Tortora & Grabowski 9/e 2000 JWS 15-1 Chapter 15 Sensory, Motor & Integrative Systems Levels and...

Tortora & Grabowski 9/e 2000 JWS 15-1

Chapter 15Sensory, Motor & Integrative Systems

• 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


Is Sensation Different from Perception?

• Sensation is any stimuli the body is aware of– What are we not aware of?

• X-rays, ultra high frequency sound waves, UV light

– We have no sensory receptors for those stimuli

• Perception is the conscious awareness & interpretation of a sensation.– precisely localization & identification– memories of our perceptions are stored in cortex


Sensory Modalities

• Different types of sensations– touch, pain, temperature, vibration, hearing, vision

• Each type of sensory neuron can respond to only one type of stimuli

• Two classes of sensory modalities– general senses

• somatic are sensations from body walls

• visceral are sensations from internal organs

– special senses • smell, taste, hearing, vision, and balance


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


Sensory Receptors• Selectively respond to only one kind of stimuli

• Have simple or complex structures– 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


Classification of Sensory Receptors

• Structural classification

• Type of response to a stimulus

• Location of receptors & origin of stimuli

• Type of stimuli they detect


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


Structural Classification

• Compare free nerve ending, encapsulated nerve ending and sensory receptor cell


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 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


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


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


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

• Receptors vary in their ability to adapt– Rapidly adapting receptors (smell, pressure, touch)

• adapt quickly; specialized for signaling stimulus changes

– Slowly adapting receptors (pain, body position)• continuation of nerve impulses as long as stimulus persists


Somatic Tactile Sensations• 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


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


•Free nerve endings found around follicles, detects movement of hair

Hair Root Plexus


Merkel’s Disc

• Flattened dendrites touching cells of stratum basale

• Used in discriminative touch (25% of receptors in hands)


Ruffini Corpuscle

• Found deep in dermis of skin• Detect heavy touch, continuous touch, & pressure


Pacinian Corpuscle

• Onion-like connective tissue capsule enclosing a dendrite

• Found in subcutaneous tissues & certain viscera

• Sensations of pressure or high-frequency vibration


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.


Pain Sensations

• Nociceptors = pain receptors

• Free nerve endings found in every tissue of body except the brain

• Stimulated by excessive distension, muscle spasm, & inadequate blood flow

• Tissue injury releases chemicals such as K+, kinins or prostaglandins that stimulate nociceptors

• Little adaptation occurs


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


Localization of Pain

• Superficial Somatic Pain arises from skin areas

• Deep Somatic Pain arises from muscle, joints, tendons & fascia

• Visceral Pain arises from receptors in visceral organs– localized damage (cutting) intestines causes no pain– diffuse visceral stimulation can be severe

• distension of a bile duct from a gallstone

• distension of the ureter from a kidney stone

• Phantom limb sensations -- cells in cortex still


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


Pain Relief

• 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.


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– from muscle, tendon, joint capsules & hair cells

in the vestibular apparatus


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


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


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


Somatic Sensory Pathways

• First-order neuron conduct impulses to brainstem or spinal cord– either spinal or cranial nerves

• Second-order neurons conducts impulses from spinal cord or brainstem to thalamus--cross over to opposite side before reaching thalamus

• Third-order neuron conducts impulses from thalamus to primary somatosensory cortex (postcentral gyrus of parietal lobe)


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


Spinothalamic Pathways• 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


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


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


Tertiary Syphilis

• 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 still uncoordinated and jerky


Somatic Motor Pathways• 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


Primary Motor Cortex

• Precentral gyrus initiates voluntary movement

• Cells are called upper motor neurons• Muscles represented unequally

(according 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


Direct Pathway (Pyramidal Pathway)• 1 million upper motor neurons in cerebral cortex

– 60% in precentral gyrus & 40% in postcentral gyrus

• 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 or anterior horns of spinal cord

• Integrate excitatory & inhibitory input to become final common pathway


Details of Motor 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


Location of Direct Pathways

• Lateral corticospinal tract• Anterior corticospinal tract• Corticobulbar tract


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


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


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


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• Damage is characterized by tremors or twitches


Basal Ganglia Connections

• 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


Cerebellar FunctionAspects 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


Wakefulness and Sleep

• Circadian rhythm– 24 hour cycle of sleep and awakening– established by hypothalamus

• Awake means to be able to react consciously to stimuli

• EEG recordings show large amount of activity in cerebral cortex when awake


Reticular Activating System

• RAS has connections tocortex & spinal cord.

• Many types of inputsactivate the RAS---pain,light, noise, muscle activity, touch

• Produces state of wakefulness called consciousness

• Coma is sleeplike state– deep coma has no reflexes

– death if cardiovascular reflexes are lost


Sleep

• State of altered or partial consciousness from which a person can be aroused

• Triggers for sleep are unclear– adenosine levels increase with brain activity– adenosine levels inhibit activity in RAS– caffeine prevents adenosine from inhibiting RAS

• Two types of normal sleep– NREM = non-rapid eye movement sleep– REM = rapid eye movement sleep


Non-Rapid Eye Movement Sleep• Stage 1

– person is drifting off with eyesclosed (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


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 highest in REM sleep

• Total sleeping & dreaming time decreases with age


Learning & Memory• Learning is acquiring new knowledge• Memory is retaining that knowledge

– short-term memory• recall phone number while dialing• depends upon electrical events (reverberating circuits)

– long-term memory• frequent retrieval of specific information helps with memory

consolidation (learning)• structural or biochemical changes occurs

– increase in dendrites, enlarge endbulbs, increase in presynaptic terminals or formation of additional membrane receptors

• Recently acquired memory lost first with coma or shock treatments


Spinal Cord Injury• Damaged by tumor, herniated disc, clot or trauma• Complete transection is cord severed resulting loss

of both sensation & movement below the injury• 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


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


Parkinson Disease• Progressive disorder striking victims at age 60• Environmental toxins may be the cause• 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, even facial expression

• Treatments– drugs to increase dopamine levels, or to prevent its

breakdown, surgery to transplant fetal tissue or removal of part of globus pallidus to slow tremors

Tortora & Grabowski 9/e 2000 JWS 15-1 Chapter 15 Sensory, Motor & Integrative Systems Levels and...

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