ANS Flashcards
What parts of the body does the ANS innervate and control?
Visceral organs, smooth muscle, skin and secretory glands.
What is the main function of the ANS?
Homeostasis (CVR, digestive, excretory and thermoregulatory mechanisms) - Automatic
What do the afferent sensory divisions of the ANS include?
Somatic and visceral sensory
What does the efferent motor division of the ANS include?
Somatic motor and visceral motor.
Visceral motor functions are divided into sympathetic and parasympathetic nervous pathways.
(These pathways typically innervate identical organs with antagonistically stimulating effects.)
Outline the structure of the sympathetic division of the ANS.
Myelinated preganglionic fibres leave CNS and then synapse in a ganglion (collection of cell bodies) with un-myelinated post-ganglionic fibres. Ganglia are close to the CNS, therefore the preganglionic fibres are shorter, and the post-ganglionic fibres connecting to the target organ are longer compared to that of the parasympathetic system.
What does the sympathetic division of the ANS do? What affect does it have on HR, pupils, GI motility etc.?
Fight or flight
Increased HR and BP, dilated bronchi to increase airflow, vasodilation in skeletal muscle allowing increase blood flow; GI motility decreases. Increased blood glucose to support high ATP demand.
From which region of the SC do sympathetic preganglionic sympathetic neurones come from?
Thoracic and upper 2/3 lumbar segments of SC, residing within the lateral horn of the spinal grey matter.
From which nerve roots do preganglionic axons leave the cord?
Ventral nerve roots, joining the mixed spinal nerve.
Where doe postganglionic sympathetic neurones have their cell bodies?
Sympathetic chain of ganglia lying either side of the vertebral column or the plexuses (coeliac, superior and inferior mesenteric) that surround the main branches of the abdominal aorta.
How do preganglionic axons in spinal nerves enter the sympathetic/paravertebral chain?
White ramus communicans
Through what do post-ganglionic fibres return to the SC?
Grey ramus communicans
What is special about preganglionic sympathetic fibres concerned with innervation of pelvic and abdominal viscera?
Pass uninterrupted through the sympathetic chain and travel to the plexuses where corresponding postganglionic cell bodies are located.
What NT is released in the pre and post-ganglionic sympathetic fibres respectively?
Pre - ACh
Post - NA
What does the parasympathetic division of the ANS do? How does it effect HR, pupils etc. ?
Inhibitory effect on viscera, an antagonistic effect to sympathetic division. Rest and digest.
Outflow of paraNS?
Craniosacral outflow
(Preganglionic parasympathetic neurones reside within the brainstem and the SC. Within the brainstem, such cells lie in cranial nerve nuclei associated with the oculomotor, facial, glossopharyngeal and vagus nerves. Preganglionic parasympathetic neurones are present in S2-4, provide innervation of pelvic viscera.)
What NT does parasympathetic division release?
ACh in pre and post ganglionic neurones.
Do cell bodies of postganglionic parasympathetic neurones lie close or fare from innervated structures?
Close
From where do visceral motor nuclei originate?
Hypothalamus
(these visceral motor neurones project to the brain stem or the SC where they synapse with autonomic sympathetic/parasympathetic neurones. )
Where is the sympathetic trunk?
Lateral to the vertebral bodies for the entirety of the vertebral column - contains ganglionic fibres.
Outline the innervation of the adrenal gland and what it releases.
1 sympathetic nerve to adrenal gland releasing adrenaline, gland behaves as a post-ganglionic fibre - hormone released instead of NT.
Explain what happens when exercise starts.
Blood vessels dilate in response to adrenaline, constituting to a reduction in BP. This reduces the stretch on the baroreceptors, reduced stimulation is immediately responded by the cardiac control centre - sends signals to the sympathetic nerve through the MO to stimulate HR and increase the BP by vasoconstriction. Increased electrical stimulation results in release of NA onto the SAN, ^ frequency of waves of excitation and thus contraction (systole).
Explain what happens when exercise stops.
