29 - Tactile Perception (11.7.25 & 11.10.25)

Tactile Perception

11.7.25

Announcements

• Exam 2 makeups being scheduled today

• The entire next unit will be on Ch. 13 (the body senses)
• This is what Exam 3 will be on

The Body Senses

• Body senses = ways of monitoring many aspects of our external and internal environments
• They include the following
• Tactile perception, or “touch”
• proprioception, or position/movement of muscles & joints
• thermoception, or “temperature”
• haptics, or object perception
• nociception, or “pain”
• vestibular senses, or “balance”
• Unique in contrast to other senses, which are usually restricted to detecting one aspect of a stimulus

Tactile Perception

• Tactile perception (touch) – results from any indentation, vibration, or stretching of the skin
• relies on the use of mechanoreceptors (sensory receptors that transduce mechanical force on the skin into neural signals)

Decomposing the Skin

Hairy skin vs glabrous skin both contain mechanoreceptors Two layers: dermis and epidermis most mechanoreceptors are found in the dermis

Types of Mechanoreceptors

• Slow-adapting (SA)
• produce a burst of action potentials at stimulus onset (i.e. something presses on the skin)
• have a lower and sustained response until the stimulus is removed

• Fast-adapting (FA)
• produce a burst of action potentials at stimulus onset and offset only
• in other words, they adapt fast to the stimulus’s presence and stop responding

Slow- and fast-adapting mechanoreceptors

Types of Mechanoreceptors

Types of Mechanoreceptors

Mnemonics for the Types of Mechanoreceptors

• Meissner's (Messy): Found in superficial layers (papillary dermis), detect light touch, and adapt quickly.
• Think of a 'messy' desk you lightly touch; it's a superficial, quick sensation.

Mnemonics for the Types of Mechanoreceptors

• Merkel's (Mark): Located in the epidermis, detect texture and sustained pressure.
• Think of the mark a texture leaves on your skin.

Mnemonics for the Types of Mechanoreceptors

• Pacinian (Pacinian Pressure): Located deep in the skin (dermis and hypodermis) and detect deep pressure and vibration.
• Think of "Pacinian Pressure" to link them with deep pressure sensations.

Mnemonics for the Types of Mechanoreceptors

• Ruffini (Rough Stretch): Located deep in the skin, ligaments, and tendons, they detect skin stretch and sustained pressure.
• Think of "Rough Stretch" to associate them with the sensation of stretching. 

How the Mechanoreceptors Work Together

C-tactile Mechanoreceptors

Respond to slow, gentle touch Free nerve ending, present specifically in hairy skin Unmyelinated (signals transmitted slowly to the brain) Activity correlates with perceived pleasantness (peaks for neutral temperature and medium speed)

Mechanoreceptor Transduction

Scientifically, still a work in progress Generally thought that mechanical forces cause ion channels to open Some evidence that the mechanism is analogous to transduction by hair cells in the cochlea

Proprioception

Provides direct and precise information about body position and movement Muscle spindles respond to changes in muscle length or isometric forces on the muscle thought to provide the most important information for proprioception

Proprioception

Provides direct and precise information about body position and movement Golgi tendon organs respond to changes in muscle force (related to length)

Proprioception

Provides direct and precise information about body position and movement Joint receptors provide information about joint angle, specifically when joint has reached the limit of normal motion

Thermoreception: Perceiving Temperature

• Warm fibers
• Both warm and cold receptors can respond between 23° and 40°C (73° and 104°F)
• Heat receptors tend to detect temperatures over 25° (77°F), but they do not continue to detect heat when it gets too hot (e.g., extremely hot and harmful temperature of 45°C (113°F) or hotter)

• Cold fibers
• Cold receptors are about 30 times more numerous than warm receptors
• They respond to cool temperatures between 10°C (50°F) and 20°C (68°F), but they do not respond to very cold temperatures, below 10°C
• When skin temperature is maintained at 30° to 36°C (86° to 97°F), a person does not notice a thermal sensation

Thermoreceptor Responses to Changes inSkin Temperature

Thermoreception: Perceiving Temperature

• Importance of abrupt changes in temperature for perception
• If skin temperature is abruptly warmed from a sustained neutral temperature, the firing rate of warm fibers increases
• If skin temperature is abruptly cooled from a sustained neutral temperature, the firing rate of cold fibers increases
• Abrupt changes in temperature signal that some feature of the environment has changed and perhaps needs to be responded to

Haptic Perception

Actively using touch to perceive and identify objects by their 3D shape and other material properties involves the integration of information from tactile perception, proprioception, and themoreception

Haptic Perception

Tactile perception: shape: edges, corners, curvature surface features: texture, hardness, stickiness

Haptic Perception

Proprioception: shape: position and conformation of the hand holding the object weight: force the object applies to the limbs

Haptic Perception

Themoreception: material properties that would affect temperature (e.g., metal tends to be cold to the touch)

The Vestibular System

The Vestibular System

• Semicircular canals: the three hollowed tubes in the inner ear filled with endolymph (same fluid as cochlear duct)
• Rotating the head moves the endolymph in one or more of the semicircular canals, displacing the cupula that surrounds the hair cells
• Different pattern of displacement, and consequent neural firing, for each type of rotation

The Vestibular System

• Otolith organs: made up of the utricle and saccule
• Acceleration or tilt causes the otoconia to drag, moving the gelatinous layer and causing the stereocilia to move
• Stereocilia in the maculae are oriented in different directions, allowing for a different complexion of displacement with different patterns of acceleration and tilt

The Vestibular System

• Vestibular nerve: bundles together axons from both semicircular canals and otolith organs
• 1st stop: vestibular complex of the brain stem
• Major cortical target in the parietal insular vestibular cortex
• Signals are combined from other parts of the body to form a unified representation of whole- body position

The Vestibular System

• Allows you to sense motion that involves a change in speed or direction
• Critical for maintaining balance
• Vestibulo-ocular reflex - signals about head movement are sent to the frontal eye fields so that eye movements can compensate

Resources

Exit Ticket