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BIO 435


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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