The autonomic nervous system Flashcards
what is the autonomic nervous system ?
A collection of motor neurones (efferents) in the central and peripheral nervous system that innervate smooth muscle, cardiac muscle and glands to regulate their activity
what are the three 3 subdivisions of the autonomic nervous system ?
Enteric
– Sympathetic
– Parasympathetic
whats the enteric nervous system ?
Works autonomously to control the activity of the GIT
• Consists mainly of the myenteric plexus
• Receives autonomic innervation from the parasympathetic and sympathetic divisions
what do you think of when you read sympathetic
fight or flight
what do you think of when you read parasympathetic
rest and digest
difference between cranial and spinal nerves?
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), in contrast to spinal nerves (which emerge from segments of the spinal cord)
where does the parasympathetic nervous system originate ?
in the brainstem and sacral spinal cord
what do the sacral preganglionic neurons not join with ?
the spinal nerve
what do cranial preganglionic neurons travel with ?
axons in the cranial nerves
give me four examples of cranial nerves
vagus (X): lungs, heart, stomach, small intestines, liver
occulomotor(III) pupil size, lens strength
facial (VII): salivary glands
glossopharyngeal (IX): smooth muscle and glands of throat, viscera of thorax and abdomen
regarding the parasymptateic nervous system: are preganglionic fibres long or short and are they branched ?
long and branched
where is the ganglia of the parasympathetic nervous system ?
located on or close to their target organs
what are the properties of the postganglionic neurons of the parasympthathetic nervous system ?
short projections to innervate their target organs
regarding the parasympathetic nervous system.. whats the type of receptor in the ganglion
nicotinic cholinergic receptor (ionotropic)
regarding the parasympathetic nervous system.. whats the type of receptor in the effector organ
muscarinic cholinergic receptor (M1-5)
where does the sympathetic nervous system arise from ?
from the thoracic and upper lumbar cord
properties of preganglionic neurones in the sympathetic nervous system
short un branching preganglionic neurons
where is the ganglia located in the sympathetic nervous system ?
close to the vertebral column
properties of postganglionic neurones in the sympathetic nervous system ?
long branching projections to innervate their target organs
where do sympathetic preganglionic neurones arise from ?
the lateral horn of the spinal grey matter and they axons leave through the ventral root, travel via the white rami to enter the sympathetic chain
what do sympathetic neurons do after entering the sympathetic chain
Synapse with postganglionic neurones in the sympathetic chain
– Travel along the sympathetic chain before leaving along a nerve to innervate an outlying ganglion or the adrenal gland
– Leave the sympathetic chain to innervate a collateral ganglion
what would sympathetic innervation of blood vessels result in ? whats the neurotransmitter involved
vasodilation.. epinephrine
what would sympathetic innervation of cardiac muscle result in ?
contraction.. epinephrine is the neurotransmitter
whats receptor type does the preganglionic neuron synapse in the sympathetic nervous system ?
nicotinic cholinergic receptor
what receptor type does the postganglionic neuron synapse with in the sympathetic nervous system ?
adrenergic receptor.. a and beta adrenoceptors
what are adrenergic receptors ?
The adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines, especially norepinephrine (noradrenaline) and epinephrine (adrenaline).
what are other transmitters are often co-released in autonomic neurones
neuropeptides (VIP, NPY, substance P) and small molecules like 5-HT, ATP and NO
what are the 3 main classes of muscarinic cholinergic receptors ?
5 types encoded by 5 different genes (M1- M5)
M1 receptors: generally an excitatory effect e.g stimulation of vagus nerve causes secretion of gastric acid
M2 receptors: generally inhibitory effect e.g in heart and on nerve terminals of CNS and peripheral neurones e.g. slowing of heart via vagus nerve
M3: in secretory glands and smooth muscle. generally excitatory e.g. contraction of visceral smooth muscle
what are adrenergic receptors spit into ?
split into alpha and beta
alpha are excitatory
beta can be excitatory or inhibitory
whats the effect of symp on the eye
pupil dilation
whats the effect of symp on lacrimal gland ?
no effect
whats the effect of psymp on lacrimal gland ?
secretion of tears
in the SAN what do beta adrenergic receptors do ?
