Chapter 15: Autonomic Nervous System

spinal nerve pathway

preganglionic neuron → sympathetic trunk ganglion → postganglionic axon extends through gray ramus at same “level” to join spinal nerve of effector (skin of neck, torso, and limbs)

postganglionic sympathetic nerve pathway

preganglionic neuron → sympathetic trunk ganglion (paravertebral ganglion) → (does not leave trunk via gray ramus) visceral branch to effector (skin of head, eye, and organs in neck)

splanchnic nerve pathway

preganglionic neuron → prevertebral ganglion (passes trunk) → effector (abdominal and pelvic organs)

adrenal medulla pathway

preganglionic neuron → neurosecretory cells within adrenal medulla (passes trunk and prevertebral)

Where do the preganglionic neurons from the parasympathetic division extend from?

brainstem or lateral gray matter of S2-S4

(cranial and sacral; craniosacral)

Where do the preganglionic neurons from the sympathetic division extend from?

lateral horns of T1-L2

(thoracic and lumbar; thoracolumbar)

oculomotor nerve (CN III)

smooth muscle of eye

facial nerve (CN VII)

submandibular and sublingual salivary glands in floor of the mouth; lacrimal glands; glands of nasal cavity, oral cavity, and palate

glossopharyngeal nerve (CN IX)

parotid salivary gland

vagus nerve (CN X)

thoracic organs and most abdominal organs and gonads

pelvic splanchnic nerves

some abdominal organs and most pelvic organs; originate from S2-S4

Which division has higher neuronal divergence?

sympathetic nervous system (think mass activation)

Which division has higher neuronal convergence?

parasympathetic nervous system

cardiovascular reflex

↓ blood pressure (parasympathetic ↓ heart rate and cardiac output)

gastrointestinal reflex

rectum contracts and internal anal sphincter relaxes (parasympathetic promotes defectation)

micturition reflex

contraction of smooth muscle in bladder wall and relaxation of urinary sphincters (parasympthetic promotes urination)

autonomic plexus

sympathetic postganglionic axons and parasympathetic preganglionic axons

cardiac plexus

innervates the heart

pulmonary plexus

innervates the bronchi and bronchioles of the lungs

esophageal plexus

innervates the esophagus

What does the abdominal aortic plexus consist of?

celiac plexus, superior mesenteric plexus, and inferior mesenteric plexus

enteric nervous system

innervates smooth muscle and glands of GI tract

What two plexuses are in the enteric nervous system?

submucosal plexus and myenteric plexus

cholinergic neurons release ?

acetylcholine (ACh)

cholinergic receptors

nicotinic receptors and muscarinic receptors

adrenergic neurons release ?

norephinephrine (NE)

adrenergic receptors

alpha (α) receptors and beta (β) receptors

Describe parasympathetic pathway for neurotransmitters and receptors.

preganglionic releases ACh → nicotinic receptors on ganglion → postganglionic releases ACh → muscarinic receptors on effector

Describe the typical sympathetic pathway for neurotransmitters and receptors.

preganglionic releases ACh → nicotinic receptors on ganglion → postganglionic releases NE → adrenergic receptors on effector

Describe the sweat glands sympathetic pathway for neurotransmitters and receptors.

preganglionic releases ACh → nicotinic receptors on ganglion → postganglionic release ACh → muscarinic receptors on effector

Describe adrenal medulla sympathetic pathway for neurotransmitters and receptors.

preganglionic release ACh → nicotinic receptors on effector → E/NE into blood

α₁ receptor locations

vascular smooth muscle; dilator pupillae; internal urethral sphincter

α₁ receptor effects

smooth-muscle contraction → vasoconstriction, pupil dilation, urinary retention (squeeze)

α₂ receptor locations

presynaptic sympathetic terminals; CNS; pancreatic β cells

α₂ receptor effects

decreases neurotransmitter or hormone release → especially reduced norepinephrine release (suppress)

β₁ receptor locations

heart; kidney

β₁ receptor effects

increases cardiac activity → heart rate, contractility, conduction; also increases renin release (beat)

β₂ receptor locations

bronchiolar smooth muscle; vascular smooth muscle supplying skeletal muscle; uterus

β₂ receptor effects

smooth-muscle relaxation → bronchodilation, vasodilation, uterine relaxation (breathe/open)

β₃ receptor locations

adipose tissue; urinary bladder detrusor muscle

β₃ receptor effects

promotes lipolysis and detrusor relaxation which stores urine (burn/bladder)