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What is the function of the motor system?
Which part of the motor system is responsible for initiating and controlling skilled movements?
What is the function of the corticospinal tract?
What type of movement is dominated by flexor muscles?
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What is the function of the rubrospinal tract?
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What is the function of the reticulospinal tract?
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What is the function of the gamma loop?
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What is the function of the crossed-extensor reflex?
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What is the function of central pattern generators?
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What is the function of the stretch reflex?
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What happens in the opposite limb around 0.2 to 0.5 seconds after a withdrawal reflex is triggered in one limb?
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What is the main function of the positive supportive reaction?
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What type of neurons are involved in central pattern generators (CPGs)?
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What is the role of the cerebellum in posture and movement?
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What type of sensory input is involved in the reflex circuits of spinal interneurons?
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What is the main role of the spinal cord reflexes in walking?
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What is the location of control centers that initiate and terminate rhythmical activity associated with central pattern generators?
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What type of reflex helps protect the body against injury?
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Which type of receptors provide proprioceptive information essential for movement?
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During the swing phase of walking, which type of muscles are mediating the movement?
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What type of reflex contracts the muscle being stretched?
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Which type of reflex relaxes the muscle being tensioned?
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What is essential to know in order to move a limb toward a particular location?
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What is generated by spinal cord reflexes during walking?
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Which descending motor pathway is involved in the regulation of antigravity muscle tone?
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Which of the following tracts is involved in controlling the speed of central pattern generators in the spinal cord?
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Which of the following statements is true about the spinal cord?
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Which tract is involved in the reflex orientation of the head towards environmental stimuli?
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What type of movement is dominated by extensor muscles?
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Where are the UMN tracts that facilitate flexor muscles and inhibit extensors located?
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What is the primary function of the cerebellum in motor control?
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Which of the following structures is involved in the planning and sequencing of movements?
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What is the primary function of the motor cortex?
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Which of the following spinal cord reflexes is involved in the withdrawal of a limb in response to a stimulus?
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What is the primary function of the gamma loop?
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Which of the following descending motor pathways is involved in the control of postural muscles?
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What type of motor control is primarily influenced by the pyramidal tract?
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Where are the neuronal bodies located in the corticospinal tracts?
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What is the primary function of the brainstem UMN pathways?
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Which type of sensory information is used to detect discrepancies between intended and actual movement?
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What type of movement is primarily influenced by the extrapyramidal tracts?
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What is the primary function of the CNS in controlling body movement?
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What type of neurons are involved in the direct projection from the cerebral cortex to the spinal cord?
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What percentage of fibers decussate in humans?
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What is the primary function of the muscle spindles and Golgi tendon organs?
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What is the effect of lesions to the motor cortex on one side of the body?
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What is the primary function of the LMNs in controlling body movement?
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How do the axons in the corticospinal tracts influence skilled voluntary movement?
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Which of the following tracts originates in the brainstem and influences spinal LMNs?
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What is the primary role of the medial pathways?
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Which tract is involved in the subconscious control of postural musculature?
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Which of the following is a characteristic of the rubrospinal tract?
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What is the consequence of damage to the pathways involved in subconscious control of postural musculature?
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The UMN tracts ________, __________, and ___________ muscle activity of he limbs and body
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The two major descending motor system pathways from the brain to the spinal cord are __________ and ________
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Study Notes
Motor System Functions
- The motor system has three main functions: supporting the body against gravity and maintaining posture, controlling voluntary movement and locomotion, and controlling visceral motor function.
- All movement results from the excitation or relaxation of muscles.
Hierarchical Organization of Motor System
- The motor system has a hierarchical organization, with higher centers responsible for planning and direction, and lower centers responsible for executing movement.
- Higher centers include the motor cortex, basal nuclei, thalamus, cerebellum, and brain stem, which are involved in complex and skilled movement patterns.
- Lower centers include the spinal cord and peripheral nerves, which are responsible for simple movement patterns.
Pathways of Movement
- The motor system has two main pathways: the upper motor neuron (UMN) pathway and the lower motor neuron (LMN) pathway.
- The UMN pathway is responsible for initiating, modifying, and terminating muscle activity, and includes the corticospinal tract (pyramidal tract) and the brainstem UMN pathway (extrapyramidal tract).
