Ch. 14 Flashcards
Define neuron.
A nerve cell; the fundamental signaling unit of the nervous system, composed of a cell body and elongated processes (dendrites and axon) that carry electrical signals
Define presynaptic.
Transmission of a signal to a postsynaptic cell at a synapse
Define postsynaptic.
Reception of a signal from a presynaptic cell at a synapse
Define axon.
Elongated process of a neuron specialized for conveying action potentials away from the cell body
Define dendrites.
The receptive element of most neurons, which receives synaptic input from other neurons
Define axon terminals.
The part of a neuron that makes synaptic connections with another nerve cell or with an effector cell
Define voltage.
A measure of the potential energy present because of charge separation (electric potential)
Define current.
The flow of electric charge
Define resting membrane potential.
The normal electrical potential across the cell membrane of a cell at rest
Define action potential.
A brief electrical signal of about 100 mV across the cell membrane of a neuron or other excitable cell
Define passive current.
Current conducted by neurons without action potentials
Define depolarization.
Any increase in the inside positivity of a cell membrane
Define hyperpolarization.
Any increase in the inside negativity of a cell membrane
Define sensitivity.
The ability of a sensory cell to distinguish stimuli of different intensity
Define specificity.
The ability to distinguish among different stimulus types
Define stimulus.
A change in the external environment or in internal conditions that an animal can detect and respond to
Define ionotrophic.
A kind of sensory transduction in which a sensory receptor molecule is itself an ion channel, changing ion flow into the cell in direct response to a sensory stimulus
Define metabotrophic.
A kind of sensory transduction in which a sensory receptor molecule is a G protein that activates a second messenger, eventually producing a receptor potential.
Define mechanoreceptor.
A sensory receptor cell specialized to respond to mechanical stimulation
Define adaptation.
A decrease in the frequency of action potentials in response to a stimulus
Define proprioceptors.
A sensory receptor that provides an animal with information about the relative position or movement of parts of its body
Define hair cell.
A sensory epithelial cell in a vertebrate acoustico-lateralis system that transduces displacement of its apical stereocilia into an electrical signal
Define vestibular system.
System that functions to detect the position and movement of our head in space, allowing for the coordination of eye movements, posture, and equilibrium
Define hearing system.
System that functions to process how we hear and understand sounds within the environment
Define cochlear amplification.
An increase in the movement of the basilar membrane in the cochlea in response to sound
Define GPCR.
G protein-coupled receptor; a membrane receptor protein that, when it binds to its specific extracellular signal ligand, relays a signal into the cell by activating G proteins in the cell membrane
Define photoreceptor.
Sensory cell that responds to light stimulation through a photopigment that absorbs light and triggers a response
Define phototransduction.
Generation of an electrical response in a photoreceptor cell in response to a light stimulus
Define dark current.
The ionic current, carried mainly by Na+ ions, that flows into the outer segments of vertebrate photoreceptors in the dark
What is the predominant form of neurotransmission?
Action potential
Name the four functional regions of a neuron.
- Dendrite
- Cell body
- Axon
- Presynaptic terminal
In general, cell interiors are ________________. (+/-)
Negatively-charged
The addition of positive ions leads to __________________.
depolarization
The addition of negative ions leads to __________________.
hyperpolarization
The removal of positive ions leads to __________________.
hyperpolarization
The removal of negative ions leads to ______________________.
depolarization
Describe the four phases of action potential production.
- Resting membrane potential - the voltage at which the neuron is at rest (typically around -65 mV)
- Rising phase - the neuron is depolarized by Na+ entering the cell, must pass the depolarization threshold to start firing and eventually peak
- Falling phase - K+ exits the cell to cause gradual hyperpolarization
- Recovery phase - typically too much K+ exits and the cell is overshot, K+ must both enter and exit the cell to recover from over-depolarization
Name and describe the two types of signal transduction.
- Ionotropic - depolarization caused by ions reacting with a sensory cell leads to the production of an action potential
- Metabotropic - multi-step series usually involving a G-protein coupled receptor
Define exteroceptor.
Receptor that responds to outside stimuli (i.e., sound)
Define interoceptor.
Receptor that responds to internal stimuli (i.e., upset stomach)
Explain the labeled-lines principle.
Each sensory cell has an independent path of neurons to the brain (“no crossed wires”)
Define the central nervous system.
The integrative part of an animal’s nervous system, consisting of the brain and spinal cord in vertebrates
Define the peripheral nervous system.
The portion of the nervous system outside of the CNS, consisting of afferent and efferent nerves that connect the CNS to various parts of the body
Explain how an insect sensillum works to detect touch.
