Module 3 Flashcards
- neural pathways that control the sequence and pattern of muscle contractions
- distributed throughout brain and spinal cord
Motor System
- consists of a single motor neuron and the muscle fibers that it innervates
- for fine control, a single motor neuron innervates only a few muscle fibers
- EXAMPLE: eye muscle
- for larger movements, a single motor neuron may innervate thousands of muscle fibers
- EXAMPLE: postural muscles
Motor Unit
- is the set of motoneurons innervating fibers within the same muscle
motoneuron pool
- force of muscle contraction is graded by recruitment of additional motor units (graded response)
- as additional motor units are recruited, more motor neurons are involved and more tension is generated
Size Principle of Muscles
Types of Motor Neurons
- Alpha Motor Neurons
2. Gamma Motoneurons
- innervate extrafusal skeletal muscle fibers
- action potentials in α motor neurons lead to action potentials in the extrafusal muscle fibers they innervate, which results in contraction
Alpha Motor Neurons
- innervate specialized intrafusal muscle fibers
- adjust the sensitivity of the muscle spindles(so that they respond appropriately as the extrafusal fibers contract and
shorten)
Gamma Motor neurons
Types of Muscle Fibers
- Extrafusal Fibers
- Intrafusal Fibers
- make up the bulk of muscle
- innervated by alpha motor neurons
- provide the force for muscle contraction
Extrafusal Fibers
- smaller than extrafusal muscle fibers
- are innervated by gamma motor neurons
- encapsulated in sheaths to form muscle spindles
- are too small to generate significant force
Intrafusal Fibers
- central role in skeletal muscle control
- cell bodies are topographically arranged within the ventral horn of the spinal cord
- axons innervate skeletal muscle fibers
- cell bodies receive numerous synaptic connections from:
o proprioceptors
higher levels of the CNS including the brainstem, basal ganglia, cerebellum, and motor cortex
Alpha Motor Neuron
Topographic Arrangement
- muscles of the trunk are medial
- muscles of the extremities are lateral
- limb flexors are dorsal
- limb extensors are ventral
¥ synapse with the pool of motor neurons by which they are stimulated
¥ predominantly inhibitory
¥ bring about recurrent or feedback inhibition
Renshaw Cells
What type of synaptic arrangement is exemplified by Renshaw cells?
one to many
What neurotransmitter is released by Renshaw cells?
Glycine
What type of neuronal circuit is exemplified by Renshaw cells?
Divergent
sense of awareness of:
- position of the body in space
- progress of the movement by sensory receptors within the muscles and joints
Proprioception
- mechanoreceptors within muscles and joints
- provide the CNS with information regarding muscle length, position and tension (force)
Proprioceptors
More than half of all the nerve fibers that ascend and descend in the spinal cord are __.
Propiospinal fibers
two major proprioceptors:
O Muscle Spindle
O Golgi Tendon Organ
- small, encapsulated intrafusal fibers
- lie in parallel with extrafusal muscle fibers
- send information to the nervous system about muscle length or rate of change of length
- innervation is as follows:
1. efferents via gamma motor neurons - regulates sensitivity of the spindles
2. afferents via group Ia (primary or annulospiral endings) and group II fibers (secondary endings) - respond to muscle stretch
Muscle Spindles
True or False
The finer the movement required, the greater the number of muscle spindles in a muscle.
True
Types of Intrafusal Fibers in Muscle Spindles
- Nuclear Bag Fibers
o detect the rate of change in muscle length (fast, dynamic changes)
o innervated by group Ia afferents
o have nuclei collected in a central “bag” region
2. Nuclear Chain Fibers o detect static changes in muscle length o innervated by group II afferents o more numerous than nuclear bag fibers o have nuclei arranged in rows
Role of Muscle Spindles
- comparators for maintenance of muscle length
- important during goal-directed voluntary movements
o voluntary changes in muscle length are initiated by motor areas of the brain
o includes changes to the set-point of the muscle spindle system
- simultaneous activation of extrafusal fibers (by alpha motor neurons) and intrafusal fibers (by gamma motor neurons)
- readjusts the sensitivity of muscle spindles continuously as the muscle shortens
- allows the muscle spindles to be functional at all times during a muscle contraction
Co-activation
- mechanoreceptors that lie within the tendons of muscles immediately beyond their attachments to the muscle fibers
- respond to degree of tension within muscles
- group Ib afferent fibers relay this information to the CNS (in particular the spinal cord and cerebellum)
Golgi Tendon Organ
- rapidly executed, automatic, and stereotyped response to a given stimulus
- simplest form of irritability associated with the nervous system
Reflex
- neurons participating in a reflex form a reflex arc, which includes:
o receptor
o afferent neuron that synapses in the CNS
o efferent neuron that sends impulses to an effector
o interneurons may be present between the afferent and efferent neurons
Reflex arc
Afferent vs Efferent
Remember SAME!
