Transcript Chapter 3

Chapter 16
Sensory, Motor & Integrative Systems
Lecture Outline
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INTRODUCTION
• The components of the brain interact to receive sensory
input, integrate and store the information, and transmit
motor responses.
• To accomplish the primary functions of the nervous system
there are neural pathways to transmit impulses from
receptors to the circuitry of the brain, which manipulates the
circuitry to form directives that are transmitted via neural
pathways to effectors as a response.
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Chapter 16
Sensory, Motor & Integrative Systems
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Levels and components of sensation
Pathways for sensations from body to brain
Pathways for motor signals from brain to body
Integration Process
– wakefulness and sleep
– learning and memory
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SENSATION
• Sensation is a conscious or unconscious awareness
of external or internal stimuli.
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Is Sensation Different from Perception?
• Perception is the conscious awareness & interpretation of a
sensation.
– precisely localization & identification
– memories of our perceptions are stored in the cortex
• Sensation is any stimuli the body is aware of
– Chemoreceptors, thermoreceptors, nociceptors, baroreceptors
– What are we not aware of?
• X-rays, ultra high frequency sound waves, UV light
– We have no sensory receptors for those stimuli
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Sensory Modalities
• Sensory Modality is the property by which one sensation
is distinguished from another.
• Different types of sensations
– touch, pain, temperature, vibration, hearing, vision
– Generally, each type of sensory neuron can respond
to only one type of stimulus.
• Two classes of sensory modalities
– general senses
– special senses
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Sensory Modalities
• The classes of sensory modalities are general senses and
special senses.
– The general senses include both somatic and visceral
senses, which provide information about conditions
within internal organs.
– The special senses include the modalities of smell, taste,
vision, hearing, and equilibrium.
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Process of Sensation
• Sensory receptors demonstrate selectivity
– respond to only one type of stimuli
• Events occurring within a sensation
– stimulation of the receptor
– transduction (conversion) of stimulus into a graded
potential
• vary in amplitude and are not propagated
– generation of impulses when graded potential
reaches threshold
– integration of sensory input by the CNS
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Sensory Receptors
• Receptor Structure may be simple or complex
– General Sensory Receptors (Somatic Receptors)
• no structural specializations in free nerve endings
that provide us with pain, tickle, itch, temperatures
• some structural specializations in receptors for
touch, pressure & vibration
– Special Sensory Receptors (Special Sense Receptors)
• very complex structures---vision, hearing, taste, &
smell
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Alternate Classifications of Sensory Receptors
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•
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Structural classification
Type of response to a stimulus
Location of receptors & origin of stimuli
Type of stimuli they detect
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Structural Classification of Receptors
• Free nerve endings
– bare dendrites
– pain, temperature, tickle, itch & light touch
• Encapsulated nerve endings
– dendrites enclosed in connective tissue capsule
– pressure, vibration & deep touch
• Separate sensory cells
– specialized cells that respond to stimuli
– vision, taste, hearing, balance
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Structural Classification
• Compare free nerve ending, encapsulated nerve ending and
sensory receptor cell
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Classification by Stimuli Detected
• Mechanoreceptors
– detect pressure or stretch
– touch, pressure, vibration, hearing, proprioception,
equilibrium & blood pressure
• Thermoreceptors detect temperature
• Nociceptors detect damage to tissues
• Photoreceptors detect light
• Chemoreceptors detect molecules
– taste, smell & changes in body fluid chemistry
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Classification by Response to Stimuli
• Generator potential
– free nerve endings, encapsulated nerve endings &
olfactory receptors produce generator potentials
– when large enough, it generates a nerve impulse in a firstorder neuron
• Receptor potential
– vision, hearing, equilibrium and taste receptors produce
receptor potentials
– receptor cells release neurotransmitter molecules on firstorder neurons producing postsynaptic potentials
– PSP may trigger a nerve impulse
• Amplitude of potentials vary with stimulus intensity
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Classification by Location
• Exteroceptors
– near surface of body
– receive external stimuli
– hearing, vision, smell, taste, touch, pressure, pain,
vibration & temperature
• Interoceptors
– monitors internal environment (BV or viscera)
– not conscious except for pain or pressure
• Proprioceptors
– muscle, tendon, joint & internal ear
– senses body position & movement
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Adaptation in Sensory Receptors
• Most sensory receptors exhibit adaptation – the tendency
for the generator or receptor potential to decrease in
amplitude during a maintained constant stimulus.
