Spinal Tracts Flashcards
What is the function of cerebral cell bodies of the cortex?
Initiate, maintain and plan voluntary movement
What is the function of Cell bodies of the brainstem?
regulation of muscle tone. posture and basic navigational movement
Where are the cell bodies of the CNS Upper Motor Neurons located?
cerebral cortex
brainstem
Where are the axons of the UMNs located?
white matter of the spinal cord
synapse in ventral horn grey matter with inter neurons or LMN
List the 5 main upper motor neuron pathways.
Corticospinal Tract (lateral and ventral)
Rubrospinal Tract
ReticuloSpinal (medullary and pontine) Tracts
Tectospinal Tract
Vestibulospinal Tract
Where does the corticospinal tract originate and insert. List the structures it passes through.
O: cerebral cortex Travels through: red nucleus crus cerebri pyramids I: lateral or ventral corticospinal tract
How does the pathway of the lateral corticospinal tract differ to the ventral tract?
75% of the neurons will decussate at the medulla to insert in the lateral corticospinal tract
Remaining 25% of neurons will continue ventrally to insert on the ventral corticospinal tract
Name where along the vertebrae the lateral corticospinal tract will insert.
50% cervical grey matter
20% thoracic grey matter
30% lumbosacral grey matter
What is the function of the llateral and ventral corticospinal tracts?
Lateral: flexion and fine activity
ventral: axial and proximal limb muscles contribute to posture
Which group of species is the corticospinal tract most prevalent?
primates
Name the origin and insertion of the rubrospinal tract.
O: red nucleus of midbrain –> axons immediately decussate at brainstem
I: lateral funiculus of spinal cord: rubrospinal tract
What is the function of the rubrospinal tract?
enables motor cortices indirect functioning in semi skilled movement in cats and locomotion : limb protraction
Name the origin and insertion of the Reticulospinal tracts, listing the structures that it passes.
O: cerebral cortex
Medullary: reticular formation of the medulla
Pontine: reticular formation of the pons
I: lateral funiculus (medullary), ventral funiculus (pontine)
What is the function of the reticulospinal tracts?
Medullar: ipsilateral and contralateral strong inhibitor of y-LMN of extensor muscles and excitation of flexors
Pontine: stimulates ipsilateral y-LMNs antigravity extensor muscles
What is the origin and insertion of the lateral and medial vestibulospinal tracts?
O: vesibular nuclei of the brainstem
- lateral: lateral vestibular nucleus
- medial: medial, rostral. caudal vestibular nuclei
I:
Lateral: ipsilateral ventral funiculus, all levels spinal cord esp intumescences. Some decussate to inhibit contralateral LMNs
Medial: medial aspect ventral funiculus + medial longitudinal fasciculus, cervical and cranial thoracic
What is the function of the lateral and medial vestibulospinal tracts?l
Overall: maintenance and balance
Lateral: senses static head position –> maintanence of posture against gravity through extensor activity and inhibition of flexors
medial: reinforces activity in cervical and thoracic limb muscle maintains posture despite changes to head position
What stimulates the Lateral vestibulospinal tract to stimulate extensors and inhibit flexors?
input from utricle (forwards and back wards motions)
saccule (up and down motion)
–> static head position
What activates the medial vestibulospinal tract?
angular acceleration of head detected by vestibular apparatus
What is the origin and insertion of the tectospinal tract?
O: rostral and caudal colliculi of midbrain (visual tectum)
I: ventral funiculus, cervical and upper thoracic spinal cord
What is the function of the tectospinal tract?
maintenance of balance and posture.
reflex and postural movements of head and neck in response to visual and auditory stimuli through control of the axial musculature of neck
What is the main function of the tracts located within the ventral funiculus?
stimulators of extensor muscles
What is the main function of the tracts of the lateral funiculus?
stimulators of the flexor muscles or inhbitors of extensors
Which spinal tracts do not run the entire length of the spinal cord?
tectospinal tract
medial vestibulospinal tract
What is the function of the spinothalamic ventrallateral tract?
Ventral: crude touch, pressure
Lateral: temperature, pain
Describe the pathway of the spinothalamic ventral lateral pathways.
1st order neuron: dorsal root ganglion
2nd order neuron: synapse in dorsal horn grey matter decussates to other side
3rd order neuron: synapse at ventral posterior lateral nucleus of the thalamus and inserts at the cerebral cortex
What is the function of the dorsal column medial laminuscus system?
conscious proprioception
vibration
tactile sensation
two point discrimination
How does the fibers of the fasiculus gracillus differ to the fasiculus cuneatus?
fasiculus gracillus: information from lower part of the body, present throughout spinal cord
fasiculus cuneatus: info from upper body, not present below T6
What is the function of the spinocerebellar systems?
unconscious proprioception (doesnt ascend to cerebral cortex)
provide cerebellum with spatial information about trunk and limbs during movement and during fixed posture
How many neurons does the spinocerebellar system consist of?
