Physiology of Touch: Receptors and Pathways, Animation

Summary

The tactile sense allows us to perceive mechanical stimuli like pressure and vibration through specialized receptors in the skin. These receptors, categorized as either rapidly or slowly adapting, differ in their sensitivity and response to touch. A sensory pathway involving three types of neurons transmits signals from the skin to the brain, ensuring that sensory information from one side of the body is processed in the opposite hemisphere. The sensory cortex's spatial organization reflects the density of sensory receptors in different body areas, with more sensitive regions like fingers and the face receiving a larger cortical representation.

Takeaways

• 🖐️ the sense of touch is the perception of objects that contact the skin, activated by mechanical stimuli like pressure and vibration.
• 🔍 tactile receptors are specialized nerve endings that can be classified into encapsulated (wrapped) and unencapsulated (not wrapped) types.
• ⚡ rapidly-adapting receptors generate signals when first stimulated but quickly reduce or stop signaling, making them sensitive to changes and movements.
• ⏳ slowly-adapting receptors continue to generate signals over time, providing information about steady pressure, texture, and shapes of objects.
• 👁️ the sensitivity of touch receptors varies, with some responding to light touch and others detecting heavy pressure.
• 🔬 a sensory neuron has a receptive field, where any touch stimulates that neuron, sending a single signal to the brain.
• 🤚 the ability to distinguish between two points of contact varies by body part, with fingertips having higher sensitivity than the back.
• 📊 small receptive fields increase sensitivity, allowing detection of lower frequencies of vibration, while large receptive fields respond to higher frequencies.
• 🧠 the touch sensory pathway consists of three neurons: first-order neurons in touch receptors, second-order neurons that cross to the opposite side of the cord, and third-order neurons that relay information to the sensory cortex.
• 🌐 the sensory cortex is organized so that adjacent areas represent neighboring body regions, with larger cortical areas corresponding to regions with higher receptor density, such as fingers and face.

Q & A

What is the primary function of the sense of touch?

The primary function of the sense of touch, or tactile sense, is to perceive objects that come into contact with the skin.

What types of stimuli can activate tactile receptors?

Tactile receptors can be activated by mechanical stimuli such as pressure, stretch, vibration, and movement.

How do tactile receptors work?

Tactile receptors undergo physical deformation due to stimuli, leading to the opening of ion channels that allow ions to flow, resulting in cellular depolarization and the generation of action potentials.

What are the two main types of tactile receptors based on their adaptation rates?

Tactile receptors can be classified as rapidly-adapting, which respond quickly to initial stimulation, and slowly-adapting, which continue to generate signals over a longer duration.

What do rapidly-adapting receptors detect?

Rapidly-adapting receptors detect changes in stimuli, such as movements and sequences of events, rather than static objects.

What information do slowly-adapting receptors convey?

Slowly-adapting receptors provide information about steady pressure on the skin and help sense an object's texture, edges, and shapes.

How does the size of a receptive field affect sensitivity?

Receptors with smaller receptive fields are more sensitive and can detect lower frequencies of vibration, while those with larger receptive fields typically respond to higher frequencies.

Describe the sensory pathway for touch perception.

The sensory pathway for touch involves three neurons: first-order neurons (touch receptors), second-order neurons (which synapse in the spinal cord or brainstem), and third-order neurons (which transmit information to the sensory cortex).

What is the significance of the organization of the sensory cortex?

The sensory cortex is organized spatially so that adjacent areas correspond to neighboring body regions, with larger areas representing regions with a higher density of sensory receptors, like the fingers or face.

How does sensory information from different sides of the body reach the brain?

Sensory information from one side of the body is transmitted to the opposite side of the brain due to the crossing over (decussation) of second-order neurons in the spinal cord or brainstem.