• Receptors may be rapidly or slowly adapting.
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Adaptation of Sensory Receptors
• Change in sensitivity to long-lasting stimuli
– decrease in responsiveness of a receptor
• bad smells disappear
• very hot water starts to feel only warm
– potential amplitudes decrease during a maintained,
constant stimulus
• Variability in tendency to adapt:
– Rapidly adapting receptors (smell, pressure, touch)
• specialized for detecting changes
– Slowly adapting receptors (pain, body position)
• nerve impulses continue as long as the stimulus
persists – Pain is not easily ignored.
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SOMATIC SENSATIONS
• Receptors for somatic sensation are summarized in
Table 16.2)
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Tactile Sensations
• Tactile sensations are touch, pressure, and vibration plus
itch and tickle.
• receptors include (Figure 16.2)
– corpuscles of touch (Meissner’s corpuscles),
– hair root plexuses,
– type I (Merkel’s discs)
– type II cutaneous (Ruffini’s corpuscles)
– mechanoreceptors,
– lamellated (Pacinian) corpuscles,
– free nerve endings
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Touch
• Crude touch refers to the ability to perceive that something
has simply touched the skin
• Discriminative touch (fine touch) provides specific
information about a touch sensation such as location,
shape, size, and texture of the source of stimulation.
• Receptors for touch include corpuscles of touch (Meissner’s
corpuscles) and hair root plexuses; these are rapidly
adapting receptors.
• Type I cutaneous mechanoreceptors (tactile or Merkel discs)
and type II cutaneous mechanoreceptors (end organs of
Ruffini) are slowly adapting receptors for touch (Figure
16.2).
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Pressure and Vibration
• Pressure is a sustained sensation that is felt over a larger
area than touch.
– Pressure sensations generally result from stimulation of
tactile receptors in deeper tissues and are longer lasting
and have less variation in intensity than touch sensations
– Receptors for pressure are type II cutaneous
mechanoreceptors and lamellated (Pacinian) corpuscles.
• Like corpuscles of touch (Meissner’s corpuscles),
lamellated corpuscles adapt rapidly.
• Vibration sensations result from rapidly repetitive sensory
signals from tactile receptors
– receptors for vibration sensations are corpuscles of touch
and lamellated corpuscles, which detect low-frequency
and high-frequency vibrations, respectively.
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Itch and Tickle
• Itch and tickle receptors are free nerve endings.
– Tickle is the only sensation that you may not elicit on
yourself.
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Meissner’s Corpuscle
• Dendrites enclosed in CT in dermal papillae of hairless skin
• Discriminative touch & vibration-- rapidly adapting
• Generate impulses mainly at onset of a touch
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Hair Root Plexus
•Free nerve endings found around follicles, detects
movement of hair
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Merkel’s Disc
• Flattened dendrites touching cells of stratum basale
• Used in discriminative touch (25% of receptors in hands)
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Ruffini Corpuscle
• Found deep in dermis of skin
• Detect heavy touch, continuous touch, & pressure
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Pacinian Corpuscle
• Onion-like connective tissue capsule enclosing a dendrite
• Found in subcutaneous tissues & certain viscera
• Sensations of pressure or high-frequency vibration
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Somatic Tactile Sensations - Summary
• Touch
– crude touch is ability to perceive something has touched
the skin
– discriminative touch provides location and texture of
source
• Pressure is sustained sensation over a large area
• Vibration is rapidly repetitive sensory signals
• Itching is chemical stimulation of free nerve endings
• Tickle is stimulation of free nerve endings only by someone
else
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Thermal Sensations
• Free nerve endings with 1mm diameter receptive fields on
the skin surface
– Cold receptors in the stratum basale respond to
temperatures between 50-105 degrees F
– Warm receptors in the dermis respond to temperatures
between 90-118 degrees F
• Both adapt rapidly at first, but continue to generate
impulses at a low frequency
• Pain is produced below 50 and over 118
degrees F.
