Autonomic control of structures in head

Question 1

Briefly describe the differences between somatic and autonomic nervous systems

Answer 1

Somatic vs. autonomic control
Recall the difference between somatic and autonomic control:
- In the somatic nervous system, sensory nerves (With cell bodies just outside the CNS, in the dorsal root ganglion ^[or named, if cranial nerves] and motor neurons innervate various targets in the periphery, such as skin, and skeletal muscle (respectively)
- In the autonomic nervous system, sensory neurons (With cell bodies just outside CNS, in dorsal root ganglion) innervate viscera, and sympathetic and parasympathetic fibres innervate smooth muscle, cardiac muscle and glands (see also [[Neurophysiology Lecture 7]])
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Note: sensory somatic fibres, sympathetic and parasympathetic fibres will always have ganglia.

Sensory fibres of somatic NS and autonomic NS are very similar.

Sympathetic and parasympathetic fibres have synapses in their ganglia.

Also note that postganglionic fibres or secondary fibres of the parasympathetic nervous system have their ganglia much closer to their peripheral targets, while postganglionic fibres of sympathetic nervous system have ganglia closer to the CNS. Aditionally, postganglionic fibres of the parasympathetic nervous system are muchshorter than the postganglionic fibres of the sympathetic nervous system. Conversely the preganglionic fibres of the sympathetic nervou ssytem are much shorter than those of the parasymapthetic nervous system.

Question 2

Which fibres of the nervous system have ganglia?

Answer 2

Sensory fibres of somatic NS and autonomic NS are very similar. sensory somatic fibres, sympathetic and parasympathetic fibres will always have ganglia.

Sympathetic and parasympathetic fibres have synapses in their ganglia.
Sensory synapses in peripheral targets e.g. skin

Question 3

Which smooth muscles in the head are controlled by the ANS?

Answer 3

• superior tarsal muscle (sns)^[1]
• pupillary muscles (2)
• ciliary body
• vessel walls
  Note: all of the above muscles are found in the orbit/eye

1. The innervation of the superior tarsal muscle is from the sympathetic nervous system. Specifically, postganglionic sympathetic fibers originating from the superior sympathetic cervical ganglion reach the muscle by forming fibers. These fibers wrap around the carotid artery as the pericarotid plexus and enter the skull, reach the cavernous sinus, and then access the orbit to reach the muscle.
2. The iris sphincter muscle receives its parasympathetic innervation via the short ciliary nerves (branches of CNIII, from ciliary ganglion) which lead to pupillary constriction (miosis) and accommodation. [3] The parasympathetic fibers that serve the sphincter muscle originate from the Edinger-Westphal nucleus of cranial nerve III.

Question 4

List the glands of the head innervated by the ANS

Answer 4

• lacrimal gland (CNV1, via pterygopalatine ganglion for sensory, secretomotor from 7– via pterygopalatine ganaglion via greater petrosal nerve)
• salivary gland (three), via submand ganglion, CNVII
• sweat gland (found all over the skin of face), SNS

also will have sns, usually superior cervical ganglion

^[note, by extension, secretions of the face include tears, sweat and ‘spit’]

Question 5

Where is ACh found in the parasympathetic nervous system?

Answer 5

the neurotransmitter acetylcholine is found at synapses in both pre-ganglionic and post-ganglionic

ACh is generally an excitatory neurotransmitter, has ionotropic(nicotinic) and metabotropic(muscarinic) receptors

Recall M for M

Question 6

Descriibe the type of receptor at the first and second syndapses in the parasympathetic nervous system

Answer 6

The first receptor i.e. the receptor on the surface of the post-ganglionic neuron (in the autonomic ganglion)
is nicotinic (ionotropic) and the second i.e. where the post-ganglionic neuron synapses with the target organ, is muscarinic (M1-5; metabotropic).