2 neurons as there is no third required to reach the cerebral cortex
Describe the pathway of the ventral spinocerebellar system
1st order neuron: dorsal root ganglion
2nd order: decussates to opposite site entering spinocerebral tract –>
continues dorsally until reaches the cranial cerebral peduncle –>
decussates to opposite side
Describe the pathway of the dorsal spinocerebellar system and how it differs from the pathway of the ventral spinocerebellar system.
1st order neuron: dorsal root ganglion
2nd order: synapses at dorsal horn grey matter –> ascends the same side (no decussation)–>
ventral cerebellar peduncle (medulla connection to cerebellum)
What is the function of the spinaltectal tract?
regulates spinovisual reflexes
Where does the spinotectal tract insert.
cranial colliculus (midbrain)
What are the 4 mechanoreceptors of the skin?
Ruffini ending
Pacinian corpuscle
Merkel disc receptor
Meissner’s corpuscle
Where do the fasciculus gracilis and cuneatus tracts lay within the vertebral column?
fusciculus gracilis: caudal to T6
fasciculus cuneatus: cranial to T6
What is the general function of the trigeminal pathway?
carries information from the face
Describe the pathway of the trigeminal tract.
1st neuron: trigeminal ganglion –> synapse at principle nucleus of tigeminal complex
2nd order: immediately decussates at the level of the midbrain through the medial lemniscus –> synapses in ventral posterior medial nucleus of thalamus
3rd order: synapses in primary somatic sensory cortex
Describe the pathway of the dorsal column medial lemniscus tract with reference to the funiculus gracilis.
1st order neuron: dorsal horn grey matter at level of lumbar spinal cord –> continues dorsally ipsilaterally
2nd order: synapse at gracile nucleus in the caudal medulla and decussates immediately –> continues through medial leminiscus until reaches thalamus (VPL nucleus)
3rd order: towards primary somatic sensory cortex
Describe the pathway of the dorsal column-medial leminiscus pathway with reference to the fasciculus cuneatus.
1st order: dorsal horn grey matter at level of the cervical spinal cord –> continues ipsilaterally
2nd order: synapses at cuneate nucleas in caudal medulla –> decussates immediately –> continues through medial leminiscus of midbrain until the VML nucleus of the thalamus
3rd order: synapses at the primary somatic sensory cortex
Name the branches of the trigeminal nerve.
ophthalmic
maxillary
mandibular
How does the function of the dorsal and ventral spinocerebellar tracts differ from the rostral spinocerebellar and spinocuneocerebellar tracts?
ventral and dorsal spinocerebellar: information received from pelvic limbs and trunk
rostral and cuneo: information received from thoracic limbs
Name all the tracts of the spinocerebellar pathway.
Dorsal spinocerebellar
ventral spinocerebellar
rostral spinocerebellar
spinocuneocerebellar
Provide a general description of the pathways occurring below L3/L4 for the spinocerebellar tract
1st order: ascend in in fasciculus gracilis
2nd order: synapse in nucleus of dorsal spinocerebellar tract or ventral spinocerebellar tract–> ipsilaterally to cerebellum
Describe the pathway of the spinocuneocerebellar tract.
1st order: C1 to T8 axons ascend in fasciculus cuneatus
2nd order: synapse in lateral accessory cuneate nucleus –> ipsilateral cerebellum via spino cuneocerebellar tract
What would be the effect of a lesion at C1-C5?
Loss of proprioception and sensory input of the thoacic and pelvic limbs, tail and trunk
UMN signs in the TL and PL
No LMN signs in TL or PL. Cutaneous trunci and perineal reflexes intact.
UMN bladder and faecal incontinence
What would be the effect of a lesion within C6 to T2?
Loss of proprioception and sensory input from TL, PL, trunk and tail.
UMN signs in PL only.
LMN signs present in TL only, loss of cutaneous trunci reflex if lesion in C8-T1
perineal reflex intact
UMN bladder, faecal incontinence
What would be the effect of a lesion within T3-L3 (thoracolumbar)?
loss of proprioception and sensory input of the trunk caudal to the lesion, PL and tail
Presence of UMN signs in PL
no LMN signs in TL and PL
cutaneous trunci reflex lost caudal to lesion
perineal reflex intact
UMN bladder, faecal incontinence
What would be the effect of a lesion within the cranial lumbosacral region (L4-S1)
Loss of proprioceptive and sensory input at the PL and tail
No UMN signs to limbs
LMN signs in PL
cutaneous trunci and perineal reflexes intact
UMN bladder
faecal incontinence
What would be the effect of a lesion in the caudal lumbosacral region (S1-S3)?
