Ascending Spinal Cord Flashcards
Agraphesthesia
The inability to recognize letters and numbers drawn on the palm of the hand
Three tracts in the anterolateral pathway
1) Spinothalamic
2) Spinoreticular
3) Spinomesencephalic
Two ways Rostral Ventral Medulla (RVM) modulates pain
1) Inhibits pain by signaling to dorsal horn of spinal cord
2) Promotes Locus Ceruleus (Rostral Pons) which sends noradrenergic projections to regulate spinal cord
Origin of Posterior Spinocerebellar Tract
Clarke’s Nucleus (medial part of Vamina VII). Axons run to the lateral funiculus of that same side to form the posterior spinocerebellar tract
Note: Both the tract and Clarke’s Nucleus do not exist caudal to L2
Function(s) of Spinothalamic Tract
Believe to interact with spinoreticular in the emotional and arousal aspects of pain
Bare nerve endings use which sensory neuron fiber type(s)? [Involve Pain, temperature, and itch]
A-delta and C
Two types of non-conscious sensation. They’re not not perceived but routed to the cerebellum
1) Proprioception - afferent information reaching the cerebellum though the spinocerebellar pathways, essential for smooth motor coordination
2) Interoception - References unconscious afferent signals involved in visceral reflexes
Subacute Combined Degeneration
Chronic demyelination and loss of axons in the dorsal and dorsolateral columns; more posterior columns than lateral corticospinal tract. May also involve deep white matter of hemispheres (dementia).
Patient shows loss of proprioception, discriminative touch, vibration, ataxia, and spastic weakness/paralysis
Location of decussation for Anterolateral Pathway
Spinal Cord Anterior Commissure
Laminae from which Spinomesencephalic Tract arises from
Laminae I & V of dorsal horn
Two major major pathways involved in somatic sensory perception (therefore ascending)
1) Posterior (Dorsal) Column-Medial Lemniscal Pathway
2) Spinothalamic (Anterolateral) Pathway
Location of the somatosensory cortex
post central gyrus
SNRIs, TCAs (Tricyclic Antidepressants), and SSRIs – which are analgesic
SNRIs and TCAs. SSRIs are not
Contralateral Neglect is a sign of what?
Cortical sign (occurs only from cortex lesion)
Function of Posterior Spinocerebellar Tract
Conveys tactile, pressure, and proprioceptive information about the ipsilateral leg
Function of Cuneocerebellar Tract
Sensory from ipsilateral upper thorax and arm
Difference in function between Posterior/Anterior Spinocerebellar Tracts – which both deal with the leg
Anterior S.C Tract not only has Group I fibers (from mainly Golgi tendon organs) but also wide variety of cutaneous receptors like spinal interneurons and fibers of descending tracts. Activity is related more to attempted movement than simply to sensory signals!
Termination of Cuneocerebellar Tract
Vermis
Function(s) of Spinomesecephalic Tract
Involved in central regulation of pain
The Spinocerebellar pathways enter the cerebellum from either the inferior or superior peduncles. Which is which?
Posterior Spinocerebellar Tract - Inferior
Anterior Spinocerebellar Tract - Superior
Cuneocerebellar Tract - Inferior
Two types of conscious sensation perceived at the level of the cerebral cortex
1) Exteroceptive - sensations from the external world
2) Proprioceptive - arise within the body
Function(s) of Spinoreticular Tract
Involved with pain and emotions.
- Arouses cerebral cortex to induce/maintain waking state
- Reports to the limbic cortex of anterior cingulate gyrus about nature of a stimulus
- emotional response may be pleasurable (stroking) or aversive (pinprick)
Ascending pathway which carries touch, joint sensation, two-point discrimination, and vibratory sense from receptors to the cortex
Posterior Column-Medial Lemniscal Pathway
Cause of Subacute Combined Degeneration
Deficiency in Vitamin B12 intake or metabolism
Medial Medullary Lesion
Lesion involves the medial lemniscus. Causes contralateral loss of vibration and joint position sense
Areas most noticeably affected (somatosensory) with a lesion in the thalamic region
Contralateral deficit most noticeable in face, hands, and foot
Termination of Anterior Spinocerebellar Tract
Vermis
Paresthias
Abnormal tingling/prickling sensation
- Lesions in the anterolateral system more likely to produce painful paresthesias
- Lesions in the dorsal column/medial lemniscal system are more likely to produce numbness or tingling
What region does the Periaqueductal Gray Matter (Midbrain), itself controlled by higher brain regions and spinal cord, send signals to regulate pain?
