GSE and GSA pathways (Quiz 5) Flashcards
The voluntary motor system is composed of descending tracts from the brain to the periphery. It involves a 2 neuron chain. What are the 2 neurons?
1) UMN located in CNS
2) LMN that stimulates effectors in the periphery and is a GSE
What does a motor unit include?
-1 motor neuron
-its axon
-myocytes innervated by that motor neuron
GSE or somatic motor fibers arise from motor neuron cell bodies in the ___________ horns of the gray matter within the spinal cord
ventral
GSE or somatic motor fibers arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord. They exit the spinal cord through the _________ roots, carrying motor impulses to skeletal muscle
ventral
Somatic efferent neurons can be either….
-alpha motor neurons that target extrafusal muscle fibers (fast)
-gamma motor neurons that target intrafusal muscle fibers (slow)
The corticospinal tract (the cell bodies sit in cerebral cortex/motor cortex and the axons descend into spinal cord) is the descending motor pathway that sends info to _________. Since these fibers travel in the medullary pyramids, the path is often called the pyramidal tract
GSEs
Electrical stimulation of the primary motor area/precentral gyrus in conscious patients evokes movements of _______________ parts of the body
contralateral
Where are UMNs usually found?
cerebral cortex/ motor cortex
Where are LMNs usually found?
ventral horn
What is the corticospinal pathway?
cortex> internal capsule> cerebral peduncles> pons> pyramid> pyramidal decussation> lateral column
The ____________________ is a general term for cortical and subcortical areas and the paths from them participating in motor activity. They supplement the primary motor cortex and pass through the tegmentum
extrapyramidal system
What are the 4 other ways to activate GSE besides corticospinal tract?
1) rubrospinal tract (starts at red nucleus)
2) tectospinal tract (roof of midbrain at the superior and inferior colliculus)
3) reticulospinal tract (reticular formation)
4) vestibulospinal tract (vestibule of inner ear and then comes into brainstem vestibular nuclei (equilibrium))
so bc of this, there are 4 other locations besides motor cortex where UMNs are found
GSAs from the body transmit….
-pain and temp
-crude touch and pressure
-discriminative touch and pressure
-light touch (can feel a feather, loose thread, etc.)
-proprioception
GSAs have a 3 neuron system. What are they?
1st order, 2nd order, and 3rd order neurons
GSAs are found in which root?
dorsal
For a GSA pathway, there are 3 neurons. The 1st receptor is at the peripheral end of the primary neuron is neuron 1. The cell body is in a spinal ganglion or in the __________ ganglion and is always on the same side as the receptor. GSA synapses in the dorsal horn and the laminae is dependent on type of info. The 2nd synapse on the secondary neuron is in the dorsal horn of the spinal cord, its axon/process contributes to an ascending tract (neuron 2). The 3rd synapse is in the thalamus (nuclei dependent on info). A tertiary neuron in the thalamus projects to a neuron in the cerebral cortex (neuron 3). A receptor along with peripheral and central processes of sensory neurons, can be functionally modified or modulated along the pathway (neuron 1,2, or 3). These neurons are ____________________. Interneurons in the spinal cord add complexity to this circuit (touch neurons do have input to pain projection pathways, but local interneurons keep this under strong inhibition under healthy conditions)
trigeminal, pseudounipolar
What is the 1st neuron modality of GSAs?
transmits pain (has nociceptors) and temp (has thermoreceptors)
The primary path carrying impulses for sharp, well localized somatic pain and temp from the limbs, trunk, neck, and back of the head is the ________________________ tract
lateral spinothalamic
Fiber distribution in the lateral spinothalamic tract has ___________________
somatotopic and modality-topic organization
Light touch/stimuli without pressure like a wisp of cotton, a strand of hair on your skin, or air blowing on you is a GSA 3 neuron system. The GSA enters the medial part of the dorsal root and synapses in lamina 3 (nucleus proprius) and the axons cross as ventral white commissaral fibers. They ascend as the _______________________ tract
ventral/anterior spinothalamic
note: this tract does not have great localization, we just can feel the hair or air in a general area
memory cue:
air VENT feels like soft touch or ANT goes up leg ANTERIORLY
Where does the ventral spinothalamic tract end?
at the thalamus (medial to the lateral spinothalamic tract)
An alternative pathway transmits impulses for tactile discrimination, pressure, proprioception, and vibration. These receptors of GSA provide detail on the object, location, and texture. Discriminative or 2 point touch is the ability to distinguish the sensations at each point when 2 points are simultaneously stimulated. The cell bodies of primary neurons in this pathway occur in all spinal ganglia and the axons enter through the dorsal root and enter the ipsilateral dorsal funiculus. This pathway is called…..
dosal/posterior column medial lemniscus tract (DCML or PCML)
What is proprioception?
subjective awareness of the position and movement of joints, limbs, and other body parts with awareness of movement or kinesthesia or positional sense
What are the 2 fiber bundles in the dorsal column medial lemniscus tract?
1) fasciculus gracilis
2) fasciculus cuneatus
Fibers that enter the DCML caudally to T6 travel in the….
fasciculus gracilis
Fibers that enter the DCML rostrally to T6 travel in the….
fasciculus cuneatus
Where do the DCML primary neurons ascend and synapse in?
medulla at their corresponding nuclei (nucleus gracilis or nucleus cuneatus)
after leaving the nuclei, they cross the median plane as the sensory decussation/decussation of the medial lemnisci and project to the thalamus and then sensory cortex
