Cranial Nerves Flashcards
Which of the cranial nerves are exclusively sensory?
- Olfactory (1)
- Optic (2)
- Vestibulocochlear (8)
Compare the locations of motor nuclei in spinal nerves and in cranial nerves
Spinal: ventral horn of grey matter
Cranial: medial part of the brainstem
Compare the locations of sensory nuclei in spinal nerves and in cranial nerves
Spinal: dorsal horn of the grey matter
Cranial: lateral part of the brainstem
What divides the alar and basal plates into their respective sensory and motor components?
the sulcus limitans
Which four cranial nerves contain parasympathetic fibres, and where do they synapse?
- ciliary ganglion (3)
- pyterogopalatine ganglion (7)
- submandibular ganglion (7)
- otic ganglion (9)
Which of the three cervical ganglion only innervates the neck?
- superior cervical ganglion
Where do the olfactory nerve fibres originate, project through, and synapse?
Originate: nasal olfactory epithelium
Project: through the cribriform plate
Synapse: olfactory bulb
Where do second-order neurons in the olfactory bulb connect, and via what means?
primary olfactory cortex via the olfactory tract
True or false, the sense of olfaction has thalamic relay.
False
What connects the two olfactory bulbs and the piriform cortices?
The anterior commissure
What are the primary olfactory cortical areas?
- Anterior olfactory nucleus
- Amygdala
- Olfactory tubercle
- Piriform cortex
- Entorhinal cortex
Discuss the process of primary olfactory sensory neurons expressing on their receptors
- express only one of ~1000 olfactory receptors, and converge their inputs onto single second-order neurons via the large synaptic meshwork (the glomeruli) at the olfactory bulb
Under what conditions do cone cells function?
Light
What are cone cells responsible for, and what are their visual acuity like?
- colour vision (blue, green, red)
- high visual acuity as they connect to few bipolar cells
Under what conditions do rod cells function under?
- low light
Why do rod cells have decreased visual acuity?
- they connect to many bipolar cells, which increases sensitivity but decreases acuity.
What cells sharpen contrast?
- horizontal cells
What cells regulate sensitivity?
- amacrine cells
What nerve carries visual information to the brain?
- optic nerve (carried by retinal ganglion cells)
Where do retinal ganglion cell axons leave the eye?
- the optic disk
Light falling through the cornea is focused onto what, by what?
- focused onto the retina by the lens
What is the fovea, and what is distinct about its cells?
- the point of highest visual resolution
- highest concentration of cone cells
What are the hemiretinae of each eye?
- nasal and temporal hemiretinae
Where do most retinal ganglion cell axons from the nasal hemiretinae decussate?
- optic chiasm
Why don’t all retinal ganglion cell axons decussate at the optic chiasm?
- the crossover of fibres from the nasal hemiretinae allows for complete crossover of visual information
What is the organisation of the primary visual cortex (V1)?
- contralaterally and upside-down
What nucleus of the thalamus does visual input enter into?
- the lateral geniculate nucleus
What columns segregate the visual input from both eyes in V1?
ocular dominance columns:
- meaning the layers of V1 are striped such that they are represented; ipsi, contra, ipsi, contra
How many layers does the lateral geniculate nucleus have, and what inputs do they each receive?
6 layers, each receiving exclusive input from either the ipsi- or contra- eye
Where do M-type retinal ganglion cells project to?
the magnocellular layers of the LGN (ventral 2x)
Where do P-type retinal ganglion cells project to?
- the parvocellular layers of the LGN (dorsal, 4x)
Where are the intralaminar neurons located, and what do they do?
- between the layers of the LGN
- receive and relay information relating to colour to V1
What do the M-type retinal ganglion cells d?
- form the basis for a visual pathway that is specialised for movement detection
What do the P-type retinal ganglion cells do?
- form part of the parallel pathway that relays information on form and colour
What is the purpose of the ocular dominance columns?
- such that visual information from the ipsilateral and contralateral eye is kept segregated all the way up the visual cortex
What are the functions of V1, V2, V4 and V5 in the visual pathway?
