3.3 Autonomic Nervous System

Question 1

Components of the autonomic nervous system

Control of the autonomic nervous system occurs below our level of consciousness and is regulated by the hypothalamus in the brain.

• From the _____________, central autonomic fibers project downward to form synapses with preganglionic neurons in both the brain stem and the spinal cord.
• From the preganglionic neurons, preganglionic axon fibers emerge to form synaptic connections with post-ganglionic neurons in the autonomic ganglia.
• From there, neurons in the autonomic ganglia will project postganglionic axon fibres that form terminal networks which innervate various organs and tissues.

Answer 1

hypothalamus

Question 2

Efferent neurons in the autonomic nervous system

In the autonomic nervous system, the visceral efferent projections involves a simple circuit of 2 _________ neurons.
- The first neuron in the circuit is known as the pre-ganglionic neuron whose cell body resides in central nervous system either at the __________ or the ___________________. Preganglionic neurons in the spinal cord sends out preganglionic axon fibres which form synaptic contacts with postganglionic neurons that are located in the autonomic ganglia. These autonomic ganglia are located outside of the CNS.

Postganglionic neuron:

• Nerve cell body located in ______________
• Fibres terminate in _____________________

Note that while the autonomic nervous system requires an additional synaptic contact at the autonomic ganglion, the somatic motor system neuron in the spinal cord forms a direct neuromuscular junction at muscle fibres.

Answer 2

multipolar;

brain stem; intermediolateral horn of the spinal cord;

autonomic ganglia outside of CNS;

effector organ (smooth muscle, modified cardiac muscles or glands)

Question 3

In the sympathetic system, cell bodies that project preganglionic axon fibres are found mainly at the thoracic and lumbar regions of the spinal column, particular from _____________ segments.

• Sympathetic ganglia lie closer to the ______ than to the __________
• Sympathetic system is also referred to as the thoraco-lumbar outflow
• The preganglionic cell bodies in the spinal cord are organized _____________. This means that preganglionic cell bodies involved in the innervation of the head are located superiorly in the CNS while those that innervate the pelvic region are located in the inferior part of the spinal column.
• Preganglionic axons from the spinal cord synapse directly upon the adrenal medulla. Unlike other sympathetic innervation that involves a synaptic contact between pre and postganglionic neurons, the adrenal medulla receives direct innervation from the preganglionic axon fibres that project from the spinal cord.

Answer 3

thoracic T1 to lumbar L2/L3;

spinal cord; target organs

somatotopically

Question 4

Sympathetic outflow

• Preganglionic axons from the spinal cord project and synapse with postganglionic neurons in both the paravertebral and prevertebral sympathetic ganglia
• Preganglionic neurons found at the intermediolateral cell column project axon fibers through the ____________ to synapse with postganglionic neurons located at autonomic ganglia.

There are two types of ganglia in this system: the paravertebral ganglia and the prevertebral ganglia.

• Innervation of the paravertebral ganglia in the sympathetic chain from the spinal cord occurs through the ______________, while innervation of the prevertebral ganglia from the spinal cord goes through the _____________.
• The chromaffin cells in the adrenal medulla receives _________________

Dorsal root ganglion is not part of the autonomic nervous system and are afferent neurons that relay sensory information from target tissues into the central nervous system.

Answer 4

ventral root;

ramus communicates;

splanchnic nerves;

direct input from preganglionic neurons from the spinal cord.

Question 5

Pre-ganglionic neurons are found in the _______________

Axons from preganglionic neurons from the lateral column of the gray matter emerge as visceral efferent fibers at the ventral root and enter the sympathetic trunk via the _______________. Here the fibers will diverge:

1) Stay at the same level and synapse at the nearest paravertebral ganglia in the sympathetic trunk and send postganglionic fibers to different target organs via ______________
2) Ascend and synapse at a higher (toward head) paravertebral ganglion.
3) Descend and synapse at a lower (toward feet) paravertebral ganglion.
4) Transverse sympathetic chain, passing through paravertebral ganglia and forming synapses with distant prevertebral ganglia via the splanchnic nerves

Preganglion axon fibers that emerge from the spinal cord can either ascend, descend or stay at the same level and synapse with paravertebral ganglion; or pass through the sympathetic chain and form terminal synaptic connections with the prevetebral ganglia closer to target effector organs.

Answer 5

lateral column grey matter of spinal cord T1 to L3;

white rami communicantes (white communicating ramus)

grey ramus communicantes (grey communicating ramus)

Question 6

The paravertebral ganglia extends bilaterally on the sympathetic chain from either side of the spinal column from the cervical to the sacral segments. In general each segment contains one ganglion

The sympathetic chain stretches from the first cervical to the last sacral segment and is segmentally distributed such that each segment contains one ganglion.

There are two important exceptions : the cervical and stellate ganglia.

• The cervical ganglia consists of both the __________________ that supply innervation to the entire head as well as the cerebral vasculature.
• The stellate ganglion meanwhile is located at the __________________ and is a coalescence of different ganglia that innervates the hearts and lungs.

Apart from ascending to synapse at the cervical and stellate ganglia, the preganglionic neurons which supply innervation of the blood vessels in the lower limb can also send projections to the lumbar and sacral segments of the sympathetic chains.

Answer 6

superior and middle cervical ganglia;

lower cervical and upper thoracic segments in the spinal column

Question 7

Sympathetic outflow: prevertebral ganglia

The prevertebral ganglia are located further away from the spinal column and closer to the _____________ for which the ganglia are named after.

Preganglionic axon fibers that emerge from the spinal cord traverse the sympathetic chains and do not form synapses at the paravertebral ganglia.
Instead, the axon projections continue via the splanchnic nerves before form synapses with postganglionic neurons at the prevertebral ganglia.

There are three major groups of prevertebral ganglia:

1) The celiac ganglion which innervates the _________________
2) The Superior mesenteric ganglion which innervates the __________________
3) The Inferior mesenteric ganglion which projects to the _____________________

In all cases above, the postganglionic neurons in the prevertebral ganglia will follow the arteries to innervate the target organs of the viscera.

Answer 7

origins of the arteries in the abdominal aorta ;

digestive tract, liver and kidney lies near the origin of the celiac artery;

small intestines and colon is located at the origin of the superior mesenteric artery;

colon, rectum, bladder and sexual organs is found near the origins of the inferior mesenteric artery

Question 8

Sympathetic innervation of the adrenal medulla

Adrenal glands are located on top of the kidneys and is known as the suprarenal glands.

• Both the medulla and cortex of the adrenal glands develop independently and secrete different hormones.
• The adrenal medulla is directly innervated by the preganglionic neurons in the spinal cord by way of the ____________.
• Unlike other preganglionic axons, these neurons do not form synapses at the prevertebral ganglia but directly innervate the ______________ cells in the adrenal medulla.
• Once stimulated, the chromaffin cells will secrete different catecholamines.

Answer 8

thoracic splanchnic nerves (lesser).;

chromaffin

Question 9

effect of sympathetic system on iris muscle

Answer 9

pupil dilated, slightly relaxed

Question 10

effect of sympathetic system on blood vessels in head

Answer 10

vasoconstriction

Question 11

effect of sympathetic system on salivary glands

Answer 11

secretion inhibited

Question 12

effect of sympathetic system on oral and nasal mucosa

Answer 12

mucus secretion inhibited

Question 13

effect of sympathetic system on skeletal blood vessels

Answer 13

vasodilation

Question 14

effect of sympathetic system on on heart

Answer 14

rate and force of contraction is increased

Question 15

effect of sympathetic system on coronary arteries

Answer 15

vasodilation

Question 16

effect of sympathetic system on trachea and bronchi

Answer 16

bronchodilation

Question 17

effect of sympathetic system on stomach/ intestines/ large and small intestine

Answer 17

peristalsis, sphincters closed

Question 18

effect of sympathetic system on adrenal medulla

Answer 18

adrenaline or noradrenaline secreted in blood

Question 19

effect of sympathetic system on kidney

Answer 19

urine secretion decrease

Question 20

effect of sympathetic system on bladder

Answer 20

smooth muscle wall relaxed, sphincter closed

Question 21

effect of sympathetic system on sex organs and genitilia

Answer 21

generally vasoconstriction

Question 22

Parasympathetic cranial outflow
Preganglionic cell bodies are located at the brain stem with axon fibers exiting the CNS via cranial nerves 3, 7, 9 and 10
Most of these cranial nerves supply innervation to the head, thoracic and abdominal viscera.
Of the four parasympathetic cranial nerves, three of these cranial nerves project to four discrete parasympathetic ganglia located at the head.

