II. Neurological Neuroanatomy

1
II. Neurological Neuroanatomy

• Lecture 2

2
Neurological Histology

• Histology is the microscopic study of the
  structure of tissues.
• In the nervous system, the two broad classes of
  cells are neurons and glia.
• Within each class there are many different types
  of cells that differ based on their structure,
  chemistry, and function.

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Classes of Cells

• Neurons are the most important cells of the
  unique functions of the brain.
• They sense changes in the environment,
  communicate these changes to other neurons, and
  command the bodys responses to these sensations.

4
Classes of Cells

• Glia are thought to contribute to brain function
  mainly by insulating, supporting, and nourishing
  neighboring neurons.
• In fact, the term glia is derived from the Greek
  word for glue, giving the impression that the
  main function of these cells is to keep the brain
  from running out of our ears.

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Analogy Cookie and Brain

• If your brain were a chocolate-chip cookie and
  the neurons the chocolate chips, the glia would
  be the cookie dough that fill all the other
  spaces and ensures that the chips are suspended
  in their appropriate locations.

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Brainstem Structure and Function

• We are going to spend a bit of time looking more
  thoroughly at the structure and function of the
  brainstem.
• In particular, we will focus on cranial nerves
  and their nuclei, ascending and descending
  tracts, specific nuclei of the reticular
  formation, and other select special nuclei.

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Cranial Nerves

• Cranial nerves (CN) I Olfactory and II Optic are
  part of the forebrain.
• The other 10 cranial nerves originate in the
  brainstem.
• Some cranial nerves serve only sensory functions
  other serve only motor functions.
• Many of the nerves are mixed, serving both
  sensory and motor functions.

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Cranial Nerves

• The three main functions of the cranial nerves
  are as follows
• Motor and sensory innervation of the head and
  neck
• Innervation of special sense organs
• Innervation of the parasympathetic autonomic
  ganglia that control important visceral
  functions such as breathing, heart rate, blood
  pressure, coughing, and swallowing.

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Cranial Nerves

• An assessment of the functioning of the cranial
  nerves is an extremely important part of a
  clinical neurological examination.
• Disease states in the brain are often reflected
  in functional abnormalities of one or more of the
  cranial nerves.

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Cranial Nerves

• Since the cranial nerves originate from different
  regions in the brainstem, disorder in the
  function of one or more nerves can provide
  valuable information about the site of lesion.

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Ventrally Located Cranial Nerves

• Cranial nerves III, VI, and XII are seen exiting
  from the ventral side of the brainstem, close to
  the midline.

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Ventrally Located Cranial Nerves

• The oculomotor nerve (III) emerges at the caudal
  border of the midbrain.
• It innervates the extraocular muscles

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Ventrally Located Cranial Nerves

• The abducens nerve (VI) emerges at the caudal
  border of the pons.
• It also innervates the extraocular muscles

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Ventrally Located Cranial Nerves

• The hypoglossal nerve (XII) emerges from the
  medulla just lateral to the medullary pyramids.
• It innervates the intrinsic muscles of the tongue

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Dorsally Located Cranial Nerve

• Only one cranial nerve, the trochlear nerve (IV)
  exits from the dorsal aspect of the brainstem.
• The trochlear nerve exits from the midbrain just
  below the inferior colliculus near the midline to
  innervate the superior oblique muscle of the eye.

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Laterally Located Cranial Nerves

• The 8 remaining cranial nerves exit laterally
  from the brainstem.
• The trigeminal nerve (V) exits the pons.
• It mediates sensation from facial skin and
  innervates the muscles of mastication.

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Laterally Located Cranial Nerves

• The facial (VII) and the vestibulocochlear (VIII)
  nerves originate at the junction between the pons
  and medulla.

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Laterally Located Cranial Nerves

• The glossopharyngeal (IX), vagus (X), and
  accessory (XI) nerves arise in the medulla as a
  series of fine rootlets just dorsal to the
  inferior olive.

19
Functional Classification of CNs

• Cranial nerves serve general motor and general
  sensory functions as well as special functions
  resulting from the use of special receptors and
  neurons.
• The general and special function of CNs can be
  further classified by
• whether the nerve innervates somatic muscles or
  visceral structures
• Whether it is involved in sensory (afferent) or
  motor (efferent) information.

