Lecture 11/12 NS - Anatomy of ANS and Autonomic Reflexes

Question 1

What is the ANS role?

Answer 1

Responsible for involuntary control of the viscera

Question 2

What is the physiolgical action of the PSNS?

Answer 2

Localised and conserves body energy

Question 3

What is the physiological action of the SNS?

Answer 3

Mass responses and mobilises the body energies for increased activity

Question 4

Where is the central ANS control?

Answer 4

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

Question 5

What is the structure of the ANS pathway?

Answer 5

Preganglionic neuron, ganglion and postganglionic neuron

Question 6

What is an afferent nerve?

Answer 6

Sensory info from PNS into CNS

Question 7

What is an efferent nerve?

Answer 7

Motor info from CNS to PNS

Question 8

Where do the pre/postganglionic neurons lie in the SNS?

Answer 8

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)

Question 9

Where do SNS preganglionic neurons synapse?

Answer 9

Synapse with ganglion right outside or move up/down symp trunk to synapse at another ganglion or disperse into body to subsidiary ganglion

Question 10

Where are the cells of the preganglionic SNS cells found?

Answer 10

In lateral horns of grey matter in the spinal cord

Question 11

Where are the sympathetic trunks located?

Answer 11

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

Question 12

What are the SNS nerves located?

Answer 12

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

Question 13

What are the actions of the SNS?

Answer 13

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)

Question 14

What is the sacral outflow of PSNS?

Answer 14

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

Question 15

What do the pelvic splanchnic nerves control?

Answer 15

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

Question 16

What is the oculomotor nerve?

Answer 16

CNIII -> ciiary ganglion, with postganglionic fibres to sphincter pupillae muscle and ciliary muscle behind the eye

Question 17

What is the facial nerve?

Answer 17

CNVII -> Submandibular ganglion (submandibular and sublingual salivary glands); pterygopalatine ganglion (paranasal sinuses and lacrimal glands)

Question 18

What is the glossopharyngeal nerve?

Answer 18

CNIX -> optic ganglion (parotid gland)

Question 19

What is the vagus nerve?

Answer 19

CNX -> enters neck and thorax via carotid sheath, branches to lungs, heart, oesophagus, stomach, intestines

Question 20

What is the ENS?

Answer 20

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

Question 21

What are the 2 types of sympathetic stimulation of the heart?

Answer 21

Ionotropic effect (increased SV) and chronotropic effect (increased HR) -> so increases CO

Question 22

What is the baroreceptor reflex?

Answer 22

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

Question 23

What do baroreceptors do?

Answer 23

Increased activity inhibits the SNS -> decreases BP

Question 24

Where are baroreceptors located?

Answer 24

Carotid sinus and aortic arch

Question 25

How does the baroreceptor reflex regulate loss of BP?

Answer 25

Question 26

How does the baroreceptor reflex regulate increase of BP?

Answer 26

Question 27

What is the normal CV response to gaining an upright posture?

Answer 27

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

Question 28

How does the normal CV response to upright posture fail in postural hypertension?

Answer 28

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

Question 29

How can the pupil diameter affected using drugs that change the PSNS stimulation?

Answer 29

Piocarpine -> decreases pupil diameter with PSNS-like stimulation (miosis). Atropine -> blocks PSNS stimulation, so increases pupil diameter (mydriasis)

Question 30

How does the light reflex work in the eye?

Answer 30

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