Cranial nerve III (Oculomotor nerve)

• Projects to _______________
• Postganglionic fibres innervates _________________ inside the eye

Cranial nerve VII (Facial nerve)

• Projects to submandibular and pterygopalatine ganglia
• Postganglionic fibres from submandibular ganglion innervates __________________
• Postganglionic fibres from pterygopalatine ganglion innervates ____________________

Cranial nerve IX (Glossopharyngeal nerve)

• Projects to ____________
• Postganglionic fibres innervates _____________

Cranial nerve X (Vagus nerve)
- Enters neck, thorax via carotid sheath
Innervates multiple organs in the lungs, heart, oesophagus, stomach and intestines

Answer 22

ciliary ganglion ; sphincter pupillae and ciliary muscle;

submandibular and sublingual salivary glands;

paranasal sinuses and lacrimal glands;

otic ganglion; parotid salivary gland

Question 23

Parasympathetic sacral outflow
Preganglionic cell bodies are located in the spinal cord at the sacral segment of the spinal cord (S2-S4)
- Axon fibres exit spinal cord through _____________________ which innervates part of the gastrointestinal tract, rectum, bladder and reproduction organs
- Postganglionic neurons found close to the wall of the viscera and give rise to the postganglionic fibres

Answer 23

anterior roots of sacral spinal nerves and pelvic splanchnic nerves

Question 24

effect of parasympathetic system on iris muscle

Answer 24

pupil constricted, contracted

Question 25

effect of parasympathetic system on lacrimal gland

Answer 25

tear secretion increased

Question 26

effect of parasympathetic system on salivary glands

Answer 26

saliva secretion increased

Question 27

effect of parasympathetic system on on heart

Answer 27

rate and force of contraction decrease

Question 28

effect of parasympathetic system on coronary arteries

Answer 28

vasoconstriction

Question 29

effect of parasympathetic system on trachea and bronchi

Answer 29

bronchoconstriction

Question 30

effect of parasympathetic system on stomach/ intestines/ large and small intestine

Answer 30

stomach- secretion of gastric juice and peristalsis increase

small intestine- digestion and absorption increased , secretion of intestinal juice and peristalsis increased

large intestine- secretions and parastalsis increased, sphincter relaxed

Question 31

effect of parasympathetic system on liver and gall bladder

Answer 31

blood vessels dilated, secretion of bile increased

Question 32

effect of parasympathetic system on kidney

Answer 32

urine secretion increase

Question 33

effect of parasympathetic system on bladder

Answer 33

muscle of wall contracted, sphincter relaxed

Question 34

effect of parasympathetic system on sex organs and genitilia

Answer 34

male: erection, female: variable, depending on stage in cycle

Question 35

Sympathetic and parasympathetic divisions release different types of neurotransmitters.

All preganglionic neurons in the autonomic nervous system, whether sympathetic and parasympathetic, mainly uses acetylcholine as their primary neurotransmitter.

• The acetylcholine released from these presynaptic neurons binds to and activates the receptors in the postganglionic neurons.
• The acetylcholine receptors in the preganglionic neurons are also known as _______________ because they are also able to bind to the compound nicotine

The post-ganglionic axons that innervate target tissues and organs releases different neurotransmitters

• In sympathetic neurons, the majority of postganglionic neurons releases noradrenaline that targets the smooth muscles, heart and glands within the viscera.
• -> Noradrenaline, which is also known as norepinephrine is detected by the ________________ receptors at the target cells.
• -> In sweat glands and some blood vessels, ______________ is released from the postganglionic neurons.
• In contrast, postganglionic neurons in the parasympathetic system release acetylcholine to their target effector organs. These acetylcholine receptors at the effector organs are also known as ______________because unlike nicotinic receptors, these receptors recognize and bind to acetylcoline and muscarine but is less sensitive to nicotine.

In the case of direct preganglionic sympathetic innervation to the adrenal medulla, ______________ is also the primary neurotransmitter that is released by the splanchnic nerves.
Once the adrenal medulla is stimulated, it will release adrenalin and noradrenalin directly into the blood stream.

Answer 35

nicotinic receptors;

alpha/beta adrenergic;

acetylcholine;

muscaric receptors ;

acetylcholine

Question 36

The postganglionic synapses are unique and not like the neuromuscular junction.

• ________________ are unmyelinated
• Axons from postganglionic neurons branch out to become several thin filaments (0.1-0.5 microns) which then run alongside the muscle fibers.

Each filament have multiple swellings called varicosities also known as _______________ which means boutons “in passing”.

