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Biology 102 > Lecture 8 - Sensory System > Flashcards

Lecture 8 - Sensory System Flashcards

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1
Q

Sensory Systems

A
  • Olfaction
  • Taste
  • Touch
  • Hearing
  • Vision
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2
Q

Chemical Stimuli

A

(chemoreceptors) Olfaction Taste

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3
Q

Mechanical Stimuli

A

(mechanoreceptors)

touch hearing

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4
Q

Electromagnetic Stimuli/light waves

A

(photoreceptors)

vision

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5
Q

Sensory Receptor Cells - Initial stimuli Conversion

A
  • convert physical and chemical stimuli into neural signals
  • stimulus causes change in neurotransmitter release
    1. sensory receptor detects stimuli and directly or indirectly opens/closes ion channels
    2. change in membrane potential –> neurotransmitter release
  • some sensory cells do not use action potentials
  • graded depolarization causes neurotransmitter release
  • released neurotransmitter can cause AP in subsequent neurons downstrea,
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6
Q

What is a sensation and how is it interpreted? How are different ones interpreted?

A
  • the sensations we perceive
  • specific sensation = which combinations of neurons are firing action potentials (smell vs round, rose vs vanilla)
  • intensity of stimulus = frequency of action potentials (how many APs fire, not which ones)
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7
Q

Olfactory Receptor Neurons

A

Location: epithelium on top pf nasal cavity

  • receptors on cilia of cells extending into nasal cavity
  • chemoreceptors
  • odorant
  • axons extend up to olfactory bulb in brain

*travel farther, DO need action potential

* humans have 20 million olfactory receptors in our nose * dogs have 1 billion

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8
Q

Olfaction

How? Process?

A
  • odorant - molecules that activate an olfactory receptor
  • olfactory receptors - sensitive for particular types of odorant molecules
  • one cell receives the stimulus and carries signal all the way to the brain

Process:

  1. Odorant binds to receptor
  2. activation of receptor causes increased levels of cAMP - second messenger (odorant stays outside)
  3. cAMP opens Na+ channels
  4. Na+ influx –> depolarization –> action potential
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9
Q

Distinctness of olfactory receptors

A

~ 350 different types in humans (mice have 1,000)

  • each receptor recognizes a unique aspect of smell
  • each type of receptor is found in a limited number of receptor neurons
  • each receptor neuron expresses just one type of receptor

*not a 1:1 relationship of smell:receptor

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10
Q

How a “smell” originates

A
  • the combined activity of multiple distinct receptors
  • more than one “odor” can activate a receptor
  • one odor can activate more than one receptor
  • almost infinite combinations
  • population coding
  • a particular smell = unique combo of receptors activated
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11
Q

Taste Receptor Cells

A

PAPILLAE - large bumps

–> each papillae has several hundred TASTE BUDS

–> each taste bud has 50-150 TASTE RECEPTOR CELLS

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12
Q

5 Basic Tastes

A

Bitter

Sour

Salty

Sweet

Umami

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13
Q

5 Types of taste receptor cells

A

Each cell recognizes one of the 5 tastes: salty, sweet, sour, bitter, umami

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14
Q

Process of Taste Reception

A
  1. cause depolarization of cell (NO action potential) (different mechanism of depolarization for each cell)
  2. depolarization leads to the Ca++ channels to open
  3. triggers neurotransmitter release onto sensory neurons
  4. sensory neurons convey the information to the brain via action potential
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15
Q

Transduction for Salty Taste

A

NaCl/Na+

type of Na+ pump that is always open

  1. increase in sodium concentration from food
  2. ions flow across this channel into receptor cell
  3. depolarization
  4. ca++ influx
  5. neurotransmitter release
  6. other cell carries signal to brain
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16
Q

Transmission for sour taste

A

H+ - sourness = acidity

  1. H+ flows in through Na+ channel (and H+ blocks K+ channel)
  2. depolarization
  3. Ca++ influx
  4. neurotransmitter release
  5. Other cell carries signal to brain
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17
Q

Transduction for bitter, sweet and umami

A
  1. molecule binds to outside
  2. activates second messengers on inside - not ion channels themselves
  3. second messengers open unique type of Na+ channel
  4. Na+ flows in = depolarization
  5. ca++ influx
  6. neurotransmitter release
  7. other cell carries signal to brain
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18
Q

