Term
| What neural systems and subsystems are required to perform most motor behaviors? |
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Definition
1) Planning (frontal and parietal cortex)
2) Execution (Motor cortex, Cerebellum, Basal Ganglia, Thalamus, Brainstem, Pons, Spinal chord)
3) Feedback (Proprioception, Vestibular, Visual and somatosensory)
4) Learning (Cortex, Basal ganglia, Cerebellum, ect.) |
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Term
| Which motor structures have Direct access to LMNs? |
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Definition
1) M1 (area 4) for a- and y-motonuerons for agonist/antagonist muscle group control in distal extremities (Paresis following lesion)
2) Broca's area (44/45) for motor speech
3) Spinal Chord (sensory-motor reflex) |
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Term
| What are the 5 sub-areas of the Motor cortex and their functions/deficits from lesion? |
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Definition
Supplementary and Premotor Cortices (area 6), Primary Motor (area 4), Frontal eye fields (area 8) and Broca's (area 44/45)
1) Supplementary (area 6) for strategy or program for execution sequences (Apraxia)
2) Premotor (area 6) for sensory guidance of limb movements and preparatory role for tactile and visually-elicited movements (Apraxia)
3) M1 (area 4) activates alpha and gamma motoneurons for agonist/antagonist muscle groups of distal extremities (Paresis)
4) Frontal eye fields (area 8) for voluntary saccades (gaze deficits)
5) Brocas (44/45) speech production (expressive aphasia) |
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Term
| What are the 3 sub-areas of the Basal Ganglia and their functions/deficits from lesion? |
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Definition
1) Caudate/Putamen/Globus Pallidus modulate control of limb, body and eye muscles (Huntington's chorea)
2) Substantia nigra is Dopaminergic input to caudate and putamen (Parkinson's)
3) Subthalamic nucleus (hemiballismus) |
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Term
| What is the function/associated deficits of the Cerebellum? |
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Definition
| Compares intention to performance to coordinate limg, eye and posture (Ataxia) |
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Term
| What is the primary function of the Pons? |
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Definition
| Relay and integrate information to cerebellum from spinal cord, brainstem and cortex. |
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Term
| What are the 2 laterally running motor tracts in the SC? |
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Definition
Both are for ipsilateral motor control of extremeties
1) Lateral Corticospinal for hand and fingers
2) Rubrospinal (red nucleus) for arm and hand |
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Term
| What are the 4 medially running motor tracts in the SC? |
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Definition
1) Vestibulospinal (Vestibular nuclei for head and neck posture and balance via anti-gravity muscles).
2) Tectospinal (Superior colliculus for postural adjustment of head/neck and head and eye orient toward target).
3) Reticulospinal (from pontine and medullary RF for muscle tone, posture and gait-related movement)
4) Anterior corticospinal (from motor rotex to proximal and axial muscles of upper body). |
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Term
| What is the balance of sensory:motor neurons innervating muscle? |
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Definition
80% are sensory and 20% are motor.
Sensory feedback is a BIG deal |
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Term
| What are the different types of sensory neurons that innervate muscles? |
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Definition
1) Groups I and II are rapid and they innervate Muscle Spindles (muscle length) and Golgi tendons
2) Group III (small myelinated) and group IV (unmyelinated) terminate as free nerve endings and subserve chemoreception and nociception (like somatosensory counterparts). |
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Term
| Explain the structure and innervation of Muscle Spindles |
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Definition
Transducers of muscle length (motoneurons change length and sensory fibers sense the change)
1) Groups of muscle fibers encased in fluid-filled capsule with intrafusal and alligned in parallel to extrafusal (innervated by a-Motoneurons) fibers.
- Found in areas requiring fine motor control
2) Innervation
- Group 1a are most sensitive to "Changes in muscle length" and they rap around equatorial region (annulo-spiral endings)
- Group II fibers arborize and innervate smaller intrafusal fibers, sensing muscle length, but not "change in length"
- y-motoneurons (Fusimotor fibers) innervate intrafusil fibers and affect Primary and Secondary spindle afferents (they have smaller axons and are slower than a-motoneurons) |
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Term
| What is the functional significance of the fact that Muscle spindles are arranged in parallel with extrafusal muscle fibers? |
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Definition
Sensory afferents need to be able to respond to small changes in muscle length throughout full range of muscle movement.