• Varicosities have synaptic vesicles loaded with acetylcholine (parasympathetic) or noradrenaline (Sympathetic).
• Boutons are not structured like an NMJ as they don’t have an active zone in the presynaptic terminals but they do contain many presynaptic elements, mitochondria, cytoskeleton support.
• The advantage of varicosities is that release of neurotransmitter is slower, but ____________________. Part of the reason is that some of the synaptic cleft in en-passant boutons can be much larger.
• Neurotransmitter release activates specific receptor in the muscle fibers

Answer 36

Autonomic post-ganglionic neurons;

“En Passant” boutons;

more widespread and can influence a larger area or multiple cells within the target zone

Question 37

The gastrointestinal system is innervated by the ANS but also contains an independent nervous system.

• Both the sympathetic and parasympathetic systems send projections to the enteric nervous system, and the intrinsic neurons of the gut.
• In particular, the ________________ sends parasympathetic responses to the gut via the Vagus nerve.
• Meanwhile, the gut also receives sympathetic innervation from the postganglionic neurons via the

________________
These ANS innervations allow the body to modulate peristalsis, secretion of different gastric juices, control absorption rates as necessary.
- Surprisingly, if these ANS connections are severed, many gut muscle activity such as peristalsis remains functional with its own reflex rules, indicating the presence of an independent nervous system for local control.
- This is way the _____________, while often associated with the ANS, can also be classified as a separate component of the visceral motor system.

Answer 37

dorsal motor nucleus in the medulla;

celiac ganglia;

enteric nervous system

Question 38

The enteric nervous system receives input from the sympathetic and parasympathetic pathways which enhances or GI function.

• The enteric nervous system contain two plexuses that are sandwich between the layers of the gut. Each plexus contains a dense network of ganglia and surrounded by a network of neuronal fibers.

The sensory neurons in the gut wall monitor chemical and mechanical changes and local circuits will integrate the information, allowing motor neurons to regulate the smooth muscles and glandular secretion

• The myenteric (Auerbach’s) plexus is located between the ______________ and regulates gut motility. Neurons in the Myenteric plexus receive ANS innervations and regulate the gut musculature in respond to sensory inputs.
• The submucosal (Meissner’s) plexus is located at the ______________ and is involved in ion and fluid transport. It is also responsible for ________________

Both plexuses receive parasympathetic vagus nerve innervation and postganglionic sympathetic innervation via the celiac ganglion. The autonomic nervous system modulates GI activity but even when they are severed, the enteric nervous system operates independently with their own reflex rules

Answer 38

longitudinal and circular muscle layers;

submucosal layer of the gut;

chemical sensing and glandular secretion;

Question 39

Visceral afferent fibres

General visceral afferent (GVA) fibres conduct sensory stimuli from the blood vessels and viscera back to the central nervous system. GVA participate in important reflexes involved in control of circulation, respiration, digestion, micturition & coition.

Signals from the GVA fibers synapse with neurons in the dorsal root ganglia before being relayed to the spinal cord via the _________________.

The general visceral afferent fibers are a central part of the ANS, but the fibers are neither classified as sympathetic or parasympathetic. The afferent fibers are part of the visceral nervous system that conduct sensory stimuli such as pain and reflex responses from the blood vessels and target effector organs back to the central nervous system.

While the visceral afferent fibers from the thoracic and abdominal viscera follow _______________________, the neurons that relay this information is not the same set of neurons as those previously described in the autonomic nervous system.’

While the efferent fibers of the sympathetic and parasympathetic system leave the spinal cord via the ventral roots, visceral afferent fibers will synapse with the dorsal root ganglia neurons before entering the spinal cord via the dorsal horn of the spinal column.

Answer 39

dorsal horn of the spinal column;

sympathetic nerve bundles back to the central nervous system

Question 40

Autonomic regulation of the cardiovascular function
Two type of receptors that gauge homeostasis mechanisms in cardiovascular functions: mechanoreceptors and chemoreceptors.
- Chemoreceptors are found at _____________________. Primarily senses ______________________. Afferent fibers at the carotid bodies send information back to the CNS. The cells in the carotid bodies can secrete neurotransmitters to activate the neurons which also senses pH and temperature.
- Mechanoreceptors known as barosensors or receptors detect ______________.

