L13 Autonomic Nervous System Flashcards
Neurotransmission
Process by which a nerve transmits its signal across a synapse to activate another nerve or other structure (muscle, gland cell)
The actual signal comes from a chemical, a neurotransmitter, synthesized in and released from the nerve into the synapse
Ganglion
A collection of many synapses. In the ANS many presynaptic nerves communicate with many postsynaptic nerves at structures called ganglia
Preganglionic nerves
Nerves leading into a ganglion structure
Postganglionic nerves
Nerves leading a ganglion structure to innervate effector cells
Cholingeric nerves
Nerves that synthesize and release ACh as their neurotransmitter
Cholingeric receptors
Receptors for ACh
There are two main types: nicotinic (N) and muscarinic (M)
Adrenergic nerves
Nerves that synthesize and release norepinephrine (NE) as their neurotransmitters
Adrenergic receptors
Receptors for norepinephrine (NE) and epinephrine (EPI)
Two main types:
Alpha
Beta
CNS
Brain and spinal cord
PNS
Peripheral
Outside CNS
Afferent division: sensory stimuli or visceral stimuli
Efferent division: SNS and ANS
ANS
Sympathetic (SNS)
Parasympathetic (PNS)
Smooth muscle, cardiac muscle, exocrine glands, some endocrine glands
Somatic
NOT part of ANS
Motor neurons commanding skeletal muscles
Autonomic pathways originate in where and consist of what
Brain or spinal cord
Preganlionic and postganlionic nerves connected in series by ganglion
SNS
Highlight the core
Lumbar and thoracic regions
Adrenal medulla only innervated by SNS (an exception)
Have 2 neurons (one leaving spinal cord, interacting with ganglion neuron, and that one carries info to target organ)
A lot of branching
Gives broad command, a lot of divergence
PNS
Highlight upper and lower part
Brain and saccryl part
Have two neurons in some regions with shorter distance to travel
Some neurons travel directly to target
Minimal branching
More of direct message
Somatic division innervation
Cell bodies of motor neurons reside in CNS
Their axons (myelinated in spinal nerves) extend all the way to their skeletal muscles
Autonomic system innervation
Chain of two motor neurons
1st: preganglionic neuron (Brain or spinal cord
2nd: postganlionic neuron (Cell body in ganglion outside CNS)
Slower because lightly myelinated or unmyleinated
SNS vs PNS
All target organs typically have dual, reciprocal innervation from PNS and SNS
division that dominates is the function that takes place
None inactive, it’s more of a ratio of innervation
PNS neurotransmitters and receptors
Preganlionic
Fiber: Cholingeric
Neurotransmitter: ACh
Receptor: nicotinic type 2
Postganlionic
Fiber: Cholingeric
Neurotransmitter: ACh
Receptor: muscarinic
SNS neurotransmitters and receptors
Preganlionic
Fiber: Cholingeric
Neurotransmitter: ACh
Receptor: nicotinic type 2
Postganlionic Fiber: adrenergic Neurotransmitter: NE Receptor: adrenergic receptors (alpha or beta) OR exception of sweat glands Fiber: cholingeric Neurotransmitter: ACh Receptor: muscarinic
Adrenal medulla neurotransmitters and receptors
Sympathetic but an exception
Preganlionic
Fiber: Cholingeric
Neurotransmitter: ACh
Receptor: nicotinic type 2
To circulation- acts like postganlionic neuron but not as fast
Neurotransmitter: 80% EPI, 20% NE
(Hormones amp up sympathetic response)
Synapse in gland/modified ganglia
Cholingeric neurons
ACh
All SNS and PNS preganlionic
All PNS postganlionic
Those SNS postganlionic for the sweat glands
ACh
Synthesis and degradation
Synthesized from AcCoA and choline by choline acetylcholine transferase
Stored in vesicles
Released when AP increase Ca entry into nerve ending
Binds to receptor
Broken down in synaptic cleft by acetylcholinesterase
Acetylcholinesterase inhibitors are used to treat glaucoma, to increase GI motility, to treat myasthenia gravis
NE
Synthesis
Tyrosine enters nerve terminal. Converted to DOPA, converted to dopamine, concreted to NE
