Unit 2 physiology lectures 1-3

five taste sensations

-salty (NaCl) -sour (acids) -bitter (quinine, toxic plants) -sweet (stereochemical configuration of glucose) -umami (glutamate)

characteristics of fast pain (pricking pain)

-transmitted by thicker nerve fibers (Adelta fibers) -well localized -mainly skin, mouth, anus -immediate withdrawal on stimulation to avoid further damage -pain doesn't radiate -short duration i.e. pain from surgical incision

thin nerve fibers for slow pain

C fibers

define adaptation

a measure of how well a sensory receptor maintains its response to a constant stimulus i.e. slowly adapting vs rapidly adapting sensory receptors

chemically sensitive, mechanically insensitive nociceptors respond to

a variety of agents from the environment or from the tissue itself i.e. potassium, extremes of pH, neuroactive substances like histamine and bradykinin, and various irritants

mucus is

a water base with dissolved salts, mucopolysaccharides and odarant-binding proteins. The odarant-binding proteins contribute to odorant concentration or removal

chemosenses of the internal environment include

pCO2, cO2, and osmolarity

example of specialized endings on nerve fibers

pacinian corpuscle

in the CNS, the action potential from the encoder of the sensory receptor moves through which 3 components (in order)?

sensory systems association systems effector (motor) systems

sensory receptors are connected to

sensory units- all the terminals of any one sensory unit have the same kind of receptor

olfactory receptor cells have a ___ peripheral process that extends to the surface of ____. They also have a ____ central process that runs from the nasal cavity to the olfactory bulb. These are unmyelinated axons as small as 1/10th of a micron in diameter. They have super slow APs.

short the mucosa long

thermal nociceptors respond to

burning heat (>45 C, tissue proteins become denatured and damage occurs) or extreme cold

describe fungiform papillae

(mushrooms), top and sides of the tongue.

describe circumvallate papillae

(pimples), posterior 1/3 of the tongue.

describe foliate papillae

(ridges) posterior and lateral surface of the tongue.

substances that activate nociceptors

** damage to tissues results in a release of a variety of substances from lysed cells and new substances synthesized at the site of injury globulin and protein kinases arachidonic acid histamine nerve growth factor substance P and calcitonin gene related peptide potassium serotonin, ACh, low pH, ATP muscle spasm and lactic acid

cues that account for taste perception

Taste, tactile, visual, auditory and olfactory cues

polymodal nociceptors respond to

high intensity stimuli that are combinations of mechanical, thermal, and chemical stimuli ** are present in most body tissues except for the brain

the frequency of action potentials ____ with the quantity of taste molecules

increases

warm receptors fire faster during

increases in temperature

these have taste receptors on their feet, antennae, and mouthparts

insects

mechanonociceptors respond to

intense mechanical stimulation i.e. pinching, cutting, stretching

how is intensity (magnitude) coding done?

intensity coding is done by the total number of impulses per second coming from the receptor population

*** mechanism of taste transduction

ionic stimuli let ions in, and complex stimuli start a g-protein second messenger system depolarization occurs, allowing Na+ in and K+ out... Ca2+ is released from endoplasmic reticulum, leading to vesicle neurotransmitter release into synaptic cleft serotonin receptors receive neurotransmitter and lead to action potential

taste cell types

- Receptor cells, are modified epithelial cells, 50-150 per taste bud. - Supporting cells develop into receptor cells. - Basal cells develop into supporting cells.

characteristics of slow pain (burning or soreness pain)

-transmitted by very thin nerve fibers (C fibers) -poorly localized -all internal organs (except the brain) -body wants to be immobile to allow healing (guarding, spasm, rigidity) -often radiates or is referred -diffuse, slower to onset and longer in duration i.e. labor pain pain starting after fast pain from an injury, chemical burn

flavor is

-what people commonly refer to as the "taste" of food; a combination of smell, taste, spiciness, pain (capsaicin, found in hot peppers), temperature, sound and texture.

roles of a filter

1) limits access 2) changes stimulus parameters

what are the four categories of nociceptors?

1. mechanonociceptors 2. thermal 3. chemically sensitive, mechanically insensitive 4. polymodal

mucus flow constantly and is replaced every

10 minutes

how many taste buds are in the walls of papillae

10,000

Humans can detect the presence of as few as ___ molecules of an odorant in a room. Dogs can detect much fewer than this.

