Function and neurochemistry of the autonomic nervous system (ANS)- Theme 6 – Flashcards
Unlock all answers in this set
Unlock answersquestion
What are the two rapid responses to changes in the environment?
answer
1) Voluntary: Somatic nervous system acts on skeletal muscles. 2) Involuntary: Autonomic nervous system acts on cardiovascular system and other organs.
question
What is the slow response to changes in the environment?
answer
Hormones, neurotransmitters, growth factors, cytokines and other substances cause changes in gene expression leading to long term adaptation.
question
What is the autonomic nervous system?
answer
The neuronal groups and fibre connections that control the activity of the heart, visceral organs, blood vessels and glands.
question
What is the function of the autonomic nervous system?
answer
Maintains homeostasis by directly or indirectly facilitating the response of every system to external and internal changes.
question
What are the four components of the peripheral nervous system?
answer
1) Somatic motor nerve fibres 2) visceral afferents 3) Autonomic efferent nerve fibres 4) Other afferents
question
Define afferent
answer
Conducting towards the CNS in nerves (sensory neurones) or towards the organ supplied in blood vessels.
question
Define efferent
answer
Conducting away from the CNS in nerves (motor neurones) or away from the organ supplied in blood vessels.
question
What are the three subdivisions of autonomic efferent nerve fibres?
answer
1) Enteric nervous system 2) Sympathetic nervous system 3) Parasympathetic nervous system
question
What is the parasympathetic branch of the autonomic nervous system?
answer
Mainly important for digestion, excretion and visual accommodation. Promotes the 'couch potato' state. Less widespread innervation and effects than the sympathetic branch.
question
What is the sympathetic branch of the autonomic nervous system?
answer
Mainly important for ongoing control of the cardiovascular system and reflex responses to stressful situations. Controls fight or flight response. More widespread innervation and effects.
question
What are preganglionic nerve fibres?
answer
Fibres from the central nervous system to the ganglion.
question
Are all preganglionic nerve fibres cholinergic?
answer
Yes, regardless of whether they are in the sympathetic/ parasympathetic nervous system.
question
Hence what do all preganglionic fibres release at the ganglion (in the sympathetic/ parasympathetic nervous system)?
answer
Acetylcholine
question
What are cholinergic fibres?
answer
Nerve fibres which use acetylcholine as their neurotransmitter.
question
Why are sympathetic preganglionic fibres shorter than parasympathetic postganglionic fibres?
answer
Sympathetic ganglia are often closer to the spinal cord than the parasympathetic ganglia, so the parasympathetic fibres have further to travel.
question
What is an autonomic ganglion?
answer
A cluster of nerve cell bodies in the autonomic nervous system. There are two types- sympathetic ganglion and parasympathetic ganglion.
question
What are 5 types of efferent nerve fibres (away from the CNS in nerves/ organs in blood vessels)?
answer
1) Salivary gland 2) Blood vessel 3) Sweat gland 4) Alpha and beta receptors 5) Muscle fibre
question
What are the effects of the parasympathetic nervous system on heart rate?
answer
Decreased heart rate
question
What effect does the PNS have on the GI tract?
answer
Increased gastrointestinal and other secretions Increased peristalsis (GI contractions which mix and propel GI contents)
question
What effect does the PNS have on visual accommodation?
answer
Pupil constriction (allows for focussing)
question
What effect does the PNS have on micturition (urination)?
answer
Detrusor muscle contracts (a smooth muscle found in the wall of the bladder, which relaxes to store urine and contracts to release urine).
question
What other effect does it have on the digestive system?
answer
Defaecation
question
What effect does the sympathetic nervous system have on heart rate?
answer
Increased heart rate and force of contraction
question
What effect does the sympathetic nervous system have on blood vessels?
answer
Vasoconstriction and increased renin release (which raises BP)
question
What effect does the sympathetic nervous system have on the lungs?
answer
Bronchodilation
question
What effect does the SNS have on blood glucose?
answer
Increased blood glucose from free fatty acids (beta oxidation)
question
What effect does the SNS have on pupils?
answer
Pupil dilation
question
What effect does it have on the sweat glands?
answer
Increased activity
question
What effect does it have on the bladder?
answer
Bladder relaxation (stores urine)
question
What effect does the parasympathetic nervous system have on arteries?
answer
Usually no effect
question
What effect does the sympathetic nervous system have on arteries?
answer
Constriction
question
What effect does the sympathetic nervous system have on the exocrine glands?
answer
No effect
question
What effect does the parasympathetic NS have on the exocrine glands?
answer
Increases secretion
question
What effect does the sympathetic and parasympathetic NS have on metabolism?
