Spinal Cord, Spinal Nerves, and Somatic Reflexes - PowerPoint PPT Presentation

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Spinal Cord, Spinal Nerves, and Somatic Reflexes

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Spinal Cord, Spinal Nerves, and Somatic Reflexes Functions of the Spinal Cord Conduction sends information up and down the cord Locomotion Reflexes ... – PowerPoint PPT presentation

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Title: Spinal Cord, Spinal Nerves, and Somatic Reflexes


1
Spinal Cord, Spinal Nerves, and Somatic Reflexes
2
Functions of the Spinal Cord
  • Conduction sends information up and down the
    cord
  • Locomotion
  • Reflexes involuntary responses to stimuli

3
Anatomy of the Spinal Cord
  • Occupies C1 through L1 starting at the foramen
    magnum
  • Cauda equina
  • Filum terminale
  • Divided into 4 regions
  • Cervical
  • Thoracic
  • Lumbar
  • Sacral

4
Meninges
  • Enclose the spinal cord
  • Three layers
  • Dura mater superficial
  • Arachnoid mater
  • Pia mater deep
  • Space between
  • Epidural between dura mater and vertebral bone
  • Subarachnoid between arachnoid and pia mater

5
Nervous tissue
  • Gray matter
  • Contains somas, dendrites, and synapses
  • Little myelin
  • Site of information processing
  • White matter
  • Contains nerve fibers (axons)
  • Abundance of myelin
  • Carry signals from one part
  • of the CNS to another

6
Gray Matter
  • Looks like a butterfly
  • 2 dorsal horns
  • 2 ventral horns
  • Central canal
  • Spinal nerve branches into a dorsal root and
    ventral root
  • Dorsal root
  • Ventral root

7
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8
White Matter
  • Surrounds the gray matter
  • Bundles of axons that provide avenues of
    communication up and down the spinal cord
  • Bundles are arranged in three pairs of columns
  • Dorsal
  • Lateral
  • Ventral
  • Each column has subdivisions called tracts

9
Spinal Tracts
  • Ascending
  • Travel across three neurons from their origin in
    the receptors to their destination in the sensory
    areas of the
  • First-order neuron detects stimuli and sends it
    to the spinal cord or brainstem
  • Second-order continues to the thalamus at the
    upper end of the brainstem
  • Third-order carries the signal to the sensory
    region of the cerebral cortex

10
Spinal Tracts
  • Descending
  • Two neurons
  • Upper motor neuron begins with a soma in the
    cerebral cortex or brainstem
  • Lower motor neuron where the axon terminates
    from the above mentioned soma and travels to the
    muscle or target organ

11
Spinal Nerves
  • 31 pairs
  • 8 cervical
  • 12 thoracic
  • 5 lumbar
  • 1 coccygeal
  • Spinal nerves are mixed nerves carries signals
    both ways
  • Afferent signals approach the cord by the dorsal
    root and enter the dorsal horn of the gray matter
  • Efferent signals begin at the somas in the
    ventral horn and leave the spinal cord by the
    ventral root

12
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13
  • Plexuses weblike
  • nerve bundle
  • Cervical plexus
  • Brachial plexus
  • Lumbar plexus
  • Sacral plexus
  • Coccygeal plexus
  • Dermatome an area of skin innervated by a nerve
  • Can assess spinal nerve damage

14
Reflexes
  • What is a reflex?
  • Four properties of a reflex
  • Stimulation response to sensory input
  • Quick
  • Involuntary
  • Sterotyped
  • Somatic versus Visceral reflexes
  • Involuntary contraction of a muscle
  • Unlearned skeletal muscle reflex that are
    mediated by the brainstem and spinal cord

15
Reflex Arc
16
Proprioceptors
  • Somatic reflexes are initiated by proprioceptors
  • Muscle spindles proprioceptors in skeletal
    muscles that respond to stretching of the muscle
  • Stretch reflex -
  • Reciprocal inhibition a reflex phenomenon that
    prevents muscles from working against each other
    by inhibiting antagonists

17
Proprioceptors
  • Flexor reflex withdrawal of a limb from an
    injurious stimulus
  • Crossed extensor reflex contraction of extensor
    muscles in the limb opposite from the one that is
    flexed
  • Golgi tendon reflex response to excessive
    tension on a tendon inhibits muscle so it does
    not contract stronger
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