tract anatomy

Question 1

what are the two somatic ascending pathways?

Answer 1

dorsal column medial leminiscus and anterolateral/spinothalamic

Question 2

what does the DCML concern?

Answer 2

proprioception, fine touch and vibration

Question 3

where are first order neurons in the DCML?

Answer 3

dorsal column

Question 4

where are second order neurons in the DCML?

Answer 4

gracile and cuneate nuclei

Question 5

where are third order neurons in the DCML?

Answer 5

thalamus (ventral posteroateral nucleus)

Question 6

description of DCML

Answer 6

1. primary afferent neurons enter through dorsal roots of spinal nerves
2. gracile fasciculus in sacral, lumbar and lower thoracic=below T6, cuneate fasciculus, upper thoracic and cervical=above T6
3. form the dorsal columns of the ipsilateral side of the body
4. ascend and synapse in the lower medulla to gracile and cuneate nuclei
5. decussate in medulla as internal arcuate fibres and ascend as medial lemniscus
6. synapse in the VPL of the thalamus
   7.project to somatosensory cortex via internal capsule

Question 7

what does the spinothalamic tract concern?

Answer 7

lateral- pain and temperature
anterior- crude touch and pressure

Question 8

where are first order neurons in the spinothalamic tract?

Answer 8

dorsal root ganglion

Question 9

where are second order neurons in the spinothalamic tract?

Answer 9

substantia gelatinosa

Question 10

where ate third order neurons in the spinothalamic tract?

Answer 10

VPL in thalamus

Question 11

description of spinothalamic tract

Answer 11

1. first order neurons in DRG enter spinal cord through dorsal root
2. entering sensory fibres are myelinated (alpha delta) or unmyelinated (C-fibres)
3. synapse in substantia gelatinosa in dorsal horn
4. decussates at the anterior wite commissure (contralateral)
5. forms the spinal leminscus in the brainstem
6. ascends and synapses with third order neurons in the VPL and project to somatosensory cortex

Question 12

trigeminal pathway for proprioception, fine touch and vibration

Answer 12

1.first order neurons in trigeminal ganglion outside brainstem
2. axons in TG travel along different branches of trigeminal nerve
3. second order neurons in trigeminal brainstem nuclei (e.g mescenphalic) decussate across the midline and form the trigeminal leminsicus
4. third order neurons are in the ventral posteromedial nucleus (VPM) in the thalamus
5. projected to the cerebellum and somatosensory cortex

Question 13

trigeminal pathway for pain (nociception)

Answer 13

1. first order pseduounipolar neurons in the trigeminal ganglion recieve information from nociceptors
2. synapse in the spinal trigeminal nucleus in the medulla
3. decussate in medulla at ventral trigeminal leminscus
4. third order neurons in the VPM and project to somatosensory cortex

Question 14

what is the main descending pathway?

Answer 14

corticospinal tract

Question 15

what does the corticospinal tract concern?

Answer 15

voluntary movement,fine motor control and movement precision in distal limbs and trunk

Question 16

description of the corticospinal tract

Answer 16

1. orginiates in the primary motor cortex (betz cells have largest axons)
2. motor neurons pass through corona radiata and then the internal capsule, continuing to the brainstem via the cerebral peduncles (crus cerebri)
3. decussation in the medulla oblongata at the pyramids for 80% of fibres which enter lateral corticospinal tract
4. 20% decussate in the spinal cord and form ventral corticospinal tract

Question 17

lateral cotricospinal tract

Answer 17

fine motor control and voluntary movement of distal muscles (hands, fingers)
= skilled and precise movements

Question 18

ventral corticospinal tract

Answer 18

controls postural muscles for trunk stability and gross movements
proximal limb movements (shoulder, hip)
coordination between trunks and limbs

Question 19

what is the corticobulbar/corticnuclear tract?

Answer 19

voluntary controls of the face through motor nuclei of cranial nerves

Question 20

description of corticobulbar pathway

Answer 20

1. originates in the primary motor cortex
2. descend from internal capsule to corona radiata
3. synapses with cranial nerves in the brainstem
4. does not follow a strict pattern of decussation however many cross in the medulla

Question 21

bilateral innervation of cortex in corticobulbar pathway

Answer 21

most nuclei except the facial motor nuceus and the hypoglossal nucleus which are contralateral

Question 22

what are the extrapyramidal pathways?

Answer 22

rubrospinal
vestibulospinal
tectospinal
reticulospinal

Question 23

rubrospinal tract

Answer 23

originates in the red nucleus of the midbrain and plays a role in coordinating voluntary movements of the upper limbs and shoulders
muscle tone and posture by influencing flexor muscles
ventral tegmemtal decussation- contralteral motor function

Question 24

vestibulospinal tract

Answer 24

arises from the vestibular nuclei in the pons and medulla in and near the floor of the fourth ventricle
important for maintaining balance, posture and head positioning
two tracts= lateral vestibulospinal (no decussation) and medial vestibulospinal

Question 25

tectospinal tract

Answer 25

originates from the tectum in superior colliculus and plays a key role in coordinating head and neck movements in response to visual and auditory stimuli (orientation response)
contralateral information

Question 26

reticulospinal tract

Answer 26

originates in the reticular formations (pons and medulla) and is important for postural control, muscle tone regulation and voluntary movement
medial (pontine) reticulospinal tract is ipsilateral
lateral (medullary) reticulospinal tract is bilateral