answer
Sympathetic= increase in plasma glucose Parasympathetic= no effect
question
What effect does the sympathetic and parasympathetic NS have on renin?
answer
Sympathetic= increases secretion from the kidney Parasympathetic= no effect.
question
Does the parasympathetic nervous system innervate blood vessels in humans?
answer
No, it is not involved in the dilation/ constriction of blood vessels.
question
What is generally the only nervous system involved in secretion?
answer
Parasympathetic nervous system
question
Under resting conditions, which nervous system dominates heart rate?
answer
The parasympathetic nervous system- hence why if the ANS is blocked there is a slight increase in heart rate.
question
What does it mean when the sympathetic and parasympathetic NS drive to an organ is normally reciprocal?
answer
As one drive increases the other decreases.
question
Where is the pre- ganglionic cell body located in the sympathetic and parasympathetic nervous system?
answer
SNS= thoracic or upper lumbar PNS= brain stem or sacral
question
Where length is the preganglionic axon in the sympathetic and parasympathetic nervous system?
answer
SNS= short (as ganglia are located closer to the spinal cord) PNS= long
question
Where are the ganglia located in the sympathetic and parasympathetic nervous system?
answer
SNS= paravertebral (beside or near the vertebral column) PNS= in or near organ wall
question
What is the ganglionic transmitter in both the sympathetic and parasympathetic nervous system?
answer
Acetylcholine
question
What is the ganglionic receptor in both the sympathetic and parasympathetic nervous system?
answer
Nicotinic.
question
What is the length of the post- ganglionic axon in the PNS and SNS?
answer
SNS= long, with varicosities (release points for neurotransmitter along the effector). PNS= short
question
What is the transmitter at the neuro effector junction in the SNS and PNS?
answer
Sympathetic= noradrenaline (rarely acetylcholine) Parasympathetic= acetylcholine
question
What is the receptor at the neuro-effector junction in the SNS and PNS?
answer
Sympathetic= alpha or beta adrenergic receptors (rarely muscarinic) Parasympathetic= muscarinic receptors
question
What are the three effects of the parasympathetic nervous system on the heart?
answer
1) Inhibition of cardiac pacemaker (SA node). This decreases heart rate, CO and BP. 2) Decreased conduction velocity in AV node, as when HR slows down this causes more of a delay which enables the heart to fill properly when it is beating slower. 3) Little direct effect on ventricular contraction
question
What vein mediates this response of the PNS on the heart?
answer
The vagus nerve
question
What effect does the parasympathetic nervous system have on blood vessels?
answer
Parasympathetic nervous system does not usually innervate blood vessels (the main exception being the arteries to the penis). Hence there is little effect on total peripheral resistance.
question
However would artificial injection of acetylcholine result in any parasympathetic response in blood vessels?
answer
Yes, as there are cholinergic muscarinic receptors in blood vessels, so artificial injection of acetylcholine would cause vasodilation (which would cause BP to fall)
question
What nerves mediate this induced parasympathetic response in blood vessels (vasodilation)?
answer
Vagus and sacral nerves
question
Is there normally Ach in the blood?
answer
No
question
What are the parasympathetic effects on other smooth muscle?
answer
1) Bronchioles constrict 2) GI tract: spontaneous contractions of gut wall enhanced, intestinal sphincters relaxed, which aids propulsion of GI contents. 3) Detrusor muscle of the bladder contracts (external spincter relaxed= urination).
question
What nerves mediate bronchoconstriction and contractions of the internal sphincter in the gut wall and external sphincter in the detrusor muscle?
answer
Vagus and sacral nerves
question
In what 4 parts of the body does the parasympathetic nervous system stimulate secretions?
answer
1) bronchosecretion (mucus) 2) gastrointestinal (gastric acid, pancreatic enzymes) 3) Salivary glands (watery saliva) 4) Lacrimal glands (tears)
question
What are the 2 parasympathetic effects on the eye?
answer
1) Accommodation for near vision (focuses) 2) Pupil constriction (miosis)
question
How does the PNS cause focusing of the eye?
answer
Contraction of ciliary muscle relaxes tension on the lens, allowing it to thicken and shortening focal distance.
question
How does the PNS cause pupil constriction?
answer
Contraction of sphincter pupillae muscle in the iris.
question
What nerve mediates this parasympathetic response in the eye?
answer
The oculomotor nerve
question
What is the effect of blocking the ganglionic nicotinic receptors?
answer
Loss of all autonomic function
question
What is an antagonist of the ganglionic nicotinic receptor, which blocks the receptor?
answer
Hexamethonium
question
What are 2 effects of blocking the ganglionic nicotinic receptor on the sympathetic nervous system?
