Bio 240 Test 5 Spring 2024 Study Sheet

Peripheral Nervous System

Composed of 12 pairs of cranial nerves connected directly to the brain or brainstem.

Cranial nerves are numbered by the order in which they emerge, from anterior to posterior.

Can be sensory, motor, or mixed (both).

Cranial Nerves

Learn them both by name and number (Roman numeral).

I. Olfactory Nerve:

• Sensory: Smell. Originates in the olfactory epithelium and projects to the olfactory bulb.

II. Optic Nerve:

• Sensory: Vision. Transmits visual information from the retina to the brain.

III. Oculomotor Nerve:

• Motor: Controls most of the eye's movements, including raising the eyelid, constricting the pupil, and controlling lens shape.

IV. Trochlear Nerve:

• Motor: Controls the superior oblique muscle of the eye, responsible for downward and outward eye movement.

V. Trigeminal / Cranial Nerve V

• Sensory: Skin of head & face; gums & teeth.

• Motor: Muscles of mastication.

• Disorder: Trigeminal Neuralgia / Tic Douloureux [painful twitch].

• Recurring episodes of intense stabbing pain in the face.

VI. Abducens Nerve:

• Motor: Controls the lateral rectus muscle, responsible for lateral eye movement.

VII. Facial / Cranial Nerve VII

• Sensory: Taste buds / anterior ⅔ of tongue.

• Motor: Muscles of facial expression.

• Disorder: Bell’s Palsy / drooping of ½ face / facial paralysis.

VIII. Vestibulocochlear Nerve:

• Sensory: Hearing and balance. Has two divisions: the vestibular nerve (balance) and the cochlear nerve (hearing).

IX. Glossopharyngeal Nerve:

• Sensory: Taste and sensation from the posterior 1/3 of the tongue, as well as the pharynx.

• Motor: Controls some muscles of the pharynx involved in swallowing.

X. Vagus / Cranial Nerve X

• Longest cranial nerve: stretches from the brainstem to the intestines.

• Sensory & Motor to: pharynx, larynx, trachea, heart, lungs, esophagus, stomach, intestines & gallbladder.

• Major nerve of PNS: 75% of all parasympathetic fibers travel in the vagus nerve.

• Major Functions:

• Slows down the heart.

• Promotes digestive secretions & peristalsis (wavelike contractions of the intestines).

XI. Accessory Nerve:

• Motor: Controls the sternocleidomastoid and trapezius muscles, involved in head movement and shoulder elevation.

XII. Hypoglossal Nerve:

• Motor: Controls the muscles of the tongue.

Cranial Nerve Zero

Detects pheromones.

Sexual signals, social signals, dormitory syndrome in the absence of males.

Neurotransmitters

All preganglionic neurons release Acetylcholine.

Postganglionic neurons:

Parasympathetic: release Acetylcholine.

Sympathetic: most release Norepinephrine / adrenaline-like stimulant.

Slow to break down.

Effects are more long-lasting

Reaction to Fear aka “Fight or Flight”

(physical danger, job or relationship stress):

Heart muscle:

Sympathetic Effects: \uparrow Heart rate, \uparrow strength of contractions

Parasympathetic Effects: opposite

Muscles:

Skin / blood vessels:

Sympathetic Effects: Constrict / pale face of fear

Skeletal muscle blood vessels:

Sympathetic Effects: Dilate

Cardiac blood vessels:

Sympathetic Effects: Dilate

Abdominal blood vessels:

Sympathetic Effects: Constrict

Hollow Organs & Sphincter Muscles:

Bronchioles:

Sympathetic Effects: Dilate

Digestive Tract:

Sympathetic Effects: Constrict / \downarrow Peristalsis

Parasympathetic Effects: \uparrow Peristalsis

Iris of Eye:

Sympathetic Effects: Pupil Dilation

Arrector Pili Muscle:

Sympathetic Effects: Contract / “goosebumps”

Glands:

Sweat:

Sympathetic Effects: \uparrow Activity

Salivary:

