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34 Cards in this Set
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Describe intervertebral disks
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-located between every vertebra except between:
*the skull & C1 *C1 & C2 *the sacral vertebrae FUNCTION: to unite the vertebrae and allow some movement between them -the disks are thickest in the cervical & lumbar regions, especially at the lumbosacral joint -each disk consists of: ♦an annulus fibrosus which is a thick fibrous outer ring with fibers runing obliquely between the vertebrae -it is thicker ventrally so more discs prolapse dorsally then they do ventrally in degenerative disc disease -prolapse is most common at the thoracolumbar junction (T11-L2) or the neck region where mobility is greatest in carnivores -rarely does it happen in the thoracic region because of the intercapital ligaments which reinforce the disc dorsally ♦a nucleus pulposus which is an amorphous gelatinous center to the disk (allowing some "give" in all directions) -it is a remnant of the notochord |
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What is the intercapital ligament? Where is it located? What is its function?
What are the interspinous ligaments? Where are they it located? What are the yellow ligament? Where are they located? What is the ventral longitudinal ligament? Where is it located? What is the dorsal longitudinal ligament? Where is it located? |
✤INTERCAPITAL LIGAMENT
-T2 to T11, runs from the head of one rib, over the dorsal aspect of the vertebral body, underneath the dorsal longitudinal ligment, to the head of the opposing rib -it functions to hold the heads of the ribs tightly into their sockets and prevent excessive cranial and caudal movements of the ribs ✤INTERSPINOUS LIGAMENT -connect adjacent vertebral spines -may blend dorsally with the supraspinous ligaments and laterally with the interspinalis muscles ✤YELLOW LIGAMENTS (LIGAMENTUM FLAVA) -loose thin elastic sheets between the arches of adjacent vertebrae -laterally they blend with the articular capsule surrounding the articular processes ✤VENTRAL LONGITUDINAL LIGAMENT -lies on the ventral aspect of the vertebral bodies from the axis to the sacrum and is best developed in the caudal thorax ✤DORSAL LONGITUDINAL LIGAMENT -lies along the dorsal aspect of the vertebral bodies and hence the floor of the spinal canal -it narrows over the middle of the vertebral body and flares out over the intervertebral space -it attaches to the dorsal aspect of the annulus fibrosus -it extends from the dens of the atlas to the end of the vertebral canal in the caudal vertebrae |
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What is the nuchal ligament? Where is it located?
What is the spuraspinous ligament? Where is it located? |
✤NUCHAL LIGAMENT
-longitgudinal yellow, elastic fibres, which attach cranially to the caudal part of the spinous processes of C2 and attaches caudally to the dorsal tip of the dorsal spinous process of T1 -it is a flattened paired band lying between the semispinales captii ✤SUPRASPINOUS LIGAMENT -a heavy band extending from T1 to Cd3 attaching on the dorsal spinous processes -it is continued cranially as the nuchal ligament -it blends bilaterally with the thoracolumbar fascia -it is more important for preventing separation of the spinous processes during flexion of the vertebral column than are the interspinous ligaments |
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Describe the atlantoaxial articulation. What ligaments hold the dens in place?
