Bio: Nervous System Flashcards
The nervous system enables organisms to..
The NS enables organisms to receive and respond to stimuli from external and internal environments
Neuron
Functional unit of the NS.
Converts stimuli into electrochemical signals, which are conducted through NS.
Is the ES or NS faster at responding to stimuli
NS
4 kinds of invertebrate NS
Protozoa
Cnidaria
Annelida
Arthropoda
Protozoa NS
unicellular. no organized NS.
respond to stimuli such as touch, heat, light, chemicals
Cnidaria
Nerve net
limited centralization
jellyfish.
annelida
Earthworms
Possess a PRIMITIVE CNS with defined ventral nerve cord and anterior “brain” of fused ganglia (nerve cell body clusters)
Nerve pathways from receptors to effectors
arthropoda
Arthropod brains are similar to annelid brains.
Arthropods are more specialized sense organs.
compound or simple eyes
tympanum for sounds
Neuron Structure
basic building block of NS.
Elongated cell of several dendrites, cell body, single axon.
Dendrite
cytoplasmic extensions of the cell body that receive information and transmit it to the cell.
Cell body
soma
long cellular process that transmits impulses away from cell body
Myelin
Most mammalian axons are sheathed by it.
allows for faster impulses.
Made by glial cells. (oligodendrocytes in CNS
Schwann cells produe yelin in PNS)
Nodes of anvier
gasps between myelin
Synaptic terminals
axons end. synaptic boutons or knobs
Neurotransmitters are released from?
synaptic terminals into synapse clef in gap between axon terminals of one cell and dendrites of next cell
Function of Neuron
receive signals from sensory receptors or other neurons.
Transfer this info along axon.
Action potentials
Impulses that travel the length of axon and invade nerve terminal, causing NT replease into synapse.
When a neuron is at rest potential difference between extracellular space and intracellular space is
Resting potential
Resting potential charge
Neuron is polarized here at -70 mV.
inside of neuron is more negative than the outside.
Due to selective ionic permeability of neuronal cell membrane and is maintained by active transport by sodium potassium pump.
Sodium potassium pump
Because transmission of action potentials lead to disruption of ionic gradients, the gradients are restored by Na/K pump.
uses ATP transports 3 NA OUT for every 2 K in.
AT REST. pump ensures hi conc of K inside neuron than outside and opposite for Na.
How is the resting potential created?
neuron is selectively permeable to K, so K diffuses down its concentration gradient, leaving net negative INSIDE.
Neurons at rest are impermeable to NA so that the cell remains polarized at -70 mV.
Negative proteins are trapped INSIDE cell
Action potential
if a cell is sufficiently excited or DEPOLARIZED (inside becomes less negative), then an action potential is gen
Minimum threshold membrane potential
-50 mV.
level at which AP is initiated
Ion channels in nerve cell membrane open in response to
Changes in voltage.
That’s why theyre called voltage gated ion channels
When does an action potential begin
When voltage gated Na channels open in response to small changes inmembrane potential that lead to depolarization thus letting na to rush down its electrochemical gradient, causing a rapid depolarization.
Then the Na channels close, and K channels open, letting K to come in and repolarize to a negative potential
Hyperpolarization
Neuron may shoot past the resting potential and become even more negative inside than normal.
Refractory period
very difficult or impossible to initiate another action potential… It represents the time Na+ channels need to recover from inactivation.
