Somatosensory Processing

Which of the following are NOT among the functions of dorsal root ganglion neurons? Choose one. a) relaying information about the velocity of muscle contraction b) relaying information regarding muscle tension from a Golgi tendon organ c) relaying the efferent information for the "knee-jerk" reflex d) forming direct synapses on neurons in the brainstem e) relaying afferent signals from the joint

!= a, d, e

Which of the following statements is FALSE about reflex pathways and muscle movement? Choose one. a) In the patellar tendon reflex only one synapse is necessary in order to signal contraction of the extensor muscle b) Afferent activity in Golgi tendon organs (GTOs) is greater than activity in muscle spindles when that muscle contracts c) The flexion reflex stimulated by a painful stimulus to the right foot will lead to contraction of extensor muscles in the left leg, and contraction of flexor muscle in the right leg d) Complex movements requiring coordination of multiple muscles (e.g. walking) are entirely under control of upper motor neurons in the primary motor cortex, and the spinal cord only provides basic reflex circuitry

!= b, c

Which of the following statements about cells in cortical layers of the somatosensory cortex is FALSE? Chose one. A) Within a vertical column in primary SS cortex, one finds cells responsive to the same somatotopic area B) Stimulation of the somatosensory cortex directly stimulates muscle fibers through the release of glutamate C) Primary somatosensory receive inputs from ipsilateral thalamus D) Primary motor cortex has large layer 4 pyramidal cells that project outside the cortex E) All of these are true

!= d

Which of the following is true about somatosensory signaling? Choose one. a) A sensory receptor or "generator" potential is usually an "all-or-nothing" event, much like action potentials b) Two point discrimination threshold refers to the largest distance between two objects touching the body that can be sensed as separate c) Afferent sensory neurons that relay touch information have cell bodies in the DRG s and send axons up the dorsal columns of the ipsilateral spinal cord to synapse in the brainstem d) In both the ascending touch pathway and the ascending pain pathway it is the primary (1o) neuron that crosses the midline e) The left ventral posterior thalamus sends information to the right somatosensory cortex

!= d, e

Explain the difference between areas 3a and 3b of the somatosensory cortex in terms of the types of mechanosensory neurons that send information there.

3a and 3b are both part of the primary somatosensory cortex, but 3b responds primarily to cutaneous stimuli (receiving the bulk of the information from the ventral posterior complex and serves as an obligatory 1st step in cortical processing of somatosensory info since it sends info to areas 1 and 2) and 3a responds mainly to stimulation of proprioceptors.

Explain the difference between areas 3a and 1 of the somatosensory cortex in terms of the types of mechanosensory neurons that send information there.

3a responds mainly to stimulation of proprioceptors , and 1 responds mainly to cutaneous stimuli.

Explain the difference between areas 3a and 2 of the somatosensory cortex in terms of the types of mechanosensory neurons that send information there. View keyboard shortcuts EditViewInsertFormatToolsTable 12ptParagraph

3a responds mainly to stimulation of proprioceptors , and 2 responds to both tactile and proprioceptive stimuli.

Which of the following statements about primary motor cortex (PMC) neurons is FALSE? Choose one. a) The firing of PMC neurons occurs precisely at the onset of a muscle contraction. b) PMC neurons can be directionally selective. c) The firing rate of a PMC neuron codes for or contributes to the force of a movement. d) The directional control of a movement is coded by the activity of a population of PMC neurons. e) The directional responses of PMC pyramidal cells tend to be broadly tuned in that they respond over a somewhat broad range of movement directions.

A) The firing of PMC neurons occurs precisely at the onset of a muscle contraction.

Which role do γ motor neurons play in the function of a muscle spindle? Choose one. A) They improve the accuracy of the reported sensory information by innervating extrafusal fibers. B) They improve the accuracy of the reported sensory information by innervating intrafusal fibers. C) They enhance the force of muscle contraction by innervating extrafusal fibers. D) They enhance the force of muscle contraction by innervating intrafusal fibers. E) They coordinate the contraction of extrafusal and intrafusal fibers.

B) they improve the accuracy of the reported sensory information by innervating intrafusal fibers.