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-a pivot joint between the atlas and the axis that allows the head to rotate around the longitudinal axis
-the dens (odontoid process) is a peg of bone running from cranial C2 onto the floor of the spinal canal of C1 -held in place by the apical ligament of the dens (connects the dens to the skull [basilar part of occipital bone), alar ligament (connects the lateral part of the dense to the skull [occipital condyles] & the transverse ligament (holds the dens in place on the atlas) |
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Meningitis is inflammation f the meninges
a) What are the 3 meningeal coverings of the spinal cord? b) Describe their anatomy and the anatomy of any associated meningeal spaces between them |
-dura matter, aracnoid matter, pia matter (DAP, external to internal)
-epidural space: external to dura mater and contains fat & the vertebral venous plexi -the epidural space is obliterated in the mid-cervical region, C3 (C2 to C4) by fusion of the dura with the periosteum. The fusion begins ventrally and is completely circumferential by the level of the foramen magnum ♦DURA MATER -dense, tough fibrous covering -encloses the spinal roots as they leave the spinal cord and fuses with the epineurium at the intervertebral foramen SUBDURAL SPACE = the potential space between the dura mater and the arachnoid -it is only a potential space because the CSF pushes the arachnoid against the dura mater in the live animal ♦ARACHNOID MATER -subarachnoid space lies between the arachnoid and pia mater and contains cerebrospinal fluid -arachnoid trabeculae are fine meningial filaments that cross the arachnoid space between the arachnoid mater and pia mater -the arachnoid follows the larger contours and fissures but not the absolute contours of the CNS e.g. into the longitudinal fissures but not the sulci ♦PIA MATER -very delicate membrane which is fused to, and closely follows, the contours of the CNS -denticulate ligaments form on the lateral aspect of the spinal cord, between the arachnoid and pia mater, approximately halfway between succeeding spinal nerves -these ligaments help to suspend and stabilize the spinal ord in the vertebral canal DENTICULATE LIGAMENTS = the lateral extensions of the pia mater out to the dura mater between successive nerve origins/rootlets -these anchor the spinal cord laterally in the CSF filled subarachnoid space LEPTOMEMNINGES = arachnoid + pia mater |
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What is the anatomy of the arterial supply to the spinal cord?
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♦Longitudinal arteries:
-3 longitudinally oriented arteries occur: 1) two dorsolateral arteries supply the dorsal grey matter and white matter. They are not present in all regions 2) ventral spinal artery is the major supply to lateral and ventral grey matter and the ventral white matter. It is the only consistent spinal artery -at the foramen magnum or C1, it becomes the basilar artery supplying the brain -the ventral spinal artery may split and reanastomose in the cranial areas ♦Radicular arteries -occur at each intervertebral foramen (supplied from the vertebral, intercostal, lumbar, and sacral arteries) -they follow the spinal roots entering the vertebral canal and split into dorsal and ventral radicular branches which anastamose with the longitudinal arteries providing some collateral circulation -they mostly supply lateral white matter and are not present in all regions ♦Collateral circulation -the radicular and dorsolateral arteries are somewhat inconsistent -not very efficient and spinal cord is very susceptible to hypoxia |
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How many pairs of spinal nerves does a dog have?
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-36 pairs of spinal nerves
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How many pairs of spinal nerves are associated with each section of the spinal cord?
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The vertebral formula for the dog is C7T13L7S3Cd20
-there are 8 pairs cervical nerves and 7 vertebrae ♦C1 exits from lateral vertebral foramen of the atlas ♦C2 spinal nerve exit is species variable ♦C3 to C7 exit the intervertebral foramen just ahead of the vertebrae of corresponding number ♦C8 exits between C7 and T1 vertebrae -T1 to Cd 5 exit just caudal to the vertebra of the corresponding number -there are 13 pairs of thoracic nerves in a dog, 18 pairs in a hose, 13 [12-14] in ruminants and 13 [14-16] in a pig -there are 7 pairs of lumbar nerves in the dog, and 6 pairs in the horse, ruminant and pig -there are 3 pairs of sacral nerves in the dog, 5 in horses and ruminants except sheep which have 4 pairs like the pig -the dog has around 5 caudal nerves, the horse has 4, 5-6 in ruminants, and 4-8 in pigs -there are 41 pairs of spinal nerves in the chicken |
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Describe the anatomy of a typical spinal nerve
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-dorsal root (with spinal ganglia) and ventral root fuse at the level of the intervertebral foramen to form the short proper spinal nerve which quickly divides into the dorsal and ventral branches
-the proper spinal nerve divides to form the: ♦dorsal branch supplying the epaxial muscle and skin ♦ventral branch supplying the hypaxial muscle and skin ♦ramus communicans (only in thoracic & cranial lumbar regions) which connects the ventral branch of the spinal nerve with the sympathetic trunk -spinal nerves are divided into 5 main groups for clinical neurology: ♦cervical supplying the neck region ♦brachial supplying the forelimb ♦thoracolumbar supplying the thorax and abdominal region ♦lumbosacral supplying the hindlimb and perineum ♦caudal supplying the tail -a peripheral nerve is usually formed from the fusion of parts of several spinal nerves |
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What is the difference between an autonomous zone and cutaneous zone?