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Functional Components of NS
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Functional Components of NS
22
Cranial Nerve Nuclei

• As in the spinal cord, the cell bodies of motor
  and sensory neurons differ in location from one
  another.
• The cell bodies of motor neurons that send their
  axons into the cranial nerves are located within
  the brainstem.
• The cell bodies of the afferent fibers in the
  cranial nerves lie outside the brainstem, either
  in ganglia or in specialized end-organs such as
  the eye.

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Cranial Motor Nuclei

• The cranial motor nuclei of all general somatic,
  general visceral, and special somatic motor
  neurons (shown in red) are located in the
  brainstem.
• These cranial motor neurons are called lower
  motor neurons.

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Cranial Nuclei Organization

• Cranial nerve nuclei are organized into seven
  longitudinal columns rostrocaudally in the
  brainstem according to function.

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Somatic Efferent Column

• CN nuclei III, IV, VI, and XII that innervate
  somatic muscles in the head derived from myotomes
  are situated close to the midline and immediately
  ventral to the floor of the fourth ventricle
  (red).

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Special Visceral Efferent Column

• CN nuclei V, VII, IX, X, and XI that innervate
  the branchiomeric muscles are displaced ventrally
  and laterally from the somatic motor column
  (orange).
• The cell bodies of CNs IX and X are clustered in
  a single group called the nucleus ambiguus.

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Nucleus Ambiguus

• The nucleus ambiguus is so named because it is
  penetrated by fibers running from the inferior
  olive to the cerebellum and is consequently
  difficult to identify in sections stained for
  cell bodies.
• Neurons in the nucleus ambiguus innervate
  striated muscles in the larynx and pharynx and
  are critical for speech and swallowing.

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General Visceral Efferent Column

• The parasympathetic neurons of CNs III, VII, IX,
  X are found immediately lateral to the somatic
  motor column (yellow).
• They regulate specific autonomic functions.

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GVE Column Functions

• The oculomotor cranial nerve (III) innervates the
  smooth muscle of the eyelid, the pupillary
  constrictor, and Muellers muscle, which holds
  the eye forward in the orbit.
• Damage to this autonomic component of the CN III
  results in eyelid droop (ptosis), pupil dilation
  (mydriasis) and the eye being drawn forward in
  the orbit (exophthalmos).

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GVE Column Functions

• The superior salivatory and inferior salivary
  nuclei are another group of general visceral
  column motor nuclei.
• The axons from the superior salivatory nucleus
  run in the root of the facial nerve (VII).
• The axons from the inferior salivary nucleus run
  in the glossopharyngeal (IX) nerve.
• Together they innervate various salivary and
  mucous glands.

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GVE Column Functions

• Finally, the dorsal motor nucleus of the vagus
  (X) CN innervates the viscera of the body the
  heart, the lungs, and the gut.
• In the gut, the CN X promotes peristalsis.

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Cranial Sensory Nuclei

• The cell bodies of the afferent fibers supplying
  the cranial nerves lie outside the brainstem.
• The sensory nuclei in the brainstem are composed
  of second order neurons that receive input from
  the primary sensory neurons.

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General Visceral Afferent Column

• Second order neuronal cell bodies of the general
  visceral afferent column (blue check) lie
  adjacent to the general visceral efferent column.

34
General Visceral Afferent Column

• They receive fibers conveying the sense of taste,
  as well as those carrying input from the larynx
  and pharynx, and the heart, lungs, and gut.
• In the medulla, this column of cells is called
  the nucleus tractus solitarius (NTS).

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Nucleus Tractus Solitarius

• The neurons conveying sensory input to the NTS
  have their cell bodies in ganglia that lie
  outside the brainstem in association with cranial
  nerves VII (facial), IX (glossopharyngeal), and X
  (vagus).
• The axons from these ganglia run into the
  brainstem and join the solitary tract which
  terminate in the NTS.

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Nucleus Tractus Solitarius

• The rostral end of the NTS is the relay for taste
  sensation.
• Axons from these nuclei synapse in the thalamus.
• From the thalamic nuclei, information about taste
  is relayed to the cerebral cortex.

