Exam 2 Review

In Chapter 7 Motor output variability who is the person in the slide

Carl Lewis

What is motor output variability

The Unintentional variations in the output of motor contractions

What are 2 dimensions of motor output variability

• Unsteadiness

• Inconsistency

What are variables to unsteadiness

• Trajectory Variability

• Tremor

What are variables to inconsistency

• Endpoint Variability

• Trial to Traal Variability

What is a functional consequence of unsteadiness

Tremors

Explain Inconsistency when infant age

There is significant motor inconsistency along with unpredictability

Explain inconsistency at adolescence

People are typically in health range of motor inconsistency and innaccuracy

Explain inconsistency at maturity with movement disorders

Movement disorders can play a significant role in motor inconsistency

Why do we care about factors that influence motor output variability

• Practical ways to reduce Motor output variability

• Mechanisms of variability

• Ways to manipulate it experimentally and examine its affects on motor performance

Does motor variability increase with level of effort

Yes for Standard deviation

Is it proportional to the level of effect

No, because coefficient of variation is greater at low force levels

How does CNS plan and execute complex movement

Central command

HOw do we accomplish accurate movemnts

Sensorimotor transformations

How do we accomplish theres sensorimotor transformations

• CNS determines locations of end effector and target

• Computes a difference vector that specifies the amplitude and direction

• CNS uses difference vector to develop motor plan

Explain Motor plan

• Determines the joint torques or muscle activities that are necessary to achieve the desired joint trajectories

• Depend on the dynamic properties of the arm such as the mass of the segments

How do we know that voluntary motor commands derive from sensorimotor transformations

motor equivalence

What is motor equivalence

The ability of different systems to achieve the same behavior

Who painted this painting

Peter longstaff with his feet

What is significant about Evarts experiement

The activity of a primary motor cortex neuron relates to the direction and level of force and muscle activity exerted during the movement than simply to the direction of wrist displacement

How does the CNS learn to repeat movements with accuracy

Efference copy

What are spinal reflexes

Fast responses that involve an afferent signal into the spinal cord and an efferent signal out to the muscle

What combo makes up for spinal reflexes

Sensory receptor, interneuron, efferent neuron

How do we know our own muscle length during movements

Muscle spindles

What does the muscle spindle comprise of

2-12 miniature skeletal fibers referred as intrafusal fibers

When does Ia neurons discharge

Intensely when stretch of the muscle is occurring, dynamic phase

When does II neurons discharge

Intensely when magnitude of stretch changes, Static phase

What happens during alpha gamma coactivation

• CNS activates both the MNs during contraction concurrently

What would happen if only alpha MN activation

• Slack of intrafusal fibers

• Diminished or no feedback from the muscle regarding its change in length

What are monosynaptic reflexes

When a sensory neuron synapses, or a nerve impulse is transmitted, directly to a motor neuron, resulting in an automatic reflex

Explain how Hoffman reflex can be evoked

An application of electrical stimulus to a peripheral nerve and recorded the twitch or muscle activity of the muscle that innervates

When is M wave existent

At high voltage

When is H-reflex greatest

When M wave is small

Define muscle fatigue

An acute exercise–induced reduction in force and power output of the involved muscles that dictate performance.

What is Central Fatigue

Reduction in capacity of the central nervous system to voluntarily activate muscles

What is peripheral fatigue

Decrease in contractile strength in muscle fibers

Explain voluntary activation

Electrical stimulation at the motor nerve during a maximal contraction to examine how much extra force can be evoked

What is cortical fatigue

Disruption of processes that generate the motor output at the cortical level

Explain Spinal activation

Disruption of processes that generate motor output at the spinal level

What is muscle wisdom

Ability of the brain to adapt without us knowing it

Why would mechanical state change in spinal activation

• The relaxation rate of the twitch lengthens

• Degree of fusion of the twitches increases

Muscle wisdom is

The reduction in discharge rate of MUs to match the change in the mechanical state of the muscle

What is motor fatigability

• Voluntary activation

• contractile funciton

What is considered perceptual fatigability

• Excitement

• Apathy

• Depression

Which task reaches task failure first, force or position.

Position

Why does position task reach failure first

• More rapid recruitment of MUs, as indicated by faster increase in EMG

• More frequent bursts

What does glands are part of HPA axis activation

• Hypothalamus

• Pituitary

• Adrenal

What is the differences in younger and older adults when observing feedback

Younger adults observe visual feedback better than older adults

When does motor output variability increase

With more visual information in older adults

Is it the amplitude or the speed of visual feedback that increases force output variability in older adults

Increased speed but not amplitude of visual feedback increases force variability in older adults

Explain Motor unit Reorganiation

• Large MNs die

• Sprouting occurs

• Small MNs innervate more muscle fibers

What are functional implications of the increase in motor output variability for older adults

• Endpoint accuracy decreases

• Motor learning is inhibited

• Impairs reactive driving

• Slows reaction time

What should rehabilitation innervations focus on in older adults

Reducing motor output variability

What are hypokinetic disorders

Slowness of movement

What are hyperkinetic movements

Excessive involuntary movement

What is essential tremor

involuntary rhythmic sinusoidal oscillations (4-8 Hz; shaking movements) of one or more parts of the body.

What is Deep brain stimulation

involves implanting electrodes within the thalamus. The electrodes produce electrical impulses that affect brain activity to treat certain medical conditions.

How does health aging affect motor variability

Older adults are less steady at very low forces. Older adults are more variable in repeating the same voluntary command.

Does motor variability vary with contraction type

Yes, When eccentric contractions are less steady and more variable when repeating the same voluntary command.

Predictability of the motor command is

Safety

How do we know about our own muscle force during movements

Tendon organ (Ib afferent)

When do tendon organs get excited

By a pinch of collagen

Increase GTO leads to…

excitation of the Ib inhibitory interneuron