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Flashcards in Unit 3 Deck (62):

What are the three elements of voluntary movement?

1) Target Identification/ Intent
2) Programming and planning
-praxic=how, handled in cerebral cortex
-intentional-when, function of basal ganglia and cerebellum
3) Execution, midcourse corrections done through cerebellum


Describe the differences between upper and lower motor neurons.

1) Upper motor neurons exist entirely in the CNS and control the activity of LMNs
2) Lower motor neurons have cell body in CNS, axons go into PNS to form motor end plates on skeletal muscles


What are the five areas of the cortex that deal with motor information?

-primary motor cortex (M-I)
-premotor cortex
-supplementary motor area
-frontal eye fields
-posterior parietal motor area


Primary Motor Cortex general info and functions.

-contains Brodmanns area 4
-neurons in layer 5 give rise to corticospinal tract
-primarily controls fine distal movements
-individual, simple movements, well defined
-direction controlled by a population of neurons, not a single UMN
-kept informed of limb position and speed through communication with S-1 and area 5 of PMA


What happens if there is damage to the Primary Motor Cortex?

-upper motor neuron signs, lack of fine distal movements (piano/guitar playing)


Premotor Cortex general info and functions.

-includes lateral Brodmanns area 6
-primary input from parietal lobe (PMA)
-small output to CST and reticular formation
-for more complex movements, slower than M-I ex: movement of entire limb
-plays role in planning movements, setting the stage
-integrates external stimuli such, visual, auditory to help movement
-dorsal PMC=reaching, ventral PMC=grasping
-mirror neurons


Supplementary Motor Area general info and functions.

-includes medial Brodmanns area 6
-complex movements
-coordination of movements on both sides of the body (proximal and distal muscles with CST), can do so without visual cues
-functions in mental imaging of movements
-stores learned motor programs


What happens if there is damage to the PMC?

-no paresis
-apraxia of complex tasks


What happens if there is damage to the SMA?

-no paresis
-difficulty coordinating movements on both sides
-difficulty learning new motor movements


Posterior Parietal Motor Area general info and functions.

-includes Brodmanns areas 5 and 7
-major role in correlating external world with body position and motivation
-modulated by state of attention, driven by goal oriented activities
-functions in sensorimotor transformations


What happens if there is damage to the PMA?

-no paresis
-difficulty with hand orientation
-astereognosia and agraphesthesia


Voluntary Motor Control Pathways general facts

1) monosynaptic (bineuronal): directly from cortex to LMN
2) fast, uninterrupted pathways
3) ends contralateral
-corticospinal and corticonuclear: for realization of movements (fine movements)


Corticospinal tract

Start: in one of the motor cortical areas
-fibers course somatotopically, heads down to spinomedullary junction
-here 85-90% of fibers decussate into lateral funiculus to become lateral corticospinal tract (LCST) while the other fibers DONT decussate and enter ventral funiculus to become ventral (anterior) corticospinal tract (ACST)
-eventually get to anterior commissure and end in LMN
-NOTE: all fibers end contralateral


Lateral Corticospinal Tract

activates motor neurons controlling distal musculature particularly hands/feet, fingers/toes


Ventral (anterior) corticosinal tract

-activates neurons that innervate axial musculature


Corticonuclear Tract

Start-in motor cortex areas
-synapse in cranial nerves
-some terminate in midbrain (CN 3, 4)
-some terminate in pons (5,6, 7)
-some terminate in medulla (9,10,11,12)
-bilateral with the exception of facial expression (7) and tongue muscles (12)


Extrapyramidal System

-indirect pathway, multineuronal
-for involuntary movement and synchronization of movement
-includes rubrospinal tract, vestibulospinal tract, and reticulospinal tract


Rubrospinal Tract

-starts in red nucleus of midbrain, decussate, go to lateral funiculus in spinal cord and end in LMN in ventral horns
-primarily influences flexor muscles and acts as a supplement to corticospinal
-so if lesion in corticospinal, animal still has some movements, but not the fine distal movements