Sensory = Afferent Motor = Efferent
Classification of Neural Reflexes
- Efferent division that controls the effector
- Integrating region within the Nervous system
- Time at which the reflex develops
- The number of neuron in the reflex pathway
Classification of Neural Reflexes: Efferent division that controls the effector
a. Somatic motor neurons - control skeletal muscles
b. Autonomic neurons - control smooth and cardiac muscle, glands, and adipose tissue.
Classification of Neural Reflexes: Integrating region within the Nervous system
a. Spinal reflexes do not require input from the brain
b. Cranial reflexes are integrated within the brain
Classification of Neural Reflexes: Time at which the reflex develops
a. Innate (inborn) reflexes are genetically determined.
b Learned (conditioned) reflexes are acquired through experience
Classification of Neural Reflexes: The number of neuron in the reflex pathway
a. Monosynaptic reflexes have only two neurons: one afferent (sensory) and one efferent. Only somatic motor reflexes can be monosynaptic.
b. Polysynaptic reflexes in crude one or more interneurons between the afferent and efferent neurons. All autonomic reflexes are polysynaptic because they have three neurons: one afferent and two efferent.
- also known as patellar tendon-tap reflex, knee-jerk reflex or myotactic reflex
- stretching of a muscle stimulates the muscle spindle afferents
plays an important role in the control of posture
Muscle Stretch Reflex
Components of a Muscle Stretch Reflex
- Dynamic Stretch Reflex
2. Static Stretch Reflex
- caused by rapid stretch or unstretch
- transmitted from primary sensory or annulospiral endings of the muscle spindles
- oppose sudden changes in muscle length
- lasts within a fraction of a second only
Dynamic Stretch Reflex
- elicited by the continuous static receptor signals
- transmitted by both primary and secondary endings
- causes the degree of muscle contraction to remain reasonably constant
- continues for a prolonged period
Static Stretch Reflex
Damping Function of Stretch Reflexes
- muscle spindles prevent oscillation or jerkiness of body movements
- ensure that contraction is relatively smooth, even though the motor nerve to the muscle is excited at a slow frequency
- reinforcement technique for eliciting deep tendon reflexes
o fingers are locked together and one hand pulls against the other while reflex is evoked - physiologic basis
o when one muscle is stretched, it facilitates a substantial number of alpha motor neurons
o transient increase of gamma motor neuron activity
Jendrassik’s Maneuver
Jendrassik’s maneuver facilitates multiple alpha motor neurons. What does this mean?
easier recruitment
If they are being facilitated, where are they located in the neuronal pool?
facilitated pool (it’s easier to excite)
- oscillation of a stretch reflex
- ordinarily occurs only when the stretch reflex is highly sensitized by facilitatory impulses from the brain
Clonus
- elicited by noxious stimuli
- transmitted by group II, III, IV fibers
- possesses at least one interneuron, and so the most basic flexion reflex is disynaptic
- usually many muscles are involved through polysynaptic pathways
- to achieve withdrawal of a limb:
o flexor muscles in the limb must contract while the extensor muscles relax
Flexor Withdrawal Reflex
What type of neuronal circuit is exemplified by flexor withdrawal reflex?
Divergent
Receptor that senses pain
Nociceptor
- supports the body as the weight shifts away form the painful stimuli
- stimulation of the flexion reflex frequently elicits extension of the contralateral limb about 250 ms later
- long latency between flexion and crossed extension represents the time taken to recruit interneurons
- helps to maintain posture and balance
Crossed extensor reflex
- ensures that the extensor muscles acting on a joint will relax while flexor muscles contract
- neuronal circuit that causes this reciprocal relation is called reciprocal innervation
Reciprocal Inhibition
Components of Flexor Withdrawal Reflex
- diverging circuits to spread the reflex to the necessary muscles for withdrawal
- reciprocal inhibition circuits to inhibit the antagonist muscles
- circuits to cause afterdischarge lasting many fractions of a second after the stimulus is over
What type of neuronal circuit is exemplified by prolonged afterdischarge in crossed extensor reflex?
