LAB EXERCISE 18LAB EXERCISE 18GENERAL SENSESGENERAL SENSES

Sensory Information Afferent Division of the Nervous Afferent Division of the Nervous

SystemSystem

– ReceptorsReceptors

– Sensory neuronsSensory neurons

– Sensory pathwaysSensory pathways

Spinal cord to brainSpinal cord to brain

Deliver somatic and visceral Deliver somatic and visceral

sensory information to their sensory information to their

final destinations inside the final destinations inside the

CNS using:CNS using:

– NervesNerves

– NucleiNuclei

– Sensory tractsSensory tracts

Sensoryprocessingcenters in

brain

Sensorypathways

Generalsensory

receptors

Conscious andsubconsciousmotor centers

in brain

Higher-Order Functions

Memory, learning, andintelligence may

influence interpretationof sensory information

and nature of motoractivities

Sensory Information Somatic Motor Portion of the Efferent Somatic Motor Portion of the Efferent

DivisionDivision

– Controls peripheral effectorsControls peripheral effectors

Skeletal muscleSkeletal muscle

Somatic Motor CommandsSomatic Motor Commands

– Travel from motor centers in the Travel from motor centers in the

brain along brain along somatic motor somatic motor

pathwayspathways of: of:

Motor nucleiMotor nuclei

TractsTracts

NervesNerves

Motorpathways

SomaticNervous

System (SNS)

Skeletalmuscles

Sensory Receptors General Senses General Senses

– Describe our sensitivity to:Describe our sensitivity to:

TemperatureTemperature

PainPain

TouchTouch

PressurePressure

VibrationVibration

ProprioceptionProprioception

Sensory Receptors Special SensesSpecial Senses

The Special SensesThe Special Senses

– Are provided by special sensory receptorsAre provided by special sensory receptors

– OlfactionOlfaction (smell) (smell)

– VisionVision (sight) (sight)

– GustationGustation (taste) (taste)

– EquilibriumEquilibrium (balance) (balance)

– HearingHearing

SENSATION VS PERCEPTION SensationSensation

– Occurs when Occurs when nerve impulses arrive at nerve impulses arrive at the cerebral cortexthe cerebral cortex From sensory neurons created by an From sensory neurons created by an

action potential.action potential.–ChemoreceptorsChemoreceptors–ThermoreceptorsThermoreceptors–NociceptorsNociceptors–BaroreceptorsBaroreceptors

– What we are not aware ofWhat we are not aware of

SESNSATION VS PERCEPTION

PerceptionPerception–Perception is the conscious Perception is the conscious

awareness & interpretation of a awareness & interpretation of a sensationsensation

–Occurs when the cerebral cortex Occurs when the cerebral cortex interprets the meaning of interprets the meaning of sensations.sensations.

We have no perception of some information because it never reaches the cortex.

Blood pressure is received in the medulla

Sensory Integration Input comes fromInput comes from

– ExteroceptorsExteroceptors

– InteroceptorsInteroceptors

– ProprioceptorsProprioceptors

Input is relayed toward the Input is relayed toward the head, and is processed along head, and is processed along the waythe way

Sensory Receptors1.1. ExteroceptorsExteroceptors

– Respond to stimuli arising Respond to stimuli arising outside the bodyoutside the body

– Receptors in the skinReceptors in the skin TouchTouch PressurePressure PainPain TemperatureTemperature

– Most special sense organsMost special sense organs VisionVision HearingHearing EquilibriumEquilibrium TasteTaste SmellSmell

Sensory Receptors2.2. InteroceptorsInteroceptors

**Visceroceptors**Visceroceptors

– Respond to stimuli Respond to stimuli arising in internal arising in internal viscera and blood viscera and blood vesselsvessels

– Sensitive toSensitive to Chemical changesChemical changes Tissue stretchTissue stretch Temperature changesTemperature changes PainPain DiscomfortDiscomfort Hunger Hunger ThirstThirst

Sensory Receptors3.3. ProprioceptorsProprioceptors

– Provide a purely somatic sensationProvide a purely somatic sensation– Respond to stretch inRespond to stretch in

Skeletal musclesSkeletal muscles TendonsTendons JointsJoints LigamentsLigaments Connective tissue coverings of bones Connective tissue coverings of bones

and musclesand muscles

– Inform the brain of one’s body Inform the brain of one’s body movementsmovements

