Chapters 11 Motor System

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Chapters 11 Motor System Spinal Cord

• Chris Rorden
• University of South Carolina
• Norman J. Arnold School of Public Health
• Department of Communication Sciences and
  Disorders
• University of South Carolina

Previously Ascending sensory fibers Today
Descending motor fibers
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Six Neuraxial Levels

• Spinal Cord
• Brainstem
• Cerebellum
• Diencephalon
• Basal Ganglia
• Cerebral Cortex
• Neuraxial Brain and Spinal Cord Axis

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Functional Levels

• Spinal Level
• Simple Reflexes
• Regulation of Higher Skilled or Patterned
  Movements
• Upper Levels
• Initiation, Inhibition or Facilitation of Motor
  Functions
• Voluntary Motor Movements

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Spinal Cord

• 43.5cm long, 1cm diameter
• Five Spinal Segments and Spinal Nerve Groups
• Cervical (8)
• Thoracic (12)
• Lumbar (5)
• Sacral (5 fused vertebrae), "Holy Bone"
• Coccygeal (3-5 fused vertebrae) tailbone,
  (coccyx cuckoo's beak)

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Spine and Pelvis

• Spine can rotate with respect to pelvis

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Spinal Nerves

• There are a total of 31 bilaterally-paired spinal
  nerves
• 8 cervical nerves (C1-C8)
• 12 thoracic nerves (T1-T12)
• 5 lumbar nerves (L1-L5)
• 5 sacral nerves (S1-S5)
• 1 coccygeal nerve (Co, skin of lower back)
• C1 to C7 exit vertebral canal above the
  respective cervical vertebra (e.g. C1 exits above
  the first cervical vertebra).
• All the other spinal nerves (C8, T, L, S,Co)
  leave below their corresponding vertebra.

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Spinal Cord and Vertebrae
YellowCSF

• Vertebral Column Longer Than Spinal Cord
• Conus Medullaris
• End of Spinal Cord at L2
• Cauda Equina (Horses Tail nerve roots)
• Stretched nerve root fibers from L3 to S5
• Filum Terminale - fibrous tissue
• Stretched Spinal Cord Remnant Attached to Coccyx
• Cauda equina
• Contains Lumbosacral Cistern
• Fluid Filled Space for Spinal Puncture
• Spinal cord stops growth during infancy, spine
  grows through adolescence.

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Lumbar Nerves
L1
Conus medullaris
L2
Cauda equina (horses tail) saddle area,
sphincters, parasympathetic Bladder/bowel
L3
L4
L5
Filum terminale
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Sacral Nerves
S1
S2
S3
S4
S5
Co
Filum terminale coccygeal ligament. connective
tissue (pia mater) From medullary cone to the
termination of the vertebral canal.
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Meninges

• "The meninges PAD the brain and spinal column."
  -- Pia Arachnoid Dura.
• Dentate Ligaments
• The pia mater has 21 pairs of denticulate
  ligaments which attach it to the arachnoid and
  dura maters.
• provide stability for the spinal cord against
  motion within the vertebral column.

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Spinal Cord

• Internal Structure
• White Matter outer parts of the cord
• Gray Matter Horns and Commissures the internal
  sections
• Varies in Shape With Level of Spinal Segment
• Dorsal Root and Root Ganglia
• Ventral Root

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Spinal Nerves

• Exit Vertebra Through Intervertebral Foramina
• Dorsal and Ventral Rami Form Spinal Nerve
• Dorsal Roots - Sensory Information
• Ventral Roots - Motor Information
• Except between T-2 and T-11, Ventral Roots Form
  Plexi to Serve Groups of Muscles
• A nerve plexus is a network of intersecting
  nerves. They combine sets of spinal nerves that
  serve the same area of the body into one large
  grouped nerve.

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Cross Section

• Gray matter of the Spinal Cord
• Dorsal Horn
• Ventral Horn

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Cross sections
L4
T2
White Matter (tracts)
S3
Gray Matter (interneurons)
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Motor Units

• Lower Motor Neuron
• Lower motor neurons (LMNs) are the motor neurons
  bring the nerve impulses from the upper motor
  neurons out to the muscles.
• Path for Efferent Impulses
• Final Common Pathway (to Muscles)
• Four Components
• Motor Cell body
• Efferent Fiber
• Motor End Plate - Myoneural-Neuromuscular
  Junction
• Muscle Fibers Innervated by Axon

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Tracts of Spinal Cord

• Neural impulses are carried through white matter
• Three Major Bundles
• Dorsal Column Primarily Ascending Fibers
• Lateral Ascending and Descending Fibers
• Anterior (aka Ventral) Ascending and Descending
  Fibers

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Descending Tracts

• Pyramidal (aka Corticospinal) Tracts
• From cortex Betz Cells (large pyramidal cells)
  in precentral gyrus.
• Through Internal Capsule, Pes Pedunculi, Pontine
  Nuclei, Pyramidal Decussation (medulla) 90
  decussate, Spinal Cord
• Extrapyramidal Tract
• not directly from motor or premotor cortex
• Autonomic Pathways
• pathways from thalamus to spinal cord and
  brainstem regulates motor functions of the
  sympathetic and parasympathetic systems
  (inspiration, vomiting, and coughing reflexes)

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Upper Motor Neurons

• Upper motor neurons motor neurons that are NOT
  directly responsible for stimulating the target
  muscle

