SHLD500 Neuroanatomy for the SpeechLanguage Pathologist

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SHLD500 Neuroanatomy for the Speech-Language
Pathologist

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I. Organization of the Nervous System

• The nervous system is the bodys principal
  control and integrating center.
• It serves three broad functions sensory,
  integrative, and motor.
• It senses changes within the body and in the
  outside environment.
• It interprets the change.
• It responds to the interpretation by initiating
  action by muscular contraction or glandular
  secretion.
• Through sensation, integration, and response, the
  nervous system rapidly maintains the bodys
  homeostasis.

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A. Divisions of the Nervous System

• The nervous system has two principal divisions
• the central nervous system (CNS) and
• the peripheral nervous system (PNS).

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1. The Central Nervous System

• The CNS is command central for the entire
  nervous system.
• It consists of the brain and the spinal cord.

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1. The Central Nervous System Brain

• The term brain comes from the old Anglo-Saxon
  word braegen which means the center of the
  nervous system.
• In Greek, the word enkephalos pertains to the
  mass of nerve tissue housed within the bony
  confines of the head and provides the root word
  encephalon.
• The brain is responsible for higher level human
  functions such as reasoning and language.

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1. The Central Nervous System Brain

• The brain is one of the bodys largest organs,
  weighing about three pounds.
• It is mushroom-shaped and is divided into four
  principal parts the brainstem, the diencephalon,
  the cerebrum, and the cerebellum.

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1. The Central Nervous System Brain

• The brainstem is like the stalk of the mushroom.
• The lower end is continuous with the spinal cord.
• As it ascends from the spinal cord, it has three
  divisions the medulla oblongata, the pons, and
  the midbrain.

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1. The Central Nervous System Brain

• Above the brainstem, the diencephalon consists
  primarily of the thalamus and hypothalamus.
• The cerebrum spreads over the diencephalon,
  constituting about 7/8 of the total brain, and
  occupying most to the cranium.

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1. The Central Nervous System Brain

• Below the cerebrum and behind the brainstem is
  the cerebellum.

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1.The Central Nervous System Spinal Cord

• The spinal cord begins as a continuation of the
  medulla from where it exits the cranium at the
  foramen magnum of the occipital bone.

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1.The Central Nervous System Spinal Cord

• It continues for approximately 16-18 to end at
  the level of the upper border of the second
  lumbar vertebra.

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1.The Central Nervous System Spinal Cord

• The cord serves as a conduit for the ascending
  and descending fiber tracts that connect the
  peripheral and spinal nerves with the brain.
• It is functionally segmented into 31 sections,
  which each give rise to a pair of spinal nerves.

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1.The Central Nervous System Spinal Cord

• The adult spinal cord is about 1 in
  circumference, except in the mid-cervical and
  mid-lumbar regions where it is slightly larger.
• The superior enlargement is termed the cervical
  enlargement.
• It extends from C4 to T1.
• Nerves serving the upper extremities arise from
  this area of the spinal cord.
• The inferior enlargement is termed the lumbar
  enlargement, extending from T9-T12.
• Nerves serving the lower extremities arise from
  this area of the spinal cord.

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1.The Central Nervous System Spinal Cord

• Below the lumbar enlargement, the spinal cord
  tapers off between L1 and L2 into a conical
  portion known as the conus medullaris.

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1.The Central Nervous System Spinal Cord

• From the conus medullaris, the filum terminale, a
  non-nervous fibrous tissue, extends to attach to
  the coccyx.
• Nerves arising from the lower portion of the cord
  must angle inferiorly in the vertebral canal
  before leaving it.

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1.The Central Nervous System Spinal Cord

• Because it looks likes wisps of coarse hair
  flowing from the end of the cord, it is aptly
  named cauda equinahorses tail.

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2.The Peripheral Nervous System

• The PNS consists of all nervous tissue found
  outside of the bony confines of the skull and
  vertebral column.
• The PNS serves the communication link between the
  body and the CNS.
• The PNS connects the brain and spinal cord with
  receptors, muscles, and glands.
• The PNS is broadly divided into spinal and
  cranial nerves.

