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Organ Systems > Somatosensory 1, 2 and Motor > Flashcards

Somatosensory 1, 2 and Motor Flashcards

1
Q

What is compound action potential?

A

the sum of the activity in a number of nerve fibers. It is the summed APs over time at a particular site on a nerve. The peaks are different in axons with different conduction velocity and degrees of myelination.

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2
Q

What is intensity coding?

A

FREQUENCY CODING : increase the firing rate of individual primary afferent fibres by increasing the size of the receptor potential

Graded potentials can fire more frequently with increase in temperature.

All over none APs release NTs once they’re over a given threshold.

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3
Q

What impact does slow versus rapid adapting receptors have on the message sent to the brain?

A

Slow (SA): gradual decrease in activity; Merkel cells (epidermis - texture) and Ruffini (dermis skin stretch); “what is occurring”

Rapid (RA): Fast ion channel inactivation, decrease in receptor potential; Axons surrounded by Schwann cells and CT in dermis; Meissner corpuscle (movement) and Pacinian corpuscles (high frequency vibration releases glutamate) and hair follicles (touch); “that it’s happening”

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4
Q

What are cutaneous receptive fields?

A

Area of skin innervated by a single sensory neuron
Peripheral RFs: densely innervated and small; Meissner and Merkel i.e. fingertips
Proximal RFs: less innervated and large; Pacinian and Ruffini i.e. back

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5
Q

How do cutaneous receptive fields contribute to tactile localization?

A

Tactile sensations - Discriminative and nondiscriminative touch, pain, temp
Size varies for different degrees of acuity
Density - peripheral versus proximal
Secondary RFs overlap for specificity because spinal neurons can discern subtle differences among them

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6
Q

How are sensory modalities distinguished by the peripheral nerves?

A

Conduction velocity is different
They have separate populations of specialized sensory neurons
CT capsules, modified epithelium, hair
Membrane receptors of free nerve endings

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7
Q

Describe some examples of the kinds of information that slow and fast adapting exteroceptors mediate.

A

A-alpha: proprioceptor, motor
A-beta: light touch
A-delta: fast pain
C: slow pain

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8
Q

What type of axons mediate pain, temperature, and non-discriminative touch?

A

A-delta and C type axons
From free nerve endings
Slow adapting, conducting, smaller

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9
Q

What is the anterolateral system?

A

Sensory neurons synapse in the dorsal horn using glutamate, NO, substance P –> Rexed’s lamina (pain and touch)–> Second order neurons that decussate and enter anterolateral column

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10
Q

Compare the difference between neo- and paleospinothalamic pathways.

A

Neospinothalamic: pain info to lateral thalamus –> somatosensory cortex; quantitative discrimination and localization

Paleospinothalamic: pain info to reticular formation –>medial thalamus–>limbic cortex; qualitative pain, temperature, non-discriminative touch, alerting responses, dull, persistent pain

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11
Q

What are symptoms for syringomyelia syndrome?

A

Bilateral loss of pain and temperature

Defect of cervicothoracic anterolateral decussation of secondary neurons

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12
Q

What are symptoms for Brown-Sequard syndrome?

A

Contralateral loss of pain and temperature; ipsilateral loss of discriminative touch and motor control
Hemisection of spinal cord

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13
Q

What is the anatomy and sensory projections of the trigeminal nerve?

A

Concentric dermatome - onion skin
V1 - ophthalmic
V2 - maxillary
V3 - mandibular

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14
Q

What are the different nuclei in CN V that mediate different modalities?

A

Principle (main) sensory nucleus - discriminative touch from face–>thalamic VPM–>primary somatosensory cortex

Spinal trigeminal nucleus - pain and temperature from face –>thalamic VPM–>cingulate gyrus + insula

Lower nucleus - peripheral face
Higher - central face (nose, lips)
Highest - mouth, teeth, pharyngeal cavity

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15
Q

What are dermatomes?

