Chapter 6.1: Sensory Physiology

Question 1

Sensory physiology

Answer 1

perception of environment by sensory organs (ex/ears). Provides the ability to perceive incoming stimuli, learn, and respond to changes in both the internal and external environments

Question 2

sensory physiology involves the ____ division of the nervous system

Answer 2

AFFERENT division (to the CNS)

Question 3

sensory cells are specialized to perform ____; conversion of one form of energy (an external stimulus) into electrical energy that can be interpreted by a nervous system

Answer 3

transduction.

Question 4

4 types of gated channels. these opening and closing of these gated ion channels is due to the actions of ___ ___

Answer 4

4 types.

1) mechnically gated channels
2) chemically gated
3) thermally gated
4) voltage gated

closing and opening of these channels are due to the actions of receptor proteins.

Question 5

receptor protein types (7)

Answer 5

1) mechano receptors
2) chemo receptors
3) thermoreceptors
4) photoreceptors
5) electroreceptors
6) magenetoreceptors
7) nociceptors

Question 6

photoreceptors are sensitive to ____ energy, and the light activated receptor proteins turn on ___ gated channels.

Answer 6

photoreceptors are sensitive to PHOTIC energy, and the light activated receptor proteins turn on CHEMICALLY gated channels.

Question 7

3 primary roles of receptor cells

Answer 7

1) to act as INTERORECEPTORS
2) to act as proprioceptors
3) to act as exteroreceptors

Question 8

intereoreceptors

Answer 8

: detect info about the internal bodily fluids cruciial for homeostasis

Question 9

proprioceptors

Answer 9

sends info about body position and movement

Question 10

exteroreceptors

Answer 10

classic senses (taste, touch, sight) that allow us to sense EXTERNAL environments.

Question 11

exteroreceptors are involved in ___ sensation: senses arising mainly from the bodily surface, as well as ___ senses: taste vision and smell.

Answer 11

exteroreceptors are involved in SOMESTETHIC sensation: senses arising mainly from the bodily surface, as well as SPECIAL senses: taste vision and smell.

Question 12

What is perception?

Answer 12

an animal’s interpretation of the external world, created by the brain from a pattern of nerve impulses delivered to it from sensory cells.

Question 13

How is an animal’s perception limited?

Answer 13

limited by the function of their senses, past experiences, and processing capabilities.

Question 14

A receptor is typically a ___ or __ ___

Answer 14

protein or whole cell.

Question 15

A receptor cell may be located on two different locations:

Answer 15

1) on an afferent neuron with a speciailized dendrite

2) on a separate cell closely associated with a dendrite on an afferent neuron.

Question 16

change in conformation of a protein activates ___ _____ pathways within the ___ ___, resulting in a change in membrane potential.

Answer 16

change in conformation of a protein activates SIGNAL TRANSDUCTION pathways within the SENSORY RECEPTOR, resulting in a change in membrane potential.

Question 17

magneto receptors open ___ gated channels

Answer 17

mechanically gated channels.

Question 18

electro receptors open ____ gated channels

Answer 18

leak or voltage gated channels.

Question 19

What is a receptor potential?

Answer 19

local depolarizing change in potential when the receptor is a separate cell (closely associated with a dendrite on an afferent neuron).

Question 20

What is a generator potential?

Answer 20

a local depolarizing chnage if the receptor itself is a specialized afferent neuron.

Question 21

the stronger the stimulus, the ____ the permeability change and the____ the potential.

Answer 21

The GREATER the permeability change and the LARGER the potential.

Question 22

T/F receptor and generator potentials do not have refractory periods.

Answer 22

TRUE. this allows for SUMMATION and thus larger potential changes in order to convey strong stimuli

Question 23

Outline the mechanism of a receptor potenital

Answer 23

1) in sensory receptors that are separate cells, stimulus opens STIMULUS SENSITIVE CHANNELS, permitting net Na2+ entry that produces receptor potenital
2) this local depolarizaiton opens VOLTAGE GATED Ca2+ channels
3) Ca2+ entry triggers exocytosis of NTs
4) NT binding opens CHEMICALLY GATED receptor channels at the AFFERENT NEURON ending, permitting net Na+ entry in the afferent neuron
5) Resultant depolarization opens voltage gated Na+ channels in adjacent region
6) Na+ entry intiates action potential in afferent fiber that self propagates to CNS

Question 24

5 Properties of sensory receptors

Answer 24

1) perceive stimuli; approrpaite receptor must be used for stimulus type, must be able to ignore inappropriate stimuli and be sensitive to a specific change in the environment.
2) transducer. Perceived stimulus must be translated into a CHANGE IN MEMBRANE POTENTIAL
3) Amplification. Requires the use of strored potential energy

4) Response and Impulse Conduction.
- receptor must act on incoming signal, resulting in a change of RATE OF FIRING.

