PHYL 2041 > Lecture 7 > Flashcards

Lecture 7 Flashcards

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1
Q

Somatic (outside world + body sense) Sensory input

A

Vision
Hearing
Gustation (taste)
Olfaction (smell)
Equilibrioception (balance)
Tactile perception (touch)
Thermoreception (temp change)
Nociception (pain)
Proprioception (body conformation)

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2
Q

Visceral (inside world) Sensory input

A

Pressure, stretch (blood pressure)
Thermoreception (body temp)
Chemical changes (O2, CO2, etc)
Nociception (visceral pain)

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3
Q

Proprioception

A

Know the position of body parts with respect to each other. Like how you know where your arm is when you close your eyes.

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4
Q

sensory inputs

A

Some sensory inputs reach conscious awareness.
Some sensory inputs are used for internal functions/homeostasis.
Many inputs elicit multiple responses: reflex, homeostasis, awareness/cognition of sensory input.

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5
Q

Special senses

A

have own dedicated areas of the brain.

Vision
Hearing
Gustation (taste)
Olfaction (smell)
Equilibrioception (balance)

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6
Q

Somatosensory

A

Targeted to same place in the brain. Tactile perception (touch)
Thermoreception (temp change)
Nociception (pain)
Proprioception (body conformation).

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7
Q

Sensory neurons have what sometimes

A

Specialized afferent endings or synapses with receptor cells, they detect stimuli.

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8
Q

Sensory receptors big picture (speciliazed sensory neuron)

A

There is a stimulus thats detected and converted info into action potenial (ie. touch receptors). This happens in the first-order neuron (primary sensory afferent that come through the dorsal root ganglia) in the PNS. It then synapses with the Second-order
neuron in the CNS and etc.

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9
Q

Sensory receptors big picture (specialized receptor withsensory neuron)

A

Theres a specialized receptor cells that detects stimulus and synapses with the first-order neuron. Then it’s like the normal pathway.

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10
Q

Specialized ending

A
  1. Stimulus opens non-specific cation channel.
  2. Depolarization opens voltage-gated Na+ channels → action potenial.
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11
Q

Sensory receptors

A

receptor cells are like photoreceptors, they have receptor proteins in them.

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12
Q

Separate receptor cell

A
  1. Stimulus opens non-specific cation channel.
  2. Depolarization opens voltage-gated Ca2+ channels.
  3. Neurotransmitter release.
  4. Neurotransmitter opens ligand-gated channels.
  5. Depolarization opens voltage-gated Na+ channels → action potenital.
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13
Q

Mechanisms are different for what

A

every type of receptor

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14
Q

Stimulus intensity is encoded by what

A

action potential frequency. Stimulus of different strengths elicts depolarization of different magnitudes.

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15
Q

Stimulus intensity

A

stronger the stimulus, the stronger the receptor potenials, to higher frequencey of action potential, tomore neurotransmitter release.

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16
Q

Receptor potentials (graded potentials)

A

Stimulus intensity encoded by magnitude of
depolarization

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17
Q

Action potentials (all-or-none)

A

Stimulus intensity encoded by frequency of action potentials

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18
Q

Neurotransmitter release

A

Stimulus intensity encoded by rate of
synaptic release.

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19
Q

Tonic Receptor (slowly adapting)

A

Signal continuously while the stimulus remains on. The receptor potenial is slowly adapting/reduction in receptor potenial. Continuous information about stimulus intensity, information about stimulus duration.
Example: muscle stretch receptors
- need continuous info to maintain balance.

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20
Q

Phasic Receptor (rapidly adapting)

A

Provides information about changes in the
stimulus (intensity). The receptor potential has a big jump then returns to baseline and small bump during off response. Example: some tactile (touch) receptors - why you don’t feel your clothes all day.

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21
Q

Tonic Receptor (action potenials)

A

It keeps firing action potential more spaced out the whole time.

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22
Q

Phasic Receptor (actions potenials)

A

Only fires action potenials at the on and off parts with high instenity.

