Term
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Definition
Provide afferent
information regarding position, movement
and balance of the body or any of its parts. |
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Term
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Definition
Refers to movement that is accompanied by a conscious awareness of
what we are doing, and why we are doing it. |
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Term
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Definition
Involuntary movement is unconscious and
automatic, such as a motor reflex.
Movement and posture depend upon both voluntary actions controlled by higher brain centers,
and involuntary reflexes coordinated at the level of the spinal cord. |
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Term
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Definition
Alpha motorneurons innervate the extrafusal muscle
fibers that generate force. The majority of muscle fibers
are extrafusal. The cell bodies of a-motorneurons are located in the
ventral horn of the spinal cord. These cell bodies
receive input from descending motor pathways and
spinal reflex circuits |
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Term
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Definition
A motor unit consists of a single motorneuron and the
muscle fibers it innervates. A motor unit may consist of
a few muscle fibers, or many thousands of muscle
fibers, depending upon the type of motor activity. |
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Term
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Definition
A motorneuron pool is the set of motorneurons innervating fibers within the same
muscle. An increase in the force of contraction of a muscle can be increased through
recruitment of more motor units. |
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Term
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Definition
Gamma motorneurons innervate intrafusal
muscle fibers, which are components of muscle
spindles. The intrafusal fibers are too small to
generate any significant force. The g-motorneurons are co-activated with the
corresponding a-motorneuron. The cell bodies of g-motorneurons are located in the ventral horn of the spinal cord. These cell
bodies receive input from descending motor
pathways and spinal reflex circuits. |
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Term
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Definition
Interneurons comprise 90% of spinal cord neurons. Spinal interneurons integrate inputs from higher centers, peripheral receptors, and other interneurons. They are crucial in determining which muscles are activated and when they are activated. |
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Term
Sensory Receptors - Length Monitoring Systems Muscle Spindles |
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Definition
Stretch receptors, collectively called muscle spindles, are embedded within the muscle and monitor both absolute muscle length and change in muscle length. There are two types of muscle spindles:
Nuclear chain fibers respond to muscle stretch
Nuclear bag fibers respond to the speed with which the stretch occurs. Muscle spindles wrap around intrafusal fibers, which are parallel to the extrafusal fibers. |
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Term
Sensory Receptors - Length Monitoring Systems Muscle Spindles (2) |
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Definition
An external force that passively stretches a muscle pulls on the intrafusal fibers activates the muscle spindle, and increases the rate of stretch receptor firing. In contrast, an active muscular contraction of the extrafusal muscle fibers removes tension from the muscle spindles. This slows the rate of stretch receptor firing. |
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Term
Sensory Receptors - Length Monitoring Systems Alpha-Gamma Coactivation |
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Definition
When the extrafusal fibers have been stimulated to contract by alpha MN activation, the gamma MN is simultaneously excited. When a muscle shortens, there is decreased stretch on the intrafusal fibers. This limits the ability of the stretch receptors to provide further information about muscle length. To prevent this loss of information, when a-motorneurons cause contraction of extrafusal muscle fibers, g-motorneurons cause a simultaneous contraction of intrafusal muscle fibers. The contraction of the intrafusal fibers maintains tension on the muscle stretch receptors, and thus afferent information about muscle length continues to reach the CNS.
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Term
Sensory Receptors - Tension Monitoring Systems |
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Definition
Muscle tension depends upon muscle length, the load on the muscle, and degree of muscle fatigue. [image][image] |
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Term
Sensory Receptors - Tension Monitoring Systems Golgi tendon organs |
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Definition
- Located in tendons near their junction with the muscle.
- Connected in series with extrafusal fibers, and when the muscle contracts, tension is placed upon the tendon.
- The Golgi tendon organ discharges in response to the tension generated by the contracting muscle.
- Activation of Golgi tendon organs causes widespread inhibition of the contracting muscle, and stimulation of antagonistic muscles
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Term
SPINAL REFLEXES Reflex and Reflex Arc |
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Definition
A reflex is a stereotypical motor response to a specific stimulus. A reflex arc consists of sensory receptors attached to an afferent (sensory) nerve, an efferent (motor) nerve that innervates a muscle, and may contain one or more spinal cord interneurons. |
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Term
SPINAL REFLEXES I. Stretch (Myotatic) Reflex |
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Definition
- “knee jerk” reflex
- Both the extrafusal and intrafusal muscle fibers and associated muscle spindles --> simultaneously stretched.
- muscle spindle stretch causes activation of the a-motorneuron that innervates the same stretched muscle.
- The stretched muscle contracts, and there is a simultaneous relaxation of antagonistic muscles. During this reflex there is alpha-gamma coactivation. The stretch reflex provides local homeostatic control of muscle length.
- Proper performance of the knee jerk reflex tells a physician that the afferent fibers, the synaptic input to the motor neurons, the motor neurons, the neuromuscular junctions, and the muscles themselves are all functioning normally.
