BIOLOGY 2401 ANATOMY

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BIOLOGY 2401ANATOMY PHYSIOLOGYPART I

• Ch 12 Spinal Cord and Spinal Nerves

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Spinal Cord

• CNS tissue is enclosed in the vertebral column
• Protected by bone, meninges, and cerebrospinal
  fluid (CSF)
• Epidural space space between the vertebrae and
  the dural sheath (dura mater)

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THE MENINGES

• The meninges are a set of 3 connective tissue
  layers that surround the brain and spinal cord.
• The dura mater toughest outermost
• The arachnoid mater middle layer containing
  most major blood vessels and cerebrospinal fluid.
• The pia mater inner most layer with fine blood
  vessels.

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Meninges
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Spinal Cord

• Cervical and lumbosacral enlargements sites
  where nerves serving the limbs emerge
• Conus medullaris terminal portion of the spinal
  cord
• Cauda equina collection of nerve roots at the
  inferior end of the vertebral canal
• Spinal nerves 31 pairs

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Spinal Gray Matter

• Gray matter consists of soma, unmyelinated
  processes, and neuroglia
• Gray commissure connects masses of gray matter
  encloses central canal
• Posterior (dorsal) horns interneurons (sensory)
• Anterior (ventral) horns some interneurons but
  mostly somatic motor neurons
• Lateral horns contain autonomic nerve fibers

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Gray Matter and Spinal Roots
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Cross Section of Spinal Cord
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Reflex Arc

• Basic functional unit of nervous system and
  simplest portion capable of receiving a stimulus
  and producing a response
• Automatic response to stimulus, occurs without
  conscious thought.
• Components
• Action potentials produced in sensory receptors
  transmitted to
• Sensory neuron. To-
• Interneurons. To-
• Motor neuron. To-
• Effector organ which responds with a reflex

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Variety of Reflexes

• Some integrated within spinal cord some within
  brain
• Some involve excitatory neurons yielding a
  response some involve inhibitory neurons that
  prevent an action
• Higher brain centers can influence, suppress, or
  exaggerate reflex responses

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Spinal Nerve Organization

• Dorsal half sensory roots and ganglia
• Ventral half motor roots
• Dorsal ventral roots fuse laterally to form
  spinal nerves

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Cross-Sectional Anatomy of Spinal Cord
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Spinal Nerves

• 31 pairs of mixed nerves supply all parts of body
  except head
• Named according to their point of issue
• 8 cervical (C1-C8)
• 12 thoracic (T1-T12)
• 5 Lumbar (L1-L5)
• 5 Sacral (S1-S5)
• 1 Coccygeal (C0)

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Spinal Nerves Roots

• Each spinal nerve connects to the spinal cord via
  two medial roots
• Each root forms a series of rootlets that attach
  to the spinal cord
• Ventral roots arise from the ventral horn and
  contain motor (efferent) fibers
• Dorsal roots arise from sensory neurons in the
  dorsal root ganglion and contain sensory
  (afferent) fibers

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Spinal Nerves Roots
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Nerve Plexuses

• All ventral rami except T2-T12 form interlacing
  networks called plexuses
• Plexuses are found in the
• cervical,
• brachial,
• lumbar,
• and sacral regions
• Each resulting branch of a plexus contains fibers
  from several spinal nerves
• Each muscle receives a nerve supply from more
  than one spinal nerve
• Damage to one spinal segment cannot completely
  paralyze a muscle

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Cervical Plexus

• The cervical plexus is formed by ventral rami of
  C1-C4
• Most branches are cutaneous nerves of the neck,
  ear, back of head, and shoulders
• The most important nerve of this plexus is the
  phrenic nerve - major motor and sensory nerve of
  the diaphragm

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Cervical Plexus
Figure 13.8
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Brachial Plexus

• Formed by C5-C8 and T1 (C4 and T2 may also
  contribute to this plexus)
• It gives rise to the nerves that innervate the
  upper limb
• 5 major ones
• Axillary
• Radial
• Musculocutaneous
• Ulnar
• Median

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Brachial Plexus

• C4 from cervical plus C5-T1
• Five ventral rami form
• three trunks that separate into six divisions
  then form
• three cords that give rise to
• Branches/nerves
• Axillary
• Radial
• Musculocutaneous
• Ulnar
• Median
• Smaller nerves, too.

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Brachial Plexus Distribution of Nerves
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Lumbosacral Plexus(Lumbar and Sacral Plexuses)

• Arises from L1-L4 L4-S4 and innervates the
  thigh, abdominal wall, psoas muscle, the buttock,
  lower limb, pelvic structures, and the perineum
• The major nerves are the
• Femoral (Lumbar)
• Obturator (Lumbar)
• Sciatic (Sacral)
• Tibial
• Common fibular (peroneal)

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Practice Questions
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• Which of the following is NOT a nerve plexus? 
• The thoracic rami 
• The lumbosacral plexus 
• The cervical plexus  
• The brachial plexus 

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• Which of the following nerves does NOT arise from
  the brachial plexus? 
• The musculocutaneous nerve 
• The radial nerve 
• The axillary nerve 
• The ulnar nerve 
• The phrenic nerve

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• The muscle fiber or gland cell that responds to
  the efferent impulses is known as the  
• Effector  
• Motor neuron 
• Integration center 
• Sensory neuron 
• Receptor

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• The basic pattern of the CNS in the spinal cord
  is a central cavity surrounded by a gray matter
  core and a white matter layer lying outside of
  that.  True False

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• Although the pairs of spinal nerves correspond to
  the number of vertebrae in the each area, there
  are eight pairs of cervical cranial nerves, but
  only seven cervical vertebrae.  True False

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• Each muscle in a limb receives its nerve supply
  from one spinal nerve.  True False

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• A sensory neuron transmits afferent impulses to
  the CNS.  True False