Nakamura Human Physiology Lecture 5

Question 1

Sensory receptors

Answer 1

.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.

Question 2

Law of specific nerve energies

Answer 2

.•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

Question 3

Functional categories of sensory receptors

Answer 3

.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

Question 4

Classification of sensory receptors by rate of adaptation

Answer 4

.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)

Question 5

Receptor potentials

Answer 5

.•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

Question 6

Cutaneous sensations

Answer 6

.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

Question 7

Receptive fields on skin

Answer 7

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)

Question 8

Two point touch threshold

Answer 8

.•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

Question 9

Lateral inhibition

Answer 9

.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

Question 10

Taste and smell

Answer 10

-Receptors for taste (gustation) and smell (olfaction) are chemoreceptors
•Relationship between taste and smell

Question 11

Taste

Answer 11

-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

Question 12

Taste receptor distribution

Answer 12

• sweet: tip of tongue (anterior)
• sour: lateral sides
• salty: edge of tongue
• bitter: back of tongue (posterior)

Question 13

How we perceive salty

Answer 13

–Na+ passes through ion channels

• opens calcium channels and depolarizes the receptor cells by letting calcium in
• neurotransmitters are then released

Question 14

How we perceive sour

Answer 14

• H+ through ion channel
• opens calcium channels, depolarizes
• neurotransmitters released

Question 15

How we perceive sweet and bitter

Answer 15

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

Question 16

Smell

Answer 16

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

Question 17

Sound waves

Answer 17

.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)

Question 18

Outer ear

Answer 18

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

Question 19

Middle ear and ossicles

Answer 19

-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

Question 20

Inner ear

Answer 20

*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

Question 21

Sensory hair cells

Answer 21

.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

Question 22

Organ of corti

Answer 22

.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

Question 23

Outer hair cells

Answer 23

• 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.

Question 24

Inner hair cells

Answer 24

-detect vibrations from outer hair cells and send electrical signals to the brain

Question 25

Hearing neural pathway

Answer 25

- spiral organ of corti - vestibular nerve - medulla - cochlear nucleus - midbrain - medial geniculate body of thalamus (in thalamus, Diencephalon) - auditory cortex in temporal lobe

Question 26

Correlation btwn pitch location in the cochlea and auditory cortex

Answer 26

.different tones go to different locations in the temporal lobe - low tones lower level - high pitch, higher level - sounds of different frequencies (pitches) cause vibration of different parts of the basilar membrane, exciting different sensory neurons in the cochlea

Question 27

Visible light in EM spectrum

Answer 27

.•Photoreceptors in the retina transduce photons of light into electrical activity •Visible light within wavelengths of 400 (purple) – 700 (red) nm -gamma, X-rays, ultra violet rays before 400 -infrared, microwaves, and radio waves after 700

Question 28

Refraction

Answer 28

-Light that passes from a medium of one density into a medium of another density is bent (refracted) •Difference between refractive indices of air and cornea is large so most of the refraction occurs at the air-cornea interface •Image is inverted on retina -Refractive index: the ratio of the speed of light in air or in a vacuum to the speed of light in another medium -eye: cornea, anterior chamber, pupil, lens, vitreous humor (lots of fluid), retina. Large optic nerve

Question 29

Accommodation

Answer 29

-change of curvature (lens can be rounded or flat) -controlled by ciliary muscles •Ability of the eyes to keep the image focused on the retina as the distance between the eyes and object varies.

Question 30

Changes in lens shape

Answer 30

•Ciliary muscle can vary its aperture •Distance > 20 feet (far) –ciliary muscle Relaxation places tension on the suspensory ligament (taut) –Pulls lens taut (becomes thin and focused) –Lens is least convex •Distance decreases –Ciliary muscles contract –Reduces tension on suspensory ligament –Lens becomes more rounded and more convex (light bends more)

Question 31

Eye shape affects focusing of image

Answer 31

``` .Elongated Eye –Myopia is nearsightedness •Image brought to focus in front of retina -concave lens corrects this •Short Eye –Hyperopia is farsightedness •Image brought to focus behind the retina -convex lens corrects this •Astigmatism –Asymmetrical cornea -rays do not focus -uneven lens corrects this -emmetropia -normal vision -rays focus on retina ```

Question 32

Photoreceptor neurons

Answer 32

Single layer of photoreceptor neurons –Rods- Dim light, B&W vision, 120 million per eye –Cones- Bright light, color vision, 6 million per eye

Question 33

Pathway of retina processing

Answer 33

-Light travels through vitreous humor to ganglion cell layer, to bipolar cell layer, to photoreceptor layer -electrical pathway opposite: Photoreceptors to Bipolar cells to Ganglion cells –Ganglion cell axons (1 million per eye) leave the eye as optic nerve (optic disc-no photoreceptors) –Horizontal cells and Amacrine cells provide lateral inhibition to sharpen visual response

Question 34

Retina

Answer 34

.•The output from several rods converges onto a single ganglion cell –High sensitivity/Low acuity (accuracy) -dim lights -rods most densely dispersed in regions outside the fovea centralis (few cones) •In the fovea centralis there is little or no convergence from cones to ganglion cells (each cone being connected to only one ganglion cell) -Low sensitivity/High acuity -bright lights since lower sensitivity need stronger light to reach threshold -largest density of cones -located within the macula lutea -no rods -highest focus, necessary for doing things

Question 35

Neural pathways from retina

Answer 35

-Visual field/image to retina to lateral geniculate body (LGN) to occipital lobe (visual cortex) •Right half of visual field strikes left half of retina of both eyes. •Left half of visual field strikes right half of retina of both eyes. •Left lateral geniculate body receives input from both eyes from the right half of the visual field. •Right lateral geniculate body receives input from both eyes from left half of visual field •Axons of lateral geniculate neurons (LGN) project to striate cortex (visual cortex/area 17) and visual association areas (18 & 19) -visual cortex arranged in columns. Each column represents input into either the left or right eye

Question 36

Cones and color vision

Answer 36

.Trichromatic theory of color vision –3 types of cones •Blue, green, and red •Each type of cone contains retinene associated with photopsin (conopsin) protein –Conopsin protein is unique for each of the 3 cone pigments