5) Integration: the signal must be integrated and INTERPRETED by the CNS.

Question 25

T/F: Receptor and generated potentials are all or none

Answer 25

false. they are not. stonger stimulus leads to a stronger response.

Question 26

T/F: receptor and generated potentials are self propagating.

Answer 26

false. they are not self propagating. they decay with time and distance. To have an effect, they MUST cause change in frequency of an afferent neuron FIRING RATE.

Question 27

Stimulus is intensity is distinguished by 2 codes:

Answer 27

1) frequency code: frequency of action potentials generated in the afferent neuron
2) population code: the numbers of receptors activated within the area. Stronger stimuli affect larger areas.

Question 28

What is the mechanism for a recepto potential?

Answer 28

1) in sensory receptors that are specilized afferent neuron endings themselves, stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential
2) local current flow between depolarized receptor ending and adjacent region opens voltage-gated Na+ channels
3) Na+ entry initiates action potential in afferent fibers that self propagate to CNS.

Question 29

Adaptation

Answer 29

when receptors diminish the extent of their depolarization despite sustained stimulus strength.

Question 30

Tonic receptors. Where can you find them?

Answer 30

receptors that do not adapt to sustained stimulation. Seen in muscle stretch proprioreceptors (measures muscle length) or joint proprioceptors (measures degree of joint flexion)

Question 31

Phasic receptors. Where can you find them?

Answer 31

receptors that quickly adapt and stop responding to a maintained stimulus. Seen in tactile receptors.

Question 32

which kind of receptor would you see an off response in ?

Answer 32

off response: response with a slight depolarization when the stimulus is removed. Seen in some phasic receptors.

Question 33

Why are phasic receptors important?

Answer 33

brains have a limited sensory processing capabilities and phasic receptors prevents the brain from being overloaded with too much info.

Question 34

Adaptation happens by 2 regulatory mechainsms:

Answer 34

1) intrinsic mechanisms

2) extrinsic mechanisms

Question 35

intrinsic mechanisms involves ____ and ___ intrinsic components. Explain an example

Answer 35

involves MECHANISCAL AND ELECTROCHEMICAL intrinsic components.

Seen in Pacinian Corpuscles. PC has speciailized receptor endings that consist of concentric layers of connective tissue wrapped around the TERMINAL of an afferent neuron.

As a stimulus continues, pressure energy is dissapated because it causes layers to slip, removing the physical effects of applied pressure.

The underlying afferent terminal is no longer responsive to stimulus because of the layers of connective tissue.

Question 36

Extrinsic adaptation mechanism is seen in ___ hearing. Explain the mechanism

Answer 36

adaptation hearing. Sound vibrations are detected in hair cells, which release NTs to an afferent neuron.

The brain has an EFFERENT neuron that connects to the afferent. The efferent neuron releases GABA, suppressing the signals.

This allows you to ignore WHITE NOISE.

Question 37

extrinsic mechanisms of adaptation can be modulated by ___

Answer 37

attention. If you focus on white noise, you will hear it for example.

Question 38

Adaptation is a receptor adjustment in the ____, whereas Habituation involves ____ in ___ ___ in the CNS.

Answer 38

Adaptation is a receptor adjustment in the PNS, whereas Habituation involves Modification in SYNAPTIC DIFFERENCES in the CNS.

Question 39

3 reasons why receptor adaptation is significant

Answer 39

1) enhancement of RANGE: perceive new stimulus against various backgrounds
2) improvement of sensation of change
3) reduces trivial input.

Question 40

intensity is encoded on the AFFERENT NEURON by changes in frequency of __ ___

Answer 40

Action potentials.

Question 41

dynamic range

Answer 41

the range in intensity a receptor has that it can use to encode stimuli.