Reverberating/Recurrent
- Golgi tendon organs monitor muscle tension
- negative feedback mechanism that prevents development of too much tension on muscles
- when tension becomes extreme, reflex inhibitory effects lead to instantaneous relaxation of the entire muscle (lengthening reaction)
Inverse Myotactic Reflex
What are the four major spinal cord reflexes?
- Muscle Stretch Reflex
- Golgi Tendon reflex
- Flexor withdrawal reflex
- Crossed extension reflex
of synapses: Monosynaptic
stimulus: Muscle stretch
afferent fibers: Group Ia fibers
efferent response: Muscle contraction
Muscle Stretch Reflex
of synapses: Di/polysynaptic
stimulus: Muscle tension
afferent fibers: Group Ib fibers
efferent response: Muscle relaxation
Golgi Tendon reflex
of synapses: Polysynaptic
stimulus: Pain
afferent fibers: Group II, III, IV fibers
efferent response: Ipsilateral muscle flexion
Flexor withdrawal reflex
of synapses: Polysynaptic
stimulus: Pain
afferent fibers: Group II, III, IV fibers
efferent response: Contralateral muscle extension
Crossed extension reflex
- caused by transection of the spinal cord
- loss of spinal reflexes (areflexia) and flaccid paralysis below the level of the injury
- over the ensuing weeks, spinal cord activity below the level of the lesion returns as the excitability of undamaged neurons increases
- may give rise to spasticity of the paralyzed muscle groups
Spinal Shock
Events in Spinal Shock
- Neurogenic Shock
- Areflexia
- Incontinence
- arterial blood pressure falls instantly
- demonstrates that sympathetic nervous system activity becomes blocked almost to extinction
Neurogenic Shock
- may last 2 weeks to several months
- order of return: stretch reflexes, flexor reflexes, postural antigravity reflexes, remnants of stepping reflexes
Areflexia
- sacral reflexes for control of bladder and colon evacuation are suppressed
Incontinence
- impairment or loss of motor and sensory function in the arms, trunk, legs, and pelvic organs
Tetraplegia / Quadriplegia
- impairment of function of the legs and pelvic organs
Paraplegia / Biplegia
- total paralysis of the arm, leg, and trunk on the same side of the body
- does not usually result from spinal cord injuries but from strokes
Hemiplegia
- polysynaptic reflex useful in testing for spinal shock
- checks anal sphincter contraction in response to squeezing the glans penis
o absence indicates spinal shock
o first reflex to return after spinal shock - once this reflex has returned, all remaining neurologic deficits are considered permanent
Bulbocavernosus Reflex
- contains motor areas- stimulation will elicit contralateral movements
- displays somatotopic arrangement
- areas of the body that are capable of especially refined and complex movements (i.e. fingers, lips, and tongue) have a disproportionately large area of representation
Cerebral Cortex
- divided into three sub-areas, each of which has its own topographical representation of muscle groups and specific motor functions:
o PRIMARY MOTOR CORTEX
o PREMOTOR AREA
o SUPPLEMENTARY MOTOR AREA
Motor Cortex
- located in precentral gyrus or Brodmann area 4
- responsible for the execution of movement (programmed patterns of motor neurons and voluntary movement)
- is somatotopically organized (motor homunculus)
Primary Motor Cortex
Epileptic events in the primary motor cortex cause __
Jacksonian seizures
- immediately anterior to the lateral portion of the primary motor cortex
- forms a portion of Brodmann area 6
- responsible for generating a plan for movement - transferred to primary motor cortex for execution
- stimulation causes activation of groups of muscles
Premotor Area
- located in the medial portion of Brodmann area 6 just anterior to the lower extremity portion of the precentral gyrus
- stimulation causes activation of bilateral muscle activation (usually upper extremities)
- programs complex motor sequences
- active during mental rehearsal for a movement
Supplementary Motor Area
- motor speech area
- converts simple vocal utterances into whole words and complete sentences
Broca’s Area
- controls conjugate eye movement required to shift gaze from one object to another
Frontal Eye Field (Brodmann Area 8)
- enables movement of head correlated with eyes
Head Rotation Area
- when damaged, hand movements are lost (motor apraxia)
Area For Fine Movements Of Hand
- carried by the corticospinal (pyramidal) and extrapyramidal tracts
- also sends numerous collaterals to the basal ganglia, cerebellum and brainstem
Motor Outflow of Cerebral Cortex
- motor areas receive inputs from many sources
o predominant sensory input is from the somatosensory system, which receives its input from the thalamus - afferent information is also received from the visual system, cerebellum, and basal ganglia
o used to refine movements, particularly to match the force generated in specific muscle groups to an imposed load
Motor Input of Cerebral Cortex
What are the three sub-areas of the motor cortex?
