Chapter 44: sensory systems

What are sensory receptor cells?

Specialized cells that transduce physical and chemical stimuli into neural signal

what is sensory transduction?

where are receptor protein response to a stimulus by opening or closing ion channels changing the receptor potential

What can receptor potential trigger?

Action potentials in the receptor cell

What does sensory transduction begin with?

Receptor protein that opens or closes ion channels, and the membrane changing the membrane potential

What is another word for membrane potential?

Receptor potential

How do sensory receptor proteins respond to stimuli?

directly or indirectly opening or closing ion channels

which receptors are ion channels themselves?

thermo receptors and mechano receptors

which kind of receptors use G-protein?

chemo and photo

How do electro receptors respond to depolarization?

Opening voltage gated CA2+ channels and the CA 2+ triggers neurotransmitter release

how do chemo, receptors and photoreceptors influence, ion channels indirectly?

Activating G proteins and second messengers

How are some sensory receptor cells organized with other cells?

in sensory organs

What do sensory systems include?

sensory cells, associated structures, and neural networks that process the information

What is sensory adaption?

Diminishing response to repeated stimulation

What is an example of sensory adaption?

Enables animals to ignore background conditions, but remain sensitive to changing or new stimuli

What are chemo receptors?

receptor proteins that bind to specific molecules their ligands

what are Ligands?

molecules that bind to receptors

What are chemo receptors responsible for?

taste, smell, and monitoring the internal environment such as CO2 levels in blood

What is olfaction?

sense of smell

what are olfactory receptors?

Neurons in the nasal cavity

What do the dendrites of olfactory receptors form?

Extend as olfactory cilia on the surface of the nasal epithelium

where do the axons of olfactory receptors extend?

Through holes in the overlying bone into the olfactory bulb in the brain

What is an odorant?

Molecules that binds to a specific olfactory receptor protein on the cilia of olfactory receptor neurons

what happens when an odorant binds to its receptor?

it activates a G protein, which activates the second messenger

What does the activated G protein do?

It activate the second messenger cAMP

what does cAMP do in an olfactory receptor neuron (ORN)?

it binds to carry on channels in ORN's membrane, causing an influx of Na+ and generating an action potential

What are pheromones?

Chemical signals used to communicate among individuals of the same species

What is an example of pheromones?

Female silkworm, moth release bombykol; males have receptors for bombykol on the antenna

What is gustation?

sense of taste

What structures are responsible for taste?

Clusters of chemo, receptors called taste buds

Where are human taste buds located?

Embedded in the tongue epithelium on the papillae.

How long do taste buds cells last?

About 10 days

What happens to tongue epithelium?

it is shed and is replaced at a rapid rate

How do neurons maintain connections with taste bud cells?

They formed new synopsis with new taste, bud cells as they are formed

where are human taste buds located on the papillae?

on the sides

What does microvilli do for taste buds?

Increase surface area for chemo receptors

What is papillae?

sides of tounge

What basic taste can humans detect?

Salty, sour, sweet, bitter, and umami

What is umami?

Savory meaty taste

what triggers umami?

Receptors for amino acids, including MSG

What do saltines receptor proteins do?

Allow sodium to diffuse into taste blood cells through open sodium channels depolarizing the cell

How are sourness receptors activated?

Direct effect of hydrogen ions on sodium channels

Why have receptors for bitter taste evolved?

to enable animals to detect, toxic compounds such as quinine, coffee or nicotine

what are mechano receptors?

sensory cells that respond to mechanical force by opening cation channels

how is the intensity of a mechanical stimulus registered?

a graded receptor potential

How does the CNS know the strength of a stimulus?

the amount of neurotransmitter released or rate of action potentials

What are tactile receptors?

provide sensations of touch, pressure, and vibration

What are Merkel's disc?

Tactile receptors that adapts slowly and provide continuous information about something touching the skin

What are Meissner's corpuscles?

Tactile receptors that adopted quickly and give info about changes on the skin

What are Ruffini endings?

Deep skin receptors that adapt slowly in response to low frequency vibrations

What are pacinian corpuscles?

Deep skin receptors that adapt rapidly in response to high frequency vibrations

How does the density of tactile receptors vary?

Areas like the lips and fingertips have high densities of receptors

Why do we have different mechano receptors?

to sense different textures, and pressures which helps with perception and survival

where are mechano receptor cells that monitor limb position?