108

____ chemical elements play a role in odor sensation. Only the____ and ____ are odorous as elements.

16 halogens ozone

what is a filter and what does it do?

1st functional element of a sensory receptor, usually non-neural tissue -allows only a portion of the stimulus to be conveyed to the transducer -conditions the stimulus, making receptor function with relative specificity for a single modality two roles: 1) limits access 2) changes stimulus parameters i.e. lens of the eye filters out UV light (limits access) and focuses image on the retina (changes parameters)

what is a transducer and what does it do?

2nd component of a sensory receptor -converts stimulus energy into a change in the voltage across the membrane of the sensory receptor with a minimal loss in information -creates the RECEPTOR POTENTIAL (generator potential, local potential) the receptor potential is a GRADED potential, meaning that the stronger the stimulus is on the transducer, the larger the receptor potential will be

describe the innervation of taste cells

Afferent nerves enter the buds and end on the receptor cells. Nerves are separated from the cell by synaptic clefts (chemical synapse). One nerve fiber may innervate several receptors. One receptor may be innervated by several nerves. Taste nerves continually remodel synapses on a new receptor cell. Receptors need innervation to stay healthy otherwise they will degenerate

type, sensation, adaptation of Ruffini corpuscle

Encapsulated collagen touch: skin stretch slow

what happens neurologically during the gate theory of pain

Firing of the Aβ fibers (mechanoreceptor) activates the inhibitory interneuron, reducing the chances that the projection neuron will fire, even in the presence of a firing nociceptive fiber. The Aβ mechanoreceptor excites the inhibitory interneuron and reduces the pain signal sent up the ST tract

describe intensity coding

The greater the amount of tastant, the faster the firing rate of afferent fibers.

define recruitment

a basic mechanism of intensity coding the number of units that get activated by the stimulus increases with intensity of the stimulus the stronger the stimulus, the greater the recruitment

after the encoder, what is sent to the CNS?

action potential

taste is influenced by

adaptation, memory, and conditioning

thick fibers for fast pain

adelta fibers

intracranial headache examples

alcohol- toxicity irritates meninges constipation- from absorbed toxic products or changes in circulatory system, resulting from loss of fluid in the gut

what is labeled lines

an anatomical grouping of rececptors and pathways devoted to the particular modality (Place Theory)

location coding is is done by

an anatomical sorting or organization of the pathways and their central projections (the labeled-line idea applied to a location)

define saturation

as intensity increases, eventually the nerve fiber reaches its upper limit for carrying impulses. Further icnreases in stimulus do not produce a corresopnding increase in the response.

negative chemotaxis for taste and smell help us

avoid noxious agents such as rotten smells and food

"warm" thermoreceptors begin and stop firing at what temp(s)?

begin firing above 30 C and stop firing above 45 C

In humans, ____ receptors have been found in the trachea, ____ receptors in the gut and the spine has sour receptors.

bitter sweet

describe sensory units

sensory receptors are connected to sensory units. all the terminals of any one sensory unit have the SAME kind of receptor

7 primary odors

camphoraceous, musk, floral, peppermint, ethereal, pungent, putrid there are a lot more

____ are among the oldest and most influential of all sensory mechanisms

chemosensations

taste and smell include positive and negative

chemotaxis

taste buds are innervated by

cranial nerves VII, IX, an dX (facial, glossopharyngeal, vagus)

describe free nerve endings

have no anatomical specialization at the receptor site encompass full range of sensory modalities and are the most common receptor type i.e. nociceptor (pain receptor)

the transducer sends out a...

delta Em (receptor potential)

define temporal coding

different patterns of firing may provide information about submodality a response is dependent on the rate of change of stimulus application within a particular frequency range. most receptors don't respond to constant stimuli but are more sensitive to stimulus change

•Afferent fibers show different firing patterns in response to

different substances

how can eye disorders cause extracranial headache?

difficulty focusing stresses the ciliary muscles and can cause spasms in facial and extraocular muscles excessive irradiation by light rays (especially UV) causes irritation of the membranes around the eye

what are the two parallel pathways of somatic sensation?

