Nervous System Flashcards
Nervous System
responsible for controlling most body functions, enabling organisms to receive and respond to stimuli from their external and internal environments
Neuron
- used to convert stimuli into electrochemical signals through the body
- consists of dendrites, a cell body, and an axon
Dendrites
receive information and transmit it toward the cell body
Cell Body
contains the nucleus and controls the metabolic activity of the neuron
Axon
transmits impulses or action potentials away from the cell body
Myelin
- protects the axons from leaking signals and allows for faster conduction of impulses
- produced by glial cells called oligodendrocytes in the CNS and by Schwann cells in the PNS
Nodes of Ranvier
gaps between segments of myelin where action potential propagates
Synaptic Terminals
this is where axons end and where neurotransmitters are released into the synaps
Synapses
the gap between the axon terminals of one cell and the dendrites of the next cell
Astrocytes (CNS)
maintain the integrity of the blood-brain barrier, regulate nutrient and dissolved gas concentrations, and absorb and recycle nuerotransmitters
Oligodendrocytes (CNS)
myelinate CNS axons as well as provide structural framework for the CNS
Microglia (CNS)
remove cellular debris and pathogens
Ependymal (CNS)
line the brian ventricles and aid aid in the production, circulation, and monitoring of CSF
Satellite Cells (PNS)
surround the neuron cell bodies in the ganglia
Schwann Cells (PNS)
enclose the axons in the PNS and aid in the myelination of some peripheral axons
Resting Potential
- even at rest a neuron is polarized due to unequal distribution of ions between the inside and outside of the cell
- the potential difference at rest between the extra and intracellular space is the resting potential (-70mV)
Action Potential
- the nerve cell body receives both excitatory and inhibitory impulses from other cells
- if the cell body becomes sufficiently excited and depolarized to reach threshold potential, then voltage-gated ion channels located in the nerve cell mambrane open in response
- an action potential begins when voltage-gated Na+ channels open in response to depolarization allow Na+ to rush down its electrochemical gradient into the cell causing further rapid depolarization of the segment of the axon
- Na+ also causes the next portion of the axon toward the terminal to become depolarized, causing voltage-gated Na+ channels to open these as well, continuing the process of moving the action potential toward the terminal
- once the action potential reaches the synaptic terminal, a final voltage-gated channel specific to calcium opens and rushes in and triggers the exocytosis of synaptic vesicles containing neurotransmitters
- after the signal has been propogate through a segment of the axon, the high voltage there causes voltage-gated K+ channels to open
- meanwhile the voltage-gated Na+ channels also close
- together, these processes return the cell to a negative potential in a process called repolarization
- the neuron’s voltage shoots past the resting potential and becomes even more negative inside the normal due to the K+ still being free to leave the cell (hyperpolarization)
Refractory period
a period of time after an action potential during which new action potentials are very difficult or impossible to initiate immediately
Impulse Propagation
- information transfer will occur only in one direction: from dendrite to synaptic terminal b/c synapses operate only in one direction and because refractory periods make the backward travel of action potentials impossible
- different axons propogate action potentials at different speeds
- the greater the diameter of the axons and the more heavily it is myelinated, the faster the impulses travel
- myelin increases the conduction velocity by insulating segments of the axon such that the membrane is permeable to ions only in the nodes of Ranvier
Synapse
- the gap between the axon terminal of one presynaptic neuron and the dendrites of another neuron (postsynaptic)
- neurons may also communicate with postsynaptic cells other neurons (effectors cells)
Curase
blocks postsynaptic nicotinic acetylcholine receptors. leads to muscle relaxation and paralysis by blocking the ability to constrict muscles
Botulinum Toxin
prevents the release of acetylcholine from the presynaptic membrane and also results in paralysis
Anticholinesterases
used as nerve gases and the insecticide parathion
Afferent neurons
carry sensory information about the external or internal environment to the brain or spinal cord
Efferent neurons
carry motor commands from the brain or spinal cord to various parts of the body