Whether or not the active site is accessible depends on an allosteric binding site

An allosteric effector that spans cell membranes is a receptor molecule

Largest class of receptor molecules

act as enzyme and/or channel

can be receptors for light or odorants

Membrane bound adenylate cyclase catalyses formation of cAMP

cAMP activates PKA

Activated PKA phosphorylates proteins, inhibiting or activating them

Activation of phospholipase C leads to cleavage of phosphatidylinositol bisphosphate indo diacylglycerol and inositol triphosphate.

IP₃ is water soluble, diffuses throughout cell, and can activate receptors on ER, leading to Ca²⁺ release.

Ca²⁺ causes DAG to activate TRP channels and PKC

-involved in perception of temperature, touch, pain, osmolarity, pheromones, taste, and others

-various types with little similarity

-allow cations to cross cell membrane

-comprised of six membrane spanning domains, with the ends in the cytosol

-most variable regions is the C terminus

- 4 to 20 transmembrane helixes

-gated by ligand or by a change in membrane potential

classification according to kind of adequate stimulus (modality)

classification according to source of stimulus (interoreceptors and exteroreceptors)

lowest intensity at which the stimulus is detected

Can change with age, experience, fatigue, context, practice, etc.

Usually represented by the intensity at which stimulus is detected in 50% of all presentations

Change in intensity that is just noticeable.

Depends on starting intensity

(Electrical shock example)

Free nerve endings:

-Anatomical Characteristics

-Location

-Function

-Rate of adaptation

-Threshold of Activation

-Minimally specialized nerve endings

-All skin

-Pain, Temperature, Crude touch (usually pain receptors)

-Slow rate of adaptation

-High threshold of activation

Meissner's corpuscles:

-Anatomical characteristics

-Location

-Function

-Rate of adaptation

-Threshold of activation

-Encapsulated, between dermal papillae

-Located close to skin surface (more sensitive)

-Touch, pressure

-Rapid rate of adaptation

-Low threshold of activation

Pacinian corpuscles:

-Anatomical characteristics

-Location

-Function

-Rate of adaptation

-Threshold of activation

-Encapsulated in an onionlike covering, visible to naked eye

-Subcutaneous tissue, interosseous membranes, viscera

-Deep pressure, vibration (dynamic)

-Rapid rate of adaptation

-Low threshold of activation

Merkel's disks:

-Anatomical characteristics

-Location

-Function

-Rate of adaptation

-Threshold of activation

-Encapsulated, associated with specialized cell in epithelium

-All skin, hair follicles

-Touch, pressure (static)

-Slow rate of adaptation

-Low threshold of activation

Ruffini's corpuscles:

-Anatomical characteristics

-Location

-Function

-Rate of adaptation

-Threshold of activation

-Encapsulated, oriented along stretch lines

-All skin

-Stretching of skin

-Slow rate of adaptation

-Threshold of activation

-Least known about nerve endings

-Nerve wraps around the hair bult, movement of hair stretches the nerve and opens channels in some way

-consist of a connective tissue capsule that encloses a nuclear bag and numerous nuclear chain fibers

-bag as well as chain fibers have central equatorial region which is not contractile, and polar regions which are contractile

spindle is attached to and alligned parallel to skeletal muscle fibers (extrafusal fibers)

4 sets of neurons - 2 afferent and 2 efferent per spindle

Nuclear bag fibers

-respond to ________

-two types

-action potentials conveyed to CNS via _________

-respond to the rate of change in length and amount of change in length in a muscle

-phasic and tonic

action potentials conveyed to CNS via myelinated A-alpha or IA nerve fibers

Nuclear chain

-physical description

-type of receptor

-respond to ______

-short, slender fibers that contain a series of nuclei. Two afferent fibers (A-alpha or IA around middle and A-beta or II)

