Transcript Document

Chapter 16:
Sensory, Motor,
and Integrative Systems
Copyright 2009, John Wiley & Sons, Inc.
Sensation ,Perception & Integration
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Sensation is the detection of stimulus of internal or external receptors. It
can be either conscious or subconcious
Components of sensation: Stimulation of the sensory receptor →
transduction of the stimulus (energy-to-graded potential) → generation of
nerve impulses → integration of sensory input.
Perception is the awareness and conscious interpretation of sensations. It
is how the brain makes sense of or assigns meaning to the sensation.
We not aware of X-rays, ultra high frequency sound waves, UV light
- We have no sensory receptors for those stimuli
Integration of sensory and motor functions occurs at many sites:
□spinal cord □brain stem □cerebellum □basal nuclei □cerebral cortex
Disruption of sensory, motor, or integrative structures or pathways can
cause disruptions in homeostasis
Classification of Sensory Receptors
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General senses: somatic and visceral.
Somatic- tactile, thermal, pain, pressure and proprioceptive sensations.
Visceral- provide information about conditions within internal organs.
- example: pH. Osmolarity, O2 and CO2 levels
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Special senses- smell, taste, vision, hearing and equilibrium or balance.
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Alternate Classifications of Sensory Receptors
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Structural classification
Type of response to a stimulus
Location of receptors & origin of stimuli
Type of stimuli they detect
Copyright 2009, John Wiley & Sons, Inc.
Alternate Classifications of Sensory Receptors
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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
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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 of Receptors
Copyright 2009, John Wiley & Sons, Inc.
Unencapsulated
Nerve Endings
vs
Free nerve endings
Encapsulated Nerve
Endings
Naked nerve endings surrounded
by one or more layers
Pacinian corpuscle
skin, bones, internal organs, joints
Deeper tissue, muscles
free nerve endings
Merkel disc
Meissner’s
corpuscles
Ruffini corpuscle
root hair plexus
Pacinian
corpuscles
Classification by Stimuli Detected
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Mechanoreceptors
 detect pressure or stretch
 touch, pressure, vibration, hearing, proprioception,
equilibrium & blood pressure
Thermoreceptors detect temperature
Nociceptors detect damage to tissues (pain)
Photoreceptors detect light
Chemoreceptors detect molecules
 taste, smell & changes in body fluid chemistry
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Classification by Location
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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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Classification by Response to Stimuli
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Generator potential
 free nerve endings, encapsulated nerve endings & olfactory receptors
produce generator potentials
 when large enough, it generates a nerve impulse in a first-order neuron
Receptor potential
 vision, hearing, equilibrium and taste receptors produce receptor
potentials
 receptor cells release neurotransmitter molecules on first-order
neurons producing postsynaptic potentials
 PSP may trigger a nerve impulse
Amplitude of potentials vary with stimulus intensity
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Table 15.1 pt 1
Table 15.1 pt 2
Table 15.1 pt 3
Adaptation of Sensory Receptors
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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.
Rapidly adapting receptors: detect pressure, touch and smell.
- specialized for detecting changes
Slowly adapting receptors: detect pain, body position, and chemical
composition of the blood.
-nerve impulses continue as long as the stimulus persists
– Pain is not easily ignored.
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
Copyright 2009, John Wiley & Sons, Inc.
Somatic Sensations
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Sensory receptors in the skin (cutaneous
sensations), muscles, tendons and joints and
in the inner ear.
Uneven distribution of receptors. (tongue,
lips, fingertips)
Four modalities: tactile, thermal, pain and
proprioceptive.
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Sensory Receptors in the Skin
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Tactile Sensations
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Include touch, pressure, vibration, itch and
tickle.
Tactile receptors in the skin are Meissner
corpuscles, hair root plexuses, Merkel discs,
Ruffini corpuscles, pacinian corpuscles, and
free nerve endings.
Copyright 2009, John Wiley & Sons, Inc.
Meissner Corpuscles or Corpuscles of
Touch
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Egg-shaped mass of dendrites enclosed by a
capsule of connective tissue.
Rapidly adapting receptors.
Found in the dermal papillae of hairless skin
such as in the fingertips, hands, eyelids, tip of
the tongue, lips, nipples, soles, clitoris, and
tip of the penis.
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Hair Root Plexuses
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Rapidly adapting touch receptors found in the
hairy skin.
Free nerve endings wrapped around hair
follicles.
Detect movements on the skin surface that
disturb hairs.
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Merkel Discs or Tactile Discs
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Also known as type I cutaneous
mechanoreceptors.
