Human Anatomy Test 2

Sensation

Sensory information arriving at CNS

General senses

-include temperature, pain, touch, pressure, vibration, and proprioception

-receptors generally found throughout the body

-utilize sensory (ascending) tracts and some cranial nerves

Special senses

-include olfaction, gustation, balance/equilibrium, hearing and vision

-provided by highly specialized, structurally complex sense organs, which are localized to specific parts of the body

-utilize cranial nerves only

-in narrow, specific areas of the body

Perception

-conscious awareness of a sensation

-not always aware if it is constant

Sensory receptor

-specialized cell or cell process that monitors conditions in the body or external environment

-receptors exhibit specificity

-can be free nerve endings or discrete structures

-area monitored by receptor is the receptive field

-stimuli may be physical forces, dissolved chemicals, sounds, light photons, etc., but all must be converted into action potential

How is sensory info encoded?

-identity of active neurons in the pathway indicates both the location of the stimulus and its modality (e.g. fine touch, pressure)

-pattern of action potentials provides info about stimulus strength, duration, variation, movement, etc.

Two main functional classes of receptors

-tonic receptors

-phasic receptors

Tonic receptors

-always active

Phasic receptors

-normally inactive and become active only when a change occurs in conditions being monitored

-if there is a constant stimulus they shut off until there is a change

-example of adaptation

Adaptation

-a reduction in sensitivity in the presence of a constant stimulus

Peripheral adaptation

-when receptors or sensory neurons alter levels of activity

-characteristic of phasic receptors

-typically not exhibited by tonic receptors

Central adaptation

-when sensory neurons remain active, but neurons along the sensory pathway are inhibited

Receptor classification

according to location monitored

-exteroceptors vs. interoceptors vs. proprioceptors

According to structure

-free nerve endings vs. corpuscles

According to stimulus modality

-chemicals

-photons

-sound waves

-pain

-temperature

-physical distortion, contact or pressure

Nociceptors

Free nerve endings with large receptive fields

Three different types can respond to:

-extreme temperatures

-physical damage

-dissolved chemicals (histamine, capsaicin)

Common in superficial skin, joint capsules, periostea, and vessel walls, but uncommon in deeper tissues and viscera

Referred pain

When visceral pain is felt far from the site of the stimulus due to multiple first-order sensory neurons converging on the same second-order neurons

Thermoreceptors

Free nerve endings found in the dermis, skeletal muscles, liver, and hypothalamus

Two types: cold and warm receptors

-cold receptors are 3-4x more abundant

-structurally similar

Utilize lateral spinothalamic tracts (same as nociceptors)

Fast acting phasic receptors

Mechanoreceptors

-sensitive to stimuli that stretch, compress, twist, or distort their cell membranes

-three classes:

1. Tactile receptors: provide sensations of (fine/crude) touch, (fine/crude) pressure, and vibration

2. Baroreceptors: stretch receptors that detect pressure changes by monitoring walls of hollow organs (blood vessels, digestive/reproductive/urinary tracts)

3. Proprioceptors: monitor positions of joints and muscles

Tactile receptors

Unencapsulated receptors:

-free nerve ending: crude touch

-root hair plexus: hair displacement

-tactile disk: fine touch and pressure

Encapsulated receptors:

-tactile corpuscle: light touch, pressure and vibration

-bulbous corpuscle: pressure and distortion of skin

-lamellar corpuscle: deep pressure, pulsation, and vibration

Baroreceptors

-stretch receptors that monitor stretch of the wall of an organ (thus measuring pressure changes)

Proprioceptors

-monitors the position of joints, the tension in tendons/ligaments, and the state of muscular contraction

Muscle spindles and golgi tendon organs

Chemoreceptors

Can detect small changes in the concentration of specific chemicals/compounds dissolved in surrounding fluid

-carotid and aortic bodies detect changes in pH, CO2, and O2 in blood

-chemoreceptors in medulla oblongata measure changes in pH and CO2 of cerebrospinal fluid

Lecture Activity: Paresthesia

1. What is it? What causes it to occur?

   1. “Pins and needles” feeling on skin, “falling asleep”

   2. Caused by a pinched nerve

2. What are some of the possible causes chronic paresthesia?

   1. MS, diabetes, nerve damage

3. It is a common symptom of carpal tunnel syndrome. What is occurring with this disorder?

   1. Pinched median nerve, happens with repetitive use

Olfaction

-involves the detection of air-borne chemicals (odorants) dissolved in fluids that coat nasal membranes

Olfactory epithelium contains:

Olfactory sensory neurons

-specialized bipolar neurons with 20+ cilia bearing olfactory receptor proteins

-axons bundled into fascicles, which pass through cribriform foramina to olfactory bulb

