Autonomic Nervous System Flashcards
Somatic Nervous System: motor and sensory receptors
Both from/to skeletal muscles
Autonomic Nervous System: sensory and motor
Sensory: from visceral organs
Motor: to smooth and cardiac muscles, glands
Enteric Nervous System: sensory and motor
Sensory: chemical changes and distension in GI tract
Motor: GI smooth muscles
Autonomic Tone
Balance between parasympathetic and sympathetic activity. As one increased, the other decreased.
Most organs innervated by both sympathetic and parasympathetic fibres, which release different NTs.
Regulated by hypothalamus
Organs that receive only sympathetic innervation
sweat glands kidneys most blood vessels arrector pili spleen adrenal medulla
Why would the SNS dilate blood vessels to liver?
Energy from glycogenelysis
Focus of Sympathetic responses
Increase production of ATP, support vigorous physical activity, reduce expenditures to nonessential functions
Focus of Parasympathetic responses
Functions that replenish and restore energy
SLUDD: salivation, lacrimation, urination, defecation, digestion
Somatic nervous system: sensory input
Somatic and special senses.
Consciously perceived
Autonomic nervous system: sensory input
Interoceptors mostly.
Also from somatic and special senses.
Usually non-consciously perceived
Somatic nervous system: control of motor output
Voluntary control from cerebral cortex.
Contributions from basal ganglia (regulates initiation and termination of movement), cerebellum, brain stem and spinal cord.
Autonomic nervous system: control of motor output
Involuntary control from hypothalamus, limbic system, brain stem and spinal cord.
Limited control from cerebral cortex.
Somatic nervous system: NT and hormones
Acetylcholine (ACh)
Autonomic nervous system: NT and hormones
All preganglionic neurons, all parasympathetic postganglionic neurons, and sympathetic postganglionic neurons near sweat glands release ACh.
Most sympathetic postganglionic neurons release NE.
Chromaffin cells (adrenal medulla) release epinephrine and NE.
Somatic nervous system: motor neuron pathway
One neuron pathway.
Somatic motor neurons extending from CNS synapse directly with effector.
Autonomic nervous system: motor neuron pathway
Usually two-neuron pathway.
Preganglionic neurons extend from CNS to autonomic ganglion.
Synapse with Postganglionic neurons, which extend to visceral effector.
Alternatively: preganglionic neurons may synapse with chromaffin cells in adrenal medulla
Somatic nervous system: effectors and response
skeletal muscle (contraction)
Autonomic nervous system: effectors and responses
Glands (increased or decreased secretion) Smooth muscle (contraction or relaxation) Cardiac muscle (increased or decreased rate or force of contraction)
Three parts of an autonomic pathway
- preganglionic neuron
- autonomic ganglia
- postganglionic neuron
Preganglionic neuron
First neuron in autonomic NS.
Relays signal from CNS to autonomic ganglia
Cell body is located in the CNS; axons exit CNS as part of a cranial or spinal nerve.
Axon: myelinated B fibre
Either synapses with a postganglionic fibre at an autonomic ganglion, or with a chromaffin cell in an adrenal medulla
Postganglionic neuron
Second neuron in the automic NS.
Relays signal from ganglion –> effector
Lies entirely within the PNS
Cell body and dendrites located within autonomic ganglion
Axon: unmyelinated type C fibre
Terminates in visceral effector.
Sympathetic Preganglion fibres
AKA thoracolumbar division
Cell bodies in lateral horns of gray matter in T spine and S1-2 or 3.
Parasympathetic Preganglion fibres
AKA craniosacral division
Cell bodies located in nuclei of CN III, VII, IX and X (occulomotor, facial, glossopharyngeal and vagus) in the brainstem, and in the lateral grey matter of S2-4.
Thoracolumbar outflow
The axons of the sympathetic preganglionic neurons
Craniosacral outflow
The axons of the parasympathetic preganglionic neurons
Postganglionic neuron
The second neuron in the ANS motor pathway
Peripheral nervous system
C fibre
Terminates in visceral effector
Autonomic ganglia
Where pre and post ganglionic neurons synapse
Two types of sympathetic autonomic ganglia
- sympathetic trunk/vertebral chain/paravertebral
2. prevertebral/collateral ganglia
Sympathetic trunk ganglia
AKA Vertebral Chain and Paravertebral Ganglia
Vertical row on either side of vertebral column, running from skull to coccyx
Mostly innervates organs above diaphragm
Short preganglionic and long postganglionic fibres
The named sympathetic trunk ganglia
- superior cervical
- middle cervical
- inferior cervical
Prevertebral ganglia
AKA collateral ganglia
Part of sympathetic system.
