General Somatosensory Systems Flashcards
What are General Somatosensory Systems?
Somesthetic Systems or body/perception
What tissues do somatosensations are monitored by receptors?
Superficial tissues
Deep tissues
What is considered a superficial tissue?
cutaneous skin (eidermis, dermis and hypodermis)
What are deep tissues?
Skeletal muscles, tendons, ligaments, bone
What are general somatosensory modalities?
Unique sensations from somatic tissues
What are the unique sensations that occur in somatic tissues?
1) pain/noxious
2) temperature
3) Light (nondescriminitive) touch
4) Discriminitive touch (fine)
5) Proprioception
6) Vibration
What are the two main general somatosensory systems?
Spinothalammic System
Medial Lemniscus System
What is another name for spinothalmic system?
Anterolateral system
What are spinothalamic system sensations primarily concerned with?
Pain
Temperature
Nondiscriminative touch
What is the Medial Lemniscus System also known as?
Dorsal Column System
What sensations are medial lemniscus system primarily concerned with?
Discriminitive touch
Proprioception
Vibration
How many major neurons typically relay sensory information from peripheral receptors to the cerebral cortex?
3 or 4
What are primary sensory neurons?
Cell bodies in dorsal root ganglion
What are secondary sensory neurons?
Cell bodies in spinal cord or brainstem
What are tertiary sensory neurons?
Cell bodies in the thalamus
What types of neurons are interposed between major neurons?
Interneurons
Can other neurons terminate on and influence or modify secondary pathway neurons?
Yes, therefore they modify transmission of information through the pathway
What can modifications of the pathway circuitry provide?
Modifications of the sensory experience
What are medial lemniscus systems?
Pathways for sensory modalities of discriminative touch,vibration and proprioception
What is discriminative touch?
Fine touch
What are qualities of discriminative touch?
1) The ability to recognize the precise location of a tactile stimulus (eyes closed)
2) 2 point discrimination
3) Graphesthesia
4) Receptors include receptors in cutaneous areas
What is 2 point discrimination?
The ability to distinguish when 2 points are touched simultaneously. Allows and permits to recognize different textures. Resolution of 2 pt touch varies (fingertips and back have different 2 pt touch sensitivity)
What is graphesthesia?
Traced figure identification (ability to identify a familiar pattern traced on the skin with eyes closed)
What are the receptors included in cutaneous areas?
Meissner’s corpuscles and other receptors such as merkel’s endings
What qualities are included in proprioception?
1) Kinesthesia
2) Permits one to appreciate the shape, size and weight of objects (held in the hand)
3) receptors are distributed in articular and periarticular tissues and in muscles and tendons
What is kinesthesia
Information regarding the precise position of a body part (without visual aid) and in the range and direction of movement
What are the receptors found in muscles, tendons, and articular and periarticular tissues (joint capsules, ligaments)?
Neuromuscular spindles
Neurotendinous spindles
Ruffini-like endings
Small pacinian corpuscles
What are vibration sensations?
Rapidly changing or oscillating mechanical stimulus
How are vibrations elicited artificially on the body?
By a tuning fork set in motion and placed on the body
What receptors are included on vibrations?
Pacinian corpuscles
What are the primary neurons of fine touch and vibration for the body except the face?
Large pseudounipolar neurons in the dorsal root ganglia of spinal nerves
What group fibers are the collateral processes of primary neurons in fine touch and vibration for the body except the face?
Group A-beta fibers
What are the peripheral processes of the fine touch and vibration for the body except the face?
supplies a sensory receptor in peripheral tissue
What are the central processes of the fine touch and vibration for the body except the face?
1) Processes that transverse through dorsal rootlets of a spinal nerve and enter the spinal cord through the dorsal root zone
What are the functions of peripheral processes of the fine touch and vibration for the body except the face?
Transmits a “coded” message from the receptor towards the spinal cord
Where do central process (of fine touch and vibration for the entire body except the face) branch?
