Lecture 2: Proprioception/Tactile Pathways Flashcards by Danielle Collins

Define frequency coding

Cells firing rate signals stimulus intensity or temporal aspects of the tactile stimulus

Ex. Someone repeatedly poking you over and over

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Define population coding

Distribution in time/space of the number of activated cell signals location of the stimulus as well as its motion/direction

Ex. Take your whole hand and squeeze your arm -> you will get multiple inputs bc you’re covering such a wide area

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Differentiate between a fasciculus and a tract

Fasciculus = general term referring to a bundle of nerve fibers which belong to a particular system in the CNS

Tract = a fasciculus comprised of nerve fibers that have a common origin, termination and function

**All tracts are fasciculi but not all fasciculi are tracts

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What is a lemniscus?

A bundle of crossed, secondary nerve fibers in a conscious sensory pathway -> lesions of a lemniscus would result in contralateral deficits

It has very limited and specific use

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The centra canal is a cul-de-sac extending from the obex of the fourth ventricle to C5-8. Pathologically, the central canal may enlarge and develop a cavity in the center of the cord. This is a condition referred to as __________________

Syringomyelia

**Pts with syringomyelia characteristically complain of bilateral anesthesia of the shoulder and upper limbs

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A ____________ neuron is a pseudounipolar neuron whose cell body is located in a spinal ganglia

Primary

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The soma of a ______________ neuron is located in a specific nucleus of the dorsal thalamus. The axon projects to the primary somesthetic cortex via the thalamic radiations of the internal capsule and corona radiata

Tertiary neuron

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***The lateral spinothalamic tract is formed by which of the following?
A. Axon of a secondary neuron
B. Axon of a tertiary neuron
C. Central process of a primary neuron
D. Peripheral process of a primary neuron

A. Axon of a secondary neuron

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***The fasciculus cuneatus is formed by which of the following?
A. Axon of a secondary neuron
B. Axon of a tertiary neuron
C. Central process of a primary neuron
D. Peripheral process of a primary neuron

C. Central process of a primary neuron

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***The corticospinal tract primarily affects which of the following?
A. Axial musculature
B. Distal limb musculature 
C. Masticatory muscles 
D. Mimetic muscles 
E. Proximal limb musculature

B. Distal limb musculature

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***An increase in gamma motor activity causes which of the following?
A. Areflexia 
B. Antonia
C. Hyperreflexia
D. Hyporeflexia 
E. Hypotonia

C. Hyperreflexia

**An increase in gamma motor activity causes hypertonia and hyperreflexia and a decrease causes hypotonia and hyporeflexia

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***The substantia gelatinosa is associated with which of the following?
A. Cerebellar paths
B. Pain and temperature 
C. Proprioception 
D. Visceral pain

B. Pain and temperature

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***The alpha motor neurons are associated with which of the following?
A. Autonomic nuclei
B. Intrafusal fibers 
C. Lower motor neurons
D. Upper motor neurons

C. Lower motor neurons

**Alpha and gamma motor neurons are lower motor neurons -> alpha motor neurons innervate extrafusal fibers and gamma motor neurons innervate intrafusal fibers

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***A lemniscus is formed by which of the following?
A. Axon of a secondary neuron
B. Axon of a tertiary neuron
C. Central process of a primary neuron
D. Peripheral process of a primary neuron

A. Axon of a secondary neuron

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***Spinal ganglia are comprised of which of the following?
A. Cell bodies of motor neurons
B. Cell bodies of primary neurons 
C. Cell bodies of secondary neurons
D. Cell bodies of tertiary neurons

B. Cell bodies of primary neurons

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***The axon of a tertiary neuron terminates in which of the following?
A. Primary cortex 
B. Dorsal thalamus 
C. Cerebellum 
D. Association cortex

A. Primary cortex

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***A unilateral lesion of a primary neuron in a conscious sensory pathway would result in which of the following?
A. Bilateral deficits 
B. Contralateral deficits
C. Ipsilateral deficits
D. No deficits

C. Ipsilateral deficits

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***A unilateral lesion of a lemniscus would results in which of the following?
A. Bilateral deficits 
B. Contralateral deficits 
C. Ipsilateral deficits 
D. No deficits

B. Contralateral deficits

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***The medial lemniscus is comprised of which of the following?
A. Axons of secondary neurons
B. Axons of tertiary neurons
C. Central processes of primary neurons
D. Peripheral processes of primary neurons