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23
Q

Receptive field

A

Area or field in which stimulus is detected by one sensory receptor.

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24
Q

Large receptor field

A

Low receptor density. Worse (one stimulus
detected) acuity/spatial
resolution. Example os forearm. Any stimulus that falls in the large receptive field sends its signal to one neuron. The cell might ot be able to tell if you were touched by two different things.

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25
Small receptive field
With smaller ones the stimulus will fall in two different ones, able to notice both. Has high receptor density, Better Acuity/spatial resolution. Example: fingertips.
26
Lateral inhibition
activated neurons inhibit their neighbors. - Reduces signaling from areas surrounding the stimulus (“receptive field surround”) - Improves acuity, edge detection, contrast - Most significant for touch and vision
27
Without lateral inhibiton
we have a stimulus here which falls within this receptive field. But maybe a little bit in these neighboring receptive fields as well. So this sensory neuron may be strongly activated, whereas the neighboring ones might also be a little bit activated.
28
With lateral inhibition
This strongly activated neuron will, in addition to its normal downstream connections, also make inhibitory connections with its neighbors, and this reduces the signaling from its neighbors. And with this scheme, we get an area around the receptive field where signaling is reduced. This is called the receptive field surround.
29
Large receptive field with lots of receptor cells
- Lower acuity/resolution - Higher sensitivity (because of pooling stimulus So we're more likely to catch some stimulus). And also because if stimuli hit these cells close enough together temporally they can sum up and help us get over the threshold depolarization required for triggering an action potential.
30
Small receptive field with one receptor cells
- Higher acuity/resolution - Lower sensitivity.
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Divergence
Parallel processing and amplification
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Convergence and divergence can happen at what levels?
- at sensory receptors - in the CNS
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Amplification
- Response triggered in multiple post- synaptic neurons. And if we trigger an action potential in each one of these, then our response will be amplified.
34
Parallel processing
- Post-synaptic neurons process info in distinct ways. Different types of downstream neurons, if they process their info in different ways then the result is parallel processing of sensory input.
35
What conditions result in better acuity?
Small receptive field, High receptive density, present lateral inhibition, no convergence.
36
Mechanoreceptors detect what?
Touch/pressure, Stretch, Fluid movement
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Touch/pressure used for?
Tactile perception
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Stretch used for?
Blood pressure regulation, Awareness of body position (proprioception).
39
Fluid movement used for what?
hearing and balance (equilibrioception).
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Thermoreceptors (mechano) detect what?
Heat and cold.
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Heat used for
Somatosensory warmth
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Cold used for?
Somatosensory cold
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Photoreceptors detect what?
Light
44
Light is used for
vision and Circadian entrainment, pupillary light reflex.
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Chemoreceptors detect what?
Chemicals (odorants), Chemicals (tastants), Partial pressure O2.
46
Chemicals (odorants) used for what
Smell (olfaction)
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Chemicals (tastants)
Taste (gustation)
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Partial pressure O2
Blood oxygenation regulation
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Nociceptors detect what?
Injurious stimuli
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Injurious stimuli used for
Pain sensation (nociception)
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How do sensory receptors actually detect stimuli?
Detect a specific type of energy/stimulus (light, pressure, sound, chemicals, etc). Then Sensory transduction to Convert energy to electrical signals. - Mechanisms are different for every receptor - Some general themes will be discussed here
52
Sensory transduction method 1 (GPCR cascade)
Ligand-binding to a GPCR, then GPCR (coupled to a heterotrimmeric g protein) conformational change, GTP exchange (GDP to GTP on alpha subunit) and G-protein dissociation, then Gα, Gβγ, or second messengers then Channel conformational change (opening or closing), finally Change in membrane potential.
53
Sensory transduction method 1 (GPCR cascade) examples
some taste receptors (sweet, bitter, and umami), olfactory receptors, photoreceptor
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GPCRs in photoreceptors
Rhodopsin in rods. Detects light and activates a G protein.
