6a. Sensory systems

Artistic expresion is a fundamental human behaviour

“My Grandmother’s Country” paiting is more than just intuitive or purely aesthetic use of lines, colours and dots - it is a reflect of cultural and social norms, use of symbols and colours for visual story telling

Oldest prehistoric art form

Rock art which dates back to Palaelithic period (50,000 to 12,000 years ago)

Examples of art and architecture in animals

Nest ornaments found in fish, sand gobies, raports, owls, stingless bees

What was the study used to measure perception

Many stimulus were used such as detection, discrimination, magnitude estimation and mathing. People were asked different questions relating to comparing or finding dots

Psychophysics

The origins of psychology as experimental science mid 19th century

Weber’s law

Descrives just noticeable differences

Fechner’s law

Intensity of a sensation increases as the logarithm of an increase in energy

Steven’s law

Perceptual intensity increases as the n-th power of stimulus intensity

Srnsory systems

Structures containing receptor neurons, their specialised sensory interneurons and other projection layers of neurons that are specialised for detecting and processing particular types of sensory stimuli

Transduction

Receptor cell transforms stimulus energy into neural signal

5 types of sensory systems

1. Mechanical

2. Visual

3. Thermal

4. Chemical

5. Electrical

Sensory receptor neurons

• Are specialised neurons that detect internal and external stimuli of a particular sensory modality

• The receptor neuron’s input zone usually contains accessory structures, receptor molecules and/or specialised ion channels instead of dendrites

• They trnasform stimulus energy into neural signals (=transduction) that are transmitted to sensory interneurons

• They filter stimulus energy becuase they have a defined affinity and sensitivity range

GBA (gut-brain axis)

Bidirectional communication via vagus and spinal nerves, not only to maintain gut homeostasis but also regulating brain functions

ENS (enteric nervous system)

Mesh like system of neurons that governs the functioning of the gut - supports local muscle reflexes for gut motility

Receptor thresholds

Receptors respond to a stimulus within a limited range of stimulus intensities

When there are two different low intensity stimuli…

… the low threshold neuron responds with two different spike rates while the high threshold neuron does not respond

When there are two different high intensity stimuli…

… the low threshold neuron has the same maximal spike rates for both stimuli while the high threshold neuron can respond with two different spike rates to the stimuli

Pacinian corpuscle

It is in the skin and muscles - they detect vibration and pressure, is a unipolar cell that extends one branch of its axon to skin and other to spinal cord

Small receptive fields

Free nerve endings, Merkel’s disc and Messiner’s corpuscle sense innervate the surface of the skin and are sensitive to stimuli in small areas of the skin

Wide or large receptive fields

Pacinian corpuscles and Ruffini’s endings innervate deeper layers of the skin and are sensitive to stimuli over a larger area of the skin

Tonic receptors

Receptor neurons that show a slow loss of response

Phasic receptors

Receptor neurons that show fast loss of response shortly after onset of stimulation are termed phasic receptors

Hierarchy of sensory pathway

Receptors → thalamic nuclei → primary sensory cortex → secondary sensory cortex → association cortex

Accessory organs

They reduce the intensity or alter the stimulus before it reaches the receptor

Receptive fields…

… can be mapped for neurons in different layers of a sensory pathway