Muscles, tendons, and ligaments

What info do these Mecano receptors provide to the CNS?

The position of limbs and stresses on muscle and joints

Why are these mechanical receptors important?

They are essential for maintaining posture and coordinating movement

What are muscle spindles?

mechanical receptors and muscle cells (stretch receptors)

What happens when a muscle is stretched?

Action potentials are generated in neurons

What is the golgi tendon organ?

A mechanical receptor and tendons and ligaments that provide info about the force generated by contracting muscle

Why is the golgi tendon organ important?

helps prevents muscle tearing by monitoring force during contraction

What are hair cells?

Mechanical receptors in the auditory and vestibular systems

What are stereocilia?

Finger like extensions of the cell membrane on hair cells that bend in response to pressure waves

How do hair cells detect sound?

they convert pressure waves (sound) into receptor potentials

what do minute filaments do?

Connect the tips of stereocilia and act like spring that open potassium channels

First step of action potential in stereocillia

stereocillia projects into a space that contains a fluid high in potassium and low in sodium. Potassium channels open, and potassium enters and depolarizes the cell.

Second step of action potential in stereocillia

Ion channels open when stereocilia are bent to the left

third step of action potential in stereocilia

membrane depolarization opens voltage gated calcium channels causing neurotransmitter release

Hyperpolarized stereocilia

Stereocilia are bent to the right and close ion channels

What does the outer ear include?

pinna and auditory canal

what is the function of the pinnae in the outer ear?

Collect sound waves and direct them into the auditory canal

What is the role of the auditory canal?

Channel sound waves from the pinnae to the tympanic membrane (ear drum)

what does the tympanic membrane do?

Vibrates in response to pressure waves converting them to physical forces in the middle ear

Where is the tympanic membrane located?

at the end of auditor canal

What is the middle ear?

Airfield cavity connected to the throat by the eustachian tube

why is the eustachian tube important?

So the air pressure can equilibrate between the middle ear and the environment

What are the ossicles?

The three bones, the malleus, incus and stapes

what is the function of the ossicles?

Transit vibrations from the tympanic membrane to the oval window

how do ossicles change the vibrations from the tympanic membrane?

convert large movements of the tympanic membrane into smaller movements with great force at the oval window

What happens at the oval window?

movements is translated into pressure changes in the fluid filled inner ear

What are the two sets of canals in the inner ear?

The vestibular system and cochlea

What does the vestibular system do?

balance

What does the cochlea do?

Hearing

what is the structure of the cochlea?

tapered coil chamber with three parallel canals, separated by the vestibular membrane and the basilar membrane

what is the function of the organ of Corti?

sit on the basilar membrane and transduces pressure waves into action potential

Where are the stereocilia of hair cells located?

embedded in the tectorial membrane

How do stereocilia create a neural signal?

Stereocilia bend when the basilar membrane flexes which creates a graded potential that can alter neurotransmitter release

How are the upper and lower canals of the cochlea connected?

joined at the distal end of the cochlea

What is the round window?

A flexible membrane at the end of the canal

What do the pressure waves do for the round window?

waves can travel all the way around to reach the round window

how does the basilar membrane respond to high sound frequencies?

Bends the membrane near the base

how does the basilar membrane respond to low sound frequencies?

wave flex the apical end

where do action potentials from the organ of Corti go?

send to different areas of the auditory cortex

What is conduction deafness?

loss of function of tympanic membrane or ossicles, preventing sound transmission to the inner ear

What is nerve deafness?

Damage to inner ear or auditory nerve pathways

how can hair cells in the organ of corti be damaged?

Loud sounds; damage is cumulative and irreversible

What is the function of hair cells in the vestibular system?

Detect the position and movement of head, which is essential for balance and control of eye movements

how are the semi-circular canals arranged?

there are three semi circular canals position that angles to each other, and they are aligned to the membranous ducts

What does the vestibule contain?

saccule and utricle

what are the ducts, saccule, and utricle filled with?

fluid

where is the Cupula located and function?

At the base of each semi circular canal duct that contains a cluster of hair cell stereocilia

how does fluid movement in the semi circular canals generate a signal?

shifting fluid pushes on the cupula, bending the stereocilia, generates a graded potential in the hair cell membrane