Anatomy 2 Flashcards
what’s in a neuronal circuit? exception?
stimulus –> *sensory neuron –> *spinal cord response/1+ interneuron –> *motor neuron –> effector muscle. stretch reflex (no interneurons –> monosynaptic)
Propriospinal fibers
fibers travel b/t levels of the spinal cord –> link limbs together for a single reflex; Part of white matter immediately adjacent to gray matter, present in all funiculi; Form fasciculi propri
innate vs acquired/conditioned reflexes
connections that form b/t neurons during development & are genetically programmed
o Ex: spinal reflex— occur w/o immediate conscious awareness –> sent to higher centers & conscious sensation may result (e.g., pain)
Most are never consciously sensed
Spinal reflexes can be suppressed by conscious thought arising from higher centers
vs
enhanced by repetition; more complex, learned (somatic) motor patterns
Effective spinal reflexes (in correcting & adjusting muscle movement) –> need very detailed motor output & very accurate sensory input describing fxnal status of ea muscle at ea instant. How?
2 sensory receptors in skel muscle provide subconscious, continuous feedback to the spinal cord –> cerebellum –> cortex: Golgi tendon organs for muscle tension, muscle spindle organs for muscle length. both = proprioceptors (conscious in post column, subconsc in spinocerebellar tracts)
muscle spindles. explain all their fibers
elongated, sac-like structures W/IN skel muscles. 8-12 modified intrafusal fibers in parallel w/ extrafusal fibers. 2 classes of intrafusal: nuclear bag (clustered nuclei, #2-4 per spindle) supplied by type Ia sensory nerve fibers/primary endings & dynamic y-motor neurons, nuclear chain (single-file, #6-8 per spindle) supplied by type II sensory nerve fibers/secondary endings & static y-motor neurons
how do muscle spindles receive SENSORY info about muscle length? why does CNS need to care?
intrafusal fibers in parallel w/ extrafusal –> when extrafusal stretches, intrafusal feels it too. muscle = always feeling some amt of stretch –> type Ia & II give info to CNS abt amt => static response; type Ia give info to CNS abt rate of change of stretch => dynamic response… CNS cares b/c stretching w/o correction can dmg muscle
how do muscle spindles receive MOTOR info about muscle length? –> primary vs secondary response? do alpha and y-motor neurons need to be coactivated & why?
sensory input –> activate alpha motor neurons –> extrafusal fibers ctx to counter stretch & potential injury vs activate y-motor neurons –> reg activity intrafusal fibers to report amt & rate of change. yes or else intrafusal = slack relative to extrafusal –> can’t efficiently report muscle length to CNS
what is myotatic/stretch reflex? what neurons = involved?
what’s reciprocal inhibition?
sudden stretch of muscle –> reflexive ctx of that muscle. single type Ia sensory neuron w/ homonymous alpha motor neuron
seen in patellar reflex: type Ia sensory neurons excite inhibitory interneurons that innervate motor neurons in flexors/hamstrings –> hamstrings relax –> quads ctx
dynamic/phasic vs static/tonic stretch reflex
type Ia sensory fibers oppose sudden changes in muscle length vs BOTH type Ia & II sensory fibers respond to slower/steady stretch –> make small instantaneous corrections –> prevent us from falling while standing and smooth ctx
when is stretch reflex strongest? can it be suppressed?
in gravity-opposing extensors. yes in higher centers b/c strength of reflex = low enough
golgi tendon organs. what happens to GTO w/ inc muscle tension?
encapsulated nerve endings of unmyelinated type Ib afferent fibers entwined in collagen of muscle, equalize contractile forces among groups of muscle fibers. nerve endings = compressed by collagen –> impulses sent in proportion to degree of compression
type Ib sensory fibers of GTO synapse on 2 types of interneurons in ant horn of gray matter:
inhibitory interneurons: inhibit alpha motor neurons of active muscle –> relaxes them to avoid tension overload
excitatory interneurons: activate alpha motor neurons of antagonist muscles –> ctx them to unload active muscle
what is inverse myotatic/stretch reflex? what’s lengthening rxn?
inc muscle tension –> GTO causing relaxation. spinal cord can mediate instant relaxation of entire muscles in extreme tension –> prevents tears or tendon avulsion
what’s flexor reflex? does it always involve flexor muscles? what’s crossed extensor reflex?
