11 - Motor Systems 2

what provides proprioception and kinesthetic awareness?

proprioceptors, exteroceptors

other sensory input includes vestibular, visual and auditory

proprioceptive information is used by CNS for

sensory awareness in cerebral cortex, motor control and planning in cerebral cortex and cerebellum, reflex responses in spinal cord and brainstem

where are mechanoreceptors located?

joint capsules, ligaments, menisci, tendon, muscle, skin and subQ tissue

what are the types of joint receptors?

Type I-IV

Type I joint receptors type, adaptation, information?

Ruffini-like ending

slow adapting

extremes of motion, stretch of capsule, sustained

Type II joint receptor type, adaptation, information?

lamellated corpuscle/Pacinian corpuscle-like

rapid adapting

changes in direction and speed, start/stop

Type III joint receptor type, adaptation, information?

GTO-like

slow adapting

extreme stretch, ligament of horns of menisci

Type IV type, adaptation, information?

FNE - C and A-delta

slow adapting

mechanoreceptors and nociceptors, mechanical and chemical

joint receptors respond to _______.

specific arc of motion

T/F most joint receptors have high density.

F, varies with location

what receptors are specific vs general?

general: FNE, Ruffini’s endings, Pacinian corpuscles

specific: golgi tendon organ, muscle spindles

what is an extrafusal fibers? intrafusal fibers?

skeletal muscle, contractile elements in the skeletal muscle

what attaches to a single golgi tendon organ? what does it consist of? what kind of nerve fiber in GTO?

around 20 muscle fibers

thin nerve fibers intertwined with collagen strands

Ib afferent fiber - heavily myelinated fast axon

what is the stimulus for a golgi tendon organ?

muscle tension

what is the sequence of golgi tendon organ reflex?

force → stretches GTO → Ib afferent fiber → (+) interneurons → (-) motoneurons of same muscle

muscle spindle function

gives signals of static muscle length, changing dynamic muscle length, and limb position (with info from other receptors)

CNS can adjust gain or sensitivity of muscle spindle

what are the contractile and noncontractile regions of a muscle spindle?

contractile: ends of the muscle spindle

noncontractile: center of the muscle spindle

what happens during change in muscle length?

spindles are in parallel with muscle and would shorten

what are the 2 types of intrafusal muscle fibers?

nuclear bag and nuclear chain

both carry different kinds of information back to the CNS

contractile ends are innervated by? what do they do?

noncontractile centers are innervated by? respond to? what do they contain?

gamma-motoneurons, carry information to contract/relax muscle. they adapt to the length of extrafusal fibers; by working with alpha-motoneurons in extrafusal muscle to maintain/alter sensitivity

Ia or II sensory afferent endings, respond to stretch, contain nuclei

nuclear chain and static nuclear bag (bag2) fibers respond to? type of MN?

sensitive to change in length only

static gamma-motoneurons

dynamic nuclear bag (bag1) fibers respond to? type of MN?

sensitive to rate of change in length

dynamic gamma-motoneurons

how do nuclear chain and static nuclear bag fibers and dynamic nuclear bag fibers differ?

contractile properties, passive mechanical properties

sensory fibers terminate on _______ of intrafusal fibers (IFF)

central region

what happens when muscle is stretched?

whole muscle stretch → stretch of intrafusal fibers (IFF) → stretch of central region → depolarization of afferent endings

where do primary endings (Ia) fibers (afferent) terminate? what fiber do they have the greatest response to?

all types of IFF

greatest response to stretch of dynamic nuclear bag fibers, changing length

where do secondary endings (II fibers) terminate?

nuclear chain and static nuclear bag fibers

static (absolute) length

what is alpha/gamma coactivation?

simultaneous activation of both alpha and gamma motoneurons in the CNS, helps with adjusting length of muscle spindle to length of surrounding muscle

visual of response to stretch

T/F intrafusal and extrafusal fibers generally contract simultaneously

T, CNS activates both alpha and gamma motoneurons, adjusts lengths of muscle spindle to length of surroudning muscle

often referred to as alpha/gamma coactivation

which motoneuron is task specific?

gamma motoneurons, the degree of gamma-mn activation is greater with tasks that require more precise movement

where are the control centers of gamma motoneuron activation?

