Tracts Flashcards
1
Q
Lemniscal Tract (Dorsal or Posterior Columns)
A
- Ascending
- Large afferent skin/muscle fibers (proprioception) + fine touch
- Somatotopic Organization
- Lower limbs = medial (gracile fascicle —> gracile nucleus in caudal medulla)
- Upper limbs = lateral (cuneate fascicle —> cuneate nucleus in caudal medulla)
- **As you move up brainstem - flips - lower limbs lateral and upper limbs medial
- Path - dorsal root —> fascicle —> nucleus in caudal medulla —> cross over at caudal medulla (“lemniscal decussation”) —> VPL in thalamus —> somatosensory cortex (3,1,2)
- Ipsalateral in SC - then contralateral after crossing in medulla
2
Q
Spinothalamic Tract
A
- Ascending
- Small afferents (pain, temp, corse touch)
- Cross over right away in SC itself (anterolateral part of SC)
- Somatotopic Organization
- Lower limbs = lateral
- Upper limbs = medial
- Path - ascend/descend a few levels in spine via Lissauer’s tract —> synapse in gray matter (substantial gelatinous and nucleus proprius) —> cross over in SC itself —> VPL thalamus —> somatosensory (pain) and lambic system (emotion of pain)
3
Q
Dorsal Spinocerebellar Tract
A
- Ascending
- Function = give proprioceptive info to cerebellum
- Leg info …Clark’s nucleus (T1-L3) —> up thru posterior/lateral white matter —>thru inferior cerebellar peduncle —> cerebellum
- Arm info…accessory cuneate nucleus (in caudal medulla)
- CEREBELLUM = IPSALATERAL
4
Q
Ventral Spinocerebellar Tract
A
- Get integrated info from intermediate zone interneurons of thoracic and lumbar SC
- Proprioception mixed w/ descending motor commands from pre-motor neurons
- Cross over in SC then RECROSS b/f reaching cerebellum so… CEREBELLUM = IPSILATERAL
- Path - axons from interneurons cross to other side in SC —> ascend ventrally near spinothalamic neurons —> join superior cerebellar peduncle
5
Q
Corticospinal Tracts (2)
A
AKA PYRAMIDAL
- Descending
- Voluntary movement
- Originate in 4, 3/2/1, and 6 in cortex —> SC
- Cross over in caudal medulla (pyramids)
- Path - 4,6,321 in cortex —> corona radiata —> internal capsule —> cerebral peduncles —> along ventral pons —> pyramids (CROSS) —> terminated on motoneurons in SC
- Somatotopic
- In motor cortex - legs are medial and arms lateral
- In internal capsule - legs posterior and arms anterior
- In peduncles and SC - legs lateral and arms medial
- 90% is lateral and 10% anterior (mainly axial muscles)
- Lateral - maintains somatotopic map (lower limbs lateral/upper limbs medial); CONTRALATERAL; distal muscles
- Anterior - ipsilateral; axial muscles
6
Q
Extrapyramidal Tracts (4)
A
ALL DESCENDING
- 1- Rubrospinal path - regulate upper body flexion muscles; not important in humans
- 2- Vestibulospinal tract -
- Medial - neck stability
- Lateral - keep upright/balance by moving limbs
- 3- Reticulospinal tract -
- Similar function to vestibulospinal tract (posture control)
- 4- Tectospinal tract -
- Function = coordinated eye-head movements (move head in response to sensory input)
7
Q
Brown-Dequard Syndrome
A
damage to only 1/2 SC (hemisection)
- Ipsilateral loss of proprioception, fine discrimination and vibration (dorsal columns)
- Contralateral loss of pain/temp/corse touch (spinothalamic)
- Ipsilateral paralysis of distal muscles (may recover some proximal muscles b/c bilateral influence)
8
Q
Anterior Cord Syndrome
A
If block anterior spinal artery…only dorsal columns spared
- So lose pain/temp and bilateral motor control below point of lesions BUT retain fine touch and proprioception
9
Q
Tabes Dorsalis
A
- From neurosyphillis
- infection affects dorsal columns
- Demyelination of large afferents for proprioception …sway w/ eyes closed (Romberg test)
10
Q
Afferent Fiber Classifications (4 Groups)
A
Group I or A-alpha -Large/myelinated; FASTEST; proprioception of primary muscle spindles
Group II or A-beta - Large/myelinated; SLOWER; proprioception of secondary muscle spindles; fine touch
Group III or A-gamma- Small/thinly myelinated; SLOWER; pain, temp, corse touch
Group IV or C- Small/unmyelinated; SLOWEST; pain and temp
11
Q
Rubrospinal Tract
A
- red nucleus (midbrain) —> crosses near origin (so contralateral)—> descends near lateral corticospinal tract (so posterior white matter)
- Function = regulate voluntary upper body flexion muscles (so only goes to cervical SC)
- Inputs from …motor and pre-motor cortex and cerebellum
- Controls alpha and gamma of JUST UPPER LIMBS; (flexor + extensor -)
12
Q
LVST
A
-Goal= keep upright/balance by moving limbs
by EXCITING extensors and INHIBITING flexors
- Inputs from vestibular end organs and proprioceptors in neck
- Lateral vestibular nuclei —> shift medially (ipsilateral)—> terminate in intermediate zone
- Commissural - influences both sides
- Uses gamma motoneurons to enhance spindle inputs so exaggerate reflex to keep you upright; also influences alpha motoneurons
13
Q
MVST
A
- Medial (MVST) - neck stability so only goes to cervical SC
- From medial vestibular nuclei then descend bilaterally
- Input mainly to neck alpha motoneurons
14
Q
Reticulospinal Tract
A
- From nuclei in reticular formation (diffusely organized cells)—> SC in anterior white matter
- Medial reticular formation = motor (works indirectly on both alpha and gamma motoneurons; excites both flexors and extensors)
- Lateral reticular formation = autonomic (BP, pattern generator for respiration, pontine micturition center)
- Inputs from…vestibular system, somatosensory system, cortex
15
Q
Tectospinal Tract
A
- superior colliculus (crosses near origin so contralateral)—> cervical SC (only NECK alpha motoneurons) thru anterior white matter
- Function = coordinated eye-head movements (reflective turning of head in response to visual, auditory or somatosensory info)
- Inputs from visual, auditory, frontal eye fields
