HSCI 365 Quiz 3 (WEEKS 4,5, and 6- Sensory Info, Vision, Hearing)

What are the parts of sensory information processing?

Input= input received by sensory receptor

Processing=  info is interpreted and stored in the brain

Response= a response generates based on the input 

What is a stimulus?

• change detectable by the body

  • Exists in various energy forms or modalities

  • Examples of stimulus modalities include heat, cold, pressure, sound, and light

Why can’t we hear with our eyes?

• There is a specialized receptor for each type of stimulus modality

  • I.e.: primary stimulus for eyes is light, but mechanical energy can also activate the same photosensitizers– some receptors can respond to different stimuli

What is sensory transduction?

• Sensory transduction is the conversion of stimulus energy into receptor potential

  • Converts stimulus into something the nervous system can recognize–nerve impulses

• Stimuli bring about receptor (graded) potentials which trigger action potentials in the afferent fiber 

Name the 6 different receptor types and describe each

• Photoreceptors

  • Respond to visible light energy

    • Generate electrical impulses that travel from the eye through the optic nerve to the brain

• Mechanoreceptors

  • Respond to mechanical energy

    • Convert mechanical pressure into electrical signals that travel to the brain

    • Skeletal muscle also have mechanical receptors which respond to stretch 

    • The most sensitive mechanoreceptors in humans are the hair cells found in the inner ear

• Thermoreceptors

  • Sensitive to heat and cold

    • Generate electrical impulses that travel from the skin to the brain

• Chemoreceptors

  • Respond to chemical changes in their environment

    • Convert chemical energy into electrical signals that travel to the brain

    • I.e.: taste buds, they can detect blood gases, detect chemical content of GI tract

• Osmoreceptors

  • Detect changes in solute concentration in extracellular fluid

    • Communicate changes in osmotic activity to the brain to regulate fluid balance

• Nocireceptors

  • Sensitive to tissue damage like burning or cutting

    • Transmitting signals about heat, cold, mechanical pressure, and chemicals that cause injury

What are the two types of sensory receptors?

• Those with a specialized ending of the afferent neuron

  • Sodium enters the cell when non-specific cation channel is activated → graded potential is created → local current flow is created in the active area and the adjacent regions which triggers the opening of more sodium channels → this triggers voltage-gated sodium channels to open→ more sodium rushes in → action potential is created that reaches the CNS

• Those with a separate receptor cell closely associated with the peripheral ending of the neuron

  • Sodium enters the cell when non-specific cation channel is activated → local depolarization (aka graded) triggers opening of voltage-gated calcium channels → Calcium enters the cell → this triggers these vesicles containing neurotransmitters to fuse with the membrane and release its contents → diffuse across synaptic cleft and will bind to chemical-gated receptor channels which also lets sodium in the cell → once sodium rushes in the cell, causing small depolarization (aka graded) which causes the voltage-gated Na+ channels to let sodium in → causes action potential to reach the CNS

Describe action potential direction based on neuron type

• Afferent= action potential is near the sensory receptor, away from the cell body

• Interneuron and efferent= site of action potential is at the axon hillock which is the area immediately adjacent to the cell body

How does receptor potential change in response to a stimulus?

• Stimulus alters the receptor’s permeability

  • Leads to a graded receptor potential 

• Receptor potentials may initiate action potentials in the afferent neuron

  • Mechanism is different depending on the type of sensory receptor

Can a larger receptor potential generate a larger action potential?

• NO: the magnitude of the action potential WILL NOT change, what changes is the frequency of the action potentials 

• Stronger stimulus increases the rate of action potentials

• Stronger stimulus recruits a greater number of neurons to fire

• More rapid firing means more neurotransmitter is released 

Describe the different types of receptor adaptation

• Tonic- do not adapt or adapt slowly

  • Provide continuous info about a stimulus’s duration and intensity

  • Receptor is not adapting or adapting very slowly 

    • I.e.: muscle receptors, joint proprioceptors

      • These receptors recognize spatial awareness, balance, posture

• Phasic- adapt quickly

  • Become less responsive or stop firing altogether when a stimulus is constant 

    • I.e.: Touch, pressure, olfactory receptor

Are pain receptors tonic or phasic and WHY is this important?