NE stored in vesicles complexes w ATP
Released when AP increases Ca entry into nerve ending
NE acts in adrenergic receptors (alpha or beta)
ReUptake by active pump mechanism NET (Inhibited by cocaine/antidepressants)
After reuptake in presynaptic neuron NE is metabolized by the enzyme MOA(monoamine oxidase, in presynaptic terminal) and COMT(catechol-o-methyltransferase, in liver)
Diffusion: NE is detectable in plasma small traces
Receptor substypes
Have diverse responses
Activation/reduction depending on fight/flight or rest/digest
The neurotransmitters releases are the same…receptors vary the action mechanism
SNS
Fight or flight
Mobilization and high metabolism
PNS
Rest and digest
Routine maintenance
SNS single innervation target organs
Only sympathetic cholinergic nerves
Sweat glands
Only sympathetic adrenergic nerves
Hair follicles
Brown adipose tissue
Adrenal medulla
Kidney
Most arterioles and veins:
Except penis and coronary circulation
Arteries and capillaries not innervated
Reciprocal effects
One system inhibits while other stimulates activity of the target organ
Provide fine control of organ function
Ex: control of HR and intestinal motility
Cooperative effects
Promote same goal
Ex: salivary gland secretion, male sexual response, lacrimal gland
Examples of cooperative effects
Salivary glands
SNS -viscous secretion
PNS- watery secretion
Lacrimal glands
SNS and PNS both cause secretion
Make sexual response
PNS- erection
SNS- ejaculation
Reciprocal effects
SNS v PNS
Most visceral organs are innervated by both system fibers
In general this produces opposite effects in a particular organ
Dual innervation of organs by both branches of ANS allow precise control over organ activity
Examples of reciprocal effects
SNS v PNS
SNS: Inhibit digestion (saves energy) Increase HR (tachycardia) Dilate pupil ( mydriasis) Stimulate hectic glyconeolysis; inhibit insulin release from pancreas
PNS:
enhance digestion (enhance emptying of gi and urinary tracts)
Slows HR (bradycardia)
Constricts pupil (miosis)
Release insulin from pancreas- storage of energy
Example:
Autonomic control of bladder function
Detrusor muscle (beta and muscarinic) Internal spinster (alpha) External sphincter (muscarinic, voluntary component)
Filling bladder: Sympathetic dominates
Relaxation of detrusor and contraction of internal sphincter - both SNS but diff receptors
Emptying bladder: parasympathetic dominates
Contraction of detrusor and relaxation of internal sphincter
Example:
Autonomic control of heart function
Fine tune control of both SNS and PNS
At rest heart has high PNS control and low SNS control
At defense reaction heart has high SNS control and low PNS control
At walking normal, heart has equal contribution of both
Tonic activity
Active under resting conditions (always happening)
Ability to increase and decrease activity (fine control)
Both SNS and PNS are tonically active
RATIO of PNS/SNS determines net effect
Reflex activity
Reflex activity ( May not require cortical processing)
Basic autonomic reflexes can be modulated by other inputs to CNS
Visceral reflex arcs
Many are spinal reflexes such as defecation and micturition
Enteric nervous system has 3 neuron reflex arcs entirely writhing gut wall
Regions of CNS involved in control of autonomic activities
Hypothalamus
Amygdala
Reticular formation of brain stem
Spinal cord
Amygdala
Main limbic region for emotions
Stimulates SNS activity (especially pre learned fear-related act)
Can be voluntary
Hypothalamus
Main integration center
Reticular formation
Most direct influence over autonomic function
Reg pupil size, regulation, heart, blood pressure, swallowing
Spinal cord
Urination, defecation, erection and ejaculation reflexes
Autonomic agonists
Bind to same receptor as neurotransmitter
Elicit an effect that mimics that of neurotransmitter
Autonomic antagonists
Bind with receptor
Block neurotransmitters response