Similarities and differences between bitter, sweet and umami receptors

A
  • different types of receptors, same cellular effect
  • same intracellular pathway
  • expressed on different taste cells, each connected to different target
  • for all sensory systems, end product of difference types of stimuli is always the same (neurotransmitter release)
  • matter of WHICH cells are activated
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19
Q

Population Coding (for taste)

A
  • gives us infinite flavors from 5 types of taste receptors
  • particular combination of different receptors activated (and level of activation) once again gives us large array of possible flavors
  • olfaction also influences our taste
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20
Q

Miraculin

A
  • binds to sweet receptors (but does not activate them)
  • in the presence of acid changes conformation
  • activates the receptors
  • sour food tastes sweet
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21
Q

Taste Transduction Summary

A

Salty: Na+ flows directly into Na+ channels

Sour: protons flow in through the Na+ channel and close K+ channel

Bitter, sweet and umami: receptors that are not ion channels increase levels of second messengers. these open Na+ channels

* for all: depolarization opens voltage gated Ca++ channels and causes neurotransmitter release

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22
Q

Touch

A
  • mechanoreceptors
  • physical distortion of plasma membrane causes ion channels to open
  • generates depolarization and action potential
  • diverse - generates varied sensations
  • receptors distributed throughout the body -

respond to different kinds of stimuli (touch, temperature, pain, body position)

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23
Q

Types of touch receptors

A
  • human skin packed with many different types of mechanoreceptors that generate varied sensations
  • provide different aspects of sensory information
  • sensitivity
  • rapid vs slowly adapting (change)
  • pressure and vibration
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24
Q

Spatial resolution of touch

Why more sensitive in some places?

A
  • ability to discriminate detailed features of a stimulus varies greatly across different points in the body
  • two point discrimination test
  • reasons for better resolution
    1. higher density of mechanoreceptors
    2. enriched mechanoreceptors w/small receptive field
    3. more brain tissue devoted to the sensory info of each mm of skin
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25
Q

How APs travel from skin to brain

A
  • Travel along one long axon
  • mechanoreceptors are actually located on axon
    1. stimulation induces action potential
    2. travel up spinal cord to where cell body lies
    3. axon continues on, ascending through spinal cord
    4. synapse where spinal cord meets medulla
    5. information then continues on to higher brain areas, including sensory cortex
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26
Q

Somatosensory Complex

A
  • perietal lobe, behind central sulcus Somatotopic map -homounculus (little man)
  • receptory fields of sensory neurons produce an orderly map of the body on the cortex
  • not scaled like the human body
  • plasticity –> disuse causes atrophy of a region, taken over by others –> increased use causes expansion of a region
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27
Q

What is hearing?

A

our perception of sound waves sound

  • pressure waves auditory receptors are mechanoreceptors that convert those pressure waves into changes in membrane potential
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28
Q

Parts of the Ear

A

outer ear - collects sound

middle ear - amplifies sound

  • ossicles transmit vibrations from eardrum (tympanic membrane) to oval window

inner ear - turns sound into a neural signal

in cochlea, hair cells release neurotransmitters

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29
Q

Cochlea

A
  • organ of hearing
  • composed of theee parallel canals separated by two membranes

Basilar membrane

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30
Q

Basilar membrane

A
  • transduces pressure waves into action potentials
  • contains hair cells
  • middle canal has very high concentration of k+
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31
Q

Hair cells

A
  • on basilar membrane
  • sterocilia extend out of the top
  • tips of sterocilia are embedded in over-hanging membrane
  • when basilar membrane flexes, it pushes the sterocilia up against the overhanging membrane and bends them
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32
Q

What causes basilar membrane to flex?

A
  • basilar membrane extends along cochlea
  • pressure wave from ossicles pushing on oval window causes movement o the fluid inside the cochlea
  • creates traveling waves in basilar membrane Base: narrow and stiff Apex: think and floppy
33
Q

Process

Bending of sterocilia opens mechanically gated ion channels

A
  • ion channels are at the tips of sterocilia and covered by a lid linked to other sterocilia
  • bending of sterocilia pulls lids open or pushes them closed
  • K+ influx –> depolarization
  • AT REST (straight cilial) - channel partly open (small leak of K+ in)
    1. movement of cilia in one direction
    2. tension on tip link opens channels, K+ influx –> DEPOLARIZATION
    3. cilia go other direction
    4. close tip links - HYPERPOLARIZATION
34
Q

