06_Ascending Sensory Pathways of the Spinal Cord and Brainstem Flashcards
What are the eight ascending sensory pathways of the spinal cord and brainstem?
- DCML - Dorsal column medial lemniscal pathway
- Trigeminal lemniscal pathway
- (Lateral) Spinothalamic tract
- Trigeminothalamic tract
- DSCT - Dorsal Spinocerebellar tract
- SCCT - Spinocuneocerebellar tract
- VSCT - Ventral spinocerebellar tract
- RSCT - Rostral spinocerebellar tract
What sensations do DCML and Trigeminal lemniscal carry?
DCML - Discriminative tactile sensations from the body
Trigem Lemniscal - Discriminative tactile sensations from the face
What are the five discriminative tactile sensations?
DCML and Trigeminal lemniscal pathways
- Discriminative touch
- Two-point discrimination
- Vibration
- Kinesthesis (aware of movements of legs/arms)
- Sterognosis (recognition via texture, size, spatial, and temp)
DCML
- Neuronal pathway, including decussation
1st Order: Dorsal root ganglia
2nd Order: Nucleus gracilis (LE) and nucleus cuneatus (UE) - ascend as Medial lemniscus
Decussation - internal arcuate fibers (medial lemniscus) at medulla midline
3rd Order: VPL in thalamus
Destination: Primary somatosensory tract via corona radiata
DCML and Trigeminal leminscal
- Afferent input
A-beta afferents
Trigeminal leminscal
- Neuronal pathway, including decussation
1st Order: Trigeminal ganglion in Pons
2nd Order: Main sensory nucleus (Trigeminal leminscus)
Decussation - Main sensory nucleus neurons at Pons
3rd Order: VPM in thalamus
Destination: Primary somatosensory tract via corona radiata
What sensations do (lateral) Spinothalamic tract and Trigeminothalamic tract carry?
(lateral) Spinothalamic tract - Pain, temp, and crude touch from body
Trigeminalthalamic tract - Pain, temp, and crude touch from face
(lateral) Spinothalamic tract
- Neuronal pathway, including decussation
1st Order: Dorsal root ganglia (A-delta and C afferents) via lateral regions of Lissauer’s tract
2nd Order: Substantia gelatinosa of Rexed’s lamina II
Decussation: Spinothalamic tract ascends 1-2 levels and crosses @ anterior white commissure
3rd Order: VPL in thalamus
Destination: Primary somatosensory tract via corona radiata
Some fibers of the spinothalamic tract terminate in the “brainstem reticular formation”. What are these fibers named?
Spinoreticular tract fibers
Trigeminothalamic tract
- Neuronal pathway, including decussation and destination
1st Order: Trigeminal ganglion (A-delta and C afferents)
Descend ipsilaterally
2nd Order: Spinal nucleus of trigeminal nerve (trigeminal leminscus)
Decussation: Medulla
3rd Order: VPM in thalamus
Destionation: Primary somatosensory tract via corona radiata
DSCT (Dorsal spinocerebellar tract)
SCCT (Spinocuneocerebellar tract)
- Sensations carried
DSCT - Subconscious proprioception of LE and trunk
SCCT - Subconscious proprioception of UE
(Fine coordination of posture and movement)
DSCT
- Neuronal pathway, including decussation and destination
1st Order: DRG (Group Ia, II and Ib)
2nd Order: Clark’s column in dorsal horn T6 and below - also alpha motor neurons directly
Destination: Cerebellum (via Inferior cerebellar peduncle)
No decussation, ipsilateral
SCCT
- Neuronal pathway, including decussation and destination
1st Order: DRG (Group Ia, II, and Ib)
2nd Order: Cuneate nucleus
Destination: Cerebellum (via Inferior cerebellar peduncle)
VSCT (Ventral spinocerebellar tract)
RSCT (Rostral spinocerebellar tract)
- Sensations carried
VSCT - Info about descending motor signals to thorax and lumbar SC to cerebellum
RSCT - Info about descending motor signals to cervical SC to cerebellum
VSCT
- Neuronal pathway, including decussation and destination
1st order: diffuse neurons in Lamina V, VI, and VII of thorax and lumbar SC
Decussation: Anterior white commissure
Destination: Superior cerebellar peduncle (bilateral)
RSCT
- Neuronal pathway, including decussation and destination
1st Order: diffuse neurons in Lamina V, VI, and VII of cervical SC
No decussation
Destination: Ipsilateral cerebellum via Superior and Inferior cerebellar peduncles
What is a reflex?
Involuntary, stereotyped response to a sensory input
Most reflexes involve what structures?
- A receptor
- Afferent neuron
- Efferent neuron
Why does the stretch reflex represent the simplest segmental reflex?
Only two neurons (afferent and efferent)
Most neurons involve one or more interneurons, whereas stretch reflect is monosynaptic
What are other names for the stretch reflex?
A. Knee jerk reflex (patellar tendon)
B. Deep tendon reflex (DTR)
C. Myotatic reflex
D. Ia monosynaptic reflex
Stretch reflex
- Mechanism
- What afferent neurons?
- What gets excited?
- What contracts?
A muscle stretch activates Ia (and Group II) afferents of the muscle spindle.
This activation monosynaptically excites alpha motor neurons, causing contraction of the muscle in which the muscle spindle lies (i.e. homonymous muscle).
What proprioceptor is notably not involved in the stretch reflex?
Golgi tendon organs are not involved