Vestibulospinal Tract

-both a medial and lateral
-start in vestibular nuclei, head to ventral funiculus and end in ventral horns
-mediators of postural adjustment and head movements


Reticulospinal Tract

1) Lateral: from reticular formation to ventral horns and it bilateral. INHIBITS motor neurons that innervate extensor muscles
2) Medial: from reticular formation to ventral horns and is ipsilateral. EXCITES motor neurons that innervate extensor muscles


Tectospinal Tract

-Starts in superior colliculus, end in ventral horn of cervical spinal cord only
-primarily functions in reflex control, also coordinates head/neck/eye movement in response to environmental stimuli


Functions of Basal Ganglia

-coordination and planning of voluntary movements
-thought to play a role in scaling the amplitude and velocity of movements


Basic Basal Ganglia general facts

1) corpus striatium=caudate, putamen, and globus pallidus
2) Striatum=caudate and putamen
3) lentiform nucleus= putamen and globus pallidus
-most inputs are to the striatum
-most outputs are from the globus pallidus


The Basal Ganglia connections are all ____.



Nucleus Accumbens

-area that where caudate nucleus and putamen are continuous
-thought to play a role in drug and alcohol addiction


Substantia nigra

-major source of dopamine to striatium via nigrostriatal pathway


Describe inputs to the basal ganglia

-from cortex (Premotor, SMA) to striatum
-ipsilateral via corticostriate projections which are excitatory due to glutamate
-putamen: voluntary movements
-caudate head: cognitive and behavioral functions


Describe the interconnections between basal ganglia nuclei

1) substantia nigra provides dopamine inputs via nigrostriatal fibers
-D1, excitatory, direct pathway
-D2, inhibitory, indirect pathway
2) Striatopallidal: striatum projects to both globus pallidus segments, GABA/inhibitory
3) Striatonigral: striatum to substantia nigra, GABA/inhibitory
4) subthalamic nucleus: to GP and SN, glutamate/excitatory


Describe the outputs of the basal ganglia

-outputs come from the internal globus pallidus
1) lenticular fasiculus: to VL thalamus and primary motor cortex
2) ansa lenticularis: to VA thalamus and premotor cortex
-outputs are GABA/inhibitory


Important notes about basal ganglia connections.

1) all interconnections are ipsilateral, and their indirect effects on the cortex will influence motor control on the contralateral side of the body
2) direct pathway increases flow through thalamus, is excitatory, D1
3) indirect pathway decreases flow through thalamus, is inhibitory, D2
4) GP and nigral inputs tonically active


Describe how the direct pathway works through the basal ganglia

Start in SMA or PMC, then corticostriate projections (glutamate/excitatory), then striatopalladal projections (GABA/inhibitory), then palladothalamic (GABA/inhibitory), then thalamocortical (glutamate/excitatory) and finally to LMNs and movement
-NOTE: since striatopalladal is normally tonically active, we get a double negative making a positive effect


Describe how the indirect pathway works through the basal ganglia

Start in SMA or PMC, then corticostriate projections (glutamate/excitatory), then striatopalladal projections (to externalGP, GABA/inhibitory), then GPe to subthalamic (GABA, which is the double negative allowing subthalamus to send glutamate to GPi) glutamate to GPi releases GABA to thalamus, causing inhibition to thalamocortical, and a decrease in movement


Important note about neurotransmitters that affect direct and indirect basal ganglia pathways

-Dopamine activates the direct pathway (D1 in striatum)
-Acetylcholine activates the indirect pathway (D2 in striatum)


Spinal Nerve Classifications

-general vs special, somatic vs visceral, afferent vs efferent
1) GSA: somatic sensation (touch, pain, temp)
2) GSE: skeletal muscle (3,4,6,12)
3) GVA: interoceptors
4) GVE: parasympathetic (3,7,9,10)
5) SSA: special sense for eyes and ears
6) SVA: smell and taste
7) SVE: brachiomotor innervation (5,7,9,10,11)


The pure sensory CNs

-only special afferents (SSA or SVA)
-Note: olfactory does not pass through the thalamus
-Note: for 8: vestibular nucleus in both pons/medulla, cochlear just in pons