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Nucleus Tractus Solitarius

• The other regions of the nucleus deal with
  cardiovascular functions.
• They have local connections with the reticular
  formation, and indirect connections with the
  limbic system in regulating autonomic tone.

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Special Somatic Afferent Column

• The SSA column (purple dots) lies lateral to the
  general visceral afferent column.
• The SSA nuclei in the caudal part of the pons and
  the rostral part of the medulla receive fibers of
  the vestibulocochlear nerve (VIII).

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Special Somatic Afferent Column

• The cochlear nuclei (CN) receive input from the
  cochlear division of CN VIII.
• The vestibular nuclei (VN) receive input from the
  visceral division of CN VIII.

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General Somatic Afferent Column

• The general somatic afferent column is displaced
  ventrolaterally (green dots).
• It is composed of the three separate divisions of
  the sensory trigeminal nucleus (V).

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General Somatic Afferent Column

• The portion of the nucleus which lies in the
  midbrain modulates proprioception from the
  muscles and joints of the face.

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General Somatic Afferent Column

• The main sensory nucleus lies in the pons.
• The portion of the nucleus which lies in the
  medulla receives input from the muscles, skin,
  joints of the face, and mucous membranes of the
  mouth.

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Cranial Nerve Organization

• Three principles underlie the organization of the
  cranial nerves.
• First, most of the motor nuclei associated in the
  brainstem are associated with individual cranial
  nerves.

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Cranial Nerve Organization

• For example, the trigeminal nerve has it own
  motor nucleus.
• They receive input from motor areas of the
  cerebral cortex and send their axons to muscles
  in the periphery.

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Cranial Nerve Organization

• Second, afferent nuclei in the brainstem often
  receive fibers from several cranial nerves.
• The NTS, for example, collects fibers carrying
  information about taste from the facial (VII),
  glossopharyngeal (IX), and vagus (X) nerves.

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Cranial Nerve Organization

• The medullary nucleus of the trigeminal nerve
  also receives sensory input from several cranial
  nerves.
• The interesting point is that sensory information
  of a particular type, such as taste, is forwarded
  to a single nucleus, no matter which cranial
  nerve pathway it takes.

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Cranial Nerve Organization

• The third principle is related to location
  neurons with different functional properties
  occupy consistently different positions in the
  brainstem.
• This specificity of localization arises during
  development.

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Cranial Nerve Organization

• Neurons destined for different functions arise
  from distinctive parts of the neuroepithelial
  lining of the neural tube.

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Cranial Nerve Organization

• They differentiate at characteristic times in
  development, and migrate to specific positions in
  the brainstem.

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Communicative Pathways

• There are four major communicative pathways
  through the brainstem.
• The corticospinal and the corticobulbar tracts
  constitute the motor pathways.
• The medial lemniscal and the spinothalamic tracts
  constitute the sensory pathways.

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Corticospinal Tract

• The corticospinal tract descends in the ventral
  aspect of the brainstem within the pyramids to
  the caudal border of the medulla where it crosses
  to form the lateral corticospinal tract.

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Corticobulbar Tract

• Corticobulbar fibers also run in the pyramids,
  but they peel off at various levels to reach the
  motor nuclei of the cranial nerves.

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Corticobulbar Tract

• The neurons that give rise to corticobulbar axons
  are upper motor neurons whose effects are similar
  to those exerted by the corticospinal axons upon
  spinal motor neurons.

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Medial Lemniscal Pathway

• The medial lemniscal pathway is the brainstem
  pathway component of the dorsal column nuclei
  (fasciculi cuneatus and gracilis)

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Medial Lemniscal Pathway

• The axons of the medial lemniscus pathway (blue)
  ascend initially near midline and move out
  laterally in the lemniscus as they approach the
  thalamus.

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Spinothalamic Tract

• The spinothalamic tract (red) runs near the
  medial lemniscus after ascending from its origin
  in the spinal cord.

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Reticular Neurons and Processes

• Aside from these tracts and a few others, the
  major cranial nerve nuclei, and nuclei related to
  cerebellar function, the rest of the brainstem is
  composed of reticular neurons and their
  processes.
• These neurons and processes found outside the
  major nuclear groups of the brainstem constitute
  the reticular formation.

