Cerebellum And Motor Function Flashcards
What area is the pre motor cortex? What does it do?
- area 6
- plans movements based on sensory and visual cues
What area is the supplementary motor area? What does it do?
- area 6
- retrieves and coordinates memorized motor sequences
What are the four functions of the motor cortex system?
- Provides most of activating signals to spinal cord
- Issues sequential and parallel commands that initiate various cord patterns
- Cortical patterns are usually complex and can be learned
- Cord patterns are mainly determined by heredity and are hard wired
What are the general functions of the cerebellum?
- timing of motor activities and in rapid smooth progression from one muscle movement to the next
- not essential for locomotion
- helps sequence motor activities
- monitors and makes corrective adjustments to motor activities while they are being executed
- removal of cerebellum causes body movements to become abnormal
What are some specific functions of the cerebellum as outlined in lecture?
- compares actual movements with intended movements
- aids cortex in planning next sequential movement
- learns by its mistakes
- functions with spinal cord to enhance the stretch reflex
- functions with brainstem to make postural movements
- functions with cerebral cortex to provide accessory motor functions
- turns on antagonist at appropriate time
- helps program muscle contraction in advance
- functions mainly when muscle movements have to be rapid
What divides the two hemispheres of the cerebellum?
- vermis
- divided into an intermediate zone and lateral zone
What are the three lobes of the cerebellum? Anterior to posterior. Which is associated with the vestibular system?
- anterior lobe
- posterior lobe
- flocculonodular lobe (associated with vestibular system)
What is the vermis responsible for?
- divides hemispheres
- location for control functions for muscle movements of axial body, neck, shoulders, and hips
What is the intermediate zone responsible for?
-concerned with controlling muscle contractions in the distal portions of upper and lower limbs especially hands, feet, fingers, and toes
What is the lateral zone responsible for?
-associated with cerebral cortex with planning of sequential motor movements
How is the cortex of the cerebellum organized?
- gray matter
- consists of transversely arranged narrow gyro called folia
What are the intracerebellar nuclei?
- make up inner layer of gray matter and include the following pairs of nuclei:
1. Dentate
2. Emboliform
3. Globose
4. Fastigial
What are the dentate, emboliform, and glubose nuclei responsible for?
- related to limb musculature and fine manipulative movement
- fiber project to the red nucleus
- lesions in these nuclei result in extremity ataxia
What is the fastigial nuclei responsible for?
- related to postural activity and limb movements via reticulospinal and vestiibulospinal tracts
- fibers project to reticular formation and vestibular nuclei
- lesion in the nucleus results into trunk ataxia
What are the 3 layers of the cerebellar cortex? What are some features of each?
-granular layer: innermost layer
+made up of granule cells, Golgi type II cells, glomeruli
+axons of most fibers synapse with granular cells and Golgi type II cells in the glomeruli
-Purkinje cell layer: middle layer
+contains Purkinje cells
-molecular layer: outermost layer
+contains stellate cells, basket cells, Purkinje dendrites, Golgi type II cells, and axons of granule cells (parallel fibers)
What are granular cells?
-axons form parallel fibers in cortex (+)
What are Golgi cells?
-project from parallel fibers to granular cell bodies (-)
What are basket cells?
-project from parallel fibers to Purkinje axon hillock (-)
What are stellate cells?
-project from parallel fibers to Purkinje dendrites (-)
What two cells provide lateral inhibition on adjacent Purkine cells to provide dampening?
-basket cells and stellate cells
What are some characteristics of Purkinje cells in the cerebellar cortex?
- extensive dendritic branching
- receive input from parallel fibers
- project to intracerebellar nuclei (-)
- only output from cortex
- output is always inhibitory
What are the two different afferent neurons in the cerebellum?
-climbing fibers and mossy fibers
What are some characteristics of climbing fibers?
- originate from medullary olives
- make up multiple synapses with Purkinje cells
- provide high frequency bursts (complex spikes)
- condition the Purkinje cells
- play a role in motor learning
What are some characteristics of mossy fibers?
- originate from multiple centers in brainstem and spinal cord, including vestibulocerebellar, spinocerebellar, and pontocerebellar tracts
- make multiple synapses on Purkinje cells and result in simple spikes
- synapse on granule cells in glomeruli
What is the efferent neuron of the cerebellum?
-Purkinje cell axons
+only output from cerebellar cortex
+output is always inhibitory
+GABA
+projects to deep cerebellar nuclei and vestibular nucleus
+modulates output of cerebellum and provides synergy (regulates range, rate, and direction of movement)
Describe a functional unit of the cerebellar cortex.
