WEEK 8 Flashcards
What is the Autonomic Nervous System?
Involuntary division of NS
Three sub-divisions of ANS are
Sympathetic, Parasympathetic (and Enteric NS)
What are the two general actions of the ANS?
Constancy (homeostasis) and Intermittent change in bias (promotes excretory mechanisms of the body as & when necessary/appropriate)
What are three effector organs of the ANS?
Smooth and Cardiac muscle (myogenic-generate own electrical activity), and Secretory glands
What is a ganglion?
A collection of cell bodies and glial cells in PNS
What is the general anatomical layout of the ANS?
Pre-ganglionic neurone (soma in CNS, axon in PNS) synapses with Post-ganglionic neurone via Post-g soma which forms ganglia, Post-ganglionic neurone synapses with effector
General structure of autonomic signal outflow in Parasympathetic NS
ACh released by Pre-g axon terminal, acts on nAChRs on autonomic ganglion in walls of effector organ or near branches of CNV. ACh released by Post-g axon terminal, acts on muscarinic ACh receptors on effector organ
General structure of autonomic signal outflow in Sympathetic NS
ACh released by Pre-g axon terminal, acts on nAChRs on autonomic ganglion which form paraveretebral chain or pre-vertebral ganglia. Noradrenaline or adrenaline released from Post-g axon terminal, acts on alpha- or beta-adrenoreceptors
Characteristics of autonomic innervation of organs
most receive dual innervation of SNS and PNS, most effects of SNS and PNS are reciprocal (opposing actions), autonomic tone (level of contractility) varies between SNS and PNS
Characteristics of autonomic fibres from cranio-sacral sources
Parasympathetic function with soma found in specific, named cranial nuclei (incl. vagal nuclei) or S2-S4 spinal cord segments
How do axons of cranial nuclei travel to periphery?
Hitch-hiking on cranial nerve fibres (CNIII (midbrain), CNVII, CNIX, CNX (medulla))
Characteristics of autonomic fibres from thoraco-lumbar sources
Sympathetic function, from all neural segments of spinal cord between T1 and L2
What are two disorders resulting from imbalances of autonomic outflow to visceral organs due to CNS lesions?
Quadriplegia (paralysis of arms and legs) and Paraplegia (loss of sensation and movement in legs and parts of trunk)
Where are the pre-ganglionic neurones of parasympathetic autonomic outflow to viscera found?
Dorsal vagal motor neurones or spinal segmental nerves of S2-S4
Why is lateral horn in spinal cord seen from T1-L2 (+S2-S4)?
Collection of cell bodies of pre-ganglionic sympathetic (+parasympathetic) neurones
What is the difference between pre-vertebral and paravertebral chains of ganglia?
Pre-vertebral runs in front of vertebrae, Paravertebral runs lateral to vertebrae
What are the sensory components of the ANS?
viscera (eg. baroreceptors) and somatosensory/external environment-involves somatic and autonomic integration
How do autonomic motor components differ from somatic components in terms of effector innervation?
SNS=skeletal muscle by alpha-motor neurones
ANS=smooth/cardiac muscles and glandular tissue via sympathetic and parasympathetic neurones
What is the difference between no. of neurones between CNS + effector in SNS and ANS?
SNS=1
ANS=2 (pre- and post-ganglionic neurones)
What is the difference in action on target tissue between the SNS and ANS?
SNS=precise action to effector
ANS=widespread action to target tissue due to pre-ganglionic neurone innervating collection of post-ganglionic neurones
What is the difference in neurotransmitter release in SNS and ANS?
SNS=discrete (precise) release
ANS=diffuse (widespread) release via many varicosities (bulges) containing neurotransmitter-containing vesicles
What are the exceptions to the general neurotransmitters released by Sympathetic NS?
Sweat glands and Adrenal medulla
How do sweat glands innervation by ANS differ from convention?
Single innervation by Sympathetic NS, Post-ganglionic axon terminal releases ACh instead of noradrenaline
How does the adrenal medulla innervation by ANS differ from convention?
