Lecture 11/12 NS - Anatomy of ANS and Autonomic Reflexes Flashcards
What is the ANS role?
Responsible for involuntary control of the viscera
What is the physiolgical action of the PSNS?
Localised and conserves body energy
What is the physiological action of the SNS?
Mass responses and mobilises the body energies for increased activity
Where is the central ANS control?
Hypothalamus (housekeeping area of brain) -> input from higher brain centres (memory and previous situations) and homeostatic changes. Output into medulla whihc goes out in PSNS or SNS
What is the structure of the ANS pathway?
Preganglionic neuron, ganglion and postganglionic neuron
What is an afferent nerve?
Sensory info from PNS into CNS
What is an efferent nerve?
Motor info from CNS to PNS
Where do the pre/postganglionic neurons lie in the SNS?
Lateral column grey matter of spinal cord T1-L3, emerge from spinal cord via ventral root of spinal nerve passing through ventral ramus to white rami communicantes to ganglion -> post ganglionic fibres ditributed to effector organs via grey rami communicantes (into spinal nerves to the body)
Where do SNS preganglionic neurons synapse?
Synapse with ganglion right outside or move up/down symp trunk to synapse at another ganglion or disperse into body to subsidiary ganglion
Where are the cells of the preganglionic SNS cells found?
In lateral horns of grey matter in the spinal cord
Where are the sympathetic trunks located?
Base of skull to cocyx, with 3 ganglia in cervical region, 11-12 in thoracic region, 4/5 in lumbar region, 4/5 in pelvis
What are the SNS nerves located?
Plexus around pharynx, cardiac plexus, thyroid plexus, pulmonary plexus [CERVICAL]; plexus around thoracic aorta, splanchnic nerves [THORACIC]; lumbar splanchnic nerves take part in all plexi of SNS in abdominal and pelvic regions
What are the actions of the SNS?
Vasoconstriction of blood vessels; secretomotor of sweat glands; motor in hairs; accompany motor nerves to voluntary muscles but only distributed to blood vessels supplying the muscles; viscera (dilation of pupils/arterioles, movement of alimentary tract, urinary bladder)
What is the sacral outflow of PSNS?
Anterior rami of S2-4, with visceral branches passing directly to pelvic viscera via pelvic splanchnic nerves, minute ganglia in walls of viscera giving rise to post-ganglionic fibres
What do the pelvic splanchnic nerves control?
Motor fibres to rectum/bladder wall, inhibitory fibres to bladder sphincter, erection of penis/clitoris via vasodilator fibres; fibres also pass superiorly to supply large part of the gut with visceromotor innervation
What is the oculomotor nerve?
CNIII -> ciiary ganglion, with postganglionic fibres to sphincter pupillae muscle and ciliary muscle behind the eye
What is the facial nerve?
CNVII -> Submandibular ganglion (submandibular and sublingual salivary glands); pterygopalatine ganglion (paranasal sinuses and lacrimal glands)
What is the glossopharyngeal nerve?
CNIX -> optic ganglion (parotid gland)
What is the vagus nerve?
CNX -> enters neck and thorax via carotid sheath, branches to lungs, heart, oesophagus, stomach, intestines
What is the ENS?
Present in the walls of alimentary tract -> sensory (monitors mechanical, chemical and hormonal activity of the gut), motor (gut motility, secretion, vessel tone) -> can be overridden by SNS and PSNS
What are the 2 types of sympathetic stimulation of the heart?
Ionotropic effect (increased SV) and chronotropic effect (increased HR) -> so increases CO
What is the baroreceptor reflex?
Decreased BP, mean less pressure so decrease baroreceptor input on SNS nerves, so increases SNS effect on blood vessels and heart, and adrealine increased to increase BP
What do baroreceptors do?
Increased activity inhibits the SNS -> decreases BP
Where are baroreceptors located?
Carotid sinus and aortic arch
How does the baroreceptor reflex regulate loss of BP?
How does the baroreceptor reflex regulate increase of BP?
What is the normal CV response to gaining an upright posture?
Immediately, drop of BP (due to gravity pushing blood away from heart), which decreases CO, decreasing BP -> so decreased baroreceptor stimulation which increases SNS, increasing CO/TPR, increasing BP
How does the normal CV response to upright posture fail in postural hypertension?
Impaired sympathetic nerve response, so no increase in TPR, and little change in CO, so BP decreases, decreased cranial blood flow, so fainting can occur -> once supine, blood flow to brain is restored and consciousness is usually regained
How can the pupil diameter affected using drugs that change the PSNS stimulation?
Piocarpine -> decreases pupil diameter with PSNS-like stimulation (miosis). Atropine -> blocks PSNS stimulation, so increases pupil diameter (mydriasis)
How does the light reflex work in the eye?
Light in eye is sent by the optic nerve to the PSNS nerve to cause constriction -> consensual reflex, causes both eyes to constrict, unless a lesion is present
