Ch. 46 Animal Nervous System Flashcards
neuron
a cell that is specialized for the transmission of nerve impulses
- parts: dendrite, axon, soma
- do not reproduce, you have what you’ve got
(aka) nerve cell
All animals except ______ have neurons and muscles
sponges
basic types of nervous systems
1) nerve net
2) central nervous system (CNS)
nerve net
a nervous system in which neurons are diffuse instead of being clustered into large ganglia or tracts
- found in cnidarians (jellyfish, hydra, anemones) & ctenophores (comb jellies)
central nervous system (CNS)
large numbers of neurons aggregated into clusters called ganglia in bilaterian animals
- integrates info from many sensory neurons
- (vertebrates) consists of large ganglia (brain) & spinal chord
sensory receptor
sensory nerve ending that transmits streams of data about the internal/external environment via the sensory neuron
- found in: skin, eyes, ears & nose
sensory neuron
a nerve cell that carries signals from sensory receptors to the central nervous system
- found in afferent division PNS
- stimulates interneurons
What happens to the signal pathway when it encounters a dead neuron?
signal will find new pathway through different neurons
nerve
a long, tough strand of nervous tissue, typically containing thousands of axons, wrapped in connective tissue
- carries impulses between the CNS & some other part of the body
interneuron
a neuron that passes signals from one neuron to another
- connects sensory neurons
- stimulates motor neurons
motor neuron
a nerve cell that send signals from the CNS to effector (response) cells in glands or muscles
- found in efferent division of PNS
peripheral nervous system (PNS)
all the components of the nervous system that are outside the CNS
- wires CNS to whole body
- includes: somatic nervous system & autonomic nervous system
dendrite
a short extension from a neuron’s cell body that receives electrical signals from axons of adjacent cells/neurons
- extension of the cytoplasm
soma
the part of a neuron that contains the nucleus where incoming signals are integrated and generates an outgoing signal
(aka) cell body
axon
a long projection of a neuron that can propagate an action potential
- sends signal to the dendrites of other neurons
membrane potential
a difference in electric charge across a cell membrane
- a form of potential energy
- measured in millivolts (mV)
(aka) membrane voltage
There are generally ______ (more/less) negative ions on the inside of the plasma membrane than the outside.
more
membrane potentials in neurons
about 70-80 mV
electric current
flow of charge due to ion movement from area of like charge to area of unlike charge
electrochemical gradient
the combined effect of an ion’s concentration gradient & electrical (charge) gradient across a membrane that affects the diffusion of ions across the membrane
resting potential
the membrane potential of a cell at resting, or normal, state
- neuron @ rest, not communicating with other neurons
- represents energy stored as concentration gradients in a series of ions
plasma membrane
membrane that surrounds a cell
- separates it from the external environment
- selectively regulates passage of molecules & ions in/out of cell
(aka) cell membrane
ways ions can cross plasma membrane
- Along their electrochemical gradient through an ion channel
- Carried via a membrane cotransporter protein or antiporter protein
- Pumped against an electrochemical gradient by a membrane proteit hat hydrolyzes ATP
ion channel
a type of channel protein that allows certain ions to diffuse across a plasma membrane down an electrochemical gradient
cotransporter
a transmembrane protein that facilitates diffusion of an ion down its previously established electrochemical gradient
- used the energy of that process to transport some other substance, in the same or opposite direction, against its concentration gradient
(aka) secondary active transporter
antiporter
a carrier protein that allows an ion to diffuse down an electrochemical gradient using the energy of that process to transport a different substance in the opposite direction against its concentration gradient
Maintaining the resting potential is tied to the movement of _____ across the membrane & out of the cell
potassisum (K+)
As K+ moves out of the cell, the inside becomes more ________ (negatively/positively) charged relative to the outside.
negatively
equilibrium potential
the membrane potential at which there is no movement of a particular ion into or out of a cell
- each type of ion has its own equilibrium potential
sodium-potassium pump
a transmembrane protein that uses ATP to move sodium ions OUT of the cell and potassium cells IN
(aka) Na+/K+ - ATPase
action potential
a rapid, temporary charge in electrical potential across a membrane
- from negative to positive, back to negative
- occurs in cells (neurons) & muscle cells that have an excitable membrane
- all-or-none event
depolarization
phase in which the membrane becomes less negative
- moves toward a positive charge
- a normal phase in an action potential
- caused by taking in sodium ions
repolarization
return to a resting potential after a membrane potential has changed
- a normal phase in an action potential
hyperpolarization
a change in membrane potential from its resting negative state to an even negative than it was during the resting potential
- normal phase in an action potential
- caused by removal of potassium ion
threshold potential
the membrane potential that will trigger an action potential in a neuron or other excitable cell
(aka) threshold
phases of action potential
1) depolarization
2) repolarization
3) hyperpolarization
Why does an action potential occur?
because specific ion channels in the plasma membrane opened/closed in response to changes in voltages
steps to action potential propogation
1) Na+ enters a cell @ onset of an action potential, (+) charges in cell are repulsed, (-) charges are attracted; results in charge spreading away from the sodium channels
2) As positive charges are pushed farther from the initial sodium channels, they depolarize adjacent portions of the membrane
3) Nearby voltage-gated Na+ channels pop open in response to depolarization; positive feedback occurs; full-ledged action potential results
How come action potentials do not propagate back up the axon?
Because sodium channels are refractory. Once they have opened/closed, they are less likely to open again for a short period of time
refractory
no longer responding to stimuli that previously elicited a response
- lasts briefly
How come a signal does not diminish?
Because the response is all-or-none
properties of large axons
- fewer sodium channels
- less current leaks
- charge spreads farther down the membrane
- transmits action potentials much faster
- large diameter
*compared to small axons