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Reticular Formation

• As an entity, the reticular formation represents
  an extensive elaboration of the rostral portion
  of the interneuronal network found in the spinal
  cord.
• It is distributed throughout the medulla, pons,
  and midbrain.

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Reticular Neurons

• Lying in the midline are the raphe nuclei, so
  named because of their proximity to the midline
  seam or raphe.

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Reticular Neurons

• Adjacent to the raphe is the large-cell region of
  the reticular formation and more laterally still
  is the small-group region.

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Reticular Axons

• Nearly all reticular neurons have far-flung
  distribution of their axons in both caudal and
  rostral directions along the brainstem.
• Overlapping afferents, of which some are
  inhibitory and others facilitatory, converge on a
  given reticular neuron.

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Reticular Afferents

• Reticular afferents consist of all collaterals
  from the ascending and descending spinal tracts
  (pain, proprioception, tactile, temperature,
  vibration), cranial nerve nuclei, cerebellum,
  midbrain, thalamus, subthalamus, hypothalamus,
  striatum, limbic lobe, and various cortical areas.

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Reticular Nuclei

• Reticular nuclei also send input to brain
  structures such as the cochlear and vestibular
  nuclei, tectal (colliculi), and pretectal
  structures (red nucleus), geniculate nuclei, and
  thalamic nuclei that process specialized and
  general sensory input.

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Reticular Influences

• Through its direct and indirect projections, the
  reticular formation influences all nervous system
  functions.
• It sends projections to somatic and autonomic
  nuclei in general.
• Reticular afferents also project to autonomic and
  somatic motor nuclei of cranial nerves in the
  brainstem, and they relay information to
  interneuronal pools in the spinal cord.

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Reticular Influences

• There also project directly and indirectly to the
  cerebellum, red nucleus, substantia nigra,
  midbrain tectum, subthalamic nuclei,
  hypothalamus, thalamus, and limbic lobe (septum,
  hippocampus, amygdala, and cingulate gyrus).

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Reticular Influences

• Direct reticular projections influence
  information processing by either accentuating or
  attenuating the sensory (audition, vision,
  olfaction, pain, temperature, and tactile)
  stimuli.
• For example, reticulospinal projections modulate
  the quantity and quality of sensory information.

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Reticular Influences

• They employ gating mechanisms at both pre- and
  post-synaptic terminals to affect sensory impulse
  transmission at both spinal and thalamic levels.
• Within the reticular formation, specific nuclear
  cell aggregates form closed-loop circuits and
  serve as the reticular centers for regulating
  various sensorimotor, visceral, and cortical
  activating functions.

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Reticular Influences

• For example, most coma-causing lesions are found
  at the midbrain, hypothalamic, and thalamic
  junctions.
• Impairment at the level of the midbrain reticular
  formation has been implicated.
• Reticular centers may combine to form reticular
  networks that regulate complex sensorimotor and
  visceral behaviors, such as eating, swallowing,
  vomiting, coughing, sneezing, copulation, and
  fighting.

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Reticular Influences

• Integrated motor functions include activities
  that are vital to survival and are controlled by
  brainstem reticular nuclei.
• Convergent multimodal input and diffuse divergent
  output regulate cardiac activity, respiration,
  and swallowing.

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Vasomotor Functions

• The reticular nuclei regulating vasomotor
  functions of the heart extend from the rostral
  medulla to the mid pons.
• These nuclei receive extensive projections from
  peripheral receptors and are in part controlled
  by the hypothalamus.
• They project information via fibers of the vagus
  nerve.

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Vasomotor Functions

• Stimulation of the lateral reticular pressor
  center in the upper medulla increases heart rate
  and causes vasoconstriction.
• Stimulation of the lateral reticular depressor
  center in the lower medulla decreases heart rate
  and causes vasodilation.

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Vasomotor Functions

• Lesions of the medullary cardiovascular center
  can cause cardiac irregularities and blood
  pressure changes, both of which are
  life-threatening.

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Respiratory Functions

• The automatic brainstem respiratory center
  consists of several groups of scattered neurons
  in the reticular formation.
• It can be divided into two distinct centers
  pontine centers and medullary respiratory center.

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Respiratory Functions

• The medullary respiratory group consists of the
  dorsal respiratory group and the ventral
  respiratory group of neurons.