- The corticospinal tract is a direct connection between the motor cortex and the spinal cord, and is important for skilled and voluntary motor control, especially in primates and humans.
- The brainstem UMN pathway is important for gait and movement in quadrupeds.
Brainstem UMN Pathway
- The brainstem UMN pathway includes four tracts: the medial pathway, the lateral pathway, the tectospinal tract, and the rubrospinal tract.
- The medial pathway is involved in maintaining posture and regulating antigravity muscle tone, and includes the vestibulospinal tract and the reticulospinal tract.
- The lateral pathway is involved in controlling distal limb movement, and includes the rubrospinal tract, which controls flexor muscles of the distal limb.
Movement
- There are two types of movement: dominated by flexor muscles, which are involved in learned, voluntary, conscious, and skilled movement, and dominated by extensor muscles, which are involved in postural, antigravity, and subconscious movement.
- Flexor-dominated movement is controlled by the lateral system, which includes the corticospinal, rubrospinal, and medullary reticulospinal tracts.
- Extensor-dominated movement is controlled by the ventral system, which includes the pontine reticulospinal and vestibulospinal tracts.
Reflexes
- Stretch reflexes counteract gravity and help maintain equilibrium and posture.
- The gamma loop activates the alpha motor neuron, which innervates the extensor muscle.
- The crossed-extensor reflex helps avoid loss of balance when one limb is flexed.
- The positive supportive reaction helps keep an animal from falling to one side.
Walking
- There are two phases of walking: the swing phase, which is mediated by flexors, and the stance phase, which is mediated by extensors.
- Central pattern generators (CPGs) are reflex circuits of spinal interneurons that control LMNs in a repetitive, oscillating manner.
Cerebellum
- The cerebellum coordinates overall posture and creates movement that occurs at the correct rate, range, and force.
- The cerebellum does not initiate movement, but coordinates the initiated movement, actual movement, and termination of movement.
Reflexes
- A withdrawal reflex in one limb can induce an extension reflex in the opposite limb, known as the crossed-extensor reflex.
- The crossed-extensor reflex helps maintain balance and posture when a limb is flexed due to injury or stumble.
- The positive supportive reaction causes the limb to extend against pressure applied to the footpad, helping the animal maintain balance.
Central Pattern Generators (CPGs)
- CPGs are neural circuits that produce oscillatory outputs, controlling rhythmical motor activity such as locomotion, scratching, chewing, and breathing.
- CPGs associated with locomotion and scratching are located in the spinal cord intumescences.
- Control centers for initiating and terminating rhythmical activity are located in the brainstem.
Sensory Input and Motor Control
- Sensory input comes from muscle spindles, Golgi tendon organs, joints, and tactile receptors.
- Integration of sensory input in the spinal cord causes inhibition or excitation of lower motor neurons (LMNs), as appropriate.
- The cerebellum coordinates agonistic/antagonistic muscle activity to permit posture and movement.
Posture and Movement Control
- The vestibulospinal tract receives sensory information from the vestibular system and regulates antigravity muscle tone.
- The reticulospinal tract helps regulate the steady-state contraction level of antigravity muscles and assists in voluntary movement execution.
- The tectospinal tract is involved in reflex orientation of the head toward environmental stimuli.
Motor Tracts
- The rubrospinal tract is a lateral brainstem upper motor neuron (UMN) pathway that controls distal limb musculature associated with movement.
- The rubrospinal tract exerts unilateral control over a limited number of flexor muscles in the distal limb.
Movement Classification
- Movement can be divided into two forms: dominated by flexor muscles (largely learned, voluntary, and skilled) and dominated by extensor muscles (postural, antigravity, and generally subconscious).
- Different neurons and tracts in the nervous system control these two types of movements.
Neural Control of Movement
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The spinal cord is the most caudal and simplest level of movement control, containing UMN tracts, lower motor neurons, interneurons, and complex neural circuits for motor control.
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The spinal cord executes low-level commands that generate proper forces on individual muscle groups to enable adaptive movements.### Central Control of Movement
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Voluntary movement is initiated consciously but coordinated at the subcortical level of the brain.
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Flexor muscles are involved in learned, voluntary, conscious, and skilled movements.
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The primary motor cortex directs voluntary movement.
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The cerebellum coordinates agonistic and antagonistic muscle activity to permit posture and create movement.