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Pain Sensations
• Pain receptors (nociceptors) are free endings that are
located in nearly every body tissue
– Free nerve endings found in every tissue of body
except the brain
– adaptation is slight if it occurs at all.
• Stimulated by excessive distension, muscle spasm, &
inadequate blood flow
• Tissue injury releases chemicals such as K+, kinins
or prostaglandins that stimulate nociceptors
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Types of Pain
• Fast pain (acute)
– occurs rapidly after stimuli (.1 second)
– sharp pain like needle puncture or cut
– not felt in deeper tissues
– larger A nerve fibers
• Slow pain (chronic)
– begins more slowly & increases in intensity
– aching or throbbing pain of toothache
– in both superficial and deeper tissues
– smaller C nerve fibers
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Types of Pain
• Somatic pain that arises from the stimulation of
receptors in the skin is superficial, while somatic
pain that arises from skeletal muscle, joints, and
tendons is deep.
• Visceral pain, unlike somatic pain, is usually felt in or
just under the skin that overlies the stimulated organ
– localized damage (cutting) intestines may cause
no pain, but diffuse visceral stimulation can be
severe
• distension of a bile duct from a gallstone
• distension of the ureter from a kidney stone
– pain may also be felt in a surface area far from the
stimulated organ in a phenomenon known as
referred pain (Figure 16.3).
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Referred Pain
• Visceral pain that is felt just deep to the skin overlying the stimulated
organ or in a surface area far from the organ.
• Skin area & organ are served by the same segment of the spinal cord.
– Heart attack is felt in skin along left arm since both are supplied by
spinal cord segment T1-T5
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Pain Relief
Multiple sites of analgesic action:
• Aspirin and ibuprofen block formation of prostaglandins that
stimulate nociceptors
• Novocaine blocks conduction of nerve impulses along pain
fibers
• Morphine lessen the perception of pain in the brain.
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Proprioceptive Sensations
• Receptors located in skeletal muscles, in tendons, in and
around joints, and in the internal ear convey nerve impulses
related to muscle tone, movement of body parts, and body
position. This awareness of the activities of muscles,
tendons, and joints and of balance or equilibrium is provided
by the proprioceptive or kinesthetic sense.
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Proprioceptive or Kinesthetic Sense
• Awareness of body position & movement
– walk or type without looking
– estimate weight of objects
• Proprioceptors adapt only slightly
• Sensory information is sent to cerebellum & cerebral
cortex
– signals project from muscle, tendon, joint capsules
& hair cells in the vestibular apparatus
– receptors discussed here include muscle spindles,
tendon organs (Golgi tendon organs), and joint
kinesthetic receptors (Figure 16.4).
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Muscle
Spindles
• Specialized intrafusal muscle fibers enclosed in a CT capsule and
innervated by gamma motor neurons
• Stretching of the muscle stretches the muscle spindles sending sensory
information back to the CNS
• Spindle sensory fiber monitor changes in muscle length
• Brain regulates muscle tone by controlling gamma fibers
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Golgi Tendon Organs
• Found at junction of tendon & muscle
• Consists of an encapsulated bundle of collagen fibers laced with
sensory fibers
• When the tendon is overly stretched, sensory signals head for the
CNS & resulting in the muscle’s relaxation
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Joint Receptors
• Ruffini corpuscles
– found in joint capsule
– respond to pressure
• Pacinian corpuscles
– found in connective tissue around the joint
– respond to acceleration & deceleration of joints
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SOMATIC SENSORY PATHWAYS
• Somatic sensory pathways relay information from somatic
receptors to the primary somatosensory area in the cerebral
cortex.