Anterior to vertebral column, close to large abdominal arteries
Generally innervate below the diaphragm
5 Major prevertebral ganglia
- celiac
- superior mesenteric
- inferior mesenteric
- aorticortical
- renal
Terminal ganglia
AKA intramural ganglia
The ganglia of the parasympathetic system
Close to or in the actual wall of visceral organs
Terminal ganglia in the head
- ciliary (CN III occulomotor)
- pterygopalatine (CN VII facial)
- submandibular (CN VII facial)
- otic (CN IX glossopharyngeal)
4 ways Sympathetic preganglionic neurons connect with postganglionic neurons
- synapse in sympathetic trunk ganglion
- ascend or descend to a different level, and then synapse in trunk ganglion
- pass through sympathetic trunk ganglion, and synapse in prevertebral ganglion
- pass through both sympathetic trunk and prevertebral ganglion and synapse with chromaffin cells in adrenal medulla
Divergence and sympathetic preganglionic fibres
Single preganglionic fibre may synapse with more than 20 postganglionic fibres
This divergence explains the speed and spread of sympathetic responses
Parasympathetic preganglionic neurons
Synapse with 4 or 5 postganglionic neurons, in or near visceral effector, only affecting that one effector.
Autonomic plexus
Tangled network of axons of both sympathetic and parasympathetic neurons, together with sympathetic ganglia and autonomic sensory neurons
Found in thorax, abdomen and pelvis.
7 major autonomic plexuses
Cardiac (thorax -- heart) Pulmonary (thorax -- lungs) Celiac/solar Superior mesenteric (small and large intestine) Inferior mesenteric (large intestine) Hypogastric (pelvic viscera) Renal (renal arteries and uterus)
Solar/Celiac plexus
Largest autonomic plexus
In abdomen
Surrounds celiac trunk
Contains 2 large celiac ganglia
Stomach, spleen, pancreas, liver, gallbladder, kidneys, adrenal medulla, testes, ovaries
Four ways Sympathetic Postganglionic neurons connect with visceral effectors
- spinal nerves
- cephalic periarterial nerves
- sympathetic nerves
- splanchnic nerves
Spinal nerve postganglionic sympathetic pathways
White ramus + grey ramus [= Ramus communicantes]
Merges with anterior ramus of spinal nerve
Visceral effectors of neck, trunk and limbs
Cephalic periarterial nerves
Sympathetic preganglionic nerves ascend to superior cervical ganglion (sympathetic trunk).
Then synapse with cephalic periarterial nerves which wrap around arteries that pass from neck to head (ie carotid)
Visceral effectors of skin of face and rest of head.
Sympathetic Nerves
One way sympathetic postganglionic nerves connect with visceral effectors
Extend to visceral effectors in thoracic cavity, including heart and lungs.
How we get to abdominopelvic organs
Sympathetic nerve to heart
Postganglionic sympathetic innervation of the heart
From superior, middle and inferior cervical ganglia, T1-4 –> cardiac plexus
Sympathetic nerve to the lungs
Sympathetic trunk ganglia T2-4 –> pulmonary plexus
Splanchic nerves
Nerves that synapse in prevertebral ganglia. Refers to pre- and post-ganglionic tracts.
T5-L4
Four + Splanchic nerves
Greater Splanchic Lesser Splanchic Least (lower) Splanchic Lumbar Splanchic (And Splanchic nerve to adrenal medulla)
Greater Splanchic nerve
T5-9
Celiac ganglion
Blood vessels to stomach, liver, spleen, kidneys, small intestine
Lesser Splanchic nerve
T10,11. Divides. Synapses at:
Aorticorenal ganglion –> kidneys, ureters
Superior mesenteric ganglion –> blood vessels of small intestine and proximal colon
Least (lower) Splanchic nerve
T12 –> renal plexus –> kidney arterioles and ureter
Not always present.
Lumbar Splanchic nerve
L1-4 –> inferior mesenteric ganglion (inferior mesenteric plexus) –> distal colon and rectum; blood vessels of distal colon, rectum, genitals
ONLY ONE THAT DOESNT PIERCE DIAPHRAGM
Splanchic nerve to adrenal medulla
Preganglionic axons pass through sympathetic trunk, splanchic nerves, and celiac ganglion.
Extend to chromaffin cells in adrenal medulla.
Release 80% epinephrine, 20% norepinephrine, sprinkle of dopamine.
Histological similarities between adrenal medulla and sympathetic ganglia.
Both derived from neural crest.
Adrenal medulla modified sympathetic ganglia.
Chromaffin cells stripped down sympathetic postganglionic neurons (no dendrites or axons).
Horner’s Syndrome
Loss of sympathetic innervation to one side of the face
Congenital, injury (Klumpe’s or Erbs), disease.
Ptosis
Miosis
Anhidrosis
Possible enopthalmos
Parasympthetic outflow: cell bodies
Cranial: brain stem
Sacral: lateral grey matter of S2-4
Parasympathetic outflow: preganglionic fibres
Cranial: extend from brain stem along CN III, VII, IX and X
Sacral: extend from anterior roots of S2-4
Cranial Parasympathetic Ganglia
- Ciliary (III). Ciliary (accommodation) and circular (constriction) muscles
- Pterygopalentine (VII). Lacrimal gland, nasal mucosa, palate, pharynx.