A

Area of skin innervated by one spinal segment

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16
Q

How do the body and face dermatomes compare?

A

Face dermatome has more of a concentric pattern with trigeminal nerve; different dermatome for non-discriminative touch and proprioception

Body dermatome is set by spinal columns

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17
Q

What are Brodmann’s areas?

A

Area of cerebral cortex that encodes different somatosensory modalities
Object size and shape perception
Area 3a: proprioception
Area 3b: SA + RA cutaneous receptors

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18
Q

What does fMRI measure?

A

BOLD - blood oxygen level detection
Measures active areas during mental and physical activity since neuronal activity increases demand for oxygen and blood flow

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19
Q

Where and what is the primary somatosensory cortex (SI)?

A

In postcentral gyrus

Gets input from thalamus: VPL for body, VPM for head

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20
Q

What are cortical columns of the SI?

A

Columns that have similar sensory receptive properties, maps out different body areas or sensory modalities

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21
Q

What’s the pathway of thalamus projection onto various somatosensory cortical regions?

A

Ascending pathway from trigeminal nuclei to thalamus (VPM) and SI–>cortical activity spreads out to other cortical columns

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22
Q

What is somatotopy?

A

It is the homunculus representation in the CNS of the body where proportion is to the density of receptors
High density in the mouth and hand, low density in back

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23
Q

What is meant by cortical plasticity?

A

Sensory representations change with experience and learning
Cortical columns receive input from one specific part of the body normally but receive inputs from neighboring areas of columns without eliciting activity
“Latent” pathways are activated with enhanced activity of specific digits

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24
Q

Describe somatosensory receptive fields in the periphery and the CNS.

A

In the periphery - RFs are differentiated by selective activity of sensory neurons
In the CNS - RFs are finely differentiated by lateral inhibition - center is excitatory to secondary neuron, surround is inhibited by inhibitory interneurons

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25
Q

How does lateral inhibition impact incoming somatosensory information?

A

Just receive sensory information from the center to the secondary neuron in dorsal column nuclei, thalamus, and cortex

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26
Q

What is two-point discrimination?

A

Ability to distinguish between separate but simultaneous pin pricks to the skin

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27
Q

What parts of the somatosensory system are responsible for two-point discrimination?

A

Dorsal column lemniscal system
Skin receptors and lateral inhibition
Requires discriminative touch mechanoreceptors

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28
Q

How does feedback from sensory and motor cortices affect lateral inhibition and information processing in the ascending somatosensory system?

A

Feedback regulates lateral inhibition by selecting stimuli that’s pertinent to behavioral context (focusing), relevant to movement, allowing for greater tactile resolution
Sensory cortex directly enhances DCN neurons from RF #2 instead of #1 by lateral inhibition on #1 and inhibiting inhibition on #2

29
Q

What are the somatosensory “dorsal and ventral streams”?

A

Somatosensory info spreads from primary somatosensory into SII and association cortices along dorsal and ventral streams.

Dorsal SI–>posterior parietal cortex (PPC), multi-sensory integration, attention, interaction with motor cortex; senses where and how

Ventral SI–>secondary somatosensory (SII) cortex bilaterally sees size and shape

30
Q

What aspects of somatosensory information are associated with posterior parietal cortex?

A

Convergence of visual, auditory, somatosensory input, body awareness and peripheral space, extending to Wiernicke’s area for reading and writing

31
Q

What aspects of info are associated with the secondary (SII) cortex?

A

Orientation of object, interconnected with the hippocampus and amygdala for memories

32
Q

What role does the posterior parietal cortex play in how vision and somatosensory information impacts somatosensory awareness?

A

PPC local area and premotor areas establish embodiment of rubber hand into one’s body

33
Q

What are the characteristics and cortical issues associated with phantom limb phenomena?

A

Disconnection of somatorepresentation (knowing the limb is gone) and somatoperception (what the limb feels like)
Peripheral structures with more cortical space take longer to reorganize
Telescoping: early reorganization of cortex responding to lower density of receptors in proximal structures

34
Q

What is astereognosis?