• The pathways consist of three neurons
– first-order,
– second-order, and
– third-order
• Axon collaterals of somatic sensory neurons simultaneously
carry signals into the cerebellum and the reticular formation
of the brain stem.
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Somatic Sensory Pathways
• First-order neuron conduct impulses to the CNS
(brainstem or spinal cord)
– either spinal or cranial nerves
• Second-order neurons conducts impulses from brain stem
or spinal cord to thalamus
– cross over to opposite side of body
• Third-order neuron conducts impulses from thalamus to
primary somatosensory cortex (postcentral gyrus of
parietal lobe)
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Posterior Column-Medial Lemniscus
Pathway to the Cortex
• The nerve impulses for conscious proprioception and most
tactile sensations ascend to the cortex along a common
pathway formed by three-neuron sets (Figure 16.16a).
• These neurons are a part of the posterior (dorsal) columns
– consist of the gracile fasciculus and cuneate fasciculus
• Impulses conducted along this pathway
– fine touch,
– stereognosis,
– proprioception, and
– vibratory sensations
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Posterior Column-Medial
Lemniscus Pathway of CNS
• Proprioception, vibration,
discriminative touch, weight
discrimination & stereognosis
• Signals travel up spinal cord
in posterior column
• Fibers cross-over in medulla
to become the medial
lemniscus pathway ending in
thalamus
• Thalamic fibers reach cortex
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Anterolateral Pathways to the Cortex
• 3-neuron pathway
• The anterolateral or spinothalamic pathways carry
mainly pain and temperature impulses (Figure 16.5b).
• They also relay the sensations of tickle and itch and
some tactile impulses.
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Spinothalamic
Pathway of CNS
• Lateral spinothalamic tract
carries pain & temperature
• Anterior tract carries tickle,
itch, crude touch & pressure
• First cell body in DRG with
synapses in cord
• 2nd cell body in gray matter
of cord, sends fibers to other
side of cord & up through
white matter to synapse in
thalamus
• 3rd cell body in thalamus
projects to cerebral cortex
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Somatosensory Map of Postcentral Gyrus
• Relative sizes of cortical
areas
– proportional to number of
sensory receptors
– proportional to the
sensitivity of each part of
the body
• Can be modified with learning
– learn to read Braille & will
have larger area
representing fingertips
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Somatic Sensory Pathways to the Cerebellum
• The posterior spinocerebellar and the anterior
spinocerebellar tracts are the major routes whereby
proprioceptive impulses reach the cerebellum.
– impulses conveyed to the cerebellum are critical for
posture, balance, and coordination of skilled
movements.
• Table 16.3 summarizes the major sensory tracts in the
spinal cord and pathways in the brain.
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Sensory Pathways to the Cerebellum
• Major routes for proprioceptive
signals to reach the cerebellum
– anterior spinocerebellar tract
– posterior spinocerebellar
tract
• Subconscious information used
by cerebellum for adjusting
posture, balance & skilled
movements
• Signal travels up to same side
inferior cerebellar peduncle
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Clinical Application - Syphilis
Syphilis causes a progressive degeneration of the posterior
portions of the spinal cord.
– Sexually transmitted disease caused by bacterium
Treponema pallidum.
– Third clinical stage known as tertiary syphilis
– Progressive degeneration of posterior portions of spinal
cord & neurological loss
• loss of somatic sensations
• proprioceptive impulses fail to reach cerebellum
– People watch their feet while walking, but are still
uncoordinated and jerky
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SOMATIC MOTOR PATHWAYS
• Lower motor neurons extend from the brain stem or spinal
cord to skeletal muscles.
• These lower motor neurons are called the final common
pathway because many regulatory mechanisms converge
on these peripheral neurons.
