Physiological psych Test 3

6 qualities of taste

Sweet, Sour, Salty, Bitter, Umami, Fat

how does flavor differ from taste

• involves the synthesis of taste and smell

Umami receptors

• savory taste

• sensitive to glutamate which suggests that it is sensitive to protein content in food

fat quality of taste

• is not typically associated with a particular taste

• receptors in the mouth that detect fatty acids

• fatty acid receptors are activated when fat is converted to fatty
  acids by the actions of lingual lipase

Saltiness receptors

• detect the presence of sodium chloride

sweetness receptors

detect sugars

causes for sour and bitter tastes

• sour: acidity

• bitter: alkaloid

retronasal olfaction

• when odorants enter from “the back" (i.e. when you eat food)

• projection is sent to a different area of the brain that combines
  this information with taste

location of taste buds

• tongue (highest concentration), palate, pharynx, and larynx

where are taste receptors located

along the papillae (bumps of the tongue)

3 types of papillae

• fungiform papillae

• foliate papillae

• circumvallate papillae

fungiform papillae

• located on the front 2/3 of the tongue

• contain up to eight taste buds, along with receptors for pressure,
  touch, and temperature

foliate papillae

• found on the edge near the back of the tongue

• approx 1300 taste buds

circumvallate taste buds

• located on the back 1/3 of the tongue

• approx 250 taste buds

anatomy of a taste bud

• consists of 20-50 receptor cells

• Cilia are located at the end of each cell and project through the opening of the taste bud (the pore) into the saliva that coats the tongue

how do taste receptor cells rely info

• Taste receptor cells form synapses with dendrites of bipolar neurons whose axons convey gustatory information to the brain through the seventh, ninth, and tenth cranial nerves

• The neurotransmitter released by the receptor cells is adenosine triphosphate (ATP)

perception of saltiness

• requires ionization

• perception of saltiness is mediated through the actions of Na on taste cells (i.e., Na enters and depolarizes the cell = release ATP)

perception of sourness

• mediated by PKD2L1

• respond to the hydrogen ions present in acidic solutions

perception of bitterness and sweetness

• metabotropic receptors linked to gustducin (a G protein)

• molecule binds with the receptor, the G protein activates an enzyme that begins a cycle of chemical reactions that causes the release of ATP

perception of umami

• metabotropic receptors linked to gustducin and transducin

• molecule binds with the receptor, the G protein activates an enzyme that begins a cycle of chemical reactions that causes the release of ATP

Gustatory brain pathway

1. Cranial nerves carry information to the forebrain via the medulla (nucleus of the solitary tract - relay station)

2. from the medulla, information is carried to the ventral posteromedial nucleus of the thalamus then to the primary gustatory cortex

3. primary gustatory cortex is located in the base of the frontal cortex and
   in the insular cortex (in close proximity to the olfactory cortex)

olfactory epithelium

• patches of mucous membrane that contain millions of olfactory receptor cells

• located at the top of the nasal cavity

• also contains free nerve endings which permit sensation of pain through
  inhalation

olfactory pathway

• do not carry information via a cranial nerve to the brain but project, via
  the axons of the mitral cells, to the amygdala, piriform cortex, and entorhinal cortex

• amygdala sends olfactory information to the hypothalamus

• the entorhinal cortex sends info to the hippocampus

• the piriform cortex sends info to the hypothalamus and to the orbitofrontal cortex via the dorsomedial nucleus of the thalamus

olfactory receptor cells anatomy and physiology

• are bipolar neurons whose cell bodies lie within the olfactory mucosa

• send a process toward the surface of the mucosa, which divides into 10 to 20 cilia that penetrate the layer of mucus

