Lecture 5: Autonomic System

Question 0

E.g homeostasis

Heart

Answer 0

Sympathetic: increase rate and strength of contractions, inhibits effect of parasympathetic system to allow blood vessels to dilate

Parasympathetic: decrease rate and strength of contractions, constricts coronary vessels in accordance with decreased demand

Question 1

E.g of homeostasis

Eye

Answer 1

Parasympathetic: constrict pupil, contract ciliary muscles to allow lens to thicken for near vision
Sympathetic: dilate pupil

Question 2

E.g homeostasis

Genital organs

Answer 2

Sympathetic: ejaculation and constriction causing remission of erection

Parasympathetic: produces engorgement of erectile tissue

Question 3

Autonomic nerves

Answer 3

All sympathetic and parasympathetic nerves contain BOTH general visceral sensory and general visceral motor fibres

Question 4

General visceral sensory (afferent)

Answer 4

Usually parasympathetic
Visceral reflexes (gag reflex)
Organic sensation
Pain only accompany sympathetic nerves e.g heart attack

Question 5

Sympathetic comes from what region?

Answer 5

Thoracolumbar region

Question 6

Parasympathetic comes from what region?

Answer 6

Craniosacral region

Question 7

Sympathetic ganglia are located where?

Answer 7

Close to spinal cord in a chain

Question 8

Parasympathetic ganglia are located where?

Answer 8

Close to target organ

Question 9

Sympathetic post ganglionic fibres are what length in general?

Answer 9

Long

Question 10

Parasympathetic post ganglionic fibres are what length in general?

Answer 10

Short

Question 11

Sympathetic branching?

Answer 11

Lots of branching so that more than one organ can be targeted at once

Question 12

Parasympathetic branching?

Answer 12

Not much branching

Question 13

Sympathetic nerve system pre-synaptic fibres are located where?

Answer 13

in lateral horn of grey matter of T1-L2.

Question 14

Para vertebral ganglia of sympathetic system are located where?

Answer 14

sympathetic trunk

Question 15

Prevertebral ganglia sympathetic nerve system are located where?

Answer 15

plexuses on abdominal aorta.

Question 16

Sympathetic activity

Answer 16

• Dilates pupil.
• Reduces secretions from lacrimal and salivary glands.
• Increased viscosity of saliva.
• Increases heart rate and CO.
• Relaxes bronchial muscles.
• Dilates or constricts skeletal muscle.
• Constricts arteries to skin and viscera.
• Reduced gut motility and secretions.
• Sphincters contract.
• Relaxes gallbladder.
• Increases secretion from sweat glands

Question 17

Interomediolateral cell column

Answer 17

Interomediolateral cell column contains pre-ganglionic sympathetic neurons for the entire body.

Lies between segments T1-L2 (“thoracolumbar outflow”).

Question 18

Courses of sympathetic motor fibres

Answer 18

Axons leave spinal cord through anterior (motor) root.
• Enter anterior rami of spinal nerves (T1-L2).
• Enter into WHITE rami communicantes and pass into sympathetic trunk.
4 pathways:
1. Ascend and then synapse
2. Synapse at same level
3. Descend and then synapse
4. Pass through and continue on through abdomino-pelvic
splanchnic nerve.
Synapse in paravertebral or prevertebral ganglia.
• Exit via GREY rami communicantes.
• Enter all branches of all 31 pairs of spinal nerves
(to reach all blood vessels, sweat glands etc).

Question 19

Pathways of sympathetic neurons: C1-C8 levels

Answer 19

Cell body of pre-synaptic sympathetic neuron in interomediolateral cell column of T1-L2 spinal cord.

Pre-synaptic sympathetic neurons ASCEND to cervical level and
synapse in one of three cervical ganglia.

Post-synaptic neuron leaves sympathetic trunk and enters grey
rami communicante before entering anterior and posterior
rami of spinal nerves.

Note: no white rami in cervical region

Question 20

Pathways of sympathetic neurons: T1-L2 levels

Answer 20

Cell body of pre-ganglionic sympathetic neuron in interomediolateral cell column of T1-L2.

Myelinated axon leaves spinal cord via anterior (motor) root and enters white rami communicante.

Synapses in sympathetic trunk (splanchnic nerves synapse in prevertebral ganglia instead)

Post-ganglionic unmyelinated neuron leaves via grey rami communicante and enters anterior and posterior rami of spinal nerves.

Note: both white and grey rami communicante in thoracic region

Question 21

Pathways of sympathetic neurons: L3-Co levels

Answer 21

Cell body of pre-ganglionic sympathetic neuron in interomediolateral cell column of T1-L2.

Myelinated pre-synaptic sympathetic neuron axon descends in sympathetic trunk and synapses with post-ganglionic neuron in the ganglia of the trunk.

Post-ganglionic unmyelinated neuron leaves the sympathetic trunk via grey rami communicante and enters anterior and
posterior rami of spinal nerves.

Note: no white ramicommunicante in lumbar or sacral region

Question 22

Sympathetic fibres always leave through grey rami, why?

Answer 22

Post-synaptic sympathetic neurons pass out of sympathetic chain via the grey rami communicantes.

This way they can reach virtually all areas of the body to innervate
blood vessels, sweat glands and visceral structures.

Question 23

Splanchnic nerves

Answer 23

Convey visceral motor and visceral sensory fibres from autonomic system to and from viscera of the body cavities (pericardial, pleural and peritoneal)

Question 24

Splanchnic nerves for peritoneal, plural and pericardial cavities

Answer 24

* Thoracic (pericardial + pleural) cavity = cadiopulmonary splanchnic => cardiac, pulmonary and oesophageal plexuses. * Peritoneal cavity = abdominopelvic splanchnic (greater, lesser, least & lumbar splanchnics).

