BIO127 – Chapter 7, Senses in Nervous System

Course Context

  • BIO127 – Intro to Body Structure & Function

  • Chapter focus: How the Nervous System Helps Us Sense (Teacher: Cecelia Szakolczay, from the Respiratory Care Program at Pima Medical Institute)

Objectives (Big Goals for the Course)

  • Spot the main body systems & their key parts

  • Explain how the heart & lungs are built and how they work

  • Build & define medical words using word parts (roots, combining forms, prefixes, suffixes)

  • Know & understand common medical shortcuts (abbreviations)

Chapter-Specific Things You'll Learn

  • 7.1 Use medical words for the senses

  • 7.2 Sort senses by what triggers them & where their sensors are located

  • 7.3 Describe what the skin's sensors (general senses) do

  • 7.4 Explain the info sent by skin sensors

  • 7.6 Find taste sensors; 7.7 tell the difference between tastes & how we sense flavor

  • 7.9 Find smell sensors; 7.10 explain how we sense odors

  • 7.12 Describe how the ear is built; 7.13 explain how we hear sounds

  • 7.15 Describe the balance system (vestibular apparatus); 7.16 explain how we keep our balance

  • 7.18 Describe how the eye is built; 7.19 explain how we see

  • 7.21 Talk about how aging affects the senses

  • 7.22 Sum up common tests for the senses

  • 7.23 Connect sensory problems to diseases

Essential Word Roots & Combining Forms

  • audi/o – hearing; aur/o – ear; cochle/o – cochlea (part of inner ear); corne/o – cornea (clear front of eye)

  • lacrim/o – tears; lith/o – stone; ocul/o, opt/o, ophthalm/o – eye/vision

  • ot/o – ear; presby/o – old age; propri/o – one’s own (self); retin/o – retina (back of eye)

  • scler/o – sclera (white of eye); tympan/o – eardrum

Nervous System (Simple View)

  • Main parts: brain, spinal cord, nerves

  • Extra parts: meninges (coverings), sympathetic ganglia (nerve clusters)

  • Main jobs: send messages, control movement, feel sensations

General Senses

  • Things felt all over the body: touch, pressure, stretch, hot, cold, pain

  • How sensors are grouped by what they react to:

    • Thermoreceptors → temperature (hot/cold)

    • Mechanoreceptors → touch, shaking, stretching, pressure

    • Nociceptors → pain from body damage

  • Receptive fields (areas where sensors pick up info)

    • Each nerve fiber covers a skin area (its field)

    • Four types of info sent:

    1. What kind of feeling it is (type)

    2. Where it is (location)

    3. How strong it is (intensity)

    4. How long it lasts (duration)

Special Senses Overview

  • Only found in the head; need special organs for them

  • Taste, Smell, Hearing, Balance, Vision

Taste (Gustation)

  • Small bumps (lingual papillae) on the tongue hold taste buds

  • Taste bud parts:

    • Taste cells with tiny hairs that sense taste

    • Basal cells (new cell makers) & supporting cells

    • Nerve cell connects at the bottom

  • Five main tastes: sweet, sour, salty, bitter, umami (savory)

  • Flavor = mix of taste + smell + how it feels in your mouth + its temperature

Smell (Olfaction)

  • Olfactory epithelium (smell tissue) in nose → olfactory bulbs (smell centers in brain) → olfactory tracts (smell pathways)

  • Brain processing:

    • Main smell area: temporal lobe (side of brain)

    • Thinking area: frontal lobe (front of brain); compares new smells to old memories (like recognizing the smell of French fries)

Hearing & Ear Anatomy

  • Ear's jobs: hearing & balance

Outer Ear

  • Pinna/auricle (outer ear cartilage) collects sound

  • External auditory meatus → ear canal

    • Has wax glands (produce earwax) & hairs to catch dirt

  • Tympanic membrane (eardrum) divides outer from middle ear

Middle Ear

  • Air-filled space with three tiny hearing bones (auditory ossicles):

    1. Malleus (hammer) – attached to eardrum (tympanic membrane)

    2. Incus (anvil) – connects malleus & stapes

    3. Stapes (stirrup) – footplate sits on oval window (door to inner ear)

  • These bones make eardrum vibrations about imes20 stronger

  • Eustachian (auditory) tube:

    • Connects middle ear ↔ back of throat (nasopharynx)

    • Opens when you swallow/yawn to balance air pressure across eardrum

    • functions of the middle ear include amplifying sound waves, transmitting vibrations to the inner ear, and protecting the inner ear from loud sounds through the stapedius muscle.

    • (SEE SLIDE 25 FOR MORE)

Inner Ear

  • Fluid-filled maze inside the temporal bone (skull bone)

  • Vestibule (central room) holds 3 semicircular canals → balance & posture and assist with equilibrium.

