Proprioception And Tactile Pathways Flashcards
____ system transmits and analyzes touch or tactile information from external and internal locations on the body and head.
Somatic sensations are subdivided into submodalities called what?
Somatosensory system
Discriminative touch, flutter-vibration, proprioception (position), crude touch, thermal sensation, nociception (pain/tissue damage)
Multiple pathways transmit signals of somatosensory by ____.
The primary pathway that transmits discriminative touch, flutter vibration, and proprioceptive information is the ___.
Posterior column medial lemniscal pathway (PCML)
Trigeminothalamic pathway
Spinocerebellar pathway
Anterolateral system
Posterior column medial lemniscal (PCMLS)
PCMLS has the basis for accurate localization of touch with high fidelity and a high degree of _____.
PCMLS uses two types of coding?
Spatial/temporal resolution
Frequency coding: cells firing rate signals stimulus intensity or temporal aspects of the tactile stimulus
Population coding: distribution in time/space of the number of activated cell signals location of the stimulus as wall as its motion/direction
PCML is involved with _____ and _____ of mechanical stimuli.
Examples?
It contains afferent fibers with ____ velocities and limited number of synaptic relays and precise ____ organization.
Perception and appreciation
Size, shape, texture, 3D shapes (stereognosis), motion detection, awareness of body position (proprioception), limb movement (kinesthesia)
Fast conduction; somatotopic
PCMLS has a high degree of resolution resulting from _____ like feed-forward, feedback, lateral inhibition
They sharpen the discrimination between separate points on the skin and is critical for ____.
Inhibitory mechanisms
Two-point discrimination: ability to discriminate between two stimuli simultaneously; related to the density of peripheral nerve endings
Activation of _____ can evoke somatic sensations of touch.
Mechanical pressure is transduced into an electrical signal by the _____.
If this depolarizes the neuron to threshold, a _____ is produced and relayed from the periphery to the DRG to the CNS via PCMLS.
Peripheral mechanoreceptors
Primary afferent neuron
Action potential
Accuracy of the location of a tactile stimulus depends on receptor density and receptor field size. A _____ exists between body parts. Digits and perioral region have greater density of _____. Areas like the back have a lower density.
Receptor density gradient
Tactile receptors
____ is an area of skin innervated by branches of a somatic afferent fiber.
_____ is found in fingertips, where the tactile receptor density is high. Low receptor density contains ____.
Densely innervated body parts are represented by a _____.
Receptive field
Small receptive field: greater discrimination between sensations
Large receptive field: less discrimination between sensations
Greater number of neurons
Primary afferent fibers consist of what three things?
Peripheral distribution of the afferent nerves arising from each spinal level delineates the segmental pattern of ____.
Peripheral process: extending from the DRG (mechanoreceptor or free nerve ending)
Central process: extending from DRG into the CNS
Pseudounipolar cell body: in the DRG
Dermatomes
Large diameter fibers relay ____. They enter the spinal cord via the medial division of the _____, then they branch.
Where do their branches terminate?
Discriminative touch, flutter vibration, proprioception
Posterior root
Branches terminate in second-order neurons in SC grey matter; the largest branches ascend cranially and contribute to the formation of white matter tracts called the fasciculus gracilis and fasciculus cuneatus (the posterior columns)
Fibers in the posterior column are organized topographically.
Sacral level fibers are positioned ____ and fibers from more rostral levels (up to T6) are added _____ to form the _____.
Thoracic fibers above T6 and cervical fibers form the laterally placed ____.
Medially
Laterally
Fasciculus gracilis
Fasciculus cuneatus
SC lesions result in ____ loss of discriminative, positional, and vibratory tactile sensations at and below the segmental level of injury.
Also causes ____, loss of muscle stretch reflexes, and proprioceptive losses from the extremities due to lack of sensory input.
Pt may also have a wide-based stance and may place feet to the floor with force, in an effort to creat the missing ____.
Ipsilateral
Sensory ataxia
Proprioceptive input
____ and ______ are in the posterior medulla.
They contain the _____ of the PCMLS and receive input from first-order neurons (primary afferents) from the ipsilateral DRG.
Nucleus gracilis and nucleus cuneatus
Second order neurons
Each nucleus receives inputs from its corresponding fasciculus.
Segregation of tactile inputs occurs within the nuclei and contain ____ and _____.
Fasciculus gracilis -> nucleus gracilis
Fasciculus cuneatus -> nucleus cuneatus
Core clusters: receive input from rapidly and slowly adapting afferents
Outer shells: receive input form muscle spindles, joints, and pacinian corpuscles
Second-order neurons of the PC nucleus send axons to the _____ thalamus.
The internal arcuate fibers loop anteromedially in the ____ and cross the midline as the sensory decussation. They then ascend as the ____ on the opposite side.