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Respiratory Functions

• The dorsal medullary respiratory center contains
  reticular nuclei which are responsive to
  afferents from the carotid and aortic
  chemoreceptors through the vagus and
  glossopharyngeal nerves.
• These signals, along with sensory information
  from the lungs, help control respiratory activity.

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Respiratory Functions

• The fibers descending from the dorsal medullary
  respiratory neurons cross to activitate spinal
  cord nerves to cause contraction of the diaphragm
  to begin the cycle of inspiration.

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Respiratory Functions

• The ventral group of respiratory nuclei are
  inactive during the normal respiratory cycle.
• It is activated when high levels of pulmonary
  ventilation are required.

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Respiratory Function

• Projections from the ventral medullary
  respiratory nuclei cross to activate the needed
  thoracic muscles.
• Both the dorsal and ventral respiratory nuclei of
  the medulla contain the mechanism responsible for
  controlling the rhythmic activity of the
  respiratory muscles.

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Respiratory Function

• The pontine respiratory centers generally control
  the duration, depth, and rate of the respiratory
  cycle.
• Because exhalation is normally passive, the
  pneumotaxic area seeks to limit the duration of
  inspiratory phase of the lungs by constant
  inhibition of the medullary respiratory centers.

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Respiratory Function

• A lesion in the ponto-medullary respiratory
  center causes asphyxia and eventually death if
  artificial respiration is not administered.
• As with respiration, the reticular formation
  regulate the acts of swallowing, vomiting, and
  coughing, by integrating the function of several
  nerve pathways.

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Swallowing Function

• For swallowing, the reticular formation
  integrates functions of cranial nerves V, VII,
  IX, X, and XII.
• Specifically, the reticular swallowing center
  directs projections to the adjacent respiratory
  center and to the nuclei of V, VII, IX, X, and
  XII, to initiate a series of fixed action motor
  patterns that ensure proper breathing management
  while the bolus passes through the pharynx.

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Swallowing Function

• As the bolus passes out of the pharynx, the
  reticular respiratory center regulates the
  reopening of the respiratory passageway.
• Brainstem lesions interrupting afferent and
  efferent projections of the reticular formation
  can alter the integrity of the swallow response.

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Vomiting Function

• Vomiting is regulated in the medullary reticular
  formation where it receives input from the
  oropharynx and gastrointestinal tract.
• Noxious impulses mediating irritations of the
  intestinal tract and oropharynx initiate
  reflexive vomiting.

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Vomiting Function

• Projections from the vomiting center in the
  medulla descend through the fibers of cranial
  nerves X and IX and coordinate the contraction of
  the abdominal, diaphragmatic, and intercostal
  muscles.
• The oropharyngeal musculature, which facilitates
  vomiting, works with all of these muscles.

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Coughing Function

• Coughing is a reflexive response to irritation of
  laryngeal and tracheal tissues.
• Afferents mediating irritation initiate the
  coughing reflex via cranial nerve X and the NTS.
• Diaphragm, abdominal, and intercostal muscles are
  involved, but they contract alternately, not
  simultaneously, as with vomiting.

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Reticular Functions

• The functions of the reticular formation can be
  divided into three types cortical arousal,
  sensorimotor elaboration, and visceral integrated
  activity.
• The activation of cortical arousal are the best
  known functions of the reticular formation.

87
Reticular Functions

• The reticular formation uses various
  neurotransmitters to communicate with the brain,
  spinal cord, and neighboring reticular regions to
  contribute to cortical arousal.
• These neurotransmitters are synthesized by a
  specialized population of the cells.

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Reticular Functions

• Studies of the brain using histochemical
  techniques have shown that many reticular neurons
  contain biogenic amines and neuroactive peptides
  that are believed to be used as chemical
  messengers.

89
Reticular Functions

• In sections of a brain that have been exposed to
  radiolabeled transmitter substances, it is
  possible to identify the distinctive fluorescence
  emitted by each of these biogenic amines and to
  map their distribution throughout the reticular
  formation.

90
Reticular Transmitters

• The three most prominent groups of reticular
  neurons are those that contain norepinephrine,
  dopamine, or serotonin.
• A monoamine imbalance can generate somatic and
  psychic symptoms of excitement, agitation,
  anxiety, and insomnia.

