Lower Motor Neurons and Spinal Motor Function

Motor neural activity begins with a decision made in the _______________ lobe

frontal

Motor neural activity begins with a decision made in the frontal lobe. Next, motor planning areas and control circuits are

activated

_______________: cerebellum and basal ganglia, regular the activity in UMN

control circuits

___________________: cell bodies in cerebral cortex; axons project to spinal cord, deliver signals to spinal interneurons and LMNs

UMN

_________s: transmit signal directly to skeletal muscles, eliciting the contraction of muscle fibers

LMN

_____________ movement is controlled from the top down

voluntary

______ lesion: more muscle contraction (spastic), more muscle tone (hypertonic), more muscle reflexes (hyperreflexic), more disuse of the muscle (disuse atrophy), toes point up (+Babinski)

UMN

_______ lesion: less muscle contraction (flaccid), less muscle tone (hypotonic), less muscle reflexes (hyporeflexic), less muscle innervation, toes point down (- Babinski)

LMN

_____________ refers to the anticipatory use of sensory information to prepare for movement. Ex: what is anticipated to happen

feedforward

____________ refers to the use of sensory information during or after movement to make corrections either to the ongoing movement or to future movements. Ex: what actually happened

feedback

Ex: while typing, you anticipate (__________) what it will feel like to press a specific key, once you press a key you have proprioceptive feedback whether it was the correct key even before you have visual feedback -> this influences your next motor response

feedforward

In the absence of ___________ reaching depends on somatosensation and proprioception to locate objects

vision

Loss of _________________ in individuals with deafferentation disrupts positioning of limbs

somatosensation

_________muscle is excitable, contractile, extensile, and elastic

skeletal

Muscle fiber is made of

myofibrils

Myofibrils are proteins arranged into

sarcomeres

Structural proteins and contractile proteins make up

sarcomeres

Z line, M line, and tint are

structural proteins

myosin, actin, tropomyosin, and troponin are

contractile proteins

Muscle contraction is produced when ____________ slides relative to myosin

actin

Repeated attachment, swiveling, and detachment of myosin heads produce _________ of the muscle

contraction

_________ prevents sarcomere from being pulled apart with stretch and maintains position of myosin at rest, helps with elasticity

titin

Resting in one position for prolonged period allows for _______ actin and myosin bonds which creates increased resistance to stretch

weak

Muscles behave somewhat like springs: the resistance to stretch depends on their

length

_____________ is the resistance to stretch in a resting muscle

muscle tone

When muscle tone is normal, resistance to passive stretch is

minimal

Normal resting muscle tone is provided by titan and __________ actin-myosin bonds

weak

__________ is clinically assessed via PROM and quick stretch

tone

complete loss of muscle tone

flaccid

reduction in muscle stiffness

hypotonia

excessive muscle tone

hypertonia

motor disorder characterized by a velocity0dependent increase in the stretch reflex with exaggerated tendon jerks, resulting from hyperexcitability

spasticity

heightened resistance to passive movement, but independent of the velocity of that stretch or movement

rigidity

A constant resistance to movement through the range is ___________ rigidity

lead pipe

______________ rigidity is characterized by alternative episodes of resistance and relaxation

cogwheel

When healthy innervated muscle is continuously immobilized in a shortened position for a prolonged period, ______________ disappear from the ends of myofibrils

sarcomeres

Loss of sarcomeres is a __________________ to the shortened position so that the muscle generates optimal force at the new resting length

structural adaptations

When a structurally shortened muscle is stretched, it will _____________ reach the limits of its elasticity and will be resistant to stretching.

quickly

If the muscle is immobalized in a lengthened position, the muscle will ________ sarcomeres

add

_________ casting -> goal to lengthen soft tissue to improve biomechanics advantage for movement DOES NOT have an affect on tone

serial

Neurons that transmit signs directly to skeletal muscles

LMN

In LMN, cell bodies are in the _______________ horn of the spinal cord

anterior/ventral

In the LMN, Axons leave via _____________

ventral roots

In the LMN, Axons leave via ventral roots ->__________________

spinal nerve

In the LMN, Axons leave via ventral roots ->spinal nerve -> _________________

peripheral nerve

In the LMN, Axons leave via ventral roots ->spinal nerve -> peripheral nerve ->

muscle contraction

What are the two types of LMN

alpha and gamma motor neurons

Alpha or gamma: have large cell bodies and large myelinated axons

alpha

Normally, an alpha motor neuron releases enough ______ that all of the muscle fibers it innervates contract