• Pain receptors are TONIC–meaning they adapt slowly or not at all. This is important since this is the body’s way to communicate something is wrong and needs to be healed. It is a protective mechanism to avoid in the future as well.

What are the two different types of sensory info?

Somatic- touch, pressure, pain, itch, proprioception

Special Senses- vision, hearing, equilibrium, smell, taste

What are somatosensory pathways?

Sensory receptors mainly respond to one type of stimulus (Some can respond to others (eyes have photoreceptors, sometimes will see stars from head injuries))

Somatosensory pathways are “labeled” and projected to specific cortex area 

What does “labeled lines” mean?

Series of neurons connected by synapses

• sensory receptor 

• second order sensory neuron in the CNS

• third order sensory neuron in the CNS

Important characteristics of a stimulus

Type/modality: type of receptor activated and specific pathways used

Location: location of the activated receptors; pathways for specific cortex regions

Strength: frequency of action potentials; number of activated receptors  

What is acuity?

Influenced by receptive field size and lateral inhibition—helps body and brain realize where on the body is being stimulated

What is a sensory unit?

Location of sensory receptors

Axon processes reach peripherally and centrally from the cell body

Terminals in the CNS

What is a receptive field?

region of the skin surface surrounding the somesthetic sensory neuron 

Two receptive fields stimulated by the two points of stimulation: two points felt (region with small receptive fields)

Only one receptive field stimulated by the two points of the same distance apart: one distance felt (region with large receptive field)

Ex: The calf vs fingertip

• The fingertip has smaller receptive fields since it is better at perceiving the world 

What is lateral inhibition?

• Enables the localization of a stimulus site for some
  sensory systems
  • Information from afferent neurons with receptors at
  the edge of a stimulus is inhibited compared to
  information from afferent neurons at the center
  • Enhances the contrast between the center and
  periphery of a stimulated region, increasing the brain’s
  ability to localize a sensory input
  • Exact localization is possible because lateral inhibition
  removes the information from the peripheral regions

Sensation vs Perception

Sensation- initial detection of stimuli by sensory organ

Perception- brain organizes and interprets leading to conscious awareness of surroundings

Describe perception

• Humans have receptors that detect limited number of energy forms
  • Response range is limited
  • During pre-cortical processing some
  stimuli are accentuated, suppressed, or
  ignored
  • Cortex compares sensory info with other incoming info, memories, and will fill in or distort info to abstract a logical perception
  

Factors that affect perception

• Sensory receptor adaptation, afferent pathway
processing
• Emotions, personality, prejudices, experience
• Motivation
• Lack of receptors for certain stimuli
• Damaged neural pathways
• Drugs
• Mental illness such as schizophrenia

What are the four components of vision?

• Optimal component- focuses the visual image on the receptor cells 

• Neural component- transforms the visual image into a pattern of graded and action potentials

• Central (what we focus on straight ahead) and peripheral vision (side)

Summarize vision BREIFLY

• Light enters through pupils → light rays are focused on retina photoreceptor cells → photoreceptors transform light energy into electrical signals → image is transmitted and processed until it is consciously perceived 

Describe the outer, middle, and inner parts of the eye

• Outer- sclera, cornea

• Middle- choroid, ciliary, body, iris

• Inner- retina

Describe the sclera

• Connective layer forms the white part of the eye

• Protects the inside of the eye 

Describe the cornea

• Transparent

• Light rays pass through here into the interior part of the eye

Describe the choroid

• Middle layer of the wall of the eye

• Highly pigmented

• Filled with blood vessels that bring oxygen and nutrients to the retina

Describe the ciliary body

• Specialized anterior portion of choroid

• Capillary network makes aqueous humor (5 mL/day) that drains via Canal of Schlemm into blood 

Describe the iris

• Thin, pigmented smooth muscle (eye color)

• Controls the amount of light that enters

• Radial muscles and circular muscles 

Describe the retina

• Outer, pigmented layer, inner nervous system layer (rods and cones)

