Somatosensory System Flashcards by joy nauman

What are receptors? (2)

Either modified non-neural tissue cells or axons themselves

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Receptors translate environmental energy into generator potentials which in turn trigger action potentials. How are APs conducted?

Along nerves to the CNS in spatio-temporal patterns that our nervous system can process.

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Are AP conducted faster or slower on myelinated axons (as oppossed to unmyelinated)?

faster

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What are compound action potentials?

Recordings of the summed APs measured over time at a particular site on the nerve

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The further along the nerve you record, the more the compound AP ___ by velocity. Peaks correspond to ____ ____ with different conduction velocities and degrees of myelination.

Seperate; axonal clusters

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Nerve compound APs are classified by either letters or numbers depending on how the original physiology labs classified them. Roman numerals apply to ____, while letters apply to ____.

Motor nerves; sensory nerves

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Which classification of axons are most myelinated and fastest?

A or I

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Despite the wide range of types of information to be sensed and acted on, a small set of common principles underlie all sensory processes. Sensory systems mediate four attributes of stimuli that be correlated with sensation. What are they?

Intesity, sensory adaptation, localization, modality

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How does intensity coding produce a gradient of sensation?

Increased stimulus energy enhances action potential frequency and vice versa.

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What is the decrease in neural activity with sustained stimulation and is used to convey a message concerning the rate of change of a stimulus or status of the sensation?

Sensory adaptation

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What mechanisms take place in rapid adaptation?

Ion channel inactivation or receptor deformation

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What mechanisms take place in slow adaptation?

Inactivation of Ca or Na channels

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What is the area of skin innervated by the branching of a single sensory neuron?

Cutaneous receptive field (RF) - RFs that are densely innervated tend to be the smalles in area

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Modalities are subserved by seperate populations of sensory neurons specialized in detecting stimuli of different qualities. These specializations are structures that transform physical energy into neural signals. Axons have membrane receptors that respond to specific stimuli delivered in what two ways?

“Indirectly through CT capsules or modified epithelial cells

Directly through the membrane of the free nerve endings”

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What are sensory receptor proteins and what do they do?

Transient receptor (TRP) type ion channels. Each responds maximally to one stimulus (adequate stimulus) and less to others.

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What do you call the energy that elicits the greatest response and largely determines which neurons will be responsible for the perception of the sensory modality?

Adequate stimulus

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What term usually refers to environmental stimuli of cutaneous receptors that mediate discriminative and non-discriminative touch, temperature and pain?

Somatosensory exteroception

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Discriminative touch is mediated by exteroceptive mechanoreceptors embedded in CT or around hairs. Merkel cells and Ruffini corpuscles are ____, while Meissner and Pacinian corpuscles and hair follicles are ___. (fast or slow adapting)

SA; FA

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What is the area of skin that when impacted can stimulate a single specific neuron/receptor?

Mechanoreceptor receptive field

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What are the three distinct somatocensory modalities that are all mediated by free nerve endings, have slower conducting and smaller A-delta and C type axons, and are all slow adapting?

“Non-discriminative touch
Temperature
Pain”

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What type of receptor is used to tap, squeeze, rub, skin stretch, non-discriminative touch?

Mechanoreceptor

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What type of receptor is used for hot and cold?

Thermoreceptor

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What type of receptor is used for mechanical or thermal tissue damage?

Mechano-thermal nociceptors

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What type of receptor is used for heat, tissue damage, chemicals?

Polymodal nociceptor

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What type of receptor is used for nociception (sympathetic); physiological (parasympathetic)?

Visceral

Interoception involves sensitivity to what?

Visceral physiological information

What constitutes "the material me" and relates to how we perceive feelings from our bodies that determine our mood, sense of well-being and emotions?

Interoception

Describe interoceptive receptors.

They are visceral afferent free nerve endings that mediate pain, pressure, temperature, chemicals and stretch in organs and blood vessels

Proprioceptive receptors mediate what using what type of neurons?

Muscle/joint position and movement using fast conducting, large axons (A-alpha, beta)

The major categories of perceived somatosensory modalities are distinguished not just by their receptors and conduction velocity, but also by what?

Their ascending pathways

Proprioception ascends in what columns?

Dorsal

What information ascends in both the dorsal column and anterolateral system?

Visceral sensory

What modality(ies) is characterized by sensitive mechanoreceptors, rapid AP conduction, dorsal column-leminiscal system, and quantitative sense that provides localization of the stimulus?

Discriminative touch, vibration and proprioception

What modality(ies) is characterized by free nerve endings, slower AP conduction, anterolateral system, and provides qualitative experience of the stimulus?

"Non-discriminative touch Temperature Pain"

The dorsal column-lemniscal system is responsible for conveying first, second, and third order neuron information of touch, vibration, proprioception and visceral (partially) to the cerebral cortex via what three CNS structures?

