Muscle Physiology Quiz

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Questions and Answers

What are the two types of muscle fibers found in a skeletal muscle?

Intrafusal and connective muscle fibers

Extrafusal and intrafusal muscle fibers (correct)

Extrafusal and smooth muscle fibers

Extrafusal and intrinsic muscle fibers

Which type of muscle contraction is responsible for moving a limb toward the body?

Passive stretching

Agonistic contraction

Flexion (correct)

Extension

What role do gamma motor neurons play in muscle fibers?

They directly cause muscle fibers to generate force

They modify the sensitivity of muscle spindles to stretch (correct)

They connect skeletal muscle to tendon

They innervate extrafusal muscle fibers

What characterizes a motor unit?

A single alpha motor neuron and multiple extrafusal muscle fibers Signup and view all the answers

In what scenario would the ratio of muscle fibers to alpha motor neurons be lower?

In muscles requiring precise control, like those in fingers Signup and view all the answers

What structure forms the synapse between a motor neuron and a muscle fiber?

Neuromuscular junction Signup and view all the answers

What is the primary function of intrafusal muscle fibers?

To provide sensory feedback about muscle stretch Signup and view all the answers

Which muscles are likely to be synergistic in function?

Flexor digitorum and flexor carpi Signup and view all the answers

What happens at the motor endplates of muscle fibers when an axon fires?

ACh is released, leading to depolarization. Signup and view all the answers

How does the endplate potential compare to an EPSP?

It is much larger than an EPSP. Signup and view all the answers

What determines the strength of a muscular contraction?

The average rate of firing of various motor units. Signup and view all the answers

Which type of sensory neuron detects muscle length?

Intrafusal muscle fiber afferent neurons. Signup and view all the answers

What is the function of the Golgi tendon organ?

Signals changes in muscle tension. Signup and view all the answers

During passive lengthening of the muscles, what occurs with MS1 neuron activity?

MS1 activity increases. Signup and view all the answers

What triggers the firing of both MS1 and MS2 neurons when weight is suddenly dropped into the hand?

The rapid change in muscle length. Signup and view all the answers

What aspect of reflexes is controlled by the spinal cord despite input from the brain?

They operate independently to some degree. Signup and view all the answers

What is the primary function of the monosynaptic stretch reflex?

To maintain equilibrium during movement Signup and view all the answers

Which component initiates the monosynaptic stretch reflex?

Muscle spindles Signup and view all the answers

What occurs when the muscle spindle is elongating due to increased weight?

The firing rate of muscle spindle afferent neurons increases Signup and view all the answers

What happens to the muscle spindles when the gamma motor neurons are active?

They become shorter and more responsive Signup and view all the answers

What is an example of a monosynaptic stretch reflex in the body?

Patellar tendon reflex Signup and view all the answers

What role do terminal buttons in the spinal cord play in the monosynaptic stretch reflex?

They synapse on alpha motor neurons Signup and view all the answers

How do muscle spindles help maintain upright posture during oscillation?

By detecting muscle lengthening Signup and view all the answers

What effect does a sudden stretch of the quadriceps muscle have?

It causes an increase in alpha motor neuron firing Signup and view all the answers

What is the role of the supplementary motor area (SMA) in movement?

It is responsible for learning and performing sequences of movements. Signup and view all the answers

Which area is specifically involved in the perception of control for spontaneous movements?

Pre-supplementary motor area (pre-SMA) Signup and view all the answers

What happens to SMA activity when a movement is about to be initiated?

Neurons become more active before and during the movement. Signup and view all the answers

How does the premotor cortex contribute to voluntary movement?

It processes arbitrary information to dictate movements. Signup and view all the answers

What type of information is the supplementary motor area involved with?

Arbitrary information denoting learned movement responses. Signup and view all the answers

What is the effect of electrical stimulation of the medial frontal lobes?

It evokes a sense of automatic and involuntary movements. Signup and view all the answers

When does activity in the pre-supplementary motor area begin in relation to a conscious decision?

Approximately 2-3 seconds before the conscious decision. Signup and view all the answers

What occurs when there is damage to the supplementary motor area?

There is an inability to execute well-learned movement sequences. Signup and view all the answers

What happens when the muscle spindle contracts faster than the muscle as a whole?

There is considerable afferent activity. Signup and view all the answers

What role do alpha motor neurons play during a limb movement command from the brain?

They initiate muscle contraction. Signup and view all the answers

In a situation with high resistance, what occurs between the intrafusal and extrafusal muscle fibers?

Intrafusal fibers shorten more than extrafusal fibers. Signup and view all the answers

What distinguishes polysynaptic reflexes from monosynaptic ones?

Polysynaptic reflexes involve multiple synapses. Signup and view all the answers

What is the function of the inhibitory Golgi tendon organ reflex?

To decrease contraction strength in case of danger. Signup and view all the answers

Which of the following best describes the state of a decerebrate cat?

The cat shows extended stiff legs and arched back. Signup and view all the answers

How do less sensitive afferent axons from the Golgi tendon organ function?

