6. From Signals to Sensations Flashcards
What do the senses convey specific information about?
Some source of physical energy
Each what has a ‘labelled line’ which means high level specificity?
Each sensory modality
Which receptor can only convey info to the brain when the skin is stretched?
The Pacinian Corpuscle
Each time you stretch your skin, what happens to the membrane?
It moves and opens the ion channels and triggers an AP
List 3 things that each sensory modality responds to/has
- Responds to a range of stimuli
- Has evolved to fit the animal’s need
- Has a specific set of codes
Sensory receptor organs act as filters of the environment to detect and respond to what?
Specific events
Sensory receptor organs are known as the gate between what?
The external environment and the brain
Define stimulus
Event that affects the sensory organ
Describe the task that sensory systems complete
They convert environmental signals into neural activity that can influence the motor system of the animal
What are the 3 methods of studying sensory processing?
- Psychophysics
- Electrophysiological
- Neuroimaging
Describe psychophysics
Use behavioural testing to establish the sensitivity of a sensory system and the ‘rules’ of its operation
Describe electrophysiological
Recording from single neurons or small groups of neurons along the sensory pathway to find out how the neural circuitry gives rise to the perceptual abilities
Describe neuroimaging
In humans that are doing perceptual tasks to identify the brain areas responsible
Describe qualitative features of sensory signals and what it is often referred to
Feature such as colour or odourant (often referred to as modality)
Describe quantitative features of the sensory signal and what it is often referred to
Features such as magnitude (often referred to as the intensity)
What is a common strategy of sensory systems?
Separate neural pathways specialised for estimating different types of stimulus features
What are the 2 main functions of each sensory system?
Detection and discrimination
Define detection
The detection of a signal (i.e. is the signal present)
Define discrimination
Discrimination of some aspects of a sensory input (often referred to as estimation) (i.e. is this strong)
Define adequate stimulus
Type of stimulus for which a given sensory organ is particularly adapted (essential because each organ can only detect specific stimuli)
Define transducer function of receptors
The process in which a stimulus energy is transducer into an electrical response
What type of cells does sensory processing start with?
Receptor cells
Upon exposure to a stimulus, a receptor cells can convert energy into a…
Change in electrical potential across its membrane
Define sensory transduction
Changing physical energy to electrical potentials/neural activity - when the ion channels open
The structure of the receptor determines what?
The form of energy to which it will respond
Describe receptor potential
Step between the arrival of energy at receptor cell and the initiation of an AP
The AP goes through the pathway and to the brain
Describe the 4 stages of an excitatory event (specifically in the Pacinian Corpuscle)
- Mechanical stimulation deforms the corpuscle
- Deformation of the corpuscle stretches the tip of the axon
- Stretching the axon opens mechanically gated ion channels in the membrane, allowing sodium ions to enter
- When the receptor reaches the threshold amplitude, the axon produces an AP
What are the 4 stages of sensory receptors
- Sensory transduction
- Amplification
- Transmission
- Integration
Describe the process of sensory transduction in a sensory receptor
They traduce (transform/translate) the physical energy of a stimulus into a change in the membrane potential
Outline the process of amplification by a sensory receptor
The sensory receptor will strengthen the energy of the stimulus
Outline the process of transmission by a sensory receptor
AP’s from receptors, or from neurons connected to receptors, reach the CNS - the encoding of the signal
Outline the process of integration by a sensory receptor
Receptors contribute to the processing of a signal e.g. many receptors show sensory adaptation such as, not being able to feel clothing
What are the 4 attributes of the stimulus?
Modality
Intensity
Location
Duration
The most basic mechanism for identifying the nature of a sensory input is via what?
Labelled lines
Define somatosensory system
Receptor is a specialised peripheral element that is associated with the peripheral process of a sensory neuron
Outline auditory and visual systems
A distance type of receptor cell is present. In the auditory system, the receptor synapses directly on the ganglion cell, whereas in the visual system, an interneuron receives synapses from the photoreceptor and in turn synapses on the retinal ganglion cell
How is the brain able to recognise the different sensations as separate and distinct?
Because each sensory modality sends its APs along separate nerve tracts
Define labelled lines
Particular neurons are at the outset labelled for distinctive sensory experience (fast, parallel processing)
The estimated intensity of a stimulus is _ _ __ __ of the actual intensity
Not a linear function
Increases of a weak signal generate a ___ perceived increase than increases of a strong signal
Larger
Which best describes the relationship between stimulus strength and perceived stimulus intensity, logarithmic or power law?
A power law
How many neurons does it take to code for stimulus intensity and how does it do this?
A single neuron by increasing the frequency of APs
As the strength of the stimulus increases, what happens in terms of the neurons?
More neurons are recruited as intensity increases
Define range fractionation
Different receptors are specialist in particular segment (fractions) of an intensity scale
What does the receptive field of a sensory neurone consist of?
A region of space in which a stimulus will alter the neurone firing rate
The receptor of each primary neurone can pick up information from where?
A specific area (receptive field)
If you touch the area around the centre then what will occur?
An AP will occur (EPSP)
If you touch the surrounding area, will there be an AP?
No
Smaller receptive fields =
Greater acuity
What does lateral inhibition allow us to see?
Specificity in touch in the skin
The brain can code how many different events at the same time? and what is this due to?
2 due to lateral inhibition between
Outline sensory adaptation
Many receptors showing progressive loss of response when stimulation is maintained
What do tonic receptors produce? (and give an example)
Constant rate of firing as long as the stimulus is applied (e.g. pain)
Outline how phasic receptors respond to stimuli
They have a burst of activity but quickly reduce firing rate if the stimulus is maintained
What other way can we suppress receptors? (other than sensory adaptation)
Top down processing which can change the intensity of perceived signal
Sensory info will reach which cortical area?
The thalamus which sends signals to the cortex
Which sense is the only one whereby the sensory information does not go via the thalamus?
Smell
Sensory information enters the CNS through the ___ or the ___
Brainstem or spinal cord
Where do signals of two sensory modalities converge?
On a bimodal neuron
What does synesthesia result from?
‘Cross-wiring’ in the brain