Spinal cord, brain stem and thalamus

Which order of neurons are: associated with thalamus, form part of internal capsule, and project to primary somatosensory cortex in postcentral gyrus?

Third order

Which order of neurons are: associated with cuneate and gracile nuclei, decussate in the medulla, and axons form medial lemniscus which synapse onto neurons within the thalamus?

Second order

Which order of neurons are: associated with sensory neuron axons (A-beta), form dorsal columns, and synapse onto dorsal column nuclei in the medulla?

First order

The anterolateral system conveyes non-discriminative touch, pain and temperature senses. Only part of it has what, seen in the dorsal column-lemniscal system?

The tidy first, second, and third order neuronal pattern

In the posterolateral (lissauer's) tract, which order neurons: branch rostrally and caudally along the posterolateral tract, has sensory nerves that can extend 3-4 spinal levels in both directsion before entering the dorsal horn along several spinal segments, and is subject to painful stimuli which can elicit avoidance responces from a large region of the body because of their acces to several spinal segments?

First order A-delta and C neurons

what type of neurons synapse onto second order dorsal horn neurons using various transmitters including substance P, glutamate, and NO?

Sensory (first order) neurons

Second order neurons in the dorsal horn decussate to what?

The anterolateral system

Which anterolateral pathway projects to lateral thalamus and somatosensory cortex and is responsible for localization of sensation?

Neospinothalamic tract

Which anterolateral pathway projects to reticular formation, medial thalamus and cortex and is responsible for qualitiative aspects of pain, temperature and non-discriminative touch?

Paleospinothalamic tract

Which third order neurons (lateral or medial thalamic) project to primary somatosensory cortex and are somatotopically arranged for stimulus localization?

Lateral thalamic neurons

Which third order neurons (lateral or medial thalamic) project to cingulate gyrus and insula, are responsible for affective qualities of pain, temp, etc. and has some different nuclei that generate alerting responses or the experience of dull, persistent pain?

Medial thalamic neurons

In what condition are cysts formed in the center of the cervical grey matter interrupting decussation of anterolateral (spinothalamic) second order neurons; these lesions affect decussation of both sides leading to bilateral loss of pain and temp. (but not discriminative touch or proprioception) from the cervicothoracic area of the body?

Syringomyelia

In what condition is a hemisection of spinal cord cut through dorsal and anterolateral columns on one side causing loss of ipsilateral discriminative touch; sensory neurons ascend without decussation at the level of the lesion; loss of contralateral pain and pemperature; second order neurons decussate below level of lesion, and loss of ipsilateral motor control?

Brown-Sequard syndrome

Discriminative touch, pain, temp., and proprioception of the face are all mediated by what nerve?

Trigeminal (V)

What division of the trigeminal innervates the orbital cavity, forehead, and dorsum of the nose?

Opthalmic

What division of the trigeminal innervates the nasal cavity and cheek area of the face?

Maxillary

What division of the trigeminal innervates the oral cavity, chin, side of the face, ear, external acoustic meatus and tympanic membrane, and is motor to masticator muscles and soft palate?

Mandibular

"CN V (trigeminal) projects from the pons and divides into three divisions. Each division enters face through which foramina? Opthalmic Maxillary Mandibular"

"Opth: superior orbital fissue Max: foramen rotundum Man: foramen ovale"

Which nucleus of the trigeminal nerve mediates discriminative touch?

Principal

Which nucleus of the trigeminal nerve mediates pain and temperature?

Spinal

Which nucleus of the trigeminal nerve mediates proprioception from masticators and their reflexes?

Mesencephalic

Which nucles of the trigeminal nerve is motor to mastication muscles?

Motor

Rostralmost part of neural tube forms the telencephalon, which will become the ___ ___

Cerebral hemispheres

The cortex develops from the telencephalon after what?

Neurulation

Telencephalon includes what two things?

Basal ganglia and cerebral cortex

In development of the cerebral cortex cells migrate from lateral and medial ganglionic eminences, which will become the ___ ___.

Basal ganglia

Cell migrating to become basal ganglia migrate to cortical surface along what?

glial cells

Stellate cells in layer IV receives what?

Sensory input from the thalamus

Pyramical cells in layer V project infomation where?

To other regions of the CNS

What is the term for areas of cortex that have characteristic cells that are histologically distinguishable and each area has been numbered and is used for anatomical identification of functional areas?

Broadmann's areas

What enables one to visualize brain activity in respnse to ongoing mental and physical activity?

Functional magnetic resonance imaging (fMRI)

"Magnetic fields from an MRI affect the spin and alignment of H+ ions. What are the effects of: A vertical field? A horizontal field with a radio frequency? Recovery from the wobble?"

"V: aligns H+ ions H: makes H+ ions wobble R: creates electric current detected by the MRI"

What is BOLD and what is it used for?

Blood Oxygen Level Detection - to measure neurally related blood flow

What is related to neuronal activity via astrocytes?

