6.4 Neuro Anatomy & Physiology - Special Senses Flashcards
What is sensory transduction?
The process by which a stimulus is converted into an action potential
True or false: all senses are relayed to the thalamus before heading to the cortex
False. This is true of all senses except olfaction, which is very primitive and has its own short circuit to the cortex
What is a labelled line?
The specific pathway that transmits information about a specific modality
Does the energy that produces an action potential to stimulate a labelled line influence the modality of which sensation is produced?
No. It’s always the same modality (think: pushing on your eyes)
Describe the pathway of light through the eyeball
- Passes through cornea (protective)
- Passes through iris (determines amount of light passing through)
- Passes through lens (focuses light on retina, where photoreceptors are)
- Light is projected on retina, where photoreception occurs
Can rods detect colour? Do they allow us to see much detail? Are they good at detecting dim lights?
- Monochromatic
- Low visual acuity
- Very good at detecting dim lights
Can cones detect colour? Do they allow us to see much detail?
- Mediate perception of colour
- High visual acuity
Describe the processing of visual input from the retina to the optic nerve
Some processing occurs in retina -> relayed to bipolar cells -> ganglion cells (axons form optic nerve)
What is the pit inside the macula called? Describe its composition in terms of rods and cones
- Called the fovea
- Contains only cones (think about the implications of this…)
What is the centre of the retina of the eye called?
Macula
Describe the composition of the periphery of the retina in terms of rods and cones
Higher ratio of rods and cones (thin about the implications of this…)
Why is there a blind spot in the retina? What is this called?
- There must be a blindspot where the optic nerve leaves the retina
- This is known as the optic disc
Describe the image on the retina of the eyeball
Inverted and reversed
How many fibres in an optic nerve?
~1 million
What is the join of the two optic nerves called?
Optic chiasm
Which optic nerve fibres cross at the optic chiasm, and which don’t?
Lateral: don’t
Medial: do
What is the difference between the optic tract and the optic nerve?
Optic nerve carries information from one eye. Since the optic tract exists after the optic chiasm, it contains information from both eyes.
Where are the sites of termination of the optic tract?
- Thalamus
- Superior colliculus
In what region of the thalamus does the optic tract terminate?
Lateral geniculate nucleus
Where do the optic radiations run to?
The primary visual cortex (above and below calcarine sulcus in occipetal lobe)
Where is the what stream and what does it do?
- Located toward temporal cortex
- Recognising what something is (form, colour, faces)
Where is the where stream, and what does it do?
- Located toward parietal cortex
- Analysing motion and spatial relationships
What is the name of the opening of the external ear?
External acoustic meatus
What is the name of the membrane that separates the external ear and middle ear?
Tympanic membrane
What is the purpose of the bones of the middle ear?
Matches impedance between outer ear and inner ear (think: high heel)
Which section of the ear is connected to the nasopharynx? By what tube?
- Middle ear
- Pharyngotympanic tube
What is the name of the bones in the middle ear?
Ossicles (small bones)
What two labyrinths exist within the inner ear
- Bony
- Membranous
What two liquids fill the membranous labyrinth of the inner ear?
- Perilymph
- Endolymph
What happens in the inner ear?
Signals are analysed and transduced
Where is the inner ear located within the skull?
The petrous part of the temporal lobe
What does petrous mean?
rock (hard bone)
What is the part of the inner ear associated with hearing called?
Cochlea
Which cells are responsible for sensing sound? Describe the positioning of these cells
Three rows of outer and one row of inner hair cells in the cochlea
What membrane is on top of hair cells in the cochlea?
Tectorial membrane
Describe how the tectorial membrane helps in the generation of an action potential
Hair cells vibrate when sound is detected, causing them to shear against the tectorial membrane and resulting in the production of an action potential
What is meant by tonotopic representation?
Every tone of sound has it’s own corresponding place on the basilar membrane
Describe the pathway of a nervous signal from the cochlea to the primary auditory cortex
- Bipolar cells in spiral ganglion
- Vestibulocochlear nerve (CN VIII)
- Cochlear nuclei (Medulla -> fibres cross over to other side of CN)
- Via lateral lemniscus fibre band
- Inferior colliculi
- Medial geniculate nuclei
- Primary auditory complex
Which Brodman’s areas comprise the primary auditory cortex?
41, 42
What is the name of the part of the inner ear associated with balance?
Vestibular labyrinth
How many semicircular ducts in the vestibular labyrinth? What are their names?
- Three
- Anterior, Posterior, Lateral
What is the name of the sensors in the semicircular ducts of the vestibular labyrinth?
Ampullae
What do semicircular canals detect?
Rotation of the head
What do otolith organs detect? What are they?
