Neuro: Somatosensory System I And Ii

Front 1

what is a local potential? aka..

Back 1

recpetor potential, generator potential: electrical potential induced at site of stimulus; graded, electrical event
NOT an AP

Front 2

where and how are AP generated?

Back 2

AP generated when a local potential is large enough
AP occur in regions with VG Na+ channels (ex: nodes of ranvier; not at receptive ending)

Front 3

what happens to cause a local potential? use a touch R as an example

Back 3

touch R (Pacinian corpuscle) stretched and stimulated to open MECHANICALLY gated Na+ channels

Front 4

what happens after a local potential is generated?

Back 4

if lg enough, stim an AP to travel retrograde down axon (past DRG) to presynaptic terminal; releases NT on postsynaptic cell (often interneuron) in dorsal horn of SC; new AP (IPSP, EPSP) generated in postsynaptic neuron travles through CNS

Front 5

what are some attributes of a sensory stimulus that CNS interprets? (4)

Back 5

modality (ex: vision, taste)
intensity (proportional to stim strength)
duration (length of stim)
location

Front 6

where does a end plate potential occur?

Back 6

at n/m jxn

Front 7

what are dermatones?

Back 7

regions of the skin that are innervated by spinal nerves originating at DRGs at a specific level

Front 8

what are 4 somatic modalities?

Back 8

(sensations)
touch
proprioception
pain
thermal

Front 9

what are the types of somatosensory receptors? (3)

Back 9

mechanoreceptors- include touch and proprioception
thermoreceptors
nociceptors

Front 10

how does the distribution of somatosensory receptors determine sensation?

Back 10

if have cold probe placed over area of skin without thermoreceptors then would only feel touch (via mechanoreceptor)

Front 11

what is the general path of almost all sensory afferents? what is the exception?

Back 11

all sensory info travels through thalamus on way to the cortex (post-central gyrus)
exception is olfaction; goes to thalamus after?

Front 12

what are the 2 basic receptor structures?

Back 12

bare nerve ending (noci and thermoreceptors)
end organ-nonneural capsule around axon terminal (mechanoreceptors)

Front 13

what is a pacinian corpuscle? ruffini's endings?

Back 13

mechanoreceptor in skin that detects touch and vibration

general mechanoreceptor

Front 14

how are hair follicles innervated?

Back 14

axon nerve ending wraps around hair follicle; is activated with displacement

Front 15

what is a merkel cell?

Back 15

cell in skin assoc with touch; when stimulated, rel NT on post synaptic sensory neuron to open channels

Front 16

what is the fxn of limb proprioception?

Back 16

convey sense of position and movement of limbs
stationary position v. kinesthesia (limb movement)

Front 17

what are extrafusal v. intrafusal muscle fibers?

Back 17

extrafusal are innervated by alpha motor neurons (LMN) and are stimulated for contraction
intrafusal m. fibers comprise the muscle spindle and are contained within the extrafusal fibers

Front 18

how does the muscle spindle convey sensory info?

Back 18

intrafusal fibers are wrapped in sensory receptors (proprioceptors)
stretch m-> stretch intrafusal fibers->stretch sensory ending

Front 19

what type of fibers innvervate muscle spindles?

Back 19

Ia afferents
detect m. length/stretch

Front 20

what does the density of muscle spindles correlate to?

Back 20

more muscle spindles for finer control of movement (extraocular eye mm.)

Front 21

what are golgi tendon organs? what innervates them?

Back 21

mechanoreceptors that relay info abt m. tension
Ib afferents

Front 22

what type of axon is assoc with free nerve endings? what is their fxn?

Back 22

C, Ad(elta)
pain, temp
slow adaptation

Front 23

what type of axon is assoc with meissner's corpuscles?

Back 23

(b/w dermal papillae)
AB(eta)
touch, pressure
rapid adaptation

Front 24

what type of axon is assoc with pacinian corpuscles?

Back 24

AB(eta)
deep pressure, vibration
rapid adaptation

Front 25

what type of axon is assoc with merkel's disks?

Back 25

AB(eta)
touch pressure
slow adaptation

Front 26

what type of axon is assoc with ruffini's corpuscles?

Back 26

AB(eta)
stretching of skin
slow adaptation

Front 27

which axon/peripheral n. fiber is the largest? smallest (in diameter)?

Back 27

largest: I (a,b)
smallest: IV (C)
I (a,b), AB(eta), AD(elta), C

Front 28

which n. fibers are proprioceptors?

Back 28

Ia and Ib

Front 29

which n. fibers are mechanoreceptors? (touch, pressure)

Back 29

AB(eta)

Front 30

which n. fibers are nociceptors?

Back 30

AD(elta) and C

Front 31

which n. fibers are thermoreceptors?

Back 31

AD(elta) and C

Front 32

which part of a sensory neuron is sensitive to stimulus energy?

Back 32

the terminal of the peripheral branch of the sensory neuron

Front 33

which afferent has the fastest conduction velocity?

Back 33

A(Beta) fastest because largest diameter

Front 34

which afferents are myelinated?

Back 34

I(a,b)
AB(eta)
AD(elta)
(all except C)

Front 35

which afferents are involved in sharp pain? what abt slow, dull pain?

Back 35

sharp- AD(elta)
dull-C

Front 36

what happens in diabetics with peripheral neuropathy?

Back 36

degeneration of AD(elta) and C fibers (nociceptors) gives sensation of pain

Front 37

which n. fibers are assoc with itch?

Back 37

C fibers

Front 38

what is the relationship b/w the generator potential and the size of the stimulus?

Back 38

directly proportional

Front 39

relationship b/w AP and local potential?