- 30 million functional units
- each unit is centered on a Purkinje cell and a corresponding deep nuclear cells
- output from a functional unit is from a deep nuclear cell
- afferent inputs to the cerebellum are mainly from the climbing and mossy fibers
- all climbing fibers originate from the inferior olives
- mossy fibers enter cerebellum from a variety of sources (send excitatory collaterals to deep nuclear cells and then synapse in granular layer with thousands of granule cells)
- granule cells send axons to outer cerebellar surface, axons branch in two directions parallel to folia
- dendrites of Purkinje cells project to these parallel fibers
- direct stimulation by climbing and mossy fibers excites deep nuclear cells. Purkinje cell signals inhibit deep nuclear cells
- basket cells and stellate cells also function as inhibitory cells
What are the three systems used to coordinate motor control?
- vestibulocerebellum
- spinocerebellum
- cerebrocerebellum
Describe the vestibulocerebellar system.
- consists of flocculonodular lobes and vermis
- functions in control of balance and eye movements
- evolved at about the same time as vestibular system
- receives fibers from vestibular system and oculomotor system (pontocerebellar)
- sends out primarily to vestibular system
- loss of flocculonodular lobes -> extreme disturbance of equilibrium and postural movements
How is the vestibulocerebellum related to pendular movements?
- most body movements are pendullar (swing back and forth) -> have tendency to overshoot
- appropriate learned subconscious signals from cerebellum can stop movement precisely at intended point -> damping system
How are movements effected when the cerebellum is removed?
- movements are slow to develop
- force developed is weak
- movements are slow to turn off
Describe the spinocerebellum.
- consist mostly of vermis and intermediate zone-
- functions in synergy: control of rate, range, force, and direction of movement
Where does the spinocerebellar system receive information from? Where dies it send corrections to after comparing two sources of information?
Receives info from:
+motor cortex and red nucleus telling cerebellum intended sequential plan of movement for the next few fractions of a second
+feedback information from periphery telling cerebellum wheat actual movements result
-Sends corrections to:
+motor cortex via thalamus and magnocellular portion of red nucleus
Describe the cerebrocerebellar system.
- consists of lateral parts of hemispheres
- mostly associated with the premotor and the primary and association somatosensory areas of the cerebral cortex
- receives corticopontocerebellar projections
- involved in coordination of skilled movement and speech
- plans as much as tenths of a second in advance of actual movements (motor imagery)
What area is the primary motor cortex? What does it do?
- area 4
- signals motor neurons to contract skeletal muscle fibers
- signals via corticospinal (pyramidal) tract
- execution of commands preceded by extensive processing by cerebellum and basal nuclei
The corticopentocerebellar afferent tract. Where does it go?
-motor and pre motor cortices/somatosensory cortex -> pontine nuclei -> lateral divisions of cerebellum
Where does the vestibulocerebellar afferent tract terminate?
-flocculonodular lobes
Where does the reticulocerebellar afferent tract terminate?
-primarily in the vermis
Describe the spinocerebellar tract.
- dorsal and ventral
- transmit signals at 120m/sec
What structures form the mossy fibers that terminate on granule cells in the cerebellar cortex?
- corticopentocerebellar tract
- vestibulocerebellar tract
- reticulocerebellar tract
- spinocerebellar tract
Where does the dorsal spinocerebellar afferent tract go?
-muscle spindles ->ipsilaterally in vermis and intermediate zones
What are some of the functions of the dorsal spinocerebellar tract?
- muscle contractions
- degree of tension on the muscle spindles
- positions and rates of movement of parts of the body
- forces acting on surfaces of the body
Where does the ventral spinocerebellar tract terminate?
-ipsilaterally and contralaterally
What is the ventral spinocerebellar tract excited by?
- cortex via corticospinal and rubrospinal tracts
- internal motor pattern generators within spinal cord
What does the ventral spinocerebellar tract tell the cerebellum?
- which motor signals have arrived at the anterior horns
- feedback -> efferent copy of the anterior horn motor drive
How do the olivocerebellar tracts travel?
-neurons project from the inferior olivary nuclei in medulla to Purkinje cell dendrites and to intracerebellar nuclei
What do the olivocerebellar tract form? How do these work?
- axons form climbing fibers
- causes a single prolonged AP on each Purkinje cell with high it connects (one climbing fiber per 5-10 Purkinje cells)
- each signal starts out as a strong spike and is followed by a series of weak secondary spikes
- send + signals to granule cells
How does the cerebelloreticular efferent tract travel?
-fastigial nuclei -> reticular nuclei in pons and medulla
How does the cerebellothalamocortical efferent tract travel?