- input into higher visual cortex is from V1
- V2 involved in both the ‘what’ and ‘where’ pathways
- V4 is mostly colour and form (what it is)
- V5 is mostly movement and speed (where it is)
What is the role of the superior colliculus in the visual pathway?
- visual information is processed in the more dorsal layers of the superior colliculus
- help orient the eyes and head towards important stimuli
The vestibulocochlear nerve has fibres arising from what two nerves and their associated sensory systems?
- vestibular (balance)
- cochlear (hearing)
Where does the vestibulocochlear nerve enter the brainstem?
- at the pons-medulla border
What 3 inputs does the vestibular nerve receive?
- 3 semi-circular canals
- the utricle
- the saccule
What do the utricle and saccule do?
- detect gravity and linear acceleration
What do the semi-circular canals do?
- angular acceleration
What is the process of sound waves being heard by the human ear?
- sound waves vibrate the tympanic membrane
- auditory ossicles vibrate - pressure is amplified
- pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli
4a. sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells
4b. sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells
What are the three nuclei that the auditory pathway relays to before its thalamic target (medial geniculate nucleus)?
- cochlear nucleus (medulla)
- superior olivary complex (pons)
- inferior colliculus (midbrain)
Where is the primary auditory cortex located?
- posteriorly, on top of the superior temporal gyri, known as Heschl’s gyri
Which portions of the cochlear nucleus process sounds from the vertical and horizontal axes?
vertical: dorsal portion
horizontal: ventral portion
What is the role of the superior olivary complex in processing sounds from the horizontal plane?
- aids with spatial localisation of incoming sounds from the horizontal plane by comparing differences in the timing or stimulus intensity between the left and right ear
Discuss the tonotopic arrangement of the primary auditory cortex
- receives both complex and pure sounds
- high tones are medial
- low tones are lateral
Where is the secondary auditory cortex in relation to the primary auditory cortex, and what does it do?
- surrounds the primary adutory cortex
- facilitates/helps with interpretation of auditory input
How do we interpret where sounds come from in space?
- the auditory pathways projecting to the posterior parietal cortex, as connections from this lobe toward the prefrontal and motor regions allow for planning of movement towards source
Which of the cranial nerves are involved in eye movements and are exclusively motor?
- oculomotor (CN3)
- trochlear (CN4)
- abducens (CN6)
Where does the oculomotor nerve originate from, and where does it pass through?
- originates from the midbrain
- passes through the superior orbital fissure
Name the muscles the oculomotor nerve innervates (hint: 4/6 of the extraocular muscles, a muscle of the upper eyelid and 2 intrinsic smooth muscles of the eye)
- medial rectus
- superior rectus
- interior rectus
- inferior oblique
- levator palpebrae superior
- ciliary muscle and the sphincter pupillae (parasympathetic component - pupillary constriction in response to light)
Oculomotor nerve palsy is characterised by what features?
- downward and outward gaze for the affected eye
- dilated pupil and ptosis (drooping eyelid)
- diplopia
Where does the trochlear nerve originate and where does it pass through?
- dorsal part of midbrain
- passes through the superior orbital fissure
What extraocular muscle of the eye does the trochlear nerve innervate, what does it do and how?
- superior oblique muscle
- moves down and out
- has a hook and pulley structure (resulting in outward rotation)
What is the presentation of a lesion to the trochlear nerve?
- inability to rotate eye infero-laterally
- gaze deviates upward and also slightly inward for the affected eye
- diplopia
Where does the abducens nerve originate from, and what structure does it pass through?
- originates from the anterior border of the pons and medulla oblongata
- passes through the superior orbital fissure to enter the orbit
What extraocular muscle does the abducens nerve innervate, and what does it do?
- innervates the lateral rectus muscle, which abducts the eye
Which of the cranial nerves have both sensory and motor functions?
- trigeminal (CN5)
- facial (CN7)
- glossopharyngeal (CN9)
- vagus (CN10)
What is the broad function of the trigeminal nerve?
- principle pathway for sensation from the head and face
Where does the trigeminal nerve originate from?
- the pons (laterally)
Discuss the differences in the roots of the trigeminal nerve and how they impact the sensory and motor fibres.
