Chapter 7: Other Sensory Systems Flashcards
Pinna
- outer ear
- flesh and cartilage
- helps locate sound by altering reflections of sound waves
Auditory Canal
-sound waves pass through
Tympanic Membrane
- ear drum
- middle ear
- vibrates at same frequency as sound waves that strike it
Oval window
- membrane of inner ear
- small bones increase pressure of waves on small oval window
- more force = necessary to move viscous fluid
Cochlea
- has 3 long fluid filled tunnels (scala vestibuli, scala media, scala tympani)
- stirrup makes oval window vibrate which moves the fluid inside the cochlea
Hair cells
- auditory receptors
- inside cochlea
- vibrations displace the hair cells that open ion channels in the membrane
- hair cells excite the cells of the auditory nerve (8th cranial nerve)
Pitch Perception: Place Theory
- each area along basilar membrane is tuned to a specific frequency
- each frequency activates the hair cells at only one place along basilar membrane and neurons distinguish the frequency based on what neuron responds
Pitch Perception: Frequency Theory
- basilar membrane vibrates in synchrony with a sound which causes auditory nerve axon to produce action potentials at the same frequency
- not valid due to refractory period of neuron
Current Theory of Pitch Perception: Low Frequency Sounds (up to 100Hz)
-modification of place theory and frequency theory
LOW FREQUENCY SOUNDS: up to 100Hz
-basilar membrane vibrates in synchrony with sound waves (frequency theory)
-auditory nerve axons generate 1 axon potential per wave
-soft sound activates fewer neurons
-stronger sound activates more neurons
-frequency of impulses identifies pitch
-#of cells identifies loudness
Current Theory of Pitch Perception: High Frequency Sounds (above 100Hz)
- fire every 2nd, 3rd, or 4th etc later wave
- only at peak of sound wave
- action potentials are phase locked
- can have multiple auditory neurons that fire but not at the same time therefore take the sum of the neurons
Volley Principle
-auditory nerve as a whole produces volleys of impulses for sounds up to 4000 Hz even though there is no one specific axon that does that frequency
Sound localization
- determining direction and distance of a sound requires comparing responses of the 2 ears
- difference in intensity between 2 ears
- difference of time of arrival
- low frequency: phase difference, at different angles sounds are out of phase
- high frequency: loudness differences
- localize most by time of onset
types of hearing loss and the conditions that can cause them.
-disease, infections, or tumorous bone growth prevent middle ear from transmitting sound waves to cochlea
=conductive deafness
=middle ear deafness
-damage to cochlea, hair cells, or auditory nerve
=nerve deafness
=inner ear deafness
-can be inherited or from a variety of disorders
-exposure to loud noises=long term damage to synapses and neurons of auditory system
Tinnitus
- ringing in ear
- can be from nerve deafness
Role of otoliths
- calcium carbonate particles next to hair cells
- when head tilts in different directions otoliths push against different sets of hair cells and excite them
Role of semi-circular canals
- oriented in perpendicular plane filled with jelly substance
- lined with hair cells
- acceleration of head causes jelly to push against hair cells
- action potentials initiated by cells of vestibular system travel through 8th cranial nerve to brainstem and cerebellum
Action Potentials initiated by vestibular system go…
-action potentials initiated by cells of vestibular system travel through 8th cranial nerve to brainstem and cerebellum
Free nerve ending
- unmyelinated or thinly myelinated axons
- near base of hairs and elsewhere in skin
- pain, warmth, cold
Hair follicle receptors
- hair covered skin
- movement of hairs
Meissner’s corpuscles
- hairless areas
- sudden displacement of skin
- low frequency vibration (flutter)
Pacinian corpuscles
- Both hairy and hairless skin
- sudden displacement of skin
- high frequency vibration
Merkel’s disks
- both hairy and hairless skin
- light touch
Ruffini endings
- both hairy and hairless skin
- stretch of skin
Krause end bulbs
- mostly or entirely hairless areas
- may include genitals
- uncertain what they respond to
cortical processing of somatosensory information
- information from touch receptors on head enter CNS through cranial nerves
- information from below head goes through spinal nerves
- info travels through spinal cord on well defined pathways to brain
- separate axons/pathways for deep touch and light touch
- nervous system codes differences in sensory sensations in terms of which cells are active
