Nervous System Flashcards
nervous system
enables organisms to receive and respond to stimuli from their internal and external environments. responds faster than endocrine system
Neurons
functional units of the nervous system. a neuron converts stimuli into electrochemical signals which are conducted through the nervous system.
protazoa nervous systems
posses no organized nervous system. single celled organisms may respond to stimuli like heat, touch, light and chemicals
cnidaria
simple nervous systems called nerve net. network of nerves may have limited centraliztion
annelida systems
earthworms possess a primitive central nervous system consisting of ventral nerve cord and anterior brain of fused ganglia. Definite nerve pathways lead from receptors to effectors
arthropoda systems
arthopod brains are similar to those of annelids but more specialized sense organs are present.
neuron structure
it is an elongated cell consisting of several dendrites, cell body, and a single axon.
dendrites
are cystoplasmic extensions of the cell body that receive information and transmit it towards the cell.
cell body
containing the nucleus and controls the metabolic activity of the neuron.
axon
a long cellular process that transmits impulse away from the cell body. most mammalian axons are sheathed by insulating substance called mylein.
myelin
allows axons to conduct impulses faster. it is produced by cells known as glial cells.
Oligodendrocytes
produce the mylein sheath in the central nervous system
Schwann cells
produce the myleain sheath in the peripheral nervous system.
nodes of Ranvier
the gaps between the mylein sheath
synaptic terminals
the axons endings that release neurotransmitters into the synapse, which is the gap between the axon terminals of the one cell and the dendrites of the next.
neurons function
specialized to recieve signals from sensory receptors or other neurons in the body to transfer information along the length of the axon.
action potentials
impulses that travel the axon and invade the nerve terminal thereby cuasing a release of neurotransmitter into the synapse
resting potential
when the neuron is at rest, the potential difference between the extracellular space and the intracellular space. the neuron is polarized
typical resting membrane potential is
-70 millivolts which means that the inside of the neuron is more negative than the outside.
Na+/K+ pump
active transport system that maintains the selective permeability of ions in the neuron membrane. the pump using ATP energy transports 3 Na+ out for every 2 K+ it puts in. Action potentials mess up the gradient and this pump restores it.
At rest the Na+/ K+ pump ensures
that the concentration of K+ is higher on the inside of the neuron and Na+ concentration is higher on the outside.
Action potential (detailed)
if the cell becomes excited or depolarized an action potential is generated. the minimum threshold membrane potential is around -50mV which the level that action potential is generated.
-voltage gated ions in the nerve membrane open in response to the change in voltage
the action potential begins when the Na+ voltage opens and Na+ rushes down its gradient leading to depolarizing. then it closes and K+ voltage does the same. repolarizing the cell.
hyperpolarization
if the neuron skips past the resting potential and becomes more negative inside than normal. this makes it impossible to initiate another action potential.
refractory period
the time the Na+ channels need to recover from inactivation after hyperpolarization.
Synapse operation direction
information will only travel from dendrite to synaptic terminal. they only operate in one direction because refractory periods make backward travel impossible.
impulse propagation
different axons can propagate at diff speeds. the greater the diameter of the axon and more heavily the mylein sheath, the faster the impulses will travel.
Synapse
the gap between the axon terminal of one neuron (called pre-synaptic neuron) and the dendrites of another neuron (post synaptic neuron/ cells) .
effector cells
if neuron is communicating with another cells they are called effector cells.
synapse function
When the action potential arrives at the nerve terminal end, the synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter into the synapse. which fuses across the synapse and acts of the receptor proteins on the postsynaptic membrane. which leads to depolarization of the post synaptic membrane leading to the firing of an action potential.
Neurtransmitter removal from synapse
it can be taken up into the nerve terminal (via uptake carrier), may be degraded by enzymes in the synapse or it may simply diffuse out of the synapse.
Curare
blocks the postsynaptic acetylcholine receptors so that acetylcholine is unable to interact with the receptor. this leads to paralysis by blocking impulses to muscles
Botulism toxin
prevents the release of acetylcholine from the presynaptic membrane and also results is paralysis
anticholinesterases
uses as nerve gases in insecticides, inhibits activity of the acetylcholinesterase enzyme. so it is not degraded in the synapse preventing coordination of muscles
