Ascending and Descending Pathways Flashcards
What is the term for when a neuron which crosses over the midline of the spinal cord?
Axonal decussation
How many neurons are involved in the spine-thalamic pathway?
X3
What type of sensory information does the spinal-thalamic pathway carry?
Pain, temperature, light touch
Where does the first order neuron of the spino-thalamic pathway enter the spinal cord?
Via the dorsal root into the dorsal horn
Where does the first order neuron synapse with the second order neuron in the spino-thalamic pathway?
In the dorsal horn of the spinal cord
What happens to the second order neuron in the spino-thalamic pathway?
It undergoes axonal decussation and also travels centrally into the spine-thalami tract, which from here ascends to the thalamus
Where do the second and third order neurons in the spinal-thalami tract synapse?
In the thalamus
Where is the soma for the third order neuron of the spino-thalamic pathway?
In the VPL, ventro-posterior lateral nucleus of the thalamus
Which tract does the 3rd order neuron in the spino-thalami pathway use to reach the somatosensory cortex?
The thalamo-cortical tract
Where is the 3rd synapse in the cortico-spinal pathway?
It is the 3rd order neuron synapsing in the somatosensory cortex.
What sensory information does the dorsal column - medial lemniscus pathway carry?
Touch, proprioception and vibrations
What is the name of the X2 tracts which relay sensory information from different levels of the the body in the dorsal column - medial lemniscus pathway?
The gracile and cuneate tracts
Where does the gracile tract relay information from?
Where does this sit in relation to the cuneate fascicles in the dorsal horn?
It relays information from below T6
It sits in the dorsal horn, medially to the cuneate fascicles
Where does the cuneate tract relay information from?
Where does this sit in relation to the gracile fascicles in the dorsal horn?
It relays information from above T6
It sits in the dorsal horn, laterally to the cuneate fascicles
Where is the soma of the first order neuron of the dorsal column - medial lemniscus pathway?
In the dorsal root ganglia
What is the journey of the first order neuron in the dorsal column - medial lemniscus pathway?
It travels into the dorsal horn and into either the gracile or cuneate fascicles (depending on level of entry) and ascends in these dorsal columns until it reaches the gracile/cuneate nucleus in the medulla
Where do the first and second order neurons in the dorsal column - medial lemniscus pathway synapse?
In the gracile/cuneate nucleus of the medulla
Where is the soma of the second order neuron in the dorsal column - medial lemniscus pathway?
In the medulla
What happens to the second order neuron in the dorsal column - medial lemniscus pathway?
It undergoes axonal decussation and also travels ventrally into a tract called the medial lemniscus. It ascends via this tract into the thalamus where it synapses with the third order neuron of the pathway.
Where is the soma of the third order neuron of the dorsal column - medial lemniscus pathway?
In the VPL of the thalamus
What tract does the third order neuron of the dorsal column - medial lemniscus pathway use to ascend to the somatosensory cortex?
The thalamo-cortical tract
Where is the third synapse in the dorsal column - medial lemniscus pathway?
At the somatosensory cortex involving the third order neuron
What type of pathway is the cortical-spinal pathway?
A descending pathway
How many neurons are involved in the cortical-spinal pathway?
X2
What information does the cortical-spinal pathway carry?
Somatic motor command
Where is the soma of the first order neuron in the cortical-spinal pathway?
In the primary motor cortex, located in the frontal lobe just in front of the central sulcus.
Where does the first order neuron in the cortical-spinal pathway terminate?
At a level close to that of its target motor neuron
85% of axons in the cortical-spinal pathway undergo axonal decussation at which level?
What is this type of decussation called?
What type of cortical-spinal tract do these axons form?
In the pyramids of the ventral medulla
This is called pyramidal decussation
They form the LATERAL cortical-spinal tract
15% of axons in the cortical-spinal pathway undergo axonal decussation at which level?
What type of cortical-spinal tract do these axons form?
They decussate at a level close to where they terminate
They form the ANTERIOR/VENTRAL cortico-spinal tract
Where is the soma of the second order neuron in the cortico-spinal pathway?
It is in the ventral horn of the CNS at the level at which it is exiting the CNS, as it is a motor neuron.
Which ascending pathway is fast and which is slow conducting?
Spino-thalamic = slow conducting
Dorsal column - medial lemniscus = fast conducting
How many neurons are involved in the dorsal column - medial lemniscus pathway?
X3