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An dermatome is an area of skin innvervated by one spinal nerve
A cutaneous zone is an area of skin innervated by one peripheral nerve (this often means that several spinal nerves are involved) - there is often considerable overlap of adjacent cutaneous zones An autonomous zone is innervated by only one peripheral nerve -the autonomous zones are used clinically to determine if the sensory innervation of a particular peripheral nerve is intact |
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What are the autonomous zones of the canine forepaw & hindpaw?
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Clinical neurological examination of the canine forepaw (autonomous zones):
♦DORSAL: skin over digits III and IV for radial nerve ♦PALMAR: skin over digits II and III for median nerve ♦LATERAL: skin over abaxial digit V for ulnar nerve Clinical examination of the canine lower hindlimb (autonomous zones) ♦DORSAL: skin over digits II, III, and IV - peroneal nerve ♦PALMAR: skin over digits II, III - tibial ♦LATERAL: skin of medial leg (stifle to tarsus) - saphenous |
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What clinical signs would you expect to see if the following nerves were damaged?
♦radial ♦obturator ♦femoral |
♦RADIAL
✩Radial (nerve) parasis: -most common & clinically significant nerve problem in the forelimb -it is usually due to traumatic injury -clinical manifestations vary with location of the injury ✩HIGH radial nerve paralysis: -proximal to where the nerve innervates the triceps brachii muscle -this results in an inability to extend the elbow, thus inability to bear weight on the limb ✩LOW radial nerve paralysis: -occurs distal to the triceps innervation, thus weight cannot be born on the lib -the extensor muscles of the carpus and digits are affected, manifesting clinically in "knuckling over" (dragging the dorsum of the foot on the ground) -most of the animals compensate by "flipping" the foot forward when moving the limbs so the foot lands in proper position ♦OBTURATOR NERVE PARALYSIS -can be caused by injury to the intrapelvic part of the nerve during parturition (birth) -this results in inability to adduct the limb and is most noticible on slippery floors where the limbs slip sideways -this is common in foaling and calving "Downer cow" - a postpartum cow that cannot rise to stand -this syndrome, having many etiologies, can be cause by injury to the pelvic part of the obturator nerve due to trauma during parturition -the animal cannot adduct its limb to stand, but may recover ♦FEMORAL NERVE DEFICIENCY -inability to extend the stifle results in inability to bear weight on limb -there may also be a loss of sensation on the medial side of the limb (saphenous nerve) |
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Describe the anatomy of the spinal cord: Where are the enlargements? Why are they enlarged
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✤Cervical Enlargement:
-the enlargement of the spinal cord (C5-T2) in the region over the 5th-7th cervical vertebrae -it is enlarged because it supplies the brachial plexus to the thoracic limb ✤Lumbar Enlargement -the enlargement of the spinal cord (L4-S1) beginning over the 5th lumbar vertebrae and tapering down to the end of the spinal cord -it is enlarged because its nerves supply the pelvic limb -the size of the spinal cord is proportional to the amount of peripheral tissue innervating it |
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What is the cauda equina? Where does the spinal cord end? What is the filum terminale?
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✤Conus medullaris: the cone shaped end of the spinal cord
✤Cauda equina -the spinal nerves arising from the conus medullaris extending caudally to reach their exit points from the spinal canal ✤End of spinal cord: -roughly over the intervertebral space between the 6th and 7th lumbar vertebrae in the dog and sacrum in the cat ✤Filum terminale -the narrow cord of pia mater and glial cells extending caudally from the conus medullaris to attach to the dura mater (caudal ligament) -the caudal ligament is the extension of the dura mater surrounding the filum terminale -it attaches to the caudal vertebrae to anchor the spinal cord caudally |
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What does the spinal cord look like on cross section? What is the dorsal root, ventral root?