91
Noradrenergic System

• Those neurons that contain norepinephrine are
  part of the noradrenergic system.
• In humans, each locus coeruleus (LC) lying on
  either side of the caudal midbrain and upper
  pons, is made up of approximately 12,000
  noradrenergic neurons that have extensive axonal
  connections with the entire CNS.

92
Noradrenergic System

• At least five noradrenergic tracts have been
  identified, fanning out from the LC to innervate
  just about every part of the brain.

93
Noradrenergic System

• All of the cerebral cortex, the thalamus, the
  hypothalamus, the olfactory bulb, the
  hippocampus, the midbrain, the cerebellum and the
  spinal cord receive LC projections.

94
Noradrenergic Functions

• LC cells seem to be involved in the regulation of
  attention, arousal, and sleep-wake cycles, as
  well as learning, memory, anxiety and pain, mood,
  and brain metabolism.
• Because of its widespread connections, the LC can
  influence virtually all parts of the brain.

95
Noradrenergic Functions

• Studies with rats and monkeys have shown that LC
  neurons are activated by new, unexpected,
  non-painful, sensory stimuli in the animals
  environment.
• They are least active when the animals are not
  vigilant, just sitting around quietly digesting a
  meal.

96
Noradrenergic Functions

• Therefore, the LC neurons may participate in a
  general arousal of the brain in situations that
  are startling or interesting or that call for
  watchfulness, playing a role in maintaining
  attention and vigilance.
• They may also have a general function in
  increasing efficiency and responsiveness to
  salient sensory stimuli by speeding information
  processing through point-to-point sensory and
  motor systems.

97
Noradrenergic Functions

• Noradrenergic projections are known also to
  regulate brain tone by inhibiting background
  activity to enhance the signal-to-noise ratio in
  the brain.
• Behaviorally, the LC contributes to the
  generation of REM sleep.
• Therefore, the effects of norepinephrine are
  varied, depending on the part of the brain that
  it activates.

98
Whats love go to do with it?

• Norepinephrine is associated also with increased
  memory for new stimuli.
• It has also been associated with imprinting, the
  curious animal habit of doggedly concentrating
  ones attention on another and following this
  individual everywhere that he or she wanders.

99
Whats love go to do with it?

• Infatuation may be a human form of imprinting.
• Moreover, increasing levels of norepinephrine
  could explain why the lover can remember the
  smallest details of the beloveds actions and
  vividly remember novel moments spent together.

100
Whats love go to do with it?

• Finally, increasing levels of norepinephrine also
  produce exhilaration, excessive energy,
  sleeplessness, and loss of appetitesome of the
  basic characteristics of romantic love.

101
Serotonergic System

• The clusters of serotonergic neurons are found
  along the raphe.
• Each of these nine nuclei projects to different
  regions of the brain.
• The more caudal, in the medulla, innervate the
  spinal cord, where they modulate pain-related
  sensory signals.
• Those more rostral, in the pons and midbrain,
  innervate most of the brain much the same way as
  do the LC neurons.

102
Serotonergic System

• Specifically, serotonin pathways supply the
  hippocampus, the frontal lobes, the caudate and
  putamen, the hypothalamus, and thalamus.

103
Serotonergic System

• Similar to LC neurons, raphe nuclei cells fire
  most rapidly during wakefulness, when the animal
  is aroused and active and they are quietest
  during sleep.
• These neurons seem to be intimately involved in
  the control of sleep-wake cycles as well as the
  different stages of sleep.

104
Serotonergic System

• Serotonin raphe neurons have also been implicated
  in the control of mood and certain types of
  emotional behavior.
• Human studies suggest that having normal to
  slightly higher levels of serotonin function may
  tend to translate into a number of socially
  useful, salutary effects on mood and behavior.

105
Serotonergic System

• High levels of serotonin can be useful for
  multi-tasking, but they can play havoc on ones
  libido.
• In contrast, low serotonin levels correlate with
  depression and well as impulsivity.

106
Serotonergic System

• Doctors who treat individuals with most forms of
  obsessive-compulsive disorder prescribe slective
  serotonin reuptake inhibitors (SSRIs) like Prozac
  or Zoloft to elevate levels of serotonin in the
  brain.