A

Inability to identify object by touch

35
Q

What is neglect syndrome?

A

Right lesion of inferior parietal lobe: lose attention in left side of body and vision
Right side is often involved in neglect because it can compensate for left side in a left-sided lesion

36
Q

What is the difference between somatosensation, somatoperception, and somatorepresentation?

A

Somatosensation is what you feel from SI and SII about size and shape, leading to somatoperception (how you perceive things to feel) and comparing it to your somatorepresentation (what you know abstractly about how it SHOULD feel)

37
Q

What is meant by somatosensory attention? What cortical areas are involved?

A

Each side of the brain pays attention to the opposite sides of the body, visual, auditory fields

38
Q

What is the difference between lower and upper motor neurons?

A

Lower - gamma and alpha (somatotopic in ventral horn, monosynaptic innervation of muscle); all movements are done from a selective group of 1 million lower motor neurons
Upper - cerebral cortex, reticular formation, vestibular nuclei

39
Q

What is a muscle spindle and how does it respond to changing muscle length?

A

It regulates muscle length via intrafusal muscle fibers 1a + II afferents detecting changes in length and velocity
When there’s a stretch, it distorts the axon membrane and therefore, opens physically-gated Na/Ca channels to depolarize cell
Sensory neuron stimulates dorsal horn at interneuron or directly onto motor neurons

40
Q

Describe the myotactic reflex

A

Homeostatic negative feedback to maintain muscle length - contracts synergistic muscles, relax antagonists

41
Q

How does gamma motor neuron activity affect myotactic reflex?

A

Gamma motor neurons increases sensitivity of muscle spindles (1a + II afferents) during movement via control of brain, not receptors

42
Q

What is a Golgi Tendon Organ and how does it respond to muscle tension? Is it regulated by gamma motor neurons?

A

GTOs are in musculo-tendon junction that protect against excess force by having an opposing reflex to the myotactic reflex - excites antagonist, relaxes synergist
Coordinates stability
Not regulated by gamma motor neurons

43
Q

Describe propriospinal neurons and their action on spinal reflexes.

A

Intersegmentally organized motor patterns where upper limb skin stimulation impacts lower limb reflexes.

44
Q

What are some general functions of upper motor neurons?

A

Posture, balance, fine movements in extremities from the brainstem

45
Q

Describe motor control functions of the vestibulospinal and reticulospinal tracts. What is the antigravity posture and what produces it?

A

They are descending motor tracts in the extrapyramidal pathway in the white matter.
Vestibulospinal controls head with the body posture, activating extensors of lower limbs and flexors of upper limb.
Reticulospinal is reticular nuclei in pons and medulla that go to proximal muscles of the trunk, upper and lower limb, providing anti-gravity extensor muscles

46
Q

What are the three parts of the descending corticospinal tract system and where does it span?

A

Spinal cord: Corticospinal, corticonuclear, corticoreticular

47
Q

What are the three portions of the corticospinal (pyramidal) tract and what does it do?

A

Pyramidal corticospinal tract - contains the internal capsule (stroke), cerebral peduncles, and decussation at the pyramids.
Lateral corticospinal tract - contains 90% of the decussate in medulla and controls fine movement
Ventral corticospinal - contains 10% of the uncrossed and controls posture of the neck and trunk

48
Q

What is the corticonuclear tract and what does it do?

A

CN motor nuclei that controls the muscles of the face, head, and neck

49
Q

What is the corticoreticular (extrapyramidal) and what does it do?

A

Pontine and medullary reticular formation: coordinates head movement with body posture and balance
Smoothes movements by limiting inhibition on extensors of lower limb and flexors of upper limb

50
Q

What is the significance of the internal capsule? Of the medullary decussation?

A

Common site of stroke

Pyramidal and lateral corticospinal tract project to opposite sides of the body from cortex

51
Q

How do the anterior and lateral corticospinal tracts differ in structure and function?

