L13 Autonomic Nervous System Flashcards by LeeAnn Nolan (AZ BioMed MA 20)

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

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Ganglion

A collection of many synapses. In the ANS many presynaptic nerves communicate with many postsynaptic nerves at structures called ganglia

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Preganglionic nerves

Nerves leading into a ganglion structure

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Postganglionic nerves

Nerves leading a ganglion structure to innervate effector cells

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Cholingeric nerves

Nerves that synthesize and release ACh as their neurotransmitter

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Cholingeric receptors

Receptors for ACh

There are two main types: nicotinic (N) and muscarinic (M)

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Adrenergic nerves

Nerves that synthesize and release norepinephrine (NE) as their neurotransmitters

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Adrenergic receptors

Receptors for norepinephrine (NE) and epinephrine (EPI)

Two main types:
Alpha
Beta

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CNS

Brain and spinal cord

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PNS

Peripheral
Outside CNS

Afferent division: sensory stimuli or visceral stimuli

Efferent division: SNS and ANS

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ANS

Sympathetic (SNS)

Parasympathetic (PNS)

Smooth muscle, cardiac muscle, exocrine glands, some endocrine glands

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Somatic

NOT part of ANS

Motor neurons commanding skeletal muscles

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Autonomic pathways originate in where and consist of what

Brain or spinal cord

Preganlionic and postganlionic nerves connected in series by ganglion

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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

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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

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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

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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

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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

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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

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