W4 L1 (Sensory Transduction) Flashcards
What is an example of a sensory input we are conscious of but then forget about?
Wearing clothes
What is sensory info used for?
For perception and to guide action
What is the PNS a link between?
The periphery and the CNS
What is the somatic and what is autonomic?
Somatic-Efferent nerves that are consciously used
Autonomic-Afferent nerves that are unconsciously used
What is another name for afferent neurons?
Sensory or receptor neurons
Do we perceive the world as it is, why or why not?
No, we don’t have receptors for everything. Our limited bandwidth also decreases with age.
How does our brain play tricks on us so that we are more functional?
Our brain often tunes out irrelevant information and adds some that aren’t there
What do out sense organs do?
Give us a useful model of the world, might not be realistic
How have howler monkeys adapted?
They gained color vision over time which aided in them seeing the more nutritious leaves
What are 4 key components of sensory physiology?
- Understand the stimulus being coded
- Understand the perception that results from varying the stimulus
- Understand how the receptor at the periphery transduces the stimulus
- Understand neural coding in the CNS
What is the method of adjustment?
A method of slowly increasing a stimulus to find a threshold
What is the method of constant stimuli?
A stimulus is transduced on a person the person says whether they can feel it or not at the given level.
What is the method of limits?
The stimuli is slowly brought from outside of the range until it just meets the threshold
Explain a descending and ascending series in the method of limits
Ascending series-Start below lower threshold and work up until detectable
Descending series-Start above higher threshold and work down until detectable
What is the staircase method?
Go from undetectable to detectable then turn around and go other direction (back and forth)
What is a psychometric function?
A model that shows when certain stimuli can be detected and at which intensities
What is the path of sensory info from receptors on the skin?
- Skin receptors
- Spinal nerve
- Spinal cord
- Brainstem
- Thalamus
- Cortex
What is the path of sensory info from receptors on the skin?
1. Skin receptors 1st order neuron (afferent) 2. Spinal nerve 3. Spinal cord 4. Brainstem 2nd order neuron 5. Thalamus 3rd order neuron 6. Cortex
What does it mean that receptor potential is graded?
It is graded based on stimulus intensity
What does receptor potential turn into?
An action potential
What 4 properties must the brain be able to distinguish between?
- Stimulus Modality
- Stimulus Location
- Stimulus Intensity
- Stimulus Duration
What is stimulus modality?
The type of stimulus
What is stimulus location?
The receptive field or coverage of a stimulus
What is stimulus intensity?
The frequency of coding
What is stimulus duration?
The time of a stimulus
How does the brain determine stimulus modality?
Each receptor is most sensitive to a particular type of stimulus. The brain thus associates a signal coming from a specific group of receptors with a
specific modality.
How does the brain determine stimulus modality?
Each receptor is most sensitive to a particular type of stimulus. The brain thus associates a signal coming from a specific group of receptors with a
specific modality
What is label line coding?
The direct association between a receptor and a sensation
How does a receptor determine the location of a stimulus?
Each sensory receptor is most sensitive to stimulation of a specific area (Receptive field)
What is a receptive field?
An area of the body, of out sight etc. that a receptor is most sensitive to
What is lateral inhibition?
A method used to give a more precise location of stimuli, it enhances the contrast between the site of stimulation
What do inhibitory neurons do?
They localize a stimulus by silencing receptors around the main point of stimulation
What happens to the level of action potentials around a central stimulated neuron when there is lateral inhibition?
The stimulated neuron is at a peak and the neurons to the sides drop below the baseline level
What do more intense stimuli lead to?
More frequent action potentials being fired
What is population coding and how is it a way to measure stimuli strength?
More neurons are activated ie. the population activated
Explain stimulus duration
Receptors can respond slow or fast to sustained stimulation (tonic or phasic)
Modality example (1)
Labeled line coding
Location example (3)
Receptive field, convergence, lateral inhibition
Intensity example (2)
Population, frequency coding
Duration example (1)
Best reflects change in stimulus
Somatosensory and receptors
Feeling, receptors all over body
Vision and receptors
Sight, rods and cones in the retina
Audition
Hearing, hair cells in cochlea
Olfaction
Smell, olfactory receptors
Gustation
Taste, taste receptors
What do tonic and phasic receptors mark?
Tonic-Ap
Phasic-On/Off
Describe the structure of afferent neurons
Long dendrite, short axon, smooth and round cell body
What is the dorsal root ganglion made up of?
Tons of afferent neuron cell bodies
Where is the primary motor cortex located?
The parietal lobe of the cerebral cortex
What is the difference between visceral and sensory afferent?
Visceral-Subconscious info from the organs inside the body
Sensory-Information that reaches our level of consciousness
What are the two types of sensory afferent categories?
- Somatic sensation
2. Special Senses
What is somatic sensation?
Arising from the body surface, including somaesthetic sensation from the skin and proprioception from the muscles, joints, skin, and inner ear; or
What are the special senses?
Vision, hearing, taste, smell, and equilibrium
What is perception?
The conscious interpretation of the external world as created by the brain from a pattern of nerve impulses delivered to it from sensory receptors
What are 3 reasons for why we don’t see reality as it is?
- Don’t have receptors for everything
- During processing, some things are ignored and some are heightened
- The cortex manipulates sensing by filling in the blanks
What is a stimulus?
A change detectable by the body that meets a minimum threshold
What is a somatosensory receptor?
A neuron with a free receptor
What is a special senses receptor?
A receptor that turns mechanical stress into electrical by synapsing onto a sensory neuron
What is transduction?
Conversion of stimuli to action potentials by sensory receptors
What are photoreceptors?
Receptors that sense light
What are mechanoreceptors?
Receptors that respond to mechanical energy (touch)
What are thermoreceptors?
Receptors that respond to changes in heat
What are chemoreceptors?
Receptors that respond to specific chemicals
What 2 things can a receptor be?
- The end of an afferent neuron
2. A separate cell closely associated with a peripheral neuron
What is receptor potential?
The graded potential change that occurs in a sensory receptor in response to a stimulus; generates action potentials in the afferent neuron fibre
What is generator potential?
The same thing as receptor potential but when the receptor is attached to the afferent neuron
Do receptors have a refractory period?
No
If a stimulus is great enough what does a receptor do?
It causes Na+ channels to open in an afferent neuron leading to an action potential
What are the 3 steps of signal transduction in a receptor that is built into a neuron?
- Stimulus opens channels allowing Na+ to enter
- Current flows between depolarized ending and opens Na+ channels down the axon
- Na+ entry leads to an AP that propagates to the CNS
What are the 6 steps of signal transduction in a receptor that is not attached to a neuron?
- Stimuli leads to Na+ entry and depolarization
- Ca2+ enters
- Ca2+ triggers exocytosis of neurotransmitters
- Neurotransmitters bind chemical-gated channels allowing Na+ to enter the fibre
- Depolarization opens Na+ in adjacent regions
- Na+ entry leads to an AP traveling to the CNS
What initiates the action potential in efferent neurons?
The axon hillock
What is adaptation?
A reduction in the receptor potential despite the same level of stimulus. Ie. The receptor responds to the stimulus by adapting to it and minimizing its signaling.
How quickly do tonic receptors adapt?
Slowly or not at all
What are tonic receptors important for?
They are important in situations where maintaining information about the stimulus is important. It is important that they don’t adapt to a stimulus but rather continue to send info to the CNS
What is an example of a tonic receptor?
A receptor that maintains posture and balance
How quickly do phasic receptors adapt?
Rapidly
What are phasic receptors important for?
They are receptors that respond and adapt (get rid of the stimuli) quickly
What is the off response in phasic receptors?
The receptor rapidly adapts by no longer responding to a maintained stimulus, but when the stimulus is removed, the receptor typically responds with a slight depolarization called the off response
What is an example of a phasic receptor?
Touch receptors ex. not conscious of wearing a ring unless it is put on or taken off
Once afferent info reaches the spinal cord what are its two options?
- Become part of the reflex arc and bring about a response
2. Be relayed to the brain for further processing
What is the first order sensory neuron?
The neuron with its receptor that first detects the stimulus
What is a secondary order sensory neuron?
Primary sensory neurons synapse onto “second order” neurons or visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract, that integrates all visceral information
What is a third order sensory neuron?
The long sensory tract that ascends in the spinal cord; found in the thalamic nuclei and transmit information from that thalamus to the primary sensory cortex
What is the receptive field?
The area surrounding a receptor at which a receptor can detect stimuli
What does acuity mean with regards to a receptive field?
Discriminative ability; the ability to discern between two different points of stimulation
What is lateral inhibition?
The phenomenon in which the most strongly activated signal pathway originating from the center of a stimulus area inhibits the less excited pathways from the fringe areas by means of lateral inhibitory connections within sensory pathways
List the 5 types of mechanoreceptors
- Pacinian corpuscles
- Meissner’s corpuscles
- Merkel’s discs
- Ruffini corpuscles
- Free nerve endings.
What do Pacinian corpuscles respond to?
Touch and deep pressure
What do Meissner’s corpuscles respond to?
Light touching
What do Merkel’s discs respond to?
Low-frequency vibrations
What do Ruffini corpuscles respond to?
Stretch or torque
What do free nerve endings respond to?
Touch, pressure, pain