– No proprioceptors in the visceral organs of No proprioceptors in the visceral organs of

the thoracic and abdominopelvic cavitiesthe thoracic and abdominopelvic cavities

You cannot tell where your spleen, You cannot tell where your spleen,

appendix, or pancreas is at the appendix, or pancreas is at the

momentmoment

Processing at the Circuit Level This level consists of This level consists of

pathways of three pathways of three neurons conduct sensory neurons conduct sensory impulses upward to the impulses upward to the appropriate brain regionsappropriate brain regions

– First order neuronsFirst order neurons– Second order neuronsSecond order neurons– Third order neuronsThird order neurons

Processing at the Circuit Level First order First order

neuronsneurons– Conduct Conduct

impulses from impulses from the receptor the receptor level to the level to the second-order second-order neurons in the neurons in the brain stem or brain stem or spinal cordspinal cord

Processing at the Circuit Level Second-order neuronsSecond-order neurons

– Transmit impulses to theTransmit impulses to the ThalamusThalamus

–Tracts cross overTracts cross over

Processing at the Circuit Level Third-order neuronsThird-order neurons

– Conduct impulses Conduct impulses fromfrom The thalamus to The thalamus to The The

somatosensory somatosensory cortexcortex–Perceptual Perceptual

levellevel

The axons of the third order The axons of the third order continue to ascend without continue to ascend without crossing over to the crossing over to the somatosensory area.somatosensory area.– As a resultAs a result

Left cerebral hemispheres Left cerebral hemispheres receive info from the right receive info from the right sideside

Right cerebral Right cerebral hemispheres receive info hemispheres receive info from the left sidefrom the left side

Processing at the Perceptual Level

Sensory Receptors

Learning OutcomesLearning Outcomes

15-3 15-3 Identify the receptors for theIdentify the receptors for the general senses, and describegeneral senses, and describe how they function.how they function.

Sensory Receptors General Sensory Receptors General Sensory Receptors

– Are divided into four types by the nature of the stimulus that excites Are divided into four types by the nature of the stimulus that excites

themthem

1.1. ChemoreceptorsChemoreceptors

**Chemical concentration**Chemical concentration

2.2. NociceptorsNociceptors

**P**Painain

3. Thermoreceptors3. Thermoreceptors

**Temperature**Temperature

4. Mechanoreceptors4. Mechanoreceptors

**Physical distortion**Physical distortion

Classifying Sensory Receptors Nociceptors Nociceptors (Pain Receptors)(Pain Receptors)

– MostMost concentrated in the superficial portions of the skin concentrated in the superficial portions of the skin

– In joint capsules In joint capsules

– Within the periostea of bones Within the periostea of bones

– Around the walls of blood vesselsAround the walls of blood vessels

Classifying Sensory Receptors Nociceptors Nociceptors

– Are free nerve endingsAre free nerve endings with large receptive fieldswith large receptive fields

– May be sensitive to:May be sensitive to:

1.1. Temperature extremes Temperature extremes

2.2. Mechanical damage Mechanical damage

3.3. Dissolved chemicals, such as chemicals Dissolved chemicals, such as chemicals

released by injured cellsreleased by injured cells

*Associated with tissue damage*Associated with tissue damage

Type A or Type CType A or Type C

Classifying Sensory Receptors

– Myelinated Type A Nociceptor fibersMyelinated Type A Nociceptor fibers

Carry sensations of Carry sensations of fast painfast pain, or , or prickling painprickling pain, ,

such as that caused by an injection or a deep cutsuch as that caused by an injection or a deep cut

Sensations reach the CNS quickly and often Sensations reach the CNS quickly and often

trigger somatic reflexestrigger somatic reflexes

Relayed to the primary sensory cortex and receive Relayed to the primary sensory cortex and receive

conscious attentionconscious attention

Classifying Sensory Receptors

– Type C Nociceptor fibersType C Nociceptor fibers

Carry sensations of Carry sensations of slow painslow pain, or , or burning and burning and

aching painaching pain

Cause a generalized activation of the reticular Cause a generalized activation of the reticular

formation and thalamusformation and thalamus

You become aware of the pain but only have a You become aware of the pain but only have a

general idea of the area affectedgeneral idea of the area affected

-Referred pain -Referred pain

“ “Incorrect" source perceivedIncorrect" source perceived

*Pain in the forehead when eating ice cream too quick*Pain in the forehead when eating ice cream too quick

*Heartburn*Heartburn

*Dentistry *Dentistry

*Angina *Angina

––Pain in the arm when the heart does not receive enough oxygenPain in the arm when the heart does not receive enough oxygen

Classifying Sensory Receptors

Classifying Sensory Receptors ThermoreceptorsThermoreceptors

– Also called temperature receptorsAlso called temperature receptors

– Are free nerve endings located in:Are free nerve endings located in:

The dermisThe dermis

Skeletal musclesSkeletal muscles

The liverThe liver

The hypothalamusThe hypothalamus

Classifying Sensory Receptors Mechanoreceptors Mechanoreceptors

– Sensitive to stimuli that distort their plasma Sensitive to stimuli that distort their plasma

membranesmembranes

– Contain Contain mechanically gated ion channelsmechanically gated ion channels

whose gates open or close in response to:whose gates open or close in response to: StretchingStretching

CompressionCompression

TwistingTwisting

Other distortions of the membraneOther distortions of the membrane

Classifying Sensory Receptors Three Classes of Mechanoreceptors Three Classes of Mechanoreceptors

1.1. Tactile receptorsTactile receptors Provide the sensations ofProvide the sensations of

– TouchTouch

» Shape & textureShape & texture

– PressurePressure

» Degree of distortionDegree of distortion

– VibrationVibration

» Pulsing or oscillating pressurePulsing or oscillating pressure

Classifying Sensory Receptors Three Classes of Mechanoreceptors Three Classes of Mechanoreceptors

2.2. Baroreceptors Baroreceptors

Detect pressure changes in Detect pressure changes in

– Walls of blood vessels Walls of blood vessels

– Portions of the digestivePortions of the digestive

– Portions of the reproductivePortions of the reproductive

– Portions of the urinary tractsPortions of the urinary tracts

Classifying Sensory Receptors

Three Classes of Mechanoreceptors Three Classes of Mechanoreceptors

3.3. Proprioceptors Proprioceptors

Monitor the positions of joints and musclesMonitor the positions of joints and muscles

The most structurally and functionally complex of The most structurally and functionally complex of

general sensory receptorsgeneral sensory receptors

Classifying Sensory Receptors Tactile ReceptorsTactile Receptors

– Fine touch Fine touch andand pressure receptors pressure receptors

Are extremely sensitiveAre extremely sensitive

Have a relatively narrow receptive fieldHave a relatively narrow receptive field

Provide detailed information about a source of Provide detailed information about a source of

stimulation stimulation

– Including its exact location, shape, size, texture, Including its exact location, shape, size, texture,

movementmovement

Classifying Sensory Receptors Tactile ReceptorsTactile Receptors

– Fine touch Fine touch andand pressure receptors pressure receptors

Are extremely sensitiveAre extremely sensitive

Have a relatively narrow receptive fieldHave a relatively narrow receptive field

Provide detailed information about a source of Provide detailed information about a source of

stimulation stimulation

– Including its exact location, shape, size, texture, Including its exact location, shape, size, texture,

movementmovement

Classifying Sensory Receptors

Tactile ReceptorsTactile Receptors

– Crude touch Crude touch andand pressure receptors pressure receptors

Have relatively large receptive fieldsHave relatively large receptive fields

Provide poor localizationProvide poor localization

Give little information about the stimulusGive little information about the stimulus

Classifying Sensory Receptors Six Types of Tactile Receptors in the SkinSix Types of Tactile Receptors in the Skin

1.1. Free Nerve Endings Free Nerve Endings

Sensitive to touch and pressureSensitive to touch and pressure

Situated between epidermal cellsSituated between epidermal cells

Free nerve endings providing Free nerve endings providing touch sensations are tonic touch sensations are tonic

receptors with small receptive fieldsreceptors with small receptive fields

Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Six Types of Tactile Receptors in the Skin

2.2. Root hair plexus Root hair plexus nerve endingsnerve endings

Monitor distortions and movements across the body surface Monitor distortions and movements across the body surface

wherever hairs are locatedwherever hairs are located

Adapt rapidly, so are best at detecting initial contact and Adapt rapidly, so are best at detecting initial contact and

subsequent movementssubsequent movements

Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Six Types of Tactile Receptors in the Skin

3.3. Tactile discsTactile discs

Also called Also called Merkel discsMerkel discs

Fine touch and pressure receptorsFine touch and pressure receptors

Extremely sensitive to tonic receptors Extremely sensitive to tonic receptors

Have very small receptive fieldsHave very small receptive fields

Classifying Sensory Receptors Six Types of Tactile Receptors in the SkinSix Types of Tactile Receptors in the Skin

4.4. Tactile corpusclesTactile corpuscles

Also called Also called Meissner’s corpusclesMeissner’s corpuscles

Perceive sensations of fine touch, pressure, and low-Perceive sensations of fine touch, pressure, and low-

frequency vibrationfrequency vibration

Adapt to stimulation within 1 second after contactAdapt to stimulation within 1 second after contact

