DeLahunta Chapter 9 - GP and GSA Flashcards
How are receptors classified based on their location in the body (3 groups)?
Exteroceptors are located on or near the surface of the body and are sensitive to changes in the external environment that affect the body’s surface. They include the general somatic afferent (GSA) neurons for touch, temperature, pressure, and noxious stimuli and special somatic afferent neurons for light and sound.
Proprioceptors are sensitive to movement and include those for general proprioception, which are diffusely located in the internal mass of the body in muscles, tendons, and joints and the receptors for special proprioception located in the labyrinth in the inner ear.
Interoreceptors are located within the viscera of the body and are sensitive to changes in the internal environment. They include the general visceral afferent neurons for body temperature, blood pressure, gas concentration, pressure and movement in body viscera, and the special visceral afferent neurons for the chemical energy concerned with taste and smell.
Between what spinal cord segments does the nucleus thoracicus extend in the
cat?
The nucleus thoracicus extends from approximately the C8-L4 spinal cord segments in the cat.
Describe the two cerebellar transmission from the trunk and pelvic limbs.
The dorsal spinocerebellar and ventral spinocerebellar tracts.
The dorsal spinocerebellar tracts have the GP axons entering the dorsal grey horn and synapse on the neuronal cell bodies on the medial aspect of the base of the dorsal grey horn. They enter the nucleus thoracicus (between C8-L4 in cats), then enter the lateral funiculus ipsilateral and pass cranially on the suface of the dorsal portion of the lateral funiculus in the dorsal spinocerebellar tract. Cranially to medulla, the caudal cerebellar peduncle by way of the superficial arcuate fibres, the axons reach the cerebellar cortex of vermal and paravermal lobules.
The ventral spinocerebellar tract, have the GP axons enter the dorsal grey horn and synapse near its base laterally. Cell bodies form a continuous column from cranial thoracic spinal cord segment through the lumbar and sacral. Most axons cross theopposite lateral funiculus by ventral white commissure. Here the ventral spinocerebellar tract goes cranially, gets to the medulla, pons, the through the rostral cerebellar peduncle, in the cerebellum it crosses back, into the vermal and paravermal lobules.
Describe the four transmission from thoracic limbs in the cervical region.
The cuneocerebellar tract. The cranial rostral spinocerebellar tract. The cervicocerebellar tract. Cervicovestibular pathway.
The cuneocerebellar tract is for providing a GP cerebellar pathway for the thoracic limbs. The GP axons from the dorsal roots of the spinal nerves from C1 to T8 enter the spinal cord along the dorsolateral sulcus and continue dorsal to the dorsal grey horn to enter the lateral portion of the dorsal funiculus without synapsing. This lateral prtion of the dorsal funiculus is the fasciculus cuneatus. The GP axons just pass cranially through this fasculus cuneatus, and reach the caudal medulla, where they terminate by forming synapses with neuronal cell bodies in the lateral cuneate nucleus. Axons of neuronal cell bodies enter the adjacent caudal cerebellar peduncle and pass into the cerebellum.
Cranial spinocerebellar tract The GP pathway from the thoracic limbs, the GP axons enter the dorsal roots associated with the cervical intumescence and enter the dorsal grey hor and synapse on neuronal cell bodies near its base in the centrobasilar nucleus. The axons enter the ipsilateral lateral funiculus and course cranially, medial to the ventral spinocerebellar tract. They continue into the medulla and pons and enter the cerebellum through medulla, pons via the caudal and rostral cerebellar peduncles.
Cervicospinocerebellar pathway for the GP of the neck. The central cervical nucleus is located in the intermediate grey column in C1-C4 spinal cord segments. Receives axons in dorsal roots from cervical spinal ganglion neuronal cell bodies. Axons then cross to the contralateral lateral funiculus. They continue cranially into the medulla, caudal cerebellar peduncle and cerebellum.
Cervicospinovestibular pathway special proprioceptive for the vestibular system in the neck. Provided by the spinovestibular tract in the ventral funiculus. This tract receives axons from the ipsilateral dorsal grey horn, and terminates in the medulla by forming synapses in the caudal vestibular nucleus.
Where does the medial lemniscus synapse to?
The medial lemniscus terminates by synapsing on neuronal cell bodies in the ventral caudal lateral nucleus of the thalamus.
Nucleus Z: where is located? Receives axons from where? The axons of cell bodies from the nucleus Z join the ipsilateral or contralateral medial lemniscus?
Nucleus Z is a small nucleus located at the rostral aspect of nucleus gracilis in the caudal medulla. It receives axons from the lateral funiculus that originate from ipsilateral dorsal gray column neuronal cell bodies located in spinal cord segments caudal to the cervical intumescence. Nucleus Z also receives collateral branches from axons in the dorsal spinocerebellar tract. The axons of neuronal cell bodies in nucleus Z cross in the caudal medulla to join the contralateral medial lemniscus, where they course to the thalamus and somesthetic cortex, as described earlier.
