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.