Week 5 Lecture 12: Ascending Pathways Flashcards
What sensations is the spinothalamic pathway responsible for?
crude touch
pressure
pain
temperature
What sensations is the dorsal column medial lemniscus pathway responsible for?
proprioception discriminative touch vibration pressure (ipsilateral)
What is a dermatome?
a specific region of skin of the BODY innervated by the sensory fibres of a single segmental spinal nerve
How are sensory roots of specific spinal nerves affected in herpes zooster
- infection of the sensory roots of specific spinal nerves
- virus can remain dormant in specific sensory root of specific cranial nerve
- these dormant viral vesicles can then reactivate in later life as shingles
Which modalities are essential to survival and how are they conducted?
- pain and temperature
- some touch and pressure
- carried via thin, poorly myelinated or unmyelinated fibres
- conduction slow
Which modalities increase detail and how are they conducted?
- discriminative touch
- vibration
- proprioception
- carried via large diameter, heavily myelinated fibres
- fast conduction
What does ipsilateral mean?
occurring at same side of body
Explain the 3 neuron chain
- 1st neuron:
- pseudounipolar
- brings information from the receptor
- cell bodies located in the dorsal root ganglion - 2nd neuron:
- at the level of the spinal cord, the 1st neuron makes contact with the 2nd neuron
- the axon of the 2nd neuron crosses the midline and travels to the ventroposterior nuclei in the thalamus on the opposite side - 3rd neuron
- relays information from thalamus to primary sensory cortex
If information is coming from the body, where in the thalamus does it travel to?
VPL
If information is coming from the face, where in the thalamus does it travel to?
VPM
Which order neurones transfer info from the PNS to CNS and have their cell bodies in the peripheral ganglia?
first order neurone
Where do the cell bodies of 2nd order neurones reside?
CNS ipsilateral grey matter
Where do the cell bodies of 3rd order neurones reside?
in the thalamus
Explain the pathway in the spinothalamic tract? (5 steps)
- thin, slow fibre from receptor in periphery reaches 1st neurone with cell bodies in dorsal root ganglion
- sensory fibres enter the dorsal horn of the spinal cord by travelling through the Lissauer’s tract
- Fibres synapse with the 2nd order neurone in the dorsal grey horn
- crossing over of fibres of the 2nd order neurone occurs at the white ventral commissure
- 2nd order fibres ascend in spinothalamic tract to the opposite side of the thalamus
When fibres reach the thalamus, how are they organised?
somatotopically
- fibres containing information from the arm travel more medially
- fibres containing information from the legs travel more laterally
Which lamina is the substantial gelatinosa found in?
lamina II
Which modality is the substantia gelatinosa nucleus responsible for?
pain and temperature
Except from the substantia gelatinosa, which nuclei contain synapses from the spinothalamic tract?
- marginal zone (lamina I)
2. Nucleus proprius (lamina III and IV)
Why do different modalities travel through slightly different pathways? e.g different lamina
so we can differentiate whether the impulse is is pain, touch, pressure or temperature
At the level of the medulla, the spinothalamic tract changes name to what?
spinal lemniscus
Where in the post central gyrus are the fibres projected?
to the body region of the sensory homunculus
e.g if the fibres are coming from the hand, they will end in the hand region of the post central gyrus (somatotropin map)
What is a lamina?
a region of the dorsal grey horn that contains specific composition of cells
Explain the 3 neuron chain in the dorsal column medial lemniscus (6 steps)
- 1st order neuron brings information from the periphery of touch, vibration, proprioception and pressure to the cell body at the DRG
- Enters dorsal aspect of cord using lissauers tract but doesn’t synapse
- jumps out to join the white matter to ascend ipsilaterally in the cord
- 2nd order neurone send axon to midline at level of medulla and now ascending fibres travel through a region called the medial lemniscus
- if information comes from above T6, it will travel in the cuneate fascicle. if information travels in the gracile fascicle, it is from below T6
- travels to thalamus
- 3rd order neurones project to the post central gyrus
What do the gracile and cuneate fascicules contain?
axons
What do the gracile and cuneate tubercles contain?
cell bodies
In the DCML pathway, what are the fibres that cross the midline called?
internal arcuate fibres
How are the medial lemniscus fibres organised?
somatotopically
A 1st order neuron from the leg would travel through which fascicle?
gracile fascicle because it is below T6
What is meant by somatotopic mapping?
different areas of the body are perceived by specific regions on the post central gyrus
What does contralateral mean?
the side of the body opposite to that on which a particular structure or condition occurs
What is the difference between the spinothalamic pathway and the dorsal column medial lemniscus pathway?
Spinothalamic pathway:
- travel contra laterally in cord
- fibres cross at the level of spinal cord entry
Dorsal column medial lemniscus:
- travel ipsilaterally in cord
- cross at the level of the closed medulla
What is a diverging circuit?
if the first neuron is modified, the following neurone all become modified
What is a converging circuit?
many neurone have an input on one neuron
What structure do ascending sensory axons travel through on their way to the post central gyrus?
posterior limb of the internal capsule
What is thermoanaesthesia?
inability to feel changes in temperature
What is somatotopy?
the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex (postcentral gyrus).
Which cranial nerves carry general somatic sensation from the head?
CN V, VII, IX and X
Which cranial nerve is the major carrier of general sensory information from the face, nose, scalp and dura?
trigeminal , CN V
CN VII carries somatic sensation from which part of face?
external ear
CN VIII carries somatic sensation from which part of face?
posterior 1/3rd tongue
pharynx
middle ear
CN X carries somatic sensation from which part of face?
Auditory canal
larynx
pharynx
oesophagus
Which pathway does sensory information from the face travel in?
trigeminal sensory pathway
What is the association between cranial nerves and cranial nerve nuclei?
for each fibre type a cranial nerve has, there is a specific cranial nerve nuclei associated to it
What are the 4 trigeminal nuclei and where is each located?
- mesencephalic nucleus (in the midbrain)
- pontine/ chief sensory nucleus (in the pons)
- spinal nucleus (medulla)
- motor nucleus
Where are all first order cranial nerve neuron cell bodies found? (with one exception)
in the trigeminal ganglion
(instead of a dorsal root ganglion for dorsal root nerves)
so cell bodies from V1, V2 and V3 go through the trigeminal ganglion
Which sensory nucleus is associated with proprioception?
mesencephalic nucleus (this pathway is an exception to the generalisation that 1st order cell bodies are in the peripheral ganglia)
Which sensory nucleus is associated with discriminative touch?
pontine nucleus
Which sensory nucleus is associated with simple touch and pressure?
rostral part of spinal nucleus
Which sensory nucleus is associated with pain and temperature?
caudal part of spinal nucleus
Pain and temperature fibres that travel through the spinal tract of the trigeminal travel to which part of the thalamus?
VPM (because from face)
Explain the pathway for pain and temperature fibres in the face (5 steps)
- 1st order neuron travels through trigeminal ganglion
- 1st order fibres run caudally in spinal tract of trigeminal
- fibres synapse with 2nd order neurones in caudal spinal nucleus
- 2nd order axons cross and ascend in trigeminothalamic tract
- ascend to VPM of thalamus
What is the difference between the pathway for pain and temperature, and the pathway for crude touch and pressure?
Same process but the 1st order neurones from crude touch and pressure reach the rostral part of the spinal nucleus (not the caudal)
Where are the 1st order neurone cell bodies in the proprioception pathway?
in the mesencephalic nucleus (not in the trigeminal ganglion)
