peripheral NS anatomy and phys Flashcards
- List the neurotransmitters and receptors that mediate neurotransmission at the ganglia and/or end organs in the parasympathetic nervous system
Parasympathetic: Ach released from pre-ganglionic neuron (cell body in brainstem) > binds to nicotinic cholinergic receptor on post ganglionic neuron in the ganglia > Ach released from post ganglionic terminal and binds to muscarinic receptor to act on cardiac/smooth muscle, gland cells or nerve terminals
- List the neurotransmitters and receptors that mediate neurotransmission at the ganglia and/or end organs in the sympathetic nervous system
Sympathetic: Ach released from pre-ganglionic neuron (cell body in spinal cord) > Binds to nicotinic cholinergic receptor at ganglia > post ganglionic terminal releases Ach (muscarinic receptors on sweat glands), NE (adrenergic receptors on cardiac muscle, smooth muscle, gland cells or nerve terminals), or dopamine (dopamine receptors on renal vascular smooth muscl)
- List the neurotransmitters and receptors that mediate neurotransmission in the somatic nervous system
Ach released from motor nerve (cell body in spinal cord)> binds to nicotinic receptor on skeletal muscle
- List the neurotransmitters and receptors that mediate neurotransmissionfrom the adrenal medulla
Ach released from pre-ganglionic neuron > EPI and some NE released from adrenal medulla (acts as sympathetic ganglion) into general circulation > binds adrenergic receptors
Where do PSNS and SNS neurons originate in CNS?
PSNS: neurons originate in cranial nerve nuclei (tectal region of brain stem) and sacral segments (S2-S4) of spinal cord. SNS: neurons originate in the thoracic (T1-T12) and lumbar (L1-L5)
segments of spinal cord
Location of PSNS and SNS ganglia
Parasympathetic ganglia (most) are located in the innervated organs. Sympathetic ganglia are located in two paravertebral chains along spinal cord (most) or in prevertebral ganglia in the abdomen (some).
Length of pre- and post-ganglionic neurons
PSNS: preganglionic are long, postganglionic are short. SNS: preganglionic are short, postganglionic are long
Ratio of pre- to post-ganglionic neurons
PSNS: 1:1 (localized). SNS: 1:20-50 (diffuse)
Which organs are innervated by PSNS and which by SNS?
Most organs are dually innervated except blood vessels receive sympathetic innervation only. Resistance Vessels have non-innervated muscarinic cholinergic receptors (activated by muscarinic agonists but NOT by activation of the parasympathetic nervous system)
Which receptors are ionotropic and which are metabotropic
nicotinic are ionotropic. Muscarinic and adrenergic are metabotropic
- Discuss the concept of “tone” and the exception
An organs intrinsic level of activity determined by which branch of the autonomic nervous system is dominant. Parasympathetic branch is almost always predominant, except in control of vasculature tone where SNS is dominant.
- Describe homeostasis, flight-or-fight, and rest-and-digest with regard to sympathetic and parasympathetic activity.
PSNS: essential for life, rest and digest, produces discrete/localized discharges. SNS: not essetial for life, flight or fight, widespread discharges
- Describe the responses of end organs to physiologic activation of the sympathetic and parasympathetic nervous systems. (HR, BP, blood flow, pupils, saliva)
PSNS: slows HR, lowers BP, stimulate GI motility and secretions, increase nutrient absorption, empty bladder and rectum, pupil constriction (near focus), stimulate profuse and watery saliva. SNS: stimulates scant and viscous saliva, increase HR, increase contractility and BP, shift blood from skin/organs to muscles, rise in glucose, dilate bronchioles and pupils
What effects are mediated by muscarinic receptors in cardiovascular, respiratory, GI, genitourinary and eye
CV: decreased HR and AV conduction, vasodilation (indirect effect mediated by NO and cGMP, no innervation by PNS). Respiratory: bronchial muscle contraction. GI: Increase in secretory and motor activity. Genitourinary: promote voiding. Eye: miosis (constriction of pupil), accommodation (lens focusing), outflow of aqueous humor.