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2.The Peripheral Nervous System

• There are direct connections between the brain
  and the cranial nerves, and the spinal cord and
  the spinal nerves.
• The PNS is also divided into afferent and
  efferent systems.
• The afferent system consists of nerve cells that
  convey information from receptors in the
  periphery of the body to the CNS.
• The efferent system consists of nerve cells that
  convey information from the CNS to skeletal
  muscles and glands.

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2.The Peripheral Nervous System Spinal Nerves

• There are 31 pairs of spinal nerves named and
  numbered according to the region and the level of
  the spinal cord from which they emerge.
• There are eight pairs of cervical nerves, 12
  pairs of thoracic nerves, 5 pairs of lumbar
  nerves, 5 pairs of sacral nerves, and 1 coccygeal
  spinal nerve pair.

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2.The Peripheral Nervous System Spinal Nerves

• C1 emerges between the occipital bone and the
  atlas.
• All other spinal nerves leave the vertebral
  column from the intervertebral foramina between
  the adjoining vertebrae.

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2.The Peripheral Nervous System Spinal Nerves

• Each spinal nerve as two points of attachments or
  roots.
• The posterior root contains the sensory fibers.
• The anterior root contains the motor fibers.

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2.The Peripheral Nervous System Spinal Nerves

• Peripheral nerves to and from the spinal cord
  segregate their sensory and motor neurons.
• Sensory neurons enter the cord dorsally, through
  the dorsal or posterior root.
• Motor neurons leave the cord ventrally, through
  the ventral or anterior root.
• Then the sensory and motor components fuse
  together to form the peripheral nerve.

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2.The Peripheral Nervous System Spinal Nerves

• This principlethat the dorsal nerve root is only
  sensory and the ventral nerve root only motoris
  named the Bell-Magendie Law for Sir Charles Bell
  and Francois Magendie who first stated it.
• The spinal nerves act on visceral or somatic
  structures.
• The functional component of a given spinal nerve
  fits one of four categories.

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2.The Peripheral Nervous System Spinal Nerves

• General somatic afferent nerves convey
  information about pain, temperature, and
  mechanical stimuli from receptors in the skin,
  muscles, and joints.
• General visceral afferent nerves convey
  information from receptors in visceral
  structures, e.g., walls of the digestive tract.
• General visceral efferent nerves convey
  information to an autonomic nerve fiber.
• General somatic efferent nerves convey
  information to a skeletal.

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2.The Peripheral Nervous System Cranial Nerves

• There are 12 pairs of cranial nerves.
• All pairs leave the cranium through the foramina
  of the skull.
• They are designated with Roman numerals and
  names.
• The Roman numerals indicate the level at which
  the nerve arises from the brain.
• The name indicates the nerve distribution or
  function.

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2.The Peripheral Nervous System Cranial Nerves

• I-Olfactory II-Optic
• IIIOculomotor IV-Trochlear
• V-Trigeminal VI-Abducens
• VII-Facial
• VIII-Vestibulocochlear
• IX-Glossopharyngeal
• X-Vagus
• XI-Accessory
• XII-Hypoglossal

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2.The Peripheral Nervous System Cranial Nerves

• Based on the functional components of each nerve,
  there are three types of cranial nerves
• Somatic efferent nerves (III, IV, VI, XII)
  contain mostly fibers innervating skeletal
  musculature.
• Special sensory nerves (I, II, VIII) contain
  fibers relating to the special senses of sight,
  smell and taste, and hearing and equilibrium.
• Branchiomeric nerves (V, VII, IX, X, XI) contain
  special visceral efferents that innervate the
  striated muscles of the larynx, pharynx, and face.

