General and Special Senses - Anatomy - Lecture Slides, Slides for Dental Anatomy. All India Institute of Medical Sciences

Dental Anatomy

Description: Main topics of Human Anatomy are adult spinal cord, articulations, autonomic nervous system, blood, circulation, classification of joints, functions of heart, glands, gall bladder, general osteology, head and neck, human development, tissues, major control system, neural tissues, muscle tissues, naming of joints and mammary glands. It contains: Senses, Structures, Pathways, Receptors, Classification, Gustatory, Cochlea, Organ.
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Chapter 10

Chapter 18:

General & Special Senses

1. Distinguish between general and specific senses

2. Classify receptors according to stimulus detected, body location, and histological structure

3. Describe the structures of the ear and eye

4. Explain the pathways of sound in the ear and light in the eye

5. Identify, describe, and discuss the receptors and neural pathways involved in each of the five special senses

Chapter objectives:

Classification of Sensory System

by structural Complexity

4 general senses





5 special senses Olfaction







= specialized cells or cell processes monitoring

conditions in/outside body (→ extero- and


Receptors are specific for a certain type of stimulus

→ “receptor specificity”

All sensory receptors are transducers, changing

incoming stimulus of pressure, vibration, light,

etc., into electro-chemical neuron impulses.

simplest receptor type:

free nerve endings

Area monitored

by one receptor:


The larger the receptive field, the poorer ability to

localize stimulus (2 pt. discrimination test)

Fig 18-1

Complexity Range of Receptors

Free nerve



nerve ending


receptor cells

Four General Senses

1. Nociceptors Respond to heat, mechanical

stress and chemicals –

associated with tissue damage

Most concentrated in skin

Fast pain (to cortex, usually triggers reflex)

Slow pain (later, persistent, indistinct


Referred pain (visceral, "incorrect" source


2) Thermoreceptors

Respond to changes in temperature

In dermis, skeletal muscles, liver and hypothalamus

Free nerve endings

Cold receptors

> warm receptors

3) Mechanoreceptors

Respond to physical distortion of cell membrane (e.g.: stretching, twisting, compression)

Subdivided into

1. Baroreceptors Sensitive to internal pressures: blood pressure, lung stretch, digestive tract tension

2. Proprioceptors monitors of muscle stretch

3. Tactile receptors - touch, pressure, vibration Unencapsulated: free nerve endings, Merkels dics - fine


Encapsulated: Meissners corpuscles - fine touch; Pacinian corpuscles - deep pressure

4) Chemoreceptors

Respond to small

concentration changes of

specific molecules


Internal chemoreceptors

monitor blood composition

(e.g. Na+, pH, pCO2 )

Found within aortic and carotid


Very important for homeostasis

Fig 18-5

Special Senses






Organ responsible ??

Olfaction: Paired Olfactory Organs

Olfactory epithelium (10-20 Mio receptors / 5 cm2)

Responds to molecules dissolved in mucus or lipids

Easy to recognize – hard to categorize

(Only) neuron that can be replaced in adult

Through cribriform plate of ethmoid to olfactory bulb

Type of receptor??

Olfactory Pathways

Receptor neurons pass into cranium through cribiform plate and synapse in olfactory bulbs.

Olfactory neurons are the only neurons known

1. to routinely replace themselves

2. to reach the cerebrum without synapsing in the thalamus

Olfactory discrimination - Although difficult to describe, the number of different odors recognizable is immense.


3 types of papillae

1) Filiform - thin, thread like projections

2) Fungiform - shaped like mushrooms.

3) Circumvallate - large target- shaped bumps near the back of the tongue

Papillae contain taste buds

Taste buds contain group of receptor & support cells

How many 1o taste

sensations? Fig 18.7

Gustatory Pathway

Cranial nerves VII, IX and X to nucleus solitarius

in medulla oblongata to gustatory cortex

Fig 18.8

Hearing & Equilibrium

2 other names??

Middle Ear

Function of the

2 muscles?

Inner Ear

Bony labyrinth vs. membranous labyrinth

Perilymph vs. endolymph

Cochlea & vestibular complex

Structure of cochlea: 2.5 turns of ducts

central hub of cochlea

Organ of Corti Basilar membrane on which sit hair cells with stereocilia

Tectorial membrane above the hair cells

Sound causes hair cells to bounce and touch tectorial

membrane causing transduction

Auditory Pathway

To inferior colliculus of

opposite side of midbrain

To thalamus

To auditory cortex

Cochlear branch of CN VIII

To cochlear

nucleus of


Vestibular Complex: Semicircular canals with ampullae (mutually


Saccule and utricle (= fill up vestibule)

Two Receptor Organs: Maculae of Vestibule (or: macula of saccule plus

macula of utricle)

Cristae ampullaris (how many?)

Vision: Eyeball +

Accessory Structures

Palpebrae = Eyelid

Continuation of skin


Meibomian glands (on inner margin of lid) lipid rich product, fu?

bacterial infection chalazion

Conjunctiva (= mucous membrane) over cornea very thin (5-7 cells thick)

Lacrimal Apparatus

Lacrimal gland with several ducts - superior and

lateral to eye

Lacrimal puncta (superior and inferior) - holes near

nose to drain tears

Lacrimal canaliculi - drain

tears to

Nasolacrimal duct -

empties to nasal cavity

Secretion contains lysozyme

Compare to fig 18.18

Extrinsic Eyemuscles (see p.272)

4 recti

2 oblique


The Three Tunics:

1) Fibrous Tunic (tough outer layer) sclera - white part of fibrous tunic

cornea - transparent avascular anterior part

limbus - boundary between the above

2) Vascular Tunic (= Uvea) choroid - heavily vascular

iris with pupil hole - inner sphincter and outer radial muscles

ciliary body - muscle attached to suspensory ligaments, regulates focus of lens

Lens and Chambers of the Eye Ciliary body

Suspensory ligaments

Anterior and posterior

chambers (= anterior

cavity) with aqueous


Posterior cavity with

vitreous humor



See fig 18.21

3) Nervous Tunic: Retina

Outer layer pigmented - inner layer photoreceptors a) rods - black/white vision, dim light

b) cones - color vision, intense light

Bipolar cells - synapse with rods and cones

Ganglion cells - synapse with bipolar cells

Ora serrata - anterior edge of retina

Macula lutea – fovea centralis - all cones, best vision

Optic disc – blind spot, where optic nerve exits eye

Optic nerve See Fig 18.22


Eye Fundus: clinical significance ?

Visual Pathway

Optic chiasma - optic nerves partially

cross (right side of the field of each eye

combining and going to the lateral

geniculate on the right, those from the

left to the left)

To superior colliculus and thalamus

To visual cortex in __________ lobe

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