dorsal column-medial lemniscal pathway spinothalamic pathway

labeled line:

each chemical is a preferred stimulus which has its own receptor and circuit

describe pattern coding

each taste cell responds differently to four tastants

extracranial headache: what happens during a muscle spasm?

emotion/tension causes muscles of the head to become spastic pain is referred to overlying areas of the head

type, sensation, adaptation of Pacinian corpuscle

encapsulated and layered Touch: vibration Rapid

type, sensation, adaptation of Meissner's corpuscle

encapsulated and layered touch: flutter and movement rapid

the bigger the primary afferent axon, the ____ the reaction/impulse

faster i.e. skeletal muscle has a diameter of 12-20 Mm while temperature, pain, itch sensory receptors have a diameter of about 0.2-1.5. temp, pain, and itch has a speed of 0.5-2 m/sec while proprioceptors of skeletal muscle are 80/120 m/sec

components of sensory receptors?

filter transducer encoder

positive chemotaxis for taste and smell examples

find nutrients or locate a mate

fish can taste with what

fins, tail and mouth

"cold" thermoreceptors do what?

fire faster than warm receptors over a broad range of skin temperatures from about 30 C down to 10 C

describe spinothalamic pathway

for pain, temperature, and some touch dorsal root axon (Asigma, C) --> lateral spinothalamic tract--> thalamus --> cerebral cortex

describe dorsal column medial lemniscal pathway

for touch, vibration, two-point discrimination, proprioception dorsal root axon (Aa, AB, Asig) --> dorsal column --> dorsal solumn nuclei --> medial lemniscus --> cerebral cortex

have no anatomical specialization at the receptor site encompass full range of sensory modalities and are the most common receptor type

free nerve endings i.e. nociceptor

the larger the receptor potential, the higher the ____ of action potentials

frequency

receptor potentials of taste receptor cells are ____

graded, changing (either depolarizing or hyperpolarizing) by an appropriate chemical.

purpose of pain?

it's a protective mechanism! occurs in response to tissue damage & causes individual to react to remove stimulus

slowly adapting sensory receptors ______ when the stimulus is still present

keep producing membrane potentials

our nervous system codes for chemicals in our environment by using a mixture of

labeled line and population coding

Place theory AKA

labeled lines

modality coding is done by

labeled lines (place theory)

receptive fields of Pacinian corpuscles are ___ while those of Meissner's sorpuscles are ____

large small

the sensory unit with the greatest number of sensory receptors has the _____ receptive field

largest

hair receptors, pacinian corpuscles, ruffini endings, meissner corpuscle, and merkel's disks are all examples of what?

mechanoreceptors

most of the sensory receptors in the skin are _________.

mechanoreceptors

name the 6 types of sensory receptors

mechanoreceptors thermoreceptors chemoreceptors osmoreceptors photoreceptors nociceptors

five attributes of sensory coding?

modality location intensity temporal affect

vision is a _____, while color vision, black and white vision is a ____

modality sub-modality

the filter sends out a...

modified stimulus

how is the gustatory pathway distinct from others?

most of its fibers are uncrossed

describe specialized receptor cells

most sensitive receptor types i.e. photoreceptor

supporting cells produce

mucus

three extracranial headache examples

muscle spasm sinus headache eye disorders

if a force is applied other than at the free nerve ending, then ____

no receptor potential is generated

the only neurons that undergo constant renewal are

olfactory receptor cells ***rapid turnover every 4-8 wks from basal cells to receptor cells; new receptor cells establish new synaptic connections. these are the only known neurons of the adult nervous system capable of mitotic division

•The sense of smell is carried by _____ in the _____, lying deep within the nasal cavity just below the _____.

olfactory receptors olfactory epithelium cribriform plate

gate theory of pain

pain can be modified by nonpainful sensory input and by neural activity from various nuclei within the brain -pain evoked by activity in nociceptors (adelta and C fibers) can be reduced by simultaneous activity in low-threshold mechanoreceptors (Aalph and Abeta fibers) this explains why is feels good to rub the skin around your shin when you get a bruise

extracranial headache: what is a sinus headache?

pain from mucous membranes of nose and nasal sinuses pain is referred behind the eyes or forehead or face

what is phantom pain?

pain of a missing limb

what is referred pain?