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Term
SPINAL REFLEX II. Golgi Tendon (Inverse Myotatic) Reflex |
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Definition
- Disynaptic reflex
- Contraction of extrafusal muscle fibers increases tension in the attached Golgi tendon organ.
- The Golgi tendon afferents synapse on inhibitory interneurons in the spinal cord.
- The activation of these inhibitory interneurons inhibits the firing of the a-motoneuron that innervates the same contracted muscle.
- The contracted muscle relaxes, and there is simultaneous contraction of antagonist muscles
- This Golgi tendon reflex provides local homeostatic control of muscle tension.
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Term
SPINAL REFLEXES I. Stretch (Myotatic) Reflex |
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Definition
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Term
SPINAL REFLEX II. Golgi Tendon (Inverse Myotatic) Reflex |
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Definition
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Term
SPINAL REFLEXES Flexor Withdrawal Reflex |
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Definition
- Polysynaptic reflex
- Painful stimulation of the skin initiates the reflex.
- On the side ipsilateral to the stimulus the a-motorneuron to flexor muscle is stimulated, while the a-motorneuron to the extensor muscle is inhibited.
- This causes a withdrawal of the limb from the stimulus.
- On the side contralateral to the stimulus, the a-motoneuron to the flexor muscle is inhibited and the a-motoneuron to the extensor muscle is stimulated.
- This causes an extension of contralateral limb. This crossed-extensor reflex supports the body’s weight as the injured limb is withdrawn from the painful stimulus.
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Term
SPINAL REFLEXES - Flexor Withdrawal Reflex |
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Definition
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Term
| CONTROL OF VOLUNTARY MOVEMENT |
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Definition
The control of voluntary movement originates in the cerebral cortex and is transmitted via
descending motor pathways (corticospinal and corticobulbar) to the spinal cord where the
appropriate motor program is implemented. |
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex
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Definition
Cortical areas involved in control of voluntary movement are anatomically and functionally distinct, but are heavily interconnected.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Primary Motor Cortex |
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Definition
- Located in the precentral gyrus (Brodmann’s area 4)
- Receives input from the premotor cortex, supplementary motor cortex, thalamus and somatosensory cortex.
- Somatotopically organized
- Contains the motor homunculus
- Parts of body that perform tasks of high precision and fine control (i.e. hands and face) have greater representation within the primary
motor cortex.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Primary Motor Cortex (PtII) |
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Definition
- The primary motor cortex is responsible for execution of a movement by activating upper motor neurons (those neurons that give rise to axons that travel in the corticospinal or corticobulbar tract and terminate in spinal ventral horn). Upper motor neurons synapse with a-motoneurons (or interneurons) that innervate distal musculature.
- Individual corticospinal axons frequently diverge (collateralize) to influence the
motor neurons that innervate several muscles. - Divergence is small for distal muscles (this giving fine motor control), and greater for proximal muscles (thus giving lower degree of motor control).
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Primary Motor Cortex (PtIII) |
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Definition
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Premotor Cortex |
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Definition
- Located in the superior and middle frontal gyri (Brodmann’s area 6).
- It has reciprocal connections with the primary motor cortex and the supplementary motor cortex.
- Responsible for generating a plan of movement which is then transferred to the primary motor cortex for execution.
- Has a small contribution to the corticospinal tract.
- Somatotopically organized.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Supplementary Motor Area |
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Definition
- The supplementary motor area is located in the
medial and superiolateral portion of the frontal lobes (Brodmann’s area 6).
- It has connections with the primary motor cortex and the premotor cortex.
- The supplementary motor area is responsible for programming motor sequences. It contributes fibers to the corticospinal tract
- Somatotopically organized.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Parietal Motor Area |
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Definition
- Located in the parietal lobe (Brodmann’s areas 5 and 7).
- It receives somatosensory, auditory, visual and vestibular inputs from various cortical areas, and sends information to the primary motor cortex, premotor cortex, and supplementary motor cortex.
- The parietal motor area correlates information about the external world with information about the position of the limbs and the body.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cortex Prefrontal Cortex |
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Definition
- Located in frontal lobes (anterior to
Broadmann’s areas 6 and 8). - It receives information about sensory modalities
and motivational and emotional state of the individual. - The prefrontal cortex is responsible for plans, goals, and intentions.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cerebellum |
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Definition
- The term “cerebellum” means “little brain”.
- Although small in size when compared with the cerebral hemispheres, the cerebellum contains more than half of all the neurons in the human brain.
- Functions at an unconscious level.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cerebellum Spinocerebellum (or paleocerebellum) |
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Definition
- Receives input from the primary motor cortex describing the planned motor program
- Somatotopically organized proprioceptive information from the spinal cord indicating the position of body parts and muscle tone.
- The spinocerebellum then compares movements being executed with the intended movement.