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✤GRAY MATTER
-part of the central nervous system (brain & spinal coed) consisting of neuronal cell bodies (giving its gray color) -in the spinal cord it is butterfly shaped and is subdivided into regions called horns: ●Ventral (motor) gray horn -contains somatic motor neurons and nuclei that control contraction of skeletal muscle ●Dorsal (sensory) gray horn -contains somatic and autonomic sensory nuclei that control contraction of skeletal muscle ●Lateral (intermediolateral) gray horn -located between the dorsal and ventral horns in the thoracolumbar region and sacral region -it contains autonomic motor neurons controlling smooth muscle, cardiac muscle and glands ✤WHITE MATTER: -part of the nervous tissue consisting mainly of myelinated and nonmyelinated axons (white color comes from myelin) -it is divided in the spinal cord into columns/funiculi which contain distinct bundles of axons called tracts ✤DORSAL BRANCH -roughly innervate (sensory & motor) he structures dorsal to the vertebral transverse processes (epaxial muscles of the trunk and skin over the back) -they form plexuses by joining each other -it also supplies sensation to skin part way below the transverse processes ✤VENTRAL BRANCH -rougly supply (sensory and motor) structures ventral to the vertebral transverse processes (hypaxial muscles, trunk muscles, almost all of the muscles of the limb and the skin) -as the spinal nerve and the dorsal branches they contain both sensory and motor axons -themotor neurons are also called lower motor neurons (LMN) -ventral branches form plexuses in all areas, except the thoracic area, where they pass individually as intercostal nerves in the intercostal spaces ✤RAMUS COMMUNICANS (only in thoracic and cranial lumbar regions) -connects the ventral branch of the spinal nerve with the sympathetic trunk ✤GANGLION -a group of neuron cell bodies outside the central nervous system, manifested as a swelling of a nerve ✤CENTRAL CANAL -extending the length of the spinal cord, it is the direct continuation of the ventricular system of the brain and contains CSF ✤DORSAL MEDIAN SULCUS -shallow groove the length of the spinal cord ✤DORSOLATERAL SULCUS -longitudinal furrow where the dorsal roots enter the spinal cord ✤VENTROLATERAL SULCUS -where the ventral rootlets exit the spinal cord ✤VENTRAL MEDIAN FISSURE -ventral longitudinal groove ✤DORSAL WHITE COLUMN/FUNICULUS -between the dorsal median sulcus and the dorsolateral sulcus -ascending proprioceptive function ✤LATERAL WHITE COLUMN/FUNICULUS -between the dorsolateral and ventrolateral sulci -both sensory (pinprick pain, temperature) & motor (flexor facilitation) ✤VENTRAL WHITE COLUMN/FUNICULUS -between the ventrolateral sulci and ventral median fissure -extensor facilitation |
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What divisions do we have for the spinal nerves?
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1) cervical supplying the neck region
2) brachial supplying the forelimb 3) thoracolumbar supplying the thorax and abdominal area 4) lumbosacral supplying the hindlimb and perineum 5) caudal supplying the tail |
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Describe the location of the spinal cord segments>
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-the spinal cord segment is the area of spinal cord to which the rootlets of a specific pair of spinal nerves are attached
-in the embryo the spinal cord is the same length as the spinal column -during development, the vertebral column elongates more than the spinal cord, therefore at maturity the spinal cord terminates cranial to the end of the vertebral column -the nerve roots are elongated so that they can travel back to the appropriate intervertebral foramen ✤DOG SPINAL CORD SEGMENTS -C1 to T11 cord segments are generally one ahead of the corresponding vertebrae eg. the T5 segment is associated with the T4 vertebrae -T12 to L3 segments correspond well to the vertebrae of the same number -L4 to L7 segments are associated with the L4 vertebra and the cranial and caudal intervertebral segments -the sacral segments are associated with the L5 vertebrae -caudal segments with L6 vertebra |
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What are interneurons?
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-exist between afferent & efferent neurons which allow for coordination of autonomous neural activities of the individual body segments
-interneurons are particularly abundant in the head region and comprise most of the brain |
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What is an example of a local reflex?
