Anatomy Chapter 16 Sense Organs

sensory receptor

structure specialized to detect stimulus

transducer

any device that turns one form of energy into another

a stimulus causes a \____ potential

receptor

sense organs

structure that combines nervous tissue with other tissues that enhance its response to a certain type of stimulus

transduction

conversion of one form of energy to another (light to nerve signals)

the fundamental purpose of any sensory receptor:

transduction

receptor potential

small, local electrical change on receptor cell caused by initial stimulus, results in nerve signals being sent to CNS

sensory cells have \____ at their base and release \____, stimulating an adjacent neuron

synaptic vesicles, neurotransmitters

sensation

subjective awareness of stimulus

modality

type of stimulus or sensation produced (vision, hearing, taste)

modality is determined by

where signals end in the brain

location is determined by

which nerve fibers issue signals to the brain

receptive field

any sensory neuron that detects stimuli in a given area

intensity is encoded by (3)

firing frequency, number of neurons firing (recruitment), which neurons are firing (sensitive vs. not sensitive neurons)

duration is encoded by

changes in firing frequency over time

sensory adaptation

prolonged stimulus leads to slower firing over time, person becomes less aware of stimulus

phasic receptors

generate burst of action potentials when first stimulated, quickly adapts

ex. smell, hair movement, cutaneous pressure

tonic receptors

generate signals more steadily, adapt slowly

ex. pain, proprioceptors

simple receptors

1 or few sensory nerve fibers and not much connective tissue

unencapsulated nerve endings

dendrites without connective tissue wrapping

free nerve endings

bare dendrites without special association with specific accessory cells or tissues; abundant in skin and mucous membranes

examples of free nerve ending receptors

warm receptors, cold receptors, nociceptors

tactile discs

flattened nerve endings that terminate adjacent to specialized tactile cells in basal layer of epidermis; tonic receptors for light touch

examples of tactile disc receptors

texture, edges, shapes, respond to skin compression

hair receptors

aka root hair plexuses, dendrites that coil around hair follicle, respond to movements of hair, phasic

encapsulated nerve endings

nerve fibers wrapped in glial cells or connective tissue, most are mechanoreceptors

tactile corpuscles

tall, oval, consist of 2-3 nerve fibers that move up through fluid-filled capsule of Schwann cells, mechanically linked to edges of dermal papillae, phasic receptors for light touch and texture

where are tactile corpuscles concentrated

sensitive hairless areas: fingertips, palms, eyelids, lips

end bulbs

ovoid bodies composed of connective tissue sheath around sensory nerve fiber

where are end bulbs found

mucous membranes of lips/tongue, conjunctiva on anterior surface of eye, epineurum of large nerves

bulbous corpuscles

flattened, elongated capsules containing a few nerve fibers; tonic receptors for heavy touch, pressure, stretch of skin, deformation of nails, joint movement

where are bulbous corpuscles found

dermis, subcutaneous tissue, joint capsules

lamellar (pacinian) corpuscles

ovoid up to 1-2mm, consist of single dendrite running up core of organ encapsulated by multiple concentric layers of cells, phasic receptors for vibration, respond to 1-2 action potentials when pressure is applied and lifted

where are lamellar corpuscles found

periosteum, joint capsules, pancreas, deep in dermis

how many neurons are involved in sensation

3 (1st, 2nd, 3rd order neurons)

sensory projection

transmission of info from receptor/receptive field to specific locality in cerebral cortex

pain

uncomfortable perception of tissue injury or noxious stimulation

nociceptive pain

pain from damage (cuts, burns, chemical irritation)

visceral pain

dull, diffuse pain caused by stretch, chemical irritation, ischemia; feels like squeezing, cramping, nausea

deep somatic pain

pain in bones, joints, muscles often caused by excessive stretch; ex. arthritis, sprains, fractures

superficial somatic pain

pain from skin; ex. cuts, burns, insect stings

neuropathic pain

pain from injuries to nerves, spinal cord, meninges, brain; feels like stabbing, burning, tingling, electrical sensations; ex. headaches, phantom limb, fibromyalgia, etc.

fast pain

immediate, sharp pain mediated by type A fibers

slow pain

delayed, aching pain mediated by type C fibers

which cranial nerves do head pain signals use to travel to brainstem (4)

