sense organs and special senses

7/29/2019 Sense Organs and Special Senses

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Sense Organs and Special

Senses

Mid-Term

01/29/2013



Overview

• Receptor

Classification

– Properties and types

• General senses• Chemical senses

• Hearing and

Equilibrium• Vision



Properties of Receptors

• Sensory transduction

– convert stimulus energy into nerve energy

• Receptor potential – local electrical change in receptor cell

• Adaptation

– conscious sensation declines with continuedstimulation



Receptors Transmit Information

• Modality - type of stimulus

• Location – each sensory receptor receives input from its receptive field

– sensory projection - brain identifies site of stimulation

• Intensity – frequency, number of fibers and which fibers

• Duration - change in firing frequency over time

– phasic receptor - burst of activity and quickly adapt (smell andhair receptors)

– tonic receptor - adapt slowly, generate impulses continually(proprioceptor)



Receptive Fields



Receptor Types

• By modality: – chemo-, thermo-, mechano-, photoreceptors and

nociceptors

• By origin of stimuli – interoceptors - detect internal stimuli

– proprioceptors - sense body position and movements

– exteroceptors - detect external stimuli

• By distribution – general senses - widely distributed

– special senses - limited to head



Unencapsulated Nerve Endings

• Not wrapped in

connective tissue

• Types

– Free nerve endings• Warm

• Cold

• Nociceptors (pain)

– Tactile discs• Tonic for light touch

– Hair receptors



Encapsulated Nerve Endings

• Wrapped in glial cells or connective tissue

• Types

– Meissner’s corpuscles

• Phasic for light touch,

sensitive to hairless areas likefingertips

– Krause end bulbs

• Phasic for light touch, mucousmembrane

– Pacinian corpuscles

• Phasic for deep pressure,stretch, tickle, vibration

– Ruffini endings

• Tonic for heavy touch,pressure and joint movement



Pain

• Nociceptors – allow awareness of tissue injuries – found in all tissues except the brain

• Fast pain travels in myelinated fibers at 30 m/sec – sharp, localized, stabbing pain perceived with injury

• Slow pain travels unmyelinated fibers at 2 m/sec – longer-lasting, dull, diffuse feeling

• Somatic pain from skin, muscles and joints

• Visceral pain from stretch, chemical irritants or ischemia

of viscera (poorly localized)• Injured tissues release chemicals that stimulate pain

fibers (bradykinin, histamine, prostaglandin)



Referred Pain

• Misinterpreted pain

– brain “assumes”

visceral pain is coming

from skin – heart pain felt in

shoulder or arm

because both send

pain input to spinal

cord segments T1 to

T5



CNS Modulation of Pain

• Intensity of pain - affected by state of mind

• Endogenous opiods (enkephalins,

endorphins and dynorphins)

– produced by CNS and other organs under

stress

– in dorsal horn of spinal cord (spinal gating)

– act as neuromodulators block transmission of

pain



Chemical Senses

• Smell

– Describe the olfactory receptors and the

neural pathways for olfaction

• Taste

– Describe the gustatory receptors and the

neural pathways for gustation



Olfaction: Sense of Smell

• Nose has 10-100

million receptors for

olfaction

• Olfactory epithelium is5 cm2

• Sensitive up to

10,000 odors



Olfactory Epithelial Cells

• Olfactory cells – olfactory hairs neurons with

20 cilia

• bind odor molecules inthin layer of mucus

– axons pass throughcribriform plate

– survive 60 days

• Supporting cells

• Basal cells – Divide

– Produce new receptors



Anatomy and Physiology of Smell

• Olfactory Pathway

– Unmyelinated axons extendthrough the cribriform plate;forms olfactory (CNI) nerve

– CNI terminates in olfactory

bulbs – Olfactory tract project to the

lateral olfactory area of thetemporal lobe

– From lateral areas, pathwaysextend to frontal lobe.

• Molecules bind to receptor onolfactory hair

– hydrophilic - diffuse throughmucus

– hydrophobic - transport by

odorant-binding protein• Activate G protein and cAMP

system

• Opens ion channels for Na+ or Ca2+

– creates a receptor potential

• Action potential travels to brain

• Receptors adapt quickly

– due to synaptic inhibition inolfactory bulbs



Gustation: Sense of Taste

• Five primary tastes can be distinguished

– Sour, sweet, bitter, salty and umani (meaty or savory)

• Odors from food can pass into nasal cavity

where they stimulate olfactory receptors.• Olfaction is more sensitive than taste, food may

stimulate olfaction over taste.

