PHYS Block A

• automatic, involuntary system that serves to maintain homeostasis
• effectors: cardiac, smooth muscle & glands
• afferent sensory neurons respond to stretch, glucose, PCO2, PO2, osmolarity & pH, temperature
• efferent motor neurons: innervate viscera & involuntary muscle
• sympathetic & parasympathetic systems

• two neuron pathway
• pathway leading from the CNS (preganglionic neuron) to a peripheral ganglion (postganglionic neuron) to the target tissue

• short preganglionic neurons from thoracolumbar spinal cord (T1-L3) are cholinergic (release ACh)
• long postganglionic neurons from paravertebral or prevertebral ganglia are adrenergic (release NE)

• part of peripheral nervous system (operates largely independently of CNS)
• 3 neuron system: sensory neuron, interneuron, motor neuron
• function: coordinates GI function, monitors state of lumen & gut wall, respons appropriately
• networks: myenteric (motility) & submucous (secretions)

• N2 receptor
• binds ACh on postganglionic (adrenergic) neuron

• binds NE on target cell
• a1: vasculature
• a2: presynaptic
• B1: heart, adipose
• B2: bronchioles, vasculature
• B3: adipose (thermogenic)

postganglionic neuron releases ACh that binds to muscarinic receptors in sweat glands & vessels

• a1q: vascular smooth muscle contraction, skin, GI tract, kidney
• a2i: decrease neurotransmitter release; SM contraction (GI sphincters), decrease insulin release
• Bs: increase heart rate, SM relaxation (bronchi, uterus), glycogenolysis, lipolysis

• long preganglionic neurons from brainstem (CN III, VII, IX, X) and sacral spinal cord
• short postganglionic neurons from parasympathetic ganglia near or in wall of target organ
• both neurons are cholinergic (release ACh)
• preganglionic ACh binds to nicotinic receptors
• postganglionic ACh binds to muscarinic receptors

• effectors: skeletal muscles
• efferent: heavily myelinated axons from CNS to muscle
• NT effects: ACh excitatory effect in nicotinic receptors

• nicotinic: ligand gated ion channel
• muscarinic: G protein coupled; ACh binds to receptor & triggers signaling cascade

• acetylcholine
• norepinephrine
• ATP
• nitric oxide

• acetylcholine: increase motility, increase intestinal secretions, increased enteric hormone release
• norepinephrine: decrease effects of acetylcholine
• others: VIP, opiods, 5-HT, substance P, NO, etc.

• "fight or flight"
• exercise, excitement, embarrassment
• dilation of pupils
• increase HR, contractility & BP
• blood flow decreased to non-essential organs
• increased bronchial dilation
• increased respiratory rate
• increase fuel mobilization (glucose & FFA)

• "rest & digest" - conserve & restore energy
• normally PSNS tone > SNS
• digestion, defecation, diuresis
• SLUDD response: salivation, lacrimation, urination, digestion & defecation
• decreases: HR, airway & pupil diameter

• GI
• cardiovascular: sensory input - chemo & stretch receptors at carotid sinus & aortic arch

• adrenal medulla
• sweat glands
• erector pili muscles
• kidneys (renin-angiotensis system)
• most blood vessels

erectile tissue

• decrease SNS activity (decrease BP)
• increase PSNS activity (decrease HR)

increase SNS activity (increase HR & BP)

• PSNS favors digestive processes: increased gut motility, acid & enzyme secretions; relaxation of sphincters
• SNS inhibits digestive processes: contraction of sphincters (pyloric, ileocecal, & internal anal); inhibition of motor neurons throughout gut

exclusive SNS modulation of internal body temp

• sweat gland activation
• skin vasodilation (bring warm blood to surface)

• skin vasoconstriction (blood retained in vital organs)
• shivering
• piloerection
• no sweating

• erection: PSNS (vasodilation of erectile tissue); SNS (decreased tone during erection)
• ejaculation: SNS (smooth muscle contraction at distal epididymis)