What effects are mediated by nicotinic receptors at autonomic ganglia (cardiovascular, GI/urinary) and at neuromuscular junction
Autonomic ganglia: sympathetic effects at cardiovascular organs (vasoconstriction, tachycardia, elevated BP) and parasympathetic effects at GI/urinary (nauseau, vomiting, diarrhea, urination). NMJ: contraction of muscles
What effect do adrenergic receptors have on vasculature (cutaneous, mucus membranes, splanchnic, skeletal muscle, renal vasculature)
- Cutaneous, mucous membranes, splanchnic vasculature : Vasoconstriction mediated via a1 receptors, increase in total peripheral
resistance. 2. Skeletal muscle vasculature: vasoconstriction (a1) or vasodilation (B2). B2 activation results in increased blood flow to muscle and an overall decrease in total peripheral resistance. - Renal vasculature: Relaxation via D1 dopamine receptors balanced by constriction via a1 receptors.
- Coronary vasculature: increase blood flow.
What effect do adrenergic receptors have on the heart
largely mediated by B1 receptors. 1. SA node: Increase in heart rate (positive chronotropy). 2. AV node: Increase in conduction velocity; refractory period decreased. 3. Atrial and ventricular cardiac muscle: Increase in force of contraction (positive inotropy)
What effect do adrenergic receptors have on the blood pressure
α1: Vasoconstriction increases TPR and BP (reflex bradycardia occurs)
β1: Increased heart rate and increased force of contraction increases CO and BP β2: Vasodilation decreases TPR and BP (reflex tachycardia occurs)
a2: Decrease in SNS outflow (via action in CNS) decreases BP
Describe activation of baroreceptor reflex arc
Vessels is stretched by increased arterial pressure - inhibits sympathetic discharge from medulla resulting in vasodilation and decreased heart
rate (reflex bradycardia)> decreased arterial pressure - vagus nerve activity also increasedVessels is stretched by increased arterial pressure - inhibits sympathetic discharge from medulla resulting in vasodilation and decreased heart
rate (reflex bradycardia)> decreased arterial pressure - vagus nerve activity also increased
Describe relaxation of baroreceptor reflex arc
decrease in arterial pressure “disinhibits” tonic sympathetic discharge and results in SNS-mediated release of norepinephrine at the heart (1 receptors > reflex tachycardia) and blood vessels (1 receptors > vasoconstriction) that produces an increase in arterial blood pressure
Describe the renin angiotensin aldosterone system
decrease in renal blood flow > release of renin from the kidney > formation of angiotensin II > release
of aldosterone from adrenal cortex > retention of Na+ and water > increase in vascular volume and
blood pressuredecrease in renal blood flow > release of renin from the kidney > formation of angiotensin II > release
of aldosterone from adrenal cortex > retention of Na+ and water > increase in vascular volume and
blood pressure
What effect do adrenergic receptors have on the kidney
Increased release of renin via NE acting on B1 receptors on juxtoglomerular cells, ultimately
resulting in vasoconstriction, fluid retention (via aldosterone) and increased BP.
What effect do adrenergic receptors have on the respiratory tract
Bronchial smooth muscle: Relaxation and bronchodilation via B2 receptors
What effect do adrenergic receptors have on the eye
Pupil dilation (mydriasis) by a1 receptors, Increased production of aqueous humor via B2 receptors, increased outflow of humor by A1
What effect do adrenergic receptors have on the GI tract
Indirect relaxtion via a2, direct relaxation by B2
What effect do adrenergic receptors have on genitourinary tract
Uterine smooth muscle: Relaxation via B2 receptors. Uretal sphincter, bladder base, prostate: Contraction via a1 receptors to promote continence. Bladder wall musculature: Relaxation via B3 receptors promoting urinary continence. Ejaculation: Via a1 receptor activation in vas deferens, seminal vesicles, and prostate
What effect do adrenergic receptors have on skeletal muscle
Action on contractile proteins via B2 receptors > marked tremor
What effect do adrenergic receptors have on skeletal metabolic effects
Liver: increased blood glucose via B2 receptors (glycogenolysis). Fat cells: Increased lipolysis (fat breakdown) via B3 receptors. Pancreas Beta cells: Decreased insulin secretion via a2 receptor (major effect) or increased insulin
release via B2 receptors