involves whole limb (stretch reflex and GTO reflex involve single muscle) –> quicker ctx of flexor muscles to w/draw from noxious stimuli detected by nociceptors to type II & III afferents. no. after flexor reflex –> contralat limb extends to support & push body away from stimulus (LE) and provide bal (UE)
hyperalgesia vs analgesia vs allodynia
inc pain from something that nmlly provokes pain vs no pain from something that nmlly provokes pain vs pain for something that doesn’t provoke pain
what are nociceptors? where are their free nerve endings?
sensory receptors detecting stimuli that elicit tissue dmg, or signals/chemicals from dmged tissue; free/bare nerve endings in skin, muscle, joints/bone, viscera
Aalpha/beta vs Adelta vs C fibers
myelinated, lg, proprioception/light touch vs lightly myelinated, medium, nociception vs unmyelinated, small, innocuous temp/itch/nociception, responds to inflam –> gives pain sensation after a cut
what is pain? acute vs chronic pain. mechanism for chronic pain?
submodality of somatic sensation –> unpleasant sensory & emotional experiences assoc w/ tissue dmg. activation of nociceptors for short time, no sig tissue dmg vs pain lasting mo+ from tissue injury, inflamm, nerve dmg, tumor/lesion, occluded blood vessels –> evoke chemical, fxnal, structural changes (like activating G proteins). noxious peripheral stimuli –> excitatory gluE and asp bind to NMDA receptors –> hyperalgesia, neuropathic pain
pain categories: fast pain/pinprick/sensory pain vs burning/soreness pain vs aching pain
sharp/stinging pain, well localized, on skin, neospinothalamic tract; Adelta vs inflamm secondary to tissue dmg, diffuse & lasts longer, on skin or muscle, paleospinothalamic & archispinothalamic tracts; C fibers vs poorly localized pain form deep structures like joints or viscera, paleospinothalamic & archispinothalamic tracts; C fibers
know how pain = transmitted
noxious stimulus from periphery –> primary afferent neurons (A or C fibers) –> DRG –> dorsal root projection neurons in spinal cord –> higher centers
somatic pain = classified into: superficial/cutaneous/peripheral pain vs deep pain
pain from skin, muscle, peripheral nerves; has initial response then later response vs pain form joint receptors, tendon, fascia; has autonomic response like sweating, nausea, change in bp & HR
visceral nociceptors. where are their free nerve endings?
contain mechanical pressure, temp, chemical and silent nociceptors. free nerve endings = scattered –> any stimulus that excites them cause visceral pain
cause vs s/s of visceral pain
GI lesions/tumors, artery thrombosis, tissue obstruction or stretching vs low grade diffuse pain, low HR and bp, cold sweats, nausea, hunger, thirst, electrolyte imbal, irreg circ/resp systems
referred pain vs phantom pain
pain from same myotome b/c innervated by same nerve, but not where pain actually originated from vs pain receptors = activated post amputation b/c brain can’t understand it
gate control theory
nonpainful input closes painful/noxious input –> prevent pain sensation from traveling to CNS; large sensory fibers w/ cutaneous sensory input activate inhibitory interneurons –> inhibit pain transmission by pain fibers
syringomyelia. s/s?
when fluid-filled cavity/cyst forms w/in spinal cord => syrinx; syrinx can expand over time –> destroy surrounding nerve tissue. pain in neck & shoulders, pain & stiffness in legs, muscle weakness, numbess/dec sensation, scoliosis, chiari malformation
mechanoreceptors: rapidly adapting vs slowly adapting
signal a change in stimulus; Meissner corpuscles (touch), Pacinian corpuscles (pressure, vibration); respond at beginning & end of stimulus vs signal continued presence and intensity of stimulus; Merkel discs (touch), Ruffini corpuscles (steady pressure); respond at beginning of stimulus then dec then stops when stimulus stops
what is a receptor potential?
when sesnsory receptors transduce physical stimulus ot electrical signal –> open/close ion channels
mechanoreceptors produce what type of RP? deformation of ion channels are?
depolarizing RPs. stretch-gated –> dendrite stretches –> ions flow in/out
short duration vs long duration stimuli
make constant RP and AP; proportion to duration vs time dependent decline in RP and AP; more robust NT release
what is receptive field?
area of sensory space = stimulated –> elicits neuronal responses