Loss of priprioceptive and sensory input at the perineum, tail
PL probably normal
No UMN signs to limbs
LMN signs in pelvic viscera
loss perineal reflex
LMN bladder and anal sphincter –> incontinence with dropping faeces via dilated anus
What would be the effect of a lesion within the caudal nerves (Cd1-5)?
loss of sensory and proprioceptive input at the tail.
No UMN signs
LMN signs in tail
normal continence
What is meant by an UMN bladder?
turgid, full, difficult to express
what is meant by a LMN bladder?
flaccid, distended, easily expressed, dribbling urine
Where are the cell bodies of nociceptors located?
trigeminal ganglion
dorsal root ganglion
Where are the proprioceptive receptor organs located?
muscle
tendon
joints
List the 4 categories of skin nociceptors.
high threshold mechanonociceptors: intense mechanical stimulation IE pinching, cutting etc.
thermal nociceptors
chemical nociceptors
polymodal nociceptors: high intensity stimuli such as mechanical, thermal and chemical
List the characteristics of the C-fibre mechano-heat sensitive axons.
small unmyelinated axons
slow conducting
l
what type of stimuli does C-fibre mechano heat sensitive fibers respond to?
deep, visceral, burning and aching pains
–>
high intensity mechanical, chemical and thermal stimulation
Compare the precision of pain reception in the C-fiber mechano heat and A-fiber mechano heat sensitive fibers.
C fibers: large receptive field –> less precise pain localisation
A-fibers: small receptive fields –> precise localisation of pain
Compare the synapse location of C-fiber mechano heat sensitive and A-fiber mechano heat sensitive fibers in the dorsal root horn.
C fibers: rexed layer 1 or 2 (substantia gelatinosa) depending on fiber class type
A fibers: rexed layer 1 (nucleus posterior marginalis)
What type of pain does the A fiber mechano heat sensitive fibers respond to?
low intensity non-noxious stimuli
prickling, sharp pain
Name the origin of the spinothalamic pathway afferent sensory fibers and where they combine to form a single pathway.
O: sacral, lumbar, thoracic and cervical spinal cord segments
all sensory afferent fibers combine at C8 to form one pathway
Define cingulate
unpleasant component of pain
Define insula
autonomic component of pain response
define Amygdala
fear and anxiety response to pain
What is the tract of lissauer and where is it located?
dorsolateral fasciculus
axons branch into ascending and descending collaterals, running up or down 2 spinal segments before penetrating dorsal horn grey matter forming lissauers tract
What is the substantia gelatinosa?
modulation of nociception and temperature
What are the 3 categories of pain?
nociceptive
inflamamtory
neuropathic
What is the function of substance P?
plasma extravasation
histamine release
vasodilation
What is the category of pain associated with sensory amplification aiming to protect by producing pain hypersensitivity during healing and is evoked by both high and low intensity stimuli and is not associated with a nervous system lesion?
inflammatory
What is the category of pain that involves a nervous system lesion or disease and maladaptivr and persistent serving no useful purpose via the transcription of GFs involved in the construction of new synaptic contacts?
Neuropathic
What is the category of pain associated with no lesion, is envoked by high intensity stimuli only and aims to protect by signalling potential tissue damage?
nociceptive.
What is central sensitisation?
enhancement, potentiation or facilitation of synaptic activity in dorsal horn –>
reduced the threshold of nociceptors
–> early activation 2nd order neurons
What is secondary hyperalgesia?
allows for a larger number of nociceptors outside the usual range of site damage to reach threshold
How is secondary hyperalgesia achieved?
2nd order neuron activation: depolarisation
activation of voltage dependent L type Ca channels and
NMDA (Mg removal) receptors –> prolonged depolarization + increased number of receptors available for glutamate and other excitatory neurotransmitters
Elevated Ca –> andenylate cyclase –> cAMP –> protein kinases –> insertion AMPA receptors –> increased sensitivity to glutamate
How is pain modulated?
activation of inhibitory interneurons
endogenous opioids: enkephalins, endorphins
How does enkephalin function?
inhibits the release of substnace P
–> inhibits vasodilation, histamine release and angiogenesis.
What are the major clinical signs of an animal in pain?
increased BP, HR, adrenaline, sweating Dilated pupils anxiety, fear, aggression : vocalisation, posture reduced apetite and activity response to handling
