Chapter 8: Control Of Movement Flashcards
are the ones that move us around and thus are responsible for our actions. Most of them are attached to bones at each end and move the bones when they contract.
Skeletal muscle
Muscles are fastened to bones via ____________, strong bands of connective tissue.
Tendons
Several different classes of movement can be accomplished by the skeletal muscles, but we will refer principally to two of them: ____________
Flexion and extension
Contraction of a flexor muscle produces ___________, moving a limb toward the body.
Flexion
_____________, which is the opposite movement or moving a limb away from the body, is produced by contraction of extensor muscles.
Extension
The ______________ are served by axons of the alpha motor neurons. Contraction of these fibers provides the muscle’s motive force.
Extrafusal muscle fibers
The intrafusal muscle fibers are specialized sensory organs that are served by two axons, one sensory and one motor. These organs are also called muscle spindles because of their shape. In fact, theLatin word fusus means “spindle”; hence, intrafusal muscle fibers are found within the spindles, and extrafusal muscle fibers are found outside them.
Intrafusal muscle fibers
The efferent axon of the __________________ causes the intrafusal muscle fiber to contract; however, this contraction contributes an insubstantial amount of force.
Gamma motor neuron
An alpha motor neuron, its axon, and associated extrafusal muscle fibers constitute a _____________
Motor neurons
A single muscle fiber consists of a bundle of ____________, each of which consists of overlapping strands of ________________
Myofibrils;
Actin and myosin
The regions in which the actin and myosin filaments overlap produce dark stripes, or striations; hence, skeletal muscle is often referred to as ___________________
Striated muscle
The synapse between the terminal button of an efferent neuron and the membrane of a muscle fiber is called a _________________
Neuromuscular junction
The terminal buttons of the neurons synapse on ______________, located in grooves along the surface of the muscle fibers.
Motor endplates
When an axon fires, acetylcholine is liberated by the terminal buttons and produces a depolarization of the postsynaptic membrane— an ______________
Endplate potential
The depolarization of a muscle fiber opens the gates of voltage-dependent calcium channels, permitting calcium ions to enter the cytoplasm. This event triggers the contraction.
afferent neurons are ____________, they serve as muscle length _________. This distinction is important. Stretch receptors are also located within the tendons, in the ______________.
Stretch receptors;
Length detectors;
Golgi Tendon organ
Describe the structures of a skeletal muscle.
Skeletal muscles contain extrafusal muscle fibers, which provide the force of contraction. The alpha motor neurons form synapses with the extrafusal muscle fibers and control their contraction. Skeletal muscles also contain intrafusal muscle fibers, which detect changes in muscle length. The length of the intrafusal muscle fiber, and hence its sensitivity to increases in muscle length, is controlled by the gamma motor neuron. Besides the intrafusal muscle fibers, the muscles contain stretch receptors in the Golgi tendon organs, located at the ends of the muscles.
List the steps involved in neurotransmission at the neuromuscular junction that result in a muscle fibertwitch.
When a neuron synapses on a muscle fiber at the neuro muscular junction, the neuron releases acetylcholine (ACh) into the synapse. ACh binds to receptors on the muscle fiber to produce an endplate potential. The depolarization of a muscle fiber opens the gates of voltage-dependent calcium channels, permitting calcium ions to enter the cytoplasm. This event triggers the contraction. Calcium allows the muscle cell to use ATP to allow cross bridges to “row” along actin to produce the contraction.
Contrast the types of information detected by afferent axons of muscle spindles and Golgi tendon organs
Intrafusal muscle fibers contain sensory endings that are sensitive to stretch. Receptors on intrafusal muscle fibers detect muscle length. Golgi tendon organs contain stretch receptors for tendons.
Only one synapse is encountered along the route from receptor to effector.
Another important role played by the ________________ is control of posture.
monosynaptic stretch reflex.
Explain the function of the gamma motor system and its role in regulating the length of muscles.
The gamma motor system functions to help regulate the length of an entire muscle. This feedback is used by the brain to help coordinate limb movement.
Explain the function of monosynaptic stretch reflexes.
Monosynaptic stretch responses function to control limb movements when weight is applied or removed quickly and to maintain upright posture.
