From Signals to sensations Flashcards
what are the senses?
SYNAPSES The senses convey specific information about some source of physical energy
Each sensory modality has a “labelled line”
Each sensory modality has specialised receptors for transduction
e.g. the pancian corpuscle
Pit Vipers and thermoreception
Can sense temperature changes as little as 0.002 degC
hearing freqiencies
elephants hear lower freq than humans and cats hear higher
what are the codes of a sensory modality?
Intensity coding
Location coding
Coding for specific object properties (colors, shapes, pitch)
what is a stmilulus and what is a sensory receptor organ?
Sensory Receptor Organs act as filters of the environment: they detect and respond to some events and not others
Stimulus event that affects the sensory organ
what are the principles of sensory coding?
Sensory systems appear to be very diverse
Yet they all solve the same task:
They convert environmental signals into neural activity that can influence the motor system of the animal
Methods for studying sensory processing:
- Psychophysics:behavioral testing to establish the sensitivity of a sensory system and the “rules” of its operation.
- Electrophysiological recording: from single neuron or small groups of neurons along the sensory pathway to find out how the neural circuitry gives rise to the perceptual abilities. 3. Neuroimaging in humans: perceptual tasks to identify the brain areas responsible.
what must be sensed?
Qualitative features such as colour or odorant à often referred to as modality- what is it?
• Quantitative features such as magnitude à often referred to as the intensity of a stimulus
• Temporal features such as duration or frequency of a signal à often referred to as the duration of a stimulus
• Spatial location of a stimulus
where is it?
Typically, all these aspects are estimated at once: a common strategy of sensory systems is to have separate neural pathways specialized for estimating different types ofstimulus features.
Visual system analyzes colour, shape and movement in different brain regions.
what are the areas of the occipital cortex?
V1: segregates pattern vision from motion signals
V2: 3D vision, seeing camouflage, more complex patterns
V3: shape perception
V4: colour area and shape perception
V5: motion area
what are the 2 main functions of each sensory system?
Detection
The detection of a signal.
Weak signals can be detected without the animal being able to finely discriminate any of its features.
Discrimination
Discrimination of some aspects of a sensory input.
This is often referred to as estimation
what is an adequate stimulus?
type of stimulus for which a given sensory organ is particularly adapted
Transducer function of receptors the process in which a stimulus energy is transduced into the electrical response
stimulus –> electrical responce –> Brain
what is sensory processing?
Sensory processingstartswithreceptorcells • A give receptor cell is specialized to detect particular energies or chemicals • Upon exposure to the stimulus, a receptor cell converts that energy intoachangeinelectricalpotentialsacrossitsmembrane • Changing thesignal àSENSORYTRANSDUCTION
how is a stimuli transduced?
The structure of the receptor determines the form of energy to which it will respond
Receptor Potential
step between the arrival of energy at receptor cell and the initiation of an action potential It is usually an EPSP
outline transductino of mechanical signals
Excitatory events:
- 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 potential reaches the threshold amplitude, the axon produces an action potential
what are the 4 stages of sensing something
Sensory transduction They transduce [transform/translate] the energy of a stimulus into a change in membrane potential
- Amplification They strengthen the energy of the stimulus The action potential conducted from the eye to the brain contains 100,000 times more energy than the few photons of light that stimulated the receptor
- Transmission Action potentials from receptors, or from neurons connected to receptors, reach the CNS
- Integration Receptors contribute to the processing of a signal. For example many receptors show sensory adaptation. This term means that they respond less during continued stimulation
explain modality as a attribute of the sesnes
The most basic mechanism for identifying the nature of a sensory input is via labeled lines
Input from the optic nerve is always interpreted by the brain as visual input
The connections of “pain” and “touch” fibers in the somatosensory system are entirely different àstimulation of either leads to the appropriate sensation
Much finer discriminations
how are receptors different based on what system they#re part of?
auditory and visual systems: a distinct 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.
somatosensory system: receptor is a specialized peripheral element that is associated with the peripheral process of a sensory neuron
What is the labeled line concept?
Messages from different senses use the same type of energy:
Action Potentials
Labeled Lines
particular neurons are at the outset labelled for distinctive sensory experience
The brain recognises the different sensations as separate and distinct:
each sensory modality sends its action potentials along separate nerve tracts
outline the intensity attribute of a sesne
estimated intensity of a stimulus is not a linear function of the actual intensity
A power law relation best describes the relation between stimulus strength and perceived stimulus intensity
increases of a weak signal generate a larger perceived increase than increases of a strong signal -the percept saturates logarithmic or power law
how are different intensities represented inside the nervous system?
A single neuron can code for stimulus intensity by changing the frequency of action potential transmitted
Only a limited range if intensities can be coded in this way
INTENSITY Multiple receptor cells acting in parallel manner provide broader range for coding the intensity: as the strength of the stimulus increases new neurons are recruited Intensity can be represented by the number of activated cells
what is range fractionation?
different receptors are specialist in particular segment (fractions) of an intensity scale
SUMMATION OF RESPONSES
outline location as a sensory attribute
LOCATION
The position of an object or event (either outside or inside the body)
Receptive fields
receptive field of a sensory neuron = a region of space in which a stimulus will alter the neuron firing rate
what is a receptive field?
Receptive field of a sensory neuron = a region of space in which a stimulus will alter the neuron firing rate
The receptor of each primary neuron can pick up information from a specific area (receptive field)
subthreshold stimuli can be summed by the secondary neuron
Receptive fields can be irregular in shape and overlap with receptive fields of other neurons
what is two-point discrimination
Each sensory receptor activates pathways that convey unique positional information
Receptivefields varyin size
Smallerreceptivefields= GREATER ACUITY
Two-point discrimination Minimum distance at which 2 points of touch can be perceived as separate
what is lateral inhibition
lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbours
Center-surround organization of cutaneous receptive fields results in lateral inhibition Serves to enhance contrast
increased sensory perception: lateral inhibition disables the spreading ofaction potentials from excited neurons to neighbouring neurons in the lateral direction
what is cortical magnification
In our somatosensory cortex our fingertips have representations that are disproportionally large compared to the skin surface area that is not clearly explained by innervation patterns. The large representations of our fingertips is correlated with higher acuity touch in these regions. Disproportionate cortical representation of sensory surfaces is termed cortical magnification.
outline duration as a sensory attribute
Many receptors show progressive loss of response when stimulation is maintained
Tonic receptors: • produce constant rate of firing as long as the stimulus is applied • pain
Phasic receptors: • burst of activity but quickly reduce firing rate (adapt) if stimulus is maintained • sensory adaptation
Tonic= every time stimulus is applied and AP will constantly be generated till stimulus is removed.
Phasic= fire quite a lot when stimulus first applied but after a while start to be silent.
what are the ways to surpress a receptor
sensory adaption
Top Down Proccessing
what are the levels of sensory processing
Sensory information enters the CNS through the brainstem or the spinal cord
This organization is present in all sensory systems, except smell
Sensory information reaches the thalamus, which send the signals to the cortex
Primary sensory cortex swaps information with non primary sensory cortex
what is multisensory integration
Multisensory Integration:
One sensory system influences the perception derived from another sensory system
Association areas (Multisensory areas) areas that do not represent exclusively a single modality bot show a mixture of inputs from different sensory modalities
signals of two sensory modalities converge on a bimodal neuron