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G protein in rhodopsin
It's called transduction
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GPCRs in sweet taste receptors
A heterodimer of Tas1R2 and Tas1R3. Binding of any ligand that activates the sensory transduction pathway will result in perception of a sweet taste. So any molecule that can bind here and activate is this GPCR dimer, resulting in sensory transduction, in the receptor cell, is going to result in the perception of a sweet taste.
57
Sensory transduction method 2 (Mechanosensitive ion channel)
Physical distortion of membrane and/or ion channel protein. Channel conformational change (opening or closing). Change in membrane potential. Ex: mechanoreceptors, thermoreceptors.
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TRPV1 channel in heat and pain receptors
- Member of the Transient Receptor Potential (TRP) family. - Nonselective cation channel. - Detects heat by a mechanosensitive mechanism. - Can also be activated by chemical ligands. It's easier to determine the structure of a protein in a presence of a ligand. Closed conformation is closed at selective filter and lower gate. With capsaicin: Open lower gate. What makes peppers hot. With two toxins: Fully open Permeation pathway is where cations go through.
59
PIEZO channels in mechanoreceptors
Touch, proprioception Internal sensing (blood pressure, bladder stretch). Detect mechanical force by detecting changes in currative of the membrane which makes the channels open. It's a huge protein with 38 transmembrane helices in each subunit.
60
Cross-talk of sensory systems Most sensory receptors are specific for a particular stimulus type. But...counterexamples
Ion channel in heat receptors (TRPV1) also activated by capsaicin. Ion channel in cold receptors (TRPM8) also activated by menthol. At the level of afferent sensory neurons, all the signals look the same (electrical)- that’s why spicy pepper feels “hot” and menthol feels “cold.” Can elicit sensory perception with electrical stimulation of the right neurons.
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Counterexamples: Polymodal receptors
Some thermoreceptor cells detect both hot and cold (bimodal). Glomus cells in carotid body detect multiple blood parameters. Mechanisms still unclear, but cells likely have multiple transduction pathways that detect different stimuli.
62
Somatotopic map:
Correspondence of locations on body to locations in somatosensory cortex. - Some body parts are allotted more “space” in the somatosensory cortex - Cortical representation corresponds to innervation density / receptive field size - Maps vary between individuals and change dynamically with experience, use. Hands and lips have most space.
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Primary somatosensory cortex
Where somasensory ingo goes to.
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Ascending somatosensory “awareness." Example: holding a hot coffee cup.
Thalamus: awareness of something hot touching you somewhere. Then to Somatosensory cortex: localizes source to hand/fingers, intensity of heat. Then to Other higher sensory areas: more elaboration, analysis, integration – texture, firmness, shape, comparison to memories of other cups.
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WHAT IS ERY IMPORTANT TO KNOW
VIUSAL PATHWAYS. retina to optic nerve to primary visual cortex.
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Retinotopic map:
Correspondence of locations in visual field to locations in visual cortex. Central retina (macula) has larger representation in the visual cortex. - Cortical representation reflects receptive field size.
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Dynamic stimulation of visual cortex produces form vision in sighted and blind humans
Electrodes on blind people and stimulate the area make them see it. Taking advantage of: 1. Electrical stimulation of sensory neurons elicits sensory perception 2. Retinotopic map in the visual cortex
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Tonotopic map
Correspondence of frequency sensitivity in cochlea to locations in auditory cortex.
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Photorecptors dont produce whst?
action potentials.
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The spinal cord has what?
Meninges and the cerebal spinal fluid.
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Hz
Is the inverse seconds sec. sec-1. Cycles per seconds. or anything per seconds.
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Color vision:
Humans have three cone types (R, G, B) but can discriminate ~1,000,000 colors - Differential activation of three cones
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Gustation:
Humans have five primary receptor types (salty, sour, sweet, bitter, umami) but can discriminate thousands of tastes - Differential activation of 5 receptors + odor inputs.
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How does rich perception arise from a few receptors?
RGB image, color vision, gustation.
75
Do we perceive the world as it really is?
No. Visual detection range is limited For example, visible light is a small part of the EM spectrum.
PHYL 2041
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