Back 39

amplitude of local potential dir proportional to frequency of AP

Front 40

what is adaptation of a n. fiber receptor?

Back 40

habituation to stimulus
slow-pain and m. tension
fast-touch, pressure

Front 41

what is the mxn of nociceptor detection of pain? what is the stimulus?

Back 41

stimulus is tissue damage
damaged cells rel bradykinin, prostaglandins, K+ to activate nociceptor

Front 42

what happens after activation of nociceptor?

Back 42

nerve endings rel substance P: increases vessel permeability, vasodilation-> more inflammation; activates mast cells to release histamine ->activate nociceptors

Front 43

what is the rel b/w density of receptor terminals in an area and the size of the receptive field?

Back 43

highly innervated areas (sensitive areas, lip) have small receptor fields

Front 44

what is the 2 point discrimination threshold?

Back 44

the distance that needs to separate 2 stimuli before it can be distinguished as 2 stimuli

Front 45

what are some ex of things that have hi v low 2 pt discrimination?

Back 45

highly innervated areas (with small receptive fields) have a small 2 pt threshold (fingers, lips, nose, cheek)
sparsely innervated areas (w/ lg receptive fields) have large 2 pt discrimination values (calf, back, thigh, upper arm)

Front 46

what is a dermatone?

Back 46

the region (receptive field) that is innervated by each spinal n.

Front 47

what is the path of sensory info on its way to the brain?

Back 47

peripheral afferent->central afferent-> synapses in the spinal cord-> ascends to the medulla and thalamus-> to somatosensory cortex

Front 48

what is somatotopy?

Back 48

idea that receptors in adjacent portions of peripheral receptive fields project neurons to regions adjacent in CNS

Front 49

what is the path for a pain/temp afferent? what type of afferent?

Back 49

C, AD(elta)
3 neuron track
primary afferent synapses immediately on a projection interneuron in dorsal horn
secondary afferent crosses SC and ascends through ventral-lateral funiculus to synapse in thalamus
tertiary afferent goes from thalamus to somatosensory cortex

Front 50

how does the path of a mechanoreceptor afferent differ from the pain/temp afferent?

Back 50

mechanoreceptor afferent doesnt synapse immediately upon entering SC

Front 51

what is the path of a mechanoreceptor afferent?

Back 51

primary enters dorsal horn; travels to medulla where it synapses in dorsal funiculus (cuneate nucleus-from above T6; gracile nucleus-from below T6)
secondary crosses in medulla and then travels up to synapse in thalamus
tertiary travels to synapse in somatosensory cortex

Front 52

what would be the result of a lesion above the medulla? (in terms of mechanoreceptors and pain/temp receptors?

Back 52

a lesion above the medulla on the right would cause loss on contralateral side (left)

Front 53

whats the result of a lesion on the right between the medulla and the level of crossing for the pain/temp?

Back 53

ipsilateral loss for mechanoreceptors (touch, pressure)
contralateral loss for pain/temp receptors

Front 54

what is contained in the dorsal horn?

Back 54

interneurons and ascending sensory neurons

Front 55

what is contained in the intermediate zone?

Back 55

autonomic preganglionic neurons
afferents traveling to cerebellum

Front 56

what is contained in the ventral horn?

Back 56

interneurons and motor axons

Front 57

what are the lamina of the gray matter and what "horns" do they rel to?

Back 57

dorsal horn: I-VI

intermediate zone: VII

ventral horn: VIII-IX

Front 58

what sensory neurons synapse in lamina I, II?

Back 58

AD(elta) and C fibers (pain, temp)

Front 59

what afferents synapse in lamina III-VI?

Back 59

Ia and AB(eta) -proprioceptors and mechanoreceptors

Front 60

what is Lissauer's tract?

Back 60

region where A(Delta) and C fibers enter the spinal cord

Front 61

what are the 3 general paths for an A(Beta) or Ia fiber entering the spinal cord?

Back 61

1. can travel up dorsal column to synapse in medulla
2. can synapse in clark's nucleus and cont to cerebellum
3. can enter ventral horn to directly synapse on LMN (reflex; Ia muscle spindles)

Front 62

what is clark's nucleus and where is it located?

Back 62

in intermediate zone, lamina VII
present T1-L2 only
relays info about body position to cerebellum
location of synapse for Ia and AB(eta) fibers

Front 63

what is the intermediolateral column?

Back 63

in intermediate zone; lamina VII; T1-L3
contains presynaptic cell bodies for autonomic system
presynaptic axons leave through ventral horn to synapse in sympathetic ganglia

Front 64

what is contained primarily in lamina VIII?

Back 64

interneurons for skeletal m. contraction

Front 65

where is the phrenic nucleus?

Back 65

lamina IX- medial portion of ventral horn from C3-C5

Front 66

which would cause more damage? a lesion to a peripheral n. or a spinal n?

Back 66

peripheral n
covers many dermatones and contains spinal nerves from several (2-4) DRG

Front 67

what is the substantia gelatinosa?

Back 67

in lamina II of all levels of spinal cord
receives afferent info (pain, temp) from non-finely myelinated fibers (Adelta, C)

Front 68

where are the preganglionic autonomic cell bodies located in the spinal cord? at what level?

Back 68

in the intermediolateral nucleus
T1-L3
lamina VII

Front 69

what are 4 things that can clue you in when determining the level of a spinal cord section?

Back 69

1. dorsal columns get smaller caudally
2. above T6: funiculus gracilis and funiculus cuneatus; below T6: only funiculus gracilis
3. C8, L5- large ventral horns; LMN to supply limbs
4. lateral funiculus decr in size caudally (corticospinal tract)

Front 70

which afferent fibers are not myelinated?

Back 70

C fibers (dull pain, itch, warm temps)