• Converts light from the lens into nerve impulses

• Pigment absorbs light to prevent scattering

Describe the optic disc

• Blood vessels carry blood, oxygen, nutrients to the eye

• Axons of ganglion cells form optic nerve

• Transmits electrical impulses from the eye to the brain 

  • Blind Spot

    • Point on retina in which the optic nerve leaves and blood vessels pass (optic disc)

    • Lacks photoreceptors

Describe the lens

• Clear part that receives light that enters the eye

• Bends and focuses light rays onto the retina

Describe vitreous humor

• Transparent gel that gives the eye its shape 

Describe aqueous humor

• Clear watery fluid carries nutrients for the cornea and lens which lack a blood supply

Describe what happens in glaucoma

• Excess pressure will compress/damage the retina and optic nerve

• Neurons carrying info from the peripheral visual fields are damaged first 

Describe the field test

• Procedure used to assess peripheral vision (automate, kinetic)

• For automated, patient sits looks at a central target. Small lights appear at various locations in the periphery, and the patient presses a button when they see them 

Describe tonometry

• Procedure used to measure fluid pressure (air puff, rebound)

• For air puff, measures how much your cornea flattens in response to a puff of air 

How does the iris process light?

• Iris controls the amount of light entering

  • Thin, pigmented, smooth muscle

  • Forms ringlike structure in the aqueous humor 

    • Controls amount of light entering by constricting or dilating

Describe the circular and radial muscles and their function

• Circular muscles

  • Constricting muscles 

  • To constrict pupil, circular muscles are responsible under parasympathetic activation

  • In bright light, pupils will constrict

• Radial muscles

  • Dilating muscle

  • Under sympathetic activation

Briefly describe the electromagnetic spectrum and what light we are able to see

• Light is a form of electromagnetic radiation. Photoreceptors are only sensitive to a small portion of the total spectrum (400-700 nm) 

• Short waves= cosmic (aka short)

• Long waves= radio

• Our photoreceptors are only sensitive to a small portion (400-700 nm)

How do the cornea and lens refract light to focus on an image?

• Forward movement of light (light ray) → our eyes will bend the light to focus it on the retina 

• Structure responsible for bending the light rays is cornea and lens

  • Cornea does not change its shape, but the lens is able to change its shape to distinguish sources or near and far light

• Convex (outward) brings light rays closer together into a focal point

• Concave (inward) spreads light rays farther apart

What is the function of the aqueous humor in terms of refracting light?

• Light travels fastest through air → in fluid sources, it slows down 

  • Between cornea and lens is aqueous humor (watery like) → if light enters eye, aqueous humor will slow down which plays a significant role in refracting of light 

Describe the difference and how light changes for a distant light source vs near light source

• Distant light sources (will be parallel by the time it reaches the eye)

  • Can be focused at a focal point 

• Near light source (radiating upward or downward by the time it reaches the eye)

  • Focal point is much further back since light is not parallel → therefore, we need to adjust the focal point so its where the distant light source focal point is → lens changes shape so its wider and stronger to focus near light rays on the same focal point as those that are coming from distant light rays → called Accomodation

Describe accomodation

• Accomodation

  • Ciliary muscles increases lens strength (relax or contract) for near vision 

  • Suspensory ligaments connects to lens and ciliary muscles 

    • Relaxed= ligaments are very tight which keeps the lens in a flattened/weak shape 

    • Contracted= ligaments are loosened which allows lens to round which makes the lens stronger to refract the light 

Describe near-sightedness/myopia

• People can see better near, rather than far

• The eyeball is too long or the lens is too strong

• If the eye is too long → far light sources when entering lens will be focused too far away from the retina, ahead of the photoreceptors, so image is not clear 

• Near source → eye does not need to accommodate since the light source coming from near will focus directly on retina 

• Correction: concave lens will diverge light rays so that your eye will be able to allow light at the retina (focal point)

Describe far-sightedness/hyperopia

• People can see better far, rather than near

• The eyeball is too short 

• They can see far since they have the ability to accommodate so that it can focus on the back of the retina where the photoreceptors are

• Near source → eye ball is too short and light is focused past the retina 

• Convex lens: converge light rays before they reach the eye so that your eye is able to focus them back on the retina 

Describe where is the direction of light (photoreceptors, rods and cones)

