Lecture 9: Somatosensory Pathways Part 1 Flashcards
What information does the PCML and trigeminothalamic pathway transmit?
Discriminative Touch
Pressure
Vibration
Proprioception
What is two point discrimination?
Ability to discriminate between two stimuli simultaneously
What areas would have high density of tactile receptors?
Digits
Perioral region
What areas would have low density of tactile receptors?
Back
Small receptive fields have ____ receptor density.
Large receptive fields have ____ receptor density.
Small receptive fields have HIGH receptor density.
Large receptive fields have LOW receptor density.
What type of axons are primary afferent fibers?
Sensory
Where do primary afferent fibers have their cell bodies?
Dorsal Root Ganglion
In the PCML pathway, where do primary afferent fibers enter the spinal cord?
Medial division of posterior root
In the PCML pathway, where do primary afferent fibers go after entering the spinal cord?
Posterior Columns: Fasciculus Gracilis and Cuneatus
Where is Fasciculus Gracilis found?
Sacral Region to T6
Where is Fasciculus Cuneatus found?
T6 and above
Which fibers are found more medially?
Sacral and the more rostral you go, the more lateral those fibers are found
What supplies the posterior columns?
Posterior Spinal Artery
If the PCML pathway is affected from a spinal cord lesion, what can happen?
Ipsilateral reduction or loss of discriminative, positional, and vibratory tactile sensations
Will happen at and below level of injury
What is sensory ataxia?
Loss of muscle tendon reflex and proprioceptive losses from extremities due to lack of sensory input
Can lead to difficulty walking and wide based stance
In the PCML pathway, where are 2nd order neurons found?
Gracile and Cuneate Nuclei in the posterior medulla
Where are the gracile and cuneate nuclei receiving their input from?
First order neurons (primary afferents) from ipsilateral dorsal root ganglion
What are internal arcuate fibers?
After synapsing at the gracile and cuneate nuclei, they are the fibers that cross anteromedially in the medulla
What is medial lemniscus?
The new name of the fibers after they cross at the medulla until they terminate
In the medial lemniscus, where do the upper and lower extremity fibers now reside after the rotation in the pons?
Upper: Medial
Lower: Lateral
Where does the medial lemniscus terminate?
Ventral Posterolateral Nucleus of the Thalamus
What supplies the medial lemniscus?
Anterior Spinal Artery
What supplies the Ventral Posterolateral Nucleus of the Thalamus?
Thalamogeniculate Branches of Posterior Cerebral Artery
From the Ventral Posterolateral Nucleus of the Thalamus, where do the third order neurons go to?
Primary and Secondary Somatosensory Cortices
How do third third order neurons reach the somatosensory cortices?
Via Posterior Limb of Internal Capsule
What compromises the Primary Somatosensory Cortex (S1)?
Postcentral gyrus and Posterior Paracentral Gyrus
What are the Brodmann Areas of the Primary Somatosensory Cortex?
31, 3b, 1, and 2
If there is a lesion to the Middle Cerebral Artery, where would there be tactile loss?
Contralateral upper body and face
If there is a lesion to the Anterior Cerebral Artery, where would there be tactile loss?
Contralateral lower limb
What does the secondary somatosensory cortex sense?
Inner face
Where does secondary somatosensory cortex gets its input from?
Ipsilateral SI cortex and Ventral Posterior Inferior Nucleus of the Thalamus
What happens if the parietal cortical region is lesioned?
Agnosia: cannot recognize own limb
What is the role the mesencephalic nucleus?
Conveys unconscious proprioceptive afferents and pressure afferents from TMJ, masticatory, and extraocular muscles
What is the role the principal/chief sensory nucleus?
Discriminative touch and pressure from face
What is the role the spinal nucleus?
Pain, temperature, and non-discriminative touch from face
In the Sensory Trigeminothalamic Pathway, where are primary afferents from?
Trigeminal Ganglion
In the Sensory Trigeminothalamic Pathway, where are 2nd order neurons found?
Principal/Chief Sensory Nucleus
What supplies the Principal/Chief Sensory Nucleus?
Superior Cerebellar Artery
Long Circumferential branches of Basilar Artery
What are the two divisions of the principal/chief sensory nucleus and what do they receive information from?
Dorsomedial: Oral Cavity
Ventrolateral: V1, V2, V3
How does the dorsomedial division reach the thalamus?
Travels ipsilaterally via posterior trigeminothalamic tract to
How does the ventrolateral division reach the thalamus?
Travels contralaterally via anterior trigeminothalamic tract
Where do both anterior and posterior trigeminothalamic tracts synapse at?
Ventral Posteromedial Nucleus of the Thalamus
- Oral Cavity: Medial part of nucleus
- External Face: Lateral part of nucleus
From the Ventral Posteromedial Nucleus of the Thalamus, where do the third order neurons go to?
Primary somatosensory nucleus via posterior limb of internal capsule
What reflex is initiated when there is a downward tap on the chin?
Jaw-Jaw Reflex: Stretching of masseter muscle causes it to contract bilaterally
What is the pathway of a jaw-jaw reflex?
- Innervation of Mesencephalic Trigeminal Neuron
- Innervation of masseter muscle spindle
- Synapse on trigeminal motor neuron