Primary Motor Area- execution of movement
Premotor Area - planning of movement
Supplementary Motor Area - bilateral muscle movement
- originates over a wide area of cortex including both motor and somatosensory areas
- more than 80 per cent of the fibers decussate at the pyramids (cervicomedullary junction)
- predominant pathway for the control of fine skilled manipulative movements of the extremities
- loss of precise hand movements is a hallmark feature of lesions to the corticospinal tract
Corticospinal Tract
CORTICOSPINAL TRACT
- Motor Cortex
- Corona radiata
- Internal capsule
- Cerebral peduncle
- Brainstem
- Cervicomedullary junction*
- Corticospinal tract (A/L)
- Anterior horn cell
- Ventral root
- Peripheral nerve
- Neuromuscular junction
- Muscle
- conveys nerve impulses from the motor cortex to skeletal muscles of the head and neck
- axons of UMNs descend from the cortex into the brain stem, where some decussate and others do not
- provide input to lower motor neurons in the nuclei of cranial nerves III, IV, V, VI, VII, IX, X, XI, and XII
- control voluntary movements of the eyes, tongue and neck, chewing, facial expression and speech
Corticobulbar Tract
- also called Cerebrovascular Disease
- cessation of blood flow to the brain due to:
o ruptured blood vessel that bleeds into the brain
o thrombosis of a vessel, producing local ischemia - muscles controlled by the damaged areas show a corresponding loss of function
o clumsiness and loss of fine muscle control
o postural movements may not be affected
o hyperreflexia, hypertonia and spasticity occur with extension of involvement
Strokes
- due to lesions to supplementary and premotor areas
- loss of the ability to prepare for voluntary movement
- ability to execute simple movements is retained
Apraxia
- above the anterior horn cell
- motor neurons that originate in the motor region of the cerebral cortex or the brain stem
- main effector neurons for voluntary movement in layer V of the primary motor cortex (Betz cells)
- UMN pathways (above anterior horn cell) include:
▪ corticospinal tract
▪ corticobulbar tracts
▪ extrapyramidal tracts
Upper Motor Neuron
- below the anterior horn cell
- motor neurons connecting the brainstem and spinal cord to muscle fibers
- bring nerve impulses from the upper motor neurons out to the muscles
- begins at the level of the anterior horn cell in the spinal cord
Lower Motor Neuron
- total loss of motor function associated with an increase in muscle tone
- associated with clasp-knife phenomenon and hyperreflexia
Spastic Paralysis
- total loss of motor function associated with a decrease in muscle tone
- associated with floppiness, areflexia or hyporeflexia
Flaccid Paralysis
- reflex extension of the great toe with flexion of the other toes
- evoked by stroking the lateral sole of the foot
- presence indicates an upper motor neuron lesion
Babinski Reflex
- small, local, involuntary muscle contractions visible under the skin
- arise from spontaneous discharge of a bundle of skeletal muscle fibers
- presence indicates a lower motor neuron lesion
Fasciculations
muscle tone: Increased paralysis: Spastic Paralysis deep tendon reflex: Hyperreflexia babinski sign: Present clonus: Present fasciculations: Absent atrophy: Atrophy of Disuse
Upper Motor Neuron (UMN) Lesion
muscle tone: decreased paralysis: Flaccid Paralysis deep tendon reflex: Hypo/Areflexia babinski sign: Absent clonus: Absent fasciculations: Present atrophy: Atrophy of Denervation
Lower Motor Neuron (LMN) Lesion
- composed of midbrain, pons and medulla
- special functions include:
o control of respiration
o control of the cardiovascular system
o partial control of gastrointestinal function
o control of many stereotyped movements of the body
o control of equilibrium
o control of eye movements
o way station for command signals from higher centers
Brainstem
- activity of the neural circuitry within the spinal cord is modified and refined by descending motor control pathways
o pyramidal tract
▪ CORTICOSPINAL TRACT
o extrapyramidal tracts ▪ RETICULOSPINAL TRACT ▪ VESTIBULOSPINAL TRACT ▪ RUBROSPINAL TRACT ▪ TECTOSPINAL TRACT
Descending Motor Control Pathways
- influence mainly the muscles of the trunk and proximal parts of the limbs
- important in maintenance of certain postures and in startle reactions
