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The Sensory System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The Sensory System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

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Page 1: The Sensory System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display

The Sensory System

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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Introduction

A stimulated sensory receptor sends a signal to the brain

Signals are interpreted in the brain

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Introduction

Five types of sensory receptorsMechanoreceptors – stimulated by changes in

pressure or body movementThermoreceptors – stimulated by changes in the

external or internal temperaturePain receptors – stimulated by damage or oxygen

deprivation to the tissuesChemoreceptors – stimulated by changes in the

chemical concentrations of substancesPhotoreceptors – stimulated by light energy

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General Senses

ProprioceptorsMechanoreceptors involved in reflex actionsMaintain equilibrium and posture

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Fig 9.1

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General Senses Cutaneous Receptors

Located in the deepest layer of the epidermis and the entire dermis

Make skin sensitive to touch, pressure, pain, and temperature

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General Senses Pain Receptors (nociceptors)

Somatic nociceptors○ Skin and skeletal muscle○ Respond to mechanical, thermal, electrical or

chemical damage

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Senses of Taste and Smell

Chemical senses Sensitive to molecules in food and in the air Other chemoreceptors in the body

Govern respiratory rateSensitive to the hydrogen ion concentration of the

blood

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Senses of Taste and Smell Sense of Taste

Sensory receptors located in the taste buds○ Primarily on the tongue○ Also present on the hard palate, the pharynx, and

the epiglottisTypes of taste sensations

○ Sweet○ Sour○ Salty○ Bitter○ Umami – meat

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Senses of Taste and Smell

How the brain receives taste information○ Molecules in food bind with receptor proteins on

microvilli on taste cells○ Nerve impulses are generated and go to the brain○ Sensory receiving and memory areas for taste are

located in the insula

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Senses of Taste and Smell

Sense of SmellDependent on olfactory cells

○ Located in olfactory epithelium in the roof of the nasal cavity

○ Modified neurons○ Olfactory cilia have receptor proteins for odor

moleculesHow the brain receives odor information

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Senses of Taste and Smell

How the brain receives odor information○ Nerve fibers lead to the olfactory bulb○ Combinations of activated receptor proteins account

for different odors ○ An odor’s signature is determined by which neurons

are stimulated in the olfactory bulb○ Neurons send signals through the olfactory tract to

the olfactory areas of the cerebral cortex in the temporal lobe

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Senses of Taste and Smell

Sense of taste and sense of smell○ Both work together○ Smell can enhance taste○ Part of what is referred to as smell may actually be

taste

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Sense of Vision

Accessory Organs of the EyeEyebrows, eyelids, and eyelashes

○ Eyebrows shade the eyes from the sun and protect eyes from perspiration or debris

○ Eyelids are continuations of the skin○ Eyelashes can block debris from entering the eye○ Secretions from sebaceous glands associated with

eyelashes lubricate the eye○ Eyelids help keep the eye lubricated

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Fig 9.5a

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Sense of Vision

Lacrimal apparatus○ Lacrimal gland produces

tears○ Tears collect in lacrimal

sac○ Tears drain into the nose

by the nasolacrimal duct

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Sense of Vision

Extrinsic muscles○ Contractions move the eyes○ Superior rectus rolls eye upward○ Inferior rectus rolls eye downward○ Lateral rectus turns eye outward○ Medial rectus turns eye inward○ Superior oblique rotates eye counterclockwise○ Inferior oblique rotates eye clockwise○ Three cranial nerves control these muscles

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Fig 9.6

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Sense of Vision Anatomy and Physiology of the Eye

Three layers○ Sclera

White and fibrousCornea is transparent

○ ChoroidMiddle, vascularized layerBecomes the iris towards the front

Regulates the size of the pupil Colored portion of eye

The ciliary body is behind the iris Contains the ciliary muscle Controls the shape of the lens

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Sense of Vision

○ Lens – divides the eye into two compartmentsAnterior compartment contains aqueous humorPosterior compartment contains the retina and the vitreous

humor

○ RetinaContains photoreceptors

- Rod cells – night vision and peripheral vision- Cone cells – distinguish colors

Fovea centralis – area of retina where cone cells are densely packed

Optic nerve – formed from sensory fibers from the retina

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Sense of Vision

Function of the lens○ Focuses images on the retina○ Image produced is smaller than the object○ Image on retina is inverted and reversed○ Accommodation

Maintaining focus on a distant and then near objectLens must change shape

- Controlled by the ciliary muscle- Ciliary muscle is relaxed for a distant object- Ciliary muscle contracts to view a near object

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Sense of VisionVision pathway

Light is refracted by cornea, aqueous humor, lens, vitreous humor

Image is formed on the retinaNerve impulses travel to the visual area of the cerebral

cortex

○ Color visionDepends on three kinds of conesColor blindness is caused by the inherited absence of the

color pigments in the cones

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Sense of Vision○ Function of the retina

Rod cells and cone cells are located in the deepest layer

Light must penetrate to the back of the retina

○ Blind spotNo rods and cones where the optic nerve leaves the retinaNo vision is possible in this area

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Sense of Vision

○ From the retina to the visual cortexThe right and left visual cortex rebuilds and rights image

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Sense of Hearing

Two sensory functions of the ear Sensory receptors located in the inner ear

Consists of hair cellsSensitive to mechanical stimulation

(mechanoreceptors)

Anatomy of the Ear Sound Pathway

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Sense of Hearing Anatomy of the Ear

Outer ear○ Pinna○ Auditory canal

Lined with hair Modified sweat glands secret cerumen

Middle ear○ Begins at the tympanic membrane○ Ends at bony wall with two small openings

Oval window Round window

○ Three small bones (ossicles) Malleus Incus Stapes

○ Auditory tube (eustachian tube) extends from the middle ear to the nasopharynx

Inner ear○ Filled with fluid○ Three areas

Semicircular canals Vestibule Cochlea

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Sense of HearingSound pathway

○ Through the auditory canal and middle earSound travels by the vibrations of air moleculesSound waves strike the tympanic membrane causing it to

vibratePressure from the tympanic membrane causes the malleus,

the incus, and then the stapes, to vibrateThe stapes strikes the oval windowVibrations from the oval window are passed to the fluid

within the cochlea of the inner ear

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Sense of Hearing○ Impulses travel From the cochlea to the auditory

cortexThe spiral organ (organ of Corti) is the sense

organ for hearing- Located in cochlear canal

Pressure waves cause the hair cells to bendNerve impulses begin in the cochlear nerve and

travel to the brain stem and then the auditory cortex

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Sense of Equilibrium Mechanoreceptors in the semicircular canals

are responsible for rotational equilibrium Mechanoreceptors in the vestibule are

responsible for gravitational equilibrium

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Sense of Equilibrium Rotational Equilibrium Pathway

Involves the three semicircular canals Motion sickness

○ Continuous movement of fluid within the semicircular canals○ Sensory input from the inner ear that is different from visual

sensations Vertigo is dizziness and a sensation of rotation

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Effects of Aging The lens of the eye does not accommodate as

well Three visual disorders seen frequently:

CataractsAge-related macular degenerationGlaucoma

The need for a hearing aid increases with agePresbycusis (age-related hearing decline)Otosclerosis is the most frequent cause of conduction

deafness in adults Dizziness and the inability to maintain balance