mechanical stretch, vibration and grasping5. How do we respond to mechanical deformations?• Expansion of a cortical representation by a repetitive behavioral task• Skinniest afferents meaning the slowestBISC 421 1st EditionFinal Exam Study GuideI. SOMATOSENSATION 1. What are the four basic somatosensations? •1. Touch •2. Proprioception ( not detected by the skin) •3. Pain (nociception) •4. Temperature 2. Where are the sensory neurons located? And What is so special about them? •IN the Dorsal root ganglia or the trigeminal ganglion for the face •They are pseudounipolar (2 axons and no dendrite) •Each ganglion innervates a single region of the body called a dermatome 3. For touch what are the four basic receptors and what are some characteristics of these receptors? •1. Merkel Receptors-‐ small receptve feld, slow adaptng, medium threshold for mechanical stretch, edges and points and fine texture, braille •2. Messiner receptors-‐ medium receptve feld, rapid adaptng, small threshold for mechanical stretch, motion and grip •3. Rufini-‐ large receptve feld size, slowly adaptng, very large threshold for mechanical stretch, skin stretch and finger position •4. Pacinian-‐ entre fnger for receptve feld size, rapidly adaptng, and very small threshold for mechanical stretch, vibraton and grasping3. What are the 4 somatosensory response characterizations? •1. Speed of conduction •2. Adapting or non adapting •3. Receptive field size •4. Threshold of activation 4. Where in the body is the best two-‐point discrimination? (smallest receptive field size) •In the fngers 5. How do we respond to mechanical deformations?•At level of nerve endings there are ion channels that exist in the closed state prior to the mechanical change and then when they are stretched Na+ is allowed in-‐ For example piezo1 and piezo2 are essental components of distnct mechanically actvated caton channels5. Describe the pathway for touch sensation•Mechanosensory input ascends ipsilaterally through the dorsal columns and synapsesand crosses at the midline near the brain (gracile and cuneate nucleusextends through the medial lemniscus to the thalamus and then the cortex•Main point: don't synapse untl the brainstem6. What do proprioceptors detect?•They detect change in muscle length and tension in on the muscle to detect body positioning•Projects to the cerebellum and underlies the knee jerk reflex7. Why should you practce the piano?•Expansion of a cortcal representaton by a repettve behavioral taskII. NOCICEPTION1. The cells that mediate pain and temperature are cells that terminate in what?•Free nerve endings2. What is congenital insensitvity to pain and what is happening in individuals who have this disorder?•Individuals with this disorder cannot feel pain but can feel normal touch3. What are the 2 types of nerve fbers that detect pain and what kind of pain?•Alpha delta= sharp pain•C fbers = slow dull pain•Skinniest aferents meaning the slowest4. What are the 3 molecules of temperature and pain?•1. TRPV1-‐ heat and chili peppers•2. TRPM8-‐ cold and menthol•3, TRPA1-‐ pain and mustard5. What was the experimental method for isolatng the TRPV1 or capsaicin recptor•Used cloning: isolated total mRNA from DRG and introduced to tssue culturethat don't normally repond to capsaicin-‐ measured infux of calcium with intracellular calcium imaging•Then isolates the single mRNA that can generate response to capsaicin (calcium ion channel) and determine receptor amino acid sequence•This receptor is opened by heat, capsaicin, and acidification•Knocking out TRPV1 causes inability to taste chili peppers and less sensitve to hot temperatures6. What happens with a knockout of TRPA1•By injectng formalin into the paw of a mouse and measuring the tme spent licking the paw, see that with knockout all phases of the pain response are decreased andeliminate response to carbonation•TRPA1 also responds to carbonation7. What happens in an infammatory reaction?•Infammatory mediators (NGF) up regulate TRPA1 and TRPV1 actvity causing morepain and heat sensation•NGFs enhance the response of the cell to stmuli that aren’t very strong (why a warm shower feels hot when you have a sunburn)8. What tract do the nociceptor aferents ascend through?•The anteriolateral tract•Cross at the spinal cord•If have a lesion will not be able to feel pain on the opposite side as opposed to touch which will be unable to feel on the same side9. What do we mean by saying that pain has descending control? What is the gate theory of pain•Percepton of pain depends on context – the placebo efect is real (we have central mechanisms that “gate” pain)-‐ CALLED THE GATE THEORY OF PAIN•Opiates bind to opiate receptors on nociceptor and dorsal horn cells to inhibit activity-‐ theseendogenous ligands are peptides•Also skin mechanoreceptors can reduce pain (rubbing the site)III. OLFACTORY SYSTEM1. What are the 3 chemical senses?•1. Smell•2. Taste•3. Vomeronasal (not in humans)2. Are there odor primaries?•No there are not3. What is the general anatomy (pathway) for olfaction?•Olfactory sensory neuronsolfactory bulbthese axons pass through the cribiform plateodorants are detected on sensory cilia that project into the olfactory mucosa (these cilia increase the SA over which the odorants can be detected . SENSORY RESPONSE IS INITIATES IN THE CILIA•This sensory response is and inward current (acton potental depolarization)•Sensitvity for odorant is in the cilia not the cell body4. Why do humans have lower ability to smell than other animals?•1. We have fewer receptors than other animals•2. Humans have fewer receptor genes5. What is the olfactory sensory transducton pathway (all steps)•1. Receptor binds ligand•2. G protein exchanges GDP for GTP•3. Adenylate cyclase makes cAMP from ATP•4. cAMP opens a CNG (cyclic-‐nucleotide gated) ion channel•5. Na+ and Ca2+ comes into cell causing depolarization•6. Ca2+ opens a Cl-‐ channel, ensuring a response in the absence of Na+6. What provides the specifcity? What are the characteristcs of these receptors?•The odorant receptor-‐ because we can respond to many odorants we must have a lot of odorant receptors•They are – 7 TM G protein coupled, encoded in intronless genes, scatered throughout the genome, number in the hundreds (we have 388 functonal receptors)7. What