Contralateral
Medulla; medial lemniscus (ML)
The medial lemniscus extends rostrally and rotates laterally in the ____.
Upper extremity fibers now lie _____ and lower extremity fibers lie _____.
ML will terminate in the ____ of the thalamus.
Pons
Medially
Laterally
Ventral posterolateral nucleus (VPL)
Damage at brainstem levels lead to deficits in discriminative touch, vibratory, and positional sensibilities over the ____.
R sided midbrain lesion produces ____.
Contralateral side of the body
L sided loss of proprioception and discriminative touch
Ventral posterior nuclei is a wedge shaped cell group located in caudal thalamus. Contains ____ and ____ nucleus. Separated by fibers of the ____.
Head proprioceptive info is ____ and somatotopic arrangement of the body is ____. Compromise of these nuclei (stroke) can result in ____.
VPL and VPM are supplied by thalamogeniculate branches of the ____.
Ventral posterolateral nucleus (VPL) and ventral posteriomedial nucleus (VMP)
Arcuate lamina
VPM; VPL
Loss of all tactile sensation of the contralateral body and head
Posterior cerebral A
VPL receives ascending input from the _____.
Fibers from the contralateral nucleus cuneatus terminate _____ to the nucleus gracilis.
The fibers of the medial lemniscal fibers terminate in the VPL and are segregated: Rapidly and slowly adapting inputs target the ____; pacinian and join/muscle inputs target the ____.
Medial lemniscus
Medial
VPL core
VPL shell
The VPL for the trunk and extremities contain two populations of neurons:
Third-order neurons which are large-diameter axons that traverse the posterior limb of the internal capsule and terminate in the ____ and _____.
Local circuit interneurons (inhibitory) that receive excitatory corticothalamic inputs and influence the _____.
Primary (SI) and secondary (SI) somatosensory cortices
Firing rates of third-order neurons
Somatosensory (SI) cortex contain the termination of axons from ____.
It is located in the ____ and ____.
It is bordered by the _____ anteriorly and the _____ posteriorly.
Third-order neurons
Postcentral gyrus and posterior paracentral gyrus
Central sulcus; postcentral sulcus
The ____ is the “foot to tongue” pattern along the medial -> lateral axis.
Regions with greater receptor density (hand/lips) have a ____ amount of dedicated cortical tissue.
Regions with a small receptor density (back) have a ____ cortical representations.
Homunculus
Large
Small
Blood supply to the SI cortical areas is provided by the ____ and ____.
_____ lesions produce a tactile loss over the contralateral upper body and face;
____ lesions affect the contralateral lower limb.
Anterior and middle cerebral A
MCA
ACA
What and where are the Brodmann areas located in the primary somatosensory cortex (SI)?
Area 3a: located in the depths of the central sulcus, abuts area 4 (primary motor cortex)
Areas 3b and 1: extend up the back of the sulcus onto the shoulder of the postcentral gyrus
Area 2: lies on the gyrus surface and abuts area 5 (somatosensory association cortex)
Small lesions in the somatosensory cortex can result in sensory loss but may not impact another area because of the subdivisions of SI. All these deficits causes an affect on the ____ side.
Lesions of area 1 produce a deficit in ____; damage to area 2 causes ____.
Injury to area 3b causes deficits in _____. 3b does the initial processing and then distributes info to ____.
Contralateral
Texture discrimination
Loss of size and shape discrimination (astereognosis)
Both texture and size/shape discrimination; areas 1 and 2
____ is a brainstem or SC lesions that results in deficits that differ between each half of the body depending on where the fibers cross.
Brainstem lesions cause?
SC lesions cause?
Cross sensory syndrome
Sensory deficits of trunk/extremities contralateral to the lesion, but sensory deficits of the face/CN ipsilateral to the lesion
Proprioceptive deficits on the right, but anesthesia on the left (or vice versa)
Secondary somatosensory (SII) cortex lies deep in the inner face of the upper back of the _____. It contains _____ representation of the body surface. Inputs arise from the ____ and _____ of the thalamus.
Lateral sulcus
Somatotopically
Ipsilateral SI cortex and ventral posterior inferior nucleus (VPI)
Parietal cortical regions receive ____ inputs. They are posterior to ____ but also include area 5 and area 7 (7b).
They receive input from the _____ and the SI.
Lesions in parietal association area can produce ____.
Tactile
Area 2
Medial lemniscus
Agnosia: contralateral body parts are lost from the personal body map; sensation is not radically altered but the limb is not recognized as part of the pt’s own body
____ pathways transmit proprioceptive and limited cutaneous info to the cerebellum. It includes info about limb position, joint angles, and muscle tension/length.
____ plays a integral role in guiding control of body muscle tone, movement, and posture.
Spinocerebellar
Cerebellar input
