Autonomic nervous system Flashcards
Overall function of ANS
•Homeostasis: Maintaining a stable internal environment amid changing external conditions
ANS vs. somatic motor system
ANS is: Involuntary (vs voluntary), Diffuse projections (vs specific projections), Slow action (vs rapid), Innervates smooth and cardiac muscle, and gland cells (vs. skeletal muscle), Disynaptic (vs Monosynaptic)
Which fibers are fast and which are slow, preganglionic or postganglionic?
preganglionic are myelinated and fast. Postganglionic are unmyelinated and slow
Inputs to the ANS
Nucleus of solitary tract conveys visceral sensory input, other brainstem nucle convey environmental stimuli, hypothalamus conveys internal states
3 subdivisions of ANS
Sympathetic, parasympathetic and enteric (semi-autonomous control of digestion)
Anatomy of sympathetic NS
•Preganglionic neurons originate in thoracic and lumbar spinal cord, Ganglia located near spinal cord(sympathetic trunk), 1:10 ratio of pre- to post-ganglionic neurons
Anatomy of parasympathetic NS
•Preganglionic neurons originate in brainstem and sacral spinal cord, Ganglia located near target organs, 1:3 ratio of pre- to post-ganglionic neurons
Sympathetic neurotransmitters and receptors
Ach is released from preganglionic neuron, binds to nicotinic receptor on postganglionic neuron. Postganglionic neuron releases norepinephrine and epinephrine which bind to alpha and Beta adrenergic receptors on the organ
Parasympathetic neurotransmitters and receptors
Ach is released from preganglionic neuron, binds to nicotinic receptor on postganglionic neuron. Postganglionic neuron releases Ach which binds to muscarinic receptor on organ.
Compare nicotinic and muscarinic Ach receptors
Nicotinic is ligant-gated cation channel that opens and leads to depolarization. Muscarinic is liked to a G protein which can cause depolarization or hyperpolarization depending the type of muscarinic receptor
Vasodilation and constrictions are mainly controlled by?
sympathetic NS- increased SNS causes vasoconstriction and decreases SNS causes vasodilation
SNS vs PSNS affect on blood pressure
SNS: increases blood pressure (increases HR, contractile force and constriction of blood vessels). PSNS: decreases BP (decreases HR and contractile force)
What was the Loewi experiment
First identification of chemical neurotransmission: two hearts were connected by a pump and the first heart was stimulated. The second heart had same HR as first heart
What is Atropine?
Sympathomimetic drugs – mimic sympathetic activation. Acts as a muscarinic antagonist in heart to increase HR
What is Propranolol?
•Parasympathomimetic drugs – mimic parasympathetic activation. Acts as beta adrenergic antagonist in heart to decrease HR
Describe humoral regulation from hypothalamus
Hormones are made in hypothalamus then released into the pituitary. Posterior pituitary is a direct extension of hypothalamus axons. Anterior pituitary is a gland
Vasopressin- released from where? Results in?
Aka ADH. Released from posterior pituitary in response to low blood pressure detected by subfornical organ. Causes vasoconstriction and Acts on kidneys to increase water retention
Renin- Released from where? Function?
Released from kidneys in response to low BP. Converts Angiotensinogen to Angiotensin I
Angiotensin II - functions
Constricts blood vessels, increases water retention in kidney, activates neurons in subfornical organ
The adrenal medulla functionally is a ___________
sympathetic ganglion
What does adrenal medulla do?
Innervated by preganglionic sympathetic neurons and releases NE and epi into blood, with widespread sympathomimetic effects. NE and epi thus become hormones that regulate activity of disant tissues
Which neurotransmitter can activate all 4 subtypes of adrenergic receptors?
Epinephrine from adrenal medulla- activates alpha 1,2 and beta 1,2
Explain baroreceptor reflex
low blood pressure leads to increased sympathetic output. High blood pressure leads to increased parasympathetic output
CV related action of agonists of adrenergic receptors: alpha1, alpha2, Beta1, beta 2
alpha1: vasoconstriction in skin. Alpha 2: presynaptic inhibition of NE release and some vasoconstriction. Beta1: increased HR. Beta2: incrased HR, vasodilation in skeletal muscle
“head ganglion”
hypothalamus
Why is hypothalamus called the head ganglion
It integrates info from several brain regions in order to convey the needs of the organisms to preganglionic autonomic centers in brainstem and spinal cord. Also coordinates humoral respose via pituitary