Question 7

List the four nuclei associated with oautonomic i.e. parasympathtic control of structuraes in head, their location, and the cranial nerves assoctaed woth them

Answer 7

The parasympathetic control of the structures in the head emanates from four nuclei in the brainstem, which in turn send information to four respective ganglia
- Edinger- Westphal nucleus (III - or oculomotor nerve) – located in midbrain,
- Superior salivatory nucleus (VII- facial nerve)- located in pons
- Inferior salivatory nucleus (IX - glossopharyngeal nerve)
- Dorsal nucleus of vagus (X) - 9 and 10 in medulla oblongata

3 7 9 10

Question 8

Describe the pathway of neurons from Edinger-Westphal nucleus

Answer 8

The neurons from the Edinger- Westphal nucleus (or E-W nucleus)
i.e. the pre-ganglionic fibres, synapse with the post-ganglionic neuron in the ciliary ganglion. The post-ganglionic neuron then synapses at its targets - the sphincter pupillae and the ciliary muscle

Question 9

Describe the pathway of nerve fibres emanating from the superior salivatory nucleus

Answer 9

The superior salivatory nuceleus sends its preganglionic parasympathetic fibres to two ganglia: the pterygopalatine ganglion and the submandibular ganglion.
The postganglionic fibres then travel to innervate the lacrimal, nasal and palatal glands, and the submandibular and sublingual glands respectively.

Question 10

Describe the pathway of nerve fibres from the inferior salivatory nucleus

Answer 10

The inferior salivatory nucleus sends its preganglionic fibres to the otic ganglion where the postganglionic fibre travels to innervate the parotid gland.

Question 11

Describe the pathway of fibres from dorsal nucleus of vagus nerve

Answer 11

Fibres from the dorsal nucleus of the vagus nerve synapse with post-ganglionic fibres in multiple ganglia in or around the target organ. In other words, the vagus nerve innervates thoracic and vertebral viscera e.g. the GIT all the way to the splenic fixture.
The remaining parasympathetic innervation is conducted by the preganglionic fibres from S2-S4, and they innervate the sigmoid and descending colon, rectum, the kidney, bladder gonads and external reproductive organs ^[https://www.physio-pedia.com/Parasympathetic_System]

Note: there is always one nucleus assigned to one function, therefore autonomic nerves will be housed in specific nuclei

Question 12

Describe the function and control of the sphincter pupillae muscle

Answer 12

Sphincter pupillae muscle
The sphincter pupillae (pupillary sphincter, or iris sphincter muscle) is located in the iris ^[note: slightly anterior to the iris’ pigmented epithelium, near pupillary margin]. ^[https://www.ncbi.nlm.nih.gov/books/NBK532252/]

Its function is to decrease the diameter of the pupil, or its aperture. This is termed miosis.
The sphincter pupillae muscle is activated during increased illumination or during close work (known as the accommodation reflex).

It is under the control of the parasympathetic component of CN III (oculomotor nerve).

Note: sphincter pupillae is an antagonist to dilator pupillae which surrounds it, and is involved in mydriasis or the enlargement of the aperture of the pupil.
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Question 13

Describe the pupillary response or pupillary reflex

Answer 13

The pupillary response or pupil reflex constricts the pupil in response to light [9].

The afferent segment of the pupillary response, or the optic nerve, starts in the retina and travels to the pretectal olivary nuclei. It decussates in the nasal retina (at a point called the optic chaism) but not in the temporal retina.

The interneuron segment of the pupillary response runs from the pretectal olivary nuclei to the Edinger-Westphal nuclei, preganglionic parasympathetic nuclei in the midbrain.

The efferent segment runs from the Edinger- Westphal nuclei to the pupillary constrictor muscle to constrict the pupil, via the ciliary ganglion, which sends postganglionic axons to directly innervate the iris sphincter muscles [10].

The direct response is constriction of pupil in the ipsilateral eye; the consensual response is constriction of pupil in the contralateral eye.
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Because of the crossing of the optic fibres at the optic chiasm, information from both eyes is collated at the same time at both E-W nuclei.