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3.The Autonomic Nervous System (ANS)

• The ANS is a unique component of the PNS.
• It regulates the activities of smooth muscles,
  cardiac muscle, and certain glands.
• Through its afferents and efferents, the ANS
  automatically and involuntarily regulates
  visceral activities, such as pupillary size
  change, lens accommodation, dilation of blood
  vessels, adjustments to the rate and force of
  heartbeat, movements of the GI tract, and most
  glandular secretions.

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3.The Autonomic Nervous System (ANS)

• The three subdivisions of the ANS include
• The enteric subdivision
• The sympathetic subdivision and
• The parasympathetic subdivision.
• The enteric nervous system consists of two
  interconnected plexuses of sensory neurons,
  interneurons, and visceral motor neurons, in the
  walls of the alimentary canal.
• The enteric nervous system coordinates gut
  motility.

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3.The Autonomic Nervous System (ANS)

• The sympathetic nervous system prepares us for
  situations in which energy needs to be expended.
• Its the bodys alerting system.
• It increases our heart rate, decreases
  peristaltic actions, and diverts blood from the
  gut to the skeletal muscles.
• The parasympathetic nervous system has a calming
  effect on bodily function by decreasing heart
  rate and blood pressure, increasing intestinal
  peristalsis and salivation, and opening
  sphincters.

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3.The Autonomic Nervous System (ANS)

• The parasympathetic nervous system enhances
  energy storage through conservation and
  restoration.
• Both the sympathetic and parasympathetic nervous
  systems work with the endocrine system to
  maintain the stability of the bodys internal
  environment.

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B. Embryological Levels of the Brain

• The brain develops very rapidly during the first
  few years of life.
• Growth is mainly due to an increase in the size
  of cells already present, proliferation and
  growth of neuroglia, development of synaptic
  contacts and dendritic branching, and myelination
  of various fiber tracts.

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B. Embryological Levels of the Brain

• 1. Development of the CNS and PNS
•  The development of the NS begins at about the
  third week of life with a thickening of the
  ectoderm of the neural plate.

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B. Embryological Levels of the Brain

• 1. Development of the CNS and PNS
•  The plate folds inward and forms a longitudinal
  groove, called the neural groove.
• The raised edges of the neural plate are called
  neural folds.

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B. Embryological Levels of the Brain

• Development of the CNS and PNS
• As development continues, the folds increase in
  height, meet, and form a tube, the neural tube.

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B. Embryological Levels of the Brain

• The neural tube forms first in the region that
  will become the cervical area and then closes
  like a zipper with progression passing both
  caudally and cranially.
• The opening at the cranial end is called the
  anterior neuropore.
• The opening at the caudal end is called the
  posterior neuropore.
• Closure of the anterior neuropore takes place by
  day 24 and the posterior neuropore by day 26.

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B. Embryological Levels of the Brain

• The primitive CNS is now a hollow tubular
  structure closed at both ends.
• The fluid filled cavity of this tube is called
  the neural canal which will develop into the
  ventricular system of the brain and the central
  canal of the spinal cord.
• If the cranial portion of the neural tube fails
  to close, the result is anacephaly, and the
  overall structure of the brain is grossly
  disturbed.
• If the posterior neuropore fails to close, the
  result is spina bifida.

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B. Embryological Levels of the Brain

• 2. Development of the Cerebral Vesicles
• By the fourth week, three distinct bulges, the
  primary vesicles, appear in the anterior
  neuropore.
• From the top down, we have the prosencephalon
  (forebrain), the mesencephalon (midbrain), and
  the rhombencephalon (hindbrain).

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B. Embryological Levels of the Brain

• By the fifth week, five secondary vesicles
  develop.
• The prosencephalon divides into the two
  telecephalon, which become the cerebral
  hemispheres of the brain, and the single
  diencephalon, which gives rise to the thalamus
  and hypothalamus.

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B. Embryological Levels of the Brain

• The mesencephalon remains unchanged and becomes
  the midbrain.
• The rhombencephalon divides into the
  metencephalon, which becomes the pons and
  cerebellum, and the myelencephalon, which becomes
  the medulla oblongata.