Sympathetic Effects: \downarrow Activity

Parasympathetic Effects: \uparrow Activity

Liver:

Sympathetic Effects: \uparrow Blood Sugar & FA Levels

Adrenal Medulla:

Sympathetic Effects: \uparrow Epinephrine / Adrenaline (prolongs effects of Norepinephrine)

Immune System

Sympathetic Effects: \downarrow Activity ( \uparrow Cortisol)

Cortisol

Cortisol is a hormone released in stressful situations:

e.g., Smoking:

\uparrow Cortisol by 77% >> Immune problems

\uparrow Adrenalin by 84% >> Heart attack

Sense Organs

Sense Organs / Receptors

Specialized structures of the nervous system able to respond to external or internal stimuli by producing an action potential.

The brain must respond to this stimuli in order to maintain homeostasis.

Somatic Senses / General

Distributed throughout the body densely or sparsely.

Relay sensations of touch, pressure, temperature, pain.

Special Senses

Grouped in the tongue, nose, eyes, ears.

Produce sensations of taste, smell, sight, sound, and balance /imbalance

All sense organs & receptors initiate reflexes necessary for maintaining homeostasis

Sensory Adaptation

In response to continuous stimulation,

the magnitude of the receptor potential decreases.

Sensory impulse conduction slows down and

Intensity of the sensation decreases.

Fast Adapting

touch, temperature, smell, light, sound, pressure, taste

Slow Adapting

pain, proprioceptors / stretch receptors

Classification of Receptors by Type of Stimulus

Mechanoreceptors

respond to mechanical force that in some way moves or changes the shape or position of receptors.

Like pushing a lever on a machine to activate it.

e.g., hearing & touch, pressure / blood vessels, skin; stretch / muscles, tendons, lungs, balance

Chemoreceptors

respond to amount or changing concentration of chemicals

e.g., taste & smell (tastants & odorants) also monitor blood levels of glucose, CO2, O2, H^+ / Hydrogen ions (acidic)

Thermoreceptors

found everywhere. Respond to changes in temperature

Photoreceptors

located only in eyes. Respond to light, if enough is present

Baroreceptors (Osmoreceptors)

Concentrated in the hypothalamus.

Sometimes described as pressure sensors, not to be confused with mechanoreceptors, they detect osmotic pressure or osmolarity.

This is the ionic concentration or concentration of electrolytes in body fluids.

Important in stimulating the hypothalamic thirst center.

Nociceptors/ pain receptors

respond to “noxious” stimuli (intense stimuli of any type that results in tissue damage) due to toxic chemicals (including chemicals released from damaged tissue), intense light, sound, pressure, or heat;

Referred Pain: originates from deep structures and is referred to surface areas

Theory: Somatic neurons & sensory autonomic neurons share same interneurons / synapses in spinal cord

Heart attack pain:

In men: may be felt as pain in sides of the face, left shoulder & chest, down inside of left arm & hand.

In women: pain may be felt in back

Classification by Structure

Free Nerve Endings

Simplest, most common receptors

Respond to pain, itching, tickling, touch, temperature, movement, stretch

Encapsulated Nerve Endings

Touch & pressure receptors, e.g,

Meissner’s corpuscles: light touch; fingertips

Pacinian corpuscles: deep pressure& stretch; deep dermis of skin

Merkel’s disks: light touch, 2 point discrimination, closer together on tongue & fingertips, further apart on the back.

Stretch Receptors

Golgi Tendon Organ: Proprioceptor / prevents muscle & tendon injury

Muscle Spindle: Proprioceptor / prevents muscle & tendon injury

SMELL (OLFACTION)

Olfactory Receptors

Chemoreceptors for our sense of smell

Specialized bipolar neurons

Only neurons to regenerate throughout adult life

Used as adult stem cells to re-grow nerve tissue

Knob at the end of dendrite contains cilia

Cilia: moves odor molecules toward the receptor binding sites / \uparrow contact with surface area for binding

Humans: ≈ 10 million olfactory receptors

Dogs: ≈ 1 billion olfactory receptors / 100X human smell capacity

Olfactory receptors also carry pain, touch, pressure & temperature sensations to CN-V (Trigeminal)

Anosmia

loss of sense of smell from Infection, Injury (concussion), Cigarette smoking (immobilizes cilia), Cocaine use, Zinc deficiency (sources of dietary zinc: eggs, pumpkin seeds) Genetics

TASTE (GUSTATION)

Gustatory Receptors

Chemoreceptors for our sense of taste

“Taste Hairs” replaced every 3-10 days

Located inside taste buds on the superior surface of the tongue, throat, lining of mouth and duodenum!

