Pt7 Sensory System II Flashcards
Describe somatic sensations.
-detected by peripheral receptors
-touch, pain, temp, position of body
-ascending tracts are signals from somatosensory receptors = “somesthetic tracts”
>modality neurons carry signals to thalamus, & then to areas of somatosensory CC
>ascending spinal tracts reach the brainstem; thalamus or cerebellum
a nerve tract is a bundle of nerve fibers (axons) connecting the nuclei of the CNS
Describe somesthetic tracts.
all go from spinal cord to CC
SPINAL CORD -> THALAMUS
-spinothalamic tract (ventral)
-spinocervicothalamic tract (dorsal)
SPINAL CORD -> BRAIN STEM
-fasciculus cuneatus (exception: touch & proprioception from thoracic limb to medial cuneate nucleus which relay info to thalamus for conscious perception or to lateral cuneate nucleus & cerebellum for subconscious proprioception)
-spinomedullary tract
-spinopontine tract
-spinoolivary tract
SPINAL CORD -> CEREBELLUM
-spinocuneocerebellar tract
-dorsal spinocerebellar tract
-ventral spinocerebellar tract
[2 names = 1st -> origin & 2nd -> site of termination]
[3 names = middle -> site where axons from origin synapse with neurons that project axons to destination]
Describe nociception.
-pain = conscious perception
-nociceptors = free nerve endings
>in superficial layers of skin & internal tissues
>periosteum, arterial walls, joint surfaces, skull
>deep tissue = sparse pain endings
dont adapt = warning sign
-noxious stimulus = somatic & autonomic responses/reflexes
>can be transmitted to brain (somatosensory cortex)
What are the 3 nonverbal ways animal convey pain?
- Avoiding the noxious stimulus
- Depression/withdrawal
- Self selection of analgesia (seen in lab animals)
*test: pedal/withdrawal reflex (dont need cortex)
What are the two pain fibers?
A delta & C fibers
both fibers enter via dorsal root & synapse in dorsal horn = reflex activity
Describe A delta fibers.
-fast pain (0.1 sec)
-superficial pain (origin in skin)
-sharp & localized pain
EX. Needle, knife cut
-warns the brain of potential tissue damage = rapid response
TEST: squeeze skin
Describe C fibers.
-slow pain (1 sec)
-deep pain
-tissue destruction
-prolonged unbearable suffering = withdraw & rest to heal
-occur in skin, deep tissue, organ
TEST: squeeze digits
Describe nociceptive input cranially.
-pain transmitted cranially in many pathways (bilateral) found in funiculi
>funiculus = bundle of one or more nerve fascicles in spinal cord (portions of white matter)
-to have conscious perception of pain, sensory inputs must reach the cortex
Describe the clinical importance of cranial nociception.
-spinal cord lesions must be extensively destroyed across the width of the cord to destroy all tracts and cause loss of nociception caudal to the lesion
-withdrawal response = intact reflex arc (peripheral nerves & spinal segment) sensory inputs dont reach the cortex
-behavioral response = conscious perception of pain (turning head/vocalization) sensory inputs reach the cortex
-animals with a complete spinal cord transection at the thoracolumbar junction (cranial to lumbar intumescence) = intact flexor withdrawal reflex in pelvic limbs but wont show signs of pain [conscious perception]
What are the 3 different types of stimuli that can excite pain receptors?
- Mechanical (F&S)
- Thermal (F&S)
- Chemical (S)
Describe the modulation of pain.
-pain is endogenously modulated by NS
-body can inhibit pain conduction recognition through central & peripheral antinociceptive mechanisms
-stimulation of CNS areas by release/alterations in conc of neurotransmitters
>endorphin, encephalin, serotonin, norepinephrine etc
-pain transmissions may be blocked locally at the spinal cord
-alpha delta fibers transmit touch, pressure, vibration = stimulate the inhibitory interneurons
-non painful mechanical stimuli decrease pain transmission
Describe enkephalin.
-cause inhibition of incoming C and delta A pain fibers where they synapse in dorsal horns
Describe unmodulated pain.
pain ascending to higher centers = facilitated or attenuated
-C fibers transmit pain from periphery inhibit these interneurons
-interneurons = inhibit 2nd order neurons that transmit pain to thalamus
How do encephalin and endorphins act in the CNS?
-inhibit presynaptic neurons transmitting pain sensation
-neurotransmitters bind to opioid receptors & terminate pain signals
-inhibit release of substance P from presynaptic neurons
-pinprick axons excite inhibitory encephalinergic interneurons = inhibit neurons that project true pain
Describe proprioception.
-knowledge of ones position (conscious/unconscious)
-know degree of angulation of joints in all planes & rates of change