Enters the ipsilateral dorsal funiculus and branches into ascending and descending collaterals
What type of central process collaterals can modify cord mediated activity in fine touch and vibration for the entire body except the face?
Short ascending and descending collaterals terminate in spinal cord gray to modify cord mediated activity such as reflexes, sensory and motor activity
Where do long ascending collaterals that enter the spinal cord below T6 (of the central process of fine touch and vibration for the body except the face) travel?
Project through the ipsilateral fasciculous gracili to terminate in the nucleus gracilis on the posterior surface of the medulla
Where do long ascending collaterals that enter the spinal cord above T6 (of the central process of fine touch and vibration for the body except the face) travel?
Project through the ipsilateral fasciculus cuneatus to terminate in the nucleus cuneatus on the posterior surface of the medulla
How is the primary neuronal fibers based on location organized in the dorsal funiculus from medial to lateral?
Fasciculus gracillis
- Sacral
- Lumbar
- Below T6
Fasciculus Cuneatus
- Above T6
- Cervical
Which side of the body do neuron cell bodies located in the nucleus gracillis and cuneatus receive information in regards to fine touch in the body (excluding the face)?
Ipsilateral side of the body
Where do the neuron fibers from the nucleus gracillis and cuneatus project in regards to fine touch in the body (excluding the face)?
Project ventrally, decussate and form a fiber tract known as the medial lemniscus
Where does the medial lemniscus ascend in regards to fine touch in the body (excluding the face)?
Ascends the contralateral side of the brainstem
Where do the secondary fibers from the nucleus gracillis and nucleus cuneatus ascend through and where do they
terminate in regards to fine touch in the body (excluding the face)?
Ascend through the medulla, pons and midbrain to terminate on teritary neurons in the thalamus
What order neurons comprise the ventral posterior lateral nucleus of the thalamus for fine touch in the body (excluding the face) ?
Third order
Neuronal fibers that leave the ventral posterior lateral nucleus project through in regards to fine touch in the body (excluding the face)?
The posterior limb of the internal capsule to the post central gyrus and the posterior part of the paracentral lobule of the parietal lobe
True or false: Projection of fine touch infromation into the parietal lobe finishes the process of subjective assessment of data.
False, it initiates the process of subjective (conscious) assessment of the data
What are the primary neurons of proprioception for the body except the face?
Large pseudounipolar neurons in the dorsal root ganglia of spinal nerves
What group fibers are the collateral processes of primary neurons in proprioception for the body except the face?
Group A-alpha fibers
Group A-beta fibers
What are the peripheral processes of the proprioception for the body except the face?
supplies a sensory receptor in peripheral tissue
What are the central processes of the proprioception for the body except the face?
1) Processes that transverse through dorsal rootlets of a spinal nerve and enter the spinal cord through the dorsal root zone
What are the functions of peripheral processes of the proprioception for the body except the face?
Transmits a “coded” message from the receptor towards the spinal cord
Where do central process (proprioception for the entire body except the face) branch and where do they branch?
Enters the ipsilateral dorsal funiculus and branches into ascending and descending collaterals
What type of central process collaterals can modify cord mediated activity in proprioception for the entire body except the face?
Short ascending and descending collaterals terminate in spinal cord gray to modify cord mediated activity such as reflexes, sensory and motor activity
Where do long ascending collaterals for the upper body (of the central process of proprioception) travel??
Project through the ipsilateral fasciculous cuneatus to terminate in the cuneate nucleus on the ipsilateral side of the medulla
Where do long ascending collaterals for the lower body (of the central process of proprioception for the body except the face) travel?
Project through the ipsilateral fasciculous gracili to terminate in the ipsilateral nucleus dorsalis (clarke’s nucleus) in the spinal cord gray (lamina VII)
Where do the neurons of clarke’s nucles project axons in regards to proprioception for the entire body (except face)?
Ascend as the ipsilateral dorsal spinocerebellar tract into the medulla
Where do some axon collaterals in the medulla travel in regards to proprioception for the entire body (except face)?
