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- •The ability to sense temperature and pain
any agent detectable by an organism—such as light, vibration, and so on.
the conversion of one form of energy—an external stimulus—into electrical energy that can be interpreted by a nervous system.
Ion Channels fall into two broad types
–Gated channels, open and/or close in response specific stimuli
4 types of gated channels
- (1) mechanically gated,
- (2) chemically gated,
- (3) voltage-gated, and
- (4) thermally gated channels.
Mechanically gated channels
- •Sensitive to stretch,
- -they may have served as osmotic stress sensors in prokaryotes, opening when a cell was deformed by changes in cell volume;
Chemically gated channels
- •Sense chemicals in the environment
- -Involves chemoreceptor proteins rather than, or in addition to, gated channels
- -necessary for chemotaxis
mechanism of chemotaxis
- •Binding of the molecules to surface-membrane receptor proteins transduce the signal to the cell interior to alter flagellar motions;
- –Primitive mechanism of cell to cell communication during evolution of multicellularity;
–Starvation induces the single-celled amoeba to secrete ___ into the environment;
- -Primitive mechanism of cell to cell communication during evolution of multicellularity
How does binding external cAMP effect cell behavior?
-Leads the amoebas to aggregate into large-bodied slugs (move to food, or reproduce to spread spores to new habitat)
-cAMP receptor protein triggers a G-protein
-essential to long-range signaling involved in both sensory input and effector control
Voltage-gated K+ channels are also found in the plasma membranes of __ cells
Voltage gated ___ channels are found only in animals and a few protists;
Thermally gated channels
Widespread in animals, including in some animal-like protists like Paramecium
- a protozoa with swimming cilia;
- –Considered free-swimming sensory cells with most of the sensory capabilities of animals;
Paramecium is a living proof that the machinery associated with the function of ___ ___ arose long before the evolution of ___ ___
- sensory neurons
- nervous systems
Paramecium Respond to what environmental stimuli?(5)
- Thermal, mechanical, chemical, photic, and ionic
- –through changes in their membrane potentials;
How do Paramecium respond to stimuli?
by changing either their cell shape or the pattern of ciliary beating
What types of gated channels do paramecium have?
- all 4
Paramecium have ___ ___ that react to chemicals that affect membrane potential via second messenger
- A TRP protein found in fruit flies
- -mechanically gated Ca2+ channel.
- transient receptor-potential
- -a family of proteins involved in sensory transduction in eukaryotes from yeast to mammals
What stimuli do TRP proteins respond to?
- heat, cold, intense heat, mechanical, mustard oil, ethanol, etc….
- signals such as ATP, acetyl-choline… in channels
- mechanical energy
respond to cold and heat
- pain receptors:
- •respond to extreme heat, cold, and pressure, as well as to certain molecules such as acids;
:•Detect radiation within a wide range of the electromagnetic spectrum; ex pigeons
•respond to visible light energy
respond to specific chemicals
sense mechanical changes at numerous sites, mainly in association with blood vessels and gutfluids;
- detect external stimuli:
- –light, chemicals (taste, smell), touch, temperature, electromagnetic fields, and sound
- -also known as somesthetic
located mainly in the muscles, tendons, and joints, and also in the inner ear. Can detect position in the environment
Two different types of receptor cells.
- specialized afferent neuron endings
- seperate cell receptor
signaling process for specialized afferent neuron endings
- 1. stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential.
- 2.Local current flow between depolarized receptor ending and adjacent region opens voltage-gated Na+ channels.
- 3.Na+ entry initiates action potential in afferent fiber that self-propagates to CNS.
- -no neurotransmitter necessary
signaling process for seperate cell receptor
1. stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential.
2.This local depolarization opens voltage-gated Ca2+ channels.
3.Ca2+ entry triggers exocytosis of neurotransmitter.
4. Neurotransmitter binding opens chemically gated receptor-channels at afferent ending, permitting net Na+ entry.
5. Resultant depolarization opens voltage-gated Na+ channels in adjacent region.
6. Na+ entry initiates action potential in afferent fiber that self-propagates to CNS.
afferent neurons differ from interneurons and efferent neurons how
- -the sit of initiation of action potential occurs after a sensory receptor and before the cell body (cell body is external to path of propagation)
- - in others cell body is first
Tonic sensory input adapts slowly to a stimulus and continues to produce action potentials over the duration of the stimulus
fast-adapting receptors, active for a short period of time whenever there is a change in the conditions
amount of neurotransmitter released is directly dependent of what?
Frequency of action potentials which is dependent on
magnitude of receptor potential which is dependent on
- Meissner’s corpuscles
- Pacinian corpuscles
- Ruffini corpuscles
–sense touch and light pressure–lie just beneath skin surface
senses deep pressure and skin distortion
The Pacinian corpuscle
- •Consists of concentric layers of connective tissue
- -detects deep pressure and vibration
Bristle Mechanoreceptor in Drosophila
- a bristle and three cells:
- a socket cell, a sheath cell, and a neuron;
Bristle Mechanoreceptor inDrosophila
how does it operate?
–When the bristle moves, it distorts the membrane of the neuron’s dendrites, opening up mechanogated channels depolarizing it
Vertebrate skin mechanoreceptors include free nerve endings that:
wrap around the base of the hair shaft
- The most intensely activated receptor pathway halts transmission of impulses in the less intensely stimulated pathways through lateral inhibition.
- -this accomplished with inhibitory interneurons
- •Commonly found in the walls of organs that can be distended
- -Stretching deforms them and they depolarize
Specialized Epithelial Cells
Work as mechanoreceptors that release a chemical neurotransmitter when stimulated
The lateral line system consists of a row of ____ set in pits and canals along each sideof the body;
- a mechanoreceptive organ which allows the sensing of mechanical changes in water through a cupula similar to that found in the ear
- -cupula contains kinocilium and stereo cilia attached to hair cells
tip link in sound transduction
connection between tips of hairs attached to half of a channel that pulls channels open when hairs spread apart allowing K+ in to depolarized cel and open voltage gated Ca++ channels