The Sensory System Hearing General Senses RAD 101 Chapter 10.

The Sensory SystemHearing

General SensesRAD 101

Chapter 10

Anatomy of the EarAnatomy of the Ear

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The ear is divided into three areas Outer

(external) ear

Middle ear

Inner ear

Figure 8.12

The External EarThe External Ear

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Involved in hearing only

Structures of the external ear Pinna

(auricle)

External auditory canal

Figure 8.12

The External Auditory CanalThe External Auditory Canal

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Narrow chamber in the temporal bone

Lined with skin

Ceruminous (wax) glands are present

Ends at the tympanic membrane

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

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Air-filled cavity within the temporal bone

Only involved in the sense of hearing

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

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Two tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic membrane

The eustachian (auditory) tube connecting the middle ear with the throat

Allows for equalizing pressure during yawning or swallowing

This tube is otherwise collapsed

Bones of the Tympanic CavityBones of the Tympanic Cavity

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Three bones span the cavity

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Figure 8.12

Bones of the Tympanic CavityBones of the Tympanic Cavity

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Vibrations from eardrum move the ossicles

These bones transfer sound to the inner ear through the oval window

Figure 8.12

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

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Includes sense organs for hearing and balance

Filled with perilymph

Figure 8.12

Inner Ear or Bony LabrynthInner Ear or Bony Labrynth

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A maze of bony chambers within the temporal bone

Cochlea

Vestibule

Semicircular canals

Figure 8.12

Organs of HearingOrgans of Hearing

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Organ of Corti

Located within the cochlea

Receptors = hair cells on the basilar membrane

Gel-like tectorial membrane is capable of bending hair cells

Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of HearingOrgans of Hearing

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Figure 8.13

Mechanisms of HearingMechanisms of Hearing

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Vibrations from sound waves move tectorial membrane

Hair cells are bent by the membrane

An action potential starts in the cochlear nerve

Continued stimulation can lead to adaptation

Mechanisms of HearingMechanisms of Hearing

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Figure 8.14

Organs of EquilibriumOrgans of Equilibrium

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Receptor cells are in two structures

Vestibule

Semicircular canals

Figure 8.16a, b

Organs of EquilibriumOrgans of Equilibrium

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Equilibrium has two functional parts

Static equilibrium

Dynamic equilibrium

Figure 8.16a, b

Static EquilibriumStatic Equilibrium

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Maculae – receptors in the vestibule Report on the position of the head

Send information via the vestibular nerve

Anatomy of the maculae Hair cells are embedded in the otolithic

membrane

Otoliths (tiny stones) float in a gel around the hair cells

Movements cause otoliths to bend the hair cells

Function of MaculaeFunction of Maculae

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Figure 8.15

Dynamic EquilibriumDynamic Equilibrium

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Cristae – receptors in the semicircular canals

Function when the body is spinning or moving in different directions

An impulse is sent via the vestibular nerve to the cerebellum

Figure 8.16c

Chemical Senses – Taste and Chemical Senses – Taste and SmellSmell

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Both senses use chemoreceptors

Stimulated by chemicals in solution

Taste has four types of receptors

Smell can differentiate a large range of chemicals

Both senses complement each other and respond to many of the same stimuli

Olfaction – The Sense of SmellOlfaction – The Sense of Smell

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Olfactory receptors are in the roof of the nasal cavity

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex

Olfactory EpitheliumOlfactory Epithelium

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Figure 8.17

The Sense of TasteThe Sense of Taste

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Taste buds house the receptor organs

Location of taste buds Most are on

the tongue

Soft palate

Cheeks Figure 8.18a, b

The Tongue and TasteThe Tongue and Taste

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The tongue is covered with projections called papillae

Taste buds are found on the sides of papillae

Structure of Taste BudsStructure of Taste Buds

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Gustatory cells are the receptors

Have gustatory hairs (long microvilli)

Hairs are stimulated by chemicals dissolved in saliva

Structure of Taste BudsStructure of Taste Buds

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Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas

Facial nerve

Glossopharyngeal nerve

Vagus nerve

Taste SensationsTaste Sensations

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Sweet receptors (tip of tongue) Sugars Saccharine Some amino acids

Sour receptors (laterally on the tongue Acids

Bitter receptors (posterior part of tongue) Alkaloids

Salty receptors (anterior sides of the tongue) Metal ions

Developmental Aspects of the Developmental Aspects of the Special SensesSpecial Senses

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Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth

The General SensesThe General Senses

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Touch

Tactile receptors found in the dermis of the skin

Sensitivity varies with number of touch receptors

Pressure

Receptors for deep touch located in the subcutaneous tissue

Sense of temperatureSense of temperature

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Free nerve endings widely distributed in the skin

Separate receptors for heat and cold

Temperature receptors in the hypothalamus help to adjust body temperature

Sense of PositionSense of Position

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Proprioreceptors located in muscles, tendons and joints

Relay impulses that help to judge position and changes in location of body parts

Inform the brain of muscle and tendon tension

Aided by equilibrium receptors in the internal ear

Kinesthesia Sense of body movement

Sense of PainSense of Pain

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Receptors are widely distributed nerve endings

Two pathways to brain

Sharp acute pain

Slow, chronic pain

Pain ReliefPain Relief

• Analgesic drugs• Nonnarcotic analgesics

• Act locally to reduce inflammation• Non-steroidal antiflammatory drugs (NSAIDS)

• Ibuprofen, naproxen

• Narcotic• Act on the CNS to alter the reception and response to pain

• Anesthetics• Prevent pain during surgery• Used to prevent chronic pain

• Endorphins

Pain ReliefPain Relief

• Endorphins• Released naturally from certain areas of the

brain• Associated with pain relief

• Applications of heat and cold• Relaxation or distraction techniques

Sensory AdaptationSensory Adaptation

• When exposed to continuous stimulus, sensory receptors adjust themselves so the sensation becomes less acute