Spinal Cord and PNS

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Spinal Cord and PNS

• SENSORY, MOTOR, AND INTEGRATIVE SYSTEMS
• BIOL 242

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Spinal cord

• 42-45cm long
• External Structures
• Meninges
• Pia mater denticulate ligaments - prevent die to
  side movement
• Arachnoid mater (spinal tap)
• Dura mater - Epidural space
• Cervical enlargement - C4 to T1 N to and from the
  upper extremities
• Lumbar enlargement - T9 to T12 N to and from the
  lower extremities
• Conus Medullaris - cone point
• Filum terminal - extension of pia matter,
  attaches to coccyx
• Cauda Equina - where the rest of the nerves come
  off
• Development - up until 4 years old elongates
  and enlarges
• then just enlarges and produces the cauda equina
• Anterior Median Fissure and Posterior Median
  Sulcus
• makes R/L sides
• Dorsal Root DRG Ventral Root
• Spinal Nerves - dermatomes 31 segments

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Internal structure - structurally and
functionally integrated w/brain

• Gray matter - unmyelinated neurons and supporting
  cells - inner portion
• dorsal and ventral horns - H or butterfly shape
• anterior - nerve cell bodies of somatic motor
  neurons
• axons go out ventral root to skeletal muscles
• thickness varies as to number of neurons going
  out
• more to limbs, less to other areas
• ANS Sympathetic connections to visceral
  organs
• axons leave from ventral root

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The ANS regulates

• Muscles
• in the skin (around hair follicles smooth
  muscle)
• around blood vessels (smooth muscle)
• in the eye (the iris smooth muscle)
• in the stomach, intestines and bladder (smooth
  muscle)
• of the heart (cardiac muscle)
• Glands
• The ANS is divided into three parts
• The sympathetic nervous system
• The parasympathetic nervous system
• The enteric nervous system.

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Gray matter

• unmyelinated neurons and supporting cells - inner
  portion
• dorsal and ventral horns - H or butterfly shape
• posterior - arrival of sensory input through
  dorsal root
• DRG prior
• after enter cord take a number of routes
  up/down, across
• lateral horns - only in the thoracic, upper
  lumbar, and some sacral

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• Gray Commissure - cross bar of the H, encloses
  central canal
• White matter - myelinated axons that ascend and
  descend
• outer portion
• sensory (ascending) and motor (descending)
  neurons and
• commissural (one side to other)
• Funiculi (columns) - three on each side
• anterior posterior lateral
• Multiple sclerosis - appears 1st in lateral and
  posterior columns
• Tracts - common origin, termination, and function
  -
• groups of neuron fibers
• most cross over at some point
• most are chain of 2-3 neurons,
  contribute to successive tracts
• map out the body somatotopy
• all are paired w/ R and L sides
• Found in white matter of cord names give origin
  and destination
• Anterior White Commissure - connects R and L of
  the white matter
• Central canal - length of cord, connected to 4th
  ventricle

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• Nuclei clusters of neuron cell bodies
  w/neuroglia
• Dorsal and ventral roots continue to form spinal
  nerves

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Poliomyelitis

• gray matter and inflammation
• destruction of anterior horn motor neurons
• fever, head ache, muscle pain, then loss of motor
  control, later paralysis
• may also affect the medulla

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Disorders

• Paralysis - loss of motor function
• Paresthesias - loss of sensation
• Flaccid - loss to skeletal muscles, atrophy
• Spastic - spinal motor neurons intact
• just not under voluntary control
• Transections - paraplegia - lower limbs,
  quadriplegia
• Neuritis - inflammation - trauma to spinal cord
• Sciatica - neuritis to sciatic n. - often slipped
  disc
• Herpes Zoster (Shingles) - dorsal roots of
  thoracic n's
• pain, blisters, discolored skin
• ID via Dermatomes
• Genital Herpes - dorsal root of S2 and/or S3 -
  pain, pustules
• Meningitis - bacteria or viral
• Epidural blocks - anesthesia to block pain -
  usually lumbar or sacral
• Multiple sclerosis - lateral and posterior tracts
• Polio viral

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Spinal Cord Physiology

• White travel ways Gray receive and integrate
  info
• Sensory and Motor Tracts
• Three sensory major pathways
• segmental reflexes to regulate posture and
  movement
• branches of sensory afferent
• remain w/in a given segment of cord
• interneurons
• Spinothalamic - lateral and anterior
• pain, crude touch, temp. and deep pressure
• slow pain - slower pathway then Posterior
  column
• cross spinal cord upon entrance and go up
  opposite side
• land on nonspecific nuclei - do reach the cortex
  directly
• brain limbic system mediate perception
• not able to localize
• not conscious sensation
• abnormalities - referred pain, phantom limb pain