They synapse on spinal cord interneurons. Signup and view all the answers

What effect does the caudal reticular formation have on stretch reflexes?

It enhances activity in the gamma motor system. Signup and view all the answers

What does the response-chunking hypothesis suggest about behavior practice?

It combines individual responses into sequences of behavior. Signup and view all the answers

What role do mirror neurons play in understanding actions?

They help the observer's motor system resonate with observed actions. Signup and view all the answers

What is a defining characteristic of apraxia?

Difficulty in imitating movements despite having strength. Signup and view all the answers

What triggers the activation of the mirror neuron system most strongly?

Watching a behavior one is already competent in performing. Signup and view all the answers

What type of apraxia involves issues with arm and hand movements?

Limb apraxia Signup and view all the answers

What distinguishes apraxia from paralysis?

Apraxia occurs with intact strength but impaired movement execution. Signup and view all the answers

Which of the following statements about perceptual learning is true?

It helps refine the mirror neuron responses. Signup and view all the answers

What occurs when the motor system of the observer resonates with another's actions?

The observer recognizes the action being performed. Signup and view all the answers

Study Notes

Learning Goals

Understanding the anatomy and function of skeletal muscles is crucial for comprehending movement.
Reflexes are rapid, automatic responses mediated by neural pathways within the spinal cord.
Various types of reflexes, such as monosynaptic stretch reflex and inhibitory Golgi tendon organ reflex, play important roles in movement control and posture.
Inhibiting reflexes involves controlling the spinal cord's activity.
Different brain structures like motor association cortex, secondary motor cortex, primary motor cortex and cerebellum are dedicated to specific aspects of movement control.
Learning movements involves sensorimotor programs: established patterns of activity for initiating different actions.
Mirror neurons in the premotor cortex and inferior parietal lobule are involved in understanding and imitating others' actions.
Several neurological disorders, including apraxia, limb apraxia and constructional apraxia, involve problems with voluntary movement control.

Skeletal Muscle Anatomy and Contraction

Skeletal muscles are attached to bones by tendons and move them when they contract.
Flexion brings a limb towards the body, while extension moves it away.
Synergistic and antagonistic muscles work together or in opposition to produce specific movements.
Extrafusal muscle fibers, controlled by alpha motor neurons, comprise the bulk of muscle.
Intrafusal muscle fibers within muscle spindles are sensitive to stretch, receiving both sensory and motor input.
The neuromuscular junction is the synapse between a motor neuron and a muscle fiber, where acetylcholine (ACh) transmission initiates contraction.

Reflexes

Reflexes are rapid motor responses mediated by neural pathways primarily in the spinal cord.
Monosynaptic reflexes, like the stretch reflex, have one synapse between the sensory and motor neurons.
Polysynaptic reflexes involve multiple synapses, as in the Golgi tendon reflex or withdrawal reflex.
The monosynaptic stretch reflex helps maintain posture by responding to changes in muscle length.

Motor Pathways

The motor system is a hierarchical organization with commands cascading from the brain's motor association cortex through intermediate levels to muscles.
Posterior parietal association cortex and dorsolateral prefrontal cortex are crucial for initiating voluntary movements.
The secondary motor cortex, particularly the supplementary motor area (SMA) and premotor cortex, plays vital roles coordinating sequences of movements.
Primary motor cortex controls specific movements, exhibiting a somatotopic organization.
Major descending pathways (dorsolateral and ventromedial) carry signals from the brain stem to specific skeletal muscles.
Different tracts, such as corticospinal, rubrospinal, vestibulospinal, tectospinal, and reticulospinal, coordinate different types of movements.

Learning Movements and Mirror Neurons

Sensorimotor programs are fundamental patterns of actions pre-programmed in the nervous system.
Motor equivalence means the same movement can be performed using different muscles.
Practice can also establish central sensorimotor programs, allowing efficient and learned actions.
Mirror neurons in the premotor cortex and inferior parietal lobule, activated by observing actions, are involved in understanding and imitating them. This system plays a key role in learning by observation.

Motor Disorders

Apraxia is a disorder of voluntary movement, often caused by damage to the frontal or posterior parietal cortex.
Limb apraxia involves problems with limb movements.
Constructional apraxia affects the ability to draw or assemble objects, frequently associated with lesions in the right parietal lobe.
Apraxic agraphia is a particular writing difficulty, while oral apraxia impacts speech movements.
Huntington's disease leads to involuntary movements and cognitive impairment, due to damage in the basal ganglia.
Contralateral neglect occurs when stimuli on one side of the body or space are ignored.
Astereognosia is a deficit in recognizing objects by touch.
Muscular dystrophy and amyotrophic lateral sclerosis (ALS) are characterized by progressive muscle weakness due to various pathological causes.

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Description

Test your knowledge on muscle physiology, including the types of muscle fibers, motor units, and sensory neurons involved in muscle function. This quiz covers essential concepts related to skeletal muscle and its interactions with the nervous system.