Cranial Nerves continued Flashcards
What are secretomotor nerves?
a. Secretomotor nerves specifically control the secretion of glands.
b. Part of the autonomic nervous system (responsible for regulating involuntary bodily functions.
Tell me about the Facial nerve.
Facial Nerve Path:
Enters through internal acoustic meatus along with nervus intermedius.
Both merge to form the facial nerve proper inside the facial canal.
Travels via facial canal with two bends: first and second genu.
Geniculate ganglion at first genu (contains sensory/taste fibers mainly from the nervus intermedius).
Greater petrosal nerve branches at first genu → goes to pterygopalatine ganglion (parasympathetic fibers from nervus intermedius contribute).
Chorda tympani branches after second genu → carries taste (from nervus intermedius) and parasympathetic fibers to submandibular and sublingual glands.
Nerve to stapedius branches off before stylomastoid foramen.
Main trunk exits skull through stylomastoid foramen.
Traverses parotid gland and divides into five motor branches (Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical).
Parotid Gland & Saliva Secretion:
Facial nerve doesn’t provide secretomotor innervation to parotid.
Secretomotor innervation: glossopharyngeal nerve (CN IX) via otic ganglion and auriculotemporal nerve.
Facial nerve is insulated; doesn’t interact to stimulate gland secretion.
Tell me about the vestibulocochlear nerve.
a. Each nerve has a distinct nucleus within the brainstem.
b. Consists of the vestibular and cochlear nerves.
Tell me about the glossopharyngeal nerve.
a. Carries secretomotor fibres to the parotid gland controlling the secretion of saliva.
b. glossopharyngeal nerve → tympanic branch → tympanic plexus → lesser petrosal nerve → otic ganglion → auriculotemporal nerve → parotid gland.
b. Carries autonomic sensory input from the carotid sinus (carotid sinus helps to regulate blood pressure) and carotid body (carotid body helps regulate levels of oxygen and carbon dioxide in the blood).
Tell me about the vagus nerve.
a. It is the longest cranial nerve.
b. Accessory nerve motor fibres and vagus nerve motor fibres merge together and are often considered together.
c. Passes through neck and thorax to abdomen so wide distribution throughout the upper body.
d. Provides sensation to part of the upper respiratory tract.
e. Motor nerves allowing muscles associated with speech and swallowing to work.
f. Key role in HR regulation and blood pressure regulation.
Tell me about the hypoglossal nerve.
Hypoglossal nerve fibres are also involved in controlling the reflex movements of chewing and swallowing.
What do all cranial nerves originate from?
a. They all originate from nuclei in the brain.
b. Olfactory and Optic originate from the forebrain.
c. Accessory has a nucleus in the spinal cord.
d. Rest has a nuclei in the brainstem.
Which are not true nerves?
Olfactory and Optic nerve are ‘outgrowths’ from the cerebrum.
What’s special about the Olfactory nerve?
a. It is an outgrowth of the olfactory bulb, located in the forebrain.
b. Contains multiple axons which pass through the cribriform plate, acting as olfactory receptors – allowing for smell.
c. These receptor axons are mitotically active (constantly renewing), ensuring the sense of smell, remains sensitive and responsive.
d. Bowman glands located in mucous membrane lining the nasal cavity – secrete a watery, serous fluid, dissolving airborne chemicals we inhale, and allows detection by the olfactory receptors in the nasal epithelium.
e. In humans – the sense of smell is relatively poor compared to some other species.
What’s so special about the Optic nerve?
a. It has very thick nerves with >10^6 axons.
b. Sensory nerve impulses from retina, carry information to visual centres (occipital lobes) in the brain, bypassing the spinal cord so not true peripheral nerves.
c. Encased with meninges (protective layer of tissue that surrounds the CNS).
What are meninges?
a. Meninges are a protective layer of tissue to the CNS (the brain and the spinal cord)
b. They are composed of three layers: dura mater (outer most layer), arachnoid mater (middle layer), and pia mater (inner layer).
c. The cerebrospinal fluid is located in the subarachnoid space (between the arachnoid mater and pia mater layers)
How do sensory fibres enter the spinal cord?
Sensory fibres enter through dorsal roots.
How do motor fibres leave the spinal cord?
Motor fibres leave through ventral roots.
