Senses and Perception

What are the basic principles of psychophysics?

- Studies relationship between physical stimuli and sensations

- Key laws:

- Weber's Law: Just noticeable differences

- Fechner's Law: Sensation increases logarithmically with stimulus

- Stevens' Law: Perception increases as power of stimulus intensity

What is signal transduction in sensory systems?

- Process where receptor cells transform stimulus energy into neural signals

- Different receptors specialized for different sensory modalities

- Receptors filter stimulus energy based on affinity and sensitivity range

- Can be either spiking or non-spiking neurons

What is the gut-brain axis (GBA)?

- Bidirectional communication via vagus and spinal nerves

- Maintains gut homeostasis

- Regulates brain functions

Involves enteric nervous system (ENS) and gut microbiota

- May play role in neurodegenerative disorders

What are the main types of mechanoreceptors?

1. Touch and pain receptors in skin

2. Proprioceptors in muscles and joints

3. Hair cells in inner ear

4. Vestibular receptors for balance Each type has distinct pathway to brain

How do skin mechanoreceptors differ?

Small receptive fields:

- Free nerve endings

- Merkel's disc

- Meissner's corpuscle

- Surface skin sensitivity

Large receptive fields:

- Pacinian corpuscles

- Ruffini endings

- Deep skin sensitivity

What is the difference between tonic and phasic receptors?

Tonic receptors:

- Show slow loss of response

- Maintain activity during continued stimulation

Phasic receptors:

- Show fast loss of response

- Respond mainly to stimulus onset/change

How do response thresholds work in sensory systems?

- Absolute threshold: lowest detectable stimulus intensity

- Upper threshold: highest discriminable intensity

- Different receptors have different sensitivity ranges

- Response probability above 50% indicates stimulus detection

What is somatotopic mapping?

- Adjacent body regions encoded in adjacent cortical regions

- Found in primary somatosensory cortex

- Located in postcentral gyrus

- Maintains spatial relationships of body parts

- Different sized cortical areas based on sensitivity

How can sensory input be suppressed?

Two main methods:

1. Accessory organs:

- Eyelids

- Middle ear muscles

- Reduce stimulus intensity

2. Neural top-down processes:

- Brain stem control

- Selective dampening of signals

What is the labeled line principle?

- Different receptors project to different brain areas

- Maintains segregation of different sensory qualities

- Preserves spatial location information

- Involves parallel processing streams

- Important for identifying stimulus location on body