CNs for eye movement muscles

3: for superior, medial, and inferior rectus, inferior oblique
4: superior oblique
6: lateral rectus


Oculomotor Nerve

-for conscious eye movements and reflexes
-lesion causes ptosis, mydriasis, and lateral strabismus


Trochlear Nerve

-depression and intorsion of the eye
-smallest CN


Abducens Nerve

-mediates lateral eye movements
-lesion results in diplopia


Spinal Accessory Nerve

-mediates head turning
-works with sternocleidomastoid to turn head opposite direction and works with trapezius to elevate shoulder


Hypoglossal Nerve

-mediates movement of tongue
-lesion results in deviation of tongue towards the damaged side


Trigeminal Nerve

-facial sensation and chewing
-GSA: touch, pain, temp, proprioception for face
-SVE: mastication muscles
-lesion: jaw jerk reflex


Facial Nerve

-expression of taste, crying, salivation
-SVA: taste anterior 2/3 of tongue
-GSA: skin sensation behind ear
-SVE: facial expression muscles
-GVE: parasympathetic to salivary glands
-unilateral lesion=paralysis of lower facial muscles, bilateral both upper and lower


Glossopharyngeal Nerve

-swallowing and salivation
-taste for posterior 1/3 of tongue
-SVE: stylopharyngeous muscle
-GVE: parasympathetic for parotid gland


Vagus Nerve

-the major parasympathetic nerve
-unilateral lesion-ipsilateral plegia of soft palate, bilateral fatal


What are the functions of the cerebellum? Note about injury?

-equilibrium and coordination of eye movements
-maintenance of muscle tone and posture
-mid course adjustments of movement
-planning and programming voluntary movements
-motor learning
NOTE: if injured, signs are ipsilateral


cerebellar peduncles

1) SCP: brachium conjuctivum, efferent (thalamus) and afferent (spinocerebellar)
2) MCP: brachium ponti, afferent (pontine nuclei)
3) ICP: restiform body


Cerebellar cortex

1) molecular layer (outermost)
2) purkinje layer: only neurons to project OUT of cerebellar cortex
3) granule cell layer:


Cerebellar cortex afferents

1) Climbing fibers: project through ICP, terminate on purkinje dendrites (molecular layer), carry "training" info
2) Mossy fibers: terminate in granule layer, cary "state" info


Cerebellar cortex efferents

-purkinje cell layer and deep cerebellar nuclei


Spinocerebellar tracts general info

-ALL ipsilateral
-unconscious sensations
-includes vestibulocerebellum, spinocerebellum (vermal and paravermal), and cerebrocerebellum



-mostly flocconodular lobe
-functions in equilibrium and coordinated eye movements


Spinocerebellum (general)

-for mid course corrections
-if damaged, movements occur without corrections when periphery changes


vermal spinocerebellum

-for trunk, leg, head, eye movements, posture
-damage effects eye movements and accuracy of movement


paravermal spinocerebellum

-regulates voluntary reaching and grasping



-for programmin, planning, and motor learning


Spinal interneurons

-90% of spinal cord
-interconnected to form central pattern generators (CPGs) that play a role in rhythmic movements that are relatively automatic like breathing, chewing, walking


Alpha motor neurons

-innervate extrafusal muscle fibers
-the major force generators


Gamma motor neurons

-innervate intrafusal muscle fibers
-don't generate significant force on their own
-components of muscle spindles


Muscle length monitoring system

-muscle spindles
-monitor absolute length and rate of change
-two types: nuclear chain fibers and nuclear bag fibers
-group 1a fibers (both chain and bag) sensitive to onset of stretch
-group 2 fibers (chain) sensitive to absolute length
-efferent gamma motor neurons involved


Muscle tension monitoring system

-golgi tendon organs at tendon/muscle junction
-active contraction has a much bigger effect than passive stretching
-golgi tendons act to inhibit contracting muscles as a protective effect
-golgi tendons fire faster in a contraction than muscle spindle


Renshaw cells

-motor inhibitory interneurons in spinal cord
-tetanus blocks this inhibition