Autonomic control of structures in head Flashcards
Briefly describe the differences between somatic and autonomic nervous systems
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.
Which fibres of the nervous system have ganglia?
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
Which smooth muscles in the head are controlled by the ANS?
- superior tarsal muscle (sns)^[1]
- pupillary muscles (2)
- ciliary body
- vessel walls
Note: all of the above muscles are found in the orbit/eye
- 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.
- 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.
List the glands of the head innervated by the ANS
- 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’]
Where is ACh found in the parasympathetic nervous system?
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
Descriibe the type of receptor at the first and second syndapses in the parasympathetic nervous system
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).
List the four nuclei associated with oautonomic i.e. parasympathtic control of structuraes in head, their location, and the cranial nerves assoctaed woth them
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
Describe the pathway of neurons from Edinger-Westphal nucleus
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
Describe the pathway of nerve fibres emanating from the superior salivatory nucleus
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.
Describe the pathway of nerve fibres from the inferior salivatory nucleus
The inferior salivatory nucleus sends its preganglionic fibres to the otic ganglion where the postganglionic fibre travels to innervate the parotid gland.
Describe the pathway of fibres from dorsal nucleus of vagus nerve
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
Describe the function and control of the sphincter pupillae muscle
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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Describe the pupillary response or pupillary reflex
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.
Describe the ciliary muscle
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
Describe the lacrimal apparatus
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*)