When the bristle shaft is moved by a stimulus, stretch-activated channels such as NOMPC are opened.
Define TRP channels.
(Transient receptor potential) A kind of ion channel found in membranes of many sensory cells; it opens in response to stimuli and produces a receptor potential
Contrast tonic and phasic receptors.
Tonic receptors are slow-adapting, and phasic receptors are fast-adapting.
Give two examples of tonic receptors in mammals.
Merkel discs and Ruffini endings
Give two examples of phasic receptors in mammals.
Meissner corpuscles and Pacinian corpuscles
What is the sensory cell involved in the acoustic/vestibular systems?
Hair cell
Explain how hair cells transduce signals.
A stimulus interacts with stereocillia within the hair bundle. The stronger the stimulus, the more intense the stereocillia “hit” the kinocilium. The kinocilium signals to the cell to produce neurotransmitters to send through neurons.
The outer ear is filled with __________, and the middle ear is filled with ___________.
air, fluid
What is the tympanic membrane?
Eardrum
What are the three bones in the ear?
Malleus, incus, stapes
Why is it important for the semicircular canals to be oriented within 90° of one another?
It allows for detection of head movements across all planes.
How do the semicircular canals work?
Head movement pushes fluid around the canal, eventually pressurizing the crista ampullaris and activating the hair cell.
What is the main organ for hearing?
Cochlea
As frequency increases, the distance at which it is detected by the cochlea ___________________.
decreases
As frequency decreases, the distance at which it is detected by the cochlea ___________________.
increases
How is the cochlea stimulated by sound?
The tectorial membrane resting within the cochlea is stimulated by soundwaves, pushing into hair cells.
Contrast camera eye and compound eye.
Camera eyes focus on one picture, whereas compound eyes focus on multiple repeating images in a mosaic style. For examples, people have camera eyes and flies have compound eyes.
What is the main protein involved in phototransduction?
Opsin (commonly found as rhodopsin)
What is rhodopsin composed of?
- The opsin protein, composed of seven alpha-helical regions within the membrane
- Retinal, smushed in the middle
How do compound eyes differ from camera eyes anatomically?
Compound eyes are composed of many lens to form the ommatidium, whereas camera eyes have one lens.
Phototransduction ______________ (does/does not) produce action potentials.
does not
What happens when rhodopsin is exposed to light in compound eyes?
Light changes rhodopsin confirmation, leading to the G-protein to send its alpha subunit off when activated by GTP. The alpha subunit binds phospholipase C to produce IP3 and DAG, which opens TRP cation channels.
In mammalian eyes, light is focused by the _________ and received by the ___________.
lens, retina
The two photoreceptors are _______ and ________.
rods, cones
Rods measure light ___________.
intensity
Cones measure light ______________.
color
Why is it important for the photoreceptors to have many discs?
The discs increase surface area to allow a lot of membrane space for transduction.
How do rods work when stimulated?
Rhodopsin within a rod disc is activated and changes conformation. Transducin (G-protein) loses its alpha subunit when activated by GTP, which is sent off to bind cGMP phosphodiesterase. This enzyme catalyzes the reaction of active cGMP to inactive 5’-GMP. This decreases the use of cGMP-gated Na+ channels in the membrane, decreasing depolarization and thus signal transduction.
Light ____________________ vertebrate photoreceptors.
hyperpolarizes
Membrane potential is ______________ in the dark than in light.
lower
Suppose that a sensory neuron in the periphery generates a train of action potentials, and synaptically excites an interneuron in the CNS. What does this signal mean? What additional information does the interneuron need in order to decode the message?
This signal indicates a sensory cell received some sort of stimulus. The interneuron would need to know which sensory cell was activated, which occurs following the leading lines principle.
What is adaptation of a sensory receptor? At what stage(s) does it occur? What are its functions?
Adaptation refers to the decrease in action potential frequency in response to prolonged stimulation. Depending on the type of receptor, this could occur quickly (phasic) or slowly (tonic). This allows differentiation for the type of stimulus.
Where is rhodopsin localized in a vertebrate retinal rod? Where is the receptor potential generated? How does the transdution mechanism of the rod connect these two sites? How does it increase light sensitivity?
Rhodopsin is located in the discs within the outer segment of rods. The outer segment membrane holds Na+ channels that rely on cGMP to open. Activated rhodopsin leads to a decrease in cGMP; rather, 5’-GMP is synthesized from cGMP. More signals are sent in the dark due to less light activating rhodopsin.
