Autonomic Nervous System Flashcards
Why study the ANS?
- homeostasis (internal milieu)
- tightly controlled internal environment
- drug actions
- some classes of drugs work on the ANS
- drug side effects
- > 200 drugs that don’t work primarily at
this site have side effects due to activation of the ANS.
Body functions are integrated by:
endocrine system
• hormones released into the blood
• eg. Insulin
nervous system
• electrical transmission with chemical “links” (neurotransmitters)
Describe Sensory Nerves
- also known as the “afferent” division (flows to CNS)
- information from the periphery (sensory) to the spinal cord and/or the central nervous system
(come in from outside)
Describe Motor Nerves
- also known as “efferent” division (flows from CNS)
- information from central nervous system or spinal chord to the periphery
- result in some peripheral change - “motor”
- altered muscle activity
(go outside)
What is the Somatic NS?
• largely not automatic
• consciously controlled functions
• movement - locomotion, respiration, posture
• involves electrical and chemical transmission
(going to skeletal muscles)
What is the ANS?
• “automatic” and involuntary
• control of organs and glands
• involves electrical and chemical transmission
• control of internal environment / milieu
PNS & SNS
What are 3 key points about the SNS/PNS?
- majority affect SNS opposed to PNS
- not balanced
- BOTH active (unless damaged) at all time
What are similarities b/t the PNS & SNS?
• Both are efferent (motor) systems: “visceromotor”
• Both involve regulation of the “internal” environment generally outside of our conscious control: “autonomous”
• Both involve 2 neurons that synapse in a peripheral ganglion
• Innervate glands, smooth muscle, cardiac muscle
Sympathetic vs Parasympathetic:
Basic Function
Sympathetic Nervous System
- widespread or local
- “ergotropic” – leading to energy expenditure - fight or flight
- thoracic lumbar segments
- cardiac stimulation, INCREASE blood sugar, cutaneous
vasoconstriction.
(specifically for emergencies - NEED BF to brain, heart & muscles)
Sympathetic vs Parasympathetic:
Basic Function
Parasympathetic Nervous System
- “trophotropic” – leading to growth
- cranial sacral segment
- energy conserving
- slowing of heart, stimulation of digestion
(also widespread or local but never massively activated, but can also protect you long term, & you can pick organs it wants to activate)
SNS vs PNS Relative Lengths of Axon
SNS (rapid response)
- short pre-g
- long post-g
PNS (slow response)
- long pre-g
- short post-g
Since Symp. ganglia have short pre-g axon what does that mean?
ganglia are right beside the spinal column (CNS)
- rapid response
tend to be alongside CNS b/c when you get a widespread of SNS, its going to all targets
Since parasymp. pre-ganglia are long, what does that mean?
ganglia is close to a target –> imp. b/c its an anatomical analog for how the 2 work diff.
PNS: can target specific organs separately so its ganglia tends to be close to its target so it can target it separately
Where do the SNS ganglia run along?
all along SC
Where do the PNS ganglia run along?
most ganglia out from brainstem except for some at spinal column
What NT’s do the SNS release?
pregangl - ACh, +
postgangl - NE (& only place ACh @ SNS is at sweat glands), +/-, alpha & beta receptors
What NT’s do the PNS release?
pregangl & postgangl = Ach, +
What are the target tissues for sympathetic?
• Organs of head, neck, trunk, & external genitalia
• Adrenal medulla
• Sweat glands in skin
• Arrector muscles of hair
• ALL vascular smooth muscle
Sympathetic system is distributed to essentially all tissues (because of vascular smooth muscle)
(GET GLOBAL COORDINATION)
What are the target tissues for parasympathetic?
• Organs of head, neck, trunk, & external genitalia (whatever is necessary at a time)
Parasympathetic system never reaches limbs or body wall (except for external genitalia)
What are SNS & PNS functional differences?
Sympathetic
• “Fight or flight”
• Catabolic (expend energy) - using energy globally
Parasympathetic
• “Feed & breed”, “rest & digest”
• Homeostasis
- saving energy globally
What is unique about the genitals?
both SNS/PNS work together
What is the clinical relevance of “Pre-ganglionic neurons are located along the spinal cord? for SNS?
Dysfunction due to cord injury
Spinal nerve impingement & OMM
- damage to vagus nerve will result in loss to PNS & then can kill you b/c only SNS so it’ll have a heart attack/stroke & it’ll kill you
Catecholamine biochemistry pathways
L-tyrosine –(tyrosine hydroxylase)-> DOPA –(dopamine decarboxylase)-> Dopamine –(dopamine b-hydroxylase)–> Norepinephrine –(phenylethanolamine N-methyl transferase)-> Epinephrine
What are the adrenergic receptors?
a1
a2
b1 &b2
a1 adrenergic receptor is a…
activator
a2 adrenergic receptor is a…
inhibitor (symp. drug but inhibits it)
b-adrenergic receptors are a…
?
a1 key points:
activates PLC
increases Ca2+
smooth muscle contraction (vasoconstriction, sphincter, mydriasis)
a2 key points:
inhibits Ad Cyc
increases K+ hyperpolarization
inhibits NE release
inhibits insulin release
presynaptic neuron pancreatic B cells
b key points:
activates Ad Cyc
increases PKA act.
heart, lung & energy regulation
increase HR, contractility, bronchodilation, vasodilation, glyconeogenesis, lipolysis
What are the 6 parts of a synapse?
- Synthesis of Norephinephrine
- Uptake into storage vesicles
- Release of NT
- Binding to receptor
- Removal of norepinephrine
- Metabolism
What are sites to alter activity of a NT?
- Synthesis
- Storage
- Release
- Receptors
- Degradation / termination
What is the clinical relevance of “In cord injury, some organs/tissues will lose only SNS, while others will lose both SNS and PNS”?
Pre-ganglionic neurons are located in the brain stem with important exceptions
- therefore, PNS won’t be damaged with spinal damage
___ nerve is the main one to supply
vagus
What is the clinical relevance of “Surgery for colorectal cancer puts pelvic splanchnics at risk & Damage causes bladder & sexual dysfunction”?
b/c these nerves are difficult to see & are variable in ppl
Which are cholinergic receptors?
nicotinic (ion channels) on skeletal muscle that activate pre SNS & PNS ganglion
muscarinic - hit target organs
M1, M3, M5, M2 & M4
Muscarinic receptors (M1, M3, M5)…
activates contraction
activates PLC –> increases Ca2+, activates PKC
- excitation (gastric release, smooth muscl, bladder, etc.)
Muscarinic receptors (M2 & M4)…
inhibitors of contraction
inhibits Ad. Cyc
activates K+ channels
inhibits PKA
inhibition (cardiac, smooth muscle)
How does Ach go through a synapse?
- Synthesis of Ach
- Uptake into storage vesicles
- Release of NT
- Binding to the receptor
- Degradation of Acetylcholine
- Recycling of choline
Variety of Interactions Between SNS and PNS
- Opposite effects at the same site
- sinoartrial node - heart rate
- NE (B) increases, Ach (M) decreases - Opposite effects at different site - size of pupil of the eye
- NE (a) increases (mydriasis), Ach (M) decreases (miosis) - Sympathetic nerves act on parasympathetic nerve endings
- NE (a) decreases Ach release in intestinal wall - Complementary - male genital organ
- parasympathetic (erection); sympathetic
(ejaculation) - Some organs receive only one system
- ciliary muscles of the eye - Ach
- arterioles of most organs - NE
or another ex is: lacrimal gland (PNS) & adrenal gland (SNS)