Which of the following statements about the organization of muscles and motor neurons is FALSE? Choose one. a) Many postural muscle fibers contract slowly and produce a sustained force b) γ-MN innervate extrafusal fibers in order to help maintain muscle tone c) Large motor neurons are recruited only at higher levels of stimulus intensity. d) γ-MN have high firing rates during unpredictable conditions e.g. when standing on the subway

B) γ-MN innervate extrafusal fibers in order to help maintain muscle tone

Explain the differences between Merkel sensory afferents and Pacinian corpuscles in terms of localization, adaptation, and types of stimuli that activate them. View keyboard shortcuts EditViewInsertFormatToolsTable 12ptParagraph

Pacinian corpuscles are rapidly adapting fibers found deep in the dermis or subcutaneous tissue that act as a filter only responding to transient disturbances at high frequencies. Merkel sensory afferents however are slow adapting fibers most commonly found in fingertips that receive information from receptors in the epidermis, so they are in the tips of the primary epidermal ridges and are activated by mechanosensory stimuli.

Explain the differences between Ruffini corpuscles and Meissner sensory afferents in terms of localization, adaptation, and types of stimuli that activate them.

Ruffini corpuscles are deep in the dermis layer of the skin whereas Meissner sensory afferents are closer to the skin's surface in the tips of the dermal papillae adjacent to the primary ridges. Ruffini corpuscles are slow adapting fibers that detect heavy touch, pressure, joint movements and especially skin stretching. Meissner afferents are rapidly adapting fibers that sense skin deformation and low-frequency vibrations.

If a person can identify two pins placed 1cm apart on their upper arm, how do you know that they will also be able to identify the two pins on their fingertip?

The finger tip has greater two-point discrimination and sensitivity than the upper arm.

Explain the basic pathway between proprioceptive neurons innervating muscles of the abdomen and the somatosensory cortex including the location of the neurons in the pathway and whether they are localized ipsilateral or contralateral to the stimulus.

The proprioceptive neurons innervating muscles on the abdomen travel travel back to the DRG where the soma is and then travel further to synapse both on the ventral horn of the spinal cord which goes to the cuneate nucleus and go through the cuneate tract to the gracile nucleus (up to this point everything was ipsilateral but now it will be contralateral). The gracile nucleus then sends its axons to the ventral posterior lateral nucleus of the thalamus, which sends information up to the somatosensory cortex.

Explain the basic pathway between proprioceptive neurons innervating muscles of the lower leg and the somatosensory cortex including the location of the neurons in the pathway and whether they are localized ipsilateral or contralateral to the stimulus.

The proprioceptive neurons innervating muscles on the lower leg travel travel back to the DRG where the soma is and then travel further to synapse both on the ventral horn of the spinal cord which goes to the gracile nucleus and go through the gracile tract to the gracile nucleus (up to this point everything was ipsilateral but now it will be contralateral). The gracile nucleus then sends its axons to the ventral posterior lateral nucleus of the thalamus, which sends information up to the somatosensory cortex.

Explain why a person can identify two pins placed 5mm apart on the finger but not on the back of the leg.

This is possible because the finger has greater sensitivity and two point discrimination than the back of the leg.

Where are the gracile and cuneate tracts located? a) Primary somatosensory cortex SI b) Brodmann's area 1 c) Brodmann's area 2 d) Secondary somatosensory cortex SII e) Hypothalamus

a) Primary somatosensory cortex SI

Functional reorganization in the somatosensory cortex: a) occurs at all ages, all of the time. b) occurs after nerve damage, amputation, and skill training. c) results in a temporary loss of sensory input. d) occurs only during the first ten years of life.

b) occurs after nerve damage, amputation, and skill training.

Ruffini corpuscles

detect heavy touch, pressure, joint movements and skin stretching; found in the dermis

True or false? If group II sensory afferents in a limb were not functions, detection of the velocity of limb movement would be disrupted.

false

True or false? Mechanosensory sensory afferents are distinct from proprioceptive sensory afferents because distortion of the membrane opens ion channels.

false

True or false? Sensory adaptation is the sustained response of a sensory neuron to continuous stimulation.

false

The axons of the medial lemniscus synapse with neurons of the: a) cuneate nucleus. b) primary sensory cortex. c) thalamus d) gracile nucleus. e) dorsal root ganglion

thalamus

Sensory Transduction

the process of converting the energy of a stimulus into an electrical signal

True or False? Both the gracile and cuneate tracts are located in the dorsal columns of the spinal cord.

true

True or false? A sensory afferent with a small receptive field is likely to confer greater fine discrimination than one with a large receptive field.

true

True or false? Force is produced by the extrafusal muscle fibers, whereas the intrafusal muscle fibers contribute very little to the overall force produced by the muscle.

true

True or false? Primary sensory afferents from the muscle bifurcate to make synapses with neurons in both the spinal cord and the brain stem

true

True or false? Rapidly adapting sensory neurons respond briefly to the stimulus when it is first presented and again when the stimulus is removed.

true