-supporting cells

-basal epithelial cells: stem cells

Lamina propria contains:

-loose connective tissue

-blood vessels

-nerves

-olfactory glands: secrete mucus

Olfactory receptors

very specific

-humans have at least 400 “smell genes”

-each gene codes for a particular kind of olfactory receptor

-each receptor can bind to 1+ odorants

Humans can distinguish about 10,000 different odors, each is a distinct combination of different odorants

A smell will activate multiple receptors at the same time

Gustation

Involves detection of tastants dissolved in saliva

Taste buds

Found throughout the oral cavity along the sides of lingual papillae

They contain:

-gustatory epithelial cells

-possess microvilli with receptors

-multiple different types within each taste bud

-basal epithelial cells: stem cells

-dendrites from CNs VII, IX, and X

Perception of taste

Involves:

-sensory data regarding the texture and temp of food from CN V

-stimulation of olfactory receptors (taste is 80% smell)

-olfation plays a big role in smell

Gustatory discrimination

1. Sweet: elicited by sugars, alcohols, some amino acids, and some lead salts

2. Sour: produced by acids (specifically H+)

3. Salty: produced by metal ions (e.g. inorganic salts like NaCl)

4. Bitter: elicited by alkaloids (e.g. nicotine, caffeine, morphine) and some non-alkaloids (aspirin)

5. Umami: “savory” flavor elicited by glutamate and aspartate

6. Water: no flavor per se, but detect the ingestion of water; receptors concentrated in pharynx

-different regions of the tongue may be more sensitive to certain gustatory stimuli, but different receptor types are not confined to particular regions

Gustatory receptors

-bitter and sweet receptors are now known throughout the body and appear to trigger rapid immune responses that can kill bacteria!

External ear

collects sound waves and directs them to middle ear

Structures

-auricle (pinna)

-external acoustic meatus

-tympanic membrane

-ceruminous glands secrete cerumen along the external acoustic meatus

-hairs

Middle ear

-tympanic cavity

-structures

-auditory tube

-auditory ossicles (little bones)

-malleus (“hammer”)

-incus (“anvil”)

-stapes (“stirrup”)-articulates with oval window

-muscles

-tensor tympani

-stapedius

Lecture activity: Otitis Media

1. What is it? What most commonly causes it?

   1. Infection or inflammation of the middle ear

   2. Most commonly caused by auditory tube dysfunction, triggered by a viral upper respiratory infection or bacteria

2. Why is it more common in children than adults?

   1. Their auditory tubes are shorter, narrower, and more horizontally aligned

3. How is the acute version typically treated? What might be done if infections are chronic?

   1. Pain management, observation, targeted oral antibiotics

   2. Medical and surgical interventions: ear tubes, fluid suctioning, tympanoplasty, adenoidectomy

Internal ear

Houses receptors for the senses of hearing and equilibrium

Bony labyrinth

Passages through temporal bone (filled with perilymph)

-vestibule

-semicircular canals

-cochlea

Membraneous labyrinth

Soft tissue tubes and sacs within bony labyrinth (filled with endolymph)

-utricle

-saccule

-semicircular ducts

-cochlear duct

Utricle + Saccule

-pair of membraneous sacs within the vestibule

-contain clusters of hair cells called maculae (sing. Macula)

-cilia of hair cells are embedded in the otolithic membrane, which is packed with otoliths

-hair cells monitored by sensory neurons from vestibular nerve (branch of CN VIII)

Utricle

Oriented to sense horizontal movements

Saccule

Oriented to sense vertical movements

Semicircular ducts

-anterior, posterior, and lateral

-ampulla (pl. ampullae) of each duct houses hair cells on an ampullary crest

-cilia of hair cells embedded in ampullary cupula (pl. cupulae)

Vestibular pathways

-hair cells monitored by sensory neurons from the vestibular ganglion and vestibular nerve (branch of CN VIII)

-sensory neurons synapse on neurons within the vestibular nuclei, which send signals to various parts of the brain to coordinate movements of the eyes, head, and neck (e.g. nystagmus)

Cochlea

central cochlear duct: filled with endolymph; found between:

-vestibular duct: filled with perilymph; adjacent to the oval window

-tympanic duct: filled with perilymph; adjacent to the round window

Spiral organ

-located within cochlear duct

-hair cells and supporting cells rest on flexible basilar membrane

-steriocilia of hair cells are in contact with the less flexible tectorial membrane

-hair cells monitored by sensory neurons from the spiral ganglion and cochlear nerve (branch of CN VIII)

-distortions in the basilar membrane cause stereocilia of hair cells to bend against tectorial membrane, altering their chemical signals to sensory neurons

Pathways for auditory sensations

Cochlear nerve (CN VIII)—>ipsilateral coclear nucleus in medulla oblongata—>pons and inferior colliculi on both sides—> thalami on both sides—>auditory cortices on both sides

Cochlea to cerebrum: 4 neurons in the pathway!

