Somesthesis I

Front 1

exteroreceptors

Back 1

respond to external stimuli impinging on the skin

Front 2

proprioception

Back 2

Perception of body projections and movement (including info from muscles, joint capsules, ligaments, tendons, and vestibular system)

More deeply situated by groups I-a, I-b, and II afferents

Nervous system must compare output to muscle with input from muscle and tendons

Front 3

proprioceptors

Back 3

more deeply situated

signal the status of muscles, tendons, and joints

Front 4

interoreceptors

Back 4

located within the viscera

respond to changes in the internal environment

Front 5

light touch

Back 5

Detected by cutaneous extero-receptors that are rapidly adapting (detect transient events)

Transmitted by A-beta fibers

Front 6

gross touch

Back 6

Detected by cutaneous extra-receptors that are rapidly adapting (detect transient events)

Transmitted by A-beta and A-delta fibers

Front 7

temperature receptors

Back 7

Separate sets of fibers and thermoreceptors that respond to increases and decreases in skin temperature

Slowly adapting neurons

Cold receptors: A-delta and C fibers
Warmth receptors: unmyelinated afferents

Front 8

fast pain

Back 8

Pain from cutaneous tissues comes from A-delta fibers

Front 9

slow pain

Back 9

Pain from cutaneous tissues comes from C fibers

Front 10

adaption rate

Back 10

ability of an afferent to rapidly or slowly adapt to a constant stimulus

Front 11

rapidly adapting

Back 11

Discharges briefly, then stops

Potentials at start and end of stimulus

Transient or high frequency events

Front 12

slowly adapting

Back 12

Discharges for the duration of the stimulus

Maintained events

Front 13

I-a fibers

Back 13

Fast conduction axons involved in muscle stretch, primary spindle receptors in proprioception

Front 14

A-beta fibers

Back 14

Large diameter, more rapidly conducting axons

Supply majority of touch receptors

Front 15

A-delta fibers

Back 15

Large diameter, conduct slightly slower than A-beta

Touch, temperature, and pain

Front 16

Pelage hair receptors

Back 16

Supplied by A-beta fibers that are quickly adapting

Discharge briefly at the onset of hair bending, and some also discharge when the hair returns to the normal position

No sustained discharge if hair is bent for more than a few seconds

​Parallel to hair shafts and consist of neuritis (nerve terminals) and bordered by Schwann cell cytoplasm

Front 17

Vibrissae receptors

Back 17

variety of rapidly adapting and slowly adapting receptors supplies vibrissae

Front 18

vibrissae

Back 18

whiskers, sinus hairs, or tactile hairs

most are present on the upper lip or muzzle, chin, and above the eyes, but also present on other parts of the body in some taxa (manatees)

Front 19

rapidly adapting touch receptors

Back 19

transduce low intensity mechanical deformation of the skin

Front 20

Pacinian corpuscles

Back 20

Located primarily in subcutaneous tissue

Fast adapting A-beta touch fibers

Laminated with central neurotic, sensitive to minimal gingival or skin distortion

More sensitive

Front 21

Meissner's corpuscles

Back 21

Located superficially within dermal papillae of glabrous skin

Fast adapting A-beta touch fibers

Less sensitive than Pacinian corpuscles

Laminated and supplied by several neuritis that intertwine through the lamellae

Front 22

Merkel cell

Back 22

Slowly adapting skin receptor

Located in hairy skin of the face, glabrous skin of the hand, and the closely related gingival mucosa

Front 23

dorsal columns

Back 23

Make up one functionally distinct ascending pathway

Gracile fasciculus and cuneate fasciculus

Transmit information related to fine touch and proprioception from the trunk and limbs

Comprised mostly of primary dorsal root afferents that ascend ipsilaterally to the medulla

Major input from rapidly adapting muscle, joint, hair, and touch receptors

Front 24

gracile fasciculus

Back 24

located in the dorsal columns

receives input from the sacral, lumbar, and lower thoracic roots, representing the lower trunk and legs

Front 25

cuneate fasciculus

Back 25

added lateral to the fascicles gracilis at mid-thoracic cord levels

transmits input from the upper trunk, arms, and neck

Front 26

lemniscal tracts

Back 26

cuneate and gracile fasciculi

ascending projections to the thalamus travel in the medial lemniscus

Front 27

spinothalamic tract

Back 27

Formed by axons that cross the spinal cord at levels in which their cell bodies are located

Interruption reduces pain and temp sensations contra laterally, targets ventrocaudal thalamus

Front 28

spinoreticular tract

Back 28

Many fibers terminate in medullary reticular formation, some relay in midbrain reticular formation, involved in arousal and motivational-affective reactions to nociceptive stimulation

