burst appendix have dual pain?

parietal = tissues surrounding appendix (sharp, stabbing pain from RLQ) - autonomic ganglia and ascends 2-3 levels, then enters cord visceral = felt in umbilical region (T10); pain fibers routed through sympathetic chain

What type of pain can't be suppressed by lateral inhibition? Why?

visceral - because not routed the same way as other pain

______ is the ease or difficulty of eliciting a painful feeling; the point at which someone identifies pain

pain threshold

Another name for lateral inhibition

pain of decompresison

Where does slow pain terminate in the brain?

slow pain projected to brain stem and end (reticular formation) or make it up further (but not to parietal lobe) → limbic system right above brainstem - amygdala

What are the 3 parts of the limbic system?

amygdala + hypthalamus + cingulate gyrus - deeper than fast pain

Where is the cingulate gyrus located?

outside of corpus callosum; part of cerebral cortex

if there's going to be one of these cerebral cortex structures that is connected to the slow pain system, it's going to be the _____

cingulate gyrus

What nerve fibers are a part of the more primitive, autonomic nervous system?

B and C fibers (less myelinated)

motor neurons are ____ fibers

A alpha

muscle spindles and tendons are ____ fibers

A alpha

The DCML pathway uses ____ fibers

A alpha - A gamma

lateral inhibition is ____ fibers

A beta

crude pain travels via ____ fibers

Order of sensing pain

pressure → sharp pain → dull, achy pain (probably worst long-term because of emotional response)

How does tramadol treat pain?

- SSRI - NMDA-R blocker not great for treating pain

What does kainate do?

mediate GABA

Lecture 13: Spinal cord internal structures Flashcards

Exam 3