Touch Sensation Overview

The sense of touch isn't just one thing, but a combination of various sensations like pressure, texture, temperature, and more.

Our sense of touch works together with our senses of balance and body position to create a complete understanding of objects and how we interact with them.

The process of using your hands to explore and gather information about an object through touch.

The skin is our largest sensory organ, and it's divided into two layers: the epidermis and the dermis.

Receptors in the skin responsible for detecting fine pressure and providing detailed information about textures.

Receptors in the skin sensitive to light touch and changes in texture, helping us to perceive the surface of objects.

A test that measures touch sensitivity by determining the smallest distance between two points that can be perceived as separate.

Areas of the body with a higher density of Merkel's and Meissner's discs, resulting in greater sensitivity and the ability to perceive finer details.

Specialized nerve endings in the skin that detect temperature changes.

Nerve endings that respond to temperatures below body temperature.

Nerve endings that respond to temperatures above body temperature.

Specialized nerve endings that detect harmful stimuli and generate pain perception.

A rapid response to harmful stimuli that bypasses the brain.

A pathway that sends pain signals to the brain for conscious perception and decision-making.

A pathway that regulates pain perception by releasing endorphins to inhibit pain signals.

A genetic condition where individuals cannot perceive pain due to mutations in the SCN9A gene.

The lack of pain awareness can lead to serious injuries going unnoticed, resulting in complications.

The somatosensory system collects sensory information from the body, while the motor system directs movement. They work together in a closed loop to plan and execute actions.

The somatosensory cortex receives and interprets sensory signals from the body, including touch and body position, integrating them with spatial awareness to plan movement and interactions with the environment.

These pathways send sensory information from the skin and muscles to the brain, allowing us to experience sensations.

This pathway carries tactile and proprioceptive information, providing detailed sensory input about touch and body position.

The central processing unit for sensory neurons, located in the dorsal root ganglia, where sensory input enters the spinal cord.

A bundle of nerve fibers that carries sensory information from the medulla to the thalamus in the brain.

A relay station in the brain that processes and forwards sensory input to the somatosensory cortex for further processing.

The somatosensory cortex (S1) receives and processes signals related to touch, temperature, and pain. It consists of four subregions: areas 1, 2, 3a, and 3b, each specialized for processing specific types of sensory information.

The spinothalamic pathway transmits pain and temperature signals from the body to the brain. Sensory neurons arising from the dorsal root ganglia synapse in the spinal cord's dorsal horn, cross sides at the spinal cord level, and ascend via the spinothalamic tract to the thalamus. Finally, signals reach the somatosensory cortex and insular cortex for processing.

Hemisection of the spinal cord, also known as Brown-Séquard syndrome, results in specific sensory loss on both sides of the body. Due to the differential crossing of sensory pathways at different levels, the same side of the injury loses tactile and proprioceptive sensations, while the opposite side loses pain and temperature sensations.

The somatosensory cortex (S1) is organized in a way that reflects the distribution of sensory receptors on the body. Neighboring body parts are represented by neighboring cortical regions. This organization is called the somatosensory homunculus. The size of each body part representation is proportional to its sensory importance, not its actual size.

The somatosensory cortex shows remarkable neuroplasticity. The size of cortical areas representing specific body parts can expand or shrink based on experience or injury. For instance, after finger amputation, the adjacent cortical area expands to represent the missing finger.

Proprioception is our sense of body position and movement. It is crucial for balance and movement planning. Inputs from joint receptors, tendon receptors, and muscle spindles all contribute to this sense.

Reflex arcs are rapid, automatic responses to stimuli that occur without conscious brain involvement. For example, the patellar reflex involves tapping the patellar tendon, triggering stretch receptors, activating spinal interneurons, and eventually leading to quadriceps contraction.

The brain receives pain signals through ascending pathways. However, pain perception can be modulated by descending pathways, which release endorphins to inhibit pain signals. This allows the brain to actively regulate our experience of pain.