cranial nerves Flashcards
what are the cranial nerves?
- a set of **12 **paired nerves **arising directly **from the brain
where do the cranial nerves emerge from?
- they emerge from the cranial cavity via the foramina or fissures in the cranium
what are the 2 main origins of cranial nerves?
- The **cerebrum **( CN I & II)
- The brain stem (CN III- XII)
where in the brain stem do the CN III- XII originate from?
* midbrain (pontine junction) - CN III - oculomotor
* **midbrain **- trochlear (IV) arises from posterior side of midbrain
* **Pons **- the trigeminal (3 branches) V
* **Medulla Oblongata **(IX - XI)
what are the 12 cranial nerves?
One Of Our Top Teachers Asked For Very Good Vinegar And Honey
- Olfactory
- Optic
- Oculomtor
- Trochlear
- Trigeminal
- Abducent
- Facial
- Vestibulocochlear
- Glossopharyngeal
- Vagus
- Accessory (spinal)
- Hypoglossal nerve
What is a motor (efferent) nerve?
carries information from the brain to the periphery
what is a sensory (afferent) nerve?
- Carries information** from the periphery to the brain**
Define general somatic afferent
converys general sensation from the skin
Define** general visceral afferent **
converys general sensation from viscera
Define special somatic afferent
conveys senses derived from ectoderm eg sight balance
Define general somatic efferent
conveys motor innervation for skeletal muscles
Define general visceral efferent
conveys motor innervation for smooth muscle, cardiac muscle and glands
Describe the **olfactory nerve **
function
- CN I
- function : carries special sensory fibres for** sense of smell**
- speciailised nerve fibres located in olfactory mucosa
- these fibres** enter the cranial cavity** via the cribiform plate of ethmoid bone
what can happen if there is severe head trauma / injury to the anterior cranial fossa (hint - to do with olfactory nerve)
- it can cause seperation of the olfactory bulb from the nerves
- can cause anosmia - loss of sense of smell
what other cranial nerve also innervates the nasal mucosa and what is it’s function?
- CN V
- function - chemoreceptor - senses coldness
Describe the optic nerve (CN II)
- special somatic afferent
- transmits all visual information - including colour & brightness perception
what is the optic chiasm?
what is it formed from? function?
- formed by merging fibers from the optic nerve
- function - receives visual information from the optic nerve and **transmits this information to the optic tracts **
what is the CNII surrounded by?
it is surrounded by extensions of the cranial meninges and subarachnoid space - which is filled with CSF
what is the function of the visual pathway?
- the visual pathway transmits information interpreted from **visual light from the eyes to the visual cortex in the brain
what is the** visual field**?
- the visual field is what is seen by a person with both eyes wide open and looking straight ahead
Describe the visual pathway
the beginning - ie light - ocular bulb-retina-optic nerve - chiasm
- visual pathway begins with light entering the ocular bulb and being processed by the retina
- information then passed on from the retina by the optic nerve which travels to the optic chiasm
Describe the visual pathway** from the optic chiasm**
- from the optic chiasm, the axons are now called the optic tract
- the axons then synapse at the** lateral geniculate nucleus**
how do axons from the lateral geniculate nucleus reach the visual cortex of the brain?
they travel via the optic radiation
where are inputs from the right and left visual field carried by?
- information from the left visual field carried in right optic tract
- information from right visual field carried in left optic tract
where does oculomotor nerve CNIII supply?
- this nerve supplies all extra ocular muscles of the eye** EXCEPT** the** lateral rectus and superior oblique **
what are the functions of the oculomotor nerve?
- eye movement
- pupil constriction (through parasynpathetic innervation)
- maintaining open eyelid
NB - somatic efferent (motor) - as info goes from brain to periphery (eyes)
Describe the trochlear nerve CN IV
- motor innervation of the** superior oblique muscle -** like a pulley system (trochlear = pulley)
- unique - exits from posterior side of brain stem
Describe the CN VI - abducens nerve
- provides motor innervation of the lateral rectus muscle
- leaves brainstem at junction of pons and medulla
Describe the trigeminal nerve - CN V
* mixed nerve - carries both sensory and motor information
* primary sensory nerve for face and anterior scalp
* motor nerve for muscles of mastication and other small muscles
* trigeminal = triplet
what 3 terminal nerves does the sensory route of the trigeminal nerve CN V divide into?
- Ophthalmic nerve
- maxillary nerve
- mandibular nerve
Describe the **facial nerve **
- CN VII
- supplies motor innervation to the muscles of facial expression
- supplies parasympathetic innervation to the salivary glands, lacrimal glands, and mucous glands
Describe the vestibulocochlear nerve CN VIII
- carries special sensory fibres for hearing and balance
- can be divided into 2 components - cochlear part (transmits auditory info to brain) and vestibular part (transmits info about balance to the brain)
Describe the glossopharyngeal nerve
- transmits sensory info from the carotid body & sinus, posterior third of tongue, oropharynx etc
- carries special sensory fibres for taste for posterior 1/3 of tongue
what gland does the glossopharyngeal nerve innervate?
the parotid salivary gland
what does the glossopharyngeal nerve arise from and where does it** exit the cranial cavity**?
- arises from the medulla oblongata
- exits the cranial cavity via the jugular foramen
Describe the vagus nerve CN X
vagus = wondering in latin
- most widely distributed CN
*** mixed **nerve - provides sensory info to the **heart, lungs trachea, bronchi, pharynx ** and more…
- also supplies parasympathetic info to smooth muscle and glands in the body
where does the vagus nerve arise from and where does it exit the cranial cavity?
- it arises from the medulla oblongata
- exits via the jugular foramen
What 2 muscles does the spinal accessory nerve innervate?
- Trapeqius
- SCM muscle in neck
where do the fibres of the spinal accessory nerve originate from?
the spinal cord
Describe the path of the accessory nerve
- it originates from the spinal cord and ascends into the cranial cavity via the foramen magnum
- it then exits the cranial cavity via the jugular foramen where it innervates the 2 muscles
is the hypoglossal a motor or sensory nerve?
motor
Describe the hypoglossal nerve (CN XII)
- motor nerve
- motor innervation to intrinsic and extrinsic muscles of tongue except for palatoglossus muscle
which cranial nerve innervates the palatoglossus muscle ?
vagus nerve
where does the hypoglossal nerve originate from and where does it exit the cranial cavity?
- it arises from the anterior surface of the medulla oblongata
- it exits the cranial cavity via he hypoglossal canal
which of the cranial nerves are** mixed** nerves?
- trigeminal nerve
- facial nerve
- glossopharyngeal nerve
- vagus nerve
what is a brachiomotor nerve?
-special motor to muscles from pharyngeal (brachial) arches
