Autonomic
Alongside movement and sensation, your nervous system coordinates the ongoing work of circulation, digestion and other internal functions. Explore how these signals help meet changing needs.
Automatic regulation
What the system does
The autonomic nervous system helps adjust heart activity, blood vessels, digestion and glands. It acts mainly through cardiac muscle, smooth muscle and glandular tissue.
Sympathetic & parasympathetic
These divisions coordinate different patterns of organ activity. Sympathetic activity can increase heart rate and influence blood-vessel diameter; parasympathetic activity can slow the heart and support digestion.
Their effects depend on the organ, rather than acting as one whole-body on/off switch.
Connections with skeletal muscle
Blood supply to working muscles
Sympathetic nerves influence smooth muscle in vessels supplying skeletal muscle. Local metabolic signals, vessel-wall responses and the mechanical effects of contraction also help match blood flow to muscular activity.
Movement & muscle sensing
Somatic motor neurons provide the main commands for skeletal-muscle contraction. Alpha motor neurons activate force-producing fibers; gamma motor neurons adjust the small fibers inside muscle spindles, helping these receptors remain sensitive as muscle length changes.
Gamma motor activity belongs to the somatic motor system.
Muscle spindles · research in progress
Researchers have found anatomical evidence of sympathetic innervation in human muscle spindles. How this influences spindle signaling in everyday human movement remains an open question.
One human study found no detectable change in resting spindle discharge when sympathetic activity increased in the tested relaxed leg muscles.