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Somatic Motor Pathways - Overview
• Control of body movement
– motor portions of cerebral cortex
• initiate & control precise movements
– basal ganglia help establish muscle tone &
integrate semivoluntary automatic movements
– cerebellum helps make movements smooth &
helps maintain posture & balance
• Somatic motor pathways
– direct pathway from cerebral cortex to spinal cord
& out to muscles
– indirect pathway includes synapses in basal
ganglia, thalamus, reticular formation &
cerebellum
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SOMATIC MOTOR PATHWAYS
• Four distinct neural circuits (somatic motor pathways)
participate in control of movement by providing input to
lower motor neurons (Figure 16.7).
– Local circuit neurons are located close to lower motor
neuron cell bodies in the brain stem and spinal cord.
– Local circuit neurons and lower motor neurons receive
input from upper motor neurons.
– Neurons of the basal ganglia provide input to upper
motor neurons.
– Cerebellar neurons also control activity of upper motor
neurons.
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SOMATIC MOTOR PATHWAYS
• Organization of upper motor neuron pathways
– Direct motor pathways provide input to lower motor
neurons via axons that extend directly from the cerebral
cortex.
– Indirect pathways provide input to lower motor neurons
from motor centers in the brain stem
• Paralysis: damage of lower motor neurons produces flaccid
paralysis while injury to upper motor neurons causes spastic
paralysis.
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Primary Motor Cortex
Principles of Human Anatomy and Physiology, 11e
• The primary motor area is located in
the precentral gyrus of the frontal
lobe (Figure 16.6b)
– upper motor neurons initiate
voluntary movement
• The adjacent premotor area and
somatosensory area of the
postcentral gyrus also contribute
axons to descending motor
pathways.
• The cortical area devoted to a
muscle is proportional to the number
of motor units.
– More cortical area is needed if
number of motor units in a
muscle is high
• vocal cords, tongue, lips,
fingers & thumb
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Direct motor pathways
• The direct pathways (pyramidal tracts) include (Figure
16.8).
– lateral and anterior corticospinal tracts
– corticobulbar tracts
• The various tracts of the pyramidal system convey impulses
from the cerebral cortex that result in precise muscular
movements.
• Table 16.4 summarizes the functions and pathways of the
tracts in the direct motor pathways.
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Direct Pathways (Pyramidal Pathways)
• 1 million upper motor neurons in cerebral cortex
• Axons form internal capsule in cerebrum and pyramids
in the medulla oblongata
• 90% of fibers decussate (cross over) in the medulla
– right side of brain controls left side muscles
• Terminate on interneurons which synapse on lower
motor neurons in either:
– nuclei of cranial nerves
– anterior horns of spinal cord
• Integrate excitatory & inhibitory input to become final
common pathway
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Details of Pyramidal Pathways
• Lateral corticospinal tracts
– cortex, cerebral peduncles, 90%
decussation of axons in medulla,
tract formed in lateral column.
– skilled movements (hands & feet)
• Anterior corticospinal tracts
– the 10% of axons that do not cross
– controls neck & trunk muscles
• Corticobulbar tracts
– cortex to nuclei of CNs
• III, IV, V, VI, VII, IX, X, XI & XII
– movements of eyes, tongue,
chewing, expressions & speech
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Location of Direct Pathways
• Lateral corticospinal tract
• Anterior corticospinal tract
• Corticobulbar tract
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Application
• Amyotrophic Lateral Sclerosis (ALS) is a disease hat attacks
motor areas of the cerebral cortex, axons of upper motor
neurons and cell bodies of lower motor neurons.
• It causes progressive muscle weakness.
• There are several theories as to its cause. While there is no
cure, several drugs are used to treat the symptoms.
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Paralysis
• Flaccid paralysis = damage lower motor neurons
– no voluntary movement on same side as damage
– no reflex actions
– muscle limp & flaccid
– decreased muscle tone
• Spastic paralysis = damage upper motor neurons
– paralysis on opposite side from injury
– increased muscle tone
– exaggerated reflexes
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Indirect Pathways
• Indirect or extrapyramidal pathways include all somatic
motor tracts other than the corticospinal and corticobulbar
tracts.