The pupillary response is tested by shining a light into one pupil and looking for a response in the other pupil (which constricts as well).

The test can also identify if a defect is sensory/afferent or motor/efferent in nature e.g.:

if light is pointed at left eye, its pupil should constrict, and right pupil should also constrict
if light is pointed at left eye, and there is no constriction of left pupil, but constriction of right pupil, this means there is a motor defect on the right (i.e. received information but could not act on it)
[11]
[12]
[13]

The swinging lamp test: move light to the contralateral pupil; the ipsilateral pupil will then dilate after light has moved away from it (this is called an afferent pupillary defect) [14]

The pupillary reflex exam is considered part of a neurological exam.

Question 14

Describe the ciliary muscle

Answer 14

Ciliary muscles
Ciliary muscles are smooth muscles formed as rings.
It is one of three intrinsic muscles of the eye, including the sphincter and dilator pupillae.
Together with ciliary processes, they make up the ciliary body.
Ciliary muscles have two key functions: production of aqueous humour and control of accommodation.
Attachments of the ciliary muscles include to the lens via zonular fibres within the ciliary body, and to the sclera via ‘scleral spur’.

During distance vision, the lends capsule hold the lens tight, hence the ciliary muscles are flattened or relaxed.

During near vision, miosis is required.
The ciliary muscles contract, and the ciliary body is drawn anteriorly, closer to the spur. This reduces tension in the zonular fibres, and allows the lens to bulge, and to focus on near objects.

The action of the ciliary muscles is controlled by the parasympathetic components of the oculomotor nerve (CNIII).

the orbicularis oculi, responsible for closing the eye, is innervated by CNVII, facial nerve

Question 15

Describe the lacrimal apparatus

Answer 15

Lacrimal apparatus
The purpose of the lacrimal apparatus is to keep the surface of the eye moist. It is found on the lateral upper part of the orbit - above the eye.
The components of the lacrimal apparatus include:

the lacrimal gland - which produces lacrimal fluid
nasolacrimal duct - where fluid empties into nasal cavity
The lacrimal apparatus is innervated by the greater petrosal nerve of CNVII (facial nerve). The nerve synapses in the pterygopalatine ganglion, and innervates lacrimal, nasal and palatine glands.
Tears are very important - they supply the cornea (Which is an avascular structure). Additionally, the fluid on cornea/conjunctiva helps avoid dryness, which would otherwise feel ‘sandy’.

note: tiny punctures in the eyelid, known as canaliculi, pick up tears, which flow into nasolacrimal duct, which empties fluid in nasal cavity (under inferior nasal conchae*)

Question 16

Describe the salivary glands

Answer 16

Saliva is a substance composed of water, mucins, enzymes and immune components.
It keeps the mucosa in the mouth and pharynx moist, and contains amylase, which initiates carbohydrate digestion.
There are several salivary glands:

the sublingual gland
submandibular gland
parotid glands
(these are also known as major salivary glands)

minors include: Minor salivary gland tissue is comprised of 800-1000 small salivary glands dispersed throughout the submucosa of the sinonasal cavity, oral cavity, pharynx, larynx, trachea, lungs, and middle ear cavity. Although minor salivary gland tissue can be found anywhere along the aerodigestive tract, it is most concentrated along the buccal mucosa, labial mucosa, lingual mucosa, soft/hard palate, and floor of mouth

Question 17

Defien the sublingual gland

Answer 17

The sublingual gland
This gland is positioned anterolaterally running below the tongue.
It makes an impression on the inner surface of the mandible.

Question 18

Define the submandibular gland

Answer 18

The submandibular gland
This gland is C-shaped, and encloses the posterior border of the mylohyoid muscle.
The duct of the submandibular gland is crossed by the lingual n., as it passes forward to the sublingual papilla.

Question 19

Describe the supply to the submandibularand sublingual glands

Answer 19

Both submandibular and sublingual glands are supplied by the lingual nerve [15] (V3 - pain fibres) and chorda tympani (VII - secretomotor)

Question 20

Describe the chorda tympani

Answer 20

The chorda tympani is a branch of the facial nerve or VII.
It has a secretomotor function, innervating the submandibular and sublingual glands (2/3 of the major salivary glands).
It is considered an autonomic sensory nerve, and is responsible for taste on the anterior 2/3s of the tongue.
Note that it is responsible for a specific sensory function. The trigeminal nerve or cranial nerve 5 is responsible for general sensations in the oral cavity such as pressure of food on the tongue, temperature etc.

The chorda tympani exits the skull via the stylomastoid foramen.
It goes just behind the eardrum/tympanic membrane (hence the name).

Question 21

Describe the parasympathetic components of the facial nerve

Answer 21

The greater petrosal nerve branches off soon at the geniculate ganglion [16], the sensory ganglion of CNVII or the facial nerve.
It is a mixed peripheral nerve that carries

sensory and taste fibres from soft palate
preganglionic parasympathetic fibres, which synapse in the pterygopalatine ganglion in the pterygopalatine fossa
Note that its nuclei (i.e. its origins) are the superior salivatory and solitary nuclei.

The postganglionic fibres innervate the lactimal gland, mucosal glands of nose, palate and pharynx (by hitchiking with V1 and V2*)..

The chorda tympani branches off from the motor branch before stylomastoid foramen corsses the ear drum (medial), exits near foramen ovale (petrosotympanic fissure) and joins the lingual branch of V3.

ITt is a mised peripheral nerve that carries taste fibres from anterior 2/3s of tongue and preganglionic parasympathetic fibres to the submandibular and sublingual glands through the submandibular ganglion.
It innervate the lower part of the face.

Question 22

Describe the parotid gland

Answer 22

The parotid gland is the third of the three major salivary glands.

It is superficially placed, and its surface is seen immediately beneath the skin, below the level of the zygomatic arch [17].

The deep aspect of the parotid gland is wedge-shaped and occupies the space between the posterior margin of the mandible and the temporal bone.
The facial nerve enters its deep aspect, and branches emerge from its anterior margin.

The duct is large (roughly 5mm in diameter) and leaves the anterior margin. It pierces the buccinator muscle to open in the vestibule of the oral cavity opposite the second upper molar.

Unlike the other major salivary glands, it is innervated by the lesser petrosal nerve (CNIX) or glossopharyngeal nerve, for pain and secretomotor sensation.

lesser: contributions from 7 and 10

Question 23

Describe the sympathetic control of structures in head

Answer 23

his comes exclusively from the spinal cord.
The cell body of the pre=ganglionic fibre is find in T1 or T2 spinal segment, in the lateral horn. It synapses in the superior cervical ganglion (located paravertebral) with post-ganglionic fibre. Nicotinic receptors, acetylcholine.
Post ganglionic fibre hitchhikes* with another vessel or nerve to innervate target (at adrenergic receptors, using norepinephrine).

Examples of targets of sympathetic control in the head include the superior tarsal muscle, dilator pupillae and blood vessels.

Question 24

Describe the superior tarsal muscle

Answer 24

The superior tarsal muscle is part of the levator palpebrae superioris. It is involved in opening the eyelid.
Dilated eye a sign of emotional exprssion.
It is a smooth muscle and is thus involuntary,
It is under symapthetic control.

Question 25

Describe the dilator pupillae muscle

Answer 25

Antagonist of the sphincter pupillae muscle. Therefore it works to increase the diameter of the pupil, or mydriasis.
It is activated during decreased illumination or in a fight or flight response (accompanying elevation of the upper eyelid).
It is under sympathetic control.

Question 26

Describe the innervation of sweat glands and how they differ from…

Answer 26

Sweat glands
are also under sympathetic control. But differs from other examples of sympathetic controls as it uses ACh on muscarinic receptors on effector organs (instead of adrenergic receptors).