BIOMED 10/23b SC Anatomy II Flashcards
receptor that senses change in muscle length is
intrafusal muscle fibers in muscle spindle
Examining a patient who shows marks of burn on the left foot. You test his sensations and find that he can not feel pinprick and hot/cold on the plantar as well as dorsal aspect of the Left foot. Proprioception is in tact. Lesion may involve:
- If dorsal root is cut, lose all sensations (proprioception as well), so not dorsal root
- Right anterolateral pathway in the spinal cord
- Utilize the spinal cord location to determine the side of the injury
If left proprioception is off, but pain and temperature are normal
Left DCML tract issue
Cut dorsal root yields
no sensation at all from the same side
cut DCML
- all proprioception and vibration gone on the same side
- Temperature and pain gone on the other side
descending tracts include
lateral
medial
direct
indirect
medial system of descending tracts entails
anti-gravity
Descend in the anteromedial column of the spinal cord
□ Anterior corticospinal tract
□ Vestibulospinal tracts (vestibular nuclei to spinal cord)
□ Reticulospinal (reticulum to spinal cord)tracts
□Tectospinal tract(midbrain/tectum to spinal cord)
lateral systems of descending tracts include
goal directed, fine motor control
Descends in the lateral column (funiculus) of the spinal cord
□ Lateral corticospinal tract - cortex to spinal cord
□Rubrospinal tract - nuclei from which these start (red nucleus to spinal cord)
direct system of descending spinal tract
project from the cerebral cortex to the spinal cord directly
Cerebral cortex -> descend at level of spinal cord
Two main:
- lateral corticospinal tract (paramatro)
- anterior corticospinal tract
what does the lateral corticospinal tract do?
1. Arises from the cerebral cortex and project to the spinal cord 2. crosses at the medulla (80%) 3. descends at the lateral funiculus and at spinal cord synapses either directly on anterior horn cells or interneurons
what do the indirect systems of the descending spinal tracts do?
project to the brainstem nuclei and then axons of the brainstem nuclei project to
the spinal cord
what is the homunculus?
region of the cerebral cortex that is like a map of the muscles of the body
- the maps are not static
can the homonculus be reorganized?
Yes! if you practice and train different body parts, the homunculus changes
what are the main regions of the cerebral cortex?
- primary motor (homunculus lives there)
- premotor
- supplementary motor
- somatosensory motor
what instance would be monosynaptic for the lateral corticospinal tract?
for fine motor muscles (fingers/hands/feet/NOT ELBOW); corticospinal axon moves directly from white matter to the anterior horn cells that are supplying the muscle (ONLY HERE)
how does the anterior corticospinal tract work?
- Arises from the cerebral
cortex and project to the
spinal cord - does NOT cross at the medulla (20%)
- descends at the anterolateral funiculus and at spinal cord synapses either directly on anterior horn cells or interneurons
- axons leave funiculus and bifurcate
-trunk muscles on same and opposite sides
-proximal muscles on the opposite side (hand muscles)
what are the upper and lower motor neurons that are in the lateral and anterior CST?
§ Anterior horn cells - lower motor neuron sitting within spinal cord, axons project down to the muscle
§ Upper motor neuron - neurons from corticospinal cortex and descend down to spinal cord
§ Lesions have very different effets
What is a motor unit?
motor neuron muscle fiber 1. small 2. medium 3. large
what are the small muscle fibers?
slow (S) - type I, slow oxidative muscle fibers
- low threshold
- quick activation
what are the medium muscle fibers?
Fast Fatigue Resistant (FFR) - type IIa, fast oxidative glycolytic (FOG)
- fast fatigue resistant
- higher threshold than small
What are the large muscle fibers/motor units?
fast fatigue (FF) - type IIx, Fast glycolytic -high threshold
what is the size principle of motor units?
first recruit smaller motor units, then as you need more and more motor force, there are two things that occur:
- small motor units increase firing frequency
- larger motor units begin to slowly get recruited and increase firing frequency
- -all motor units get activated when high forces are required
- -both occur in parallel
if you were to have a lesion on the left corticospinal region, what would happen?
weakness is predominant in the right hand, but not as much in the trunk
what does the lateral CST predominantly innervate?
• contralateral anterior horn cells • AHCs projecting to the distal UE and LE • For hand muscles, innervation is monosynaptic
what does the anterior CST predominantly innervate?
• contralateral and ipsilateral anterior horn cells via interneurons • AHCs projecting to the proximal muslces • Synapses on interneurons that project to the AHCs.
what are the types of AHCs or lower motor neurons?
– Alpha MN- go to the extrafusal muscle fibers
(skeletal muscle fibers)
– Gamma MN- go to the intrafusal muscle fibers of
the muscle spindle
indirect descending pathways
project to the brainstem (midbrain, pons, medulla) nuclei and then axons of the brainstem nuclei project to the spinal cord
Cerebral cortex -> synapse at brainstem -> synapse at level of spinal cord
Rubrospinal Descending Motor Tract
– Crosses immediately and descends in the
lateral funiculus
– Most rubrospinal fibers terminate at cervical
and thoracic levels, but some extend to all
cord levels,
– have an inhibitory effect on extensor
muscles and an excitatory effect on the
flexor muscles
– Alternate pathway to the spinal cord
reticulospinal descending motor tract
Important in the sense that it plays a significant role in maintenance of muscle tone/spasticity after stroke/SCI
- Medial (pontine) - facilitates spinal circuits has intrinsic excitability
- Lateral (medullary) - inhibits extensor tone relies on cortical input for its function
vestibulospinal tracts
Indirect descending
- lateral vestibulospinal tract
- medial vestibulospinal tract
lateral vestibulospinal tract
– Arises from the lateral vestibular nucleus – Descends ipsilaterally in the anterior funiculus – Increases extensor motor neurons controlling antigravity muscles
medial vestibulospinal tract
– Arises from the medial and inferior vestibular nuclei – Descends bilaterally to synapse on cervical and upper thoracic spine – Maintains to stabilize the head in relation to the body
spinal cord arrangement of white matter
funiculus -> lateral -> Rubrospinal -> anterolateral
spinal reflexes
• Spinal cord reflexes are central nervous
system (CNS) pathways that lie entirely within
the spinal cord.
• The sensory afferent fibers that evoke these reflexes enter the spinal cord and activate spinal motor neurons directly or indirectly through a chain of one or more spinal interneurons.
stretch reflex
- Input from periphery to center -> alpha motor neurons and then activating the muscle
- Sensory organ = muscle spindle (stretch on intrafusal muscle fibers go to central ns and activate alpha motor neurons and get a contraction while causing inhibition of antagonistic muscle)