  • Cochlea (snail-shaped) = hearing part; changes sound vibrations into nerve signals

  • Cranial Nerve VIII (Vestibulocochlear nerve):

    • Cochlear part → hearing

    • Vestibular part (with ganglion) → balance

Sound Perception Summary

  1. Air vibrations hit the eardrum

  2. The little bones (ossicles) make the sound stronger & send it to the oval window

  3. Fluid waves in the cochlea move a membrane (basilar membrane) → tiny hair cells in the Organ of Corti bend

  4. Hair cells create electrical signals → signals go to the hearing part of CN VIII → brain's hearing area (temporal lobe) figures out how high or loud the sound is

Equilibrium (Balance)

  • Static: sensing head position & straight-line motion (like standing still or moving in an elevator)

  • Dynamic: sensing spinning or rotational movement (like twirling)

  • Sensors involved:

    • Inner ear: semicircular canals (crista ampullaris), utricle & saccule (maculae)

    • What you see & body position sensors (in joints, muscles, tendons)

  • Brain combines all this info to keep posture & coordinate movement; balance gets worse with age, leading to more falls in older people

Ear Problems (Main Examples)

  • Conductive hearing loss: problem in outer/middle ear stops sound vibrations from getting through

  • Sensorineural hearing loss: damage to the cochlea's Organ of Corti or CN VIII (nerve)

  • Otitis externa: outer ear infection ("swimmer’s ear")

  • Otitis media: middle ear infection (common in kids)

Eye Anatomy & Vision

  • Light bends (refracts) when it goes through different materials (like a straw looking bent in a glass of water)

How light travels through the eye:

  1. Conjunctiva – clear, thin lining on eyelids & white of eye

  2. Cornea – clear dome on front; first and main part that bends light and protects eye

  3. Aqueous humor (fluid in front & back chambers) – watery fluid that nourishes eye

  4. Pupil – adjustable hole that lets light in

  5. Iris – colored part of eye; controls pupil size & eye color

  6. Lens – clear, curved part; focuses light finely & changes shape to see near/far

  7. Vitreous humor – clear gel in back of eye; keeps eye shape & moves nutrients

  8. Retina – back layer with light sensors:

    • Rods: \approx120 million; for night & side vision; see in shades of gray

    • Cones: \approx6 million; for color, sharp vision; most dense in the fovea centralis (center of macula lutea)

  • Optic nerve (CN II) leaves the eye at the optic disc (blind spot)

Vision Perception

  • Phototransduction: light → changes light-sensitive chemicals in retina → electrical signals → optic nerve → visual cortex (back of brain) interprets what you see

Disorders of Vision

  • Cataracts: lens slowly gets cloudy; goes away with surgery where a new lens is put in

  • Age-related macular degeneration (AMD): breakdown of the macula (central vision area) → loss of central vision → risk of blindness

  • Color blindness: usually a genetic problem (passed down through X-chromosome) where certain color-sensing cells (cones) are missing

  • Conjunctivitis ("pink eye"): swelling/infection of the conjunctiva

  • Glaucoma: high pressure inside the eye damages the optic nerve

  • Refractive errors (when eyeball/cornea shape is off):

    • Myopia – nearsighted (light focuses in front of retina)

    • Hyperopia – farsighted (light focuses behind retina)

    • Astigmatism – uneven curve of cornea/lens → blurry vision at various distances

    • Presbyopia – age-related loss of lens's ability to focus near (arm's length vision)

Aging & Sensory Decline (Rough Ages)

  • Pain sensing \downarrow after 50 years

  • Temperature (cold/hot), pressure, touch sensitivity \downarrow with age

  • Taste buds \downarrow in number/size after 50; noticeable taste loss after 60

  • Smell: smell nerve endings \downarrow by 70 → less ability to smell flavors

  • Hearing: 30\% of people over 65 have significant hearing loss (often high-pitched sounds)

  • Balance problems: brain processing & inner ear balance function \downarrow → higher risk of falling

  • Eyes:

    • Tear creation drops → dry, irritated eyes

    • Lens gets stiffer & less clear (leading to presbyopia & cataracts)

Diagnostic Tests (Key Examples)

  • Audiometry for hearing levels

  • Otoscopic exam for outer/middle ear health

  • Tympanometry for middle ear pressure & eardrum movement

  • Tonometry for eye pressure (glaucoma check)

  • Ophthalmoscopy/retinal imaging for macula & blood vessel health

  • Visual acuity & refraction tests (Snellen eye chart, phoropter for glasses prescription)

Clinical & Ethical/Practical Implications

  • Early checks for hearing & vision keep life quality high and keep people safe (e.g., stop falls, allow driving)

  • Infections (middle ear/outer ear infection, pink eye) need good hygiene & quick treatment to prevent lasting problems

  • Cataract surgery is one of the most effective procedures for giving older people back their independence

  • Genetic advice for color blindness & inherited macula problems

Integration with Previous Content

  • Connects to pathways in the nervous system (incoming vs. outgoing signals)

  • Links to muscle and bone sensors (in joints, tendons) for balance

  • Shows how the body keeps things stable (homeostasis): sensory feedback is vital for controlling movement, breathing (e.g., chemical sensors), heart and blood vessel reflexes

Quick Abbreviation Reference

  • CN II – Optic nerve

  • CN VIII – Vestibulocochlear nerve

  • AMD – Age-related Macular Degeneration

  • IOP – Intraocular Pressure

  • TM – Tympanic Membrane

Mnemonics & Study Tips

  • Ear bones order (outer → inner): "MISO" – Malleus, Incus, Stapes, Oval window

  • Eye layers (outer→inner): Sclera, Choroid, Retina – "SCRub"

  • Taste types: "Sweet Sour Salty Bitter Umami" → initials alternate consonant/vowel for recall

  • Static vs. Dynamic balance: "Static = Still, Dynamic = Dancing"