Lecture 12: Somatosensory System 1: Touch (Body)
Biology 222 with Nagaya at University of Michigan - Ann Arbor
About this deck
By: Kristina Brooks
Textbook:
Neuroscience: Exploring the Brain
Created: 2010-11-13
Size: 59 flashcards
Views: 31
Textbook:
Neuroscience: Exploring the BrainCreated: 2010-11-13
Size: 59 flashcards
Views: 31
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What are the five classical senses?
Vision, hearing, taste, smell, touch (mechanosensation)
What are some of the additional senses that don't fall under classical category?
Vestibular (balance), pain, temperature, proprioception
What are mechanoreceptors?
Primary neurons that respond to mechanical stimuli by firing action potentials
Where are the receptors of the mechanoreceptor neurons for the body found?
Skin
Where are the cell bodies of mechanoreceptors found?
Dorsal root ganglion
Give an overview of the relay of the afferent pathway.
Primary afferent axons (skin) --> Spinal nerves --> spinal cord
How do primary afferent axons ascend the spinal cord?
Via ipsilateral dorsal columns (white matter)
What does "ipsilateral" mean?
Same side
What does "contralateral" mean?
Opposite side
What are afferent neurons?
Axons that carry information into the CNS
What are efferent neurons?
Axons that carry information away from the CNS
What is the primary afferent neuron in the mechanosensory pathway?
AB axon
Do AB axons project contralaterally or ipsilaterally to the brain?
Ipsilaterally
What group of axons from muscles are AB axons found within? What are their characteristics?
Group II
-6-12 um in diameter, 35-75 m/sec
What group of axons are Aalpha axons found within? What are their characteristics?
Group I
-13-20 um in diameter, 80-120 m/sec
-Sensory receptors: proprioceptors of skeletal muscle
What group of axons are Ad axons found within? What are their characteristics?
Group III
-1-5 um in diameter, 5-30 m/sec
-Sensory receptors: pain, temperature
What group of axons are C axons found within? What are their characteristics?
Group IV
-0.2-1.5 um in diameter, 0.5-2 m/sec
-Sensory receptors: temperature, pain, itch
What are some of the mechanoreceptors in the skin?
Merkel's disk
Meissner's corpuscle
Pacinian corpuscle
Ruffini's ending
What are the largest mechanoreceptors of the skin?
Pacinian corpuscle
What is the Pacinian corpuscle sensitive to?
High frequency vibration
What are some characteristics of the Pacinian corpuscle?
-Make up 10-15% of hand mechanoreceptors
-Low spatial acuity (10+ mm)
What are the second largest mechanoreceptors of the skin?
Ruffini's endings
What are Ruffini's endings sensitive to?
Skin stretch
What are some characteristics of Ruffini's endings?
-Make up 20% of hand mechanoreceptors
-Low spatial acuity (7mm)
How does the size of the Meissner's corpuscle compare to Pacinian corpuscle?
1/10th of Pacinian
What is the Meissner's corpuscle sensitive to?
Low frequency vibration
What are some characteristics of the Meissner's corpuscle?
-Makes up 40% of hand mechanoreceptors
-Intermediate spatial accuity (3 mm)
What are Merkel's disks sensitive to?
Edges, points, curvature
What are some characteristics of Merkel's disks?
-Make up 25% of hand mechanoreceptors, especially fingertips
-High spatial acuity (0.5 mm)
Give an overview of how receptive fields for mechanoreceptors are mapped.
-Recording electrode inserted into the median nerve of the arm
-Action potentials recorded from a single sensory axon
-Receptive fields mapped using a fine probe
What is a receptive field?
Area of skin that significantly changes action potential firing rate when stimulated
What mechanoreceptors have small receptive field sizes and rapid adaptation?
Meissner's corpuscle
What mechanoreceptors have small receptive field sizes and slow adaptation?
Merkel's disk
What mechanoreceptors have large receptive field sizes and rapid adaptation?
Pacinian corpuscle
What mechanoreceptors have large receptive field sizes and slow adaptation?
Ruffini's ending
Give an overview of the occurrence of an AP in the Pacinian corpuscle.
1) Mechanical deformation of membrane at onset/offset
2) Mechanosensitive cation channels open
3) Generator potential depolarizes axon
4) If threshold reached, action potential
What does the onion-like Pacinian corpuscle confer?
Sensitivity to high-frequency vibrating stimuli but not steady pressure
What are some of the different pathways involved in touch?
-Body to cortex pathway
-Face to cortex pathway
How is sensory innervation organized?
In segments
How many spinal segements are there in the human body?
30
What are the main divisions of the spinal segments?
Cervical (8)
Thoracic (12)
Lumbar (5)
Sacral (5)
What do each of the spinal nerves contain?
Dorsal and ventral root axons
What is the cervical region associated with?
Arms and head regions
What is the thoracic region associated with?
Chest/abdominal region
What is the lumbar region associated with?
Lower back, front of the legs
What is the sacral region associated with?
Tailbone, back of legs
What are dermatomes?
Skin innervated by right and left dorsal roots for a single spinal segment
-Numbered by spinal segment providing innervation
What pathway is associated with body receptos to the cortex?
Dorsal column-medial lemniscal pathway
Give an overview of the dorsal column-medial lemniscal pathway.
Sensory AB axons enter at dorsal roots
Axons ascend spinal cord via ipsilateral dorsal column
Dorsal columns have topographic organization
Axons synapse on second order neurons in dorsal column nuclie
Second order neurons crossover, forming medial lemniscus
Medial lemniscus ascends through medulla, pons, midbrain
Medial lemniscus synapses on cells in ventral posterior nucleus of the thalamus
VP neurons prooject via internal capsule to primary somatosensory cortex
What are the first order neurons in the DC-ML pathway?
Sensory AB axons
How are the dorsal columns organized?
-Lower body axons in fasciculus gracilis (medial)
-Upper body axons in fasciculus cuneatus (lateral)
Is the fasciculus gracilis medial or lateral?
Medial
Is the fasciculus cuneatus medial or lateral?
Lateral
What specific second order neurons do the sensory AB axons synapse onto?
-Lower body axons to nucleus gracilis
-Upper body axons to nucleus cuneatus
What are the second order neurons in the DC-ML pathway?
Internal arcuate fibers
What forms the medial lemniscus?
Second order neurons
Where do the second order neurons crossover?
Caudal medulla
What are the third order neurons in the DC-ML pathway?
Ventral posterior (VP) neurons
What does the DC-ML pathway project to?
Primary somatosensory cortex (S1)
About this deck
By: Kristina Brooks
Textbook: Neuroscience: Exploring the Brain
Created: 2010-11-13
Size: 59 flashcards
Views: 31
Textbook:
Neuroscience: Exploring the BrainCreated: 2010-11-13
Size: 59 flashcards
Views: 31
About StudyBlue
STUDYBLUE makes things that make you better at school.
Things like online flashcards with photos and audio.
Things like personalized quizzes and friendly reminders about when (and what) to study next.
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“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy
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