ascending tracts

conduit function of the brainstem

information is transmitted bidirectionally between the spinal cord and the cerebral cortex in the brainstem

ascending pathways

carry sensory information from the periphery to the CNS

1st order neuron of ascending pathways

located in a peripheral ganglion (ex. dorsal root ganglion or cranial nerve ganglion)

2nd order neuron of ascending pathways

neurons in brainstem that give rise to new tracts

dorsal column-medial lemniscus 

spinothalamic tract

two types of ascending tract 

dorsal column - medial lemniscus

transmit general sensory information - touch, pressure, vibration, fine form and texture

• 2 separate tracts

• axons are large and heavily myelinated = fast conduction rate

• low threshold

fasiculus gracilus

input from lower limb and trunk form this bundle of axons

fasiculus cuneatus 

input from upper limb and trunk form this bundle of axons 

dorsal root ganglion

dorsal root

ipsilateral dorsal column

ipsilateral nucleus gracilus 

nucleus cuneatus

caudal medulla 

1st order neuron in dorsal column-medial lemniscus tract

• primary afferent/sensory axons enter via BLANK BLANK to enter the BLANK BLANK BLANK

• ascend and synapse on neurons in BLANK BLANK BLANK and BLANK BLANK in the BLANK BLANL

nucleus gracilus and nucleus cuneatus

caudal medulla

midline

medial lemniscus 

2nd order neuron in dorsal column-medial lemniscus tract; located in BLANK BLANK

• axons arising from these nuclei cross the BLANK and form the BLANK BLANK 

ventral posterior lateral nucleus

primary sensory cortex

3rd order neuron in dorsal column-medial lemniscus pathway

• axons arising from this nucleus project to the BLANK BLANK BLANK

medial lemniscus in rostral medulla

remains as a vertical column in the tegmentum immediately adjacent to the midline as it ascends through the medulla

medial lemniscus in mid-pons

as vental brainstem expands to form the basilar pons, the tegmentum and the medial lemniscus get pushed back and assume horizontal position

mid-pons

where the MAIN SENSORY NUCLEUS is located!

trigeminal ganglion

1st order neurons of medial lemniscus tract (trigeminal portion)

main sensory nucleus

face

midline

pons

ventral posterior medial

2nd order neurons of the medial lemniscus tract (trigeminal portion)

axons from the BLANK BLANK BLANK carry general sensory information of the BLANK

• cross the BLANK and join the medial lemnicus in the BLANK

• axons terminate in the BLANK BLANK BLANK nucleus

medial lemniscus in midbrain

moves slightly more laterally and dorsally in the tegmentum

ventral posterior lateral

ventral posterior medial

internal capsule

3rd order neurons of the dorsal column-medial lemniscus pathway 

• VPL = body

• VPM = face 

course through the BLANK BLANK as they project to the pareital lobe as thalamo-cortical axons

layer 4 of neocortex

primary sensory cortex

input from the thalamus carrying specific sensory information terminates in BLANK BLANK BLANK BLANK ; this layer is BIG in the BLANK BLANK BLANK/post-central gyrus

anterolateral system

multiple tracts that convey different aspects of pain

spinothalamic tract

part of the anterolateral system, conscious awareness of nature and intensity of a painful stimulus and where it is located - also conveys temperature

• small diameter and lightly myelinated = high threshold, and slow conduction rate

dorsal root ganglion

dorsal root

dorsal horn

1st order neuron of spinothalamic tract

• primary afferent/sensory neurons enter the spinal cord via the BLANK BLANK and synapse of 2nd order neurons in the BLANK BLANK 

dorsal horn

midline

spinal cord

2nd order neurons of the spinothalamic tract

• axons cross the BLANK and form the spinothalamic tract in the anterior white matter of the BLANK BLANK

ventral posterior lateral nucleus

sensory

insular 

3rd order neurons of the spinothalmic tract

• axons arising from here project to the primary BLANK cortex and the BLANK cortex 

lower limb

lateral

upper limb

spinothalamic tract

inpur from the BLANK BLANK are pushed BLANK as input from the trunk and BLANK BLANK are added in the BLANK BLANK

spinothalamic tract and medulla

tract moves dorsally and in the rostral medulla, the tract is dorsal to the inferior olivary nucleus

• not as distinct in the cross-section because the axons are small in diamete and lightly myelinated

trigeminal ganglion

pons

medulla

spinal nucelus of V

1st order neurons of the spinothalamic tract (trigeminal/face component)

• axons enter the BLANK and descend to the BLANK and synapse onto 2nd order neurons in the BLANK BLANK BLANK BLANK

spinal nucleus of V

midline

2nd order neurons of spinothalamic tract (trigeminal/face component)

• axons cross the BLANK and join the spinothalamic tract 

ventral posterior medial

sensory

insular

3rd order neuron of spinothalamic tract (trigeminal/face component)

• project to appropriate areas of the primary BLANK cortex and BLANK cortex

spinothalamic tract in pons

shifted dorsally by the expansion of the basilar pons; lateral to the medial lemniscus

spinothalamic tract in midbrain

shifted more dorsally as cerebral peduncle replaces basilar pons