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BIO 435
Somatosensory
| Question | Answer | |
|---|---|---|
| What are the 5 types of sensory receptor cells | Superficial 1. free nerve endings 2. Merkel discs 3. Meissner's corpuscles | Deep 4. Ruffini endings 5. Pacinian corpuslces |
| How do somatosensory system cells respond when stretched? | The channels open when stretched and physical pressure applied to these neurons cause action potentials | |
| Why would a weak stimulus not cause action potentials in deep receptors? | Deep receptors are not as sensitive as superficial receptor cells and therefore do not depolarize as easily | |
| How do the receptive fields of somatosensory neurons vary? | By size | |
| Which receptor cells have small receptive fields? | Superficial sensory receptor cells 1. free nerve endings 2. Merkel discs 3. Meissner's corpuscles | |
| Which receptor cells have large receptive fields? | Deep sensory receptor cells 1. Ruffini endings 2. Pacinian corpuscles | |
| Why does rapid adaptation of the corpuscles occur? | Rapid adaptation of corpuscles occurs due to deformation of connective tissue layers | |
| Describe Pacinian corpuslces | - detects vibration - fast-adapting -large receptive fields with vague borders | |
| Describe Meissner's corpuscles | - detects touch - fast-adapting -small receptive fields with sharp borders | |
| Describe Ruffini's ending | - detects stretch - slow-adapting -large receptive fields with vague borders | |
| Describe Merkel discs | - detects touch -slow-adapting -small receptive fields with sharp borders | |
| What affects the localization of stimuli? | receptive field size | |
| What part of body has higher density of receptors and more superficial receptors? | fingertips | |
| Why is more of the somatosensory cortex dedicated to processing information from the fingers? | Because we explore things with our fingers | |
| What parts of the body have bigger receptive fields and makes it harder to located where the cell was touched? | back and forearm | |
| How is stimulus intensity coded? | It is coded by action potential frequency | |
| Where are unipolar neurons located? | Their cell bodies are in the dorsal root ganglion (ganglion is a cluster of cell bodies in peripheral NS) | |
| How do sensory neurons enter the spinal cord? | via the dorsal root (some branches of axon synapse in a spinal cord and others ascend in dorsal column) | |
| Describe the Aa (A alpha) axons from the skin | - in group I of axons from the muscles -diameter | |
| Describe the AB (A beta) axons from the skin | -Group II of axons from muscles - diameter 6-12 um-speed | |
| Describe the AS (A delta) axons on skin | - Group III of axons from muscles - diameter -1-5 um- speed | |
| Describe C axons from the skin | - Group IV axons from muscles - diameter -0.2-1.5um-speed | |
| What is a dermatome | The area of the skin connected to a specific part of the spinal segment | |
| What types of patients demonstrate dermatomes? | Shingles patients; the Herpes zoster virus can lay dormant in one dorsal root ganglia and therefore only affect one dermatome | - If the virus activates, it causes the dermatome where that dorsal root ganglia is to be affected resulting in burning and sensitization in skin |
| Which pathway is used for touch? | The dorsal column-medial lemniscal pathway | |
| Describe synapse 1 of the dorsal column-medial lemniscal pathway | 1. dorsal column nuclei 2. decussation (crosses midline of brain/medial lemniscus) 3. goes to synapse 2 | |
| Describe synapse 2 of the dorsal column-medial lemniscal pathway | 1. ventral posterior thalamus 2. to synapse 3 = primary somatosensory cortex | |
| How do most touch neurons in the face travel? | Via the trigeminal nerve (CN V) | |
| Describe the trigeminal nerve (CN V) | one of the biggest cranial nerves and brings touch information from all of the head | |
| Describe the trigeminal pathway | - carries somatosensory information from the face Synapse 1 (trigeminal nucleus) to decussation (in the pons) to synapse 2 (VP thalamus) to synapse 3 (primary somatosensory cortex (S1) | |
| What helps with localization in the somatosensory pathways? | Lateral inhibition; dorsal column neurons inhibit each other and only the strongest stimulus "survives”, inhibition of lateral neurons enhances perception of stimulus (in S1) by inhibiting neighbors of in pathway closest to the stimulus | |
| Where is touch information sorted? | S1 | |