- the largest root contains sensory fibres that connect to the trigeminal ganglion (Meckel’s cave)
- the smaller root contains motor fibres (muscles of mastication (jaw movement/chewing)
What are the three major branches of the trigeminal nerve?
- the ophthalmic nerve (V1)
- the maxillary nerve (V2)
- the mandibular nerve (V3) - the only branch with sensory and motor fibres
List the major structures innervated by the sensory component of the trigeminal nerve.
general sensory nerve of the:
- face, as well as orbital, nasal and oral cavities
- rostral tongue, all teeth, bony skull
- most parts of the meninges (dura mater)
List the major structures innervated by the motor component of the trigeminal nerve.
supplies:
- all muscles of mastication
- anterior belly of digastric
- mylohyoid
- tensor tympani
- tensor veli palatine muscles
V1 of the trigeminal nerve carries sensory information from what structures?
- orbit
- cornea
- bridge of nose
- scalp and forehead
V2 of the trigeminal nerve carries sensory information from between what structures?
- between the lateral corners of the eye and mouth
What is the thalamic relay for the sensory trigeminal pathway?
ventral posterior medial nucleus (VPM)
What representation does the sensory trigeminal pathway have at the brainstem, thalamic and cortical level?
- topographic
In the trigeminal nerve, what do touch afferents project to?
- the Principle Sensory Trigeminal nucleus
In the trigeminal nerve, where do nociceptive afferents terminate?
- in the Spinal Sensory trigeminal nuclei
Discuss the ophthalmic nerve (V1) of the trigeminal branch
- only sensory fibres
- branches into three major branches (frontal, nasociliary, lacrimal nerves) in the orbit
- afferent sensory components of the corneal/blink reflex (efferent motor part is from CN7)
Discuss the motor, parasympathetic and sensory components of the facial nerve
Motor:
- muscles of facial expression
- muscles of the scalp
- posterior belly of digastric
- stylohyoid and stapedius muscles
also contribution to corneal/blink reflex
Parasympathetic:
- tear gland
- salivary glands (submandibular and lingual)
- nasal glands
Sensory:
- taste sensation from anterior 2/3 of tongue
What are the five major branches of the facial nerve that supply the muscles of facial expression?
- temporal
- zygomatic
- buccal
- mandibular
- cervical
Discuss the a) special sensation b) pharyngeal motor component c) parasympathetic component and d) general sensation of the glossopharyngeal nerve.
a) taste sensation from the dorsal 1/3 of tongue
b) supplies stylopharyngeus muscle
c) from inferior salivatory nucleus to parotid salivary gland via the otic ganglion
d) intraoral, pharynx and dorsal 1/3 of tongue
Where do fibres for the glossopharyngeal nerve emerge and exit?
- emerge from medulla
- exit via jugular foramen
Where do fibres emerge and exit from for the vagus nerve?
- medulla
- jugular foramen
Discuss the general visceral sensory component of the vagus nerve.
- from receptors in the walls of the viscera: pharynx, larynx, thorax, abdomen, carotid body, heart, bronchi, oesophagus
Discuss the special visceral sensory component of the vagus nerve.
taste from the pharyngeal area
Discuss the motor component of the vagus nerve.
Muscles of larynx, pharynx, upper oesophagus:
- levator veli palatine muscle
- salpingopharyngeus muscle
- palatoglossus muscle
- palatopharyngeus muscle
- all muscles of the pharynx and larynx
Discuss the parasympathetic component of the vagus nerve.
- all visceral organs of the neck, thorax, upper abdomen, and parts of the intestine that are derived from the foregut and midgut
What are two structural parts of the accessory nerve?
- cranial part (originates from brainstem and merges with vagus nerve)
- spinal part (emerges from spinal cord, enters the skull via foramen magnum, merges with its cranial counterpart and both leave the skull through the jugular foramen
Where do fibres for the hypoglossal nerve arise from, and exit?
- arise from the medulla
- exit skull via hypoglossal canal
What neurons are on the alar plate?
- sensory neurons
What neurons are on the basal plate?
- motor neurons