ACh

Axons of alpha motor neurons project to ____________ skeletal muscle, branching into numerous terminals as they approach muscle

extrafusal

Alpha or gamma: consist of medium sized myelinated axons

gamma

Axons of gamma motor neurons project to ____________ fibers in the muscle spindle

intrafusal

Alpha and gamma motor neuron systems usually activate

simultaneously

Alpha-gamma _____________: maintains proper length of intrafusal fibers in the muscle spindle (role is to monitor length of the muscle) during contraction relative to the rest of the muscle

coactivation

Most sources of input to alpha MNs have ____________ that project to gamma NMS

collaterals

Overactivation of __________ motor neurons is also thought to contribute to spasticity created by UMN lesions

gamma

Alpha MN and the muscle fibers it innervates

motor units

When alpha MN is active and healthy ______ onto all of its fibers and all those fibers contract

ACh

Number of fibers innervated by one motor unit varies depending on

location

Motor neurons can be classified as slow or fast _______ depending on speed of neuron innervating the muscle fiber

twitch

_______ twitch fibers are the majority of muscle fibers in postural and slowly contracting muscles

slow

________ twitch typically activate first because their cell body is smaller and can depolarize more easily. Also maintain activation longer

slow

________ twitch fibers are important for fast, powerful contraction

fast

_______ twitch fibers are fatigue resistant and important for endurance

slow

___________ contraction: involves shortening

concentric

_____________ contraction: involving lengthening

eccentric

______________ contraction: involving no change in length of muscle

isometric

______________: acts to cause a movement

agonist

______________: acts to slow or stop a movement; action opposite of the agonist

antagonist

_______________: acts to stabilize a body part against some other force or eliminate an unwanted action produced by an agonist

stabilizer/neutralizer

With a bicep curl, the bicep would be the

agonist

With a bicep curl, the tricep would be the

antagonist

With a bicep curl, the stabilizer/neutralizer would be

pronators

______________ refers to the simultaneous contraction of antagonist and agonist muscles

cocontraction

cocontraction ______________ joints

stabilizes

In the _________ limbs, cocontraction enables precise movements

upper

In the __________ limbs, cocontraction creates stability to respond to unstable environments

lower

Proximal stability yields to __________ mobility

distal

Activity of a ________ unit depends on convergence of info from peripheral sensors, spinal connections, and descending tracts onto cell bodies onto the alpha motor neuron

motor

____________ is generated when somatosensory info is integrated with descending motor commands in the spinal cord

movement

Sensory info ascends and influences ___________ output

motor

spinal cord is organized ______________-

somatotopically

anterior pools ->

extensors

posterior pools ->

flexors

group of muscles innervated by a spinal nerve = a

myotome

_________________: inhibition of an antagonist muscle during agonist contraction

reciprocal inhibition

Reciprocal inhibition is achieved by ___________ in the spinal cord that link LMNs into functional groups

interneurons

______________: coordinated muscular action or muscles that are typically activated together in a healthy nervous system

muscle synergies

Muscle synergies are organized by ___________________ providing info to interneurons and LMNs

sensory afferents

_____________________: joint capsule and ligament receptors, muscle spindle receptors, and GTOs provide proprioceptive input required to generate the body schema which is taken into account in the spinal cord as motor movements are produced

proprioceptive body schema

Mistakes in sensory info creates mistakes in motor _________

output

_______________ contribute to proprioception by registering tendon tension

Golgi tendon organs

The role of GTOs in movement is to ___________ muscle contraction along with other proprioceptive signals and UMN signals

adjust

Does input from GTOs protect muscles from overload injury?

no

Adaptable networks of spinal interneurons that activate LMNs to elicit alternative flexing and extending pattens of the hips and knees

stepping pattern generators (SPG)

Does each LE have its own SPG?

yes

SPGS are not the only thing controlling walking, _______ input for postural control, cortical control of dorsiflexion and afferent info are essential for human locomotion

UMN

___________ inputs adjusts timing, facilitates transition from stance to swing phase, and reinforces muscle activation

afferent

In the healthy adult, most movement is ______________

automatic

____________ are examined for info about peripheral and spinal circuits as spinal reflexes require sensory receptors, afferents, synapses between afferents and LMNs and muscles

reflexes