A. Axons of secondary neurons

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***A lesion of the right fasciculus gracilis at T10 would result in which of the following?
A. Loss of crude tactile in right lower limb
B. Loss of pain sensation in left lower limb
C. Loss of pain sensation in right lower limb
D. Loss of proprioception in left lower limb
E. Loss of proprioception in right lower limb

E. Loss of proprioception in right lower limb

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***Axons in the posterior columns are which of the following?
A. Interneurons
B. Primary neurons
C. Secondary neurons
D. Tertiary neurons

B. Primary neurons

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***A unilateral lesion of the medial lemniscus would result in which of the following?
A. Bilateral deficits 
B. Contralateral deficits
C. Ipsilateral deficits
D. No deficits

B. Contralateral deficits

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***A unilateral lesion of the posterior columns would result in which of the following?
A. Bilateral deficits 
B. Contralateral deficits 
C. Ipsilateral deficits
D. No deficits

C. Ipsilateral deficits

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What is the primary pathway that transmits discriminative touch, flutter-vibration and proprioceptive information?

Posterior column/medial lemniscal pathway

Subsets include the trigeminothalamic pathways and the spnocerebellar pathways

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How are receptor density gradient and receptive field related?

Inversely -> the greater the receptor density gradient, the smaller the receptive field (bc there are more receptors in the area so each has a smaller area to supply)

Where are common locations of small receptive fields?

Perioral region Fingertips Face **Small receptive fields = high receptor density

All motor activity is based upon ____________ reflexes

Spinal cord

What 3 things do primary afferent fibers consist of?

1. A peripheral process extending from the dorsal root ganglion (DRG) 2. Central process extending from DRG into CNS 3. Pseudounipolar cell body in DRG

On the basis of cell size and fiber diameter, primary sensory fibers are categorized as large and smal. What sensory information do large-diameter fibers relay and where do they enter the spinal cord?

Discriminative touch, flutter-vibration and proprioception; enter spinal cord via medial division of posterior root then branch

Large diameter sensory fibers relay discriminative touch, flutter-vibration and proprioception. They enter the spinal cord via the medial division of the posterior root then branch. ONe set of branches terminates on second order neurons in the ____________________ and the largest set of branches ascends cranially and contributes to the formation of ____________________________

Spinal cord gray mater at, above and below level of entry; formation of fasciculus gracilis and fasciculus cuneatus -> collectively termed the posterior columns

What 2 structures make up the posterior columns?

Fasciculus gracilis and fasciculus cuneatus

Fibers within the posterior columns are organized typographically. Sacral level fibers are positioned _________ (medially/laterally) and fibers from progressively more rostral levels (up to T6) are added _________ (medially/laterally) to form the fasciculus gracilis. Thoracic fibers above T6 and cervical fibers form the ___________ (medially/laterally) placed fasciculus cuneatus in the same manner

Medially; laterally; laterally

What results from damage to the posterior columns of the spinal cord?

Ipsilateral (fibers havent crossed yet) reduction or loss of discriminative, positional and vibratory tactile sensations at and below the segmental level of injury - Sensory ataxia, pts may also have a wide-based stance and may place the feet to the floor with force

Where are the nucleus gracilis and nucleus cuneatus located?

Posterior medulla

The nucleus gracilis and nucleus cuneatus contain ____________ order neurons of the ______________ system

Second order; posterior column/medial lemniscus pathway

The nucleus gracilis and nucleus cuneatus receive inputs from their corresponding fasciculus. Segregation of tactile inputs occurs within the nuclei. What happens in the core versus outer shell?

Core “clusters” receive inputs from rapidly and slowly adapting afferents Outer “shells” receive inputs from muscle spindles, joints and pacinian corpuscles

What is the function of the substantia gelatinosa?

Modulate transmission of pain and temperature information at all levels of the spinal cord

What is the function of the nucleus proprius?

Modulate pain and temperature information and some tactile; located at all levels

What is the function of the nucleus dorsalis (Clark’s column)?

Posterior spinocerebellar tract cells -> unconscious proprioceptive information

What is the function of the interomediolateral cell column?

House preganglionic sympathetic neurons at thoracolumbar segments

What is the function of lateral versus medial motor cell columns?

Lateral: modulate fractionation movements of the distal limbs Medial: modulate movements of the axial musculature

Fibers in the medial division of the dorsal root enter the ___________ columns and convey what type of information?

Posterior columns; proprioception, 2-pt tactile discrimination and vibratory info

Fibers in the lateral division of the dorsal root enter the __________________________ and convey what type of information?

