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