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Spinal Cord Physiology

• sensory neurons
• Posterior Column
• Fasciculus gracilis (delicate)
• F. cuneatus (wedge shape) or Dorsal White
• direct pathway somatosensory axons
• don't synapse until medulla, then decussate and
  go to thalamus
• then area of cortex (L Hemisphere)
• conscious sensation
• as fibers enter going up cord, the early ones
  pushed in (medial)
• - maps out body w/in pathway
• thalamus has specific areas to map out body also
• proprioreception, movement of muscles, joints,
  and tendons
• fine/discrimination touch
• touch and pressure, 2 point
  discrimination
• vibrations

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Spinal Cord Physiology

• interneurons
• Anterior and Posterior Spinocerebellar
• proprioception to cerebellum - then coordinates
  muscle activity
• no conscious sensation
• decussation may occur or not at all
• Sensory information ? CNS where it is interpreted
  and acted upon
• Association neurons help interpret info in the
  spinal cord
• largest number of neurons located in CNS
• link sensory input w/motor output

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Motor Output in two tracts

• Pyramidal shape as it passes through medulla
• lateral corticospinal and anterior corticospinal
• part of pyramidal system
• direct pathways - fewer synapses
• impulses from cortex to limbs - voluntary
  control
• most cross to supply the other side
• highly evolved humans primates use of fingers
• precise or skilled movement - thread a needle
• Disease amyotrophic lateral sclerosis Lou
  Gerhig's disease
• destroys pyramidal tracts produces paralysis
• lose ability to speak, swallow, and breathe
• gene defect that directs production of
  superoxide dismutase
• enzyme to protect cell from ravages of free
  radicals
• treat w/antioxidants

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Motor Output in two tracts

• Extrapyramidal slower, polysynaptic
• rubrospinal - Red nucleus --gt
• crosses in midbrain --gt
• runs parallel to lateral corticospinal
• serves contralateral side of body
• muscle tone of distal limbs
• modifies or directs skeletal muscle contractions
• modifies pyramidal commands
• tectospinal - midbrain (superior colliculus) ?
  down ?lateral gray
• may or may not decussate
• coordinate head and eyes to visual targets
• reflexive movements
• visual and auditory sensations from midbrain
• project to both sides of body

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Motor Output in two tracts

• Extrapyramidal slower, polysynaptic
• rubrospinal
• tectospinal
• Vestibulospinal - medulla
• muscle tone of postural muscles and moves head
• balance during standing and moving
• Reticulospinal - from reticular formation
• regulates "awareness" of posture
• controlled unskilled movements
• sever corticospinal tracts ? fine
  movement control is lost
• able to walk because medial pathways unaffected
• sever medial motor tracts? overall
  posture is lost and manipulation of fingers
• may aid by supply external
  support for fine movement to work

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Spinal Reflexes

• predictable motor responses to stimuli,
  automatic,
• w/o help of brain - may or may not be conscious
• may be inborn or learned/acquired (driving a car)
• may alter - not drop hot pot if young child is
  nearby
• negative feedback systems
• Classifications
• Development - Innate reflexes from development
• predictable, simple, genetically programmed
• Acquired - from learning
• repeated actions
• Processing sites - spinal or cranial

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Reflex arc
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Spinal Reflexes

• stay in cord an do not use brain to respond
• may require "advice" from brain or act solely
• test of somatic reflexes - indicates status of
  spinal cord
• Ipsilateral reflex - stays on the same side
• Contralateral reflex goes to opposite side

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Stretch Reflex

• monosynaptic contraction of a muscle that was
  suddenly stretched
• Type A fibers - fastest and deal with position
  and balance
• Muscle spindles produce impulse to stretching
• ? thru somatic sensory
• ? posterior root of spinal n. to cord
• ? excitatory synapse w/motor neuron in the
  anterior gray horn
• ? strong enough impulse
• ? motor axon in the anterior root of the spinal
  cord
• ? effector where muscle is stretched
• Muscle tone - amount of stretch in muscles, set
  by the brain
• posture and location - postural reflexes
• Prevents overstretching during exercise
• Neurological exam - patellar reflex

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Golgi Tendon Reflex

• control tension of muscles and tendons
• polysynaptic
• sensory ? spinal cord ? inhibitory at the synapse
  to the motor neuron ?hyperpolerization and stop
  motor AP

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Intersegmental reflex

• sensory stimuli ascend and descend and stimulate
  other neurons in different segments of spinal
  cord
• Ipsilateral or contralateral
• one sensory neuron ? several motor neuron

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Withdrawal Reflex

• pain of touching a hot stove
• painful stimulus
• contraction of muscles to pull away
• relaxation of others to make easy to pull away
• override other reflexes - for survival

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Contralateral reflex

• sensory impulses enter one side and exit another
• step on a tack do not fall over

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PERIPHERAL NS

• Cranial N - 12 pairs - look at text
• embryonic extension of cerebrum
• afferent and efferent
• Spinal N - 31 pairs 8 cervical, 12 thoracic, 5
  lumbar, 5 sacral, 1 coccygeal
• go through the intervertebral foramen
• named for vertebra that follow the nerve
• mixed nerves - both sensory and motor