Why does the heart lose its sympathetic supply when C7 is transected?

[sameeralord]

Hello everyone,

Quick question about spinal cord shock.

1. If C7 is transected, why does heart lose its sympathetic supply. I don't know much about autonomic nervous system, but isn't it coming from sympathetic trunk located outside the spinal cord, so how can it have an effect.
2. Also at C1 in hanging, why does person die, is it due to loss of breathing?

 

[bobze]

Hello everyone,

Quick question about spinal cord shock.

1. If C7 is transected, why does heart lose its sympathetic supply. I don't know much about autonomic nervous system, but isn't it coming from sympathetic trunk located outside the spinal cord, so how can it have an effect.
2. Also at C1 in hanging, why does person die, is it due to loss of breathing?

Short answer is because C7 contributes fibers to the cardiac plexuses.

No I don't think it is specifically C1 that does you in, during hanging. I think its the sum trauma that does it.

If it is a breathing problem that kills you during a hanging, remember "C3, 4, 5 keeps me alive". These are the contributors to the phrenic nerve which innervates the diaphragm.

I'll expound more later.

 

[bobze]

Okay Sameeralord, Sorry for the short answer above. I had to run to a practice practical.

So the heart gets it's sympathetic innervation from T1-T6. Preganglionic fibers from those levels travel up the chain to the cervical and thoracic ganglion and synapse before leaving the chain and traveling to the superficial and deep cardiac plexuses.

Edit: The levels of innervation maybe different depending where your source is from. I checked the levels in both Gilroy's and Netter's (which are pretty good authorities on anatomy), the former has T1-T6, the latter T1-T4. I believe in our cardio block we learned T1-T4, but it was mentioned there is variation and some innervation can come from T5/T6, but by anatomists this is generally considered a less important point. A quick look at some Google-Book previews shows listing of everything from T2-T4 to T1-T5.

Not sure where you read that about the C7, do you recall?

For number 2, when a person is hung correctly (that is they fall far enough) their neck breaks. Its the breaking of the neck and severing or damaging of the spinal cord that kills the individual. The "death knell" should be from damage to the cervical enlargement. This would plummet the blood pressure, cause the subject to loose consciousness as well as destroying innervation to the diaphragm etc.

If a person is hung incorrectly, they are generally strangled. So death would by asphyxiation (much slower).