Lecture 7/8 - Spinal Tracts Flashcards
general feature of all spinal tracts (5)
tracts are anatomically and functionally distinct from each other. ASCENDING tracts carry SENSORY info to the brain and DESCENDING tracts carry MOTOR info from the brain
most consist of a connected series of two or three neurons
tracts are often named according to where they originate and terminate
neurons in tracts often decussate at some point in the pathway between the spinal cord and brain
all pathways are paired: one tract on left and one on right
ascending (sensory/afferent) tracts: general features
the primary neuron ALWAYS enters the spinal cord in the dorsal root
the primary neurons cell body is ALWAYS in the dorsal root ganglion
sensory information usually crosses the midline to the CONTRALATERAL side. exception is for some proprioception fibers - the axon enters the spinal cord and ascends on the same (IPSILATERAL) side
ascending tracts carrying conscious information - other name for the more important one, location, resistance to injury
spinothalamic (anterolateral, ventrolateral) tract:
relays AP carrying pain and temperature information
located in the ventrolateral areas of the spinal cord white matter. carries pain and temperature sensations in fibers of moderate or small diameter and myelination
relatively resistant to injury
ascending tracts carrying conscious information - name for the second type, location, composition, injury?
dorsal column (fasciculus coneatus and fasciculus gracilis)
carry information concerning conscious proprioception, touch
located at the most dorsal aspect of the spinal cord, it includes the medial fasciculus gracilis (hindlimb, caudal to T6) and the more lateral fasciculus cutaneous (forelimb, cranial to T6)
composed of large myelinated fibers. info travelling in these tracts ultimately ascend to the cortex
these fibers have a relatively high susceptibility to injury due to myelination and location
what is usually the first type of clinical signs related to that we see, what tract is involved
proprioception problems - due to these tracts being susceptible to injury due to location and myelination
dorsal column involved
ascending tracts carrying conscious information - name for third one, where are they, where do they terminate, injuy, how is it defined
non-specific multisynaptic pathways
there are several poorly defined pathways, with different names that ascend bilaterally in the spinal cord, usually involving poorly myelinated neurons
these poorly defined tracts ascend in white matter throughout the spinal cord and terminate as part of the reticular activating system (RAS) in the brain
they synapse multile times as they ascend and because of their wide distribution and low myelination, appear resistant to injury
not actually a single defined tract. if there pathways are gone, very severe spinal cord injury
ascending tracts carrying UNCONSCIOUS sensory information - what is the name, what does it do, location of fibers, injury, ipsilateral or contralateral
spinocerebellar pathways/tracts
unconscious proprioception - the sense of where your limbs are in space. this is use by interneurons in the cerebellium to modify the activity of motor neurons
these fibers usually DO NOT decussate, instead ascending on the ipsilateral side of the spinal cord and entering the cerebellum via the caudal cerebellar peduncle
these fibers have a relatively high susceptibility to injury due to heavy myelination and location in the spinal cord
descending tracts - general features (4)
carry the motor fibers that control “somatic” muscle movement in the body
as with sensory pathways, motor impulses travels in specific tracts found in white matter
similarily, the pathways are named based on origin and destination; there are three major and two minor pathways of significance
a major portion of the clinical neurologic exam involes the examination of responses mediated by the motor tracts (in vet med), although the sensory pathways must also be intract in order for test to be normal so we often evaluate sensory and motor together
descending motor tracts - how many neurons, where do they synapse, injury?
these pathwyas have 2-3 neurons in a series which start at specific nuclei in the brain and end at a specific spinal level where they synapse on a LOWER MOTOR NEURON
moderately myelinated so susceptibility to injury falls between proprioceptive pathways (very sensitive) and pain pathways (least sensitive)
what are the three major tracts, where the start and end, do they cross over, what is the most important tract in domestic species
-rubrospinal tract = red nucleus to spinal cord, decussates in midbrain. most important in domestic species. responsible for voluntary muscle movement
-reticulospinal tract - reticular foramen (in medulla) to spinal cord, involved in balance and posture, mostly ipsilateral with some decussation to the contralateral side
vestibulospinal stract - vescibular nuclei to spinal cord, involved in synergy of muscle movements, equilibrium and balance. entirely ipsilateral
reticulo and vestibulo - often contain inhibitory neurons to prevent excessive responses to stimuli
what are the minor tracts, where do they start and end, function ?
corticospinal tract - cortex to spinal cord, similar to rubrospinal but originates in cortex. sometimes called a pyramidal tract
tectospinal tract - like the corticospinal tract but to cervical cord segments only, responsible for head movements in response to auditory/visual stimuli
upper motor neurons and lower motor neurons - refers to what, where are they, what type is in tracts
motor tracts contain UMN that initiate muscle contraction and movement after synapsing on LMN that leave the spinal cord at each level to innervate muscle
UMN - refers to all neuron in a motor tract except the FINAL neuron which leaves the spinal cord and directly innervates a muscle fiber. UMNs are entirely in the CNS (brain and spinal cord). UMNs are in tracts
LMN - refers to the FINAL NEURON in a motor pathway, which exits the spinal cord and travels, via the ventral root to the target muscle. LMS start in the CNS and terminate in the PNS. UMNs from multiple different motor tracts can synapse on a single LMN, which carries an impulse to a muscle
UMN and LMN, travel path of UMN to get to LMN, and injury
UMNs travel from the brain in different tracts and then synapse on LMNs which leave the spinal cord and innervate muscle
UMNs can ONLY be injured in the spinal cord is injured
LMNs can be injured if the spinal cord OR peripheral nerve in which they travel is injured
names of two major ascending tracts carrying CONSCIOUS info (all names for them)
spinothalamic (ventrolateral, anterolateral), dorsal column (fasciculus cuneatus, fasciculus gracilis)
names of the major ascending tract carrying UNCONSCIOUS info
spinocerebellar,