Innervated by Pre-ganglionic neurone which stimulates release of adrenaline (+NorA) from Chromaffin cells in adrenal medulla into the bloodstream which bind to non-innervated adrenergic receptors
Functions of Sympathetic NS
alert and active, defence response=fight/fright/flight
Functions of Parasympathetic NS
rest and digest, energy conservation, digestion, emptying (bladder/bowel)
How does ANS work in most organs?
Dual innervation and antagonistic action of SNS+PNS
How is the smooth muscle GI tract influenced by antagonistic SNS and PNS action?
SNS=decreased motility, decreased digestion
PNS=increased motility, increased digestion
How is the cardiac muscle of the heart influenced by antagonistic SNS and PNS action?
SNS=increased HR
PNS=decreased HR
Give an example of dual innervation and antagonistic action, but to different muscles
Smooth muscle of Pupil-dilation:
SNS=contraction of radial muscle
PNS=relaxation of circular muscle
(opposite for constriction)
Give an example of dual innervation but action isn’t antagonistic
Exocrine glands-Salivary glands
Both SNS and PNS cause excitatory (secretory) action, causing increased saliva secretion. However, due to differences in vasomotor tone via SNS and PNS, SNS causes sticky, thick saliva (low in volume) whereas PNS causes watery saliva (high in volume)
How is vasomotor tone controlled in most blood vessels?
Sympathetic NS
Increased SNS=vasoconstriction
Decreased SNS=vasodilation
What is the exception in vasomotor tone control?
Blood vessels of head and reproductive organs
SNS=vasoconstriction
PNS-vasodilation
What is the exception in blood vessel diameter control in heart and skeletal muscle vessels?
Increased SNS activity body-wide causes vasodilation as adrenaline binds to high volume of beta-adrenergic receptors located there
Example of SNS and PNS working together
male sex organ:
PNS=erection
SNS=ejaculation
(has to occur in this order)
Two examples of somatic and autonomic interaction
Focusing eye on a near object: ANS=pupil/lens adjustment SNS=eye movements Response to cold: ANS=vasoconstriction SNS=shivering
What is the role of the Enteric NS?
intrinsic innervation of GI tract (oesophagus to rectum)
What are the two major plexuses of ganglion cells and fibre bundles in ENS?
Superficial->Deep
Submucosal (Meissner’s) plexus between submucosa and circular muscle-stomach and intestines only
Myenteric (Auerbach’s) plexus between circular and longitudinal muscle-full length of GIT
Types of neurones of Enteric NS
Afferent (mechano/chemoreceptors), Interneurones (excitatory or inhibitory) and Efferent (secretomotor)
How is the GI tract set up based on the types of Enteric NS neurones?
Short reflexes to predominantly occur (involves neurones only in GI tract)
What do enteric reflexes do?
Control motility, secretion and blood flow to gut
Motor reflex of Enteric NS
Controlled by myenteric plexus (eg. Peristalsis-initiated by mucosal stimulation, causes contraction behind and relaxation in front of bolus of food)
Secretory reflex of Enteric NS
Controlled by submucosal plexus
Blood flow control in Enteric NS
Controlled by myenteric and submucosal plexuses via vasoactive neurotransmitters which influence smooth muscle contraction
What is the reflex integration with CNS in Enteric NS?
ENSSNS/PNSCNS
afferent->
What is the main characteristic of long reflexes in Enteric NS?
CNS influence (eg. sphincter control over defaecation-not present in children as they have short reflex)
What are the causes of ENS dysfunction?
Age (decrease in no. and function of neurones)
Disease (Pathology-ENS specifc or general to NS, Function)
Give three examples of ENS specific diseases
Chaga’s disease (toxin causing neurone death)
Achlasia (failure to open lower oesophageal sphincter when swallowing)
Hirschprung’s disease (known as megacolon due to halting of peristalsis in distal colon)
Give three examples of general neurological conditions affecting Enteric NS
Parkinson’s disease (Enteric neurones believed to be entry site of ‘Pathogen’)
Peripheral neuropathies
Myasthenia Gravis
What is IBS and how does it relate to the Enteric NS?
Irritable Bowel Syndrome due to dysfunctional interaction between CNS and ENS (Gut-brain axis)
Define outflow
The position where the pre-ganglionic autonomic fibres exit the CNS
