The Somatosensory System pgs. 37-44

Unlocking Taste and Smell

• Taste and Smell: Neurons encode different tastes and smells through patterns of activation.
• Somatosensation: Includes touch, pain, temperature, and limb/joint sensation.
• Skin Receptors: Mechanoreceptors transduce touch, pressure, and vibration.
• Types of Mechanoreceptors: Meissner's corpuscles, Pacinian corpuscles, Merkel's disks, and Ruffini's corpuscles.
• Adaptation and Receptive Fields: Mechanoreceptors adapt to stimuli and have different receptive field sizes based on their location.

Merkel's Disks

Merkel's disks are the receptors responsible for transducing touch, pressure, and vibration. They are located in the skin's epidermis and play a crucial role in our sense of touch. These specialized nerve endings are named after Friedrich S. Merkel, the German anatomist who first described them in 1875.

Unlocking Taste and Smell

• Two-Point Discrimination: Measure of skin's sensitivity to touch
• Dermatomes: Skin segments innervated by spinal cord levels
• Temperature Receptors: Low and high-threshold thermoreceptors
• Pain Transduction: Neural processing of injurious stimuli

Two-Point Discrimination

Trivia: Two-Point Discrimination is the ability to distinguish two separate points of contact on the skin. It varies across different parts of the body, with the fingertips being the most sensitive. This test is commonly used to assess nerve damage or sensory disorders. Fun Fact: The smallest distance at which two points can be felt as separate is around 2-3 mm on the fingertips!

Pathways to the Brain

Sensory neurons have their cell bodies in the dorsal root ganglion (DRG) and synapse onto the next neuron in the spinal cord or brainstem. These neurons have the longest axons in the body. Touch and proprioception signals travel via the dorsal column medial lemniscal (DCML) system, while pain and temperature signals travel via the anterolateral spinothalamic pathway. Both pathways cross the center of the body and synapse in the thalamus before reaching the cerebral cortex.

Touch and Proprioception

Trivia: Did you know that the Anterolateral spinothalamic pathway is responsible for transmitting touch and proprioception signals? This pathway carries information about pain, temperature, and crude touch sensations. It is an essential part of our sensory system, allowing us to perceive and respond to our environment.

Motor System

• Involuntary movement is triggered by sensory stimulus and does not require conscious effort.
• Voluntary movement is carefully planned out in the brain before execution.
• Lower motor neurons synapse directly onto muscles, releasing acetylcholine at the neuromuscular junction.
• Acetylcholine receptors depolarize muscle cells, causing contraction and movement.
• Reflex circuits allow for involuntary movement without communication with the brain.

Involuntary Movement

Trivia: Involuntary movement is triggered by sensory stimulus and does not require conscious effort. Examples include blinking, shivering, and reflex actions like pulling your hand away from a hot surface. It is an automatic response that helps protect our bodies from harm.