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Upper Motor Neurons

• Upper motor neurons Tracts
• Cortico-spinal motor cortex to spinal nerve
  roots fine voluntary movements
• Corticobulbar Cortex to pons and medulla
  involuntary maintenance of posture
• Tectospinal Superior Colliculus to lower motor
  neurons. Involuntary correction of head to visual
  stimuli
• Rubrospinal red nucleus to LMN
• Vestibulospinal vestibular nuclei- responsible
  for adjusting posture to maintain balance.
• Reticulospinal reticular formation - balance

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Corticospinal fibers
LCT

• Lateral Corticospinal Tract
• Control of Skeletal Muscle (Fingers, Toes,
  Forearm)
• Skilled Manipulations
• 90 Decussate and Form Alpha Fibers in Ventral
  Horn
• Anterior Corticospinal Tract (AKA ventral
  corticospinal tract)
• 8-10 Fibers That Did Not Cross Midline
• Cross at Spinal Horn
• Control Axial and Girdle Muscles responsible
  for moving head axial movement of head and trunk

ACT
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Descending Tracts

• Tectospinal Tract
• Response to Visual Stimulation
• Superior Colliculus to Cervical Spinal Cord
• Rubrospinal Tract
• Regulation of Muscle Tone Against Gravity
• Red N. To Motor Nerve Cells in Ventral Horn
• Vestibulospinal Tract
• Reflexive Adjustment of Body and Limbs
• Vestibular N. To Spinal Cord
• Reticular Descending Tract
• Alteration of Muscle Tone

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Descending Autonomic Tracts

• Hypothalamus
• Projects to Brainstem and Spinal Visceral Nuclei
• Regulate Autonomic Function of Sympathetic and
  Parasympathetic Systems

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Ascending (Sensory) Tracts

• Fasciculus Gracilis
• Fasciculus Cuneatus
• Anterior Spinothalamic Tract
• Lateral Spinothalamic Tract
• Ventral Spinocerebellar Tract
• Dorsal Spinocerebellar Tract
• Cuneocerebellar Tract
• Spinotectal Tract
• Spinoreticular Tract

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Types of Motor Nerve Cells

• Anterior Motor Neurons exit at the ventral
  horns
• Alpha and Y (Gamma) Motor Nerve Cells
• Lower Motor Neurons (Below 2nd Level in Neuronal
  Pathway)
• Interneurons
• Association Cells Connecting Sensory and Motor
  Neuron Pools
• Often Part of Reflexive Action

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Motor Neurons

• Alpha Neurons
• Major Motor Neurons
• Small
• Responsible for Voluntary and Reflexive Movements
  of Head, Trunk and Extremities
• One Fiber Can Innervate 200 Muscles fibers
• Y-Motor Neurons
• Smaller and Fewer
• Controlled by Reticular and Vestibular Systems

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Interneurons

• 30 Times More Than Motor Neurons
• Filter of Sensory and Motor Function
• Function As Inhibitory Cells and Association
  Cells

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Motor functions of the spinal cord

• Reflexive Motor Response
• Stereo-Typical (Rote) Response to Stimulus
• Involves Muscle Spindles, Afferent Fibers, Alpha
  Motor Neurons, Efferent Fibers and Muscles
• Independent of Voluntary Control
• Upper Centers Become Involved to Smooth Reaction
  and Return body to homeostasis

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• Muscle Receptors
• Two Types of Receptors
• Muscle Spindle
• Sensor inside muscle
• Detects and Maintains Muscle Tension
• Golgi Tendon Organs
• Sensor on tendon
• Monitors Degree of Muscle Tension During
  Contraction
• Prevents Too Much Tension

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Spinal Reflexes

• Stretch Reflex i.e. knee reflex
• Tap Patella causing tendon change (y motor
  neuron)
• Muscle spindles stimulate alpha motor neuron
  response, and muscle contracts
• Occurs at the L3 level
• Withdrawal (Flexor) Reflex i.e. Touching Hot
  Stimulus
• Protective Response to pain
• Flexion of leg or arm
• Stimulus, receptor, substantia gelatinosa,
  interneurons and alpha neuron response

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Spinal Reflexes

• Crossed (Intrasegmental) Extensor Reflex
• Protective response
• Involves both sides of the body
• As one arm is withdrawn, the other arm is
  extended
• Multisynaptic because it involves opposite body
  parts
• An example of this is when a person steps on a
  nail, the leg that is stepping on the nail pulls
  away, while the other leg takes the weight of the
  whole body.

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Neurotransmitters

• Spinal Cord (excitatory)
• Epinephrine
• Norepinephrine
• Serotonin
• PNS
• Acetylcholine

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Clinical Considerations

• Many Sources of Lesions
• Trauma
• Tumors or Infections
• Degenerative Conditions
• Compare the Function of One Side to the Other
• Hyper Quality of Movement (Spastic) (Upper Motor
  Neuron Problems)
• Hypo Quality of Movement (Spinal or Spinal Nerve
  Level - Lower Motor Neuron) Causing Flaccid
  Paralysis
• Absent Reflexes and Atrophy or Muscle Wasting

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Common Spinal Syndromes

• Complete Spinal Transection
• Dislocations, tumor, myelitis
• Function lost below the lesion
• After a period of time, reflexes may become
  spastic in nature
• Brown-Sequard Syndrome (cord tumor, trauma,
  ischemia)
• Lesion on ipsilateral half of body, ipsilateral
  sensory loss, contralateral pain and temperature
  sensation loss
• Syringomyelia
• Developmental condition cyst formation within
  spinal cord with loss of sensation and muscle
  control usually starts between ages 25-40