Where are the cell bodies of the tongue muscle afferent neurons located? P252
Retrograde studies using horseradish peroxidase have shown that the afferent neurons that supply the dog’s tongue have no cell bodies in the mesencephalic nucleus. The cell bodies of the intramuscular neurons of both the intrinsic and extrinsic tongue muscles are located in the first cervical spinal ganglia, the distal ganglia of the vagus, and the trigeminal ganglia.
Which tract is formed within the spinal cord by the GSA axons of spinal nerves?
Within the spinal cord the GSA axon forms relatively short branches that course cranially and caudally on the surface of the dorsal gray column for a distance of two or three spinal cord segments. The tract that they form there is the dorsolateral fasciculus (Lissauer tract). Collaterals of these axonal branches enter the dorsal gray column all along the segments that are traversed. They provide branches that terminate by synapsing on interneurons located at the apex of the dorsal gray horn in an area called the substantia gelatinosa.
Cutaneous dermotomes in TL and PL - which areas to test for each nerve?
TL:
1) dorsal paw: RADIAL
2) medial antibrachium: MUSCULOCUTANEOUS
3) caudal antibrachium: ULNAR
PL:
1) ventral paw: TIBIAL N.
2) dorsal paw: FIBULAR N.
3) medial crus: SAPHENOUS (FEM)
4) Inguinal (proximal medial thigh): GENITOFEMOURAL (FEM)
5) Caudal thight: CAUDAL CUTANSOU FEMORAL NERVE
6) Caudal popliteal: SCIATIC
7) Craniolateral thigh: LATERAL CUTANEOUS FEMORAL NERVE
In male dogs:
PREPUCE: Genitofemoral
Skin of penis: pudendal
Briefly which is the nociceptive pathway (conscious)?
Nociceptors > nerve (A-delta unmeylinated or C lightly myelinated axons) > spinal ganglion (GSA neuron - supstance P –> subntantia gelatinosa nuclei in dorsal horn (lamina II) but also other laminae –>
- Describe the nociception pathway. What is the role of substantia gelatinosa?
50% of afferent axons are in cutaneous nerves originate from nociceptors. Inflammation in the vicinity of nociceptors release endogenous substances: serotonin, bradykinin, prostaglandins which lowers the threshold for pain. These axons are unmyelinates (delta A) or lightly myelinated C. They pass through the dorsal root ganglia with GSA neurona cell body. Enter the dorsolateral sulcus, then dorsal grey horn. Here they synapse on neuronal dendritic zones or cell bodies in various laminae of the dorsal grey horn. There are 10 laminae in total, but from I to VI located in the dorsal grey horn. Some axons might also cross in
the contralateral dorsal grey horn. Then they course cranially, and terminate in the thalamus in the ventral caudal lateral nucleus. Then they course into the thalamocortical projection pathway, internal capsule, centrum semiovale, corona radiata and reach the somesthetic cerebral cortex of frontoparietal lobes. On the way, they also synapse in the reticular formation that function in the ARAS, to maintain conscious awake.
Interneurons in the substantia gelatinosa at the apex of the dorsal gray horn are
inhibitory to the projection pathway neurons in other dorsal gray horn laminae. These interneurons are activated by large-diameter myelinated nonnociceptive neurons.
Please name the trigeminal nerve nuclei. What is the main sensory nucleus of
CNV? What type of information is received mainly in this nucleus?
-MESENCEPHALIC N. OF TRIG –> Proprioception (facial, masticatory, EOM)
-PONTINE SENSORY N. OF TRIG–> Touch (mechanoreceptors) - conscious perception of GSA
-SPINAL N. OF TRIG NERVE–> GSA reflex activity, Nociception of head and temperature
The pontine sensory nucleus of the trigeminal nerve also is known as the chief sensory nucleus of the trigeminal nerve. The pontine sensory nucleus is believed to be primarily concerned with mechanoreception. The entire spinal nucleus is concerned with GSA reflex activity and nociception in the head.
