Special Senses Flashcards
What does CN I innervate?
CN I innervates olfactory mucosa of superior nasal cavity
How do CN I fibres pass from the olfactory bulb to the olfactory mucosa?
Via the cribriform plate
What is retronasal breathing vs. orthonasal breathing?
Retronasal smell creates flavour from smell molecules in foods or drinks shunting up through the nasal passages when chewing. Orthonasal smell is the perception of smell molecules that enter directly through the nose and up the nasal passages.
What can cause unilateral anosmia?
Meningioma or anterior cranial fossa trauma
Which parts of the cortex does the olfactory tract carry sensory neurons to?
Primarily piriform cortex but also orbital cortex.
Piriform cortex is part of temporal lobe: amygdala, parahippocampal gyrus.
Where are most taste receptors found?
On the tongue, some found in palate/pharynx
What senses taste in anterior 2/3 of tongue?
CN VII - Facial nerve via the Chorda tympani nerve
What senses taste in the posterior 1/3 of the tongue?
CN IX Glossopharyngeal nerve
What type of papillae are found in anterior 2/3 of tongue?
Fungiform
What type of papillae are found at the 2/3rd boundary of the tongue?
Filiform - NO taste buds
What type of papillae are found in posterior 1/3 of tongue?
Vallate
What are the 5 types of taste that receptors can sense?
Sweet, sour, salty, bitter, umami
What sensory nucleus do the cranial nerves carrying taste synapse on when they come into the brainstem?
Nucleus solitarius
What cranial nerves does taste sensation from the tongue travel via?
CN VII (Chorda tympani) and CN IX
What cranial nerves carry sensory innervation from the tongue?
CN Vc (Lingual branch) and CN IX
What is the Fovea Centralis?
Region of greatest visual activity
What are the three layers of the eye?
1) Retina (Photo-receptive/sensory region)
2) Choroid (vascular)
3) Sclera (white outer layer)
What is the optic papilla?
Blind spot where the optic nerve comes together
What does fundoscopy do?
Allows examination of retina
What is the optic nerve called after the optic chiasm?
Optic tract
What 2 loops make up the optic radiation?
1) Meyer’s Loop (Inferior bundle) that arches down to temporal lobe
2) Baum’s loop (superior bundle) that arches up to parietal lobe
Where does the optic radiation travel from and to?
From Lateral Geniculate Body of thalamus to the primary visual cortex (gyri around Calcarine sulcus) of occipital lobe.
Which part of the retina would the temporal visual field of the left eye hit?
Image hits the nasal retinal field.
What part of the visual field does Meyer’s loop carry?
Top half
What part of visual field does Baum’s loop carry?
Bottom half
What can happen if you damage the tip of the striate area of the occipital pole?
Loss of central macula vision - Central scotoma
What can happen if you have a vascular lesion of the occipital lobe?
Damage top and bottom visual fields on the same side and spare a central circle - Homonymous Hemianopia
Why are vascular lesions of the occipital lobe macular sparing?
The tip of the striate area of occipital lobe receives a different blood supply than the rest of the occipital cortex.
What is accomodation?
Accommodation is what enables us to look at and focus upon objects that are close to the eye
Which CN and muscle causes vergence?
CNIII nucleus –> Medial rectus
What does the Edinger-Westphal nucleus do in accommodation?
Edinger-Westphal nucleus synapses with Ciliary Ganglion. Ciliary Ganglion innervates Sphincter pupillae (pupil constriction) and ciliary body (lens fattening)
How does lens fattening occur?
The circumferential ciliary body contracts which then relaxes the suspensory ligaments - this allows the lens to recoil, relax, thus allows it to puff up (become fatter)
Where are the vestibular and cochlea apparatus found?
The vestibular and cochlea apparatus are housed in the petrous temporal bone within a bony labyrinth
How is the cochlea arranged and what is it’s sensory part called
The cochlea is arranged in a spiral and its sensory part is the Organ of Corti
Which nerve innervates the cochlea?
Cochlear Nerve (part of CN VIII)
How are vibrations transmitted?
Organ of Corti has sensory hair cells that detect vibrations. Vibrations are transmitted from the oval window in the middle ear to the perilymph of the cochlea through the vestibular membrane into the endolymph
What are the differences in the membrane between high frequency and low frequency sound?
High frequency sound - membrane narrow and stiff.
Low frequency sound - membrane wide and flexible
Which cranial nerve nucleus is for hearing and where is it located?
CNVIII nucleus for hearing is in the pons/medulla
How is auditory information distributed?
Auditory information is distributed bilaterally to the cortexes (but has a dominant hemisphere). CN VIII ascends bilaterally, there are multiple nuclei and multiple decussation points. The primary auditory cortex receives bilateral auditory sensory input.
Name some causes of sensorineural deafness
Drug linked, viral Rubella in utero or mumps
What can loss of stereo-placement of sound indicate?
Can indicate a cortical or thalamic issue/pathology
What is tinnitus and why can it occur?
Tinnitus is ringing noise in absence of sound. Occurs in Meniere’s disease, URTI or following exposure to loud sounds.
Tensor tympani/staepedius myoclonus (contractions) can cause tinnitus
What 2 parts does the vestibular system consist of?
Dynamic part and static part
Describe the dynamic part of the vestibular system
Dynamic part is formed from semi-circular canals and crista. Acts mainly on eye movements via medial-longitudinal fasciculus
Describe the static part of the vestibular system
Static part formed from maculae (utricle and saccule). Acts on vestibulospinal pathway. Pick up static changes of position of the head (even when it is still). Pick up acceleration of the head.
What does the utricle macula do?
Detect horizontal acceleration (eg. driving). Active with head in flexion or extension.
What does the saccule macula do?
Detect vertical acceleration (eg. falling). Extensor activation in a fall (strong extensor thrust) as this activates the vestibulospinal pathway. Active with head held side to side.
Where do the vestibular nuclei sit?
The vestibular nuclei sit in the pontomedullary brainstem
what are the 3 inputs needed for postural control?
Vestibular, visual and proprioception
What can tertiary syphillus damage?
Dorsal column
What might be damaged in a positive Romberg patient?
Dorsal column