Blood flow

What consists of a pair of oval shaped clusters of nuclei in the diencephalon lying on each side of the third ventricle and projects axons to all areas of the cortex?

Thalamus

True or false: each nucles in the thalamus projects axons conveying either sensory, motor, or integrated neural information to cerebral cortex.

TRUE

What anatomical structure forms the primary somatosensory cortex (S1)?

Postcentral gyrus

The VPL receives input from what two pathways?

Dorsal-lemniscal and anterolateral pathways

The VPM receives input from what?

The head via the trigeminal nerve

How does somatosensory information enter the primary somatosensory cortex?

Via the VPL and VPM nuclei of the thalamus

What part of the brain elaborates and contextualizes sensory information into meaningful experiences?

Primary and secondary somatosensory cortices

In primary sensory cortices, localization and specificity of sensory modalities are reflected in functionally and regionally specific ___ ___.

Cortical columns

What are cortical columns?

Neurons with similar sensory receptive properties. Several columns form arrays that will map different body areas or sensory modalities

Homonculus

Cortical sensory representation changes with experience and learning, what is this called?

Cortical plasticity

Cortical column neurons respond primarily to one specific area of the body, but what also projects to the same columns, but without eliciting activity?

Inputs from neighboring areas of the body surface

Cortical localization of stimulation requires what of the stimuli at various neural levels including dorsal column nuclei, thalamus and somatosensory cortex?

Differentiation of receptive fields

In peripheral structures, what are grossly differentiatted by selective activity of sensory neurons that innervate each distinct RF (localization is more specific where RF's are smaller)?

RF - receptive fields

In the CNS, RF's are more finely differentiated by neural interactions between pathways from different RF's. What does this require?

Lateral inhibition

What is the neural mechanism in cortex, thalamus, and dorsal column nuclei that enhances the difference between somatosensory receptive fields?

Lateral inhibition

Dorsal column nuclei neurons are stimulated by what?

Sensory neurons from the center of a RF

What suppresses activity from sensory neurons in the peripheral zone of a RF?

Inhibitory interneurons within the dorsal column nuclei

Lateral inhibition results in varied responces from differnt zones in the RF. What generates a positive response? A negative?

Central stimulation of the RF; peripheral stimulation of the RF

Without lateral inhibition by interneurons, what happens to the activity of the stimulus?

It is dispersed among neighboring neurons with declining amplitude

Inhibitory interneurons are normally interposed such that when they are stimulated by recurrent branches from DCN neurons, they do what?

Inhibit neighboring DCN neurons (with lateral inhibition, the central region of activation is enhanced, while the neighboring region is inhibited)

What is the term that refers to the ability to discriminate between separate but simultaneous pin-pricks to the skin, which is a common neurological test that measures integrity of the dorsal column-lemniscal system?

Two Point Discrimination

Two point discrimination involves precise localization of a physical stimulation which depends on what two things?

"Density of sensory receptors in the skin | Lateral inhibition in the CNS to precisely discriminate the stimulation of seperate receptive fields"

Descending pathways from both primary somatosensory and motor cortex modulates afferent input from upper limb during tactile exploration. This is to: (2)

"Select certain inputs relevant to the movements | Provide input to assure frequency and duration discrimination for tactile and proprioceptive information"

What kind of control of sensory pathways is the norm and provides a means to select stimuli pertinent to behavioral contect?

Feedback control

Somatosensory perception depends on what?

Movement

What happens to Meissner's rapid adapting and Merkel's slow adapting inputs in area 3b?

They are projected to separate columns

VPL projects to several regions of S1. Broadmann areas of cortex encode different somatosensory modalities. Which area does proprioception? SA and RA cutaneous receptors?

3a; 3b

The dorsal stream of S1 projects where?

To posterior parietal cortex areas 5, 7 for multisensory integration, directing attention and interacting with the motor cortex in frontal lobe.

The ventral steam of S1 projects where?

SII (2) bilaterally

What is the secondary somatosensory cortex, what does it do?

Form processing; it responds to global features of objects such as size and shape

What are the primary responsibilites of the posterior parietal association cortex (areas 5, 7)?

Generating a conscious body image; integrating touch, proprioception, vision and audition into a body schema or "ego-centric space".

Association cortices receive incoming information from primary and secondary somatosensory cortex either directly via ___ or indirectly via ___.

Arcuate fibers; thalamus

What feature of SII can be described by the same orientation of edges on different fingers unite a sense of continuity and generate perception of round disc

Orientation selectivity. It develops internal 3D picture of object

Why does SII convey information to and from the hippocampus and amygdala of the limbic system?

To form memories based on behavioral significance

"What the body is felt to be like" is the definition of what?

Somatoperception

"Abstract knowledge, beliefs and attitudes about one's own or other's bodies" is the definition of what?

Somatorepresentation

What is phantom limb sensation caused by?

Reorginazation of somatosensory cortex