pain referred from area of damage to another area i.e. kidney pain might feel like low back pain

submodality coding is done by

pattern codes: the pattern of activity within the system of labeled lines i.e. color vision uses 3 cone types, red, green, and blue. in various combinations of stimulation, different colors are perceived

mechanoreceptors are sensitive to...

physical distortion like bending or stretching

these respond to 2 or more forms of stimuli such as mechanical and thermal

poly-modal receptors

somatosensory system is to which kinds of stimuli?

pressure, position of joints and muscles, temperature of the limbs, pain

______ _____ axons come in several sizes

primary afferent

olfactory receptors are the _____. they are both the transducer and encoder of the signal

primary afferent neuron

where does the signal end up (central gustatory connections)?

primary gustatory cortex (other pathways also exist)

____ adapting sensory receptors STOP producing membrane potentials even when the stimulus is still present

rapidly

basic mechanisms of intensity coding

rate recruitment adaptation threshold saturation

basal cells (stem cells) mature into

receptor cells

taste cell turnover

receptor cells --> basal cells --> supporting cells --> receptor cells again

as long as a force is applied to the free nerve ending (transducer), _____

receptor potentials are generated with or without a filter

A constant stimulus is applied to a rapidly adapting sensory receptor. Which one is correct for the receptor? receptor will keep producing action potential as long as the stimulus is applied receptor will not perceive constant stimulus receptor stops producing action potential after some time even the stimulus is still present receptor will not generate action potential

receptor stops producing action potential after some time even the stimulus is still present

population coding (pattern coding)

receptors and circuits aren't ultimately selective. instead, the nervous system analyzes all of the chemical responses coming in and compares them in order to pinpoint what the chemical stimulus might be

how is the somatosensory system different from other sensory systems?

receptors are distributed throughout the body, rather than being concentrated at small, specialized locations is a group of at least 4 senses rather than one.

cold receptors fire faster during

reductions in temperature

neurons and supporting cells share tight junctions. what do they do?

seal the neuroepithelium against penetration of substances through the surface

Functions of sensory systems

sense and encode features of out environment transmit info to CNS for decoding and use allow CNS to communicate with outside world to answer the questions of "what, where, when, and how much" interface between internal and external environments and the nervous system. provides an "abstraction, not a replication of the real world"

Pacinian corpuscle is an example of what? What are the 3 components?

sensory receptor filter: connective tissue capsule transducer: unmyelinated free nerve ending that produces receptor potential when deformed encoder: trigger zone (1st node of Ranvier)

merkel disk receptors are the only...

sensory receptor cell type in the somatosensory system

describe olfactory transduction

simply: receptor cilia in the mucus send signals to the olfactory receptor cell, which sends it firther to the olfactory bulb -The odorant molecule is absorbed into the mucus layer. -The molecule contacts the cilia of receptor cells. -The molecule binds to receptor sites. -G-proteins are stimulated. -Adenylyl cyclase is activated. (enzyme) -Cyclic AMP is formed. (second messenger) -cAMP binds to a specific cation channel (Na+). -Cation channels open and Ca2+ influx occurs. -This opens calcium-activated chloride channels. -The membrane depolarizes generating a receptor potential. -Receptor potentials are graded depending on odorant concentration. -Strong odorants may suppress this activity. -Following activation there may be post-excitatory inhibition. -Transduction ends. •The odorants diffuse away. •Scavenger enzymes in the mucus break down odorants. •cAMP in the receptor cell may activate other signaling pathways that end the transduction process.

describe the mechanism of the change in the membrane potential when thinking about transducers.

simultaneous change in the membrane permeability of Na+ and K+ ions receptor membranes don't respond to electrical stimulation; no APs, no refractory periods receptor potentials are graded, meaning they increase in magnitude as a stimulus gets stronger the receptor potential doesn't propagate (travels only short distances)

where are somatosensory system receptors located?

skin, body wall, muscles, tendons, ligaments, CT tissue of joints, internal organs