Contrast the structures and function of polysynaptic reflexes with monosynaptic reflexes.
Monosynaptic reflexes include a single synapse involved in simple reflexes like the patellar reflex. Polysynaptic reflexes involve multiple synapses involved in more complex reflexive behavior, such as inhibiting a withdrawal reflex. Polysynaptic reflexes contain at least one interneuron between the sensory neuron and the motor neuron.
______________ organized in terms of particular movements of particular parts of the body.
Primary motor cortex
The ___________________ is located on the medial surface of the brain, just rostral to the primary motor cortex.
supplementary motor area (SMA)
The ___________________ is located primarily on the lateral surface, also just rostral to the primary motor cortex.
premotor cortex
Neurons in the primary motor cortex control movements by two groups of descending tracts, the ______________ and the _______________, named for their locations in the white matter of the spinal cord.
Lateral group;
Ventromedial group
The ________________ consists of the corticospinal tract, the corticobulbar tract, and the rubrospinal tract. This system is primarily involved in control of independent limb movements, particularly movements of the hands and fingers.
Lateral Group
The ___________________ consists of the vestibulospinal tract, the tectospinal tract, the reticulospinal tract, and the ventral corticospinal tract. These tracts control more automatic movements: gross movements of the muscles of the trunk and coordinated trunk and limb movements involved in posture and locomotion.
Ventromedial group
The _________________ consists of axons of cortical neurons that terminate in the gray matter of the spinal cord.
Corticospinal tract
The axons leave the cortex and travel through subcortical white matter to the ventral midbrain, where they enter the cerebral peduncles. They leave the peduncles in the medulla and form the _________________, so called because of their shape.
Pyramidal tracts
At the level of the caudal medulla, most of the fibers decussate (cross over) and descend through the contralateral spinal cord, forming the _________________.
Lateral corticospinal tract
The rest of the fibers descend through the ipsilateral spinal cord, forming the _________________
Ventral corticospinal tract
The second of the lateral group of descending pathways, the ______________, projects to the medulla (sometimes called the bulb). This pathway is similar to the corticospinal pathway, except that it terminates in the motor nuclei of the fifth, seventh, ninth, tenth, eleventh, and twelfth cranial nerves (the trigeminal, facial, glossopharyngeal, vagus, spinal accessory, and hypoglossal nerves). These nerves control movements of the face, neck, and tongue and parts of the extraocular eye muscles.
Corticobulbar tract
The third member of the lateral group is the _________________. This tract originates in the red nucleus (nucleus ruber) of the midbrain.
Rubrospinal tract
The red nucleus receives its most important inputs from the motor cortex via the _______________ and from the cerebellum.
Corticorubral tract
ventromedial group includes the ______________, _____________, ____________, as well as the ___________(already described).
Vestibulospinal tracts, tectospinal tract, reticulospinal tract as well as ventral corticospinal tract
Explain the functions of the motor association cortex (including the supplementary motor area and the premotor cortex) in planning and initiating movement.
The supplementary motor area is involved in well-learned behavioral sequences. Neurons there fire at particular points in behavioral sequences, and disruption or damage impairs the ability to perform these sequences. The preSMA is involved in awareness of our decisions to make spontaneous movements. The premotor cortex is involved in learning and executing complex movements that are guided by arbitrary sensory information, such as verbal instructions.
Describe the pathways and functions of cortical regions involved in control of motor behavior.
The supplementary motor area and the premotor cortex receive information from the parietal lobe and help to initiate movements through their connections with the primary motor cortex, which is responsible for causing movements of particular parts of the body.
Describe the components and functions of the descending pathways.
The descending pathways relay motor information from the cortex to the muscles of the body through the lateral and ventromedial groups. The lateral group consists of the corticospinal tract, the corticobulbar tract, and the rubrospinal tract and is involved in control of independent limb movements, particularly movements of the hands and fingers. The ventromedial group consists of the vestibulospinal tract, the tectospinal tract, the reticulospinal tract, and the ventral corticospinal tract, which control automatic trunk and limb movements involved in posture and locomotion.