Retinal cells convert light stimuli into electrical
signals for the CNS
• Outer layer of photoreceptor cells (rods and
cones) that face the choroid
• Middle layer of bipolar cells and their
interneurons
• Inner layer of ganglion cells which axons form
the optic nerve

Light passes through many retinal layers before reaching photoreceptor cells in all areas except the fovea

Describe the retinal cells

(INNER) Ganglion cell —> amacrine cell —> bipolar cell —> horizontal cell —> photoreceptor cells (cones and rods) (OUTER)

Describe the fovea

Pinhead-sized
depression in the exact
center of the retina
• Bipolar and ganglion
cell layers pulled aside
so that light strikes the
photoreceptors directly
• Only cones are found
here, so it is the point of
most distinct vision

Describe the macula lutea

Area immediately surrounding the fovea
• Also has high cone density but has less acuity
because of overlying bipolar and ganglion cells

Describe macular degeneration

Characterized by the loss of photoreceptors in the macula lutea with advancing age
• Loss occurs in the middle of visual field so left with less distinct peripheral vision

Describe night blindness

One of the most common causes of night blindness is dietary vitamin A deficiency
• Retinal is vitamin A derivative, which is required for photopigment synthesis
• Rod and cone photopigment levels are reduced but there is enough cone photopigment to respond to bright light
• Modest photopigment reductions can decrease rod sensitivity so much that they cannot respond to dim light
• The person can see in day using cones but cannot see at night because rods are not functional

Describe color vision and the trichromatic theory

Color perception depends on ratio of
stimulation of the 3 cone types and their
photopigments

Describe color blindness

• Defects in color vision result from recessive
mutations in genes encoding the cone pigments
• Most common form of color blindness, red-
green color blindness, predominantly in men,
affecting 1 in 12 (1 in 250 women)
• Either lack the red or green cone pigments
entirely or have abnormal forms
• The discrimination between shades of these
colors is poor

Briefly describe how light passes through the retina and to photoreceptors

• Light will pass in one direction through the cornea → lens → photoreceptors in the retina → rods and cones conduct phototransduction → cones are responsible for color vision → bipolar cells and amacrine cells have their own special responsibilities → bipolar cells synapse to ganglion cells, and ganglion cells have axon terminals that make up optic nerve 

Describe the structure of rods and cones

• (Rods same as cones)

• Outer segment contains sacs that have photopigments (what is absorbing light)

• Inner segment contains cells metabolic machinery (rich in mitochondria)

• Synaptic terminals have bipolar cells and ganglion cells

Describe Opsin and Retinal

• Opsin (plasma membrane protein) and retinal (absorbs light)

  • Retinal changes chemically when activated by light

Describe the relationship between photoreceptors and light

• Photoreceptors are inhibited by light

  • Photoreceptors are inhibited by light (hyperpolarized)

  • Excited in its absence (depolarized)

How does photoreceptor activity work in the dark?

• Rhodopsin is photopigment in rods

• In the dark, retinal is in the 11-cis conformation which fits into the binding site within opsin (retinal fits nicely within opsin which is the integral membrane protein in the plasma membrane of the discs)

• Chemically gated Na+ channels in outer segment respond to cGMP second messenger → cGMP is high, so Na+ channels are open → Na+ goes in and depolarized the cell → Depolarization keeps Ca2+ channels open → Ca2+ entry triggers neurotransmitter (glutamate) release → further processing by bipolar and ganglion cells 

• Further Retinal Processing 

  • Glutamate release in the dark:

    • Hyperpolarizes on-center bipolar cells, decreasing neurotransmitter release to on-center ganglion cells

    • Depolarizes off-center bipolar cells, increasing neurotransmitter release to off-center ganglion cells 

How does photoreceptor activity work in the light?

