ANS and Visceral Reflexes Outline

visceral reflex arc example (high BP)

1. detected by stretch receptors

2. carried by afferent neuron to CNS

3. response via efferent to heart

4. heart slows and BP lowers

homeostasis (negative feedback)

ANS controls

glands, cardiac muscle, and smooth muscle

sympathetic division of ANS prepares body for energy

consumption; exercise, trauma, “fight or flight”

• increases HR, BP, etc.

parasympathetic division of ANS prepares body for energy

restoration

• digestion and waste elimination

• “rest and digest”

sympathetic tone

keeps BV partially constricted, maintains BP

parasympathetic tone

maintains smooth muscle tone in intestines

autonomic nervous system has 2 motor neurons explain these and what it effects and S vs P

preganglionic neuron is myelinated and is much longer in parasympathetic system

postganglionic neuron is unmyelinated and effects smooth and cardiac muscle and glands

Preganglionic neurons exit SpC from (sympathetic)

thoracic or lumbar regions

each chain ganglion in sympathetic division are connected to spinal nerve by 2 branches called (describe these rami)

communicating rami

preganglionic fibers: myelinated fibers enter ganglion via white communicating ramus

postganglionic fibers: unmyelinated fibers leave ganglion via gray communicating ramus

nerve fibers leave sympathetic chain (spinal nerve route)

(synapses right away)

effectors: sweat glands, piloerector muscles, BVs of skin and skeletal muscles

nerve fibers leave sympathetic chain (sympathetic nerve route)

(travels up the chain and synapses higher up)

effector: iris, heart, lungs, esophagus, and thoracic BVs

nerve fibers leave sympathetic chain (splanchnic nerve route)

(passes through chain and synapses on collateral ganglion)

effectors: liver, spleen, adrenal glands, stomach, kidney, etc.

paired adrenal glands include

adrenal cortex- secretes steroid hormones

adrenal medulla- like sympathetic ganglion

• modified postganglionic neurons

Parasympathetic division comes from… and travel in…

brainstem and sacral regions of SpC and fibers travel in cranial and sacral nerves

origin of long preganglionic neurons in parasympathetic division

midbrain, pons, and medulla (brainstem)

parasympathetic cranial nerves include what 4?

oculomotor nerve

• narrows pupil, focuses lens

facial nerve

• tear, nasal, and salivary glands

glossopharyngeal nerve

• parotid salivary gland

vagus nerve

• viscera

parasympathetic fibers from S2-S4 most form pelvic nerves on target organs like

distal colon, rectum, urinary bladder, reproducing organs

enteric nervous system

3rd autonomic system

innervates smooth muscle and glands

has own ganglia and reflex arcs

megacolon (Hirschsprung’s)

massive dilation of bowel accompanied by abdominal distension and chronic constipation

2 types of cholinergic receptors (for ACh)

nicotinic receptors- on all ANS postganglionic neurons, adrenal medulla, neuromuscular junctions

muscarinic receptors- cardiac and smooth muscle, gland cells

NE secreted by nearly all

sympathetic postganglionic neurons

2 types of adrenergic receptors (for NE)

alpha-adrenergic receptors: two subclasses different second messenger systems

beta-adrenergic receptors: two subclasses cAMP second messenger system

NE only released by

sympathetic division

ACh released by

both S and P

sympathetic effects tend to last…. than parasympathetic

longer

• NE by sympathetics persists in synapse and much passes into bloodstream

• ACh released by parasympathetics broken down quickly and synapse

dual innervation

most viscera innervated by BOTH sympathetic and parasympathetic divisions

• antagonistic effect: oppose each other

• cooperative effects: act on different effectors- produce unified overall effect

antagonistic effects- same effector cells

HR: increase (sym) or decreases (para)

antagonistic effects- different cells

pupillary dilator muscle (sym) dilates pupil

constrictor pupilae (para) constricts pupil

cooperative effects act on different effectors to produce unified effect

parasympathetics: increase salivary serous cell secretion

sympathetics: increase salivary mucous cell secretion

control without dual innervation (some effectors receive only sympathetic fibers)

adrenal medulla, arrector pili muscles, sweat glands, many BVs

ex: regulation of BP, routes of blood flow

increasing firing frequency (sympathetic vasomotor tone)

vasoconstriction

decrease firing frequency (sympathetic vasomotor tone)

vasodilation

sympathetic can exert opposite effects on target organ through BVs examples (without dual innervation)

vasoconstrict BVs to skin (minimize bleeding)

prioritize BVs to skeletal muscles and heart (like running away from bear)

drugs and nervous system can influence ANS (caffeine)

caffeine competes with adenosine receptors because they have similar molecular structures so it combats sleep!

how cerebral cortex influences ANS

anger, fear, anxiety

how hypothalamus influences ANS

visceral motor control- hunger, thirst, s3x

how midbrain, pons, medulla oblongata influences ANS

cardiac and vasomotor control, salivation, swallowing, sweating, bladder, etc.

brain can inhibit consciously

if SpC damaged, smooth muscle of bowel and bladder reverts to autonomic control