- two main divisions
o PONTINE or MEDIAL RETICULOSPINAL TRACT
o MEDULLARY or LATERAL RETICULOSPINAL TRACT
Reticulospinal Tract
- originates in the pontine reticular nuclei
- projects to the ventromedial spinal cord
- general stimulatory effect on both extensors and flexors, with the predominant effect on extensors
Pontine Reticulospinal Tract
- originates in the medullary reticular formation
- projects to spinal cord interneurons in the intermediate gray area
- stimulation has a general inhibitory effect on both extensors and flexors, with the predominant effect on extensors
Medullary Reticulospinal Tract
- originates in Deiters nucleus
- projects to ipsilateral motoneurons and interneurons
- important functions include:
o control the activity of extensor muscles - stimulation causes a powerful stimulation of extensors and inhibition of flexors
o maintenance of an erect posture - selectively controls the excitatory signals to the different antigravity muscles
o making adjustments in response to signals from the vestibular apparatus
Vestibulospinal Tract
- originates in the superior colliculus
- projects to the cervical spinal cord
- decussates before entry to spinal cord - lesions are always contralateral
- important functions include
o control of neck muscles
o controlling head and eye movements
Tectospinal Tract
- most important extrapyramidal tract
- originates in the red nucleus
- afferent information from cortex, cerebellum and basal ganglia
- projects to interneurons in the lateral spinal cord
- decussates before entry to spinal cord - lesions are always ipsilateral
- controls both flexor and extensor muscles
o stimulation of the red nucleus produces stimulation of flexors and inhibition of extensors - voluntary movements are impaired with lesions
Rubrospinal Tract
origin: Pontine reticular nuclei
projection: Ventromedial SC
decussation: None (ipsilateral)
function: Stimulate flexors and extensors
Pontine Reticulospinal tract
origin: Medullary reticular nuclei
projection: Intermediate gray
decussation: None
function: Inhibits flexors and extensors
Medullary Reticulospinal tract
origin: Deiters nucleus
projection: Ventromedial SC
decussation: None
function: Stimulates flexors and extensors
Vestibulospinal Tract
origin: Superior colliculus
projection: Cervical SC
decussation: Yes (Contralateral)
function: Controls neck muscles
Tectospinal Tract
origin: Red nucleus
projection: Lateral SC
decussation: Yes
function: Stimulates flexors, inhibits extensors
Rubrospinal Tract
- involuntary flexion or extension of arms and legs
- occurs when one set of muscles becomes incapacitated while the opposing set is not
- indicates a severe medical emergency requiring immediate medical attention
- two types:
o DECORTICATE RIGIDITY
o DECEREBRATE RIGIDITY
Abnormal Posturing
- involuntary flexion of the upper extremities in response to external stimuli
- arms flexed, hands are clenched into fists, legs extended and feet turned inward
- less severe
Decorticate Rigidity
- involuntary extension of the upper extremities in response to external stimuli
- head is arched back, arms are extended by the sides, and legs are extended
Decerebrate Rigidity
- cause decerebrate rigidity because of the removal of inhibition from higher centers
Lesions Above The Lateral Vestibular Nucleus
- cause decerebrate rigidity because of the removal of central inhibition from the pontine reticular formation
Lesions Above The Pontine Reticular Formation But Below The Midbrain
- result in decorticate rigidity and intact tonic neck reflexes
Lesions Above The Red Nucleus
- also called the “little brain”
- helps control the rate, range, force, and direction of movements (synergy)
o sequences motor activities
o monitors and makes corrective adjustments in motor activities while they are being executed - silent area of the brain
o electrical excitation does not cause any sensation
o damage does not produce paralysis
Cerebellum
Anatomy of the Cerebellum
- located dorsal to the pons and medulla and protrudes from under the occipital lobes
- divided into three lobes by two deep fissures
o ANTERIOR, POSTERIOR, FLOCCULONODULAR - cerebellar cortex is actually a large folded sheet (17 x 120 cm) with crosswise folds (folia)
o deep cerebellar nuclei lie deep beneath the folded mass of cerebellar cortex
