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
What are the skin tactile receptors & deep receptors near the joints?
-muscle spindles, golgi tendon
-Pacinian corpuscle (deep pressure)
-ruffinis endings (continuous pressure)
Describe hair cells (receptors).
-in vestibular apparatus of inner ear = info about head position & movement
Describe peripheral receptors.
-proprioceptive info
-travels via spinal nerves, dorsal root & spinal cord to brain
-properioception of head (muscle & joints) = use cranial nerves VIII (vestibulocochlear) & V (trigeminal) to reach brainstem nuclei (thalamus)
Describe conscious proprioception & its deficit.
-info that terminates in somatosensory cortex of contra lateral cerebrum
-conscious awareness of body position & movement
-enables CC to plan & refine voluntary, learned movements
DEFICIT:
-animal bearing weight on abnormal part of foot (knuckling)
Describe subconscious proprioception & its deficit.
-terminate in ipsilateral cerebellum
-stretch & tension of muscles, tendons, ligaments at rest & during movement & spatial orientation of body
-cerebellum needs info to coordinate posture & locomotion
DEFICIT:
-abnormal position of limbs with respect to gravity, at rest & during locomotion
EX: hopping test
Describe the vestibular system.
-provides proprioceptive info (conscious/subconscious) about head position & movement.
-imp for balance & posture
What is the proprioception clinical relevance?
A. Dog with lumbar spinal cord lesion = knuckling (conscious proprioception)
B. Dog whose limbs are not under the center of gravity (dysfunction of subconscious proprioceptive pathway)
distinction between 2 types of proprioception not possible in some cases
->proprioceptive deficits confirm lesion in NS (PNS/CNS) cant be localized
-> localization depends on other info from neuro exam
Describe visceral sensations.
-respiration, heart rate, BP, micturition
-free nerve endings
-nociceptors or physiological receptors
Describe nociceptors in viscera.
-changes in viscera by abnormal physical/pathological conditions
EX: GI bloating, cramping, peritonitis
-visceral organs not sensitive to cutting or temp
> cutting = A fiber & temp = no temp receptor
-respond to stretching, distension, spasm, inflammation, ischemia
> diffuse stimulus = type C fiber
-visceral pain not localized
> few afferent fibers - not recognized by conscious perception
> forebrain doesn’t integrate info ascending from structures not visualized
Describe physiological receptors in viscera.
-respond to innocuous stimuli
-mechanoreceptors or chemoreceptors
-changes in BP
-changes in pCO2 or pO2
-cough reflex = receptors sensitive to inhaled particles in respiratory system
-sense of fullness = stretch/tension in smooth muscle layer
EX. Stomach, urinary bladder
Describe viscerosensory afferents.
-viscerosensory fibers carried by sympathetic & parasympathetic nerves
-physiologic receptors = send info through viscerosensory fibers of parasympathetic nerves
-nociceptors = send info through viscerosensory fibers of sympathetic nerves
[input induces autonomic reflex activity or stimulate conscious awareness]
viscerosensory fibers not part of ANS