Taste receptors are also located in the esophagus, stomach, and duodenum that will detect sweet & increase insulin production, regardless of the type of sweetener.

Saliva breaks food molecules into smaller chemicals called “tastants”.

Ciliary action moves tastants dissolved in saliva toward receptors.

70 – 75% of what we perceive as taste comes from our sense of smell (cf. slices of apple and raw potato while holding nose and blindfolded)

(Tastants and odorants are really the same thing. The name comes from which sense organ they land on.)

5 Tastes:

Sweet: from sugars or artificial sweeteners

Salty: from salts

Sour: from acidic foods

Umami/Savory: from protein

Bitter: from high alkaline foods. High concentration of bitter sensing taste hairs on the posterior 1/3 of the tongue CN-IX (Glossopharyngeal) “Bitter back nine”. The taste most likely to be dangerous, therefore elicits gag reflex and is the only taste to adapt slowly.

Spicy hot: not a taste. It is nerve damage. The sensations of pain, temperature, touch are carried by taste fibers to CN- V (Trigeminal)

CN-VII (Facial) carries taste from anterior 2/3 of the tongue.

EAR - HEARING (AUDITION) & BALANCE (EQUILIBRIUM)

Receptors

“Hair Cells” / Mechanoreceptors

Shape is changed by stimulus of sound waves or movement of otoliths

Mediate both hearing & balance (equilibrium)

Major Parts of Ear

External Ear

Auricle / Pinna: Outer Ear

External Auditory Meatus: Ear Canal

Tympanic Membrane: Eardrum

Middle Ear

Tympanic cavity

Ossicles: Malleus, Incus, Stapes (Amplify sound by 30%)

Auditory Tube/ Eustachian Tube: Connects ear to throat & equalizes pressure around the eardrum

Inner Ear

Structures Involved with Equilibrium (Balance):

Semicircular Canals

Vestibule (& Vestibular Nerve):

Utricle: * Detects head position and movement

Saccule: * Detects head position and movement

Structures Involved with Hearing:

Cochlea (& Cochlear Nerve):

Organ of Corti: Contains hair cells (mechanoreceptors)

Tectorial Membrane: Sound waves depress membrane & bend cilia \rightarrow Stimulating an action potential.

High frequency sound waves cross the proximal membrane.

Low-frequency sound waves cross distally.

Conduction Deafness

problem anywhere in sound conduction pathway from:

Damage to eardrum

Buildup of earwax

Fluid buildup

Otosclerosis (calcification of ossicles)

Scarring

Tumors

Disease

Infection

Injury

Nerve Deafness

damage to hair cells, organ of Corti or neurons (cochlear nerve)

Hair Cell Damage can be from:

Loud noises

Excessive nicotine or caffeine

Infections of the ear, nose, throat; meningitis

Some antibiotics: Kanamycin, Neomycin

Aging

Static Equilibrium

Vestibule

Maintenance of body position relative to the force of gravity (Utricle & Saccule)

Dynamic Equilibrium

Semicircular Canals

Maintenance of body position in response to sudden movement such as rotation, acceleration, deceleration

Both respond to the position of the head

Vision is our dominant sense: ½ of the cerebral cortex is devoted to interpreting vision (e.g., ballerina spinning & spotting)

VISION

Parts of the Eye

Coats/Layers/Tunics:

3. Outer/Fibrous Layer:

Sclera / “white”

Cornea: most anterior transparent part

5. Middle/Vascular Layer:

Choroid is red or pink (looks dark blue in sheep eye)and contains:

blood vessels & pigments

Ciliary body & suspensory ligaments – attach to lens

Lens – changes shape to focus light

Iris – muscle controlling (pupil size & thus) amount of light entering the eye. The colored part of the eye.

