Download Document

PowerPoint® Lecture Slide Presentation by Vince Austin
Human Anatomy & Physiology
FIFTH EDITION
Elaine N. Marieb
Chapter 15
Neural Integration
Part A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Sensory Integration
• Survival depends upon sensation and perception
• Sensation is the awareness of changes in the internal
and external environment
• Perception is the conscious interpretation of those
stimuli
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Organization of the Somatosensory System
• Input comes from
exteroceptors, proprioceptors,
and interoceptors
• The three main levels of neural
integration in the
somatosensory system are:
• Receptor level – the sensor
receptors
• Circuit level – ascending
pathways
• Perceptual level – neuronal
circuits in the cerebral cortex
Figure 15.1
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Processing at the Receptor Level
• Receptor potential – a graded potential from a
stimulated sensory receptor
• Generator potential – depolarization of the afferent
fiber caused by a receptor that is a separate cell (e.g.,
hair cell of the ear’s hearing receptor)
• If the receptor potential is above threshold, an action
potential is sent to the CNS
• Strength of stimulus is determined by the frequency
of action potentials
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Adaptation of Sensory Receptors
• Adaptation occurs when sensory receptors are
subjected to an unchanging stimulus
• Receptor membranes become less responsive
• Receptor potentials decline in frequency or stop
• Receptors responding to pressure, touch, and smell
adapt quickly
• Receptors responding slowly include Merkel’s discs,
Ruffini’s corpuscles, and interoceptors that respond to
chemical levels in the blood
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Processing at the Circuit Level
• Chains of three neurons (1st, 2nd, and 3rd order)
conduct sensory impulses upward to the brain
• First-order neurons – soma reside in dorsal root or
cranial ganglia, and conduct impulses from the skin to
the spinal cord or brain stem
• Second-order neurons – soma reside in the dorsal
horn of the spinal cord or medullary nuclei and
transmit impulses to the thalamus or cerebellum
• Third-order neurons – located in the thalamus and
conduct impulses to the somatosensory cortex of the
cerebrum
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Main Ascending Pathways
• The central processes of fist-order neurons branch
diffusely as they enter the spinal cord and medulla
• Some branches take part in spinal cord reflexes
• Others synapse with second-order neurons in the cord
and medullary nuclei
• Pain fibers synapse with substantia gelatinosa neurons
in the dorsal horn
• Fibers from touch and pressure receptors form
collateral synapses with interneurons in the dorsal
horns
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Three Ascending Pathways
• The nonspecific and specific ascending pathways
send impulses to the sensory cortex
• These pathways are responsible for discriminative
touch and conscious proprioception
• The spinocerebellar tracts send impulses to the
cerebellum and do not contribute to sensory
perception
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Specific and Posterior Spinocerebellar Tracts
• Specific ascending
pathways within
the fasciculus
gracilis and
fasciculus cuneatus
tracts, and their
continuation in the
medial lemniscal
tracts
• The posterior
spinocerebellar
tract
Figure 15.2a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Nonspecific Ascending Pathway
• Nonspecific
pathway for
pain,
temperature, and
crude touch
within the lateral
spinothalamic
tract
Figure 15.2b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Processing at the Perceptual Level
• The thalamus projects fibers to:
• The somatosensory cortex
• Sensory association areas
• First one modality is sent, then those considering
more than one
• The result is an internal, conscious image of the
stimulus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Main Aspects of Sensory Perception
• Perceptual detection – detecting that a stimulus has
occurred and requires summation
• Magnitude – how much of a stimulus is acting
• Spatial discrimination – identifying the site or pattern
of the stimulus
• Feature abstraction – used to identify a substance that
has specific texture or shape
• Quality discrimination – the ability to identify
submodalities of a sensation (e.g., sweet or sour
tastes)
• Pattern recognition – ability to recognize patterns in
stimuli (e.g., melody, familiar face)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Motor Integration
• In the motor system:
• There are effectors (muscles) instead of sensory
receptors
• The pathways are descending efferent circuits,
instead of afferent ascending ones
• There is motor behavior instead of perception
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Levels of Motor Control
• The three levels of motor control are:
• Segmental level
• Projection level
• Programs/instructions level
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Levels of Motor Control
Figure 15.3
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Segmental Level
• The segmental level is the lowest level of motor
hierarchy
• It consists of segmental circuits of the spinal cord
• Its circuits control locomotion and specific, oftrepeated motor activity
• These circuits are called central pattern generators
(CPGs)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Projection Level
• The projection level consists of:
• Cortical motor areas that produce the direct
(pyramidal) system
• Brain stem motor areas that oversee the indirect
(mulitneuronal) system
• Helps control reflex and fixed-pattern activity and
houses command neurons that modify the segmental
apparatus
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Descending (Motor) Pathways
• Descending tracts deliver efferent impulses from the
brain to the spinal cord, and are divided into two
groups
• Direct pathways equivalent to the pyramidal tracts
• Indirect pathways, essentially all others
• Motor pathways involve two neurons (upper and
lower)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Direct (Pyramidal) System
• Direct pathways
originate with the
pyramidal neurons in
the precentral gyri
• Impulses are sent
through the
corticospinal tracts and
synapse in the anterior
horn
• Stimulation of anterior
horn neurons activates
skeletal muscles
Figure 15.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Direct (Pyramidal) System
• Parts of the direct
pathway, called
corticobulbar tracts,
innervate cranial
nerve nuclei
• The direct pathway
regulates fast and
fine (skilled)
movements
Figure 15.4a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Indirect (Extrapyramidal) System
• Includes the brain stem, motor nuclei, and all motor
pathways not part of the pyramidal system
• This system includes the rubrospinal, vestibulospinal,
reticulospinal, and tectospinal tracts
• These motor pathways are complex and
multisynaptic, and regulate:
• Axial muscles that maintain balance and posture
• Muscles controlling coarse movements of the
proximal portions of limbs
• Head, neck, and eye movement
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Extrapyramidal (Multineuronal) Pathways
• Reticular nuclei –
maintain balance
• Vestibular nuclei –
receive input from the
equilibrium apparatus of
the ear and from the
cerebellum
• Vestibulospinal tracts –
control the segmental
apparatus during
standing
Figure 15.4b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Extrapyramidal (Multineuronal) Pathways
• Red nuclei – control
flexor muscles
• Superior colliculi and
tectospinal tracts
mediate head
movements
Figure 15.4b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Programs and Instructions Level
• The program/instructional level integrates the sensory
and motor systems
• This level is called the precommand area
• They are located in the cerebellum and basal nuclei
• Regulate precise start/stop movements and
coordinate movements with posture
• Block unwanted movements and monitor muscle
tone
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings