Ch 18 Sensory systems

What is sensation, what is general and special senses

• 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

What is perception

• conscious awareness of a sensation

Given sensory receptor what is the area monitored by it called

Receptive field

Whats a sensory receptor and how do they work

• 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 an action potential

What are the two types of receptors

• Tonic receptors – always active

• Phasic receptors – normally inactive and become active only when a change occurs in conditions being monitored

Whats adaptation

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

What are the types of adaptation

• 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

Exteroceptors vs. interoceptors vs. proprioceptors

Exteroceptors

• Location: On or near the body surface (skin, special sense organs).

• Interoceptors (Visceroceptors)

  • Location: Inside the body, within visceral organs and blood vessels

  • Proprioceptors

    • Location: In skeletal muscles, tendons, joints, and ligaments

Nociceptors

• Free nerve endings with large
  receptive fields

• Three different types can respond to:

  • Extreme temperatures

  • Physical damage

  • Dissolved chemicals (e.g., 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

Thermorecepters

• 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 and their types

• 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 (e.g., blood vessels, digestive/reproductive/urinary tracts)

3. Proprioceptors – monitor positions of joints and muscles

Types of tactile receptors

• Unencapsulated receptors:

  • Free nerve ending – crude touch

  • Root hair plexus – hair displacement

  • Tactile disc – 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

What are the two types of proprioceptors

• Muscle spindles

• Golgi tendon organs

Chemoreceptors

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

1. What exactly is paresthesia, and what most commonly causes it to occur?

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

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

1. an abnormal, spontaneous skin sensation—most often described as tingling, burning, prickling, or a "pins-and-needles" feeling

2. Typically a symptom of underlying nerve damage (neuropathy) or central nervous system disorders

3. The compressed nerve misfires, generating abnormal electrical signals that the brain interprets as numbness, tingling, burning, or electric-shock "pins and needles"

Olfaction

The detection of airborne chemicals (odorants) dissolved in fluids that coat nasal membranes

What does the olfactory epithelium contain

• 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

What does the Lamina propria contain

• Loose connective tissue

• Blood vessels

• Nerves

• Olfactory glands – secrete mucus

Gustation

Involves detection of tastants dissolved in saliva

Where are Taste buds found

Found throughout the oral cavity along the sides of
lingual papillae

What are taste buds composed of

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

What is gustatory discrimination (the taste)

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 (e.g., 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

What are the structures of the external ear and what is its function

• Collects sound waves and directs them to middle ear

• Structures

  • Auricle

  • External acoustic meatus

  • Tympanic membrane

  • Ceruminous glands secrete cerumen along the external acoustic meatus

  • Hairs

What composes the middle ear, where is it found and what muscles

• Tympanic cavity

• Structures

  • Auditory tube

  • Auditory ossicles

    • Malleus (“hammer”)

    • Incus (“anvil”)

    • Stapes (“stirrup”) –
      articulates with
      oval window

  • Muscles

    • Tensor tympani

    • Stapedius

1. What exactly is otitis media? What most commonly causes it?

2. Why is otitis media more common in children than adults?

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

1. Otitis media is an infection or inflammation of the middle ear space behind the eardrum. It is most commonly caused by bacterial or viral infections following an upper respiratory illness like a common cold.

2. It is more common in children because they have shorter, more horizontal eustachian tubes that trap fluid easily, larger adenoids that block drainage, and immature immune systems.

3. Acute cases are typically treated with watchful waiting, pain relievers like ibuprofen or acetaminophen, or oral antibiotics like amoxicillin. For chronic infections, tympanostomy tubes (ear tubes) or an adenoidectomy may be surgically performed to restore proper drainage.

What senses are in the internal ear

Houses receptors for the senses of hearing and equilibrium

What makes up the bony labyrinth and what fluid is in it

Fluid: Perilymph

• Vestibule

• Semicircular canals

• Cochlea

Whats in the membranous labyrinth

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

  • Utricle

  • Saccule

  • Semicircular ducts

  • Cochlear duct

  • Those 4 make up the vestibular complex

Utricle + saccule what are in them or do they make up

• Pair of membranous 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)

What movements do the Utricle and saccule do

• Utricle – oriented to sense horizontal movements

• Saccule – oriented to sense vertical movements

What are the semicircular ducts and make it up

• Anterior, posterior, and lateral semicircular ducts

• Ampulla (pl. ampullae) of each duct houses hair cells on an ampullary crest

• Cilia of hair cells embedded in ampullary cupula (pl. cupulae)

Explain the 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)

Explain the structure of the cochlea

• Central cochlear duct – filled with endolymph; found between:

  • Vestibular duct – filled with perilymph; adjacent to the oval window ( hit by stapes)

  • Tympanic duct – filled with perilymph; adjacent to the round window

Explain spiral organ and where it is

• Located within cochlear duct

• Hair cells and supporting cells rest on flexible basilar membrane 

• Stereocilia 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

What are the pathways for auditory sensations

Cochlear nerve (CN VIII) 1*

ipsilateral cochlear nucleus in medulla oblongata 2*

pons and inferior colliculi on both sides 3*

thalami on both sides

4*auditory cortices on both sides

What are the accessory eye structures

• Eyebrows

• Palpebrae (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 pocket found where the two conjunctivae meet

Name the eye structures for crying

• 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

Name extra ocular muscles and what nerve innervates them not function

• 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 looks inferiorly and laterally

• Innervated by CN VI (abducens)

  • Lateral rectus – eye looks laterally

Name outer eye structure like surface level

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

  • Sclera – 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 numerous free nerve endings

Name inner eye structure

• Vascular layer – carries blood/lymphatic vessels, regulates light entering eye, secretes/resorbs aqueous humor, and controls 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 muscle that determines shape of the lens via ciliary zonule

1. What exactly are cataracts? What can cause them? How are they typically treated?

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

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

1. Lens gets cloudy and they need to do surgery to put a fake lens in.

2. When your eye loses its flexibility and hardens called old eye; solution is eye drops, glasses or surgery

3. No LASIK doesn’t work because it reshapes the cornea