Slowly adapting touch receptors.
Saucer-shaped, flattened free nerve endings.
Found in the fingertips, hands, lips, and
external genitalia.
Copyright 2009, John Wiley & Sons, Inc.
Ruffini Corpuscles
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Also called as type II cutaneous
mechanoreceptors.
Elongated, encapsulated receptors.
Located deep in the dermis and in ligaments
and tendons.
Found in the hands, and soles.
Copyright 2009, John Wiley & Sons, Inc.
Pacinian or Lamellated Corpuscles
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Large oval structure composed of a
multilayered connective tissue capsule that
encloses a dendrite.
Fast adapting receptors.
Found around joints, tendons, and muscles;
in the periosteum, mammary glands, external
genitalia, pancreas and urinary bladder.
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Thermal Sensations
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Thermoreceptors are free nerve endings.
Two distinct thermal sensations:
cold receptorswarm receptors-
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Pain Sensations
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Protective.
Sensory receptors are nociceptors.
Free nerve endings.
Two types of pain: fast and slow.
Fast pain: acute, sharp or pricking pain.
Slow pain: chronic, burning, aching or
throbbing pain.
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Referred Pain
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Pain is felt in or just deep to the skin that
overlies the stimulated organ or in a surface
area far from the stimulated organ.
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Distribution of Referred Pain
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Proprioceptive Sensations
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Receptors are called proprioceptors.
Slow adaptation.
Weight discrimination.
Three types: muscle spindles, tendon organs
and joint kinesthetic receptors.
Copyright 2009, John Wiley & Sons, Inc.
Muscle Spindles
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Interspersed among most skeletal muscle
fibers and aligned parallel to them.
Measure muscle stretching.
Consists of intrafusal muscle fibersspecialized muscle fibers with sensory nerve
endings and motor neurons called gamma
motor neurons.
Extrafusal muscle fibers- surrounding muscle
fibers supplied by alpha motor neurons.
Copyright 2009, John Wiley & Sons, Inc.
A Muscle
Spindle and a
Tendon
Organ
Tendon Organs
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Located at the junction of a tendon and a
muscle.
Protect tendons and their associated muscles
from damage due to excessive tension.
Consists of a thin capsule of connective
tissue that encloses a few tendon fascicles.
Copyright 2009, John Wiley & Sons, Inc.
Joint Kinesthetic Receptors
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Found within or around the articular capsules
of synovial joints.
Free nerve endings and Ruffini corpuscles in
the capsules of joints respond to pressure.
Pacinian corpuscles respond to acceleration
and deceleration of joints during movement.
Copyright 2009, John Wiley & Sons, Inc.
SOMATIC SENSORY PATHWAYS
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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 neuron (somatic receptor to the brain stem or spinal cord)
- either spinal or cranial nerves
→ second order neuron(brain stem/spinal cord→thalamus; decussate
→ third-order neuron(thalamus→primary somatosensory cortex).
Axon collaterals of somatic sensory neurons simultaneously carry signals
into the cerebellum and the reticular formation of the brain stem.
Major Somatic Sensory Pathways:
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The posterior column-medial lemniscus pathway.
The anterolateral (spinothalamic) pathway.
The trigeminothalamic pathway.
The anterior and posterior spinocerebellar pathway.
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The Posterior Column-Medial Lemniscus Pathway
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Conveys nerve
impulses for touch,
pressure, vibration
and conscious
proprioception from
the limbs, trunk, neck,
and posterior head to
the cerebral cortex.
Copyright 2009, John Wiley & Sons, Inc.
The Anterolateral (spinothalamic) pathway
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Conveys nerve
impulses for pain,
cold, warmth, itch,
and tickle from the
limbs, trunk, neck,
and posterior head to
the cerebral cortex.
Trigeminothalamic Pathway
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Conveys nerve
impulses for most
somatic sensations
from the face, nasal
cavity, oral cavity and
teeth to the cerebral
cortex.
Somatic Sensory Pathways to the Cerebellum
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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.
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Subconscious information used by
cerebellum for adjusting posture, balance
& skilled movements
Signal travels up to same side inferior
cerebellar peduncle
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Somatosensory Map of Postcentral Gyrus
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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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Motor Pathways
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CNS issues motor commands in response to information provided by
sensory systems sent by the somatic nervous system (SNS) and autonomic
nervous system (ANS)
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SNS → skeletal muscle contraction
ANS→innervates visceral effectors (smooth muscle, cardiac muscle, glands)
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Motor pathways usually contain 2 neurons
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Somatic nervous system (SNS)
- upper motor neuron – cell body lies within the CNS
- lower motor neuron – located in a motor nucleus of the brain stem or
SC only axon extends to the effector
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Autonomic nervous system (ANS)
- preganglionic neuron
- ganglionic neuron
Somatic Motor Pathways
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Upper motor neurons(UMN) → lower motor neurons(LMN) → skeletal
muscles.