Front 29

Dorsal column pathway (hindlimb and caudal trunk)

Back 29

DRGC -> gracile fasiculus -> synapse in gracile nucleus -> cross as internal arcuate fibers -> medial lemniscus -> VCL -> internal capsule -> somatosensory cortex

Front 30

Dorsal column pathway (forelimb and cranial trunk)

Back 30

DRGC -> cuneate fasiculus -> synapse in cuneate fasiculus -> cross as internal arcuate fibers -> medial lemniscus -> VCL -> internal capsule -> somatosensory cortex

Front 31

internal arcuate fibers

Back 31

Axons from cells in dorsal column nuclei

Cross to other side of brainstem and form medial lemniscus

Front 32

spinocerebellar system

Back 32

primary afferents that synapse on neurons in the dorsal horn

in thoracic, lumbar and sacral levels of the cord, the axons of these dorsal horn neurons enter the dorsal and ventral spinocerebellar tracts and terminate in the cerebellum

at cervical levels, the dorsal horn axons travel in the rostral spinocerebellar tract

Front 33

dorsal column senses

Back 33

light/fine touch, proprioception of trunk and limbs

Front 34

Ventral quadrant pathways

Back 34

DRGC -> dorsal horn cells -> crossed spinothalamic tract -> VCL -> internal capsule -> somatosensory cortex
DRGC -> dorsal horn cells -> crossed spinoreticulthalamic tract -> reticular formation, IL, hypothalamus -> IL to internal capsule -> widespread cortical areas

Front 35

Ventral quadrant senses

Back 35

pain, temperature, crude touch

Front 36

Face somesthetic pathway (light touch)

Back 36

Trigeminal ganglion cells -> trigeminal nerve -> prinicpal/chief sensory nucleus -> joins medial lemniscus -> VCM -> somatosensory cortex

Front 37

Face somesthetic pathway (proprioception from muscles of mastication)

Back 37

Mesencephalic nucleus -> spinal tract of V -> trigeminal nerve -> muscles of mastication
Mesencephalic nucleus cells have peripheral processes in muscle proprioceptors, cell bodies in mesencephalon, and central processes terminating in motor nucleus of V

Front 38

Face somesthetic pathway (crude touch, pain, temp)

Back 38

Trigeminal ganglion cells -> spinal trigeminal tract -> spinal trigeminal nucleus then:
a. crossed spinothalamic tract -> VCM -> internal capsule -> somatosensory cortex
b. crossed spinoreticulothalamic tract -> reticular formation, IL, hypothalamus -> IL to internal capsule -> widespread cortical areas
c. some cross and join medial lemniscus -> VCM -> somatosensory cortex

Front 39

motor pathways

Back 39

Motor nucleus of V -> motor neurons to muscles of mastication
Trigeminal nerve -> muscles of mastication

Front 40

somesthesis

Back 40

body sensibility or somatosensory capacities

Front 41

reticular

Back 41

most primitive motor system

Front 42

tooth pulp

Back 42

Contains endings of A-delta and C afferents -> pain

A-beta afferents -> non-painful sensations
Directly sensitive to mechanical disturbances

Front 43

dentin

Back 43

Radially oriented tubules with odontoblasts protruding in at dento-pulpal interface
Changes in hydrodynamic pressure in tubules cause odontoblast to move -> afferents -> pain
A-delta = sharp localized pain
C = diffuse, poorly localized aching

Front 44

trigeminal ganglion

Back 44

cell bodies of receptors which innervate facial skin and oral cavity, analogous to dorsal root ganglia; reflects 3 incoming branches (V1, 2, 3)

Front 45

Subnucleus oralis

Back 45

Division of V spinal nucleus
Represents oral cavity (tooth pulp, gingival, palate, buccal mucosa)
Mediates oral cavity reflexes (chewing and defensive)

Front 46

Subnucleus interpolaris

Back 46

Division of V spinal nucleus
Represents head and oral cavity
Mediates tactile facial reflexes

Front 47

Subnucleus caudalis

Back 47

Division of V spinal nucleus
Complete representation of face and oral cavity
Relay of pain and thermal sensation

Front 48

Trunk and limb projections (from VCL)

Back 48

terminate medially

Front 49

Oral and facial projections (from VCM)

Back 49

terminate more laterally

Front 50

SI (primary somatosensory cortex)

Back 50

Complete map of body represented in postcruciate gyrus, projects to primary motor cortex (MI)

Front 51

cutaneous receptors

Back 51

Subserve tactile sensation

Front 52

deep receptors

Back 52

joints and proprioception

Front 53

muscle afferents

Back 53

info about contractile status