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-the axons of the dorsal horn cells can be involved in a local reflex function by synapsing within the same spinal cord segment, or travel to another spinal cord segment cranial or caudal to this one, for other reflex function
❤TENDON REFLEX -afferent via dorsal horn, usually synapses with 2+ interneurons ultimately synapsing with lower motor neurons of the same spinal cord segment to cause muscle contraction ❤CUTANEOUS TRUNCI REFLEX -afferent to dorsal horns of most thoracolumber spinal cord segments; axons of the dorsal horn cells ascend the spinal cord to C8/T1 and synapse on the lower motor neurons of these segments -efferent fibers exit in the lateral thoracic nerve to cause contraction of the cutaneous trunci muscle → skin twitch -if a panniculus response is absent caudally and then appears cranial to a specific point (e.g. transverse plane through L1), the lesion is in the spinal cord up to 2 vertebrae cranially (at T12-T13) |
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What is a lower motor neuron? What are the signs of damage to a lower motor neuron?
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❤LOWER MOTOR NEURON (LMN)
-the efferent neuron of reflex arcs that connects the brain or spinal cord to the muscles of the body (e.g. radial nerve, femoral nerve etc.) -LMNs are spontaneously active without the input of UMN (upper motor neurons) -modification of the reflex arc by higher centers produces specific actions -the cell bodies of LMNs are located in the brain and spinal cord ❤DAMAGE -can affect the nerve in the periphery (axons) or its cell body in the spinal cord segment or brainstem -partial or complete damage causes decrease or loss of activity of the muscle(s) innervated, resulting in paresis or paralysis -this is a flaccid type ("limp as a dish rag") paresis or paralysis, and decreased o absent reflexes (areflexia) -LMN damage results in fast atrophy (neurogenic atrophy) usually within one week ****WITH LMN dysfunction point your thumb down to indicate that everything decreases or disappears ❤SUMMARY OF LMN DISEASE SIGNS: -decreased to absent rel flexes (hyporeflexia to areflexia) -flaccid paralysis -rapid atrophy (neurogenic atrophy) within 5-7 days |
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What is a upper motor neuron? What are the signs of damage to a upper motor neuron?
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❤UPPER MOTOR NEURONS (UMNs)
-located totally int he central nervous system, they pass in descending motor tracts that connect higher centers (the brain) with the lower motor neurons (LMNs) of the reflex arcs -usually acting to inhibit the spontaneous activity of LMNs until an action is desired, they stimulate the LMN to produce a programmed action -LMNs are spontaneously active without the input of UMNs -if the UMNs are damaged, the loss of inhibition results in increased LMN activity ❤UMN DAMAGE -causes loss of the ability to initiate voluntary motor activity and decrease of inhibition on LMNs (Therefore point your thumb up with UMN damage to indicate that activity stays normal or goes up) -reflexes will tend to be normal or increased due to uninhibited spontaneously active LMNs -paralysis is spastic and the resulting atrophy is a slow atrophy (disuse type (not neurogenic), because the LMNs are intact and still stimulate the muscles through reflexes and spontaneous activity) -damage tot he spinal cord will result in dysfunction to the area innervated (LMN damage) and hyperactivity to muscles innervated from segments caudal to the lesion (UMN damage) -damage to spinal cord segment wil show LMN signs to the peripheral structure its reflex arc innervates, not UMN signs, this is because UMN signs require intact LMNs ❤UMN disease signs -normal to increased reflexes (hyperreflexia) -spastic paresis to paralysis -slow (disuse) atrophy |
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What is Shiff-Sherrington syndrome?
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-hyperextension of he forelimbs with lesions to the thoracic spinal cord (T3-L4)
-neurons (border cells), located in the L1-4 spinal cord ascend to the forelimb centers to synapse on interneurons (Ranshaw cells) -these interneurons synapse on and inhibit extensor lower motor neurons in the cervical enlargements -this coordinates walking movements between the limbs of quadripeds -lesions to this pathway remove inhibition, so the forelimbs are slightly hyperextended -lower and upper motor neurons are still intact to the thoracic limb, therefore, this is neither an upper or lower motor neuron sign -this is the only time a spinal cord injury will show signs cranial to the point of injury -it is usually a bad sign prognostically, indicating a serious lesion of the spinal cord -the hind limb would show upper motor neuron signs (activity goes up) when Shiff-Sherrington signs are seen in the forelimb -this often causes confusion in localization |
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Describe how we can localize lesions based on divisions of the spinal cord
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What is a nuclei?
