Physiology and pharmacology of the ANS Flashcards
What governs the pharmacology of parasympathetic and sympathetic neurones
Different neurotransmitters
What determines the state of that organ
The parasympathetic and sympathetic activity at that organ.
Summarise the autonomic nervous system
Along with the somatic nervous system, the autonomic nervous system constitutes the total neural output of the CNS.
It controls involuntary internal processes such as digestion and the regulation of blood flow.
It acts mainly on the heart, smooth muscle, metabolic processes and glandular structures.
Split into Sympathetic and parasympathetic.
List some actions of the PSNS
Constricts pupils Constricts bronchi Slows heart rate Increases flow of saliva Stimulates peristalsis and secretion Stimulates bile release Contracts bladder
List some actions of the SNS
Dilates pupils Relaxes bronchi Increases heart rate Decreases flow of heart rate Inhibits peristalsis and secretion Secretion of adrenaline and noradrenaline Inhibits bladder contraction Stimulates orgasm
What. is the flight or flight response
An extreme example of the sympathetic nervous system- both SNS and PSNS are always working
Describe the outputs of the CNS
Somatic Nervous System – Voluntary nervous system.
o Main innervated tissue is the skeletal muscle.
Autonomic Nervous System (ANS) – Continually works to maintain homeostasis. Split into the:
o Sympathetic – Activated during exercise.
o Parasympathetic – Homeostasis during rest.
Neuroendocrine System – Involves nerve fibres but the efferent way into the body is via hormones.
o Endo – Hormone released into circulation.
o Neuro – Neurotransmitter released NOT into the circulation.
What happens in the flight or flight response
pupil dilation, increased HR (better oxygen to muscles), increases diameter of bronchioles, stimulates glucose release (feed muscles), increases sweat production (prevents overheating); results from EXTREME activation of SNS - at work all time, just not to this level
Which structures does the ANS innervate
Secretory glands (salivary, sweat, tear and mucous-producing glands) Smooth muscle Cardiac muscle (to control heart rate in response to homeostatic changes). NOTE: You don’t need innervation to get an effect as certain tissues have receptors for blood bound hormones.
Describe the structure of the SNS
Column of cell bodies (intermediolateral column) in the lateral grey horn of the spinal cord
Runs from t1-L3
These ‘preganglionic’ neurones have axons that travel through the ventral roots of their segmental spinal nerves.
They contact a chain of ganglia outside the CNS lying along the vertebral column (paravertebral ganglia)
Describe the structure of the PSNS
III Oculomotor – pupil constriction
VII Facial nerve – Salivation
IX Glossopharyngeal – Salivation
X Vagus – bradycardia, gastric motility, digestion
S2-S4
Describe the ganglia associated with the SNS and PSNs
PSNS has no separate ganglia outside target organ so Vagus nerve emerges from brainstem to directly innervate the target organ (where ganglia do occur)
SNS GANGLIA OUTSIDE ORGAN, PSNS GANGLIA INSIDE ORGAN
What is meant by ganglia
*Ganglia – Structure outside CNS containing collection of neural cell bodies (somas)
Describe the anatomy of the SNS
3 neurones are involved OUTSIDE the brain
Presympathetic neurones run down the spinal cord until they reach the intermediolateral cell column which is present T1-L2/3, containing the cell bodies of pre-ganglionic neurones; here the presympathetic neurones synapse to the soma of pre-ganglionic neurones in a glutaminergic synapse in the lateral horn
The pre-ganglionic neurones exit the cord via the ventral root, passing up the lateral rami communicantes (white ramus) to enter the sympathetic chain, where they synapse to post-ganglionic neurones (cholinergic)
The post-ganglionic neurones exit the sympathetic chain using the more medial grey ramus if supplying blood vessels, sweat glands and erector pili muscles, or if innervating thoracic viscera they exit via nerves
Describe neurotransmission in the SNS
The transmitter released by preganglionic neurone at the ganglia is Ach- binds to postsynaptic nicotinic receptors
The transmitter released by postganglionc neurone is noradrenaline (norepinephrine)
What are the exceptions to neurotransmission in the SNS
In sweat glands- Ach is also the postganglionic neurotransmitter- binds to muscarinic receptors
Dopamine is the postganglionic neurotransmitter for SNS efferents to the renal vessels
Essentially, what is the neurotransmitter in SNS ganglia
Ach
What is special about the adrenal medulla
Some preganglionic fibres continue to the adrenal medulla (don’t synapse in ganglia)
Here, they are responsible for the glandular secretion of catecholamines from cells that are functionally similar to postganglionic sympathetic neurones (NA and A). the noradrenaline and adrenaline released into the blood stream affect target organs (blood vessels).
The adrenal medulla only receives pre-ganglionic fibres and stimulates Chromaffin cells (instead of a post-ganglionic fibre) to release ACh.
Describe neurotransmission in the PSNS
Preganglionic neurone release Ach onto postganglionic nicotinic receptors
At target organs postganglionic neurons release Ach onto muscarinic receptors.
Describe the anatomy of the PSNS
Postganglionic neurone are found in target organs
OR Plexi near target organs (e.g pelvic plexus from sacral PS efferents).
Describe neurotransmission of the somatic nerves
Glutamate at synapse between nerve from CNS and cell body in ventral horn
Act from motor neurone to effector organ (skeletal muscle)
Describe noradrenaline biosynthesis
L-phenylalanine (diet) - L-tyrosine - L-DOPA - Dopamine (cytoplasm) then in vesicles converted to noradrenaline
Describe Ach biosynthesis
acetate + choline uses choline acetyltransferase to produce ACh, broken down by acetylcholinesterase
What happens in Alzheimer’s
Reduction in Ach
Give Ach inhibitors
Delay its breakdown- increasing the amount of Ach present in the system
Side effects of dry mouth
Describe the intermediolateral cell column
found T1-L3 and target of presympathetic neurones; where sympathetic neurones eminate from, travelling to the sympathetic ganglia outside of the cord, synapsing to post-ganglionic neurones
Degradation of the intermediolateral cell column is seen in disease
What do baroreceptors respond to
Respond to physical distension
respond to mechanical pressure, transmitting beat-to-beat pressure information; rate of firing proportional to BP when threshold reache