increase heart rate
in the SAN what do M2
decrease heart rate
in the AVN what does Beta adrenergic receptors do ?
increase conduction
in the AVN what does M2 do
decrease conduction
in the ventricle what does Beta adrenergic do ?
increase contraction
what does beta 1 aderenrgic do ?
decrease Blood pressure
what happens during fight or flight ? sympathetic NS
Sympathetic NS – fight or flight • Increased delivery of oxygen and glucose to muscles – Inc HR and SV Inc CO – Vasodilation at muscles – Vasoconstriction at viscera – Glucose release into blood – Inc light entering eye – better visual acuity increase respiration diversion of blood to muscles
what happens during rest and digest ?
Conserve body resources – dec HR to lower BP – Inc secretion of enzymes – Inc digestion and GI motility – Promote removal of waste products
What is the baroreflex ?
The baroreflex is the fastest mechanism to regulate acute blood pressure changes via controlling heart rate, contractility, and peripheral resistance.
The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure reflexively causes the heart rate to decrease and also causes blood pressure to decrease.
what are the higher centres involved in autonomic control ?
spinal cord, brainstem hypothalamus forebrain amygdala hippocampus many other
what recognises potential danger ? we’re talking about fight or flight response here
forebrain
what initiates and maintains the response ?
hypothalamus
what des hypothalamus do ?
Activates sympathetic
• Inhibits parasympathetic
• Alters sensitivity of baroreflex
• Promotes cortisol secretion
whats the definition of the autonomic nervous system ?
motor neurons that originate from the CNS that regulate the activity of smooth, cardiac muscle and glands and neurons in the gastrointestinal tract (enteric nervous system)
where are preganglionic cell bodies found ?
Preganglionic cell bodies are found in the spinal cord from T1 to L3 segments.
where do preganglionic nerve fibres pass in the sympathetic nervous system ?
Their fibres pass via the white rami communicantes to sympathetic chain (paravertebral) ganglia which are arranged on each side of the cord
what may the axons of the preganglionic nerves synapse with ? sympathetic nervous system
The axons of preganglionic neurones may: i) synapse with postganglionic neurons in one or more of the paravertebral ganglia; ii) synapse in peripheral ganglia (prevertebral/collateral : e .g., coeliac and mesenteric); iii) synapse on adrenaline producing cells of the adrenal medulla.
what may the axons of the postganglionic nerves synapse with ?sympathetic nervous system
The axons of postganglionic neurones with cell bodies located in the sympathetic chain either: (i) pass back into spinal nerves (via grey rami) to innervate vascular smooth muscle (blood vessels of skin and skeletal muscle), sweat glands or piloerector muscles of hairs of the skin; ii) pass into visceral nerves (e.g., cardiac, splanchnic, renal sympathetic nerves).
where do the preganglionic nerves of the parasympathetic nervous system originate from ?
Preganglionic fibres originate from cranial (III, VII, IX and X) and sacral
(S2-S4) regions
where are the cell bodies of the postganglionic nerves of the parasympathetic system ?
adjacent to or within the effector organ hence the axons are short
which neartransmitter excites postganglionic nerve cells in the ganglia of the para and symp nervous system
acetylcholine
which neurotransmitter is released by the postganglionic nerves in the sympathetic nervous system ?
noradrenaline.
which neurotransmitter is released by the postganglionic nerves in the parasympathetic nervous system ?
acetylcholine
what is the ANS concerned with ?
maintaining homeostasis
give me 6 actions of the sympathetic nervous system ?
- increases heart rate and force of cardiac contraction resulting in an increase cardiac output
- relaxes smooth muscle of airways (via the action of circulating adrenaline) leading to a decrease in airway resistance,
- causes pupils to dilate
- increases blood glucose via action adrenaline from adrenal medulla 5. piloerection
- decreases activity of the gastrointestinal tract
give me 4 examples of the parasympathetic nervous system ?
- decreases heart
- constricts smooth muscle of airways (leading to an increase in airway resistance) 3. causes s pupils to constrict
- increases activity of the gastrointestinal tract
give me some areas of the brain that are involved in controlling the output of the ANS
medulla, pons, midbrain The activity of these is influenced by, and influences hypothalamic and cortical areas.
