Lecture 4a-ascending pathways 2

Question 1

what are the 3 kinds of connections that afferent info makes?

Answer 1

1. local reflex connections
2. connections destined for the cerebral cortex (perception)
3. connections destined for the cerebellum (position of joints, etc)

Question 2

what is the spinocerebellar circuitry involved in

Answer 2

pathways for fine coordination of posture, movement of limbs, muscle tone

Question 3

proprioceptive inputs to the cerebellum are ____

• inputs to the cerebellum are usually ______
• enter cerebellum via _____ or _____

Answer 3

unconscious
uncrossed
inf cerebellar peduncle or inf olive

Question 4

the dorsal spinocerebellar tract has unconscious proprioception and tells the ______ cerebellum ONly about what?

Answer 4

ipsilateral

lower body position

Question 5

the pathway “unconscious proprioception from the lower extremities” is a 2-neuron system. what is the main tract and what is the other tract called

Answer 5

main tract is the dorsal spinocerebellar tract

cuneocerebellar tract

Question 6

do somatosensory pathways from the periphery to the cerebellum pass through the thalamus? how many neurons does it involve

Answer 6

NO.

2

Question 7

where does the dorsal spinocerebellar tract start

Answer 7

at clarke’s nucleus located only in T1-L3 (prominent at lower thoracic/upper lumbar lvls)

Question 8

when propeioceptive leg info enters T1-L3, what happens

Answer 8

unconscious proprioceptive info from the legs enters and synapses right away on clarke’s
-fibers leaving clarke’s find the dorsolatreal funiculus of white in the cord and rise as the DSCT

Question 9

what happens if you have proprioceptive leg info entering below L3?

Answer 9

you have to rise to find a clarke’s to synapse on.

• hitch a ride on the dorsal columns (only fasc gracilis down there) until it sees a clarke’s nucleus
• then those fibers can happily leave FG and synpase on clarke’s
• then rise as the dorsal spinocerebellar tract

Question 10

the dorsal columns below L3 (FG below L3) carry what

Answer 10

both types of proprioceptive info-conscious and unconscious

Question 11

why is clarke’s so prominent at low thoracic levels

Answer 11

all the lower lumbar info wa waiting for it first chance to synapse

Question 12

what does the spinocerebellar tract enter the cerebellum via?

Answer 12

inferior cerebellar peduncle

Question 13

when proprioceptive info comes into the cord from the lower extremeities, it can:

Answer 13

1. participate in local reflexes
2. send info up fasc. gracilis to thalamus and then to somatosensory cortex (conscious)
3. send info to clarke’s nucleus to eventually get to cerebellum (unconscious)

Question 14

what is ataxia

Answer 14

lesions resulting in uncoordinated movement

clinically tested by heel to shin test for lower extremeites and finger to nose for upper w/ pt eyes closed

Question 15

where is the lesion located in ataxia

Answer 15

since the pathway is uncrossed, the ataxia is ipsilateral to the lesion

Question 16

theoretically:
- a lesion in the SCBT reults in….
- a lesion in the dorsal spinocerebellar tract below L3 (dorsal columns) affects what

clinically:

Answer 16

• loss of unconscous proprioception giving ipsilateral postural incoordination
• both conscious and unconscious proprioception, ipsilaterally from below that level on down

-lesions of this tract dont occur in isolation and are instead often masked by the effects of its neighbor, the coricospinal tract

Question 17

what is the cuneocerebellar tract

why does this pathway excist

Answer 17

unconscious proprioception from the upper extremity (C5-T1) from the UPPER extremities via fasciculus cuneatus

-this pathway exists bc clarke’s nucleus doesnt exist above T1

Question 18

the accessory cuneate nucleus doesn’t appear until waht

Answer 18

the medulla

-it is the homologue to clarke’s nucleus

Question 19

what happens in the cuneocerebellar tract (C5-T1)

Answer 19

1. proprioceptive info from the upper extremities coming into the cord has to hitch a ride w/ fasci. cuneatus
2. proprioceptive info rises here int he dorsal columns until finding the accessory cuneate nucleus to synapse on
   (nucleus located right next to nucleus cuneuatus of the DCML pathway)
3. rises as the cuneocerebellar tract
4. enters the cerebellum through the inf cerebellar peduncle alongise the DSCT

Question 20

fasc. cuneatus from C5-T1 contains both kinds of proprioceptive info, what are they

Answer 20

1. destined for conscious perception (travels to thalamus and then cortex via DCML pathway)
2. unconscious cerebellar cirucuits