Chapter 6.1: Sensory Physiology Flashcards
Sensory physiology
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
sensory physiology involves the ____ division of the nervous system
AFFERENT division (to the CNS)
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
transduction.
4 types of gated channels. these opening and closing of these gated ion channels is due to the actions of ___ ___
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.
receptor protein types (7)
1) mechano receptors
2) chemo receptors
3) thermoreceptors
4) photoreceptors
5) electroreceptors
6) magenetoreceptors
7) nociceptors
photoreceptors are sensitive to ____ energy, and the light activated receptor proteins turn on ___ gated channels.
photoreceptors are sensitive to PHOTIC energy, and the light activated receptor proteins turn on CHEMICALLY gated channels.
3 primary roles of receptor cells
1) to act as INTERORECEPTORS
2) to act as proprioceptors
3) to act as exteroreceptors
intereoreceptors
: detect info about the internal bodily fluids cruciial for homeostasis
proprioceptors
sends info about body position and movement
exteroreceptors
classic senses (taste, touch, sight) that allow us to sense EXTERNAL environments.
exteroreceptors are involved in ___ sensation: senses arising mainly from the bodily surface, as well as ___ senses: taste vision and smell.
exteroreceptors are involved in SOMESTETHIC sensation: senses arising mainly from the bodily surface, as well as SPECIAL senses: taste vision and smell.
What is perception?
an animal’s interpretation of the external world, created by the brain from a pattern of nerve impulses delivered to it from sensory cells.
How is an animal’s perception limited?
limited by the function of their senses, past experiences, and processing capabilities.
A receptor is typically a ___ or __ ___
protein or whole cell.
A receptor cell may be located on two different locations:
1) on an afferent neuron with a speciailized dendrite
2) on a separate cell closely associated with a dendrite on an afferent neuron.
change in conformation of a protein activates ___ _____ pathways within the ___ ___, resulting in a change in membrane potential.
change in conformation of a protein activates SIGNAL TRANSDUCTION pathways within the SENSORY RECEPTOR, resulting in a change in membrane potential.
magneto receptors open ___ gated channels
mechanically gated channels.
electro receptors open ____ gated channels
leak or voltage gated channels.
What is a receptor potential?
local depolarizing change in potential when the receptor is a separate cell (closely associated with a dendrite on an afferent neuron).
What is a generator potential?
a local depolarizing chnage if the receptor itself is a specialized afferent neuron.
the stronger the stimulus, the ____ the permeability change and the____ the potential.
The GREATER the permeability change and the LARGER the potential.
T/F receptor and generator potentials do not have refractory periods.
TRUE. this allows for SUMMATION and thus larger potential changes in order to convey strong stimuli
Outline the mechanism of a receptor potenital
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
5 Properties of sensory receptors
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.
T/F: Receptor and generated potentials are all or none
false. they are not. stonger stimulus leads to a stronger response.
T/F: receptor and generated potentials are self propagating.
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.
Stimulus is intensity is distinguished by 2 codes:
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.
What is the mechanism for a recepto potential?
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.
Adaptation
when receptors diminish the extent of their depolarization despite sustained stimulus strength.
Tonic receptors. Where can you find them?
receptors that do not adapt to sustained stimulation. Seen in muscle stretch proprioreceptors (measures muscle length) or joint proprioceptors (measures degree of joint flexion)
Phasic receptors. Where can you find them?
receptors that quickly adapt and stop responding to a maintained stimulus. Seen in tactile receptors.
which kind of receptor would you see an off response in ?
off response: response with a slight depolarization when the stimulus is removed. Seen in some phasic receptors.
Why are phasic receptors important?
brains have a limited sensory processing capabilities and phasic receptors prevents the brain from being overloaded with too much info.
Adaptation happens by 2 regulatory mechainsms:
1) intrinsic mechanisms
2) extrinsic mechanisms
intrinsic mechanisms involves ____ and ___ intrinsic components. Explain an example
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.
Extrinsic adaptation mechanism is seen in ___ hearing. Explain the mechanism
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.
extrinsic mechanisms of adaptation can be modulated by ___
attention. If you focus on white noise, you will hear it for example.
Adaptation is a receptor adjustment in the ____, whereas Habituation involves ____ in ___ ___ in the CNS.
Adaptation is a receptor adjustment in the PNS, whereas Habituation involves Modification in SYNAPTIC DIFFERENCES in the CNS.
3 reasons why receptor adaptation is significant
1) enhancement of RANGE: perceive new stimulus against various backgrounds
2) improvement of sensation of change
3) reduces trivial input.
intensity is encoded on the AFFERENT NEURON by changes in frequency of __ ___
Action potentials.
dynamic range
the range in intensity a receptor has that it can use to encode stimuli.
5 Limitations to receptor responses
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
what is threshold detection
the weakest stimulation that produces a response in a receptor 50% of the time.
At receptor saturation, there is _____ to intensity.
no change in PERCEIVED stimulus intensity because there is NO MORE CHANGE in AP FREQUENCY.
Determinants of receptor saturation
1) finite Number of ion channels
2) equilibrium potentials
3) maximum frequency of APs on afferent neurons.
Range Fractionation. Draw graph.
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.
2 main methods for dealing with receptor threshold limitations
1) range fractionation
2) logarithmic encoding
Logarithmic encoding uses a ___ receptor that gives a ___ responds to stimuli
SINGLE receptor (unlike range fractionation, which uses multiple receptors) that gives a GRADED response to stimuli.
in logarithmic encoding, there is a large increase in the response to changes in stimulus intensity when stim intensity is ___
LOW. (there is also a limited increase in response when stimulus intensity is HIGH, even if it still a very large change.
Each somatosensory pathway is labelled according to ___ and ____
modality and location.
Afferent info in the spinal cord car either become part of a __ ___ or be relayed upward to the brain via ___ ___ (or both)
Reflex arc, or be relayed upward to the brain via ASCENDING PATHWAYS
Lebelled lines
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
3 features of a stimulus that must be coded and sent to CNS
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.
What is a receptive field?
the circumscribed region of skin surface surrounding a sensory neuron where it can respod to.
the size of a receptive field is ___ ___ with the density of receptors in the region
INVERSELY PROPORTIONAL with the density of the receptors. The more receptors, the SMALLER the receptive field.
the smaller the receptive field, the ___ its acuity and discriminative ability.
the GREATER its ACUITY and dsicriminative ability.
__ ___ enhances contrast between wanted and unwanted info so that new stimuli can be precisely located
lateral inhibition.
how does lateral inhibition work?
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.