• Light causes conformational change to all-trans-retinal → This is the only light dependent step → Retinal no longer fits in opsin, opsin changes shape (membrane-bound opsin is similar to GPCR) → photopigment is activated → photopigment activation activated transducin (G protein) → transducin activates phosphodiesterase which degrades cGMP (to GMP) → This closes ligand-gated Na+ channels, stops depolarizing Na+ now cell hyperpolarizes → hyperpolarization closes voltage-gated Ca2+ channels, reduces neurotransmitter (glutamate) release → further processing by bipolar and ganglion cells

• Retinal is Recycled

  • Active photopigment quickly dissociates into opsin and retinal → retinal converted back to 11-cis form → Retinal is recycled and rejoined with opsin, back to inactive conformation  

• Further Retinal Processing

  • Glutamate decreases in light:

    • Depolarizes on-center bipolar cells increasing neurotransmitter release to on-center ganglion cells

    • Hyperpolarizes off-center bipolar cells decreasing neurotransmitter release to off-center ganglion cells

Which retinal cells generate graded potentials?

Photoreceptor cells and bipolar cells

Which retinal cells generate action potentials?

Ganglion cells

Describe on center and off center ganglion cells

• Action potentials do not initiate until ganglion cells are stimulated

• On- and Off-center cells have different receptive fields

• This patterns aids how we detect contrast and edges in visual scenes 

  • On-center= center is excited by light and the surroundings are inhibited by light

  • Off-center= center is inhibited by light and surroundings are excited by light 

Describe horizontal and amacrine cells

• Horizontal cells are between photoreceptors and bipolar cells

  • Modify glutamate release from adjacent photoreceptors

• Amacrine cells between bipolar and ganglion cells 

  • Modify bipolar cells, mostly inhibitory (GABA, glycine) 

Describe rods and cons

• Rods provide indistinct gray vision at night; cones provide sharp color vision during the day

  • Cones have lower sensitivity to light and are only activated in bright daylight

  • Cones have higher acuity than rods

  • Cones provide color vision whereas rods provide vision in shades of gray  

Describe sound

• Neural perception of sound energy

• Sound waves are vibrations of air

• Ears convert sound waves in the air to neural signals for your brain to perceive 

Formation of sound waves and the three components making up sound

• Regions of high and low pressure

• Disturbed air molecules disturb adjacent ones

• When wave is too weak to disturb air, sound dies

• Waves travel best in air

• Sound characterized by pitch, intensity, timbre

  • Pitch depends on frequency

  • Intensity depends on amplitude

  • Timbre/quality depends on overtones

    • Pure tone (like on a tuning fork with no overtone)

    • Same loudness, same note, but the wave superimposed on the wave is different 

Describe ear from outer to inner ear briefly

• Outer ear → ear canal → middle ear (contains eardrum) → inner ear (contains eustachian tube → cochlea → and auditory nerve)

Describe the outer ear

• Collects and channels sound energy. It includes the auricle/pinna, the visible portion of the ear. The pinna acts as a funnel that directs the sound deeper into the ear 

Describe ear canal

• A passageway and amplifier for sound waves. It is a tube that runs from the outer ear to the middle ear

Describe eardrum

• Also called the tympanic membrane, is a thin layer of tissue that separates the outer ear from the middle ear. The eardrum vibrates when struck by sound waves

Describe eustachian tube

• Equalizes the air pressure between the inner and outer surfaces of the ear drum 

Why is equal pressure important for the tympanic membrane? How does yawning, swallowing, or chewing gum help during flights?

• For it to vibrate normally, the air pressure on both sides of the eardrum (external ear canal and middle ear) must be equal.

• If the pressure is unequal, the eardrum can’t move freely

• Trying to equalize the pressure because the eustachian tube is connected to the throat. Open the eustachian tube because it is usually closed.

Describe the middle ear

• The middle ear contains three ossicles, which are tiny bones that transfer the vibrations from the eardrum to the inner ear

  • Malleus, Iccus, Stapes (Hammer, Anvil, Stirrup)

Describe the inner ear

Also called the labyrinth, is responsible for the body’s sense of hearing and balance. It is called a labyrinth because of its complex shape

Describe the cochlea

• Snail-shaped hearing organ made up of three chambers that spiral around a bony core. The hair cells inside the cochlea detect sound and send the information through the cochlear nerve

Describe the auditory nerve

• Cochlear nerve as well. It runs from the cochlea to the brain stem and transforms the sound vibrations into electrical impulses sent to the brain

What does the cochlea contain?

