Transcript 15-02_pptlect

Anatomy & Physiology
SIXTH EDITION
Chapter 15, part 2
Neural Integration I:
Sensory Pathways and the
Somatic Nervous System
PowerPoint® Lecture Slide Presentation prepared by
Dr. Kathleen A. Ireland, Biology Instructor, Seabury Hall, Maui, Hawaii
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Frederic H. Martini
Fundamentals of
SECTION 15-3
The Organization of Sensory Pathways
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First, second, and third order neurons
• First order neurons
• Sensory neurons that deliver sensory
information to the CNS
• Second order neurons
• First order neurons synapse on these in the
brain or spinal cord
• Third order neurons
• Found in the thalamus
• Second order neurons synapse on these
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Somatic sensory pathways
• Three major pathways carry sensory information
• Posterior column pathway
• Anterolateral pathway
• Spinocerebellar pathway
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Figure 15.6 Sensory Pathways and Ascending
Tracts in the Spinal Cord
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Figure 15.6
Posterior column pathway
• Carries fine touch, pressure and proprioceptive
sensations
• Axons ascend within the fasciculus gracilis and
fasciculus cuneatus
• Relay information to the thalamus via the medial
lemniscus
• Decussation
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Figure 15.8 The Posterior Column Pathway and
the Spinothalamic Tracts
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Figure 15.8a, b
Anterolateral pathway
• Carries poorly localized sensations of touch,
pressure, pain, and temperature
• Axons decussate in the spinal cord and ascend
within the anterior and lateral spinothalamic
tracts
• Headed toward the ventral nuclei of the thalamus
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Figure 15.8 The Posterior Column Pathway and
the Spinothalamic Tracts
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Figure 15.8c
Spinocerebellar pathway
• Includes the posterior and anterior
spinocerebellar tracts
• Carries sensation to the cerebellum concerning
position of muscles, tendons and joints
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Figure 15.9 The Spinocerebellar Pathway
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Figure 15.9
Visceral sensory pathways
• Carry information collected by interoceptors
• Information from cranial nerves V, VII, IX and X
delivered to solitary nucleus in medulla oblongata
• Dorsal roots of spinal nerves T1 – L2 carry
visceral sensory information from organs
between the diaphragm and pelvis
• Dorsal roots of spinal nerves S2 – S4 carry
sensory information below this area
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SECTION 15-4
The Somatic Nervous System
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Somatic motor pathways
• Upper motor neuron
• Cell body lies in a CNS processing center
• Lower motor neuron
• Cell body located in a motor nucleus of the
brain or spinal cord
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Figure 15.10 Descending (Motor) Tracts in the
Spinal Cord
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Figure 15.10
The corticospinal pathway
• Provides voluntary skeletal muscle control
• Corticobulbar tracts terminate at cranial
nerve nuclei
• Corticospinal tracts synapse on motor
neurons in the anterior gray horns of the
spinal cord
• Visible along medulla as pyramids
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Pyramids
• Most of the axons decussate to enter the
descending lateral corticospinal tracts
• Those that do not cross over enter the anterior
corticospinal tracts
• Provide rapid direct method for controlling
skeletal muscle
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Figure 15.11 The Corticospinal Pathway
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Figure 15.11
medial and lateral pathways
• The medial and lateral pathways
• Issue motor commands as a result of
subconscious processing
• Medial pathway
• Primarily controls gross movements of the trunk
and proximal limbs
• Includes the vestibulospinal tracts, tectospinal
tracts and reticulospinal tracts
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lateral pathways
• Lateral pathway
• Controls muscle tone and movements of the
distal muscles of the upper limbs
• Rubrospinal tracts
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The basal nuclei and cerebellum
• Basal nuclei adjust motor commands issued in
other processing centers
• Provide background patterns of movement
involved in voluntary motor movements
• Cerebellum monitors proprioceptive information,
visual information and vestibular sensations
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control and responses
• Levels of processing and motor control
• Spinal and cranial reflexes provide rapid,
involuntary, preprogrammed responses
• Voluntary responses
• More complex
• Require more time to prepare and execute
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Figure 15.12 Centers of Somatic Motor Control
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Figure 15.12
During development
• Spinal and cranial reflexes are first to appear
• Complex reflexes develop as CNS matures and
brain grows
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You should now be familiar with:
• The components of the afferent and efferent
divisions of the nervous system, and what is meant
by the somatic nervous system.
• Why receptors respond to specific stimuli and how
the organization of a receptor affects its sensitivity.
• The major sensory pathways.
• How we can distinguish among sensations that
originate in different areas of the body.
• The components, processes and functions of the
somatic motor pathways.
• The levels of information processing involved in
motor control.
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