Exam 2 Flashcards
Neurons in the spinal cord
Upper motor neurons
Lower motor neurons
Renshaw cells
Upper motor neurons
Descends the spinal cord to level of the appropriate spinal nerve root
Synapses with lower motor neuron or interneuron
What is the neurotransmitter from the UMN to the LMN?
Glutamate via glutamatergic receptors
Lower motor neurons
Typically found in anterior gray portion of SC or cranial nuclei of brainstem
Terminate at effector with acetylcholine as nt
Cranial nerves are unique LMNs
Renshaw cells
Inhibitory cells in the anterior horns of spinal cord
Receive collateral branches from alpha motor neurons
What happens when renshaw cells transmit signals to surrounding motor neurons?
lateral inhibition
fluidity of limb movement is enhanced
What happens when renshaw cells transmit signals to the same motor neuron?
Results in recurrent inhibition
Types of sensory fibers
A-aplha or A-beta: conduction rate 30-120 m/sec
A-delta: conduction rate 4-30 m/sec
C fibers: conduction rate is less than 2.5 m/sec
What fibers are nociceptors and thermoreceptors are related to?
C fibers or A-delta fibers
Muscle spindle
Consists of 3-12 intrafusal fibers
With finer movements the number of muscle spindles required increases
Innervated by small gamma motor neurons
Detects changes in muscle length
Intrafusal fibers
Innervated by small gamma motor neurons (group II afferents)
Encapsulated within a sheath to form muscle spindle
Run parallel to extrafusal fibers
Central region of the muscle spindle
no contractile fibers
functions as a sensory receptor
Extrafusal fibers
Make p the “muscle fibers” that are innervated by alpha motor neurons
Nuclear bag fibers
Type of intrafusal fiber
Detect change in muscle length
Innervated by group Ia afferents and dynamic gamma efferents
Multiple nuclei located in a central “bag-like” configuration
Nuclear chain fibers
Type of intrafusal fiber Detect static change in muscle length Innervated by group II afferents and static gamma efferents More numerous than bag fibers Multiple nuclei arranged in a single row
What corrects for increase in muscle length?
Muscle spindle
What does stimulation of the central region of intrafusal fiber result from?
Lengthening of entire muscle
Contraction of ends of intrafusal fibers
What does stimulation of sensory fibers (Ia and II) result in?
Stimulation of alpha motor neurons and contraction and shortening of muscle
Muscle spindle gamma motor neurons
Innervate intrafusal fibers
Adjust sensitivity of muscle spindle
Coactivated with alpha-motor neurons
Brain areas controlling gamma neurons
Bulboreticular region of brain stem
Cerebellum
Basal nuclei
Cerebral cortex
Types of gamma fibers
A-gamma: supply small intrafusal fibers in middle of muscle spindle
Gamma-dynamic: excite nuclear bag intrafusal fibers
Gamma-static: excite nuclear chain intrafusal fibers
Golgi tnedon organ
Encapsulated receptor through which muscle tendon fibers pass
Arranged in series with extrafusal fibers
Stimulated by contracting or stretching of muscle
Detects muscle tension
Opposite of stretch relfex
Circuitry of golgi tendon
Type Ib afferent stimulates inhibitory interneuron which inhibits the anterior alpha neuron
Reciprocal inhibition
Flexor reflex on one side will cause flexion on the same side and extension on the opposite side
Functions of premotor and supplementary motor cortex
Generate plan for movement
Cause more complex patterns of movement
Anterior part creates a motor image
Supplementary is responsible for creating a mental rehearsal of a movement
UMN classification
Classified according to where they synapse in the ventral horn
Medial activation system
Innervate postural and girdle muscles
Lateral activation system
Associated with distally located muscles used for fine movements
Nonspecific activating system
Facilitate local reflex arcs
Origin of corticospinal tract
Primary motor cortex
Premotor cortex
Somatosensory area
Pathway of corticospinal tract
Site of origin -> internal capsule -> medullary pyramids -> Crosses in lower medulla -> lateral columns of spinal cord (later corticospinal tract)
Some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract
Lateral corticospinal tract
Made up of corticospinal fibers that have crossed in the medulla
Supply all levels of spinal cord
Anterior corticospinal tract
Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs
Supply neck and upper limbs
Functions of corticospinal tract
Adds speed and agility to conscious movement (esp hand)
Provides a high degree of motor control
Where are giant pyramidal cells located?
Motor cortex
What results from lesions of the corticospinal tract?
Reduced muscle tone
Clumsiness
Weakness
Not complete paralysis (unless both pyramidal and extrapyramidal systems are involved)
Corticobulbar tract
UMNs of the cranial nerves - innervating the face, head and neck
Innervates the head
Most fibers terminate in the reticular formation near cranial nerve nuclei
Association neurons of the corticobulbar tract
Leave reticular formation and synapse in cranial nerve nuclei
Synapse with LMN
Red nucleus
Evolutionary primitive portion of the brain
Fibers from the primary motor cortex and branches from the corticospinal tract synapse in the magnocellular portion
Magnocellular portion of red nucleus
Large neurons here give rise to rubrospinal tract which decussates in lower brain stem
Has somatotopic representation of all the muscles of the body
What does stimulation of the red nucleus result in?
Stimulation of flexors
Inhibition of extensors
Vestibulospinal tract
Originates in vestibular nuclei and receives major input from vestibular nerve about changes in head position
Goal to maintain balance
Descends in anterior funiculus
Synapses in LMNs to extensor muscles - primarily involved in maintenance of upright posture
Components: Utricle, saccule, semicircular canals
Utricle
Macula on horizontal plane
Determine orientation of head when it is upright
Saccule
Macula on vertical plane
Orientation when lying down
Macula
covered by a gelatinous layer that contains a large number of embedded small calcium carbonate crystals and thousands of hair cells that project cilia in to the gelatinous layer. Cilia bend with direction of gravitational pull. Depolarization d/t change in head position is sent through vestibular nerve
Functions of cerebellum
Not essential for locomotion
Helps sequence motor activites
Makes corrections to movements while they are being executed
Role in timing and creating smooth, rapid movements
Vermis of cerebellum
Location for control functions for muscle movements of the axial body, neck, shoulders and hips
Intermediate zone of cerebellum
Concerned with controlling muscle contractions in the distal portions of the upper and lower limbs
Lateral zone of cerebellum
Associated with cerebral cortex with planning of sequential motor movements
Dentate nuclei, emboliform nuclei and globose nuclei
Lesions in these nuclei lead to extremity ataxia
Project to red nucleus
Related to limb musculature and fine manipulative movement
Fastigial nuclei
Lesions in this nucleus leads to trunk ataxia
Fibers project to reticular formation and vestibular nuclei
Related to postural activity and limb movements via reticulospinal and vestibulospinal tracts
Granular cell layer
Innermost cell layer
Made up of granular cells, golgi type II cells and glomeruli
Axons of mossy fibers synapse with granular cells and golgi type IIs in the glomeruli
Purkinje cell lyer
Middle layer
Made of purkinje cells
Molecular layer
Outermost layer
Contains stellate cells, basket cells, purkinje dendrites, golgi type II and axons of granule cells
Granular cells
Axons form parallel fibers in cortex (+)
Golgi cells
Project from parallel fibers to granular cell bodies (-)
Basket cells
Project from parallel fibers to Purkinje axon hillock (-)
Stellate cells
Project from parallel fibers to purkinje dendrites (-)
Basket cells and stellate cells do what to purkinje cells?
Provide lateral inhibition to provide dampening
Purkinje cells
Extensive dendritic branching Receive input from parallel fibers Project to intracerebellar nuclei (-) ONLY output from cortex ** Output is always inhibitory
Climbing fibers
Afferent of cerebellar cortex Originate from medullary olives Make multiple synapses with purkinje cells Provide high frequency bursts "condition" purkinje cells Play a role in motor learning
Mossy fibers
Afferent of cerebellar cortex
Originate from multiple centers in the brainstem and spinal cord including vestibulocerebelar, spinocerebelar and pontocerebellar tracts
Make multiple synapses on purkinje cells and result i simple spikes
Synapse on granule cells in glomeruli