____ adapting sensory receptors keep producing membrane potentials as long as the stimulus is applied

slowly

type, sensation, adaptation of Merkel complex (disc)

specialized epithelial cell touch, pressure, form slow

sensory receptors can be divided into

specialized receptor cells specialized endings on nerve fibers free nerve endings

describe the basic organization of the sensory systems

stimulus energy --> sensory receptors (filter, transducer, encoder) --> action potential --> CNS (sensory systems, association systems, effector (motor) systems) --> effectors --> response

rapidly adapting sensory receptors ____ when the stimulus is still present

stop producing membrane potentials after a while, even if the stimulus is still present

which of our senses provides us with the least amount of information?

taste ** most of what we perceive as taste actually comes from our sense of smell!! taste buds only identify five flavors. Our nose does the rest of the identifying by "odor molecules" from food

For central gustatory connections, The first synapse is in the ____ The second synapse is in the ____ The third synapse is in the ____

taste bud medulla thalamus **Note: The signal ends up in the primary gustatory cortex. Other pathways exist. The gustatory pathway is distinctive in that most of its fibers are uncrossed.

what are supporting cells

taste cells that develop into receptor cells.

basal cells are what

taste cells that develop into supporting cells

what are receptor cells

taste cells; modified epithelial cells, 50-150 per taste bud. ** turnover every 1 to 2 weeks; basal cells become supporting cells, which then become receptor cells

what makes Pacinian corpuscles rapidly adapting?

the capsule makes the Pacinian corpuscle exquisitely sensitive to vibrating, high frequency stimuli, and almost unresponsive to steady pressure

what is the location of the voltage-gated Na+ and K+ channels capable of producing action potentials?

the encoder (trigger zone)

sensory receptors have a receptive field. What is this?

the fraction of the total energy of a particular modality that initiates a response in a sensory receptor or sensory unit. **alt definition** The receptive field is a portion of sensory space that can elicit neuronal responses when stimulated. the sensory unit with the greatest number of sensory receptors has the largest receptive field

what is "rate" in sensory coding?

the frequency (#/sec) of action potentials in individual sensory units. the stronger the stimulus, the more APs are sent up the afferent fibers of the sensory unit intensity coding mechanism

define affect coding

the least measureable criterion takes into accound emotional content (like pain) and learning and memory, which depends on prior input

define threshold

the minimum value of intensity, just barely perceivable is the threshold stimulus

what does it mean when we say a receptor potential is a graded potential?

the stronger the stimulus on the transducer, the larger the receptor potential

describe slowly adapting mechanoreceptors

these generate a more sustained response during a long stimulus (best suited to represent static stimuli)

describe rapidly adapting mechanoreceptors

these respopnd quickly at first, then stop firing even though the stimulus continues (best suited to represent time-varying stimuli)

what is an encoder and what does it do?

third component of sensory receptor converts the magnitude of a receptor potential into a frequency code that is carried by action potentials along the axon -encoder is the location of the voltage-gated Na+ and K+ channels that produce APs -so long as the receptor potential is above threshold, cells will fire APs -the larger the receptor potential, the higher the frequency of action potentials

neurons and supporting cells share

tight junctions

type, sensation, adaptation of free nerve ending

unencapsulated pain, touch, or temperature depends!!

type, sensation, adaptation of hair follicle

unencapsulated touch: movement rapid

at low concentrations of an odor, the smell sensation is ____. At high concentrations of an odor, a specific odor is ____.

unspecific identified

modality and sub-modality coding tells the body what???

what is present; quality

location coding is especially well-developed where?

where the receprots lie in "sheets", as in the skin i.e. somatotopic organization of the skin on the cortex- pathway terminations for different parts f the body in the somatosensory cortex are located on a map called a homunculus

electrical currents applied to the transducer itself _____

will not stimulate it

Population and Temporal Coding of Olfactory Information

•As in gustation, the olfactory system uses the simultaneous responses of a large population of receptors to encode a specific stimulus. -Each olfactory receptor is sensitive to a wide variety of chemicals. -Responses of a large population of receptors encode a specific stimulus. -The smell of a particular chemical is converted into a specific map within "neural space."

types of papillae

•Circumvallate (pimples), posterior 1/3 of the tongue. • Foliate (ridges) posterior and lateral surface of the tongue. • Fungiform (mushrooms), top and sides of the tongue.

describe population coding

•The responses of four taste cells to four different tastants are combined in the brain to determine the final taste. -The height of the bars is an indication of the number of action potentials in the gustatory afferent axon.