Question 42

5 Limitations to receptor responses

Answer 42

1) minimum stimulus (threshold intensity) required for any response may be saturated
2) there is a compromise between the magnitude of effective range versus the ability to resolve or discriminate any stimulus.
3) finite number of ion channels limits the current flow and thus voltage change.
4) equilibrium potentials: magnitude of potential change on receptor current can only flow so much before reaching equilibrium
5) there is a maximum frequncy of APs on afferent neurons! (even if the separate receptor cell is generating a huge amount of depolarizing stimuli); the refractory period is a limiting factor.

READ NOTESE ON THIS!! LOOK AT GRAPHS

Question 43

what is threshold detection

Answer 43

the weakest stimulation that produces a response in a receptor 50% of the time.

Question 44

At receptor saturation, there is _____ to intensity.

Answer 44

no change in PERCEIVED stimulus intensity because there is NO MORE CHANGE in AP FREQUENCY.

Question 45

Determinants of receptor saturation

Answer 45

1) finite Number of ion channels
2) equilibrium potentials
3) maximum frequency of APs on afferent neurons.

Question 46

Range Fractionation. Draw graph.

Answer 46

several receptors can work together to provide fine discrimination across a wide range of stimulus intensities. Gives high sensitivity to wider stimulus range

see notes for graph.

Question 47

2 main methods for dealing with receptor threshold limitations

Answer 47

1) range fractionation

2) logarithmic encoding

Question 48

Logarithmic encoding uses a ___ receptor that gives a ___ responds to stimuli

Answer 48

SINGLE receptor (unlike range fractionation, which uses multiple receptors) that gives a GRADED response to stimuli.

Question 49

in logarithmic encoding, there is a large increase in the response to changes in stimulus intensity when stim intensity is ___

Answer 49

LOW. (there is also a limited increase in response when stimulus intensity is HIGH, even if it still a very large change.

Question 50

Each somatosensory pathway is labelled according to ___ and ____

Answer 50

modality and location.

Question 51

Afferent info in the spinal cord car either become part of a __ ___ or be relayed upward to the brain via ___ ___ (or both)

Answer 51

Reflex arc, or be relayed upward to the brain via ASCENDING PATHWAYS

Question 52

Lebelled lines

Answer 52

discrete chains of neurons that create a pathway to convey sensory info. These neurons are synaptically interconnected in a particular sequence to accomplish progressively more sophisticated processing of sensory info.

the brain perceives firing from a specific labelled line of neurons as the SAME regardless of what is truely causing the stimulus

ex/ the brain perceives stimuli that comes from the retinal pathway (retina, optic nerve, optic chiasm, thalamus, occipital lobe) as LIGHT, even if something POKES YOU IN THE EYE. That’s why when you get poked in the eye, you still see STARS, because your brain is processing some of the info as LIGHT due to Labelled Lines

Question 53

3 features of a stimulus that must be coded and sent to CNS

Answer 53

1) modality: type of stimulus; which is distinguished by the type of receptor activated and the specific pathway over which this info is transmitted to a particular area of the cerebral cortex.
2) LOCATION of stimulus: location of the activated RECEPTIVE FIELD and the pathway that is subsequently activated to transmit this info to the area od the somatosensory cortex representing that particular location.
3) INTENSITY of stimulus: distinguished by the frequency of APs initiated in the activated neuron, and the number of receptors that were activated.

Question 54

What is a receptive field?

Answer 54

the circumscribed region of skin surface surrounding a sensory neuron where it can respod to.

Question 55

the size of a receptive field is ___ ___ with the density of receptors in the region

Answer 55

INVERSELY PROPORTIONAL with the density of the receptors. The more receptors, the SMALLER the receptive field.

Question 56

the smaller the receptive field, the ___ its acuity and discriminative ability.

Answer 56

the GREATER its ACUITY and dsicriminative ability.

Question 57

__ ___ enhances contrast between wanted and unwanted info so that new stimuli can be precisely located

Answer 57

lateral inhibition.

Question 58

how does lateral inhibition work?

Answer 58

occurs via INHIBITORY INTERNEURONS that pass LATERALLY between ASCENDING FIBERS that serve neighboring receptive fields.

Allows you to focus on the sole receptive field being stimulated because the fields around it is being MUTED. allows for better localization.