A

Structure: Lateral contains 90% of decussates and goes to lateral funiculus; ventral contains 10% and goes to ventral funiculus

Function: lateral controls fine movement, ventral controls posture of neck and trunk

52
Q

Compare lower motor neuron and upper motor neuron disease. What are the aspects of spasticity?

A

Lower motor neuron disease - lesion of alpha motor neurons interrupts neural input to muscles, leading to flaccid paralysis and atrophy of muscles

Upper motor neuron disease - stroke in motor cortices of either lateral corticospinal tract or reticulospinal tract, leading to paresis, spastic paralysis, hypertonicity, and antigravity posture

53
Q

Compare the functions of the motor cortex: primary, supplementary, and premotor cortex.

A

Premotor cortex: integrates input from somatosensory, vestibular, visual, auditory, providing intention of a particular movement based on external and internal information
Primary: divides info from premotor and supplementary to get individual muscle contractions, controlling speed, force, direction, and extent of movements
Supplemental: strategies, transforming intention into correct dynamic motor sequences; independent of external conditions

54
Q

What is efference copy?

A

Copies of motor programs sent by motor cortex to the somatosensory cortex, integrates with incoming sensory information to predict expected sensation that will occur and asses present and future states of a limb in action

55
Q

How does efference copy play a role in self awareness?

A

Self-awareness is self recognition: depends on the sense of agency and sense of ownership, in other words, comparing motor with sensory to gather an internal sense of self

56
Q

What is self-agency?

A

The sense that you are the one causing an action

Generated when efference copy of motor commands matches the subject’s intentions

57
Q

What is self-ownership?

A

The sense that you are the one who is undergoing an experience
Generated when the sensory feedback matches the subject’s intentions

58
Q

What are mirror neurons and where are they located?

A

Mirror neurons unify action perception and action execution in the inferior premotor and inferior parietal cortex
Mirror neuron activity is highly sensitive to observed action especialy when the context reveals intention i.e. picking up cup to drink versus cleaning up

59
Q

What is the pathway from cerebellar cortex to motor cortex and back?

A

Touch and proprioceptive info–>spinocerebellar tract–>Purkinje cells–>deep cerebellar nuclei (fastigial, interposed, dentate)–>thalamus and cortex

60
Q

Where is the vestibulocerebellum and what does it do?

A

Projects to vestibular nuclei in cerebellum - enhances vestibulospinal control of posture, balance (detecting uphill) and VOR (eye contact remains on object when head moves)

61
Q

What is the spinocerebellum and what does it do?

A

Projects to fastigial and interposed nuclei - compares internal (motor) and external (sensory feedback signals) representations of the world, providing feedback control of ongoing movement to adapt motor activity to changes in environment, and reducing sensitivity of stretch reflexes

62
Q

What is the cerebrocerebellum and what does it do?

A

Projects to dentate nuclei and pontine nuclei - helps initiate voluntary movement by planning and making movements more precise and automatic with practice–>learned motor patterns can predict how limb will move before execution

63
Q

What is dysmetria?

A

inability to control range of movement

64
Q

What is ataxia?

A

Combination of dysmetria and decomposition of movement: imprecise, halting movements

65
Q

What is dysarthria?

A

Slurring and inappropriate phrasing

66
Q

What is dysdiadochokinesia?

A

Inability to do rapid alternating movements

67
Q

What is “intention tremor”?

A

Oscillatory movement of a limb as it approaches a target

Not a true tremor which is what happens in Parkinson’s

68
Q

What role does the cerebellum play in cognition and visceral functions?

A

Cognition - mental flexibility, multitasking, problem-solving and inhibition for planning and directing goal-oriented behavior; verbal fluency; personality change; spatial cognition
Visceral - gastric and intestinal motility, feeding regulation, cardiovascular baroreflex with vestibular, respiration, micturition, immune functions

Organ Systems (5 decks)

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