How does depolarization induce neurotransmitter release

A
  • without action potential - hair cells do not fire action potential
  • graded depolarization or hyperpolarization
    1. depolarization causes opening of Ca++ channels
    2. cause neurotransmitter release
    3. neurotransmitter binds to sensory neuron that sends action potentials to brain
35
Q

Wave frequency corresponds with…

A

cycles of polarization and depolarization

36
Q

Frequency map in basilar membrane

A
  • different frequencies of pressure waves cause basilar membrane to bend at different locations - high frequency sounds - bend base of membrane - low frequency sounds - bend apex of membrane - which hair cells are activated informs brain about what frequency the sound is - combined with pattern of neurotransmitter release
37
Q

Cornea and lens

A
  • focus the light rays of the retina
  • muscles contract around the lens, changing its shape to focus images at different distances into our retinas
38
Q

The retina

A
  • contains the cells that detect light
  • photoreceptors
  • plus other layers of cells that help process information from the photoreceptors
  • inside-out organization
  • light must pass through all the layers of cells to reach retina
39
Q

Two types of photoreceptors

A

rods and cones stack of membranous disks containing light sensitive photopigment

40
Q

Rods

A
  • more of them
  • more disks 1000X more sensitive to light
  • low light conditions
  • one type of photopigment
  • lower acuity
41
Q

Cones

A
  • less sensitive to light
  • daylight conditions
  • three types of photopigment
  • color
  • higher acuity
42
Q

photo transduction

A

dark = depolarized light = closes Na+ channels, hyperpolarizes cell

43
Q

Rhodopsin

A

Basis for vision

  • photosensitivity is due to the fact that photoreceptor cells contain pigment call rhodopsin
  • rhodopsin absorbs photon of light and undergoes a change in shape
44
Q

Before rhodopsin activation

A

(dark) - in the dark Na+ channels are OPEN in the photoreceptor cell
1. Na+ flows in freely
2. depolarized
3. neurotransmitters released (NO AP)

45
Q

Activation of rhodopsin by light

Process

A
  • induces Na+ channels to close
    1. rhodopsin activates a cascade of second messengers
    2. second messengers cause Na+ channels to close (degrade molecules that held them open)
    3. causes hyperpolarization
    4. NO neurotransmitter release
46
Q

Transduction summary

A

dark = depolarized (neurotransmitter released)

light = hyperpolarized (NO neurotransmitter released)

47
Q

Phototransduction in cones

A
  • similar to rod phototransduction
  • 3 different rhodopsins (differ in wavelengths they absorb best, red, green, blue)
  • color detection
  • relative contributions of blue, green and red cones mix to give hundreds of visible colors

Ex: at 470, relatively equal activation of blue and green = teal

48
Q

Red/green color blindness

A

~10% of men of euro descent -

sex linked (gene for both red and green cones is on x chromosome)

  • cant distinguish green from red
  • caused by lacking either green cones or red cones
  • cannot tease apart wavelengths in the 500-600nm range
49
Q

Color vision

A
  • some animals have fewer than 3 cones (dogs have 2 - blue and yellow)
  • some animals have more than 3
  • many birds have 4
  • shrimp have 16
  • can see shades of color we cant see also infrared and UV spectra
50
Q

Flow of visual info

A
  1. photoreceptors
  2. bipolar cells
  3. ganglion cells (first action potential)

exit retina to brain

51
Q

Cerebrum

A
  • surrounds hypothalamus and thalamus
  • CEREBRAL CORTEX = outer layer
  • LIMBIC SYSTEM = in between thalamus/hypothalamus Two hemispheres: left and right
  • control opposite sides of the body
  • connected by corpus callosum
52
Q

Two hemispheres of the brain

A
  • most information is being perceived and processed simultaneously by both hemispheres
  • integrated together lateralization of some cognitive processes
53
Q

Right hemisphere

A
  • controls left side of body
  • receives inputs from the left side of the body
  • facial recognition
  • artistic perception
54
Q

Left Hemispheres

A
  • controls the right side of the body
  • receives inputs from the right side of the body
  • language
  • exact calculation and fact retrieval
  • interpret and explain
55
Q

Corpus Callosum

A
  • “white matter”
  • huge bundle of axons that connects the two cerebral hemispheres
  • allows communication between the two halves of the brain
56
Q

