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. Author manuscript; available in PMC: 2023 Mar 9.
Published in final edited form as: Compr Physiol. 2022 Mar 9;12(2):3193–3279. doi: 10.1002/cphy.c200033

Figure 8.

Figure 8

This figure illustrates simultaneous innervation in skeletal muscle by the somatic and the autonomic nervous systems. Briefly (1104), motor neuron release of acetylcholine (Ach) promotes influx of sodium (Na+) and calcium (Ca++) into skeletal muscle cell. This promotes release of calcium from sarcoplasmic reticulum (SR), leading to contraction. The sympathetic neuron innervates muscle in close proximity and may release norepinephrine (NE) to augment Ach release. Circulating epinephrine from the endocrine system supports sympathetic activation by augmenting Ach release in addition to enhancing Na+ influx and calcium-induced calcium release and re-sequestering.