- They are the utricle and sacculus
- Detect horizontal movements of the head and orientation of head relative to gravity
Describe the pathway of an action potential in the vestibular system from hair cells
- Hair cells
- Nerve fibres of vestibular ganglion cells
- Vestibular nuclei
What structures are the vestibular nuclei connected to?
- Cerebellum
- Muscles that control eye movement
- Alpha and gamma neurons in spinal cord
- Alpha motoneurons in neck muscles
- Thalamus
- Emetic centres
What is the function of Broca’s area? Where is it located?
- Language production and comprehension
- Posterior inferior frontal gyrus
What is the function of Wernicke’s are? Where is it located?
- Comprehension of language (written and spoken)
- Posterior superior temporal gyrus
Which structure connects Broca’s area to Wernicke’s area?
Arcuate fasciculus
What is Broca’s aphasia?
Know what to say, but can’t say it
What is Wernicke’s aphasia?
Can speak, but words have no meaning and the patient is not aware of this. Inability to comprehend spoken word.
Are Wernicke’s and Broca’s area present unilaterally or bilaterally?
Unilaterally; in dominant hemisphere
Where are the cell bodies of cranial nerves situated?
Brainstem
Which cranial nerve is associated with vocal fold movement?
CN X (Vagal nerve)
Which cranial nerves are associated with supra-laryngeal muscles?
CN IX and CN X (Vagal and Glossopharyngeal)
Which cranial nerve is associated with movements of the tongue?
CN XII (hypoglossal nerve)
Which cranial nerve is associated with facial muscles?
CN VII (Facial nerve)
What are some motor movements involved in speech production?
- Vocal fold movement
- Respiration
- Supra-laryngeal muscles
- Movements of tongue
- Facial muscles
What is the nerve tract that connects the precentral gyrus to the cranial nerves called?
Corticobulbar/corticonuclear tract
Why do we need sensory feedback from muscles during speech?
- Gain feedback on sound
- Am I in any discomfort?
- Are the facial muscles/vocal folds/everything else okay?
Where does sensory feedback from speech come back to?
The post-central gyrus
Draw a summary of the sensory/motor loop of speech, and compare this to the diagram in 6.4.docx
What is the name given to the structures that branch off of the knob of olfactory receptor cells?
Receptor cilia
How many receptor types does an olfactory receptor express?
Usually one, sometimes a few
Are olfactory receptor axons myelinated or unmyelinated? How could this influence the speed at which we detect smell?
- Unmyelinated
- Slower-moving message
What do all the axons of olfactory receptor cells form? How is this different to usual?
- They form the olfactory nerve (CN I)
- Different to other cranial nerves because it is not a single bundle
In what structures is information segregated into in the olfactory bulb?
Segregated into glomeruli
Where does the olfactory tract terminate?
- Primary olfactory cortex
- Tip of temporal lobe
From the primary olfactory cortex, where is information regarding odour perception sent?
- Amygdala
- Hippocampus
- Orbitofrontal cortex (conscious perception)
What are the five tastes?
- Sweet
- Sour
- Salty
- Bitter
- Umami
Why do we have a fondness of sweet/umami substances?
These are historically rare, and so eaten to gain calories for storage
Why do we tend to dislike bitter foods?
- Poisons are often bitter
What is the name of the bumps on the surface of the tongue?
Papillae
How many taste buds do people tend to have?
2000-5000 (more: supertasters)
How often are taste receptor cells replaced?
10-14 days
Draw a diagram of a taste receptor cell. compare with image from 6.4.docx
Are taste receptor cells neurons?
No. They synapse with the ending of gustatory afferents
Why do taste buds always contain only one type of taste receptor cell?
They don’t
Describe signal transduction in taste receptor cells
- Tastant combines with saliva and binds to taste receptor cells
- Causes depolarization (Ca2+ influx)
- Causes neurotransmitter release, exciting postsynaptic sensory axons
How is it that most of the tongue is sensitive to all basic tastes?
- At concentrations just above threshold, papillae are usually sensitive to just one taste
- As concentrations increase, papillae become less selective
- Since we usually eat foods that have strong tastes (relative to threshold) most of the tongue is sensitive to most basic tastes
Describe the transmission of taste signals into the cortex
- Gustatory afferents
- Gustatory nucleus (medulla)
- Thalamus
- Gustatory cortex
Where is the gustatory cortex located?
In the insula adjacent to the primary somatosensory cortex
Are taste pathways ispilateral or contralateral?
Ipsilateral
What is a loss of taste reception called?
Ageusia
How is taste different to flavour?
Taste: Gustatory
Flavour: Gustatory and Olfactory
What is the difference between retronasal and orthonasal olfaction?
Retro: Coming from oropharynx
Ortho: Direct from surroundings
What other senses contribute to flavour?
- Texture
- Temperature
- Visual appearance