Results of split brain experiments

A

Right hemisphere

  • left visual field
  • cannot name object but can recognize it, point to it
  • facial recognition Left hemispheres
  • right visual field
  • can name object
  • interpret and explain
57
Q

Limbic System

A
  • emotion
  • sensation of pleasure, pain, rage, fear, memories
  • motivation and reward AMYGDALA
  • fear
  • kluver bucy syndrome: lack of fear, inability to recognize it in others HIPPOCAMPUS
  • declarative memory formation
  • transfer of information from short term to long term memory
  • patient H,M.
  • spatial learning (london taxi drivers, rats navigating mazes)
58
Q

4 Lobes of cerebrum + cerebellum

A

Frontal

  • front of head
  • motor functions, executive functions

Parietal

  • top
  • sensory info

Temporal

  • middle
  • hearing, speech, memory

Occipital

  • visual processing

Cerebellum

  • at brainstem
  • motor coordination
59
Q

Frontal Lobe

A
  • motor function: primary motor cortex
  • executive functions:
  • decision making and planning
  • attention
  • inhibition
  • personality
  • desires, intentions, beleifs

*last to mature –> why teenagers lack inhibition etc

60
Q

Parietal Lobe

A
  • sensory info: primary somatosensory cortex (especially spatial sense)
61
Q

Temporal lobe

A
  • auditory perception
  • semantics and understanding of language
  • recognizing, identifying and naming objects including faces
62
Q

Occippital lobe

A
  • visual processing
63
Q

Homounculus

A
  • Primary sensor cortex
  • primary motor cortex
64
Q

Primary motor cortex

A
  • controls muscles in specific parts of the body
  • parts of the body with fine motor control have disproportionate representation
  • if stimulated, muscle contraction in that area
65
Q

Primary somatosensory cortex

A
  • receives sensory information relayed from body through thalamus
  • areas of the body that have a high density of tactile mechanoreceptors capable of making fine discriminations of touch have large representation
  • if stimulated, person will report feeling touch/sensation in that part of the body

*plasticicity - if lose a finger, others will take up the space designated for it

66
Q

Cerebellum

A

“little brain” (smaller lump at the bottom of the brain)

  • motor coordination - controls coordination of movement (fine tuning, auto pilot)
  • receives input from the cortex about the intended movements and calculates the sequence of muscle contractions needed to achieve those intended movements
  • damage results in uncoordinated and inaccurate movements (NOT paralysis)
67
Q

Brainstem

A

vital functions, motor and sensory info 3 components: midbrain

pons

medulla

Function:

  • breathing, heart rate, blood pressure, temperature
  • reflexes such as coughing, sneezing, swallowing, vomiting
  • relays info between cortex and cerebellum
  • pathway of sensory and motor info damage –> “locked in syndrome” (paralyzed except for eyes) or death
68
Q

Thalamus

A

relay station of sensory information integrates incoming info

  • relay between subcortical areas and cortex
  • relays and integrates sensory information

*damage can lead to many different presentations

  • usually a disruption in sensory integration
69
Q

hypothalamus

A

under the thalamus, closely related to pituitary below it physiological and endocrine processes

  • links the nervous system to the endocrine system
  • regulates physiologial functions (thirst, hunger, temperature, fatiges, sleep, circadian shythms, sex hormones)
70
Q

cerebrum

A
  • corpus callosum - connect two hemispheres
  • amygdala - emotions, especially fear
  • hippocampus - formation of new memories
  • cortex - voluntary sensory and motor, higher cognition
71
Q

Brain structure

A

Bumps and grooves Bumps = gyri

Grooves = sulci

increases surface area of the cortex pack more nerves in

72
Q

Gyri

A

bumps

73
Q

sulci

A

grooves

74
Q

Major Structures of the Brain

A

“Oldest” evolutionary speaking

  • Cerbellum
  • Brainstem

Second “oldest”

  • thalamus
  • Hypothalamus
  • cerebrum (corpus callosum, amygdala, Hippocampus, cortex)
75
Q

The brain across species

A

Compare brain size versus body weight

Our brains are relatively large compared to our body weight

76
Q

Tastes that Use primary Messengers

A

Salty Sour

77
Q

Tastes that use Secondary Messengers

A

Bitter Sweet Umami

78
Q

Common to All taste receptors

A

depolarization opens voltage-gated Ca++ channels and causes neurotransmitter release

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