Lake Michigan College Human Anatomy 205

Human Anatomy (205)

Sensory Organs

Sensation is an awareness of stimulus
Perception recognition and interpretation of a sensory stimulus
Sensation requires
- Stimulus - environmental change can initate a response
- Receptor - a cell that converts stimulus to a.p. (action potential)
- Impulse conducted - the action potential is carried via sensory neuron pathway to brain
- Interpretation of impulse - translation of impulse to form perception in brain
Three basic types of receptors
1. Externoceptors [subdivided on basis of stimuli sensitivity]
  - chemoreceptors [olfaction and taste]
  - photoreceptors [vision]
  - mechanoreceptors [touch, pressure, balance and hearing]
  - thermoreceptors [sensations of heat and cold]
2. Viseroceptors [produce sensations arising from internal organs]
3. Proprioceptors [produce sensations related to body position and movement]
Characteristics of senses [modality, projection, and adaptation]
Somatic Sense [Cutaneous receptors - heat, cold, pressure, touch, pain]
Chemoreception [olfaction & taste]
- Olfaction (sense of smell) - see graphic
  - Receptor cells are in olfactory epithelium of upper parts of nasal cavity
  - Olfactory nerves pass from nasal epithelium through cribriform plate to olfactory bulb
  - Olfactory tract leads from bulb to temporal lobe cortex
- Gustatory (Taste)
  - Gustatory receptors are in taste buds
  - Taste buds are found on fungiform and vallate papillae on dorsum of tongue
  - Four basic tastes tongue map myth

Photoreception [ Eye Anatomy]

Eyeball is composed of three layers

1. Fibrous Tunic is made up of 2 parts:

Sclera [6] (tough, white outer layer)
Cornea [2] transparent, convex, anterior portion that covers iris; continuous with sclera

2. Vascular Tunic (middle layer containg blood vessels that nourish)

3. Nervous tunic retina (inner layer of photoreceptors and neurons)

Lens [1] is suspended in center of ciliary body and fuctions in accomodation.
See animation of lens in accomodation
Eyeball cavities and chanbers
- Posterior cavity filled with vitrous humor
- Anterior cavity filled with aqueous humor
  - Anterior cavity between iris and cornea = anterior chamber
  - Anterior cavity between iris and lens = posterior chamber
Anatomy of Retina [photoreceptors initiate a.p.]
- Two types of Photoreceptors
  1. Cones - receptors of specific colors of spectrum in bright light (color vision)
  2. Rods - more numerous, more sensitive receptors in dim light (black/white vision)
- macula lutea is a yellowish area in center of retina
- fovea centralis is a depression in center of macula
  - contains concentration of cones
  - absence of rods in the fovea
- Visual Pathway [ Retina - bipolar neuron] [Optic Nerve, chiasma, tract - ganglionic neuron] [Thalamus] [Occipital cortex]

Accessory sturctures of eye

Conjunctiva is mucus membrane on inner surface of eyelids
Lacrimal apparatus
- Lacrimal gland secretes tears
- Lacrimal punctum - collects tears from surface of eye
- Lacrimal canaliculus - duct that drains tears from puncta
- Lacrimal sac and nasolacrimal duct - drains tears into nasal cavity
Six extrinsic eye muscles to move the eyeball
- four recti [lateral rectus, superior rectus, medial rectus, inferior rectus]
- two obliques [superior oblique, inferior oblique]
- see superior view of eye on Lab model
Extrinsic eye muscles stimulated by 3 cranial nerves, III, IV and VI
1. Trochlear (IV) to superior oblique
2. Abducens (VI) to lateral rectus
3. Oculomotor (III) to inferior oblique + other 3 recti muscles
See simulation of eye movements controlled by six extrinsic eye muscles and 3 cranial nerves.

Links to more information and graphics

Lab Models

Ear subdivided into external, middle and inner ear.

External Ear

Contains ear ossicles [malleus [2], incus, and stapes [3]]
Middle ear cavity = tympanic cavity
Separated from external ear by tympanum
Communicates with two membrane covered openings on cochlea
(oval and round window [8])
Auditory (Eustachian) tube [7] connects middle ear to pharynx
External & middle ear mechanics animated,

Inner ear in temporal bone has 3 distinct parts

Inner Ear Anatomy - Inner ear is composed of two fluid filled labyrinths

Osseous labyrinth (bony cavities filled with perilymph) has 3 parts
- cochlea (hearing)
- vestibule (balance)
- semicircular canals (motion equilibrium)

Membranous labyrinth (ducts and tubes filled with endolymph and suspended in osseous labyrinth)

Membranous Part	Location in Osseous Labyrinth	Sensory Organ	Receptors
cochlear duct	within cochlea	spiral organ	hair cells
utricle; saccule	within vestibule	macula	hair cells
semicircular ducts	within semicircular canals	crista	hair cells

Inner Ear Anatomy - Cochlea for Hearing
- Snail-shaped Cochlea contains three chambers
  1. Vestibular canal [continues from oval window]
  2. Tympanic canal [ends at round window]
  3. Cochlear duct contains Spiral Organ of Corti
- See 3 chambers in cross section of cochlea [Illustration] . [lab slide]
- Know parts of Spiral Organ [tectorial membrane, basilar membrane, hair cells] see illustration
- Spiral organ animation with audio
- Summary of sequence of mechanical events for hearing
Inner Ear Anatomy - Sense of Equilibrium
- Vestibule [utricle & saccule contain macula and otolith]
  - Static equilibrium (orientation to gravity)
  - Utricle has horizontal orientation and saccule is verticle
- Three Semicircular Canals [semicircular ducts contain crista] [ animation]
  - Dynamic equilibrium (detecting acceleration and motion)
Inner ear sense organs (spiral organ, crista and macula) all contain hair cell receptors

Seeing, Hearing and Smelling the World A report from the Howard Hughes Medical Institute

Crosswords and quizzes on sensory organs

Dynamic Human
at McGraw-Hill