Ch 15 - somethesis Flashcards
exteroceptors
somesthetic systems that respond to external stimuli impinging on the skin
somesthesis
general term referring to body sensibility or somatosensory capacities
proprioceptors
more deeply situated and signal the status of muscles, tendons, joints, etc.
interoceptors
located within the viscera and respond to changes in the internal environment
touch is represented by what type of fibers?
A delta and C fibers; but majority of touch receptors are supplied by A-beta afferants
describe adaptation rate
given a constant stimulus, an afferent that is rapidly adapting will discharge briefly and then stop. an afferent that is slowly adapting discharges for the duration of the stimulus.
list the Group I afferents and what they are for
Ia - muscle stretch: primary spindle fibers
Ia - limb position and movement: spindle receptors
Ib - tendon tension: golgi tendon organs
list the A-beta afferents
II - muscle stretch: secondary spindle fibers
II - limb position and movement: joint and spindle receptor
A-beta - light touch: cutaneous receptors
A-delta afferents
III - pressure and pain: deep (muscle & visceral) receptors
A-delta - touch, temperature & pain: cutaneous receptors
C afferents
IV - pain: deep receptors
C - temperature and pain: cutaneous receptors
describe the light touch sensation: sensed by which receptors? adaptation rate? transmitted by?
- detected by cutaneous exteroceptors which are rapidly adapting
- transmitted by sensory afferents containing A-beta fibers which are fast, large and myelinated
describe the proprioception sensation: what is proprioception? detected by what type of receptor? containing what kind of fibers?
- sense of the relative position of neighboring body parts and the strength of effort employed in movement
- detected by propioceptors located more deeply which detect signals from muscles, tendons and joints
- these afferents contain 1a and 1b fibers which are the fastest, largest and most myelinated as well as A-beta which are also fast, large and myelinated
describe the gross touch sensation: what type of receptors? adaptation rate? what type of fibers?
- detected by cutaneous extero-ceptors which are rapidly adapting
- transmitted by sensory afferents containing A-beta (fast, large, myelinated) and A-delta (slow, smaller, less myelinated) fibers
describe temperature sensation:what type of receptors? what type of fibers?
- detected by exteroceptors
- contain A-delta (slow, small, less myelinated) and C afferents (slowest, smallest, no myelin)
describe fast pain sensation: type of receptor and fiber
- detected by cutaneous extero-ceptors
- contain A-delta (slow, small, less myelinated) afferent fibers
describe slow pain sensation: type of receptor and fiber
- detected by cutaneous exteroceptor
- contain C fibers (slowest, smalles, no myelin)
Pelage hair receptors
- supplied by A-beta fibers
- quickly adapting
- discharge briefly at the onset of hair bending
- arranged parallel to hair shafts and consist of neurites (nerve terminals) bordered by Schawann cell cytoplasm
vibrissae receptors
- variety of rapidly adapting and slowly adapting receptors supplies vibrissae (ie whiskers, sinus hairs, tactile hairs, etc)
Pacinian corpuscles, hair cells, free nerve endings: what they consist of, what they are supplied by
- pacinian corpuscles are mechanoreceptors found in subcutaneous tissue.
- they consist of a neurite surrounded by an inner core and numerous lamellae of connective tissue.
- they are supplied by the fastest conducting A-beta touch fibers
- they are sensitive to minimal gingival or skin distortion
Meissner’s corpuscles: where they are located, supplied by? describe structure
specialized rapidly adapting receptors in glabrous skin (eg hand)
- located superificially within dermal papillae
- supplied by A-beta fibers
- they are laminated like Pacinian but are less sensitive
- supplied by neurites that intertwine through the lamellae
Merkel cells
- slowly adapting touch receptor located in hairy skin of the face, glabrous skin of the hand and gingival mucosa
- receptors are located at the tips of finger-like extensions of the epidermis into the intermediate ridges of the dermis
- supplied by myelinated A-delta fibers that lose their myelin as they reach the disc of the merkel cell
free nerve endings
are called nociceptors
- they detect painful stimuli
fasciculus gracilis: where is located? where does it receive input from?
located within the dorsal columns which is the white matter between the dorsal horns
- it receives input from the sacral, lumbar, and lower thoracic roots (representing the lower trunk and legs)
fasciculus cuneatus: where is it located? where does it transmit input?
- located within the dorsal columns LATERAL TO the fasciculus gracilis at mid-thoracic cord levels
- transmits input from the upper trunk, arms, and neck
lemniscal tracts
= fasciculus gracilis + fasciculus cuneatus
- named so because their ascending projects to the thalamus travel in the medial lemniscus
dorsal columns: what do they detect? what is it mostly composed of and where do they go? where does the major input come from? central projections?
- detect fine touch and proprioception from the trunk limbs
- composed primarily of dorsal root afferents that ascend laterally to the medulla without synapsing in the dorsal horn
- major input comes from rapidly adpating muscle, joint, hair and touch receptors.
- cetnral projections are large caliber primary afferents which synapse in the caudal medulla
what is the pathway involving the gracilis fasciculus and what is it for? where does the signal originate from?
–> aka lemniscal pathway
for hindlimb and caudal trunk light touch and proprioception:
- originates from the mid-thoracic, lumbar and sacral segments of the spinal cord
1. dorsal root ganglia
2. fasciculus gracilis
3. synapse in nucleus gracilis (the caudal medulla)
4. cross as internal arcuate fibers
5. medial lemniscus
6. VCL (ventrocaudal lateral) nucleus
7. internal capsule
8. sensory cortex
what is the pathway involving the fasciulus cuneatus? what is it for? where does it originate from?