1) When whole muscle is stretched, spindles are also stretched, increasing the firing rate of spindle afferents
2) When only extrafusal fibers contract (a-Motoneurons), spindles slack and unload, decreasing the firing rate of spindle afferents. |
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Term
| Explain the structure and innervation of Golgi Tendon Organs (GTO's) |
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Definition
1) "In series" arrangement at ENDS of extrafusal muscle fibers (between muscle fibers and bone or tendon into which they insert) make GTOs sensitive to "active muscle tension".
2) When a-motonuerons cause Extrafusal fibers to contract and stretch, GTO's INCREASE their firing rate (in series), while Spindles (in parallel) are unloaded and DECREASE their firing.
- Sensory innervation of GTOs is Group Ib fibers (no known efferent innervation) |
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Term
| What is the difference between Passive and Active muscle contractions in terms of firing rates of Afferents in Muscle Spindles and Golgi Tendon Organs (GTOs)? |
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Definition
1) Passive muscle stretch causes y-motoneuron activation and intrafusal fiber contraction, leading to increased Group 1a afferent firing.
GTO afferents do not increase
2) Active muscle contraction leads to extrafusal fiber contraction, slackening of intrafusal fibers (parallel organization and less spindle afferent firing) and increased GTO afferent firing (in series with extrafusal fibers) |
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Term
| Explain the course of Primary Muscle Spindle Afferents (Group 1a fibers) from muscle spindle to spinal chord and back? |
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Definition
1) Afferents leave muscle spindle, enter dorsal roots of SC and project rostrally and caudally in Dorsal column.
2) Dorsal column branches enter Ventral horn (excite same muscles, excite synergistic fibers more weakly, inhibit antagonists)
- provide excitatory monosynpatic input to every motoneuron projecting back to the same muscle (Homonymous connections)
- provide weaker monosynaptic excitation to synergistic motoneurons (don't over-activate the same function)
- Provide disynaptic inhibition to motoneurons innervating antagonistic muslces |
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Term
| How do DTRs (i.e. "stretch reflex") resist changes in muscle length imposed from the environment, increasing muscle stiffness (tone). |
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Definition
1) Passive tension stretches muscle spindle, leading to increased firing of 1a afferents
2) Afferents go to dorsal horn, branch rostrally and caudally in dorsal column and enter ventral horn
3) In ventral horn, these afferents they excite motoneurons of fibers from the same muscle and those fibers in synergism, and inhibit motonuerons of antagonistic fibers. |
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Term
| How is the "stretch reflex" effective during voluntary movements? |
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Definition
Co-activation of y-motoneurons supplying intrafusal muscle fibers by higher centers, and a-motoneurons supplying extrafusal muscle fibers innervating bulk of muscle.
Otherwise, a-motoneuron activation would cause slackening of spindles and absence of stretch reflex. |
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Term
| How do central lesions affect Muscle Tone? |
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Definition
1) Following spinal injury, there is decrease in activity of y-motonueorns innervating intrafusal fibers below the lesion (hypotonia or flaccid paralysis)
2) Over next weeks, y-motoneuron activity returns and becomes over-active, leading to hyper-reflexia and spasticity (spastic paralysis can develop)... CLONUS |
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Term
| Explain the course of Secondary Muscle Spindle Afferents (Group II fibers) from muscle spindle to spinal chord and back? |
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Definition
| Project monosynaptically to homonymous motoneurons (less excitation than 1a fibers) contributing to the same Mytatic Stretch Reflex as 1a fibers. |
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Term
| Explain the course of central projections of GTO afferents (Group 1b fibers)? |
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Definition
Act via (+) and (-) interneurons!
1) Polysynaptic inhibition to homonymous and synergistic motoneurons by monosynaptically exciting inhibitory interneruons projecting to these cells.
2) Polysynaptic Excitation to antagonistic motoneurons via excitatory interneurons. |
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Term
| How is the Inverse Myotatic Reflex achieved? |
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Definition
1) Passive Muscle Stretch
- increase in passive tension excites GTO afferents, which inhibit homonymous and synergistic motoneurons, and excite antagonistic motoneurons (relaxation of muscle, allowing further stretch).
2) Active Muscle Stretch
- When muscle is contracting actively, it is doing so in spite of continual inhibition from Ib afferents. However, as it fatigues, tension decreases, and so does this inhibition (taking off the break allows you to push further). |
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Term
| What is the role of Spinal Reflexes in Voluntary Movement? |
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Definition
Reflex circuits work in concert to regulate and coordinate movements of individual muscles.
1) Stretch reflex counteracts changes in joint position by making muscles "stiffer" (i.e. more resistant to changes in length)
2) GTO reflex maintains tension as muscle fatigues. |
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