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)
