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| innervating muscles derived from somites (III, IV, VI, and XII) |
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| innervating muscle derived from the mesoderm of the aortic arches (V, VII, IX, and X) |
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| smooth muscle, glands, and the heart (III, VII, IX, and X) |
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| Oculomotor and parasympathetic nuclei are |
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| large fiber bundle on ventral surface of upper midbrain |
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| just inferior to upper midbrain |
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| The third nerve is visibly exiting between the peduncles |
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| In the lower part of the medulla, the brainstem |
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| folds to form the central canal. The dorsal column nuclei (gracile and cuneate) are relays for sensation from the body. |
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1. Sensory receptor and sensory neuron (a DRG cell)
2. Synapse in the CNS
3. Motor neuron |
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| damage along the reflex arc will |
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| diminishor abolish the reflex (hyporeflexia or areflexia) |
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| resistance to passive movement. Damage to the reflex arc will also produce atonia or hypotonia. Atrophy of the muscle will ensue. |
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| Descending Control of Reflexes |
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• Reflexes are often reduced in magnitude by pathways from the brain.
• The corticospinal tract “dials down” the deep tendon reflexes (patellar tendon reflex as an example).
• Damage to the corticospinal tract anywhere from the cortex to the ventral horn produces hyperreflexia and hypertonia. |
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Spastic paralysis
1. Hypertonia
2. Hyperreflexia |
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Flaccid paralysis
1. Hypotonia 2. Hyporeflexia 3. Atrophy |
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| Somatosensory pathway to cortex involves a three-neuron relay.: |
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• 1storderneuroninaDRG.Abranchofitsaxon enters the spinal cord.
• 2nd order neuron receives input from the 1st order. Its axon crosses the midline and ascends to the thalamus.
• 3rd order neuron in the thalamus projects to the cortex. |
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• Joint position
• Discriminative touch • Vibration
1st order neuron—DRG. Axons enter the spinal cord and ascend in the dorsal column.
2nd order neuron—caudal medulla. Its axon crosses.
3rd order neuron— thalamus. Axon projects to the cortex. |
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• Spinothalamic
• Trigeminothalamic system
Note the somatosensory pathway.
1st order neuron—DRG.
2nd order neuron—dorsal horn. Its axon crosses.
3rd order neuron— thalamus. Axon projects to the cortex.
[image] |
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• Contralateral spastic paralysis of body and limbs
• Contralateral loss of discriminative touch
• Ipsilateral flaccid paralysis of the tongue |
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• Contralateral loss of pain and temperature from the body and limbs
• Ipsilateral loss of pain and temperature from the head
• Dysphagia
• Asymmetric gag reflex
• Hoarse voice |
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| True or false: The medial lemniscus carries the joint position, discriminative touch, and vibration from the contralateral side of the body. |
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• Caudate, putamen, globus pallidus, substantia nigra, and subthalamus (also amygdala)
• Nomenclature:
• Striatum (also neostriatum)—caudate and putamen
• Paleostriatum—globus pallidus
• Lentiform nucleus—putamen and globus pallidus |
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| The basal ganglia exert their effects on movement through |
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| the direct pathway facilitates ___ and the indirect pathway |
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| movement, inhibits movement |
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So this is a frightening diagram. And if we can sort of take some of it bit-by-bit, it shows our thalamus right here. We're interested in that.
This is our VA, ventra interior thalamus. And it projects up to the cortex. And it does so with glutamate. So it excites the cortex, and therefore facilitates movement, OK? So if we can get that in our head for a minute.
And the cortex also projects the putamen, a part of our basal ganglia. And the putamen broadly speaking has two things it can do. One thing it does is it goes directly to the globus pallidus right here. Part of the globus pallidus. So it goes there. And it inhibits. It's got GABA, so it inhibits the globus pallidus.
And what effect does that have? Well, this is why sometimes anatomy can be so confusing. The globus pallidus inhibits the thalamus. So you're in fact inhibiting an inhibitor. And the net result of that is what's called the direct pathway. It facilitates movement because it removes an inhibition, OK. And this pathway is sometimes called the direct pathway.
Now the putamen has another pathway which obviously, we are going to call the indirect pathway, which ultimately leads in some way to the subthalamic nucleus which releases glutamate. And what that glutamate does is that glutamate excites the globus pallidus. And the effect of that is it was excited. There is more GABA released, which inhibits the thalamus.
So there's two pathways, a direct pathway which eventually excites the Thalamus and an indirect pathway which eventually inhibits it. So broadly speaking then, this complex circuit produces two possibilities. One in which there is the direct pathway that facilitates movements and the indirect pathway inhibits it.
And obviously, these pathways are working together modulating movement in one way or the other. So damage to one pathway, the direct pathway is going to produce decreased movement. Damage to the indirect pathway is going to create increased movement.
So we have these as part of the pathologies associated with Parkinson's disease where there's very limited movement with small tremors, to damage to the indirect pathway which produces more elaborate movements, Huntington's chorea as an example of a writhing excessive movement disorder.
So it's a complicated story. And this is a first pass rather through it. And Dr. Duque will follow up on that as his lectures approach. |
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