The Spinal Cord Flashcards
Describe Pseudounipolar Neurons
- Peripheral receptive ending
- Cell body in the DRG
- Central Axon enter dorsal horn of spinal cord
Describe the two roots of spinal nerves
- Ventral Roots: contain motor (efferent) fibers from the ventral horn motor neurons
- Dorsal Roots: contain sensory (afferent) fibers from sensory neurons in the DRG
- Conduct impulses from peripheral receptors
Define Dermatome
Sensory area on the body that is associated with a specific spinal level
What are the two lengthwise grooves that divide the spinal cord into right and left halves?
- Ventral (anterior) median fissure
- Dorsal (posterior) median sulcus
What is the gray commissure?
connects masses of gray matter and encloses central canal
What makes up the gray matter of the spinal cord? Describe each part
- Dorsal horn: interneurons that receive somatic and visceral sensory input
- Ventral horn: somatic motor neurons whose axons exit the cord via ventral roots
- Lateral horns: (only in thoracic and lumbar segments) - sympathetic neurons
- Dorsal root ganglia (DRG): contain cell bodies of sensory neurons
What are the components of a reflex arc?
- Receptor
- Sensory neuron
- Integration center
- Motor neuron
- Effector (muscle fiber or gland cell)
What is the role of stretch reflexes?
- maintain muscle tone in large postural muscles
- cause muscle contraction in response to increased muscle length (stretch)
e.g. DTRs
What is reciprocal inhibition?
- fibers synapse with interneurons that inhibit the alpha motor neurons of antagonistic muscles
3 Types of Nerve Fibers in White Matter of Spinal Cord?
- Long Ascending: projecting to thalamus, cerebellum, and brainstem nuclei
- Long Descending: projecting from the cerebral cortex or brainstem nuclei to spinal gray matter
- Short Propriospinal: interconnecting different cord levels
Describe: Ascending Pathways - First Order Neuron
- Cell bodies in DRG
- Conducts impulses from cutaneous receptors and proprioceptors
- Branches diffusively as it enters the spinal cord or medulla
- Synapses with second-order neuron
Describe: Ascending Pathways - Second-order Neuron
- Interneuron
- Cell body in dorsal horn of spinal cord or medullary nuclei
- Axons extend to thalamus or cerebellum
Describe: Ascending Pathways - Third-order Neuron
- Interneuron
- Cell body in thalamus
- Axon extends to somatosensory cortex
Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the __________.
Intervertebral foramen
What are the contents of the White Matter of the Spinal Cord?
- Consists mostly of ascending (sensory) and descending (motor) tracts
- Transverse tracts (commissural fibers) cross from one side to the other
- Tracts are located in three white columns (funiculi [bundle of nerve fasicles] on each side—dorsal (posterior), lateral, and ventral (anterior)
- Each spinal tract is composed of axons with similar functions
How does a stretch reflex work?
- Stretch activates the muscle spindle
- Sensory neurons synapse directly with alpha motor neurons in the spinal cord
- alpha motor neurons cause the stretched muscle to contract
- All stretch reflexes are monosynaptic and ipsilateral
What is Autogenic Inhibition?
- A polysynaptic reflex that helps prevent damage due to excessive stretch
- Seen clinically as the Clasp-Knife response (a rapid decrease in resistance when attempting to flex a joint, usually during a neurological examination. It is one of the characteristic responses of an upper motor neuron lesion)
Major function of Posterior Column? Damage can result in what?
- Proprioception and Vibration
- Ataxia: incoordination of muscular movement, most pronounced with eye’s closed
What does the posterior column consist of?
Fasiculus gracilis - pathway for legs (Below T6)
Fasiculus cuneatus - pathway for arms (Above T6)
What does the spinocervical tract/ posterolateral funiculus do?
- Ipsilateral sensory information from hair receptors, some tactile, and some nociceptive neurons
- Accessory pathway for sensory information to reach thalamus in case posterior columns compromised
What is the anterolateral pathway responsible for? Damage to this area can result in what?
- pain and temperature
- contralateral anesthesia
What are the contents of the anterolateral system?
- Spinothalamic Tract - Major afferent pathway for pain and temperature localization as well as crude touch and pressure
- Spinoreticular– dull pain
- Spinomesencephalic–role in intrinsic pain control
- Spinohypothalamic– projections to autonomic control regions
What is the spinocerebellar system responsible for? Damage can result in what?
- Proprioception (joint position)
- Usually damage is concurrent with losses in posterior columns with similar effects.
Overall there will be ataxia similar to cerebellar damage, with a loss of proprioception or tactile sensation.
If just spinocerebellar deficits, then no sensory loss of conscious sensation.