To the cerebellum or Nucleus Z
What are the teriary neurons of the nucleus Z?
Anatomically and functionally similar to neurons of the nucleus gracilis therefore these neurons are part of the conscious proprioceptive pathway for the lower body
Where do the nerve fibers from the nucleus Z project for proprioception of the body?
Vnetrally into the contralateral medial lemniscus
Where do the fibers travelling from the nucleus Z terminate for proprioception of the body.
Ascend through the medulla, pons and midbrain to terminate on neurons of the ventral posterior lateral nucleus of the thalamus
Where do the neuronal processes from the VPL nucleus of the thalamus send axons through for proprioception of the body?
Posterior limb of the internal capsule
Where do the fibers travelling through the internal capsule for proprioception of the body terminate?
IN the post central gyrus and the posterior paracentral lobule of the parietal lobe
What are projections to the cerebral cortex necessary for intiating for proprioception of the body?
Permit the conscious awareness of the postion and movement of body parts
What is the cutaneous innervation of the posterior 1/3 of the head and part of the external ear provided by?
C2 & 3 spinal nerves
What is most of the anterior 2/3 of the head supplied by?
Branched of the trigeminal nerve (V1,2,3)
What cranial nerves control somatosensory for the head?
V, VII, IX, X
What are the different nuclei that make up the trigeminal sensory nuclei?
Mesencephalic nucleus
Chief sensory nucleus of V nerve
Spinal Trigeminal nucleus
Where is the mesencephalic nucleus found?
Mostly in the midbrain
Where is the chief sensory nucleus of the V nerve?
In the pons
What is the chief sensory nucleus of V nerve also known as?
Pontine trigeminal nucleus
What is the spinal trigeminal nucleus also known as?
Spinal nucleus of V nerve
Where is the spinal trigeminal nucleus located?
Extends from pons through medulla into upper three spinal cord segments
Where are the cell bodies for primary neurons that provide fine touch on the face located?
In the trigeminal sensory ganglion
What is another name for the trigeminal sensory ganglion?
Gasserian ganglion
What type of neurons (bipolar, unipolar etc.) are the primary neurons for fine touch innervation of the face?
Pseudounipolar (unipolar) neurons with peripheral and central processes
What type of fibers are the processes of primary neurons for fine touch innervation of the face?
Processes are Group A beta fibers
How are the peripheral processes of primary for fine touch innervation of the face distributed?
Via the opthalmic, maxillary or mandibular divisions to supply peripheral receptors
Where do the central processes enter and terminate for fine touch innervation of the face?
Central processes enter the pons with the V nerve and terminate in the pontine trigeminal nucleus (chief sensory of V nerve)
Which peripheral processes supply proprioceptors in peripheral tissues for the face?
The V3 (mandibular) nerve receive proprioception from receptors in peripheral tissues such as the muscles of mastication and the TMJ and relay the information back through the brainstem
Where do the central processes terminate for fine touch innervation of the face?
Central processes terminate on neurons in the pontine trigeminal nucleus
Where do cell bodies from the pontine trigeminal nucles send axons to for fine touch and proprioception innervation of the face?
Send axons to the contralateral side of the brainstem to join the ventral trigeminothalamic tract
Where do the axons from the pontine trigeminal nucleus terminate on for fine touch and proprioception innervation of the face?
The fibers of the trigeminothalamic tract ascend through the brainstem and terminate on teritiary neurons in the ventral posterior medial nucleus of the thalamus
Where do teritary neurons from the ventral posterior medial nucleus send axons through for fine touch and proprioception innervation of the face?
Posterior limb of the internal capsule
Where do teritary neurons from the ventral posterior medial nucleus terminate for fine touch and proprioception innervation of the face?
Fibers terminate in the inferior lateral part of the post central gyrus (near the lateral sulcus)
What is the functional significance of projections from the thalamus to the cerebral cortex?