– involve the motor cortex, basal ganglia, thalamus,
cerebellum, reticular formation, and nuclei in the brain
stem (Figure 16.8).
– indirect tracts are the rubrospinal, tectospinal,
vestibulospinal, lateral reticulospinal and medial
reticulospinal tracts.
• Table 16.4 summarizes the major motor tracts, their
functions, and pathways in the brain.
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Indirect Pathways
• All other descending motor
pathways
• Complex polysynaptic circuits
– include basal ganglia,
thalamus, cerebellum,
reticular formation
• Descend in spinal cord as 5
major tracts
• All 5 tracts end upon
interneurons or lower motor
neurons
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Final Common
Pathway
• Lower motor neurons
receive signals from both
direct & indirect upper
motor neurons
• Sum total of all inhibitory &
excitatory signals
determines the final
response of the lower
motor neuron & the
skeletal muscles
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Roles of the basal ganglia
• The circuit from the cerebral cortex to basal ganglia to
thalamus to cortex seems to function in initiating and
terminating movement.
– basal ganglia also suppress unwanted movements
– basal ganglia may influence aspects of cortical function
including sensory, limbic, cognitive, and linguistic
functions.
• Damage to the basal ganglia results in uncontrollable,
abnormal body movements, often accompanied by muscle
rigidity and tremors.
• Parkinson disease and Huntington disease result from
damage to the basal ganglia.
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Basal Ganglia
• Helps to program automatic movement sequences
– walking and arm swinging or laughing at a joke
• Set muscle tone by inhibiting other motor circuits
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Basal Ganglia Connections - Review
• Circuit of connections
– cortex to basal ganglia to
thalamus to cortex
– planning movements
• Output from basal ganglia to
reticular formation
– reduces muscle tone
– damage produces rigidity
of Parkinson’s disease
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Modulation of Movement by the Cerebellum
• The cerebellum is active in both learning and performing
rapid, coordinated, highly skilled movements and in
maintaining proper posture and equilibrium.
• The four aspects of cerebellar function (Figure 16.9)
– monitoring intent for movement,
– monitoring actual movement,
– comparing intent with actual performance, and
– sending out corrective signals
• Damage to the cerebellum is evidenced by ataxia and
intention tremors.
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Cerebellar
Function
Aspects of Function
• learning
• coordinated &
skilled movements
• posture &
equilibrium
1. Monitors intentions for movements -- input from cerebral cortex
2. Monitors actual movements with feedback from proprioceptors
3. Compares intentions with actual movements
4. Sends out corrective signals to motor cortex
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INTEGRATIVE FUNCTIONS OF THE CEREBRUM
• The integrative functions include sleep and wakefulness,
memory, and emotional responses.
(discussed in Chapter 14).
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Wakefulness and Sleep
Role of the Reticular Activating System (RAS)
• Sleep and wakefulness are integrative functions that are
controlled by the reticular activating system (Figure 16.10).
– Arousal, or awakening from a sleep, involves increased
activity of the RAS.
– When the RAS is activated, the cerebral cortex is also
activated and arousal occurs.
– The result is a state of wakefulness called
consciousness.
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Reticular Activating System
• RAS has connections to
cortex & spinal cord.
• Many types of inputs can
activate the RAS---pain,
light, noise, muscle
activity, touch
• Coma is sleep-like state
– A person in a deep
coma has no reflexes.
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Wakefulness and Sleep
• Circadian rhythm
– 24 hour cycle of sleep and awakening
– established by hypothalamus
• EEG recordings show large amount of activity in
cerebral cortex when awake
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Sleep
• During sleep, a state of altered consciousness or partial
unconsciousness from which an individual can be aroused
by different stimuli,
• During sleep activity in the RAS is very low.
