Lecture 26- Ascending Sensory Pathways Flashcards
What are the two ascending pathways?
- Dorsal column-medial lemniscus system
- Spinothalamic (or anterolateral) system
What two types of information does the Dorsal column-medial lemniscus pathway carry?
- Fine touch
- Proprioception-Position of the body in space
What does the Spinothalamic pathway include?
Pain, temperature, and pressure
What is a tract?
Bundle of conductile regions (axons) in the CNS
What does the first syllable of the pathway name tell you?
Where the input regions are
EX: Spinothalamic- input regions are in the spinal cord
What does the second syllable of the pathway name tell you?
Where the output regions are
EX: Spinothalamic- output regions are in the thalamus
What is the first rule that applies to both the DCML and Spinothalamic tract?
Contains three neurons
(Primary sensory, second order neuron, and third order neuron)
What type of neuron NEVER crosses the midline?
Primary sensory neuron
What type of neuron ALWAYS crosses the midline?
Second order neurons
What type of neuron ALWAYS has its input region in the thalamus and output regions in the cerebral cortex?
Third order neurons
In third order neurons where is the input and output regions ALWAYS located?
Input regions- thalamus
Output regions- cerebral cortex
What does gray and white matter contain?
Gray matter- input/output regions AND Ventral/Dorsal Horns
White matter- Conductile regions AND every other structure
What is a nerve?
Bundle of conductile regions (axons) in the PNS
What type of neurotransmitter is released to inhibit hamstring contraction?
Glycine
What is the posterior column of white matter?
Bundle of conductile regions of primary sensory afferents which carry information about fine touch/proprioception
Where does the first order neuron ascend and synapse onto in PCML?
Ascends up the spinal cord and synapses onto 2nd order in the posterior column nucleus in brain stem
Note: this is on the same side as sensory stimulus bc 1st order can’t cross midline
In PCML 2nd order neurons receive input from primary sensory neurons and cross the midline at the ______ _______
Medial Lemniscus in Dorsal column-medial lemniscus pathway
Where do 2nd order neurons synapse in PCML?
Synapse onto 3rd order neurons in the thalamic relay nucleus (OPPOSITE side as stimulus) which is located in the thalamus
Where would sensory input on the left side of the body end up in a PCML pathway?
Right side of the cerebral cortex
In the Spinothalamic tract, where does primary sensory afferent neuron immediately synapse onto?
Synapses onto the 2nd order in the dorsal horn of the spinal cord on the SAME side as the sensory stimulus
In the spinothalamic tract, where does the 2nd order neuron cross over to?
Crosses midline at the spinal cord segment to the spinothalamic tract
In the spinothalamic tract, what do the 2nd order neurons synapse onto?
2nd order synapses onto 3rd order in the thalamic relay nucleus (OPPOSITE side as stimulus)
In the spinothalamic tract, what do the 3rd order neurons synapse onto?
3rd order synapses onto the somatosensory cortex (OPPOSITE side as stimulus)
What distinguishes the PCML and Spinothalamic tracts?
In the PCML pathway, the primary sensory neuron is originally in the Ventral Horn and must go up the brain stem before synapsing on the 2nd order neuron
In the ST pathway, the primary sensory neuron immediately synapses on the 2nd order neuron, 2nd order neuron crosses midline and then ascends up to brain stem
What is Brown Sequard Syndrome?
Rare neurological condition where ascending pathways that carry sensory information can be partially impaired or completely impaired as a result of spinal cord lesions
In Brown Sequard Syndrome, if there is a lesion in the left proprioceptor, will a signal go to the brain?
NO, because PCML must travel up the brainstem before synapsing onto the 2nd order neuron
In Brown Sequard Syndrome, if there is a lesion in the right pain receptor, will you feel pain?
YES, you will feel pain on the opposite (left) side because the 2nd order neuron crosses over and then ascends up to the brain stem