Neural circuits involving basal ganglia and cerebellum regulate activity of the
upper motor neurons.
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Lower motor neurons are called the final common pathway because many
regulatory mechanisms converge on these peripheral neurons
Organization of Upper Motor Neuron Pathways:
Direct motor pathway- originates directly from the cerebral cortex.
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Corticospinal pathway: to the limbs and trunk.
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Corticobulbar pathway: to the head.
Indirect motor pathway- originates in the brain stem ; includes synapses
in basal ganglia, thalamus, reticular formation & cerebellum
Copyright 2009, John Wiley & Sons, Inc.
Paralysis
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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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Mapping of the Motor Areas
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Located in the
precentral gyrus of
the frontal lobe.
More cortical area is
devoted to those
muscles involved in
skilled, complex or
delicate movements.
The
Corticospinal
Pathways
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The Corticobulbar
Pathway
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Indirect or Extrapyramidal Pathways
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Originate in the brain stem.
Include:
 Rubrospinal tract
 Tectospinal tract
 Vestibulospinal tract
 Reticulospinal tract
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Table 5.4 pt 1
Table 5.4 pt 2
Modulation of Movement from the
Basal Ganglia and Cerebellum
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basal ganglia help establish muscle tone & integrate semivoluntary
automatic movements
cerebellum helps make movements smooth & helps maintain posture &
balance
Basal ganglia and cerebellum provide input and control activity of upper
motor neurons
Copyright 2009, John Wiley & Sons, Inc.
Motor areas of
cerebral cortex
Sagittal
plane
Corrective
feedback
Thalamus
Motor centers in
brainstem
Cortex of
cerebellum
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1
3
Pons
Pontine nuclei
2
Direct pathways
Sensory signals from
proprioceptors in muscles
and joints, vestibular
apparatus, and eyes
Sagittal section through brain and spinal cord
Indirect pathways
Signals to lower
motor neurons
Final Common
Pathway
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Lower motor neurons receive
signals from both direct &
indirect upper motor neurons
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Sum total of all inhibitory &
excitatory signals determines
the final response of the
lower motor neuron & the
skeletal muscles
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Integrative Functions of the Cerebrum
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Wakefulness and sleepLearning and memoryEmotional responses
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Wakefulness and Sleep
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Role of the Reticular Activating System (RAS)
Sleep and wakefulness are integrative functions that are controlled by the
reticular activating system
 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
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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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The role of Reticular Activating
System (RAS) in Awakening
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Consists of neurons
whose axons project from
the reticular formation
through the thalamus to
the cerebral cortex.
Increased activity of the
RAS causes awakening
from sleep (arousal).
Copyright 2009, John Wiley & Sons, Inc.
Sleep
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A state of altered consciousness.
Two components: non-rapid eye movement (NREM) sleep and rapid
eye movement (REM) sleep.
NREM sleep consists of four stages:
 Stage 1- 1-7 min transitional
 Stage 2- light sleep
 Stage 3- tem and blood pressure decrease, occures about 20
minutes after sleep
 Stage 4- deepest – sleep walking lowest brain metabolism
Dreaming occurs during REM sleep
Triggers for sleep are unclear
 adenosine levels increase with brain activity
 adenosine levels inhibit activity in RAS
 caffeine prevents adenosine from inhibiting RAS
Copyright 2009, John Wiley & Sons, Inc.
Non-Rapid Eye Movement Sleep
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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
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REM Sleep
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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
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Learning is the ability to acquire new knowledge or skills through instruction
or experience.
Memory is the process by which that knowledge is stored & retrieved.
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.
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.
Memory consolidation – frequent retrieval of a piece of information
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Learning & Memory
Stimulus
Sensory organs
perception
Sensory Memory
(millisecond-1)
repetition
attention
Short-Term Memory
Working Memory
(< 1 minute)
Long-Term Memory
( days, months, years)
forgetting
Amnesia – Loss of Memory
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Anterograde amnesia - loss of memory for
events that occur after the trauma; the
inability to form new memories.
Retrograde amnesia - loss of memory for
events that occurred before the trauma; the
inability to recall past events.
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