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General Sensory System
Terms in this set (76)
Types of Sensation
1) Touch 2) Proprioception 3) Kinesthesia 4) Thermal 5) Nociception...all depending on the receptor in the PNS and the processing within the CNS
Steps in Processing Sensation
1) Sensing stimulus-external event, energy applied 2) Sensation-what's happening, cognition 3) Perception-making internal construct of sensation
Modified axon terminals of sensory neurons, can be associated with non-neural structure (pseudounipolar) (unencapsulated and encapsulated)
1) Exteroceptors 2) Proprioceptors
Location of Exteroceptors
Location of Proprioceptors
Location of Interoceptors
Location of Special Receptors
1) Auditory 2) Visual 3) Olfactory 4) Vestibular receptors
Primary Afferent Neurons
Located in the posterior root ganglia, enters the SC through the lateral (small axons: pain and temp) and medial (larger axons: vibration, disc. touch) entry zones
Ia and Ib Afferent Fibers
These fibers have A-alpha electrophysiological properties with an extremely large diameter (13-22 micrometers) and very quick conducting velocity (70-120 ms); myelinated
II Afferent Fibers
These fibers have A beta and gamma electrophysiological properties with a good diameter size (6-13 micrometers and quick conducting velocity (35-75 ms); myelinated
III Afferent Fibers
These fibers have A delta electrophysiological properties with normal diameter size (1-5 micrometers) and average conducting velocity (12-30 ms); myelinated
IV Afferent Fibers
These fibers have C electrophysiological properties with a small diameter size (0.2-1.5 micrometers) and slow conducting velocity (0.5-2 ms); unmyelinated
1) Stimulus information is represented by a series of AP's 2) Populations of receptors activated
Rapidly Adapting (Phasic) Receptors
These receptors respond to sudden changes in stimulus energy and experience a rapid decrease in action potentials frequency with constant stimulus (inactivation of Na or Ca channels)
Slowly Adapting (Tonic) Receptors
These receptors continuously respond to stimuli. The frequency of the action potentials stimulating it may decrease slightly or increase over time (sensitization)
Mechanisms for Rapid Adaption
1) Altered channel sensitivity to prolonged stimulus (inactivation of Na or Ca channels or increased openings of Ca dependent K channels-sensitization) 2) filtering by non neural tissues
Aids in ability to localize a stimulus, very high in fingertip and low in back
Receptor Field Size
Inversely related receptor density, is the size that a single neuron can gather information from. to very small in fingertips and high in back
Happens in the CNS, aids in ability to localize stimulus
Free Nerve Endings
Cutaneous receptors that have terminate in C and A delta fibers. The are unencapsulated and slow adapting, they are found in more tissues and organs.
Types of Nociceptors
1) Mechanincal 2) thermal: < 5 degrees C and > 45 C 3) chemical: respond to chemical irritation, but may be activated by mechanical injury 4) polymodal: respond to more than 1 of the proceeding
A Delta Nociceptive FNE Fibers
Stimulation of these fibers causes sharp, fast pricking and localized pain.
C Nociceptive FNE Fibers
Stimulation of these fibers causes itching, burning, and dull aching pain.
These receptors are tonically activated and respond to cold (5-40 degrees C) and warm (29-45 degrees C) and have an increased response with tissue temperature change.
These receptors have a very large receptive field, low threshold, and play a big role in crude and non-discriminative touch.
Cutaneous Mechanoreceptors for Discriminative, A Beta Fibers
1) Merkel Endings 2) Meissner Corpuscle 3) Rufini Endings 4) Pacinian Corpuscles
Merkel Endings (SAI)
These receptors are unencapsulated, slow adapting, and have small receptive field. They reside in the deep epidermis with high concentration in glabrous skin, fingertips and palm; aids in points, edges, and curves of objects.
Meissner Corpuscle (RA/FAI)
These receptors are encapsulated, rapidly adapting, and have small receptive field. They reside in dermal papillae with high concentrations in glabrous skin and fingertips; plays role in grip force and course form, flutter, motion across skin
Rufini Endings (SAII)
These receptors are encapsulated, slowly adapting, and have large receptive field. They reside in deep dermis and subcutaneous with high concentrations in palms, joint lines, under finger nails; plays role in skin stretch, joint position in fingers and hands, direction of object motion
Pacinian Corpuscles (PC/FAII)
These receptors are encapsulated, rapidly adapting, and have large receptive field. They reside in deep dermis, subcataneous and non-cutaneous; aid in vibration, texture, texture through tool, and high frequency.
Hair Follicle Receptors
These receptor that aids in light touch and non-discriminative touch, they are unmyelinated endings of A beta fibers that have rapidly and slowly adapting fibers. They respond to displacement of hair follicles.
Activate multiple receptors of more than one type
These are coded in the CNS; include 1) stimulus intensity (including depth of indentation) 2) stimulus location 3) stimulus type 4) Resolution (discrimination between closely placed stimuli)
First Order Neuron Pathway
Pathway for primary afferent neuron (pseudounipolar neurons). Includes A-beta, A-delta, and C fibers and runs from spinal cord.
