Nervous System 2: Neurons and Neurophysiology

SLP 5235

What part of neuron are short and highly branched; receive stimulus and send to cell body?

dendrites

What part of neuron conducts impulses away from cell body to another neuron or to muscle/gland?

axon

How long might an axon be?

meter or moreax

What are branches of axons called?

axon collaterals

What do terminal branches of axons end in?

synaptic terminals

What do synaptic terminals release to transmit impulse across synapse?

neurotransmitters

What is fatty material surrounding axons of neurons outside CNS to speed up transmission of impulse?

myelin sheath

What kind of cells form insulation in myelin sheath?

Schwann cells

What kind of cells form sheath in CNS?

neuroglia

What are gaps between Schwann cells?

Nodes of Ranvier

A nerve consists of 100s or 1000s of axons wrapped together in…

connective tissue

in CNS, bundles of axons are called what?

tracts or pathways

Outside CNS, cell bodies are grouped together in masses called what?

ganglia

Inside CNS, what are a collection of cell bodies called?

nuclei

What kind of matter is found in masses of neuron bodies + in cerebral cortex?

grey matter

What kind of matter is found subcortically, connecting cerebral cortex areas, across cerebral hemispheres, and to/from remote regions?

white matter

What comprises white matter?

myelinated fibers or axons

When does myelination grow rapidly?

first 2 years of life

What are 3 types of fibers in sub-cortical white matter?

1. projection 

2. association

3. commissural

Which fibers run from remote regions to/from cerebral cortex?

projection fibers

Which fibers interconnect cortical regions in same hemisphere?

association fibers

Which fibers interconnect hemispheres?

commissural fibers

Which neurons conduct impulses from periphery into CNS?

sensory (afferent) neurons

Which neurons transmit messages from CNS to muscles or glands?

motor (efferent) neurons

Sensory receptors, afferent, and efferent neurons are part of ____ NS?

peripheral

Afferent neurons usually transmit impulses to what?

interneurons (association neurons)

What are “nerve glue” support cells for neurons in CNS?

neuroglia (glial cells)

What are 3 main types of neuroglia?

1. microglia

2. astrocytes

3. oligodendrocytes

Which neuroglia are found near blood vessels, and are phagocytes that migrate and remove foreign and degenerated material?

microglia

What are star shaped glial cells that have a variety of functions?

astrocytes

Which glial cells envelop neurons in CNS, forming insulating sheaths that speed transmission of impulse?

oligodendrocytes

What are some functions of astrocytes?

• phagocytic: remove invading microorganisms and debris from nervous tissue

• regulate concentration of potassium ions in extracellular fluid of nervous tissue

• regulate concentration of NTs

What is resting potential also called?

membrane potential

What is the rapid sequence in which charge or voltage changes across a membrane?

action potential

During cell’s resting state, which molecules are in extracellular fluid?

sodium and chloride

During cell’s resting state, which molecules are in intracellular fluid?

potassium

When electrical stimulation occurs and neuron depolarizes, what moves into cell?

sodium

During repolarization, what moves out of cell?

potassium

What is the minimum amount of stimulus needed for depolarization to occur?

threshold stimulus

What is the millisecond during which membrane is depolarized and cannot conduct an impulse?

absolute refractory period

What period is after enough Na+ channel gates have been reset so that axon can carry impulse, but threshold is higher?

relative refractory period

Do large or small diameters of axon transmit faster?

large diameters = faster

Since depolarization occurs only at nodes of Ranvier, what is it called when action potential “jumps” from one node to the next?

saltatory conduction

Influx of what releases NTs into synaptic cleft?

calcium

What kind of cells are involved in excitation?

principal cells

What kind of synapse is involved in excitation?

glutamate synapse

What kind of polarizing is involved in excitation?

depolarizing

What kind of cells are involved in inhibition?

interneurons

What kind of synapses are involved in inhibition?

GABA synapse

What kind of polarization is involved in inhibition?

hyperpolarizing

What promotes firing?

excitation

What suppresses firing?

inhibition

What is a synapse between neuron and muscle cell called?

neuromuscular junction / motor end plate

What contain neurotransmitters?

synaptic vesicles

When AP reaches axon terminal, which ions begin to diffuse in - influx?

calcium Ca+

What begins depolarization and continuation of impulse?

NT binding to specific receptors on postsynaptic membrane

What happens to extra NTs in cleft?

enzymes in cleft decompose NTs to free up receptor sites for next impulse, or NT is actively transported back into presynaptic vesicles (reuptake)

What are excitatory NTs that stimulate neurons?

• acetylcholine

• norepinephrine

• dopamine

• serotonin

Which NT stimulates muscle contraction?

acetylcholine

Which 3 excitatory NTs affect mood?

• norepinephrine

• dopamine

• serotonin

What NTs stop depolarization?

inhibitory

Which NT inhibits neurons in brain and spinal cord?

GABA: Gamma-aminobutyric acid

If a NT is excitatory, what does it result in?

EPSP: excitatory postsynaptic potential

What causes partial depolarization, bringing neuron closer to firing?

EPSP

Is one EPSP strong enough to trigger AP?

no

What occurs when NT causes postsynaptic membrane to hyperpolarize, bringing membrane potential farther away from threshold and stronger stimulus would be necessary to fire it?

IPSP: inhibitory postsynaptic potential

What is a specific pathway for neurons?

neural circuits

What is it called when a single neuron is controlled by converging signals from 2+ presynaptic neurons, and is an important mechanism by which CNS can integrate information from various sources?

convergence

What is it when a single presynaptic neuron stimulates many postsynaptic neurons?

divergence

What is it when an axon colateral synapses with an interneuron in a sequence that can send new impulses through the circuit (positive feedback)?

reverberating circuit