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B. Embryological Levels of the Brain

• In addition to the development of cerebral
  structures, the vesicles also give rise to the
  ventricular system.
• Specifically, the prosencephalon develops the two
  lateral ventricles contained within the two
  cerebral hemispheres.

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B. Embryological Levels of the Brain

• The third ventricle develops within the
  diencephalon.
• The mesencephalon gives rise to the cerebral
  aqueduct.
• The rhombencephalon gives rise to the fourth
  ventricle.

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B. Embryological Levels of the Brain

• The ventricles are a continuous series of
  fluid-filled spaces extending through all major
  divisions of the CNS.
• Each lateral ventricle communicates with the 3rd
  ventricle through the intraventricular foramen.
• The 3rd ventricle communicates with the 4th
  ventricle through the cerebral aqueduct of the
  midbrain.

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B. Embryological Levels of the Brain

• Production of the cerebral spinal fluid filling
  the ventricles is manufactured by small vascular
  tufts called the choroid plexus.
• The choroid plexus are found in the roof of the
  3rd and 4th ventricles.
• The choroid plexus of the 3rd ventricle protrude
  into the lateral ventricle.

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B. Embryological Levels of the Brain

• Neurulation is the process that establishes the
  central nervous system.
• As seen in cross section, the embryonic neural
  tube forms three layers, from neurocoel (neural
  canal) outward these are the ependymal layer, the
  mantle layer, and the marginal layer.

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B. Embryological Levels of the Brain

• Some of the cells of the ependymal layer remain
  in place to become the thin, ciliated lining of
  the adult central canal, but most migrate outward
  to join mantle cells in forming both neurons and
  neuroglia.
• These will be the gray matter of the adult.

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B. Embryological Levels of the Brain

• With cell migration, the mantle layer develops
  the characteristic butterfly shape.
• The lateral walls of the tube thicken and
  maturing neurons clump into two different plates.

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B. Embryological Levels of the Brain

• The two plates are divided by a shallow,
  longitudinal groove called the sulcus limitans.
• The sulcus limitans separates the developing gray
  matter into a dorsal alar plate and a ventral
  basal plate.

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B. Embryological Levels of the Brain

• These plates signal the future locations of
  sensory and motor functions, respectively.
• Alar and basal plates become dorsal and ventral
  horns, respectively, while intermediate regions
  develop interneurons, mixed nerves.

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B. Embryological Levels of the Brain

• Finally, cells from the marginal layer mature by
  growing out their processes (axons and
  dendrites).
• This layer is penetrated by nerve fibers growing
  out of the deeper layers.
• It becomes the white matter of the adult cord.

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B. Embryological Levels of the Brain

• The brainstem develops in a manner similar to the
  spinal cord.
• From the medulla through the midbrain, alar and
  basal plates form motor and sensory columns of
  cells that supply cranial nerves.
• However, the organization of alar and basal
  plates in the brainstem differ from those of the
  spinal cord.

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B. Embryological Levels of the Brain

• In the 6 mm embryo, the thin ependymal roof of
  the neural tube, the spinal cord, becomes even
  thinner as the ventricle of the neural tube
  begins to widen in the early stages of the
  development of the 4th ventricle.
• With continued development, alar and basal plates
  shift laterally and become located in the floor
  of the ventricle.

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B. Embryological Levels of the Brain

• The sulcus limitans continues to be identifiable
  helping to mark the boundary between sensory and
  motor areas.
• In the medulla and pons, the alar plate comes to
  lie lateral to the basal plate, not dorsal to it.
• The basal plate forms the motor nuclei of the
  cranial nerves, medial to the sulcus limitans in
  the ventricular floor.

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B. Embryological Levels of the Brain

• Lateral to the sulcus, the alar plate forms
  sensory relay nuclei.
• Rostral to the midbrain, the diencephalon and
  cerebral hemispheres develop from the alar plate.
  
• The cerebellum also develops from alar plate.
• Portions of the alar plate migrate ventrally and
  form the inferior olivary nucleus, a cerebellar
  relay nucleus.