7. Inner/Nervous Layer:

Retina, (looks beige in sheep eye) Contains:

Photoreceptors – (rods & cones) continuous with

Neurons – continuous with optic nerve (CN II)

fovea centralis (in macula lutea) – high concentration of cones

retinal blood vessels

ora serrata – (Also rich with cones, its’ function is not well understood. May reduce light scattering for purpose of color consistency.)

Cavities & Humors:

3. Anterior Chamber: small

Between cornea & iris

Contains aqueous humor / watery

5. Posterior Chamber: large

Contains vitreous humor / gel-like

Maintains shape of eye / interocular pressure & holds retina against the choroid

Accessory Structures:

3. Eyelids:

Mucous membrane lining /Conjunctiva -- keeps eyes moist

Can become inflamed: Conjunctivitis / “pink eye”

5. Lacrimal Apparatus:

Produces “tears” constantly

Contains lysozymes that clean the eyes

Found on the lateral side of each eye

Process of Seeing

Refraction, Accommodation, Constriction & Convergence

3. Refraction (Bending) of Light by passing in order through the:

Cornea

Aqueous humor

Pupil (an opening in the iris)

Lens

Vitreous humor

5. Accommodation of Lens:

Lens shape/curvature is changed by the muscles of the ciliary body thus focusing the image on the retina’s fovea centralis.

Far Vision: elongated (lens is stretched out/thinned)

Near Vision: short, rounded (lens is allowed to relax)

7. Constriction or Dilation of Pupil (a space):

Circular fibers of iris constrict pupil for Near Vision

Radial fibers of iris dilate pupil for Far Vision

9. Convergence of Eyes / Stereovision:

Near Vision: extrinsic eye muscles move eyeballs inward to maintain single vision. To demonstrate in the extreme, hold your hand in front of you and focus on your fingertip. Then move your finger toward your nose and your eyes will converge the closer you get to your nose. You will appear “cross-eyed”

Far Vision: eyes are parallel

Types of Photoreceptors

Rods

responsible for night vision / more numerous than cones & 100 X more sensitive to light

Sensitive to:

Dimly lit images

Black & white images

Movement, peripheral vision

Dark Adaptation:

Rods contain a photopigment / Rhodopsin / visual purple: made by vitamin A

Broken down by bright light

When walking into a dark room, the Rhodopsin must be made / takes < 30 seconds to adapt

Cones

responsible for day vision

Sensitive to:

Brightly lit images

Color images

Detail, central vision

Fovea Centralis: small depression in the retina with a high concentration of Cones

Humans: 1 fovea per eye

Birds of prey: 2-3 fovea per eye / 8 X the visual acuity of humans

Optic Disc: where the nerves and blood vessels exit/enter the eye. This causes a normal “blind spot” because there is no room for receptors (rods or cones) here.

Eye Disorders

3. Blindness due to vitamin A deficiency is the most common cause of blindness worldwide

Causes loss of transparency of cornea

Tx: Corneal transplants /

Successful due to lack of blood vessels

Leading causes of blindness in the U.S.:2. Aging and degeneration of retina / macular degeneration

5. Diabetes

6. Glaucoma

7. Cataracts: Degenerated lens proteins / makes lens cloudy

Occurs in > 50% of the population over age 65.

Caused by trauma, UV radiation, diabetes, aging.

Tx: replace the lens with a synthetic lens.

3. Glaucoma: Fluid pressure buildup under the cornea because the aqueous humor can’t drain.

Interocular pressure builds up in both chambers damaging the retina and optic nerve.

Extremely painful

Triggers: stress, darkness, anesthetics / all dilate the pupil

3. Floaters: Calcium granules floating in vitreous humor casting shadows on the retina

4. Diabetic retinopathy: Caused by damage to the blood vessels from unregulated blood sugar