–> aka lemniscal pathway
for cranial trunk and forelimb for light touch and proprioception
- originates from the cervical to mid-thoracic spinal cord segments
1. dorsal root ganglia
2. cuneate fasciculus
3. synapse in cuneate nucleus in caudal medulla
4. cross as internal arcuate fibers
5. medial lemniscus
6. VCL (ventrocaudal lateral) nucleus
7. internal capsule
8. sensory cortex
lemniscal pathways are the principal pathways of conduction for what? these capicities include what 5 things?
all highly discriminitive (detailed) features of somatic sensation and are critical for sensory feedback to support posture and fine movements
- ability to identify the idrection of movements of a stimulus across the skin
- capacity to discriminate between different frequencies of tactile stimulation
- capacity to discern shapes and textures
- precise localizatoin on the skin
- posture and dexterity of the distal extremities
ventrolateral quadrant: what does it detect? what fibers are used?
- detect crude touch, pain and temperature
- use small dorsal root fibers - A-delta and C which are smaller, slower, less and non-myelinated
- most axons cross to the contralateral side
describe the spinothalamic tract pathway and its principal target; what is it involved in?
part of ventral quadrant detecting pain, temperature, and gross touch
- dorsal horn cells
- tract cells
- spinothalamic tract
- VCL
- internal capsule
- widespread cortical areas
- principal target is the ventrocaudal thalamus which computes localization and intensive aspects of pain perception
- involved in the location and intensity of pain
describe the spinoreticular tract: what is it involved in? what can it be viewed as?
part of ventral quadrant: detection of pain, temperature and gross touch
- dorsal horn cells
- crossed spinoreticulothalamic tract
- reticular formation, IL (intralaminar complex), hypothalamus
- IL to internal capsule
- widespread cortical areas
- it can be viewed as the initial CNS pathway in a system responsible for arousal and for motivational-affective reactions to nociceptive stimulation
nociceptive-specific cells: where do they project?
have thier cell bodies in lamina I (the marginal zone) of the dorsal horn
- to the thalamus and important for pain perception
wide dynamic range cells: where do they project? what are they important for?
projection cells from deeper laminae that respond weakly to light tactile stimuli and vigorously to painful stimuli.
- important for intensity coding (how much it hurts)
- to the thalamus and important for pain perception
where are the cell bodies of receptors which innervate facial skin and oral cavity located?
in the trigeminal ganglion
spinal tract of V
collection of central processes from the cell bodies of trigeminal ganglion which enter the CNS and make contact with dendrites of cell bodies for subsequent relay of info to the thalamus
pathway of the principal (chief) sensory nucleus: what sense does it receive?
- receives touch input from the face and oral cavity
- split into ventral (face) and dorsal (oral) zones
- trigeminal ganglion cells
- trigeminal nerve
- principal sensory nucleus
- join medial lemniscus (crossed & uncrossed)
- VCM (ventrocaudal medial nucleus)
- somatosensory cortex
pathway of the mesencephalic nucleus of V: where is the nucleus found? what does it contain? what is its function?
- found on the lateral border of the periaqueductal gray, extending from the level of the rostral colliculus to the level of the chief sensory nucelus of V.
- contains unipolar cell bodies with peripheral sensory fibers
- provides innervation to proprioceptors of the muscles of mastication and periodontal ligaments
- plays a role in jaw closing reflexes
1. mesencephalic nucleus
2. spinal tract of V
3. trigeminal nerve
4. muscles of mastication
spinal nucleus of V: what are its 3 components?
- subnucelus oralis (oral cavity, tooth pulp gingiva, palate and buccal mucosa) - primarily concerned with mediation of oral cavity reflexes
- subnucleus interpolaris (head and oral cavity) - receives touch inputs and projects principally to the VCM
- subnucleus caudalis (face and oral cavity) - primarily concerned with the relay of pain and thermal sensation to the intralaminar nuclei of the thalamus.
what are the two different pathways of spinal nucleus of V?
- spinal nucleus of V
- ventral trigeminothalamic tract (VTT)
- ventrocaudal medial nucleus (VCM)
- sensory cortex (pain, temp, gross touch)
- intralaminar complex
- internal capsule
- widespread cortical area
- ———————————————- - spinal nucleus of V
- reticular formation
- intralaminar complex
- internal capsule
- widespread cortical areas
motor nucleus of V: contains motor neurons that innervate what? is associated with what?
- contains motor neurons that innervate the muscles of mastication
- associated with the supratrigeminal nucleus - the jaw movement motor center which integrates sensory information from both sides of the oral cavity and muscles of mastication
- motor nucleus of V
- motor neurons to muscles of mastication
- trigeminal nerve
- muscles of mastication
where do the lemniscal and spinothalamic pathways converge?
the VCL
where does the trigeminothalamic pathway terminate?
in the VCM
what 3 things do you need to know about the spinothalamic and reticulothalamic pathways?
- they converge on the intralaminar thalamic nuclei
- they are nonspecific because they distribute widely to all areas of the cortex and other brain regions
- they have large receptive fields and contribute to arousal and to modulation of sensorimotor processes.
medial lemniscus: what info does it provide? where does it terminate?
provides info from trunk and limbs; terminates in VCL
trigeminothalamic tract: what info does it provide? where does it terminate?
information from face; terminates in VCM
spinothalamic tract: where does it project?
to VCL and other thalamic nuclei including IL
spinoreticular tract: where does it end?
in brainstem reticular formation and IL
axons from thalamocortical pathways: where do they terminate?
in the postcruciate gyrus (via VCL and VCM) which constitutes the primary sensory cortex (SI)
specific vs. nonspecific
nucleus is ‘specific’ when its cells have small receptive fields that are arranged in a detailed map of the body surface that is faithfully projected to similarly organized regions of the cerebral cortex.
nonspecific is when they distribute widely to all areas of the cerebral cortex and to other brain regions.
