Lecture 26- Ascending Sensory Pathways

Question 1

What are the two ascending pathways?

Answer 1

1. Dorsal column-medial lemniscus system
2. Spinothalamic (or anterolateral) system

Question 2

What two types of information does the Dorsal column-medial lemniscus pathway carry?

Answer 2

1. Fine touch
2. Proprioception-Position of the body in space

Question 3

What does the Spinothalamic pathway include?

Answer 3

Pain, temperature, and pressure

Question 4

What is a tract?

Answer 4

Bundle of conductile regions (axons) in the CNS

Question 5

What does the first syllable of the pathway name tell you?

Answer 5

Where the input regions are

EX: Spinothalamic- input regions are in the spinal cord

Question 6

What does the second syllable of the pathway name tell you?

Answer 6

Where the output regions are

EX: Spinothalamic- output regions are in the thalamus

Question 7

What is the first rule that applies to both the DCML and Spinothalamic tract?

Answer 7

Contains three neurons

(Primary sensory, second order neuron, and third order neuron)

Question 8

What type of neuron NEVER crosses the midline?

Answer 8

Primary sensory neuron

Question 9

What type of neuron ALWAYS crosses the midline?

Answer 9

Second order neurons

Question 10

What type of neuron ALWAYS has its input region in the thalamus and output regions in the cerebral cortex?

Answer 10

Third order neurons

Question 11

In third order neurons where is the input and output regions ALWAYS located?

Answer 11

Input regions- thalamus
Output regions- cerebral cortex

Question 12

What does gray and white matter contain?

Answer 12

Gray matter- input/output regions AND Ventral/Dorsal Horns

White matter- Conductile regions AND every other structure

Question 13

What is a nerve?

Answer 13

Bundle of conductile regions (axons) in the PNS

Question 14

What type of neurotransmitter is released to inhibit hamstring contraction?

Answer 14

Glycine

Question 15

What is the posterior column of white matter?

Answer 15

Bundle of conductile regions of primary sensory afferents which carry information about fine touch/proprioception

Question 16

Where does the first order neuron ascend and synapse onto in PCML?

Answer 16

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

Question 17

In PCML 2nd order neurons receive input from primary sensory neurons and cross the midline at the ______ _______

Answer 17

Medial Lemniscus in Dorsal column-medial lemniscus pathway

Question 18

Where do 2nd order neurons synapse in PCML?

Answer 18

Synapse onto 3rd order neurons in the thalamic relay nucleus (OPPOSITE side as stimulus) which is located in the thalamus

Question 19

Where would sensory input on the left side of the body end up in a PCML pathway?

Answer 19

Right side of the cerebral cortex

Question 20

In the Spinothalamic tract, where does primary sensory afferent neuron immediately synapse onto?

Answer 20

Synapses onto the 2nd order in the dorsal horn of the spinal cord on the SAME side as the sensory stimulus

Question 21

In the spinothalamic tract, where does the 2nd order neuron cross over to?

Answer 21

Crosses midline at the spinal cord segment to the spinothalamic tract

Question 22

In the spinothalamic tract, what do the 2nd order neurons synapse onto?

Answer 22

2nd order synapses onto 3rd order in the thalamic relay nucleus (OPPOSITE side as stimulus)

Question 23

In the spinothalamic tract, what do the 3rd order neurons synapse onto?

Answer 23

3rd order synapses onto the somatosensory cortex (OPPOSITE side as stimulus)

Question 24

What distinguishes the PCML and Spinothalamic tracts?

Answer 24

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

Question 25

What is Brown Sequard Syndrome?

Answer 25

Rare neurological condition where ascending pathways that carry sensory information can be partially impaired or completely impaired as a result of spinal cord lesions

Question 26

In Brown Sequard Syndrome, if there is a lesion in the left proprioceptor, will a signal go to the brain?

Answer 26

NO, because PCML must travel up the brainstem before synapsing onto the 2nd order neuron

Question 27

In Brown Sequard Syndrome, if there is a lesion in the right pain receptor, will you feel pain?

Answer 27

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