Question 25

Abdominopelvic splanchnic nerves from peritoneal cavity

Answer 25

• All pre-synaptic sympathetic fibres of abdominopelvic splanchnic nerves (except those going to adrenal gland) synapse in prevertebral ganglia.

Question 26

Abdominopelvic splanchnic nerves | ARE ALL SYMPATHETIC

Answer 26

• Myelinated pre-ganglionic fibres passing through the sympathetic trunk without synapsing. * Greater splanchnic nerve: T5-T9 * Lesser splanchnic nerve: T10-T11 * Least (lower) splanchnic nerve: T12

Question 27

Pelvic splanchnic

Answer 27

not related to the sympathetic trunk and carry parasympathetic fibres! s2 s3 s4

Question 28

Paravertebral and prevertebral ganglia

Answer 28

Paravertebral ganglia: adjacent to vertebral column Prevertebral ganglia: on anterior surface of abdominal aorta surrounding branches of major blood vessels.

Question 29

Sympathetic division summary

Answer 29

Pre-ganglionic neurons: short, myelinated, cell bodies in lateral horns of gray matter in spinal cord from T1-L2 (Thoraco-lumbar outflow). • Ganglionic neurons: Sympathetic chain or collateral ganglia on abdominal aorta. • Post-ganglionic neurons: long, exit sympathetic trunk in gray rami  spinal nerve  effector organs.

Question 30

Parasympathetic divison

Answer 30

* “Rest and digest” * Pre-ganglionic neurons: brain stem and S2, S3, S4 (cranio-sacral outflow). * Pre-ganglionic fibres are long, myelinated, travel through cranial nerves III, VII, IX and X plus spinal nerves S2-S4. (3,7,9,10) * Synapse with short post-ganglionic fibres that are very close to, or directly on, effector organs. * Restricted distribution: head, viscera of trunk, erectile tissues of genitalia. • Not part of spinal nerves (except anterior rami S2-S4).

Question 31

Parasympathetic outflow

Answer 31

• CN III – Oculomotor nerves • => pupil constriction, lenses bulge. • CN VII – Facial nerves • => increased secretions from nasal, lacrimal and salivary glands. • CN IX – Glossopharyngeal nerves • => increased secretion from parotid salivary glands. • CN X – Vagus nerves • => slows HR, contracts bronchioles, dilates visceral arteries, increases gut motility and secretions.

Question 32

Vagus nerve/ pelvic splanchnic

Answer 32

Vagus nerve provides all parasympathetic stimulation to viscera of thorax and abdomen up to left colic (splenic) flexure. Pelvic splanchnic nerves provide PS to distal GIT and repro organs.

Question 33

Visceral afferent fibres of pain are carries how?

Answer 33

* Most visceral reflex sensation and some pain travel in visceral afferent fibres travelling with parasympathetic fibres back to brain. * Most visceral pain impulses (from heart & most organs of peritoneal cavity) travel centrally along visceral afferent fibres accompanying sympathetic fibres.

Question 34

What is referred pain?

Answer 34

• Feeling of pain at a location other than the site of origin of the stimulus but in an area supplied by same or adjacent segments of spinal cord.

Question 35

Referred abdominal pain

Answer 35

Pain from abdominal viscera follow sympathetic splanchnic nerves back to spinal cord (T5-L2). • Sensory fibres synapse in dorsal root ganglia. Pain and somatic sensory afferents( sensory of skeletal muscle) synapse in same location = confuses brain!

Question 36

Angina pectoris

Answer 36

* Painful impulses from myocardium (caused by ischaemia) projected via GVA to dorsal horn of T1-T4. * Dorsal horn of T1-T4 also receives cutaneous sensory info from corresponding dermatomes. •Painful impulses projected to brain via spinothalamic tract and misperceived as coming from nociceptors in dermatomes (T1-T4).

Question 37

Carotid sinus

Answer 37

• To maintain homeostasis, the ANS must receive sensory information from the body (via visceral AFFERENT fibres). The carotid artery in the neck, for example, has receptors (called baroreceptors,in the carotid sinus) that sense blood pressure. These receptors send high blood pressure signals via the vagus nerve to the nucleus of the solitary tract (NST). The NST projects to the nucleus ambiguus and vagal nucleus, which release acetylcholine as part of the parasympathetic system to slow down the heart.

Question 38

Hypothalamus

Answer 38

* Controls all autonomic functions of body. * Anterior hypothalamus => excitatory effect on parasympathetic nervous system. * Posterior hypothalamus => excitatory effect on sympathetic nervous system * Hypothalamospinal tract => conveys descending autonomic fibres that influence sympathetic Neurons in IML cell column and preganglionic neurons of sacral parasympathetic nucleus. * Lesion above T1 : Horner Syndrome.

Question 39

Horner's syndrome

Answer 39

• Due to lesion in pathway of sympathetic fibres travelling to the head. • Clinical signs: • Ptosis: drooping of upper eyelid due to paralysis of superior tarsal smooth muscle. • Miosis: pupillary constriction due to paralysis of pupillary dilator smooth muscle. • Anhidrosis: Loss of sweating due to loss of sweat gland innervation by sympathetic fibres. • Flushed, warm dry skin: vasodilation of subcutaneous arteries due to lack of vascular tone and sweat gland innervation.