Accessory eye structures

• eyebrows

• palpabrae (sing. Palpebra)

  • Eyelashes with tarsal glands

  • Lacrimal caruncle at the medial angle

  • Four layers

    • Skin (thinnest of the body)

    • Muscles: orbicularis oculi and Levator palpebrae superioris

    • Tarsal plate

    • Palpebral conjunctiva

      • Covers the inner surface of the eyelid

      • Continues onto the anterior surface of the eye as the bulbar conjunctiva

      • Fornix: small pockets found where the two conjunctivae meet

Lacrimal apparatus

• lacrimal gland

  • Sits in a depression in frontal bone in superior part of orbit

  • Sends 10-12 ducts to superior fornix

  • Produces slightly alkaline fluid with antibodies and lysozyme

  • Tears help to reduce friction, remove debris, prevent bacterial infection, and provide nutrients and O2 to conjunctiva and cornea

• Lacrimal canaliculi (sing. Canaliculus)

• Lacrimal sac

• Nasolacrimal duct

Extra-ocular muscles

• innervated by CN III (oculomotor)

  • Superior rectus: eye looks superiorly

  • Inferior rectus: eye looks inferiorly

  • Medial rectus: Eye looks medially

  • Inferior oblique: eye rolls and looks superiorly and laterally

• Innervated by CN IV (trochlear)

  • Superior oblique: passes through trochlea; eye rolls and look inferiorly and laterally

• Innervated by CN VI (abducens)

  • Lateral rectus: eye looks laterally

Eye structure-fibrous layer

• provides support/protection, serves as attachment surface for extra-ocular muscles, and has structures to assist in focusing

  • Sclera (white): dense fibrous connective tissue covering most of the eye

  • Cornea: transparent and continuous with sclera

    • Not covered by bulbar conjunctiva

    • Composed of multiple layers of precisely aligned collagen fibers

    • Avascular with numberous free nerve endings

Eye structure-vascular layer

• carries blood/lymphatic vessels, regulates light entering eye, secretes/resorbs aqueous humor, and control lens shape

  • Choroid: posterior 5/6 of eye; extensive capillary network to supply retina

  • Iris: pigments, vessels, and two layers of smooth muscle around the pupil

  • Ciliary body: secretes aqueous humor; includes ring of ciliary muscles that determines shape of the lens via ciliary zonule

Lecture Activity: Lens Dysfunction

1. What are cataracts? What causes them? How are they typically treated?

   1. Clouding of the normally clear natural lens inside of eye, vision is cloudy or dim

   2. Caused by natural aging, breaks down and clumps proteins in lens

   3. Surgery is only permanent treatment

2. What is presbyopia? How is it typically treated?

   1. Aging eyes, hard to focus on close objects

   2. Reading glasses, contact lenses

3. Would LASIK be an effective treatment for either of these conditions? Why or why not?

   1. No traditional lasik would not be

   2. LASIK reshapes cornea, both of these are disorders of the lens

Eye structure-inner layer/retina

• outer pigmented layer: absorbs light that passes through retina

• Inner neural layer

  • Photoreceptors

    • Rods: black and white vision in dim light

    • Cones: high acuity color vision (fovea centralis)

  • Photoreceptors—>bipolar cells—>ganglion cells—>optic nerve

• Optic disc/blind spot: no photoreceptors where optic nerve originates

Eye structure-humors

• aqueous humor

  • Inside anterior and posterior chamber

  • Produced by inner ciliary body and in posterior chamber

  • Composition like cerebrospinal fluid

  • Provides cushion and transport for nutrient/wastes

• Vitreous humor

  • Gelatinous mass that maintains shape of eye and supports retina

Visual pathways

• significant processing occurs within retina (eg horizontal cells, amacrine cells)

• Optic nerves meet at optic chiasm, where partial decussation occurs

  • Fibers from left half of each retina go to left thalamus before being routed to visual cortex (and vice versa on the right side)

  • Some fibers bypass thalamus and synapse in superior colliculi or reflex centers in brainstem

Endocrine system

Includes all endocrine cells and tissues in the body

Hormones

Chemicals released into blood, lymph, or interstitial fluid that regulate the activity of distant target cells

Effective at low concentrations

Different chemical compositions (amines, peptides, steroids)

Pituitary gland (hypophysis)

Fusion of two tissue types