OS III, Ex II somatosensory Flashcards
What is the purpose of the somatosensory system?
Give info from outside world to CNS
How do we feel our bodies based on sensation?
we feel our body pre reflectively from the inside as an object of direct perception.
How can we reflect on our bodies?
direct perception from the inside and congnitively from the outside as an object
somatic sennsation?
conciousness of stimiuli on somatic receptors
somatic perception?
interpretation of somatic objects and events plus ones own body into a picture of world
Somatic representation
abstract knowledge, beliefs and attitudes about ones own body
What are the 4 attributes of sensory systems?
intesity, sensory adaptation, modality, localization
How is intensity detected?
increased stimulus enhances amplitude of receptor potntial and thus frequency of Aps
mechanisms for sensory rapid adaptation?
rapid ion channel inactivation to decreace receptor potential
what is sensory adaptation
decreased neural activity with sustained stimulation
Mechanisms for sensory slow adaptation?
gradual reduction of receptor potential
What is the difference between rapid and slow adaptation?
Slow decreases activity but still lets CNS know its occuring, while Rapid just turns of stimulus all together after initial signal, so it only knows that it did occur
what are 2 somatic modalities?
tactile sensation and proprioception
Tactile sensation includes what?
touch, pain, temp
How do sensory receptor proteins react to stimulus?
maximally to one type and less to others.
Adequate stimulus is what?
energy that elicits greatest response and largely determines which neuron will be responsible for precepton of sensory modality.
do somatic modalities use the same neurons?
no, modalities are associated with specilized neurons for detecting different qualities
How can modalities be distinguished grossly?
by conduction velocity
what are compound action potentials?
recordings of the summed action potentials measured over time at a particular site on the nerve
what happens to compound action potentials further along a nerve?
they are separated more by velocity
so if compound actions potentials get separated by velocity, what do the peaks mean?
peaks are clusters with different conduction velocities and degrees of myleniaiton
How are nerve compound Aps classified?
Numbers or Letters
Letters apply to what?
sensory
Numbers apply to what nerves
motor nerves
do nerves contain both sensory and motor neurons?
useally they do have both sensory and motor
Peaks of compounded action potentials correspond what?
Population size of axons with specific degree of myelination and velocity
what types are most myelinated?
Type 1 or A are fastest, IV or c are slowest
Aa is for what
proprioception, motor neuron
Abeta is for?
light touch
A gamma is for
fast pain
C is for
slow pain
what is fastor sensory or pain?
sensory
what is cutaneous receptive field?
skin area innervated by branches of single neuron
What areas have largest and smallest receptor fields?
Smallest, perephery like hands, largest are proximal like our back
Why is the size and density of a receptor field importaint to the CNS?
1) stimulus location, 2) size and shape of stimulus 3)resolve spatial resolution
How is specificity determined from RF?
there is seconday overlap of fields and then subtle differences can be seen between them
what is tactile sensation mediated by?
cutaneous receptors
What are the 4 submodalities of tactile sensation?
1) discriminative touch 2) non descriminative touch 3) temp 4) pain
what are cutaneous receptors made from?
1) modified non neural tissue or 2) axons themselves
What mediates discrimitative touch?
mecanoreceptors in CT or around hairs each with its own characteristic
Merkel cell
form, tecture - brail reading
Ruffini corpuscle
skin strectc, hand shape and position
Meissner corpuscle
skin movement andslip for grip control
pacinian corpuscle
vibratory stimuli through hand held object
Hair folicle
motion/direction of tactile stimuli
What are the slow adaptine recptors?
Merkel cell - neurtire complesx and ruffini endings
What are the fast adapting rectptors?
Messiner, pacinian and hair folicles
Where are merkel cells?
basal layer of epidermis - modified non neural cell
Where are rufrini endings
deep in the dermis -large and thin spindle shaped
Where are meissner corpuscle
are nerve cells just deep to epidermis in the dermis
Where are pacinian corpuscles?
dermis of glabrous skin - encapsulate axon ending
Hair folicles do what how?
axons surround base of hair to detect touch.
how is pacian corpuscle stimulated?
physical pressure creates receptor potential that releases glutamate from axon or lamellar cell triggering AP
How do pacinian cells adapt?
GABA is releases from lamellar cells to inhibit AP
What in a small receptive field, where?
meissner and merkel, they are concentrated at fingertips
what receptors are in larger receptive fields?
