CH 7-other senses Flashcards
organization of sensory areas of cortex (audition)
primary-receive input from thalamus
secondary-receives input from primary
association-receives input from multiple primary sensory systems, but primarily from secondary system
-characterized by hierarchical organization, functional segregation and parallel processing
hierarchical organization (audition)
ranked-neurons respond to stimuli of greater specificity (receptors, thalamic relay, primary sensory cortex, secondary, association)
organized by functional complexity (from simple to complex and from general to specific)
-each level receives input from lower levels, adds new layer of analysis and then passes up
-damage in lower levels leads to loss of function
-damage in upper levels leads to specific sensory deficits (agnosias), which are really problems of perception (interpretation of stimuli, as opposed to detection)
functional segregation
primary, secondary, association cortices not functionally homogeneous (do not act together to perceive sensation, each performs a different level of analysis)
-just like in vision, we have the M path and the P path
parallel processing
is signal is analysed in different ways simultaneously by multiple parallel pathways of neural networks
-two types of parallel streams; one that influences behaviour w/o conscious awareness, another that engages conscious awareness
binding problem
- no one area receives all sensory input from a sensory system
- all perceptions must be a product of combined activity of interconnected areas
- the claustrum is a thin sheet of neurons under the neocortex, at the top of the sensory hierarchy that receives signals from all lower sensory areas and must be forming perceptions
claustrum
thin sheet of neurons under the neocortex, at the top of the sensory hierarchy that receives signals from all lower sensory areas and must be forming perceptions
sound
-vibration of air molecules
-stimulus for auditory system -recorded in waves and measured in Hz (cycles/sec)
-humans can hear 20-20,000 Hz
amplitude=loudness
frequency=pitch
complexity=timbre
pure tone
do not exist naturally, only machine produced
- simple sine waves
- close relationship btw tone and pitch
- humans have a hard time localizing pure tones and they’re generally really uncomfortable
complex sound waves and fourier analysis
- sounds in nature almost always associated w complex patterns and vibrations
- theory that auditory system performs fourier analysis, a mathematical breakdown of complex waves into component sine waves of diff frequencies/amplitudes
outer ear
auditory canal, tympanic membrane, ossicles
-sound waves travel down auditory canal, causing tympanic membrane to vibrate, which in turn pushes on malleus, then incus, then stapes, which triggers vibrations in the oval window
inner ear
transfers vibrations from oval window to endolymph of cochlea (long, coiled tube w internal membrane (organ of corti, the auditory receptor organ))
-pressure change in the oval window travels along organ of corti as a wave
organ of corti
- inside the cochlea
- composed of 2 membranes; basilar, in which hair cells are mounted, and tectorial, which rests on the hair cells
- movement of tectorial membrane shear hair cells, stimulating the and triggering aps in auditory nerve
- round window allows vibrations to dissipate
- diff components of complex sound act in diff locations
- has tonotopic map
endolymph
fluid surrounding hair cells
-rich in K+, creating an ionic imbalance maintained by tight junctions btw hair cells, and eliminating the need for Na/K+ pumps
hair cells
- sense mvmt in surrounding fluid
- tips of cell called cilia, that increase in length along consistent axis
- stimulated mechanically (transduce mechanical energy into neural impulse)
- connected by tip links; from one cilia to the cation channel of a neighbour
- tectorial membrane mvmt causes talles one to move, pulling open the K+ channel on the next one and so on (motion in the opposite direction will quiet the cell!)
- > K+ influx, opens voltage gate Ca channels, leading to NT release from basilar haircell and synapse onto auditory nerve
ear to primary auditory cortex
multiple networks of auditory pathways (different from vision)
-axons of each auditory nerve synapse onto ipsilateral cochlear nuclei in brainstem
-left and right superior olives receive these signals from each ear and project to inferior colliculi via lateral meniscus
-combined input is then passed onto medial geniculate nucleus (MGN) and then A1 in the temporal lobe
(so A1 in each hemisphere ultimately receives info from BOTH ears)
sound localization
if sound originates on left, it will be loudest in and reach the left ear first
- this is processed in the superior olives
- lateral superior olives respond to differences in amplitude while medial superior olives respond to the difference in timing btw two inputs
- olives project to retinotopic map in superior colliculi to show is where sounds come from in visual space
outer hair cells
essentially control the tightness of the tectorial membrane
-thought to be controlled by top-down process (when you are listening real hard for your phone ringer to find it, the membrane will be tightened over the frequencies of interest and loosened elsewhere)
auditory cortex
- located in temporal lobe
- receives input from medial geniculate nucleus (MGN)
- poorly understood bc labs always use pure tones for testing
- does have tonotopic map, but we don’t know what features of a frequency it cares about
- thought to be really important for communication (area responds to sign language in deaf indv)
- contains A1 and A2
- A1 harder to damage bc its at the core
- A2 has more complex, varied responses than A1
- organized into functional columns (vertical neurons respond to the same frequency)
auditory association cortex
A2 is scattered into 2 different streams
- anterior or ‘what’ pathway is in the prefrontal cortex and inferotemporal cortex, and identifies sounds
- posterior or ‘where’ pathway is in the posterior parietal cortex; it locates sounds and prepares for action
- note that the ppc also processes visual info
auditory cortex damage
rare, especially in A1, and usually caused by a stroke; often damage extends to other areas too though
-rarely severe permanent deficits (may lose ability to localize or discriminate frequencies, but hearing generally recovers w/in a few weeks), meaning subcortical levels must be doing a lot
deafness
- total deafness is rare
- generally results from damage to inner/middle ear or exiting nerves
- two main types: conductive (originate from ossicles) and nerve (loss of hair cells from age or other damage)
- cochlear implant can bypass hair cell damage by directly exciting the auditory nerve, but will not restore hearing fully, and also has best outcome when implanted early on
tinnitus
- can occur in normal hearing, common following hearing loss and with aging
- persists despite auditory nerve being cut, which suggests it must be the product of central processing and not aberrant inputs
somatosensation (touch and pain)
broken down into 3 subsystems: exteroreceptive (senses external stimuli applied to skin), proprioceptive (monitors position of body through receptors in muscles, joints, organs of balance) and interoceptive (general info on bodily conditions such as temp, blood pressure)