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Nuclei = collection of neurons int he CNS with a like function
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What are some general principles of white matter and tracts of white matter?
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1) - ascending tracts tend to be more peripherally located.
- some tracts are named for their origin and termination and hence indicate their route: eg spinocerebellar; originates in the spinal cord and ends in the cerebellum 2) - descending tracts tend to be more centrally located. - they generally do not cross the sides after entering the spinal cord. Clinically, this means that unilateral spinal cord lesions will cause ipsilateral signs. - most spinal UMN (descending) tracts have a name of ________spinal tract. The name tells you that the fibres originate in ________ and end in the spinal cord (eg corticospinal, vestibulospinal) 3) - long tracts are more peripherally located 4) - short tracts are more centrally located. 5) - funiculus is a division of spinal cord white matter (funiculus - L = diminutive of funis = rope/cord) - dorsal funiculus - ventral funiculus - lateral funiculi are separated by the dorsal and ventral spinal nerve roots. 6) - fasciculus or tract (fasciculus - L = diminutive of fascis = bundle/packet) is a group of functionally similar fibres travelling together. 7) - white commisure (commissura - L = joining together), just ventral to the spinal canal, is formed from axons crossing from one side of the cord to the other to integrate nervous function on both sides of the body, eg: crossed extensor reflex. When an animal stands on a sharp object, then that leg will be withdrawn from the painful stimulus (ipsilateral withdrawal reflex) but the opposite limb will reflexly extend to bear more weight (contralateral extension). ❤Clinical significance of the tracts - the dorsal funiculi primarily contain ascending proprioceptive tracts - the lateral funiculi contain both ascending and descending tracts - the ventral funiculi contain descending tracts The descending tracts of the ventral funiculus generally facilitate extensors The descending tracts of the lateral funiculus generally facilitate flexors |
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What is the propriospinal tract? Where is it found?
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❤PROPRIOSPINAL TRACT
This tract is entirely contained within the spinal cord. It consists of ascending and descending fibres for reflex activity within and between spinal cord segments. -may form up to 50% of the white matter -immediately surrounds the grey matter in all funiculi |
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What are the ascending tracts & where are they found?
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❤DISCRIMINATIVE TACTILE AND PROPRIOCEPTIVE SENSIBILITY
-convey to the brain by the fasciculus gracilus and faciculus cuneatus -located in the dorsal funiculus -also called the DORSAL-COLUMN-MEDIAL LEMNISCAL SYSTEM 1) FASCICULUS GRACILUS is the more medial of the tracts, lying immediately lateral to the dorsal median septum -function: conveys proprioceptive information to the brain, from the body caudal to T6 2) FASCICULUS CUNEATUS lies immediately lateral to the fasciculus gracilis -function: conveys proprioceptive information to the brain from the body cranial to T6 ♦DAMAGE These tracts are both located in the dorsal funiculus and are the only type of tracts in this funiculus. Therefore, lesions that only cause dorsal compression of the spinal cord will result only in proprioceptive deficits and no motor deficits. A lesion that causes dorsal and ventral compression of the spinal cord will cause abnormal proprioception and abnormal function of the UMN pathways facilitating extensors. The animal will not know where its feet are, and will tend to have poor extensor tone of the limbs manifesting as weakness. ❤PAIN & TEMPERATURE SENSIBILITY -LATERAL SPINOTHALAMIC TRACT which lies in the ventral part of the lateral funiculus -it projects to both sides of the CNS (ipsilateral and contralateral projections) PAIN ALSO REACHES THE CONCIOUS CENTRES BY TRAVELING IN A NUMBER OF DIFFERENT BILATERAL, MULTISYNAPTIC PATHWAYS IN THE SPINAL CORD ♦DAMAGE The clinical significance of this, is that deep pain sensation (eg more substantial than just a pin prick) travels to the brain via a number of different, bilateral pathways. Therefore, loss of deep pain sensation caudal to a lesion (eg spinal fracture) represents severe damage to the multiple pain-carrying pathways and therefore severe damage to most of the spinal cord ❤PATHWAYS TO THE CEREBELLUM AND ASSOCIATED BRAIN STEM NUCLEI -convey proprioceptive information required for posture and adjustment of posture after movement -include spinocerebellar, spino-olivay, spinovestibular tracts which have primarily ipsilateral projection |
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What are some general principles regarding descending tracts?