• Odorous molecules must dissolve in the mucus and stimulate receptor molecules on the olfactory cilia

olfactory bulbs

• lie at the base of the brain on the ends of the stalk-like olfactory tracts

• Each olfactory receptor cell sends a single axon into an olfactory bulb, where it forms synapses with dendrites of mitral cells

olfactory glomeruli

• complex axonal and dendritic arborizations where the olfactory bulb synapses with the mitral cells

perceiving specific odors

• humans have few receptors but can detect 10,000 odors

• Different odours correspond to different patterns of activation
  across a small number of receptors

cortical representation of olfaction

• abstraction of the sensation occurs in the cortex

• The piriform cortex is organized differently than the olfactory bulb

• Anterior portion reflects organization of olfactory bulb

• Posterior region is organized more abstractly - odours that
  come from related sources are grouped together

3 types of somatosensory information

1. kinesthetic feedback

2. organic senses

3. cutaneous senses

organic senses

sensations from in and around the internal organs

cutaneous senses

skin senses (touch)

kinesthetic feedback

body position and feedback from movement

proprioception

Provide information about location of the body in space

types of kinesthetic feedback

• control of movement through stretch receptors in skeletal muscles

• report changes in muscle length through stretch receptors in tendons

• Measure the force exerted by the muscles through receptors within joints between adjacent bones

• Respond to the magnitude and direction of limb movements

• Perception of position through receptors that respond to stretching of the skin

2 layers of skin

• epidermis - outer layer of the skin, which is made up of dead skin cells

• dermis - below the epidermis and contains mechanoreceptors that respond to stimuli such as pressure, stretching, and vibration

4 types of mechanoreceptors

1. Meissner corpuscles

2. Pacinian corpuscles

3. Merkel discs

4. Ruffini corpuscles

which 2 mechanoreceptors are encapsulated and fast adapting

• Meissner corpuscles (FA1)

• Pacinian corpuscles (FA2)

which 2 mechanoreceptors are not encapsulated and are slow adapting

• Merkel disks (SA1)

• Ruffini corpuscles (SA2)

difference between fast adapting and slow adapting mechanoreceptors

• fast- fire at onset and offset of stimulation

• slow- fire continuously as long as pressure is applied

two point threshold for measuring tactile acuity

minimum separation needed between two points to perceive them as two units

grating acuity for measuring tactile acuity

placing a grooved stimulus on the skin and asking the participant to indicate the
orientation of the grating

Merkel discs

• Good acuity or spatial resolution

• small receptive fields

• detection of detailed perception of spatial patterns on surfaces, form, and roughness

• densely packed on the fingertips

• detects tactile acuity

Meissner corpuscles

• Respond most strongly to low-frequency vibration

• Convey information about very small motions of the skin

• suited for perceiving slip and maintaining control over the force of
  one’s grip on an object

• small receptive fields

Ruffini corpuscles

• Very large receptive elds (poor spatial resolution)

• Important role in information about skin stretch

• Critical to perception of hand conformation

• Plays a role in the perception of movement across the skin

Pacinian Corpuscles

• Onion-like structure

• Large receptive elds (poor spatial resolution, but high sensitivity)

• Very sensitive to vibration

• Critical for perceiving texture of surfaces

2 types of thermoreceptors (TRPs)

1. Warm fibers (thin myelinated A fibres)

2. Cold fibers (unmyelinated C fibers)

Warm fiber thermoreceptors

• Deep in the skin

• Thermoreceptors that fire at an ongoing moderate rate in response
  to sustained skin temperatures in the range of 29–43 C

• Respond if skin temperature is abruptly warmed from a sustained
  neutral temperature
  

Cold fiber thermoreceptors

• Just below the epidermis

• Thermoreceptors that fire at an ongoing moderate rate in response
  to sustained skin temperatures in the range of 17–40 C

• Respond if skin temperature is abruptly cooled from a sustained
  neutral temperature

Nociception

• Unpleasant sensory and emotional experience

3 types of pain

• Nociceptive

• Inflammatory

• Neuropathic

2 types of axons(fibers) that transmit pain signals from nociceptors to the spinal cord

• Small myelinated A fibers
  - transmit action potentials relatively rapidly
  - Associated with “first pain”