The reticular formation also plays a role in locomotion. Stimulation of the _________________, located ventral to the inferior colliculus, causes a cat to make pacing movements
mesencephalic locomotor region
The ________________, located at the caudal end of the cerebellum, receives input from the vestibular system and projects axons to the vestibular nucleus.
flocculonodular lobe
The ______________, located on the midline, receives auditory and visual information from the tectum and cutaneous and kinesthetic information from the spinal cord. It sends its outputs to the _________________ (one of the set of deep cerebellar nuclei).
vermis;
fastigial nucleus
The intermediate zone of the cerebellar cortex projects to the _______________, which in turn project to the red nucleus. Thus, the intermediate zone influences the control of the rubrospinal system over movements of the arms and legs.
interposed nuclei
Both the frontal association cortex and the primary motor cortex send information about intended movements to the lateral zone of the cerebellum via the _______________. The lateral zone also receives information from the somatosensory system, which informs it about the current position and rate of movement of the limbs—information that is necessary for computing the details of a movement.
pontine nucleus
When the cerebellum receives information that the motor cortex has begun to initiate a movement, it computes the contribution that various muscles will have to make to perform that movement. The results of this computation are sent to the ________________ , another of the deep cerebellar nuclei.
dentate nucleus
Damage to the lateral zone causes weakness and _________________
decomposition of movement
____________ movements occur too fast to be modified by feedback.
ballistic movements
constitute an important component of the motor system.
basal ganglia
components of the basal ganglia: the ___________, the _____________, and the _____________. It also shows some nuclei associated with the basal ganglia: the ventral anterior nucleus and ventrolateral nucleus of the thalamus, the subthalamic nucleus, and the substantia nigra of the ventral midbrain.
caudate nucleus
putamen
globus pallidus
The subthalamic nucleus also receives excitatory input from the cerebral cortex, and it sends excitatory input to the GPi. The pathway shown in solid lines that includes the GPi is known as the ____________
direct pathway
Describe the functions of subcortical regions involved in control of motor behavior.
The reticular formation regulates muscle tone and is involved in some involuntary behaviors and movements of specific body parts. The cerebellum controls repetitive movements that require accurate aiming and timing, smoothly guides movements, stops movements at the correct time/position, and integrates sequences of movements. The basal ganglia receive input from the motor cortex regions and also direct their output to these regions and the ventromedial pathway. The basal ganglia also control inhibition of unwanted movements. Through these connections the basal ganglia influence movements under the control of the primary motor cortex and exert some direct control over the ventromedial system.
Describe the location, components, and functions of the mirror neuron system.
The mirror neuron system is located in the ventral premotor cortex. The neurons of the mirror neuron system are active when an individual engages in a behavior as well as when the individual observes (or hears) the behavior. Another circuit of mirror neurons is located in the posterior parietal lobe. The proposed function of the mirror neuron system is to help an individual understand the actions of others.
Summarize the contributions of the parietal cortex in reaching and grasping behavior.
The dorsal stream of the visual association cortex contributes spatial information to the parietal reaching region, which calculates the reaching movement that must be made and transmits this information to the motor association cortex. During the reaching movement the cortex located in the anterior intraparietal sulcus sends information to the motor association cortex that moves the hand and fingers to be ready to grasp an object
Damage to the frontal or parietal cortex on the left side of the brain can produce a category of movement deficits called ______________.
Apraxia
refers to problems with movements of the arms, hands, and fingers.
Limb apraxia
refers to difficulty in drawing or constructing objects.
Constructional apraxia
refers to problems with movements of the muscles used in speech.
Oral apraxia
refers to a particular type of writing deficit.
Apraxic agraphia
Describe how brain lesions can produce limb apraxia.
Most cases of limb apraxia are produced by lesions of the left frontal or parietal cortex. The left parietal cortex directly controls movement of the right limb by activating neurons in the left primary motor cortex and indirectly controls movement of the left limb by sending information to the right frontal association cortex.
Describe how brain lesions can produce constructional apraxia.
Constructional apraxia is caused by lesions of the right hemisphere, particularly the right parietal lobe. People with this disorder have trouble drawing pictures or assembling objects from elements such as toy building blocks.