Rostral Ventral Medulla (RVM) in the Medulla
Distal Symmetrical Polyneuropathies
Cause bilateral sensory loss in a “glove and stocking” distribution (longest nerves affected) of all modalities
Location of decussation for Posterior Column-Medial Lemniscal Pathway
Caudal medulla
Lhermitte’s Sign
Electric-like shock that occurs when there is damage to the dorsal columns in cervical areas of the spinal cord; it can be elicited by asking the patient to bend their neck forward
Most affected senses in a Somatosensory Cortex lesion
Discriminative touch and joint position sense
Where do Posterior Columns terminate
Posterior column nuclei in the medulla oblongata
Spinal segments where fasciculus cuneatus is found
Only found in the cervical segments
All afferent tertiary (neuron order) input ends up where
somatosensory cortex
Spinocerebellar Pathways
Sensory fiber tracts running from spinal cord to cerebellum.
1) Posterior Spinocerebellar Tract
2) Anterior Spinocerebellar Tract
3) Cuneocerebellar Tract
Termination of Spinoreticular Tract
Medullary-Pontine Reticular Formation
Termination of Posterior Spinocerebellar Tract
Inferior Cerebellar Peduncle
Origin of Anterior Spinocerebellar Tract
Spinal Border Cells (T12-L5)
What might you see if cervical areas of the spinal cord are affected by Multiple Sclerosis?
Lhermitte’s Sign
Tabes Dorsalis
- Caused by tertiary syphilis; inflammatory involvement of the dorsal roots results in degeneration of dorsal columns
- Patient presents with bilateral loss of fine touch, vibration and conscious proprioception
- Romberg and/or Lhermitte Signs may be present
Disturbance of posterior column function is most often associated with what group of pathologies
Demyelinating diseases such as multiple sclerosis
Another mechanism in MS besides just the demyelination
Primary loss of neurons (neurodegeneration)
Common manner in which Posterior Column-Medial Lemniscal and Spinothalamic Pathways ascend CNS
- First-order neurons occupy posterior root ganglia
- Second-order somas on same side as original first-order neurons
- Second-order neurons decussate (cross the midline) and ascend to terminate in thalamus
- third-order neurons project form thalamus to somatic sensory cortex
Laminae from which Spinoreticular Tract arises from
Laminae VI-VII of dorsal horn
Romberg’s Sign
Swaying when the patient stands with feet together and eyes closed (can be seen in demyelinating diseases and vestibular disorders)
Two-Point Discrimination test
Measures tactile perception. Posterior (Dorsal) Column-Medial Lemniscal Pathway
Synapse in the Ventral Posterior Medial (VPM) nuclei of the thalamus
Cranial nerves
Among A-alpha, A-beta, A-delta, and C sensory neuron fiber types – which is/are myelinated?
All but C are myelinated
Lesions of the Postcentral Gyrus
Large lesion results in sensory loss involving fine touch, proprioception, vibration in the part of the body represented in that somatotopic projection. Paresthesias may present
Sensory Ataxia
Patients with severe sensory ataxia can stand unsupported only with feel well apart and with gaze directed downward to include the feet. Gait broad-based with stamping action that maximizes any conscious proprioceptive function that remains
Internal Arcuate Fibers
Axons of second order sensory neurons from the nucleus gracilis/cuneatus
Manner in which sensory fibers add to the posterior columns
They add laterally.
Medial portion of gracile fasciculus starts with information from legs and lower trunk. Cuneate fasciculus adds information from upper trunk, arm, neck and then finally the occiput
Termination of Spinothalamic Tract
Some neurons of the spinothalamic terminate in the intralaminar and mediodorsal nuclei of the thalamus
Origin of Cuneocerebellar Tract
Lateral Cuneate Nucleus
Receptors involved with proprioceptive sensation (both conscious and non-conscious)
Receptors of the locomotor system (muscles, joints, bones) and of the vestibular labyrinth (ears and balance remember)
Structures carrying the Posterior Column-Medial Lemniscal Pathway
Fasciculus Gracilis and Fasciculus Cuneatus
Function of Anterior Spinocerebellar Tract
Sensory from ipsilateral leg
Receptors involved with conscious exteroceptive sensation
Somatic: Touch, pressure, heat, cold and pain
Telereceptors: Vision and hearing
Synapse in the Ventral Posterior Lateral (VPL) nucleus of the thalamus
Medial lemniscus
Lateral Pontine or Medullary Lesion
- Affects contralateral anterolateral and ipsilateral trigeminal pathway.
- Loss of pain and temperature sensation in the body opposite the lesion
- Loss of pain and temperature sensation in the face on the side of the lesion
Asterogenesis
Loss of size/shape/texture discrimination
Other names for spinothalamic pathway
Anterolateral or ventrolateral
Termination of Spinomesencephalic Tract
Deviates from the anterolateral pathway in the midbrain to project to the midbrain periaqueductal gray and superior colliculus
The Spinocerebellar pathways differ from Posterior Column-Medial Lemniscal and Anterolateral pathways by being ipsilateral. What’s odd, though, about the Anterior Spinocerebellar Tract?
It’s ipsilateral but crosses midline twice; once in spinal cord and again in cerebellum.
