Nakamura Human Physiology Lecture 5 Flashcards
(39 cards)
Sensory receptors
.Sensory Transduction–Sensory receptors convert (transduce) light energy, sound pressure waves, and airborne chemicals into APs that are sent to the brain.
•Sensory receptors respond to a particular modality (various forms of sensation, e.g., touch, vision, etc.) of environmental stimulus.
Law of specific nerve energies
.•Sensation characteristic of each sensory neuron is that produced by its normal or adequate stimulus.
•Regardless of how a sensory neuron is stimulated, only one sensory modality will be perceived.
Why we can only hear certain sounds
Functional categories of sensory receptors
.Receptors are grouped according to type of stimulus energy they transduce.
–Chemoreceptors
•Chemical stimuli in environment and blood (pH, C02)
–Photoreceptors
•Rods and cones in the eyes
–Thermoreceptors
•Temperature
–Mechanoreceptors
•Touch, pressure, and joint position (proprioceptor) (body balance)
–Nociceptors (a type of chemoreceptor)
•Pain
Classification of sensory receptors by rate of adaptation
.Tonic receptors
–Produce constant rate of firing as long as stimulus is applied
-slow adapting
•Phasic receptors
–Burst of activity but quickly reduce firing rate (adapt)
-fast adapting
-ex) smell something strong. Get used to smell quickly (adapt)
Receptor potentials
.•In response to stimulus, sensory nerve ending produces a local graded change in membrane potential.
•Potential changes are called receptor potentials (generator potentials).
-once reach threshold receptor potential occurs
-smaller depolarizations called receptor dendrites
Cutaneous sensations
.Free nerve endings
–Receptors do not adapt or adapt slowly (tonic)
–Light touch
–Temperature: heat and cold (# cold > # heat). Certain receptors just for cold and just for heat
–Pain (tonic)
•Encapsulated nerve endings
–Receptors adapt quickly (phasic)
–Pacinian corpuscle: deep pressure
-Meissner’s corpuscle: light pressure
Receptive fields on skin
Area of skin whose stimulation results in changes in the firing rate of the neuron.
•Area of each receptive field varies inversely with the density of receptors in the region.
-smaller receptive field, more receptors, so more sensitive
-larger receptive field, fewer receptors
•ex) Back and legs have few sensory endings (large receptive fields), whereas fingers have many sensory endings (small receptive fields)
Two point touch threshold
.•Minimum distance at which 2 points of touch can be perceived as separate
•Measure of distance between receptive fields
•Receptive field size is an indication of tactile (sense of touch) acuity
-smaller receptive fields have more receptors closer together, so can perceive small changes in the two points
Lateral inhibition
.Sharpening of sensation
•Sensory neurons in the center areas are stimulated more than neighboring fields
-when have large object on the skin, most of the pressure is felt in the middle, the sides have been inhibited
•Perceive single touch
Taste and smell
-Receptors for taste (gustation) and smell (olfaction) are chemoreceptors
•Relationship between taste and smell
Taste
-Taste buds are clusters of epithelial cells that have microvilli
•Although taste cells are not neurons, they depolarize upon stimulation and release chemical transmitters that stimulate sensory neurons
Taste receptor distribution
- sweet: tip of tongue (anterior)
- sour: lateral sides
- salty: edge of tongue
- bitter: back of tongue (posterior)
How we perceive salty
–Na+ passes through ion channels
- opens calcium channels and depolarizes the receptor cells by letting calcium in
- neurotransmitters are then released
How we perceive sour
- H+ through ion channel
- opens calcium channels, depolarizes
- neurotransmitters released
How we perceive sweet and bitter
Mediated by receptors coupled to G proteins
Gustducin: type of G protein associated with basic taste and gustatory system
Sweet:
1. Sugars enter
2. G protein disassociates
3. Alpha bonds to adenylate cyclase, catalyzes ATP into cAMP
4. Activates protein kinase
5. Closes potassium channel (causes depolarization)
6. Neurotransmitters released
Bitter:
Same except activated by quinine and calcium is released from endoplasmic reticulum instead of closing potassium channel
Smell
Olfaction
-Bipolar sensory neurons located within pseudostratified epithelium.
•Axon projects up into olfactory bulb of cerebrum and dendrite that terminates in cilia.
•Molecules bind to receptors and act through G-proteins-cAMP
-lobe in the brain for smell in the middle (medial aspects) right above nasal cavity
Sound waves
.Sound waves travel in all directions from their source
•Waves are characterized by frequency and intensity
–Frequency:
•Measured in hertz (Hz, cycles per second)
•Wave frequency is the pitch
•Human ear is sensitive to a wide range of frequencies (20 Hz up to 15,000 Hz). Middle C on the piano is 523 Hz
–Intensity:
•Measured in decibels (dB)
•Amplitude of sound waves (loudness)
Outer ear
Georg von Bekesy (audiometer)
•Sound waves are funneled by the auricle into the external auditory meatus.
•External auditory meatus funnels sound waves to the tympanic membrane.
–Increases sound wave intensity
-Sound wave collection
Middle ear and ossicles
-amplifies vibrations
-go from larger surface area to smaller
-Malleus (hammer)
–Attached to tympanic membrane.(terminal structure from outer ear)
–Vibrations of tympanic membrane are transmitted to the incus and then the stapes.
•Incus (anvil)
•Stapes (stirrup)
–Attached to oval window of cochlea(inner ear) note the smaller surface area compared with the tympanic membrane
–Vibrates in response to vibrations in tympanic membrane.
-round window: buffer system if vibrations to big, escape through this
Inner ear
*cochlea
Three chambers
–scala vestibuli
–cochlear duct (contains organ of corti)
–scala tympani
•Vibrations pass from scala vestibuli to the scala tympani. Movements of perilymph travel to the base of cochlea where they displace the round window.
•Pressure waves within the perilymph(part of lymphatic fluid) are transmitted through the basilar membrane
•Movement of basilar membrane stimulates the hair cells
Sensory hair cells
.Bending of hair cell stereocilia located within the vestibular apparatus in cochlear duct produces the receptor potential
•Stereocilia
–Bending toward tallest stereocilium (kinocilium) depolarizes the membrane potential (this is the receptor potential) and causes hair cell to release more NT (stimulated)
–Bending away from tallest stereocilium, membrane hyperpolarizes and releases less NT (inhibited)
-sends electricity to temporal lobe
-very sensitive, once dead, dead forever
Organ of corti
.Components
–Tectorial membrane (rigid)
–Hair cells: stereocilia embedded in tectorial membrane
•Outer hair cells (5% of afferent input)
•Inner hair cells (95%)
–Basilar membrane (flexible): able to be moved by vibrations and perilymph fluid
•Bending of stereocilia alters the amount of NT release from hair cells and influences the firing rate of sensory cells
-hair cells with both a single kinocilium and stereocilia on each hair cell
Outer hair cells
- responsible for mechanical amplification
- can rapidly change their length in response to vibrations of their stereocilia.
- So, there is a positive feedback of sound intensity, causing local amplification of membrane vibrations.
Inner hair cells
-detect vibrations from outer hair cells and send electrical signals to the brain