Dorsolateral fasciculus of Lissaur; convey pain and temperature information

What does lesions of the dorsal roots result in?

Hypotonia or Antonia -> involvement of the lumbosacral dorsal roots in tabes may result in atonic bladder

What is the lateral corticospinal tract responsible for?

Precise, individual movements of the digits; fractionation of movement

What is the lateral spinothalamic tract responsible for?

Pain and temperature info from opposite side of body

Where does the lateral spinothalamic tract decussate?

In the anterior white commissure

What does a unilateral lesion of the lateral spinothalamic tract result in?

Contralateral loss of pain and temperature TWO sensory dermatomal segments below the lesion

What does a unilateral lesion of the spinal lemniscus result in?

Contralateral hemianalgesia and thermal hemianesthesia

What is the lateral reticulospinal tract responsible for?

Voluntary control of bowel and bladder

What occurs due to a lesion of the lateral reticulospinal tract?

IF the lesion is BILATERAL then loss of voluntary control of bladder and bowel

What occurs due to lesion of the anterior horn?

Ipsilateral lower motor paralysis at the level of the lesion **Anterior horn is where LMNs leave spinal cord to go innervate muscle

What occurs due to damage of the posterior columns at the level of the BRAINSTEM (midbrain)?

Leads to deficits in discriminative touch, vibratory and positional sensibilities over the contralateral side of the body **When lesions occur above the level of the decussation then the deficits will occur on the contralateral side of the body

What sensations is the ventral spinothalamic pathway responsible for?

Crude tactile -> light (passive) touch, crude tactile sensations and pressure

What is the function of the cuneocerebellar tract?

Precise info from UE

What is the function of the dorsal spinocerebellar tract?

Precise info from individual muscles LE and Lower half of body

What is the function of the ventral spinocerebellar tract?

Gross postural and general proprioception LE and lower half of body

What tracts are responsible for unconscious precise proprioception of individual muscles in the LE versus UE?

LE = dorsal spinocerebellar tract UE = Cuneocerebellar tract

What tracts are responsible for unconscious gross proprioception of whole limbs of the UE versus LE?

LE = ventral spinocerebellar tract UE = rostral spinocerebellar tract

The ventral posterior nuclei is a wedge-shaped cell group located in the __________________ and is comprised of the ___________________ nucleus and ____________________ nucleus

Caudal thalamus; central posterolateral nucleus (VPL) & ventral posteromedial nucleus

What artery supplies the VPL & VPM and what is the result of compromise to this artery?

Thalamogeniculate branches of posterior cerebral a; compromise can result in loss of all tactile sensation over the contralateral body and head

Somatotrophs arrangement of the body is maintained in what nucleus?

Ventral posterolateral nucleus (VPL)

What information does the VPM versus VPL nuclei receive?

VPM = head proprioceptive information VPL = body

What are the ventral posterior nuclei (VPM and VPL) separated by?

Arcuate lamina

What happens to tactile sensation due to middle cerebral artery versus anterior cerebral artery lesions

MCA = Loss over contralateral upper body and face ACA = lesions affect contralateral lower limb

Axons of third order neurons (thalamus) terminate in the primary somatosensory cortex which comprises what 2 gyri?

Postcentral and posterior paracentral gyri - Bordered by central sulcus anteriorly and postcentral sulcus posteriorly

The primary somatosensory cortex is subdivided from anterior to posterior into brodmann areas. What brodmann areas are found in the primary somatosensory cortex?

Area 3a, 3b, 1 and 2

What are occurs due to a lesion in brodmann area 1 versus 2?

Area 1 produces a deficit in texture discrimination Area 2 results in loss of size and shape discrimination (astereognosis) **Area 3b performs initial processing and distributes info to these 2 areas, so injury to 3b has a more profound effect bc you will get both symptoms mentioned above

What does a lesion to the parietal association area result in?

Can produce agnosia -> sensation not radically altered, but limb is not recognized as part of pts own body, contralateral body parts are lost from the personal body map

The parietal cortical regions receive some tactile inputs. What do they receive them from?

Some medial lemniscal input and inputs from primary somatosensory cortex

WHat does the secondary somatosensory cortex receive inputs from?

Ipsilateral primary somatosensory cortex and ventral posterior inferior nucleus of the thalamus **This cortex helps you decide how to respond to input

What 4 nerve endings detect fine touch and proprioception?

Meisners corpuscles Pacinian corpuscles Ruffini endings Merkel endings

Lecture 2: Proprioception/Tactile Pathways Flashcards

(72 cards)