• Normal sleep consists of two types:
– non-rapid eye movement sleep (NREM) and
– rapid eye movement sleep (REM)
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Sleep
• Triggers for sleep are unclear
– adenosine levels increase with brain activity
– adenosine levels inhibit activity in RAS
– caffeine prevents adenosine from inhibiting RAS
• Non-rapid eye movement or slow wave sleep consists of
four stages, each of which gradually merges into the
next.
• Most dreaming occurs during rapid eye movement
sleep.
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Non-Rapid Eye Movement Sleep
• Stage 1
– person is drifting off with eyes
closed (first few minutes)
• Stage 2
– fragments of dreams
– eyes may roll from side to side
• Stage 3
– very relaxed, moderately deep
– 20 minutes, body temperature & BP have dropped
• Stage 4 = deep sleep
– bed-wetting & sleep walking occur in this phase
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REM Sleep
• Most dreams occur during REM sleep
• In first 90 minutes of sleep:
– go from stage 1 to 4 of NREM,
– go up to stage 2 of NREM
– to REM sleep
• Cycles repeat until total REM sleep totals 90 to 120
minutes
• Neuronal activity & oxygen use is highest in REM sleep
• Total sleeping & dreaming time decreases with age
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Learning and Memory
• Learning is the ability to acquire new knowledge or skills
through instruction or experience.
• Memory is the process by which that knowledge is retained
over time.
• For an experience to become part of memory, it must
produce persistent functional changes that represent the
experience in the brain.
• The capability for change with learning is called plasticity.
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Learning and Memory
• Memory occurs in stages over a period and is described as
immediate memory, short term memory, or long term
memory.
– Immediate memory is the ability to recall for a few
seconds.
– Short-term memory lasts only seconds or hours and is
the ability to recall bits of information; it is related to
electrical and chemical events.
– Long-term memory lasts from days to years and is
related to anatomical and biochemical changes at
synapses.
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Amnesia
• Amnesia refers to the loss of memory
• Anterograde amnesia is the loss of memory for events that
occur after the trauma; the inability to form new memories.
• Retrograde amnesia is the loss of memory for events that
occurred before the trauma; the inability to recall past
events.
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DISORDERS: HOMEOSTATIC IMBALANCES
• Phantom pain is the sensations of pain in a limb that has
been amputated; the brain interprets nerve impulses arising
in the remaining proximal portions of the sensory nerves as
coming from the nonexistent (phantom) limb. Another
explanation is that the neurons in the brain that received
input from the missing limbs are still active.
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Spinal Cord Injury
• Spinal cord injury can be due to damage in a number of
ways, such as compression or transection, and the location
and extent of damage determines the type and degree of loss
in neural abilities.
– tumor, herniated disc, clot, trauma …
• Paralysis
– monoplegia is paralysis of one limb only
– diplegia is paralysis of both upper or both lower
– hemiplegia is paralysis of one side
– quadriplegia is paralysis of all four limbs
• Spinal shock is loss of reflex function (areflexia)
– slow heart rate, low blood pressure, bladder problem
– reflexes gradually return
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Cerebral Palsy
• Loss of motor control and coordination
• Damage to motor areas of the brain
– infection of pregnant woman with rubella virus
– radiation during fetal life
– temporary lack of O2 during birth
• Not a progressive disease, but irreversible
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Parkinson Disease
• Parkinson’s disease is a progressive degeneration of CNS neurons of
the basal nuclei region due to unknown causes that decreases
dopamine neurotransmitter production.
– Environmental toxins may be the cause in some cases
• Neurons from the substantia nigra do not release enough dopamine
onto basal ganglia
– tremor, rigidity, bradykinesia (slow movement) or hypokinesia
(decreasing range of movement)
– may affect walking, speech, and facial expression
• Treatments
– drugs to increase dopamine levels (L-Dopa), or to prevent its
breakdown
– surgery to transplant fetal tissue or removal of part of globus
pallidus to slow tremors
– acetylcholine inhibitors
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end
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