• The cochlea contains the organ of Corti, the sense organ for hearing 

  • Fluid in scala tympani, vestibuli is perilymph

  • Fluid in cochlear duct is endolymph, secreted and recycled by stria vascularis

    • Scala tympani and scala media have fluids that have unique ionic compositions that aid hearing

    • Layer of cells (stria vascularis) produce and recycle endolymph

  • Organ of Corti is in the basilar membrane

    • There are hair cells which are receptors for sound  

  • The most sensitive mechanoreceptors in humans are the hair cells found in the inner ear

What do the auditory hair cells do?

• Auditory hair cells are the receptors for sound energy (15,000 in each cochlea)

  • Basilar membrane connects the organ of corti and the organ of corti is attached to the tectorial membrane which are all held together by the inner hair cells 

  • Hair cell itself is embedded in the organ of corti 

  • Stereocilia is what is connected to the tectorial membrane 

  • Depending on direction of movement of stereocilia, it leads to depolarization or hyperpolarization 

What are the two pathways that the perilymph follows?

• Fluid movement in the perilymph set up by oval window vibration follows 2 pathways:

  • Dissipate pressure (NO SOUND RECEPTION)

    • Sound waves travel into the oval window → vibrate through the scala vestibuli around the helicotrema → causes round window below to vibrate→ helps dissipate pressure

  • Sound reception

    • Shortcut: scala vestibuli → through basal membrane → to scala tympani → triggers activation of hair cell receptors to bend → basilar membrane and tectorial membrane will vibrate and be displaced which is what moves the hair cells 

What happens when stereocilia from hair cells are bent?

Stereocilia from the hair cells are bent, opening
ion channels and causing receptor potential

• Inner hair cells= hearing

• Outer hair cells= electromotility

• Fluid movements in the cochlea
  deflect the basilar membrane

Describe the hair cell receptors

Tip links link one
stereocilium to the
side of the next
taller one
• Stereocilium bend
towards or away
from tallest one
based on basilar
membrane
movement
• Opens or closes
tip link cation
channels,
affecting receptor
excitation

• Potassium channels open causing potassium to flow INTO the cell since endolymph has higher concentration of potassium than the hair cell

Describe the hair cell receptor potential

Tip links stretch and open ion channels when stereocilia bends towards the tallest member —>more K+ enters and depolarizes the hair cell —> depolarization opens voltage-gated Ca2+ channels —> Ca2+ entry causes release of neurotransmitters —> more action potentials

Opposite is true as well when hair cells bend away from the tallest member

Do hair cells undergo action potentials?

NO:

Inner hair cells communicate via graded receptor potentials with cochlear nerve afferent fibers
• Always some firing at rest because of low-level depolarization and neurotransmitter release
• Receptor potentials lead to changes in the rate of action potentials propagated to the brain, which are perceived as sound sensations

Summarize the pathway for sound transduction starting from sound waves

Sound waves —> tympanic membrane vibrates —> middle ear bones vibrate —> oval window vibrates —> fluid movement within cochlea (—> round window vibrates —> dissipation of sound energy) —> basilar membrane vibrates —> Bending of hairs of inner receptor hair cells of organ of Corti as basilar membrane
movement displaces these hairs in relation to the overlying tectorial membrane, which the hairs contact —> graded potential changes —> changes in rate of action potentials

Describe the high-frequency and low-frequency pitches

Different regions of the basilar membrane vibrate maximally at different frequencies
• Narrow stiff region vibrates best with high-frequency pitches
• Wide flexible end vibrates best with low-frequency pitches

What happens in loud noises or high intensity sounds?

Loud noises can induce violent vibrations that shear or permanently distort irreplaceable hair cells
• Brief exposure to high-intensity sounds but also frequent exposure to moderately loud noises

What happens in deafness?

Hearing loss may be temporary or permanent,
partial or complete
• Second most common physical disability in USA
• Conductive – sound waves are not conducted
through the external and middle ear to set the
fluid in the inner ear in motion
– Physical blockage, eardrum rupture, middle
ear infections with fluid accumulation
• Sensorineural – sound waves are transmitted to
inner ear but not translated into nerve signals
– Age, exposure to loud noises, trauma