• Unmyelinated C fibers
  - transmit action potentials relatively slowly
  - Associated with “second pain”

2 major pain pathways in the spinal cord

• Medial lemniscal pathway

• spinothalamic pathway

Medial lemniscal pathway

large fibers that carry proprioceptive and touch information

spinothalamic pathway

smaller fibers that carry temperature and pain information

cortical magnification

• Body map (homunculus) on the cortex shows more cortical space
  allocated to parts of the body that are responsible for detail organization

• There are at least 5 different maps of the body surface
  each processing info about a particular submodality

parts of the somatosensory receiving area (S1) of the parietal lobe

• Neurons in area 3a
  - proprioceptive information

• Neurons in areas 3b and 1
  - tactile information carried by signals from mechanoreceptors
  in the skin

• Neurons in area 2
  - proprioceptive and tactile information carried by signals
  from mechanoreceptors

dorsal somatosensory pathway

• information used to guide actions that require tactile and proprioceptive input

• goes from S1 to the posterior parietal cortex and then to premotor cortex

ventral somatosensory pathway

• tactile and proprioceptive information used in perceiving and
  remembering object shape and identity

• Goes from S1 to S2 and then to prefrontal cortex and hippocampus

• Damage results in tactile agnosia
  

tactile agnosia

unable to recognize objects through touch

why feel pain

• protective function - stop signal

• prevent further injury

changes in intensity of painful stimulus vs changes in the unpleasantness of stimulus

• Changes in the intensity of a painful stimulus is associated with
  somatosensory cortex.

• Changes in the unpleasantness of a stimulus is associated with anterior
  cingulate cortex

phantom limb pain

• Patients who have had a limb amputated still feel sensations from the
  missing limb

• Stimulating areas that have neural representations next to the missing
  limb in the somatosensory homunculus leads to phantom sensations

• Mirror box therapy can leverage visual feedback to override erroneous
  information from the somatosensory cortex

3 components of pain

• sensory component

• emotional response/ the unpleasantness

• long-term emotional implications

sensory component of pain involves which brain areas

• Pathway from spinal cord to thalamus to primary/secondary somatosensory cortex

immediate emotional response of pain involves which brain areas

insular cortex, anterior cingulate cortex, primary somatosensory cortex

long term emotional consequences of pain involve which brain areas

prefrontal cortex

Nociception and opioids

• Opioids produce analgesia by inhibiting pain centres at multiple locations
  in the CNS

placebo effect and opioids

Placebo analgesic effects involve opioid activity in the insula and ACC
that originates in the PAG

3 main functions of the vestibular system

1. balance

2. Maintenance of the head in an upright position

3. Adjusting eye movements to compensate for head movements

2 main components of the vestibular system

1. semicircular canals

2. vestibular sacs

function of semicircular canals

• Respond to angular acceleration (changes in the rotation of the head) but
  not steady rotation

• Three canals approximate the sagittal, transverse, and horizontal planes
  of the head

components of the semicircular canals

• The semicircular canals are filled with engorged areas called ampullae

• semicircular canals contains a fluid called endolymph

• The ampullae contain a gelatinous mass called a cupula

• the cupula has the cilia of the sensory receptors (hair cells) embedded in it

transduction mechanism of semicircular canals

1. endolymph resists movement when the head rotates

2. the resistance pushes the endolymph against the cupula, causing it to bend

3. bending of the cupula exerts a shearing force on the cilia of the hair cells

4. shearing force of the cilia opens ion channels, and the entry of potassium ions depolarizes the ciliary membrane

function of the vestibular sacs

• Respond to the force of gravity

• Provide information about the head’s orientation

names of the 2 vestibular sacs

1. utricle

2. saccule

components of the vestibular sacs

• each contain patches of receptive tissue on one side of the sac

• receptive tissue contains hair cells

• cilia of these receptor hair cells are embedded in an overlying gelatinous mass containing otoconia (calcium carbonate crystals)

transduction mechanism of vestibular sacs

1. weight of the crystals causes the gelatinous mass to shift in position as the orientation of the head changes