| Describe area 3b in S1 | -receives the most direct input from the VP thalamus -sorted into chunks according to the type of receptor info they receive | |
| Where does area 3b send primary texture information to? | area 1 of S1 | |
| Where does area 3b send size/shape information to? | area 2 of S1 | |
| Which body parts have better touch discrimination? | Body parts with more area of S1 | |
| Describe sensory plasticity in S1 | -if one area of S1 isn't used, it processes information from neighboring body parts -if one area of the body is used excessively, its cortical representation becomes larger | |
| After area 1 and 2, where do somatosensory cortex projections go to? | Amygdala and hippocampus | |
| What areas are important for tactile memory? | amygdala and hippocampus | |
| What type of information is integrated when it projected to posterior parietal cortex? | touch, pain, temperature, visual information | |
| What can damage to the posterior parietal cortex cause? | Agnosia (the inability to recognize objects; for example someone with agnosia may only see things on the left but everything on the right just doesn't exist) | |
| Describe the receptive fields of area 5 | combine receptive fields from both hands and use cross-talk via the corpus callosum | |
| What kind of stimulus do some receptor fields in the posterior parietal cortex respond best to? | a particular stimulus moving in a specific direction across the skin | |
| What are nociceptors? | special types of free nerve endings that perceive pain | |
| Describe mechanical nociceptors | Respond to strong painful tactile stimuli | |
| Describe thermal nociceptors | respond to temperature extremes | |
| Describe chemical nociceptors | Respond to chemicals released during tissue damage | |
| What kind of chemicals do nociceptors respond to | histamine, K+, bradykinin, substance P, ATP, serotonin | |
| Describe polymodal nociceptors | Respond to mechanical stimuli, thermal stimuli, and chemical stimuli | |
| What typically initiates pain signaling? | inflammation | |
| How does pain transmission occur | Via small, myelinated A-delta neurons and unmyelinated C neurons | |
| Where do nociceptor axons synapse | in the spinal cord (ascending neurons decussate to travel contralaterally | |
| What pathway transmits pain information to the brain | the spinothalamic/anterolateral pathway | |
| What pathways does pain information from the head take? | The trigeminal nerve pathway | |
| Where does touch and pain stay segregated | In the VP thalamus | |
| Describe the spinothalamic/anterolateral pathway | Synapse 1 (spinal cord) to decussation (spinal cord) to synapse 2 to VP thalamus to synapse 3 (S1) | |
| What is the dorsal column-medial lemniscal pathway responsible for | touch, vibration, 2-point discrimination, proprioception | |
| What does the spinothalamic pathway responsible for | pain, temperature, some touch | |
| What allows for perceptions of pain and emotional consequences? | Parallel pain pathway | |
| What areas receive input from the anterolateral system? | Areas from the brainstem and forebrain (areas important for emotional regulation) | |
| Who first used mirror boxes to help patients with phantom limb pain? | V.S. Ramachandran | |
| What enhances our perception of pain? | Hyperalgesia | |
| Describe allodynia | When perceived pain to a stimulus would not normally be painful | |
| What chemicals sensitize nociceptors | cytokines, bradykinin, prostaglandins, substance P | |
| Describe the role of the periaqueductal gray (PAG) of the midbrain in descending pain control | - PAG important for regulating pain perception -causes the release of NTs in the dorsal horn to enhance/suppress nociceptor activity | |
| What can the PAG be activated by | opioids (resulting in placebo effect when anything you believe will reduce pain causes the release of endogenous opioids that affect the PAG) | |
| What is the gate theory of pain? | The idea that touching damaged areas of the body can reduce pain via inhibitory suppression | |
| How many types of receptors does each thermoreceptor neuron have? | one | |
| What pathway do neurons for temperature sensation use? | spinothalamic pathway | |
| Thermoreceptor responses are transient. At what temperatures are cold receptors more active at and at what temperatures are warm receptors more active at? | cold receptors- active at low temperatures warm receptors -active at high temperatures | |
| How many types of receptors does each thermoreceptor neuron have? | one |
Created by:
keiannaowens
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