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91

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

92

- 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

93

- 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

94

- 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

95

- 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

96

- 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

97

- 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

98

- 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

99

- 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

100

origin: Pontine reticular nuclei
projection: Ventromedial SC
decussation: None (ipsilateral)
function: Stimulate flexors and extensors

Pontine Reticulospinal tract

101

origin: Medullary reticular nuclei
projection: Intermediate gray
decussation: None
function: Inhibits flexors and extensors

Medullary Reticulospinal tract

102

origin: Deiters nucleus
projection: Ventromedial SC
decussation: None
function: Stimulates flexors and extensors

Vestibulospinal Tract

103

origin: Superior colliculus
projection: Cervical SC
decussation: Yes (Contralateral)
function: Controls neck muscles

Tectospinal Tract

104

origin: Red nucleus
projection: Lateral SC
decussation: Yes
function: Stimulates flexors, inhibits extensors

Rubrospinal Tract

105

- 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

106

- 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

107

- 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

108

- cause decerebrate rigidity because of the removal of inhibition from higher centers

Lesions Above The Lateral Vestibular Nucleus

109

- 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

110

- result in decorticate rigidity and intact tonic neck reflexes

Lesions Above The Red Nucleus

111

- 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

112

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

113

Brainstem Attachments

- superior cerebellar peduncles to midbrain
- middle cerebellar peduncles to pons
- inferior cerebellar peduncles to medulla oblongata

114

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

115

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)

116

- 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

117

- 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

118

- largest afferent projections
- originate from the basilar pontine nuclei

Pontocerebellar System

119

- originate from the inferior olivary nuclei

Olivocerebellar Projections

120

- originate in spinal cord or medulla

Spinocerebellar Fibers