PNB 2XB3 Midterm 2 Review Questions And Answers Rated A+ New Update Assured Satisfaction

Benefits of Adaption in touch sensations - ️️1) Helps us to ignore constant, innocuous stimuli, reducing distraction 2) Helps to avoid saturation of neuronal firing rates, allowing us to detect changes in stimulus intensity over a larger ranger of intensities. Merkel Cells and Mechanotransduction - ️️When skin is presed: 1) Mechanically-gated ion channels in the A beta membrane open, letting in ions (Na) 2) This causes the first ("dynamic phase") action potential 3) Mechanically-gated ion channels in the Merkel cell membrane also open, letting in ions (Na) 4) This depolarizes the Merkel cell and results in the opening of voltage gated Ca channels 5) As a result, a neurotransmitter (norepinephrine) is released onto the A beta axon terminal, which contains transmitter receptors 6) This causes the second ("static") action potentials Dorsal Column Medial Lemniscus Pathway - ️️Pathway that responds to light touch A delta axons go up lumbar and cervical spinal cord, then the dorsal column nuclei, then medial lemniscus in the caudal medulla (base of brain). From there to pons, midbrain, thalamus and eventually parietal cortex using thalamocortical axons. Decussates at caudal medulla. A beta Fibers - ️️Large sensory fibers involved in rapidly transmitting sensation. Responds to touch (around 50 m/s) A delta Fibers - ️️Slower fiber that responds to sharp pain ( around 10m/s) C fibers - ️️Slow fiber that is associated with dull pain (around 1m/2s) Spinothalamic Tract - ️️Pathway that responds to painful touch. (A delta and C axons) Travels in ventral matter of the spinal cord. Decussates immediately. Brown-Sequard Syndrome - ️️Damage to half of the spinal cord.Results in loss of touch on the ipsilateral side, and on the contralateral side, no pain sensations. Upper body still has normal sensation. 4 Types of Touch Receptors - ️️Meissner corpuscle, Merkel cell-neurite complex, Ruffini ending, Pacinian corpuscle. Meissner Receptors - ️️Small receptive field size Responds best to low frequency vibration (2 to 50Hz) Located near surface (around 1mm deep into the skin) Merkel Receptors - ️️Small receptive field size. Responds best to static indentation (pressure Located near surface (around 1mm deep into the skin) Ruffini Receptors - ️️Large receptive field size Responds best to skin stretch Located deeper in skin Pacinian Receptors - ️️Large receptive field size Responds best to high frequency vibrations (greater than 50Hz) What does the sensation of vibrations help us do? - ️️Allows us to perceive the texture of materials, the "slippage" between the skin and grasped object and the small vibrations of tools. EX Detecting change in amplitude when you're running you fingers across an etched design. 4 Sections of the spinal cord - ️️1. Cervical 2. Thoracic 3. Lumbar 4. Sacral Stimulus Response Spike Train - ️️Merkel and Ruffini cells have an onset response (dynamic phase) and an ongoing response (static phase) Meissner and Pacinian cells respond to the first part of the stimulus 2 different ways to get an action potential along the A beta axon - ️️1) Deforming the A beta axon 2) Deforming the Merkel cell Both the A beta axon and the Merkel cell have voltage gated channels. Responds mainly to the ongoing part of the stimulus (ongoing indentation)2 Point Discrimination Task - ️️Calipers are used to touch the skin at the same time close together If you pull them far enough apart, you can feel the 2 distinct points The distance at which you can feel 2 distinct points is you 2 point discrimination 2 point discrimination changes as you move around the body (finger can be closer in distance, compared to leg)