-Tonic receptor

-Respond to sustained stretch in skeletal muscles

-Command to contract sent down spinal cord

-Alpha and gamma neurons transmit information

-Command sent through alpha neuron reaches muscle first (extrafusal muscle fiber)

-Intrafusal muscle fibers have no tension - sensory fibers unstimulated

-Command through gamma neurons reaches intrafusal muscle fibers and they contract

-If command to contract sent through gamma neurons requires more contrcion, tension builds up in intrafusal fibers and afferent neurons send feedback to CNS

-Feedback stimulates the alpha fibers to cause more contraction and inhibits antagonistic muscle action

-High Threshold - responds to muscle lengthening and is located in the distal attchments of tendons

-Low Threshold - responds to muscle contraction, and is found in the proximal attachments of tendons

Three general types:

-Campaniform sensilla

-Chordotonal organ

-Mechanoreceptive hairs

Campaniform sensilla:

-what are they?

-where are they located?

-What do they look like?

-what are they activated by?

-hairless mechanoreceptors

-located at antennae, legs, wings, and many other body parts

-Characterized by ellptical depression of the cuticles with a dome-like upheaval

-activated when cuticula is under stress or tension

Chordotonal sensillum

-what are they?

-What is their function?

-What are the two types?

-They are internal mechanoreceptors

-They serve as exteroceptors or proprioceptors

-Two types: Chordotonal organ

Johnston's organ (consist of 50 and 150 scolopidia)

(see pictures in notes)

Scolopidium

-What is it?

-What does it look like?

-What is its function?

-Attachment cell that surrounds the dendrites of the receptor cell and connects the distal part of the scolopidium to the inner surface of the cuticle

-The tip of the dendrite is covered by a cap and each scolopidium consists of two and three bipolar receptor cells

-Horodontal organ may function as a proprioceptoror as exteroceptor for detecting sound or substrate vibration

Cluster of the purely mechanosensory hairs located at the base of antennae, wings, or legs

-Each hair contains a single mechanoreceptor cell

-Monitor morement of body parts

The axon of the sensory neuron is called ____________.

These are grouped according to ______________.

Afferent fiber

Grouped according to speed of propagation of action potentials in A-Beta, A-delta, or C fibers

-Diameter of the fiber

-Thickness of the myelin sheath

-Deg/ENaC (Degenerin/Epithelial Na Channels)

-TRP channels

-Two-pore-domain K channel

Deg/ENaC

(Mec-4 complex)

Mechanoreceptors sensitive to flow of medium found in spiders

(see lecture notes)

-columnar body with an array of stereocilia (long microvilli) on the apical side

-may have one true cilium (kinocilium) located in preferred direction for all stereocilia

comprised of three semicircular canals connected to two membranous sacs (saccule and utricle).

The canals allow us to sense the direction and speed of angular acceleration

The saccule and utricle allow us to sense the direction and speed of linear acceleration and position of the head.

Otolith Organs

What does each sense?

Saccule is more sensitive to vertical acceleration

Utricle is more sensitive to horizontal acceleration

Each semicircular canal has an enlarged area near its base called an ________ which contains hair cells.

Rising above this is the ___________

Amuplla

Cupula

hair-like cuticular projections innervated at their bases by one or more bipolar nerve cells.

Relatively long and rest loosely in their sockets.

Scolopidia packed around antenna

Responds to the displacement of the antennal flagelum, detects near-field sound.

Consists of a thin layer of cuticle and one or several chordotonal organs attached to it on the inside.

Chordotonal organs respond to vibrations of tympanal membrane.

Usually located as far apart as possible on the insect.

-Tympanal membrane consisting of a thinned region of exoskeleton

-enlarged tracheal air chamber to which the internal face of the tympanal membrane is appressed

-one or more chordotonal organs associated either directly or indirectly

Fish need an air-filled chamber in order to hear

The swim bladder is connected to ears by weber's bones

-Located in middle ear

-responds to pressure difference between outside and inner air chamber