answer
1) Loss of vasomotor tone (as SNS stimulates vasoconstriction), so blood vessels dilate. 2) Dry skin (as sweating controlled by the CNS)
question
What are 5 effects of blocking the ganglionic nicotinic receptor on the parasympathetic nervous system?
answer
1) Heart rate increases (as PNS usually decreases HR) 2) Reduction of visual accommodation (focus, as pupils constrict normally) 3) Reduction of various secretions 4) Constipation 5) Difficulty in micturition (urination)
question
What are the effects of blocking muscarinic receptors in the ANS?
answer
Loss of all parasympathetic functions and sweating. No effect on the sympathetic nervous system, only on the sweat gland, as this is the only sympathetic pathway which has muscarinic receptors at its neuro effector junction.
question
Hence what is the effect of blocking muscarinic receptors on the sympathetic nervous system?
answer
Dry skin (due to no sweating)
question
What are 5 effects of blocking muscarinic receptors on the parasympathetic nervous system?
answer
1) Heart rate increases 2) Reduction of visual accommodation 3) Reduction of various secretions 4) Constipation 5) Difficulty in micturition (same effects as blocking ganglionic nicotinic receptors).
question
What are the effects of blocking all adrenergic receptors?
answer
Loss of all sympathetic function except sweating (as the sweat glands have muscarinic receptors at its neuro effector junction).
question
In particular what is the effect of blocking the alpha adrenergic receptors?
answer
Loss of vasomotor tone, so blood vessels dilate (as the SNS usually results in vasoconstriction)
question
What is the effect of blocking the beta 1 adrenergic receptor?
answer
Heart rate falls
question
What are 2 effects of blocking the beta 2 adrenergic receptor?
answer
1) Blood sugar and free fatty acids fall 2) Airways narrow
question
When do the effects of blocking the SNS become more important and widespread?
answer
During stress, excitement and increased physical activity.
question
What condition can be caused by stimulating the sympathetic nervous system?
answer
Phaeochromocytoma
question
What is Phaeochromocytoma?
answer
A tumour of chromaffin cells which causes secretion of large amounts of noradrenaline and adrenaline.
question
What are the 5 signs and symptoms of phaeochromocytoma?
answer
1) Increased blood pressure 2) Pallor (as redness of the skin is affected by blood flow and constriction of vessels limits blood supply to the skin). 3) Increased and irregular heart rate 4) Hyperglycaemia (increased plasma glucose) 5) Increased metabolic rate
question
What is the enteric nervous system?
answer
Complex networks (plexuses) of sensory, motor and interneurons forming 2 layers within the walls of the GI tract.
question
What are two plexuses inside the enteric nervous system?
answer
Myenteric and submucosal plexuses (together containing approximately 100 million neurones).
question
How many neurotransmitters does the enteric nervous system have approximately?
answer
30 different neurotransmitters, including non- adrenergic, non- cholinergic, acetylcholine, vasoactive intestinal polypeptide and nitric oxide.
question
What does the ENS coordinate and control?
answer
Peristalsis Fluid transport Glandular secretion Blood flow within the GI tract.
question
Are the effects of the PNS and SNS on the GI tract exerted mainly directly or indirectly?
answer
Indirectly, via modulation of enteric nervous system activity.
question
What system can be manipulated to treat MI, angina, arrhythmias, heart failure and hypertension?
answer
Block of sympathetic stimulation of the heart by blocking the beta 1 adrenergic receptor via an antagonist for this receptor at the neuro effector junction.
question
What system can be manipulated to treat asthma?
answer
B2 receptor agonists can be used to dilate the airways (activates sympathetic bronchodilation) Muscarinic receptor antagonists can also be used to dilate the airways (inhibits parasympathetic bronchoconstriction)
question
How can drugs be used to treat overactive bladder?
answer
Blocking M3 receptors (inhibits the PNS stimulating detrusor contraction) Activating B3 receptors (stimulates the SNS to stimulate detrusor relaxation) Blocking alpha1 adrenergic receptors
question
What is a treatment of hypertension achieved by blocking the SNS?
answer
Alpha 1 receptor antagonists block sympathetically- mediated vasoconstriction.
question
How can premature labour be delayed? (not very successfully)
answer
B2 receptor antagonists (inhibits sympathetic nervous system)
question
Why can Botulinum toxin (Botox) be used to treat incontinence?
answer
Reduces acetylcholine release, so relaxes muscle spasms and wrinkles.
question
Why can M antagonists be used to speed up the heart?
answer
It blocks the parasympathetic nervous system from decreasing heart rate, so HR speeds up.