107
Whats love got to do with it?

• A striking symptom of romantic love is incessant
  thinking about the beloved.
• Lovers cannot turn off their racing thoughts.
• Their obsessive cogitation about the beloved is
  thought to be due to decreased brain serotonin.

108
Whats love got to do with it?

• All those countless hours when your mind races
  like a mouse upon a treadmill is probably due to
  a negative relationship between serotonin and its
  relatives, dopamine and norepinephrine.
• As levels of dopamine and norepinephrine climb,
  they can cause serotonin levels to plummet.

109
Whats love got to do with it?

• This could explain why a lovers increasing
  romantic ecstasy actually intensifies the
  compulsion to daydream, fantasize, muse, ponder,
  obsess about a romantic partner.

110
Dopaminergic System

• The dopaminergic (DA) nuclei of the reticular
  formation are located in the midbrain.
• The substantia nigra, with its darkly pigmented
  cell bodies, projects to the motoric nuclei of
  the basal ganglia to facilitate the initiation of
  voluntary movement.

111
Dopaminergic System

• Specifically, the projections from the substantia
  nigra to the caudate nucleus and the putamen
  (collectively known as the striatum) are referred
  to as nigrostriatal or mesostriatal projections
  reflecting their midbrain origin.
• The second dopaminergic source is the ventral
  tegmental area (VTA).

112
Dopaminergic System

• The VTA is a mother lode for dopamine-making
  cells.
• With their tentacle-like axons, these nerve cells
  distribute dopamine to many brain regions
  including the caudate nucleus.
• It has projections to limbic structures such as
  the amygdala via mesolimbic fibers and to the
  cerebral cortex via mesocortical fibers.

113
Dopaminergic System

• The nigrostriatal projection and the mesocortical
  projections to the motor cortex are both
  consistent with the idea that the DA system is
  involved in the initiation of movement.

114
Dopaminergic System

• Disruption in these pathways, or degeneration of
  DA-producing cells, is instrumental in the
  movement deficits of Parkinsons disease.
• However, the extensive DA projections to limbic
  structures and other cortical areas suggest that
  this system is also involved in motivation and
  cognition.

115
Dopaminergic System

• Elevated levels of dopamine in the brain produce
  extremely focused attention, as well as
  unwavering motivation and goal-directed behavior.
• When a reward is delayed, dopamine-producing
  cells in the brain increase their work, pumping
  out more this natural stimulant to energize the
  brain, focus attention, and drive the pursuer to
  strive even harder to acquire a reward.

116
Dopaminergic System

• Dopamine has been associated also with learning
  about novel stimuli.
• Dopamine levels rise when people are in novel
  situations.
• Imbalances in the DA system are thought to play a
  role in certain forms of mental illness, such as
  schizophrenia and thought disorders.
• Very high levels of dopamine can make one feel
  anxious, fearful, even panicky.

117
Dopaminergic System

• Many drugs of abuse enhance the action of DA
  release in limbic structures producing a sense of
  pleasure.
• Dependency and craving, symptoms of addiction, as
  well as romantic love, are associated with
  elevated levels of dopamine.

118
Whats love got to do with it?

• The widespread distribution of this sprinkler
  system sends dopamine to many brain parts.
• It produces focused attention, as well as fierce
  energy, concentrated motivation to attain a
  reward, and the feelings of elation, even
  maniathe core feelings of romantic love.

119
Whats love got to do with it?

• Lovers intensely focus on the beloved, often to
  the exclusion of all around them.
• Indeed, they concentrate so relentlessly on the
  positive qualities of the adored one that they
  easily overlook his/her negative traits.

120
Whats love got to do with it?

• Ecstasy is another trait of lovers that appears
  to be associated with dopamine.
• Elevated concentrations of dopamine in the brain
  produce exhilaration, as well as many of the
  feelings that lovers reportincreased energy,
  hyperactivity, sleeplessness, loss of appetite,
  trembling, a pounding heart, accelerated
  breathing, and sometimes mania, anxiety, or fear.

121
Whats love got to do with it?

• Dopamine may explain why love-stricken
  individuals become so dependent on their romantic
  relationship and why they crave emotional union
  with their beloved.
• Dopamine probably also stimulates the intense
  motivation to see, talk with, and be with the
  beloved.

