A patient with myocardial infarction often complains of chest pain radiating to the left arm.
Describe the pathway taken by the afferent fibers in MI.
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Blocked coronary |
Complete blockage of a major branch of the coronary artery results in tissue death. This releases chemicals which stimulate the sensory fibers. |
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Superficial cardiac plexus |
Superficial cardiac plexus Some afferent fibers travel to the cardiac plexus located below the arch of the aorta (between the aorta and the pulmonary artery). It is just intermingling of fibers. There are no sympathetic ganglia here and the afferent fibers do not synapse in this location. |
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Deep cardiac plexus |
Other afferent fibers travel to the cardiac plexus located below the arch of the aorta at the bifurcation of the trachea (between the tracheal bifurcation and the aortic arch). It is just intermingling of fibers. It contains no sympathetic ganglia and the afferent fibers do not synapse here |
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Sympathetic chain |
These sensory fibers then enter the sympathetic chain (ganglia or the interganglionic part). These fibers just pass through without synapse. (They take the same path as their efferent counterparts but do not synapse.) |
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Spinal nerves |
Next they jump on to the spinal nerve (along the rami communicantes). If they don’t, they have no way of reaching perception. |
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DRG |
Impulse then reaches the DRG (T1-T4). It is here that the cell body of the sensory neuron is located. DRG is at the intervertebral foramen. |
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Spinal cord |
Fibers then enter the spinal cord via the dorsal root (T1 T4 segment) and ascend to the brain. |
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Brain - cortex |
Brain - cortex Pain is perceived once the information reaches the sensory cortex. Image226 |
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Chest and arm |
As the afferent (sensory) fibers from the skin of the chest (intercostal nerves T1-4) and medial sides of arm (intercostobrachial nerve T2) enter the same DRG as the sensory fibers from the heart, the pain is perceived to be coming from those regions. |
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Vagus |
Does the vagus contain any afferents from the heart? (Yes, most cardiac branches of the vagus and the sympathetic contain motor as well as sensory fibers.) |
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