Chapter 16: Sensory, Motor, and Integrative Systems Copyright 2009, John Wiley & Sons, Inc

Chapter 16: Sensory, Motor,

and Integrative Systems

Copyright 2009, John Wiley & Sons, Inc.

Sensation ,Perception & Integration 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 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

Special senses- smell, taste, vision, hearing and equilibrium or balance. Alternate Classifications of Sensory Receptors

Structural classification Type of response to a stimulus Location of receptors & origin of stimuli Type of stimuli they detect


Alternate Classifications of Sensory Receptors

Structural classification Type of response to a stimulus Location of receptors & origin of stimuli Type of stimuli they detect

Principles of Human Anatomy and Physiology, 11e 4

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 of Receptors

skin, bones, internal organs, joints

Naked nerve endings surrounded by one or more layers

Pacinian corpuscle

Free nerve endings

Encapsulated Nerve Encapsulated Nerve

EndingsEndingsvsUnencapsulated Unencapsulated

Nerve EndingsNerve Endings

Deeper tissue, muscles

free nerve endings

root hair plexus

Meissner’s corpuscles

Pacinian corpuscles

Ruffini corpuscle

Merkel disc

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 (pain) Photoreceptors detect light Chemoreceptors detect molecules

taste, smell & changes in body fluid chemistry


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 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


Table 15.1 pt 1

Table 15.1 pt 2

Table 15.1 pt 3

Adaptation of 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. 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


Somatic Sensations

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.


Sensory Receptors in the Skin


Tactile Sensations

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.


Meissner Corpuscles or Corpuscles of Touch 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.


Hair Root Plexuses

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.


Merkel Discs or Tactile Discs

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.


Ruffini Corpuscles

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.


Pacinian or Lamellated Corpuscles 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.


Thermal Sensations

Thermoreceptors are free nerve endings. Two distinct thermal sensations:

cold receptors-

warm receptors-


Pain Sensations

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.


Referred Pain

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.


Distribution of Referred Pain


Proprioceptive Sensations

Receptors are called proprioceptors. Slow adaptation. Weight discrimination. Three types: muscle spindles, tendon organs

and joint kinesthetic receptors.


Muscle Spindles

Interspersed among most skeletal muscle fibers and aligned parallel to them.

Measure muscle stretching. Consists of intrafusal muscle fibers-

specialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons.

Extrafusal muscle fibers- surrounding muscle fibers supplied by alpha motor neurons.


A Muscle Spindle and a Tendon Organ

Tendon Organs

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.


Joint Kinesthetic Receptors

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.


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 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: The posterior column-medial lemniscus pathway. The anterolateral (spinothalamic) pathway. The trigeminothalamic pathway. The anterior and posterior spinocerebellar pathway.

33

The Posterior Column-Medial Lemniscus Pathway

Conveys nerve impulses for touch, pressure, vibration and conscious proprioception from the limbs, trunk, neck, and posterior head to the cerebral cortex.


The Anterolateral (spinothalamic) pathway

Conveys nerve impulses for pain, cold, warmth, itch, and tickle from the limbs, trunk, neck, and posterior head to the cerebral cortex.

Trigeminothalamic Pathway

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 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.

Subconscious information used by cerebellum for adjusting posture, balance & skilled movements Signal travels up to same side inferior cerebellar peduncle


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


Motor Pathways CNS issues motor commands in response to information provided by sensory systems

sent by the somatic nervous system (SNS) and autonomic nervous system (ANS)

SNS → skeletal muscle contraction ANS→innervates visceral effectors (smooth muscle, cardiac muscle, glands)

Motor pathways usually contain 2 neurons

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

Autonomic nervous system (ANS) - preganglionic neuron - ganglionic neuron

Somatic Motor Pathways Upper motor neurons(UMN) → lower motor neurons(LMN) → skeletal muscles. Neural circuits involving basal ganglia and cerebellum regulate activity of the upper motor

neurons. 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.

Corticospinal pathway: to the limbs and trunk. Corticobulbar pathway: to the head.

Indirect motor pathway- originates in the brain stem ; includes synapses

in basal ganglia, thalamus, reticular formation & cerebellum


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


Mapping of the Motor Areas

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


The Corticobulbar Pathway


Indirect or Extrapyramidal Pathways

Originate in the brain stem. Include:

Rubrospinal tract Tectospinal tract Vestibulospinal tract Reticulospinal tract


Table 5.4 pt 1

Table 5.4 pt 2

Modulation of Movement from the Basal Ganglia and Cerebellum

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


Sagittalplane

Motor areas ofcerebral cortex

Thalamus

Correctivefeedback

Motor centers inbrainstem

Pons

Pontine nuclei

Direct pathways

Indirect pathways

Signals to lowermotor neurons

Sagittal section through brain and spinal cord

Sensory signals fromproprioceptors in musclesand joints, vestibularapparatus, and eyes

Cortex ofcerebellum

1

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

Thalamus


Pontine nuclei

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

3

Thalamus


Pontine nuclei

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

4

3

Thalamus


Pontine nuclei

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


Integrative Functions of the Cerebrum Wakefulness and sleep- Learning and memory- Emotional responses


Wakefulness and Sleep

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.


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.


The role of Reticular Activating System (RAS) in Awakening 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).


Sleep 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


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


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


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 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


Learning & Memory

Sensory organs

StimulusStimulus

Sensory Memory(millisecond-1)

Sensory Memory(millisecond-1)

Short-Term MemoryWorking Memory

(< 1 minute)

Short-Term MemoryWorking Memory

(< 1 minute)

Long-Term Memory( days, months, years)Long-Term Memory

( days, months, years)

perception

attention

forgettingrepetition

Amnesia – Loss of Memory

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.


Documents

Chapter 16: Sensory, Motor, and Integrative Systems Copyright 2009, John Wiley & Sons, Inc