chapter 013

The Human Body in Health and Illness, 4th edition

Barbara Herlihy

Chapter 13:Sensory System

Lesson 13-1 Objectives

• State the functions of the sensory system.• Define the five types of sensory receptors.• Describe the four components involved in the

perception of a sensation.• Describe the five general senses.

Copyright © 2011, 2007 by Saunders, an imprint of Elsevier Inc. All rights

reserved.2

Sensory System

• Sensory system allows us to experience the world.

• External information• Sound of a dog barking

• Internal information• Sudden change in blood pressure


reserved.3

Five Types of Sensory Receptors

• Receptor: Specialized area of a sensory neuron that detects a specific stimulus– Chemoreceptors– Pain receptors (nociceptors)– Thermoreceptors– Mechanoreceptors– Photoreceptors


reserved.4

Four Components of Sensation


reserved.5

Two Characteristics of Sensation

• Projection• Adaptation


reserved.6

Projection

• Brain refers sensation back to its sourceA. Ordinary injury B. Phantom limb pain


reserved.7

Adaptation

• Adaptation: With continuous stimulation, sensory receptors become less responsive.

• Receptors vary in their ability to adapt. Smell and temperature receptors adapt well.

Pain receptors do not adapt at all.


reserved.8

Five General Senses

• Pain• Touch• Pressure• Temperature• Proprioception


reserved.9

Pain Receptors or Nociceptors

• Consist of free nerve endings stimulated by tissue injury, chemicals, tissue hypoxia

• Widely distributed throughout the skin, viscera, other internal tissues

• Do not adapt


reserved.10

Sites of Referred Pain

• Compare heart’s location with possible sites of pain during a heart attack.

• Gallbladder attack may present with shoulder pain.


reserved.11

Touch and Pressure Receptors

• Touch (tactile) receptors– Mechanoreceptors– Found mostly in skin

• Pressure receptors– Mechanoreceptors– Located in the skin, subcutaneous tissue, and deep

tissue


reserved.12

Thermoreceptors

• Receptors for cold and heat• Located in free nerve endings and other

specialized sensory cells in the skin• Quick adaptation• Temperature extremes experienced as pain


reserved.13

Proprioception

• Proprioception: Sense of orientation or position in space

• Receptors– Located in muscles, tendons, joints, and inner ear – Sensory information parietal lobe, cerebellum


reserved.14


• Describe the five special senses.• Describe the structure of the eye.• Explain the movement of the eyes.• Describe how the size of the pupils changes.


reserved.15

Five Special Senses

• Smell• Taste• Sight• Hearing• Balance


reserved.16

Olfactory Sense: Smell

• Chemoreceptors in nasal tissue

• Nerve impulses travel on CN I to temporal lobe for interpretation


reserved.17

Gustatory Sense: Taste

• Taste receptors are chemoreceptors.

• Nerve impulses move along three cranial nerves to parietal and temporal lobes.


reserved.18

Vision: Sense of Sight

• Visual accessory structures • Primary visual structures are the eye and

visual pathway.


reserved.19

Visual Accessory Structures• Eyebrows• Eyelids• Conjunctiva• Eyelashes• Lacrimal

apparatus• Extrinsic eye

muscles


reserved.20

Eye: Organ of Vision


reserved.21

Eyeball: Three Layers

• Sclera• Choroid• Retina


reserved.22

Sclera

• Tough outer layer in posterior eyeball

• Forward extension becomes cornea

• Extrinsic eye muscles attach here


reserved.23

Choroid

• Middle layer in the posterior eyeball

• Forward extension becomes ciliary body and iris

• Highly vascular to nourish retina


reserved.24

Retina

• Inner layer in posterior eyeball

• Site of photoreceptors Rods Cones

• Optic disc Exit of CN II


reserved.25

Retinal Photoreceptors

• Rods– Located on periphery – Responsible for black and white or night vision

• Cones– Located on central part of posterior eye– Concentrated in fovea centralis in center of

macula lutea– Responsible for color vision


reserved.26

Cavities of Eyeball• Posterior cavity

– Between lens and retina

– Contains vitreous humor

• Anterior cavity– Between lens and

cornea– Contains aqueous

humorCopyright © 2011, 2007 by Saunders,

an imprint of Elsevier Inc. All rights reserved.

27

Formation and Drainage of Aqueous Humor

• Formed by ciliary body

• Circulates through pupil behind cornea

• Drains through canals of Schlemm


reserved.28

Muscles of the Eye

• Extrinsic muscles: Move eyeball in its bony orbit

• Intrinsic muscles: Move structures within eyeball– Iris– Ciliary muscles


reserved.29

Extrinsic Muscles of the Eye

• Four rectus muscles• Two obliques• Primary innervation

from CN III


reserved.30

Three Intrinsic Eye Muscles

• Iris Circular muscle

• Miosis• Muscarinic receptors

Radial muscle• Mydriasis• Alpha 1 receptors

• Ciliary muscles


reserved.31

Eye Disorders


reserved.32

Refraction: Lens

• Ciliary muscles pull on suspensory ligaments.

• Suspensory ligaments pull on lens.

• Lens changes shape.


reserved.33

Refraction

• Bending light rays to focus on retina

• Lens, primary refracting structure

• Focal point on retina


reserved.34

Errors of Refraction

• Myopia, focal point in front of retina

• Hyperopia, focal point behind retina

• Astigmatism, result of irregularly curved cornea


reserved.35

Visual Pathway

• Photoreceptors generate nerve impulse

• Nerve impulse travels along CN II to occipital lobe

• Occipital lobe “sees” Rover


reserved.36

Visual Pathway: Optic Chiasm • Lateral fibers of CN II

ascend to same side of brain.

• Medial fibers of CN II cross to opposite sides, forming the optic chiasm.

• The brain sees one image.


reserved.37

How Seeing Occurs

• Pathway of light Cornea aqueous humor pupil lens

vitreous humor rods and cones

• Pathway of nerve impulses Rods and cones CN II occipital lobe


reserved.38


• Describe the three divisions of the ear.• Describe the functions of the parts of the ear

involved in hearing.• Explain the role of the ear in maintaining the

body’s equilibrium.


reserved.39

Sense of Hearing: Three Parts of Ear

• External to tympanic membrane

• Middle from tympanic membrane to oval window

• Inner behind oval window


reserved.40

Three Parts of Ear: Contents

• External – Auricle, external auditory canal

• Middle– Malleus, incus, stapes– Eustachian tube

• Inner– Cochlea, vestibule, semicircular canals, origin of

CN VIII


reserved.41

Eustachian Tube • Connects throat with

middle ear• Equalizes pressure

across tympanic membrane

• In young child, short and horizontal

• In adults, longer and more vertical


reserved.42

Receptors : Organ of Corti

• Mechanoreceptors (hairs) in cochlea of inner ear

• Organ of Corti in endolymph

• Cochlear branch of CN VIII


reserved.43

How Hearing Occurs

• Pathway of vibrations Sound waves tympanic membrane ossicles oval window organ of Corti

• Pathway of nerve impulses Organ of Corti CN VIII (cochlear branch) temporal lobe


reserved.44

Recap: How Hearing Occurs


reserved.45

Receptors for Balance

• Mechanoreceptors (hairs) in vestibule and semicircular canals of inner ear

• Hairs in endolymph• Vestibular branch of

CN VIII


reserved.46

chapter 013

Health & Medicine