122
Loves Complex Chemistry

• Given the properties of these three related
  chemicals in the brain, they probably all play a
  role in human romantic passion
• The feelings of euphoria, sleeplessness, and loss
  of appetite
• The lovers intense energy, focused attention,
  driving motivation, and goal-oriented behaviors

123
Loves Complex Chemistry

• The lovers tendency to regard the beloved as
  novel and unique and
• The lovers increased passion in the face of
  adversity.
• Nonetheless, passionate romantic love takes a
  variety of graded forms, from pure elation when
  ones love is reciprocated to feelings of
  emptiness, despair, and often rage when ones
  love is thwarted.

124
Loves Complex Chemistry

• These chemicals undoubtedly vary in their
  concentrations and combinations as the
  relationship ebbs and flows.
• When ones passion is returned, the brain tacks
  on positive emotions, such as elation and hope.
• When ones love is spurned or thwarted instead,
  the brain links this motivation with negative
  feelings, such as despair and rage.

125
The Drive to Love

• Neuroscientist Don Pfaff (1999) defines a drive
  as a neural state that energizes and directs
  behavior to acquire a particular biological need
  to survive or reproduce.
• Drives involve primary motivation systems
  oriented around planning and pursuit of a
  specific want or need.
• We need food. We need water. We need warmth.

126
The Drive to Love

• Like all other drives, romantic love is a need, a
  craving, and the lover feels he/she needs the
  beloved.
• All drives have two components
• a generalized arousal system and
• a specific constellation of brain systems to
  produce the feelings, thoughts, and behaviors
  associated with each particular biological need.

127
The Drive to Love

• The general arousal component of all drives is
  associated with the action of dopamine,
  norepinephrine, serotonin, acetylcholine, several
  histamines, and perhaps other brain chemicals.
• The specific constellation of brain regions and
  systems associated with each particular drive
  varies considerably.

128
The Drive to Love

• In their fMRI study, Helen Fisher and her
  colleagues (2003) found the general arousal
  component of romantic love associated with the
  VTA and the distribution of central dopamine.
• They also found activation in the caudate body
  and tail, the septum, white matter of the
  posterior cingulate, and other areas, as well as
  deactivations in several brain regions.

129
The Drive to Love

• These areas may constitute part of the system
  specific to intense, early stage romantic love.
• In addition to brain system chemistry, the
  prefrontal cortex is also hypothesized to be
  involved.
• This central executive collects data from our
  senses, weighs them, integrates thoughts with
  feelings, makes choices, and controls our basic
  drives.

130
The Drive to Love

• Because romantic love is focused on a specific
  rewardthe beloved--it constitutes a primary
  motivation system.
• Several regions of the prefrontal cortex are
  associated with monitoring rewards (Schultz,
  2000).
• With respect to love, the orbitofrontal and the
  medial prefrontal cortices are specifically
  involved.

131
The Drive to Love

• The orbitofrontal cortex is involved in
  detecting, perceiving, and expecting rewards, as
  well as discriminating between rewards and making
  preferences.
• The medial prefrontal cortex experiences
  emotions, bestows meaning to our perceptions,
  guides our reward-related behaviors, creates our
  mood, and also makes preferences.

132
The Drive to Love

• The drive to love, then, is an elegant design.
• The passion of love emanates from the motor of
  the mind, the caudate nucleus.
• It is fueled by at least one of natures most
  powerful stimulants, dopamine.
• When ones passion is returned, the brain tacks
  on positive emotions, such as elation and hope.

133
The Drive to Love

• When ones love is spurned or thwarted instead,
  the brain links this motivation with negative
  feelings, such as despair and rage.
• And all the while, regions of the prefrontal
  cortex monitor the pursuit, planning tactics,
  calculating gains and losses, and registering
  ones progress toward the goal emotional,
  physical, even spiritual union with the beloved.

134
The Drive to Love

• Indeed, this three-pound blob can generate a need
  so intense that all the world has sung of it
  romantic love.
• And to make our lives even more complex, romantic
  passion is intricately enmeshed with two other
  basic mating drives, the sex drive and the urge
  to build a deep attachment to a romantic partner
  (Fisher, 2004).