Fairly large structuresFairly large structures

Most abundant in the eyelids, lips, fingertips, nipples, Most abundant in the eyelids, lips, fingertips, nipples,

and external genitaliaand external genitalia

Classifying Sensory Receptors Six Types of Tactile Receptors in the Skin Six Types of Tactile Receptors in the Skin

5.5. Lamellated corpuscles Lamellated corpuscles

Also called Also called Pacinian corpusclesPacinian corpuscles

Sensitive to deep pressureSensitive to deep pressure

Fast-adapting receptorsFast-adapting receptors

Most sensitive to pulsing or high-frequency vibrating stimuliMost sensitive to pulsing or high-frequency vibrating stimuli

Meissner’s vs Pacinian If you close your eyes and have a friend place an object in the open If you close your eyes and have a friend place an object in the open

palm of your hand, chances are good you will be able to detect the palm of your hand, chances are good you will be able to detect the object but you will not be able to identify it. object but you will not be able to identify it.

By moving the object to your finger tips where Meissner's corpuscles are By moving the object to your finger tips where Meissner's corpuscles are abundant, you gather information about its shape, texture, and density, abundant, you gather information about its shape, texture, and density, information your brain uses to identify the object. information your brain uses to identify the object.

– The Pacinian corpuscles enable you to detect the object due to its The Pacinian corpuscles enable you to detect the object due to its

weight. weight. – Meisner’s enable you to define it by fine touchMeisner’s enable you to define it by fine touch

Classifying Sensory Receptors Six Types of Tactile Receptors in the SkinSix Types of Tactile Receptors in the Skin

6.6. Ruffini corpusclesRuffini corpuscles

Also sensitive to pressure and distortion of the skinAlso sensitive to pressure and distortion of the skin

Located in the reticular (deep) dermisLocated in the reticular (deep) dermis

Tonic receptors that show little if any adaptationTonic receptors that show little if any adaptation

Classifying Sensory Receptors BaroreceptorsBaroreceptors

– Monitor change in pressureMonitor change in pressure

– Consist of free nerve endings that branch Consist of free nerve endings that branch

within elastic tissues within elastic tissues

In wall of distensible organ (such as a blood In wall of distensible organ (such as a blood

vessel)vessel)

– Respond immediately to a change in Respond immediately to a change in

pressure, but adapt rapidlypressure, but adapt rapidly

Classifying Sensory Receptors

ProprioceptorsProprioceptors

– Monitor:Monitor:

Position of jointsPosition of joints

Tension in tendons and ligamentsTension in tendons and ligaments

State of muscular contractionState of muscular contraction

Classifying Sensory Receptors

Three Major Groups of Proprioceptors Three Major Groups of Proprioceptors

1.1. Muscle spindles Muscle spindles

2.2. Golgi tendon organsGolgi tendon organs

3.3. Receptors in joint capsules Receptors in joint capsules

Classifying Sensory Receptors

Muscle Spindles Muscle Spindles

– Monitor skeletal Monitor skeletal

muscle length muscle length

– Trigger stretch Trigger stretch

reflexesreflexes

Classifying Sensory Receptors Golgi Tendon OrgansGolgi Tendon Organs

– Located at the junction between skeletal muscle and its tendon Located at the junction between skeletal muscle and its tendon

– Stimulated by tension in tendonStimulated by tension in tendon

– Monitor external tension developed during muscle contractionMonitor external tension developed during muscle contraction

Classifying Sensory Receptors Receptors in Joint Capsules Receptors in Joint Capsules

– Free nerve endings detect pressure, tension, Free nerve endings detect pressure, tension,

movement at the jointmovement at the joint

ChemoreceptorsChemoreceptors

Respond to small concentration Respond to small concentration changes of specific molecules changes of specific molecules (chemicals)(chemicals)

Internal chemoreceptors monitor Internal chemoreceptors monitor blood composition (e.g. Nablood composition (e.g. Na++, pH, , pH, pCOpCO2 2 ))

Found within aortic and carotid Found within aortic and carotid bodiesbodies

Very important for homeostasisVery important for homeostasis

ChemoreceptorsChemoreceptors

Respond to small concentration Respond to small concentration changes of specific molecules changes of specific molecules (chemicals)(chemicals)

Internal chemoreceptors monitor Internal chemoreceptors monitor blood composition (e.g. Nablood composition (e.g. Na++, pH, , pH, pCOpCO2 2 ))

Found within aortic and carotid Found within aortic and carotid bodiesbodies

Very important for homeostasisVery important for homeostasis

IN REVIEW

IN REVIEW