-dentate, emboliform, glubose nuclei -> thalamus -> motor cortex
How does the cerebellorubral efferent tract travel?
-dentate, emboliform, glubose nuclei -> red nucleus
How does the cerebellovestibular efferent tract travel?
Cerebellum -> vestibular nuclei
What are the functions of the basal nuclei?
- help plan and control complex patterns of muscle movement
- controlling relative intensities of the separate movements
- directions of movements
- sequencing of multiple successive and parallel movements
- plan and execute motor commands in concert with cerebral cortex
- help plan multiple parallel sequential patterns
- control complex patterns of motor activity
What does the motor cortex do?
-execute subconscious but learned patterns
What does the basal nuclei work with?
- receive most of their input from the cerebral cortex and return most of their output to the cerebral cortex
- principle role is to work with corticospinal system to modulate thalamic output to the motor cortex to plan a don executive smooth movements
What are the paired nuclei of the basal nuclei?
- striatum (caudate nucleus, putamen)
- globus pallidus
- substantia nigra
- subthalamic nucleus
What are the two major basal nuclei circuits? Which one is direct and which is indirect?
- putamen circuit (direct)
- caudate nucleus circuit (indirect)
What is the functions of the putamen circuit?
- subconscious execution of learned patterns of movement
- overall excitatory and tends to increase motor activity
Outline the putamen circuit and what neurotransmitters are secreted by each?
Cerebral cortex (premotor, supplementary motor, and somatosensory) - ACh (+) -> putamen/substantia nigra compacta - GABA (-) and dopamine d1 (+) -> globus pallidus internal and substantia nigra reticularis - GABA (-) -> thalamic relay nuclei - glutamate (+) -> primary motor cortex
How does dopamine act on the indirect and direct pathways of the putamen circuit?
- dopamine is inhibitory in the indirect pathway -> uses D2 receptors
- dopamine is excitatory on the direct pathway -> uses D1 receptors
- therefore, the action of dopamine is overall EXCITATORY
How does IGP/SubNigRet act on the thalamus?
- normally active and sends inhibitory signals to the thalamus
- exciting the putamen inhibits the IGP/SubNigRet and allows the thalamus to send excitatory signals to the motor cortex
What is the function of the caudate circuit?
- cognitive planning of sequential and parallel motor patterns
- plays major role in cognitive control of motor activity
- overall inhibitory -> tends to decrease motor activity
Outline the caudate circuit.
Cerebral cortex - ACh (+) -> caudate nucleus - GABA (-) -> globus pallidus external - dopamine d2 (-) -> thalamic relay nuclei - glutamate (+) -> premotor and supplementary motor cortex
for complete table see drawing
How does Huntington disease affect the caudate circuit?
-the GABA neurons are destroyed, so the indirect pathway no longer has inhibitory influence on direct pathway and motor activity
Neurotransmitter between substantia nigra and caudate nucleus/putamen
- inhibitory dopamine
Neurotransmitter between caudate nucleus and putamen -> globus pallidus and substantia nigra
GABA inhibitory
Neurotransmitter between cortex -> caudate nucleus and putamen?
ACh excitatory
What neurotransmitters are used in multiple pathways from the brainstem?
- NE
- serotonin (inhibitory)
- encepalin
What is excitatory?
Glu
What causes Parkinson’s?
-results from widespread destruction of pars compacta of substantia nigra that sends dopaminergic fibers to caudate nucleus and putamen
What happens in the direct and indirect pathways during Parkinson’s?
- dopaminergic pathways to direct and indirect pathways are lost
- direct pathway loses some of its excitatory input
- indirect pathway loses some of its inhibitory input
- both cases result in decreased motor activity
What are some characteristics of Parkinson’s?
- rigidity of much of body musculature
- involuntary tremors of involved areas even at rest at a fixed rate
- serious difficulty in initiating movement (akinesia)
- postural instability
- dysphasia, speech disorders, gait disturbances, fatigue
When do you usually become symptomatic for Huntington’s?
-30-40 years of age
What are some characteristics of Huntington’s?
- flicking movements of individual muscles
- progressive severe distortion all movements of entire body
- severe dementia
- motor dysfunctions
What causes the abnormal movements of Huntington’s?
-caused by loss of most of cell bodies of GABA secreting neurons of caudate nucleus and putamen and of ACh neurons in other parts of the brain
How are the indirect and direct pathway of Huntington’s affected?
- indirect pathway no longer has an inhibitory influence on the direct pathway
- motor activity is increased
How does GABA usually affect the brain?
-inhibit parts of the globus pallidus and substantia nigra