Ruffini is stretch and pacinian along ulnar and median nerve- over most of region
Fast adapt, small field is
Messiner
Fast and large
Pacinian
Slow and small
merkel
Slow and large
rufinni
what do free nerve ending do?
mediate the remaining somesthetic modalities
Characteristic of free nerve ending?
slow adapting and conductins, smaller A gamma and C axons
where do free nerve ending reside?
underlie the epidermis or extend into the stratum granulosum
Non descrimitative touch
high threshold sense of touch, poor localization
where do heat and cold receptors lie?
within dermis, with slow adaptation to adjust to hot or cold water
Where are pain receptors?
C and A gamma penetrate into epidermis
Mechanoreceptors
tap, squeze, rup skin stretch C, gamma
Thermoreceptors
hot or cold c gamma
Noiciceptors to types
mechano - thermal and polymodal noiciceptor
Mechano-thermal detects what?
mechanical or thermal tissue damage
Polymodal noiciceptor detects what?
heat, tissue damage and chemicals C
proprioception
somatic sensitivity to positon, location, orientation and movement of the joints muscles and fascia
what types of axons for proprioception?
A a and beta, ruffini, pacianian, spindle and golgi tendon
How can the major categories of modalities also be destinguished by?
their ascending pathways.
What goes with discrimitative touch and proprioception?
1) low threshold 2) rapid AP 3) dorsal column leminscal system 4) Quanitative sense for localization os timulus
What does wit hnon descrimitative touch pain and temp
1) high threshold 3) slower AP 3) anterolateral system 4) qualitative experience
What column does descriminative touch, and propriception?
Dorsal comumn - Leminscal system
In the Dorsal column-leminscal system, what type of neurons convey infomatio where?
First, second and third order convey info to spinal cord, brain stem ,thalamus, to cerebral cortex
What is a first order neuron?
sensory axons, form dorsal columns, and synaps
What about second order neurons?
axons from medial lemniscus that then go to thalamus
What about third order neurons?
Project to primary somatosensory cortex in postcentral gyrus
What is the anterolateral system for?
non descrimitative touch, pain and temp
Does the anterolateral sysem do the first sencond third order neruron thing?
only part of it does
What are the first order neurons and where do they go for anterlateral?
sensory axons synaps to sordal horn using substance p, glutamate and NO
what does rexed lamina consist of?
neuronal groups segregated by modality.
where do the second order neurons of the dorsal horn go to?
they decussate to anterolateral system
what are the two anterolateral pathways?
Neospinathalimic tract and paelospinothalamic tract
Neospinothalamic tract
To lateral thalamus ant somatosensory cortex
Neospinathalamic tract is for what?
localization of sensation
Paleospinothalamic tract is for what?
qualitative aspects of pain, temp and non descriminative touch
where are the third order neurons for anterolateral path?
to somatosensory from thalamic
Medial thalamic neurons for what?
alerting responses or experience of dull persistent pain
Lateral thalamic neurons for what?
stimulus localization
syringomyelia is what
cysts that form in the center of cervical grey matter interruptin decussation of anterolateral second order neurons.
what does syringomyela cause?
leads to bilateral loss of pain and temp from cericothroacic area of body
Brown Sequared syndrome?
cut through dorsal and anterolateral spinal cord on one side
What does brown sequared syndrom cause?
Ipsolateral - loss of discrimitive touch, propriceptions, Contralateral - loss of pain and temp sensations
Dermatomes
area of skin innervated by one spinal segment they overlap
what could a dermatome be used for?
to reveal sites of damage to spinal nerves or cord
Opthalimic of trigeminal
orbidal cavity forehead and top of nose
Maxillary
nasal cavity, cheel
Mandibular
oral cavity, chin side of face, ear, external acousite meatus, tympanic membrane,
Where does trigeminal nerve project from?
from the pons
Foramena of trigeminal nerve divisions?
opthalim - superior orbital fissure, maxillary - foramen rotundum, Mandibular - foramen ovale
are there other branchers to trigeminal?
yes cutaneous ones from other foramina, supraorbital, infraorbital, mental etc
What are the nucleus that are associated with trigeminal nerve?
Principal sensory, spinal trigeminal, mesencephalic, motor
Principal sensory nucleus
discriminative touch from face
Spinal trigeminal nucleus
pain and temp from face
Mesencephalic nucleus
proprioception from masticators, mediate muscle reflex
Motor nucleus
motor to masticating muscles