**Nuclei of trigeminal nerve are best described in King’s
P84-86 Kings:
The sensory nucleus of the trigeminal nerve is in fact divided into three consecutive regions with different functions. The most caudal segment is called the nucleus of the spinal tract of the trigeminal nerve, the middle segment is called the principal (pontine) sensory trigeminal nucleus, and the most rostral segment is called the nucleus of the mesencephalic tract of the trigeminal nerve. The nucleus of the spinal tract of the trigeminal nerve is the cell station of the second neuron in the pathways carrying pain and temperature sensations from the face. It is therefore strictly homologous to the cells of the dorsal horn of the spinal cord which give rise to the spinothalamic tract. The principal (pontine) sensory trigeminal nucleus consists mainly of the cell bodies of the second neurons of the pathways of touch and pressure from the face. This nucleus is therefore strictly homologous to the cuneate and gracile nuclei (see Section 7.3). The separation of pain from touch in these two continuous nuclei enables the surgeon to relieve severe trigeminal neuralgia in human patients by eliminating the spinal trigeminal nucleus, while at the same time preserving intact the pathways of touch from the face (including the all important protective corneal reflex) by leaving the principal trigeminal nucleus intact. The nucleus of the mesencephalic tract of the trigeminal nerve apparently deals with all the incoming proprioceptive impulses from the muscle spindles of the jaw muscles and probably also those from the muscles of the eyeball. The cells of the mesencephalic trigeminal nucleus resemble histologically the pseudounipolar neurons of dorsal root ganglia; they may indeed be the cell bodies of primary afferent neurons that have arisen embryonically from the neural crest but have become embedded in the brainstem instead of forming a dorsal root ganglion. If so, these neurons of the mesencephalic trigeminal nucleus break the almost universal rule that primary afferent neurons have their cell stations in dorsal root ganglia or in the homologous ganglia of cranial nerves: the only other exception to this rule is the olfactory neuroepithelial cell (see Section 9.5).
Motor nucleus of the trigeminal nerve (Vth motor nucleus), and this is responsible for the muscles of chewing (which are derived from the first pharyngeal arch).
Can you describe the pathway of the palpebral reflex?
Axons of the neuronal cell bodies in the nucleus of the spinal tract of the trigeminal nerve project to GSE-LMN nuclei of the brainstem to complete the reflex arcs. The GSA receptors of the ophthalmic and maxillary nerves. Stimulus goes through trigeminal ganglion, then spinal tract of trigeminal nerve. Axons course to the adjacent facial nucleus to synapse on GSE-LMN, who innervates the orbicularis oculi. Also the contralateral nucleus courses to the facial nucleus.
Two causes for nasal hypalgesia?
A unilateral nasal hypalgesia may be caused by an ipsilateral trigeminal nerve lesion or contralateral prosencephalic lesion.
Sites to test the autonomous zone for each of the three branches of CNV
Sites to test for the autonomous zone for each of the three branches of the trigeminal nerve include the nasal septum mucosa for the ophthalmic nerve, the superior lip for the maxillary nerve, and the inferior lip or tongue for the mandibular nerve. Response to a noxious stimulus to the inferior lip is often inconsistently observed, and it is therefore difficult to appreciate the patient’s response. However, a lesion affecting the mandibular nerve may also affect the GVE neurons and therefore result in ipsilateral atrophy of the muscles of mastication.
Clinical signs, neurological examination findings, gross pathology, histopathology, IHC of Canine Sensory Neuropathy.
AND genetic mutation (
Also called acral mutilation, described in English Pointer, Czechoslovakian short haired pointers. Other breeds would include Dachshund, Boxer, Pyrenean mountain dog, Parson Jack Russel. Neurological examination all normal except not withdrawaling when analgesic digits are stimulated. On gross pathology there is decreased size of spinal ganglia. On histopath: 20-50% reduction of neuronal cell bodies. Axonal density reduced in the dorsolateral funiculus. On IHC deficiency of the nociceptive neurotransmitter subtsnace P in the dorsal grey column. Decreased sensory nerve conduction.
Leonard et al. 2022 - https://doi.org/10.3390/vetsci9030127)
Self mutilation (loss of nociception), hypermetric gait, delayed postural reactions, reduced spinal reflexes, analgesia/hypalgesia, urinary/faecal incontinence
Owing to the progressive evolution of the lesions, the abnormal findings on neurological examination and the poor response to medical treatment, another sensory canine neuropathy, reported in the Border Collie, was suspected and a test looking for a mutation in the FAM134B gene was requested (Laboklin GMBH & Co., Bad Kissingen, Germany). The dog was homozygous mutated. A diagnosis of inherited sensory and autonomic neuropathy of the Border Collie associated with an inversion disrupting the FAM134B gene was concluded.
EXTRA:
1.Sensory Ataxic Neuropathy in Golden Retriever Dogs Is Caused by a Deletion in the Mitochondrial tRNATyr Gene. https://doi.org/10.1371/journal.pgen.1000499
2.A DOG SPONTANEOUS MODEL FOR HUMAN SENSORY NEUROPATHIES: IDENTIFICATION OF A MUTATION IN THE UPSTREAM REGION OF A NEUROTROPHIC FACTOR
DOI : 10.4267/2042/61953
In this study, we sought the genetic cause of self-mutilation syndrome in sporting dogs, which corresponds to human Hereditary Sensory and Autonomic Neuropathies (HSAN). We have identified a genetic mutation upstream of the gene encoding Glial cell line-Derived Neurotrophic Factor (GDNF).
