structure and function of somatosensory system Flashcards
Ascending tracts
Carry info from pain, thermal, tactile, muscle and joint receptors to the cerebral cortex or cerebellum and brainstem
Is cerebral cortex unconscious or conscious
CONSCIOUS
Is cerebellym and brainstem conscious or unconscious
unconscious
2 tracts that conscious level info travels in
- dorsal column
2. anterolateral system tracts
Endings of Peripheral receptors - DORSAL COLUMN
Unencapsulated/free nerve endings
Modified/encapsulated endings
Proprioceptors
Free nerve endings of peripheral receptors
pain, temp, pressure
Merkels disk, hair follices, nociceptors
Modified/encapsulated endings of peripheral receptors
Pressure, touch, vibration, stretch, pain
Pacinian corpusles
Proprioreceptors - endings of peripheral receptors
Stretch, pressure, pain
Muscle spindles, golgi tendon organs
What makes up the dorsal column POSTERIOR
Gracile fasiculus MORE CENTRAL (lower limb
dorsal column Ascending tract ? first and secondary neurones
First order neurones synapse at gracile and cuneate
Syanpse on second order neurone in the medulla oblongata of the brain stem , CROSS OVER ( contralateral) as internal acuate fibers and ascend through brainstem as the medial leminus to the thyalamus
Thalamus
Located EITHER SIDE of the 3rd ventricle
Receive info via second order neurones
Integrates, modulates and relays info
Multiple nuceli
dorsal column 3rd order neurones
Syanpse in thalamus- at ventral posterior lateral nucelus – sensory motor cortex, travel via the posterior limb of internal capsule ( white matter tract)
Thalamus
Located EITHER SIDE of the 3rd ventricle
Receive info via second order neurones
Integrates, modulates and relays info
Multiple nuclei
Anterolateral system tract
SPINOTHALAMIC
ascending - sensory
Pain, temperature, light touch and pressure
Polymodal nociceptors (pain) ANTEROLATERAL
Respond to many different stimuli ( including tissue damage)
C fibre afferents- slow pain
Mechanical nociceptors (pain) ANTERIOLATERAL
Activated by high pressure, fast conducting A fibers - sharp pain
thermal (pain) nociceptors
Extreme heat and cold
2 classes of nociceptive fibers ( anterolateral ascending tract)
A delta fibers
C fibers
A delta fibers
Small diameter, myelinated
Nociceptive specific- thermal or mechanical
Fast, sharp, well localised pain
C fibers
Non myleinated
Nociceptive specific or polymodal
Dull, aching, burning pain
A delta fibers
Small diameter, myelinated
Nociceptive specific- thermal or mechanical
Fast, sharp, well localized pain
2 parts of the spinothalmic tracts
Direct tracts
Indirect tracts
Direct tracts
Lateral spinothalmic tract - pain and temp
Anterior spinothalamic tract- crude touch and pressure
Direct tracts
Lateral spinothalmic tract - pain and temp
Anterior spinothalamic tract- crude touch and pressure
Indirect tracts
Spinothalamic
Modulate pain and can terminate in other brain regions
Spinorectular tract- reticular formation = CORTEX
Spinocerebellar tract- cereballar peduncles= CEREBELLUM
Spinotectal tract= orientates eyes and head towards stimulus
Anterolateral system
Neurones
Axons from dorsal root ganglion enter and ascend/descend a few levels before synapsing in the SUBSTANTIA GELATINOSA
Second order neurones form the reflex arc or immediately decussate and ascend in spinothalamic tract
THROUHG BRAINSTEM
Distinct tract alongside medial lemniscus
Synapses in the VPL of the hypothalamus
Spinorecticular tract
Send projections into reticular formations of brainstem
DULL ACHING PAIN
Alertness and arousal response to pain from reticular system
then to thalamus and cerebral cortex
First second third order neurones anterolateral pressure pain and temp
first = posterior root ganglion
second =substantia gelatinosa
third = ventral posterlateral nucleus of thalamus
destination to posterior central gyrus
Spinocerebellar tract
Anterolateral
Second order neurones from spinal cord that go straight to the cerebellum to help integrate info about pain into the whole system
Sensory inputs - HEAD
pathway
Somatic sensation of face = trigeminal nerves , trigeminal ganglion
facial, glossopharyngeal and vagus cranial nerves
Synapse onto second order neurones in the ipsilateral trigeminal nucelus
Axons descussate and project in the trigeminal lemniscus to the ventral posterior medial ( vpm) nucleus of the thalamus
Fibers project to the sensory cortex ( parietal lobe)
Trigeminal nerve nuceli - SENSORY NUCELI
Principle sensory nucleus - touch, pressure and conscious proprioception
Spinal nucleus- pain and termperature
Mesencephalic nucleus- non conscious proprioceptive info
Motor nucleus- trigemial nerve nuceli
Innervates muscles of mastication
Motor nucleus- trigemial nerve nuclei
Innervates muscles of mastication
SENSORY from upper face, orbit and eye
Opthalmic
Sensory from mid face, upper teeth
Maxillary
Sensory from lower face, lower teeth
Mandibular
Pain and temperature from face
Spinal nucelus
Discriminative touch from face
Principle sensor nucleus
Prioprioception from muscles of mastication - sensory from lower face, lower teeth
Mesencephalic nucelus
Motor to muscles of mastication
Motor nucelus
Homunclus ?
The cortical homunculus represents the importance of various parts of your body as seen by your brain
Distribution on cerebral cortex
PAIN
Detected by primary nociceptors
pain afferent
Signal relayed through anterolateral tract
Input via thalamus- modulating, integrating
Modulating perception of pain ASCENDING
Achieved by presynaptic inhibition
from touch or proprioceptive afferent - inhbit transmission of pain info through the spinal thalamic pathway
Descending regulation of pain
Neurones from periventricular and periaqueductal grey matter project to the Raphe nuclei
Medullary neurones project to dorsal horns
Depress activity of nociceptive neurones
