Autonomic Nervous System Review: Sympathetic vs Parasympathetic (Key Terms)

Division and Innervation

• Sympathetic: thoracolumbar division; adrenal medulla receives direct preganglionic input to release stress hormones.
• Parasympathetic: craniosacral division.

Functional Effects by Division

• Pupil size: Parasympathetic → constriction (miosis).
• Airways: Sympathetic → bronchodilation (airway relaxation); Parasympathetic → bronchoconstriction.
• Salivation: Sympathetic → decreased salivation.
• Blood flow: Sympathetic redirects blood from kidneys to skeletal muscles (fight-or-flight).

Adrenal Gland and Stress Hormones

• Adrenal medulla receives direct sympathetic innervation; releases adrenaline (epinephrine) and noradrenaline (norepinephrine) into the bloodstream.

Dual Innervation

• Most organs have dual innervation; sympathetic and parasympathetic inputs coordinate function.

Receptors and Responses

• Skeletal muscle NMJ: nicotinic acetylcholine receptor → muscle fiber contraction.
• Heart: norepinephrine acts on beta-adrenergic receptors (primarily beta-1) → excitatory effects (increased rate/force).
• If asked about receptor types:
  • Skeletal muscle receptor for ACh: nicotinic.
  • Cardiac receptor for NE: beta-adrenergic (beta-1).

Quick Quiz Highlights

• Receptor on skeletal muscle cells for acetylcholine: Nicotinic.
• Heart receptors receiving norepinephrine with excitatory effects: Beta-adrenergic (beta-1).