BP in arteries ^ as heart continues to pump harder and faster, baroreceptors are stretched. They respond by sending more sensory nerve impulses to the cardiac centre - sends impulses through the paraNS to slow down the HR (ACh on SAN) and causes vasodilation to lower BP to resting.
What type of nerves don’t innervate the lungs?
Sympathetic nerves
What exerts a sympathetic influence on the lungs?
Adrenaline - bronchodilates lungs
Outline the pupillary reflex.
High light intensity on rod and cone cells stimulate APs which reach both left and right (pretectal) nuclei. (Pretectal) nuclei stimulate both sides of the Edinger-Westphal nucleus. Both sides generate APs through the right and left CNIII causing both pupils to constrict (parasympathetic pathway).
Low light intensity causes pupil dilation (sympathetic pathway).
Outline the micturition reflex.
Parasympathetic stimulation innervates the detrusor muscles to contract, increasing bladder pressure and the internal urethral sphincter (Sphincter urethrae) relaxes, this allow urine to leave bladder.
Bladder afferents signals ascend through the SC, projecting to the pontine micturition centre and cerebrum.
Voluntary decision - neurones of pontine micturition centre transmit electrical impulses to excite the sacral preganglionic neurones.
Subsequent parasympathetic stimulation of the pelvic nerve (S2-4) → releases ACh, binding onto muscarinic ACh receptors on the detrusor muscle - stimulating contracting and increases vesicular pressure.
What receptor type mediates fast excitatory and inhibitory transmission (ms)?
Ion-channel linked receptor
Where can you find nicotinic ACh receptors (ion-channel linked) in ANS?
nACh receptors mediate responses to ACh releases from preganglionic fibres at all autonomic ganglia. Additionally, nAChRs mediate the response to ACh released by sympathetic nerves innervating the adrenal medulla.
Where can you find muscarinic ACh receptors in ANS?
Muscarinic ACh receptor responds to ACh release from post-ganglionic parasympathetic fibres.
Where can you find adrenergic ACh receptors in ANS?
Adrenergic receptors respond to NA release from postganglionic sympathetic fibres or adrenaline present in blood.
What receptor type mediates slow/prolonged excitatory and inhibitory transmission (ms)?
G-coupled receptor
What are the effectors of G-coupled receptors?
Effectors include enzymes (adenyl cyclase, phospholipase C, cGMP-PDE) or channels (Ca2+, K+).
Explain how ACh is formed.
Derived from choline and acetyl CoA, enzymatically converted by choline acetyl transferase.
Outline the WHOLE process of synaptic transmission that occurs at a cholinergic synapse.
ACh made from choline + acetyl CoA (choline acetyl transferase.) ACh is packaged into synaptic vesicles by intrinsic vesicular transporters.
AP causes Ca2+ influx, synaptic vesicles fuse with presynaptic membrane and through exocytosis release ACh into the synaptic cleft. ACh binds onto muscarinic/nicotinic receptors - activation of receptors.
ACh degraded by acetylcholinesterase in synaptic cleft into choline and acetyl CoA. Choline into presynaptic terminal (or in glial cell) by choline re-uptake protein.
What does inhibition of acetylcholinesterase do?
Accumulation and elevated concentration of ACh within the synaptic cleft > overstimulation of receptor activation.
Outline the biosynthesis of NA.
Tyrosine → DOPA (dihydroxyphenylalanine) via tyrosine hydroxylase.
DOPA → dopamine by DOPA decarboxylase.
Dopamine packaged into vesicles with dopamine-beta hydroxylase by intrinsic transporter proteins, results in NA as product.
What enzymes degrade NA?
Monoamine oxidase (MOA) and catechol-o-methyltransferase (COMT).
What converts NA to adrenaline?
Phenyl-ethanol methyl transferase
Outline the process of adrenaline release from ‘preganglionic’ sympathetic fibres.
AP causes Ca2+ influx and adrenaline exocytosis into the synaptic cleft.
Adrenaline diffuses into capillary and is transported to tissues in the blood.
