Lecture 13: Spinal cord internal structures Flashcards
Exam 3
a bundle of axons within the CNS
Tract
a bundle of axons within the PNS
Nerve
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
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
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
Which spinal tract is responsible for pain? Where is it located in the cord?
Spinothalamic Tract(s)/anterolateral system - front/sides of cord
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
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
How is the grey matter in the cord divided?
Rexed’s Laminae: numbered back to front, 10 in total
Lamina I
Lamina Marginalis
- Sharp Pain - fast pain
- Aδ Pain - myelinated nociceptors (a delta fibers)
Laminae II & III
Substantia Gelatinosa - also sometimes lamina V
- Slow Pain
- C-Fibers - non-myelinated nociceptors
Which lamina are mechanoreceptors?
Laminae I→ VI
Lamina VII
Intermediolateral Nucleus
- Lateral Grey Horn
Laminae VIII → IX
Lots of large motor neurons that hang out in the anterior horn of grey matter in the cord - descending
_______ 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
_______ 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
Efferent vs afferent
Afferent is sensory, going up to brain
Efferent is motor
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
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)
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
What is the name of the parietal lobe, post-central gyrus - topographical layout?
Homunculus
Which areas of the homunculus take up the most space? Describe where they are located
Hands (middle) and face (lateral)
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
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
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?
- Ionotropic: AMPA-R, NDMA-R, kainate
- 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
C
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