near red nucleus - UE flexion

reticular formation

vestibular nuclei - LE extension

substantia nigra pars compacta

what is the “gamma loop”?

gamma-motoneurons activated by CNS → intrafusal fiber contraction → AP along Ia fiber endings → enhance excitation of a-motoneurons → increase extrafusal muscle contraction

GTO vs muscle spindle

GTO (Ib) - muscle tension, force of contraction, tension on tendon and passive stretch

muscle spindle (Ia, II) - primary endings Ia are responsible for changing muscle length and speed of movement and secondary endings are responsible for muscle length, joint position and static position

reflex definition

involuntary stereotypes responses to specific sensory stimuli - the locus of stimulus determines the muscles that will contract, the strength of the stimulus will determine the strength of the response

spinal reflexes - all circuitry for the reflex is located in the spinal cord

why are spindle fibers important

help with proprioception

reflex def

involuntary stereotyped responses to specific sensory stimuli

the locus of stimulus determines the muscles that will contract, the strength of the stimulus will determine the strength of the response

what are spinal reflexes

all circuitry for the reflex is located in the spinal cord

what modulates the reflex response?

descending influences

what is the stretch reflex? what is the phasic component of a stretch reflex?

deep tendon reflex, muscle stretch leads to Ia afferent sending signal to alpha motoneuron for muscle contraction (homonymous/synergistic muscles)

rapid, brief muscle contraction that occurs in response to a sudden stretch

how does a stretch reflex work?

a muscle is stretched, Ia afferents travel to SC and synapse with alpha motoneuron which then sends signal back to muscle to contract homonymous and synergistic muscles

reflex categories

absent or weak

hyperactive/excessive

muscle spindle reflex connections

type Ia afferents have monosynaptic EPSPs and multisynaptic IPSPs

• monosynaptic EPSPs have homonymous muscle α-motoneuron and synergistic muscle α-motoneuron

• multisynaptic IPSPs have α-motoneuron of antagonist

type II afferents have multisynaptic EPSPs

• multisynaptic EPSPs have homonymous and synergist muscle α-motoneuron

are golgi tendon organ segmental alpha-motoneurons multi or mono synaptic? do they use EPSP or IPSP?

multisynaptic

EPSP to antagonist motoneuron to prevent damaging amounts of tension developing in the muscle

IPSP to homonymous and synergist motoneuron

flexor withdrawal and crossed extension reflexes

stepping on glass analogy

why are “upper” and “lower” motoneuron no longer neuroanatomical terms?

it implies direct connections between long tract cells and motoneurons in the spinal cord

however, they are frequently used clinically

alpha-motonuerons get input from

cerebral cortex, brain stem (vestibular nuclei, reticular formation, red nucleus, tectum), SC interneurons (including Central Pattern Generators)

what happens with a lesion to motoneurons?

weakness, flaccidity, atrophy, fibrillation potentials, fasciculation, decreased or absent reflexes

what happens with a lesion to descending pathways?

initially paralysis/paresis, flaccid muscles

develop spasticity/hypertonicity, hyperreflexia and possibly clonus, Babinski sign - upward big toe, synergistic movement -patterns of groups of muscles

what happens with a lesion to the posterior limb or genu of internal capsule?

lesion to lenticulostriate arteries (branch of MCA)

corticospinal - contralateral hemiplegia, spasticity - hyperreflexia, Babinski, increased resistance to passive movements

corticonuclear - facial motor nuclei

thalamocortical fibers - sensory loss, contralateral hemianesthesia

what happens with an M1 lesion?

paresis of voluntary movements, generally initially flaccid limbs

often regain movements of the proximal limbs but movements are not smooth and distal muscles may remain paralyzed

some return of stretch reflex (what causes spasticity from flaccidity), but not to extent as widespread stroke

review: what happens with a lesion to preMC an SMC?

decreased ability to coordinate bilateral movements

apraxia - difficulty appropriately using the limb during tasks despite ability to use limbs

review: what happens with a lesion to the PPAC?

tactile agnosias (like astereognosis)

deficits in association of tactile and visual image, initiation of contralateral movements, attention to contralateral world, visually and tacitly guided movements

most significant in non dominant side