- Discrepancy will result in the cerebellum sending a midcourse correction to the primary motor cortex during the execution of a movement.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cerebellum Cerebrocerebellum (or neocerebellum) |
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Definition
- The cerebrocerebellum is the dominant component of the human cerebellum.
- Receives input from the cerebral cortex.
- The lateral hemispheres of the cerebrocerebellum project indirectly to the premotor cortex via thalamic nuclei, which allow for cerebellar involvement in the programming or planning of movements.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Cerebellum Vestibulocerebellum (or archicerebellum) |
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Definition
Receives input from the vestibular system and controls balance and eye movements. |
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Term
CONTROL OF VOLUNTARY MOVEMENT - Basal Ganglia |
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Definition
- Contains a number of interconnected nuclei within the cerebrum.
- It consists of the striatum (composed of caudate nucleus and putamen), the globus pallidus, the subthalamic nuclei and the substantia nigra.
- Receives projections from the all areas of the cerebral cortex, especially premotor and supplemental motor cortices.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Basal Ganglia Two Output Pathways |
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Definition
- Indirect pathway that is inhibitory to the motor
cortex - Direct pathway that is excitatory to the motor cortex.
- There are no direct connections with the spinal cord.
- The primary function of the basal ganglia is in the planning of voluntary movement,
and helps control the speed and size of any movement.
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Term
CONTROL OF VOLUNTARY MOVEMENT - Motor Program [image] |
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Definition
- This includes the selection and coordination of the muscles involved in the sequence of all the movements of the entire action.
- The plans, goals and intents of voluntary movement are organized in associative areas of the cerebral cortex (i.e., prefrontal cortex)
- The parietal motor area provides sensory information that is essential to guide the movement to the goal.
- It conveys information about the spatial coordinates to the primary motor cortex, premotor cortex and the supplementary motor area.
- The premotor cortex and the supplementary motor area plan and program the movement sequences.
- This information is sent to the primary motor cortex.
- The primary motor cortex then activates upper motoneurons in the predetermined programmed pattern.
- The lower motoneurons (i.e. a-motorneurons) in the brain stem and spinal cord are then activated.
- The lower motoneurons produce contraction of the appropriate muscles.
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Term
| CONTROL OF VOLUNTARY MOVEMENT - Motor Program |
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Definition
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Term
LESIONS OF THE MOTOR SYSTEM - Cerebral Cortex Primary motor Cortex |
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Definition
Lesions in the primary motor cortex cause weakness
(paresis) of the contralateral musculature with decreased resistance to passive
manipulation (hypotonia). There are diminished muscle reflexes. |
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Term
LESIONS OF THE MOTOR SYSTEM - Cerebral Cortex Premotor Cortex |
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Definition
Lesions of the premotor cortex results in the impairment of
ability to develop an appropriate strategy for complex movements, but without any
muscular weakness. |
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Term
LESIONS OF THE MOTOR SYSTEM -Cerebellum Dysmetria and Ataxia |
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Definition
Abnormal movements (ataxia) that overshoot or
undershoot the target (dysmetria). |
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Term
LESIONS OF THE MOTOR SYSTEM -Cerebellum Decomposition of Movement |
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Definition
Components of a movement are performed in a
jerky and irregular rather than a smooth sequence. |
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Term
LESIONS OF THE MOTOR SYSTEM -Cerebellum Intention Tremor |
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Definition
A type of tremor that is present when a voluntary movement is
attempted. It intensifies as the limb nears its target. |
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Term
LESIONS OF THE MOTOR SYSTEM -Cerebellum Dysdiadochokinesia |
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Definition
| An inability to perform rapid alternating movements. |
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Term
LESIONS OF THE MOTOR SYSTEM -Basal Ganglia Globus Pallidus |
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Definition
| Writhing movements of the hand and arm or face (athetosis). |
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Term
LESIONS OF THE MOTOR SYSTEM -Basal Ganglia Subthalamic Nuclei |
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Definition
| Flailing movements of an extremity (hemiballismus). |
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Term
LESIONS OF THE MOTOR SYSTEM -Basal Ganglia Putamen |
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Definition
| Flicking movements of the hands or face (chorea). |
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Term
LESIONS OF THE MOTOR SYSTEM -Basal Ganglia Substantia Nigra |
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Definition
Characterized by rigidity in muscle groups, tremor present at
rest, and difficulty in initiating movement. There is a degeneration of dopaminesecreting
nerve fibers, as seen in Parkinson’s Disease. |
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Term
LESIONS OF THE MOTOR SYSTEM -Upper Motorneuron |
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Definition
Causes paralysis and hypotonia on the contralateral side of body. With time there is
development of hypertonia, a sustained series of rhythmic jerks (clonus) and
hyperreflexia (spasticity). |
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Term
LESIONS OF THE MOTOR SYSTEM -Lower Motorneuron |
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Definition
Limited to muscles that the a-motorneurons innervate. There is paralysis, muscle
hypotonia and atrophy, and no voluntary or reflex responses. |
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