2. this movement produces a shearing force on the cilia of the receptive hair cells

3. A shearing force of the cilia opens ion channels, and the entry of potassium ions depolarizes the ciliary membrane

vestibular ganglion

A nodule on the vestibular nerve that contains the cell bodies of the
bipolar neurons that convey vestibular information to the brain

vestibular pathway in the brain

1. vestibular ganglion collects vestibular info from the vestibular nerve

2. sends information to cranial nerves and the vestibular area of the cortex

3 functions of hearing

1. detect sounds

2. recognize the identity of the sources of sound (analyze different characteristics)

3. determine the location of the sound

what is a sound

• Objects vibrate and set air molecules in motion

• Air molecules come together and then separate in waves

• These waves push the eardrum in and out

3 characteristics of sound

1. loudness

2. pitch

3. timbre

loudness

• A function of intensity

• More rigorous vibrations of an object produce more intense sound waves and thus louder sounds

• related to amplitude

• measured in decibels

Pitch

• A sound can be high frequency of vibration (soprano) or low frequency
  of vibration (bass)

• it is measured in Hertz

Timbre

• The complexity of the sound

• Most natural sounds are complex, consisting of several different frequencies of vibration

• corresponds to quality of sound - can distinguish different instruments

7 steps of sound transmission

1. sound is captured by the pinna

2. sound is funneled up the ear canal

3. the sound causes the tympanic membrane to vibrate

4. vibrations of the eardrum cause the ossicles of the middle ear to vibrate

5. vibrations are transmitted via the ossicles to the oval window

6. a membrane behind the oval window sends vibrations through the cochlea (the ears organ of transduction)

7. the basilar membrane in the cochlea flexes back and forth

3 ossicles

1. malleus/hammer

2. incus/anvil

3. stapes/stirrup

organ of corti

consists of the basilar membrane, hair cells, and the tectorial membrane

tonotopic map

• Different parts of the basilar membrane will flex in response to different frequencies of sound

• primary auditory cortex which reflects the representational scheme all the way from basilar membrane

role of cilia in sound perception

• cilia, connected to the basilar membrane bend

• This movement leads to EPSPs or IPSPs

• Cilia are arranged in rows from shortest to tallest

• Connected together by elastic laments called tip links

• Tip links are normally slightly stretched

how does cilia increase and decrease firing rate

• Moving the bundle of cilia towards the tallest one increases the rate of
  firing

• Moving the bundle of cilia towards the shortest one decreases the rate
  of firing

inner hair cells

• primary receptors

• 3500

• single row

• flask shaped

• 95% of auditory nerve fibers

outer hair cells

• amplifying role

• 12000 3-5 rows

• cylindrical

• 5% of auditory nerve fibers

homeostatic mechanism

• A motor connected to the tip link and ion channel regulates the tension of
  the tip links

• When the ion channel is open, calcium enters the cilia

• Then, myosin molecules cause the motor to move down, decreasing the
  tension of the tip links

• Decreases probability of ring

auditory pathway after in the brain

1. signal sent to auditory nerve

2. Axons from the auditory nerve, enter the cochlear nucleus
   of the medulla and synapse there

3. axons extend to the superior olivary complex

4. cells project through the lateral lemniscus — a large fibre
   bundle — to the inferior colliculus

5. Neurons then project to the medial geniculate nucleus of the
   thalamus and then on to the cortex

decussate pathways

pathways that cross over to the other hemisphere

do contralateral pathways or ipsilateral pathways dominate in the auditory system

contralateral pathways

superior olivary complex

a group of nuclei in the medulla involved in sound localization

inferior colliculus

involved in orienting auditory attention

Three regions of the auditory cortex that receive separate
tonotopic maps from the thalamus

1. primary auditory cortex

2. belt region

3. parabelt region