Initiates cortical processing of data and allows one to consciously assess qualities of sensory stimuli
What is the somatosensory cortex of the parietal lobe?
Cortical areas that receive, process and interpret all somatosensory data including discriminitive touch, vibration, proprioception, pain and temperature
What is the primary somatosensory cortex also known as?
SS1 or S1 area
What does SS1 include anatomically?
Post central gyrus
Posterior part of para central lobule
What is the function of the SS1 area?
First cortical area to receive somatosensory data from the thalamus for subjective assessment
What is somatotopic organixation?
Specific body parts that are highly organized and mapped onto specific parts of the gyrus
Which part of the body is one side of the body’s sensation represented on?
The contralateral half of the cerebrum
Where is the face sensation area positioned on the cerebrum?
In the inferior and lateral part near the lateral sulcus and it makes up a large area of the cortex
Where is the upper extremity sensation area positioned on the cerebrum?
Intermedio-lateral part of the gyrus and makes up a large cortex
Where is the trunk sensation area positioned on the cerebrum?
Superior/lateral, making a small area
Where is the proximal part of lower extremity sensation area positioned on the cerebrum?
Superior most part, near midline
Where is the distal part of lower extremity and perineum sensation area positioned on the cerebrum?
On medial surface paracentral lobule on midline
What is a sensory homunculus?
Miniature human used to map the primary somatosensory cortex
What is the relationship between the cortical surface area for a body part in regards to its sensitvity?
Increased sensitivity of a body part results in increased cortical area
What are the functions of the primary somesthetic cortex?
Permits general awareness of all somatosensations
Localization of a stimulus
Appreciation of qualities of a stimulus
What does localization of stimulus mean?
Precision and recognition of change in body part position
What does appreciation of qualities of a stimulus include?
Appreciating different textures, size, shape, and weight of objects held in the hand
What is the secondary somatosensory cortex also known as?
SSII
WHere is the SSII located?
Inferior to the postcentral gyrus on the superior wall of the lateral sulcus (extending to the insula)
What is the SSII involved in?
Appears to be involved in less discriminative aspects of general somatosensation
What does the somatosensory association cortex include?
Includes parts of the parietal lobe:
- Superior parietal lobule
- Precuneus (medial surface)
What areas of the Brodmanns map does the somatosensory association cortex correspond with?
Map areas 5,7
What is the function of the somatosensory association cortex?
Functions to intergrate somatosensory data (complex assessment of data)
Where does the somatosensory association cortex receive input from?
Receives input from the primary somatosensory cortex and areas of the thalamus and visceral cortical areas
What are the different permitted complex assessment of data for somatosensory association cortex?
- Recognition of patterns of somatosensory info
- recognition of the significance of info
- associate info with previous experience
What is stereognosis?
Ability to identify identification based on size, shape, weight, and texture of the object without visual aid
What is graphesthesia
Traced figure identification (ability to identify a familiar pattern that’s traced on an area of skin
What is “body image”?
Ability to appreciate the precise postion of a body part in 3D space
- ability to appreciate force, range and direction of movement of a body part
What are clinical tests for the integrity of the medial lemnicsus system?
Limb/joint position recognition 2 point discrimination Graphesthesia Stereognosis Vibration
How do you perform the limb/joint position regonition?
With eyes close, passively move a body part
How do you perform the two point discrimination test?
With eyes closed, touch 2 points and compre to one point
How do you perform the graphesthesia test?
Traved figure identification
fine touch test
How do you perform a stereognosis test?
fine touch on textures and proprioception on size and shape
How do you do a vibration test?
Use a 128hz tuning fork.
What is agnosia?
Lack of appreciation of the signification of sensory info and knowledge
What is tactile agnosia?
Inability to appreciate the significance of tactile information (ie: unable to differentiate from two point discrimination, texture)
What is agraphesthesia?
Inability to identify traced figures
What is astereognosis?
Inability to perform stereogenesis (identifying objects based n size, shape, weight and texture
