EEMB 7 - Chapter 37: Neurons, Synapses, and Signaling

neurons

a nerve cell; the fundamental unit of the nervous system, having structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its plasma membrane

cell body

the part of a neuron that houses the nucleus and most other organelles

dendrites

one of usually numerous, short, highly branched extensions of a neuron that receive signals from other neurons

axon

a typically long extension, or process, of a neuron that carries nerve impulses away from the cell body toward target cells

synapse

the junction where a neuron communicates with another cell across a narrow gap via a neurotransmitter or an electrical coupling

neurotransmitter

a chemical messenger that is released from the synaptic terminal of a neuron at a chemical synapse, diffuses across the synaptic cleft, and binds to the postsynaptic cell, triggering a response

glial cell/glia

cells of the nervous system that support, regulate, and augment the functions of neurons

CNS

the portion of the nervous system where signal integration occurs; in vertebrate animals, the brain and spinal cord

PNS

The sensory and motor neurons that connect to the central nervous system

membrane potential

the difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions; affects the activity of excitable cells and the transmembrane movement of all charged substances

resting potential

the membrane potential characteristic of a nonconducting excitable cell, with the inside of the cell more negative than the outside

sodium-potassium pump

a transport protein in the plasma membrane of animal cells that actively transports three sodium out of the cell and two potassium into the cell

ion channels

a transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient

equilibrium potential

the magnitude of a cell's membrane voltage at equilibrium

gated ion channels

a gated channel for a specific ion; the opening or closing of such channels may alter a cell's membrane potential

voltage-gated ion channels

a specialized ion channel that opens or closes in response to changes in electrical membrane potential, altering conformation of channel proteins

hyperpolarization

a change in a cell's membrane potential, inside is more negative than outside; reduces the chance that a neuron will fire (inhibitory)

depolarization

a change in a cell's membrane potential; inside is less negative than outside

graded potential

in a neuron, a shift in the membrane potential that has an amplitude proportional to signal strength and that decays as it spreads

action potential

an electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization; good for transmitting signals over longer distances

threshold

the minimum potential that an excitable cell membrane must reach for an action potential to be initiated

myelin sheath

wrapped around the axon of a neuron, a lipid insulating coat of cell membranes from Schwann cells or oligodendrocyte; interrupted by nodes of Ranvier, where action potentials are generated

oligodendrocytes

a type of glial cell that forms insulating myelin sheaths around the axons of neurons in the central nervous system (CNS)

schwann cells

a type of glial cell that forms insulating myelin sheaths around the axons of neurons in the peripheral nervous system (PNS)

nodes of ranvier

gap in the myelin sheath of certain axons where an action potential may be generated

excitatory postsynaptic potential (EPSP)

depolarization in the membrane of a postsynaptic cell caused by the binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic receptor; increases likelihood of an action potential

inhibitory postsynaptic potential (IPSP)

hyperpolarization in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; action potential less likely

summation

individual postsynaptic potentials combine to produce a larger postsynaptic potential

acetylcholine (ACh)

a neurotransmitter for muscle stim, memory, learning. binds to receptors and alters the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane

neuropeptides

a relatively short chain of amino acids that serves as a neurotransmitter

endorphins

any of several hormones produced in the brain and anterior pituitary that inhibit pain perception, acting as natural pain relievers

direction of signals through a neuron

1. signal received by dendrites

2. passes through cell body

3. action potential in axon hillock

4. signal transmitted through axon

5. reaches synaptic terminal

what types of glial cells are there?

microglia, ependymal cells, astrocytes, oligodendrocytes, and schwann cells

sensory neurons

a nerve cell that receives information from the internal or external environment and transmits signals to the central nervous system

interneurons

an association neuron; a nerve cell with in the central nervous system that forms synapses with sensory and/or motor neurons and integrates sensory input and motor output

motor neurons

nerve cell that transmits signals from the brain or spinal cord to muscles or glands

order of action potentials

1. resting potential & voltage-sodium channels are closed

2. depolarization, opening the channels

3. rising phase of the action potential activating a positive feedback cycle

4. falling phase of the action potential, opening voltage-potassium channels

5. undershoot, where there's a high permability for K+ but it eventually returns to resting potential after a refractory period

evolutionary adaptations of axon structure

1. wider axon that provides less resistance to the current associated with an action potential than does a narrow axon

2. electrical insulation (in vertebrates, the myelin sheath) that causes the depolarization current associated with an action potential to spread farther along the axon interior, bringing more distant regions to the threshold sooner

order of neurotransmitter signals

1. action potential arrives, depolarizing presynaptic membrane

2. opening of voltage-gated channels; influx of Ca2+

3. elevated concentration causes synaptic vesicles to fuse with presynaptic membrnae, releasing neurotransmitter into the synaptic cleft

4. neurotransmitter binds to ligand-gated ion channels in postsynaptic membrane

spatial summation

when several synapses occur at the same time, an additive effect

temporal summation

if single EPSP synapses again before resting membrane potential is fully restored, repeating synapses can show additive effect; this is where frequency modulation for intense stimuli comes into play

glutamate def

primary excitatory neurotransmitter, playing an important role in formation of long-term memory

biogenic amines

synthesized from amino acids

dopamine

a neurotransmitter associated with movement, attention and learning and the brain's pleasure and reward system

serotonin

a neurotransmitter that affects hunger,sleep, arousal, and mood.

norepinephrine

an excitatory neurotransmitter involved in arousal, as well as in learning and mood regulation

neuro communication as a gas

some vertebrates neurons release dissolved gases, like nitric acid (NO) and carbon monoxide, as neurotransmitters

as a college student, studying for this exam what neurotransmitter would be helpful

glutamate

saltatory conduction

rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane

inhibitor drug examples and their effects

crotoxin from american rattlesnake and botulinum toxin (botox) decrease ACh release

inhibitor drugs

most act by inhibiting release of neurotransmitters

blocking agents

most act by blocking various channel proteins (like saxitoxin from red tide algae) & tetrodotoxin from pufferfishand some by blocking neurotransmitter receptor sites (like curare from a s. american tree)

enzyme destroyers example

nerve gas (sarin) kills by spastic paralysis due to its inactivation of ACh

strychnine, aka rat poison

interferes with IPSP's in spinal cord, muscles have difficulty "turning off" leading to spastic paralysis and asphyxiation