These afferent sensory projections mainly travel together with the parasympathetic nerve bundles, but instead transmit information to the CNS.
- Together these afferent inputs regulate blood pressure by relaying information to the __________________ to trigger either a sympathetic or parasympathetic response which innervates the heart muscles or the SA node that regulates heart contractions and cardiac output.
- If blood pressure is high, the information is sent down spinal cord to sympathetic outflow to inhibit the sympathetic response, and similarly, vagus nerve relays to heart and cardiac pacemaker which results in muscle relaxation and lowered cardiac output.
- Conversely, if blood pressure is low, Sympathetic system releases noradrenaline at heart NMJ to increase heart rate and cardiac output. Parasympathetic responses are then inhibited.
Other organs such as blood vessels and adrenal medulla are also activated or inhibited to modulate blood pressure. For example, decreased vasoconstriction in blood vessels and lowered catecholamine secretion from adrenal occurs to lower blood pressure in conjunction with cardiac activity.

Answer 40

bifurcation of arteries called carotid bodies;

changes in O2 and CO2 partial pressure and levels;

changes in the stretching of the vessel walls;

nucleus solitary tract and nucleus ambiguous

Question 41

Autonomic regulation of the bladder control
Bladder control is a combination of autonomic regulation (involuntary) and a cognitive response (voluntary).
- Parasympathetic activation causes contraction of the bladder and results in urination while sympathetic response allows bladder sphincters to constrict and prevent urination
- The dual control of the ANS is advantageous in the wild: Sympathetic response is necessary for fleeing a danger and urinating could be a dangerous activity prone to get animal killed. Hence, a sympathetic response overrides the decision to urinate.
- Parasympathetic outflow initiated at __________________ via pelvic biosensors pathway
- When the bladder is filled, the parasympathetic response is triggered to allow muscle contraction and opening of the external sphincter which results in emptying of the bladder.
- In parallel to parasympathetic activation, the sympathetic response is inhibited.

Sympathetic outflow initiated at _______________ preganglionic projection via ___________________

• When the bladder is empty and filling up, sympathetic activity relaxes the smooth muscles in the urinary bladder and blocks the urethral sphincter from opening. The postganglionic neurons also controls the blood vessels to the bladder.
• The stretch or distension of the bladder walls also inhibits a parasympathetic response.

Voluntary actions trigger somatic motor axons which innervates and controls contraction of urethral sphincter
There is a tonic inhibition of the somatic motor neurons (which arise from voluntary response) that project to the bladder during urination to prevent or counter parasympathetic response.

Answer 41

sacral (S2-S4) preganglionic neurons;

thoracolumbar (T10-L2) ;

inferior mesenteric and pelvic ganglia

Question 42

Visceral pain
Visceral pain is conducted via visceral afferent fibres
- Visceral pain is defined as ____________________
- Unlike cutaneous pain that is sharp and localized (such as cutting or burning), visceral pain is _________________
- Visceral pain is more sensitive toward distention, traction, inflammation excessive voluntary muscle contraction and ischemia

3 fundamental types of visceral pain:

• Pure visceral pain – vague, deep-seated pain in the region of the affected organ, usually accompanied by __________________
• Visceral referred pain – projected subjectively into the ___________________
• Viscerosomatic pain – caused by spread of disease to _______________

Answer 42

pain resulting from activation of pain receptors in the internal organs located in the abdominal, thoracic and pelvic viscera;

diffuse, poorly localized and hard to describe;

sweating & nausea;

territory of corresponding somatic nerves;

somatic structures

Question 43

Pain originating from the viscera may sometimes be deceived as pain originating from a site distant from the actual affected organ.
- One explanation is that visceral afferent fibers enter the spinal cord close to the regions as the inputs from the somatic pain fibers.
- Both types of inputs activate the same ________________ and the brain is unable to differentiate between the two sources of pain input.
- Because the density of the somatic inputs are much higher than the visceral inputs and the somatic inputs are more commonly stimulated, the brain will associate visceral pain with a somatic source.
- Referred pain is usually located in the
________________sharing the same spinal cord level as the visceral inputs.
- Central nervous system will thus “refer” visceral pain to a somatic source

Answer 43

spinothalamic pathways;

cutaneous dermatome ;

Question 44

Visceral referred pain: heart

• Cardiac pain is usually referred to the ________________.
• This is because the visceral pain fibers innervating the heart enters the spinal cord segments at ____________. The sensory afferent pain fibers that innervate the upper limb and upper thorax also synapse with the dorsal root ganglia at the same T1-T5 segment.
• Because of this anatomical arrangement, the CNS cell bodies involved in the perception of pain sensation cannot clearly differentiate the pain signals arriving from the heart and the upper limbs and upper thorax.
• Thus, patients will incorrectly ascribe pain sensations at the T1-T5 dermatome rather than from the deeper visceral organs.

Answer 44

left shoulder, the medial side of the left upper limb as well as the left precordium;

T1 – T5