Secondary Order Neuron Pathway
Pathway for tract cell of spinal cord or brainstem whose axons extends to the thalamus
Third Order Neuron Pathway
Pathway for thalamocortical neurons
Two Neuron Pathway from Periphery to Cerebellum
Pathway that excludes a thalamic relay
1) Final Resolution 2) Signal Amplification 3) Signal to Noise Ratio
Things impacted by central processing, create complex central receptive fields
Greater Convergence of Neurons
Makes for decreased resolution in central processing
Greater Divergence of Neurons
Makes for increased resolution in central processing
Inhibition & Facilitation
Enhances signal to noise ratio for characteristics of space and time (eg lateral surround inhibition-sharpens and enhances discrimination)
ALS and Posterior Columns/Medial Lemniscus
Major pathways transmitting information from spinal levels. The latter has greater disc. touch, maintain more resolution, maintain better separation of modalities, and maintain better somatotopic organization
Merkel endings-PRG-fasciculus gracilis-nucleus gracilis (synapse)-internal arcuate fibers-medial lemniscus system- VPL of thalamus-primary motor cortex
Pathway for reception of discriminative perception of mechanical stimuli
Lateral portion is for lower extremity whereas medial portion is for upper extremity
These from axons go to the ventral horn to impact motor neurons in the spinal cord; also some synapse on pain information transmitters
Post-Synaptic Posterior Column Pathway
Pathway with small percentage of axons within the posterior column, originate in the cells of the posterior horn and terminate in the nucleus gracilis and cuneatus
Craniofacial Somatosensory Pathways
Receive sensory information from cervical spinal nerves and cranial nerves (and ganglia) (trigeminal, facial, vestibulocochlear, glossopharyngeal, vagus).
Descending Central Processes of Craniofacial Pathways
These form the spinal trigeminal tract comprised of smaller afferents (C and A-delta fibers) residing in caudal aspects of spinal nucleus of V and larger afferents (A-beta fibers) residing in the rostral portions of spinal nucleus of V
Ascending Central Processes of Craciofacial Pathways
Pathway comprised solely from larger afferents (A-beta fibers) from the chief sensory nucleus
Spinal Trigeminal Nucleus of CN V
This structure has three portions, 1) Caudal-pain and temp 2) Rostral-crude, tactile touch 3) Pars Interpolaris-pain in oral cavity
Mesenphalic Nucleus of CN V
This structure is associated with Proprioception and Kinesthetic information from the face, very unique...gives off branches to the trigeminal motor nucleus
Principle Sensory Nucleus of CN V
This structure is associated with Tactile Sensation (disc.); the dorsomedial division from the oral cavity and the ventrolateral division from all three components of the trigeminal nerve.
Anterior Trigeminothalamic Tract
Carries crossed projections of pain, temp, and crude touch sensation to the thalamus
Primary General Sensory Cortex (SI)
This sits posterior to the central gyrus and is 3 (a & b), 1, and 2 of brodmann's areas. It has a somatotopic organization which is described by the sensory homunculus.
Brodmann's Areas 3b and 1
Areas within primary general sensory cortex primarily receiving info related to cutaneous mechanoreceptors, temperature, and some pain (from ruffinion, mertzel, and meissner)
Brodmann's Areas 3a and 2
Areas within primary general sensory cortex primarily receiving info related to less specificity, cutaneous and deep receptors including proprioceptors
VPL and VPM
Major thalamic afferents to primary sensory cortex (projections from posterior limb of internal capsule)
Major Intracortical Communication Areas to SI
1) contralateral SI 2) SII 3) motor regions of cortex 4) posterior parietal association cortex
Lesion to SI
This would result in 1) contralateral hemiasthesia (or specific body region) 2) loss/decreased disc. touch 3) loss/decreased position and vibratory sense 4) inability to localize painful stimuli
Secondary Somatosensory Cortex (SII)
Sits in the inner aspect of the dorsal wall of the lateral sulcus, supposed functions are pain processing and memory & recall of somatosensory information.
Afferent Fibers to SII
1) Cortical Regions, SI 2) Thalamic nuclei, VPI VM PO VPL VPM
Posterior Parietal Association Cortex
Sits in the posterior portion of the parietal lob, comprised of Brodmann's areas 5 and 7. Functions in integration of sensory information (visual, auditory, tactile), formation of perceptions, focuses attention. Also has motor function in initiation of movements, guiding movements by way of visual and tactile information processing, and manipulation of objects in space
Lesion of Posterior Parietal Association Cortex
This usually i worst when non dominant hemisphere is affected. Results in loss of integration and, attention, and spatial perception and also causes neglect syndrome, apraxia, and agnosias
Functions to take in unconscious proprioception for use of motor control
1) Mesencephalic nucleus to the cerebellum through the SCP and 2) Spinal trigeminal nucleus to the cerebellum via the ICP
This is the degeneration of the spinocerebellar tracts; which results in the inability to coordinate voluntary motor activities (unsteady gate).
This is secondary to untreated syphilis and results in degeneration of posterior columns
Receptors associated with free nerve endings
Receptors that have continuous monitoring of body functions, include rapidly adapt. mechanoreceptors, slowly adapt. mechanoreceptors, specialized visceral organ receptors, and receptors that monitor the hypothalamus
Specialized Visceral Receptors
Chemoreceptors (chemical blood make-up) and baroreceptors (blood pressure)
General Visceral Afferents
90% of these are unmyelinated or slightly myelinated and most are associated with the parasympathetic nervous system
Sacral Parasympathetic Afferents
These monitors fullness, distension, etc of pelvis viscera and some abdominal viscera. Neurons run into the posterior root ganglia, then to posterior horn and intermediate regions.
Projections of Sacral Parasympathetic Afferents
These can either 1) stay local within the spinal cord for reflexes or 2) indirectly travel to the cerebral cortex via the ALS-thalamus (including VPL)-insular and parietal SII cortex: or to the hypothalamus
Cranial Parasympathetic Afferents
These consist of cranial nerves with GVA functions and their ganglia (glossopharyngeal-inferior petrosal ganglia, vagus-inferior nodose ganglion, facial-geniculate ganglion). Their central processes form the solitary tract-solitary nucleus (intermediate and caudal regions).
THIS SET IS OFTEN IN FOLDERS WITH...
Tracts, Nuclei, etc.
Cerebellum and blood supply to brainstem
Cranial Nerves in CNS
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