Exam 2 Study Guide Touch pain temp kinesthesis Touch Anatomy Physiology What is somatosensation kinesthesis proprioception What are the types of proprioceptive receptors Where are they and what kind of info do they convey Somatosensation A collective term for sensory signals from the body Kinesthesis The perception of the position and movement of our limbs in space Proprioception Perception mediated by kinesthetic It s the ability to sense the position location orientation and movement of your different body parts Types of proprioceptive receptors Muscle spindle golgi tendon organs 1 Muscle spindle Convey the rate at which muscle fibers are changing in length So they would fire in response to stretching of a muscle and are also involved in reflexes 2 Golgi tendon organs These are receptors in the tendons connect the muscle to bone They display info about any tension in the muscles which is caused by a pull on the tendon and aid in reflexes as well Regulates sensitivity of muscle spindle so responds even during contraction Specifically monitors muscle contraction used for fine adjustments in muscle tension Such as handling a raw egg or picking up something small off the floor What are the 4 main types of touch receptors How do they differ in terms of adaptation receptive field size What tactile functions do they subserve What does it mean that they are mechanoreceptors Touch receptors are nerve fibers with specialized ending In very sensitive areas of the body there is a small and densely packed receptive field more cortical area processing touch from that area Each receptor can be categorized into 3 criteria Type of stimulation size of receptive field and rate of adaptation A mechanoreceptor responds to any mechanical stimulation such as pressure vibration or any movement Have 4 major types of mechanoreceptors that help to detect motion and stimulation on the skin 1 Pacinian Corpuscle are responsible for sensitivity of deep pressure touch and high frequency vibrations They have a large receptive field and are fast adapting They are fewer in compared to Merkel cells and Meissners corpuscle 2 Meissners Corpuscle Are fast adapting with a small receptive field And along with merkel cells abundant in the fingertips just below the epidermis It is important for tactile discrimination and detecting low frequency vibrations 3 Merkel Cells Slow adapting have a small receptive field Not exactly sure what their function is but it is believed that they aid in texture perception patterns and form detection 4 Ruffini Endings Have a large receptive field and are slow adapting Help sense warmth They are wide spread on dermis and tissue and aid in finger position and the ability to grasp something How do pacinian corpuscles work Best for quickly applied forces not maintained forces Force neuron s membrane is deflected channels become leaky to sodium action potential When you press on a Pacinian Corpuscle you deform the lamellae and cause them to press on the tip of the sensory neuron That in turn physically deforms the neuron s plasma membrane and makes it leaky to sodium ions that will depolarize the membrane at the site of the deformation The tip of the sensory neuron however is like the dendritic zone of a neuron in that it lacks voltage gated Na channels and therefore cannot generate or propagate action potentials so you can think of this depolarization as a large amplitude EPSP dVm 20 50 mV depending on how strong the pressure is The first part on the sensory neuron that does have the voltage gated Na channels required for action potential generation is the 1st Node of Ranvier In a way similar to the way an EPSP depolarizes the Initial Segment of an axon to threshold the depolarization at the tip of the neuron depolarizes the 1st Node of Ranvier to threshold and causes it to start generating action potentials which propagate toward the brain So in a sense the 1st Node of Ranvier is serving as an Initial Segment As long as the tip of the neuron is depolarized it will continue to depolarize the 1st Node of Ranvier which will respond by generating action potentials as long as the depolarization lasts This is because as soon as the 1st Node of Ranvier recovers from generating an action potential the depolarized neuron tip depolarizes the 1st Node of Ranvier back to its threshold Then as soon as the depolarized 1st Node of Ranvier gets out of its absolute refractory period which is quite short as refractory periods go it generates another action potential This continues as long as the neuron tip remains depolarized What are thermoreceptors and what kinds are there How do some tastes lead to the sensation of warmth or hot or coolness Respond to changes in skim temperature We have warm fibers that respond to warm temperatures and cold fibers that respond to cold temperatures Our body temp is 30 36C so everything we come into contact with in the environment is cooler then that Therefor cold fibers outnumber warm fibers by a ratio of 30 1 Some thermoreceptors also respond to chemicals which is why taste may lead to sensation of warmness or coolness Ruffini corpuscles help sense warmth Krause s end bulbs help sense cold What is the pathway names and all the stops along the way for touch info to get to the brain What part of the spinal cord does it enter When where does it cross to the other side of the brain What part of thalamus does it use If that touch is on the face or head what cranial nerve is involved Spinothalamic Tract responds to receptors of pain and temperature Slower track Dorsal Column Medial Lemniscus carries information to the brain about mechanoreceptors general touch Much faster track Takes the tract of mechanoreceptor SMJ thalamus cortex In both these cases the information travels up the spinal chord and crosses over contralaterally on opposite sides The DCML crosses over at the Medial lemniscus of the medulla The Spinothalamic tract crosses over the Lissauers tract If touch is on the face or hand trigeminal nerve CN V is used Also conveys info from stretch receptors from chewing muscles So both motor and sensory Are all axons the same What is the result of increasing the diameter or myelination of axons All axons differ in their degree of myelination and size Increasing myelination increases the conduction velocity of an action potential allowing information to be processed by the brain quickly and more efficiently What is the difference b t S1 S2 and somatosensory association
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