Posture and Locomotion
- Posture is maintained by a tonic excitatory bias to motor circuits that excite extensor muscles.
- The gamma loop, which includes the reticulospinal tract, activates gamma motor neurons, which then activate alpha motor neurons.
- Walking is a method of locomotion using limbs alternately to provide both support and propulsion.
- Each cycle of locomotion consists of two phases: the swing phase and the stance phase.
- The crossed-extensor reflex is a reflex that helps maintain balance and body posture.
Importance of Proprioception
- Muscle spindles and Golgi tendon organs provide proprioceptive information.
- Proprioception is essential for understanding basic motor control.
- The cerebellum receives proprioceptive inputs from all body and limb muscles.
- Proprioception helps maintain posture and movement.
Reflexes
- The stretch reflex is a reflex that contracts the muscle being stretched.
- The inverse stretch reflex is a reflex that relaxes the muscle being tensed.
- The withdrawal reflex is a reflex that causes flexion of the stimulated limb.
- The crossed-extensor reflex is a reflex that helps maintain balance and body posture.
Ataxia
- Ataxia is the inability to coordinate the position of the head, trunk, and limbs in space.
- There are different types of ataxia, including vestibular, cerebellar, and proprioceptive/sensory ataxia.
- Vestibular ataxia is characterized by head tilt, leaning, falling, rolling, circling, strabismus, and nystagmus.
- Cerebellar ataxia is characterized by dysmetria, intentional tremors, and wide pelvic stance and gait.
- Proprioceptive/sensory ataxia is related to spinal cord diseases and is characterized by truncal sway and abnormal limb stance and gait.
Tracts
- The pyramidal tract influences voluntary skilled movement but not gait.
- The corticospinal tract is involved in the initiation, modification, and termination of muscle activity.
- The extrapyramidal tract is involved in the maintenance of posture and gait.
- The rubrospinal tract, reticulospinal tract, vestibulospinal tract, and tectospinal tract are all part of the extrapyramidal tract.
Brainstem and Spinal Cord
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The brainstem controls the initiation and termination of rhythmic activities such as locomotion, scratching, and chewing.
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The spinal cord contains central pattern generators that control the rhythmic pattern of walking.
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The spinal cord also contains alpha-lower motor neurons, interneurons, and complex neural circuits for motor control.### Control of Body Movement
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To control body movement, the CNS must assess the effect of gravity on the body's muscles, determine the initial position of body parts to be moved, and detect any discrepancies between intended and actual movement.
Proprioceptive Information
- Proprioceptive information is provided by muscle spindles and Golgi tendon organs.
Lower Motor Neurons (LMNs)
- LMNs are stimulated or inhibited by both reflex connections and input from the Upper Motor Neuron (UMN) system.
Upper Motor Neurons (UMNs)
- UMN tracts initiate, modify, and terminate muscle activity of the limbs and body.
- There are two major descending motor system pathways from the brain to the spinal cord: corticospinal tracts (pyramidal tracts) and brainstem UMN pathways (extrapyramidal tracts).
Corticospinal Tracts (Pyramidal Tracts)
- These tracts have a direct connection between the motor cortex and spinal cord.
- Neuronal bodies are located in the motor area of the cerebral cortex.
- They are very important for voluntary motor control in primates and humans.
Brainstem UMN Pathways (Extrapyramidal Tracts)
- Neuronal bodies are located in brainstem nuclei.
- These tracts are most important for gait and movement in quadrupeds.
Motor Tracts in the Spinal Cord
- Pyramidal tracts influence voluntary skilled movement but have minimal influence on gait.
- Extrapiramidal tracts are most important for gait and movement in quadrupeds.
Function of Pyramidal Tracts
- Pyramidal tracts are responsible for most skilled voluntary movements of mammals, especially those involving the extremities.
- They also participate in less elaborated voluntary movements of the distal muscles.
- The ability to control skilled movements derives from the synaptic termination pattern of several axons.
- Axons bypass brainstem motor pathways and premotor neurons of the spinal cord, contacting alpha motor neurons directly.
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Description
This quiz covers the three primary functions of the motor system, including support, voluntary movement, and visceral motor function. It also explores the hierarchical organization of the motor system, including the primary motor cortex and higher centers.