- Submandibular (VII) submandibular and sublingual glands
- Optic (IX). Parotid gland.
How much of the total craniosacral outflow is carried by the vagus nerve,
80%
Sacral Parasympthetic ganglia
Travel with spinal nerves, branch off to form pelvic splanchic nerves.
Synapse with parasympthetic neurons in terminal ganglia
Innervation smooth muscle and glands in walls of colon, ureters,
Are all the Splanchic nerves sympathetic?
Nope. The sacral presympathetic axons form the Pelvic Splanchnic nerves
Cholinergic neurons
Release ACh
All preganglionic neurons
All parasympthetic postganglionic neurons
Sympathetic postganglionic neurons that innervation sweat glands
Which neurons aren’t cholinergic?
Most sympathetic postganglionic neurons (the ones that don’t innervate sweat glands)
Two types of cholinergic receptors
- Nicotinic
2. Muscarinic
Nicotinic receptors
ACh receptors found on:
- Sympathetic and parasympthetic postganglionic neurons
- Chromaffin cells
- Motor end plates at NMJ
Muscarinic receptors
ACh receptors
All parasympathetic effectors.
Sweat glands.
Acetylcholinesterase
Enzyme that quickly deactivates ACh.
The reason ACh effects are brief.
Adrenergic neurons
Release NE
Most sympathetic postganglionic neurons (except those innervation sweat glands)
Effects last longer than ACh
Adrenergic receptors
Bind to NE and epinephrine.
Alpha and beta receptors.
What do chromaffin cells release?
NE and epinephrine (as hormones)
How is NE terminated?
Reuptake or inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)
Agonist
A substance that binds to and activates a receptor.
Mimics effect of natural NT
Antagonist
Binds to receptor and blocks it so natural NT or hormone is prevented from exerting its effect.
Why are sympathetic responses more widespread and long-lasting than parasympathetic?
- Divergence. Sympathetic postganglionic axons diverge more, affect more tissues
- ACh-esterase deactivates ACh quickly. NE lingers.
- NE and epinephrine secreted as hormones in blood intensify and prolong the NT NE response.
Charcot Marie Tooth Disease
AKA hereditary motor and sensory neuropathy/progressive muscular atrophy/peroneal muscular atrophy.
Progressive hereditary demyelination disorder. Dominant, recessive or X-linked
Affects primarily the fibularis nerve (muscles in foot and leg) then progresses to forearm and hands.
Distal limb wasting and weakness
Symptoms of CMT disease
Diminished DTR Pes cavus Hammer toes Foot drop Decreased proprioception Legs appear like inverted champagne bottles (distal wasting).
CMT type 1
Most common variant. Autosomal dominant.
Duplication on Chromosome 17
CMT Type 2
Abnormalities of Chromosomes 1,8,X
Diabetic Neuropathy
Common complication of diabetes mellitus (especially Type 1)
Distal symmetric pattern. Glove and stocking.
Disturbances in peripheral microcirculation. Demyelination.
Alcoholic neuropathy
Distal symmetric glove and stocking
Direct toxic effects from ethanol, and B12 (thiamine)
Decreased sensation, ankle reflexes, foot and wrist drop.
Insidious. Slow progression. Eventually affects all four limbs.
Chronic renal failure – neuropathy
CNS and PNS dysfunction
Associated with increased uremia
CNS effects of Chronic Renal Failure
uremia encephalopathy –> memory loss, inability to concentrate, perceptual errors and decreased alertness.
PNS Effect of Chronic Failure
Demyelination and atrophy of sensory and motor neurons
Lower extremities more affected than upper.
Symmetric.
Pernicious Anemia – neuropathy
B12 deficiency
Distal, symmetric pattern
Difficulty walking; loss of proprioception.
Increasing loss of motor function.
Headache, drowsiness, dizziness, fainting, slow thought processes, poor attention.
Guiliain-Barre Syndrome
Immune mediated inflammatory response.
Most common cause of rapid motor and sensory problems.
Max weakness in 2-3 weeks; months to recover.
Rapidly ascending symmetric motor weakness and distal sensory impairment.
Flaccid paralysis, absence of DTRs
30% require mechanic ventilation
Most common form of Guillain-Barre Syndrome
Acute inflammatory demyelinating polyradiculoneuropathy
GBS: time of onset of peak impairment; and symptom cessation.
Acute: less than 4 weeks
Chronic: months
50%: progression stops within 2 weeks
90%. Progression stops within 4 weeks.
Recovery proximal to distal.
Initial symptom of GBS
Paresthesia in toes, followed by distal weakness in legs.