- areas of somatosensory thalamus send impulses to different areas of primary somatosensory cortex in parietal lobe (2 strips respond mostly to touch on skin, 2 others respond to deep pressure and movement of joints and muscles)
- damage impairs body perception
roles of the various neurotransmitters in the production of pain
- pain starts with bare nerve ending
- pain axons release 2 NTs in spinal cord
NTs for mild pain
-glutamate
NTs for strong pain
- glutamate
- substance P
Alleviation of pain
- opioid mechanisms that respond to opiate drugs and similar chemicals
- opiate receptors act by blocking release of substance P
- endorphins produced by brain are body’s own opioids
- morphine post surgery block dull slow pain
- large diameter axons are unaffected by morphine (sharp pain)
- cannabinoids also block some types of pain
Roles of NTs in production of itch
1) histamines that dilate blood vessels produce itch sensation
2) contact with certain plants
- axons are spcific for itch types also respond to heat
- itch axons activate gastrin releasing peptide
- itch pathway is slow to respond
Alleviation of itch sensation
- scratching produces mild pain
- pain alleviates itch meaning itch is not a types of pain
Labelled line principle (application to senses)
- each receptor would respond to a limited range of stimuli
- meaning would depend on which neurons are active
Across-fibre pattern principle (application to senses)
- each receptor responds to a wider range of stimuli
- response by given axon means little except in comparison to what other axons are doing
ex) colour perception - nearly all perceptions depend on pattern across array of axons (auditory, taste, smell)
mechanisms of the taste receptors
- stimulation of taste bud receptors on tongue
- different chemicals excite different receptors and produce different rhythms of action potentials
- temporal pattern may be important
- neuron responds to tastes with different patterns
- patterns code for different taste experiences
taste receptors
- modified skin cells
- have excitable membranes
- release NTs into brain
flavour
-flavour=combination of taste and smell, taste and smell axons converge in endopiriform cortex which influences food selection
Salty receptor
-permits Na+ to cross membrane
Sour receptor
-detects presence of acids
Sweetness receptor and umami receptor
- metabotropic synapse
- molecules bind and activate G-protein
Bitter receptor
- metabotropic synapse
- 25+ types of receptors
Anterior 2/3 Taste nerve pathway
-anterior 2/3 receptors travel along chorda tympani (part of cranial nerve 7 (facial nerve)
Posterior receptors and throat receptors pathway
-travel along 9th and 10th cranial nerves
Taste pathway
-from NTS information goes to pons, lateral hypothalamus and somatosensory amygdala, ventral posterior thalamus, and somatosensory cortex and insula (primary taste cortex)
Primary taste cortex
Insula
describe the operation
- response to chemicals that make contact with membranes inside the nose
- olfactory cells line olfactory epithelium in rear of nasal passage
- olfactory cell has no cillia
- olfactory receptors located on cillia
- metabotropic receptors that respond to an odorant molecules instead of NT
- each chemical excites several types of receptors
- most strongly excited receptor inhibits activity of other ones via process similar to lateral inhibition
number of olfactory receptors
-humans have several hundred olfactory receptor proteins
the implications of the numbers of receptors for coding olfactory information
-large number of types of olfactory receptors makes it possible to identify chemical precisely
why do we have so many olfactory receptors?
-olfaction processes airborne chemicals that do not range along a single continuum like wavelength
types of stimuli that the vomeronasal organ responds to and differences between the vomeronasal and olfactory systems
- sets of receptors close to olfactory receptors that respond only to pheromones
- each VNO receptor responds to 1 pheromone
- VNO receptor continually responds strongly even after prolonged stimulation (contrary to olfactory receptors)
- alter autonomic responses
ex) skin temperature
Pheromones
-chemicals released by an animal that affect behaviour of other members of same species
describe synesthesia and its possible anatomical basis
- experience some people have in which stimulation of one sense evokes a perception of that sense and also another on
ex) smelling colours - people who experience synesthesia have increased gray matter in certain brain areas and altered connections to other areas
- possible genetic predisposition