5-trigeminal, 7-facial, 9-glossalpharyngeal, 10-vagus (5 is the main cranial nerve for head pain)

which ascending tracts do neck down pain signals travel by (3)

spinothalamic, spinoreticular, gracile funiculus tracts

which ascending tract carries pain impulses to reticular formation and is associated with subconscious pain and emotional and behavioral response to pain

spinoreticular tract

which ascending tract carries pain impulses to cerebral cortex and is associated with somatic pain

spinothalamic tract

which ascending tract carries pain impulses to thalamus and is associated with visceral pain

gracile funiculus

referred pain

pain in viscera mistakenly thought to come from skin/other superficial site

what causes referred pain

convergence of neural pathways in CNS

analgesic effect

pain relieving effect in CNS caused by opium, morphine, heroin

endogenous opioids

pain relieving peptides; internally produced opium-like substances secreted by CNS, pituitary, digestive tract, other organs

3 types of endogenous opioids

enkephalins, endorphins, dynorphins

spinal gating

stops pain signals at posterior gray horn (signals for pain don't reach the brain)

what are the chemical senses (2)

gustation (taste) and olfaction (smell)

gustation is a result of \____ stimulation of sensory cells in \____

chemical, taste buds

tastants

chemical stimuli for taste

lingual papillae

visible bumps on tongue (not taste buds)

filiform papillae

tiny spikes without taste buds, important for grooming in mammals, most abundant on human tongue, innervated, serve in sense of food texture (mouth feel)

foliate papillae

parallel ridges on sides of tongue adjacent to molars/premolars with taste buds, taste buds generally degenerate by 2-3 years old

fungiform papillae

large, arranged in V at the back of the tongue, each surrounded by deep trench, contain up to half of all taste buds (250 each)

tastebuds

lemon shaped groups of 50-150 taste, supporting, and basal cells

taste cells

banana-shaped with tuft of apical microvilli (taste hairs) as receptors, epithelial cells that synapse with sensory nerve fiber at base, live for 7-10 days

taste pore

pit for taste cells to project out

basal cells

stem cells that multiply and replace taste cells, synapse with sensory nerve fibers of taste bud

supporting cells

look like taste cells but so sensory role

5 primary taste sensations

salty, sweet, umami, sour, bitter

taste is influenced by (4)

food texture, aroma, temperature, appearance

2 mechanisms of gustation

- 2nd messenger system:
tastants bind to receptors which activates G proteins and second messenger systems

- depolarizing cells directly with Na or acids that penetrate cells

both result in release of neurotransmitters

projection pathways of gustation

facial nerve (CN VII), glossopharyngeal nerve (CN IX), vagus nerve (CN X)

conscious sensation: cranial nerve, medulla, thalamus, primary gustatory area of postcentral gyrus

odorants

airborne chemicals in olfaction

olfactory mucosa

patch of epithelium in roof of nasal cavity that houses olfactory cells

olfactory cells are which type of cell

neuron, the only neurons exposed to external environment

olfactory cells are phasic or tonic?

phasic

olfactory hairs

cilia on the head of olfactory cells, have binding sites for odor molecules

olfactory cells use which mechanism

second messenger system

olfactory cells synapse in \____ on dendrites of \____ and \____ cells

olfactory bulb, mitral, tufted

glomeruli

spherical clusters of dendrites of mitral and tufted cells

synapses between olfactory nerve and mitral/tufted cells form here

hearing

response to vibrating air molecules

equilibrium

sense of body orientation, movement, balance

the ear has \____ sections

3 - outer, middle, inner

outer ear

funnel for conducting airborne vibrations to tympanic membrane (eardrum)

auricle

part of outer ear, the external structure of the ear, elastic cartilage and adipose structure on side of head

auditory canal

part of outer ear, passage leading through the temporal bone to the tympanic membrane

cerumen

ear wax

middle ear

located in tympanic cavity of temporal bone, houses tympanic membrane

tympanic membrane

part of middle ear, aka ear drum, innvervated by sensory branches of vagus and trigeminal nerves, suspended in ring shaped groove and vibrates freely

mastoid cells

part of middle ear, air filled spaces in mastoid process of temporal bond, air is from the auditory tube

auditory tube

part of middle ear, aerates and drains middle ear

tympanic cavity

2-3mm space between outer and inner ears, contains auditory ossicles

auditory ossicles (3)

malleus, incus, stapes

malleus

elongated handle attached to inner surface of tympanic membrane

incus

triangle body articulates with malleus, long limb articulates with stapes

stapes

head articulates with incus, 2 limbs form an arch, elliptical base connects to the inner ear

muscles of middle ear (2)

stapedius, tensor tympani

inner ear

housed in body labyrinth (temporal bone passages) lined by membranous labyrinth (fleshy tubes)

perilymph

part of inner ear, cushion of fluid similar to CSF between bony and membranous labyrinths

endolymph

part of inner ear, fluid within membranous labyrinth similar to intracellular fluid

vestibule

chamber in inner ear containing organs of equilibrium