o from medial to lateral: DENTATE, EMBOLIFORM, GLOBOSE, FASTIGIAL
Brainstem Attachments
- superior cerebellar peduncles to midbrain
- middle cerebellar peduncles to pons
- inferior cerebellar peduncles to medulla oblongata
Somatotopic Organization of the Cerebellum
- vermis and intermediate zone contain a somatotopic map of the body surface
o axial portions of the body lie in the vermis
o limbs and facial regions lie in the intermediate zones - lateral portions of cerebellar hemispheres do not have topographical representations
o receive input signals exclusively from cerebral cortex
o plays important roles in planning and coordinating the body’s rapid sequential muscular activities
Layers of the Cerebellar Cortex
GRANULAR LAYER - innermost layer that contains granule cells, Golgi type II cells and glomeruli
PURKINJE CELL LAYER - middle layer that contains inhibitory Purkinje cells
MOLECULAR LAYER - outermost layer that contains stellate and basket cells, dendrites of Purkinje and Golgi type II cells and parallel fibers (axons of granule cells)
- originate in the inferior olive
- demonstrate complex spikes - action potentials beginning with a strong spike and followed by a trail of weakening secondary spikes
- function in conditioning Purkinje cells (motor learning)
Climbing Fibers
- form the bulk of the input, originating in the cortico-, vestibulo-, reticulo- and spinocerebellar tracts
- demonstrate simple spikes - much weaker short-duration action potentials in Purkinje cells
Mossy Fibers
- largest afferent projections
- originate from the basilar pontine nuclei
Pontocerebellar System
- originate from the inferior olivary nuclei
Olivocerebellar Projections
- originate in spinal cord or medulla
Spinocerebellar Fibers
- originate from brainstem
Reticulocerebellar Fibers
- originate from vestibular nuclei and vestibular apparatus
Vestibular Fibers
- central neurons with fan-shaped dendritic trees
- always inhibitory with GABA as its neurotransmitter
Purkinje Cells
- smallest and most numerous neurons in the brain
- parallel fibers are axons of granule cells
- excitatory input from mossy fibers which use glutamate as its neurotransmitter
Granule Cells
o small interneurons with numerous arborizations
o inhibitory in function
Golgi Type II Cells
o inhibitory star-shaped cells found in superficial cerebellum
Stellate Cells
o inhibitory cells whose axons form baskets around Purkinje fibers and are found in deep cerebellar layers
Basket Cells
o complex of synapses having a mossy fiber at its core
o synapsing with axons of Golgi type II neurons and dendrites of granule cells
Glomerulus
- modulate Purkinje cell output
- all of the cerebellar interneurons are inhibitory EXCEPT granule cells
o granule cells have excitatory input to basket cells, stellate cells, Golgi II cells, and Purkinje cells
o basket cells and stellate cells inhibit Purkinje cells (via parallel fibers)
o Golgi II cells inhibit granule cells, thereby reducing their excitatory effect on Purkinje cells
Cerebellar Interneurons
Output of the Cerebellar Cortex
- Purkinje cells are the only output of the cerebellar cortex
o output is always inhibitory, using GABA as NT - inhibitory output modulates the output of the cerebellum and regulates rate, range, and direction of movement (synergy)
Efferent Signals from the Cerebellum
vermis - projects to fastigial nucleus, vestibular nucleus and reticular formation
intermediate zones - project to globose and emboliform nuclei (interposed nuclei)
lateral hemispheres - project to the dentate nucleus, ventral anterior thalamic nuclei and cerebral cortex
CEREBELLAR PATHWAY
Cortex Pons* Cerebellum Dentate nucleus* Red Nucleus Thalamus Corticospinal tract
o consists of the small flocculonodular lobes
o for control of balance and eye movement
Vestibulocerebellum
o consists of lateral zones of cerebellar hemispheres
o for planning and initiation of movement
Cerebrocerebellum
o consists of vermis and intermediate zones
o for control of rate, force, range, and direction of movement (synergy)
Spinocerebellum
- during nearly every movement, certain muscles must be rapidly turned on and then quick turned off
- made possible by interplay of mossy and climbing fibers and Purkinje cells
Turn On/Turn Off Function