• People with colds may complain that they cannottaste their food. This is due to blocking olfaction,

not taste



Anatomy of Gustatory Receptors

• Lingual papillae

– filiform (no taste buds)

• important for texture

– foliate (no taste buds) – fungiform

• at tips and sides of

tongue

– vallate (circumvallate)• at rear of tongue

• contains 1/2 of taste

buds



Anatomy of the Taste Bud

• Gustatory hair

projects from receptor

through taste port.

• Receptor cells aresupported by basal

cells, which replace

receptor cells every

10 days.



Physiology of Taste

• Three cranial nerves contain axons of 1st order gustatory neurons from taste buds. – Facial

– Glossopharyngeal

– Vagus

• Transfer signals to medulla oblongata

• Signal then goes to hypothalamus (salivation) or

thalamus.• Thalamus to parietal lobe of cerebrum

(conscious of the taste).



Taste Aversion

• Strong link between taste and pleasant or unpleasant emotions

• Sweet tastes evoke pleasure, bitter

evokes disgust.• Taste aversion: avoiding foods if it upset

digestive system.

• Advantage: longer survival of species• Disadvantage: Radiation Rx cause taste

aversion in patients



Vision

• Objectives:

– List and describe the accessory structures of

the eye and the structural components of the

eyeball

– Describe the neural pathway for vision



Accessory Structures

• Eyelids

– Palbebral fissure

• Lateral commissure

• Medial commissure

– Conjunctiva• Mucous membrane,

vascular

• Bloodshot eyes

• Eyelashes/Eyebrows

– Protect from foreign

objects, perspiration and

the direct rays of the sun



Accessory Structures

• Lacrimal Apparatus – Produces and drains tears.

– Lacrimal gland

• Fluid that contains abactericidal enzyme

– Moves medially to Lacrimalpunctum

– Drains into lacrimal sacand then into nasolacrimalduct

• Cry: Parasympatheticstimulation of lacrimalglands



Accessory Stuctures

• Extrinsic Eye Muscles

– Superior rectus

– Inferior rectus

– Lateral rectus – Medial rectus

– Superior oblique

– Inferior oblique



Anatomy of the Eyeball

• 2.5 cm in diameter

• Wall of the eyeball consists of:

– Fibrous tunic

– Vascular tunic

– Retina



Fibrous tunic

• Cornea

– Allows light in

• Sclera

– Shape of eyeball – White of the eye



Vascular tunic

• Choroid

• Ciliary body

• Iris

– Pupil

– Circular muscles

• Constriction

• Dilation



Retina

• Posterior ¾ of inner eyeball• Optic part has two layers

– Pigmented layer • Absorbs scattered light in eyeball, keeps image sharp

– Neural layer • Multilayered outgrowth of brain, process visual image before sending

impulses to optic nerve

• Photoreceptors: Rod and cone cells – Rod: allow us to see in dim light, do not provide color, shades of gray

only

– Cone: Produce color vision

• Detached retina – Detached between two layers – Distorted vision and blindness in corresponding field of vision

– Re-attached through laser surgery



Lens

• Posterior to pupil and

iris

• Focus images on the

retina to facilitateclear vision



Interior of the eyeball

• Anterior cavity

– Anterior chamber

– Posterior chamber

– Aqueous humor • Vitreous chamber

– Vitreous body to keep

shape of eyeball and

keep retina attached tochoroid



The visual pathway

• 1st order neurons: retina

• 2nd order neurons: optic nerve

– Advance toward optic chiasm, and split

• 3rd order neurons: thalamus to occipital

lobe



Hearing and Equilibrium

• Describe the anatomy of the structures of

the three principle regions of the ear.

• List the principle events involved in

hearing.

• Identify the receptor organs for equilibrium

• Describe the auditory and equilibrium

pathway



Anatomy of the Outer Ear

• Outer ear

– Auricle

• Helix and Lobule

– Auditory canal



Anatomy of the Middle Ear

• Air-filled tympanic cavity

• Contains

– Tympanic membrane

– Ossicles

• Malleus

• Incus

• Stapes



Anatomy of the Inner Ear

• Bony labyrinth

• Semicircular canals

– Right angles to each

other • Cochlea

– Transmission of sound

• Inner hair cells



Stimulation of Cochlear Hair Cells

• Vibration of ossicles causes vibration of

basilar membrane under hair cells

– as often as 20,000 times/second



Equilibrium Pathways

• Vestibular apparatus

– Semicircular ducts

• Static equilibrium

– Saccule and utricle are responsible

• Dynamic equilibrium

– Semicircular ducts are responbible

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