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-these are UMN tracts which originate in brain centers
-function - affect autonomic functions, and initiate voluntary behaviour, movement, and posture -there are 2 major types of tracts involved in volitional activity: 1) PYRAMIDAL -this is a direct corticospinal pathway in which fibers originate in the motor cortex of the forebrain and do not synapse until the lower motor neuron is reached -the pyramidal pathways are more important in primates and humans (their axons travel within the medullary pyramids which give these tracts their name) 2) EXTRAPYRAMIDAL -pathways originate, or relay/synapse in the brainstem and their axons do NOT travel in the medullary pyamids -the extrapuramidal pathways are more important in animals eg. rubrospinal tract |
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What descending pathways are found in the lateral funiculus?
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❤RUBROSPINAL TRACT
-the major extrapyramidal tract -a major voluntary motor pathway in animals -location: dorsomedial lateral funiculus -pathway: arises from the red nucleus and decussates in the midbrain. It is well developed in cats and in man and controls semiskilled movements. It is even more developed in lower domestic animals, being important for posture control and locomotion -projects to LMNs that innervate distal limb flexors ❤LATERAL (MEDULLARY) RETICULOSPINAL -extrapyramidal tract -from the reticular formation of the medulla oblongata -axons of the reticulospinal tract synapse with medial regions of the spinal cord gray matter that primarily controls th axial and proximal extensor musculature -portions of the tract coming from the reticular nuclei of the medulla tend to have an inhibitory effect on the lower motor neurons to anti-gravity muscles -the portions from the pons are excitatory -these opposing portions of the reticulospinal tract interact to regulate anti-gravity muscle tone ❤CORTICOSPINAL TRACT -pyramidal tract -location - dorsomedial lateral funiculus -originates in the motor cortex and crosses the midline to influence the contralateral digital flexors and extensors -majority of axons cross at brain spinal cord junction, therefore clinical signs will be ipsilateral or contralateral depending upon whether lesion is rostral or caudal to this decussation |
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What descending pathways are found in the ventral funiculus?
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❤VESTIBULOSPINAL TRACT
-originates in the vestibular nucleus of the myelencephalon (medulla oblongata) -it remains ipsilateral and influences the ipsilateral proximal extensors FUNCTION: facilitates ipsilateral extensors and inhibits ipsilateral flexors. A few fibers cross midline at the termination to cause reciprocal inhibition of the contralateral side ie inhibitory to extensors -therefore unilateral lesions will result in stumbling to the same side as the lesion because of the loss of extensor tone with maintained extension on the contralateral side of the body -a disturbance of balance detected by the vestibular apparatus results in excitation of antigravity musculature in an attempt to counteract the disturbance ❤VENTRAL (PONTINE) RETICULOSPINAL -from reticular formation to pons -axons of the reticulospinal tract synapse with medial regions of the spinal cord gray matter that primarily controls th axial and proximal extensor musculature -portions of the tract coming from the reticular nuclei of the pons tend to have an excitatory effect on the lower motor neurons to anti-gravity muscles -the portions from the medulla are inhibitory -these opposing portions of the reticulospinal tract interact to regulate anti-gravity muscle tone |
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What is the anticlinal vertebrae?
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The thoracic vertebra with the most vertically oriented spine, usually the eleventh (T11) in the dog
-all spines cranial to this vertebrae incline caudally and all caudal ones cranially -this is often used as a landmark in reading radiographs of the thorax or back |
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Describe the motor innervation of the hindlimb
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Describe the sensory innervation of the hindlimb
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Describe the motor and sensory innervation of the forelimb
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