Exam 1 Quiz 2

glial cells/glia/neuroglia

nonneuronal brain cells that provide structural, nutritional, and other types of support to the brain

thought that neurons were continuous with one another, forming a nearly endless network of connected tubes through which information flowed

Was each neuron in the brain a discrete information-processing component? Or did cells of the nervous system become fused together?

Camillo Golgi (1843-1926)

exploiting Golgi’s staining techniques, to create precise pen-and-ink studies of neurons, he proposed that although neurons come very close to one another (i.e. they are contiguous), they are not quite continuous with one another. At each point of contact between neurons, a tiny gap keeps the cells separate

Was each neuron in the brain a discrete information-processing component? Or did cells of the nervous system become fused together?

Santiago Ramon y Cajal (1852-1934)

neuron doctrine

1. neurons and other cells of the brain are structurally, metabolically, and functionally independent

2. information is transmitted from neuron to neuron across tiny gaps

synapses

the tiny gap between neurons where information is passed from one to the other

cell body/soma

the region of a neuron that is defined by the presence of the cell nucleus

input zone

where neurons collect and process information, either from the environment or from other cells

dendrites

one of the extensions of the cell body through which synaptic inputs are received; some neurons have very elaborately branched ones, providing room for many synapses

integration zone

where the decision to produce a neural signal is made by combining the information the neuron has received; contains the cell body

conduction zone

where information can be electrically transmitted over great distances/may be actively propagated; usually corresponds to the cell’s axon

axon

a single extension from the nerve cell that carries action potentials from the cell body to other neurons

axon collaterals

a branch of an axon from a single neuron

output zone

the part of a neuron, usually corresponding to the axon terminals, at which the cell sends information to another cell; where the neuron transfers information to other cells

axon terminals/synaptic bouton

the end of an axon or axon collateral, which forms a synapse on a neuron or other target cell

motor neurons/motoneurons

a nerve cell in the brain or spinal cord that transmits motor messages, stimulating a muscle or gland

sensory neurons

a neuron that is directly affected by changes in the environment, such as light, odor, or touch; carry messages from peripheral tissue back to the spinal cord and brain

interneurons

a neuron that is neither a sensory nor a motor neuron; it receives input from and sends output to other neurons; the vast majority of neurons in the brain, featuring complex dendrites and relatively short axons

multipolar neurons

a nerve cell that has many dendrites and a single axon; the most common type of neuron

bipolar neurons

a nerve cell that has a single dendrite at one end and a single axon at the other end; especially common in sensory systems

unipolar/monopolar neuron

a nerve cell with a single branch that leaves the cell body and then extends in two directions; one end is the receptive pole, the other end the output zone; transmit touch information from the body into the spinal cord

cell body

In multipolar and bipolar cells, the …. also receives synapses and so is also part of the input zone

arborization

the elaborate branching of the dendrites of some neurons; this reflects the complexity of the neuron’s information-processing

presynaptic

referring to the region of a synapse that releases neurotransmitter

postsynaptic

referring to the region of a synapse that receives and responds to neurotransmitters

presynaptic membrane

the specialized membrane of the axon terminal of the neuron that transmits information by releasing neurotransmitter

synaptic cleft

the space (20-40 nm) between the presynaptic and postsynaptic membranes

postsynaptic membrane

the specialized membrane on the surface of the cell that receives information by responding to neurotransmitters from a presynaptic neuron

synaptic vesicles

a small, spherical structure that contains molecules of neurotransmitters (30-140 nm)

synaptic transmitter/chemical transmitter/transmitter

the chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons

neurotransmitter receptors

specialized protein molecules that stud the postsynaptic membrane, where they capture and react to molecules of the neurotransmitter

cognate

matching receptor of a neurotransmitter molecule

dendritic spines

outgrowths studding the dendrites of many neurons that effectively increase the surface area of the dendrites, allowing for extra synaptic contacts

axon hillock

a cone-shaped area from which the axon originates out of the cell body; functionally the integration zone of the neuron

innervate

to provide neural input

usually one per neuron, with many terminal branches

Number of Axons

usually many per neuron

Number of Dendrites

uniform until start of terminal branching

Diameter of Axons

tapering progressively toward ending

Diameter of Dendrites

present

Presence of Hillock in axons

no hillock-like region

Presence of Hillock on Dendrites

usually covered with myelin

Sheathing on Axons

no myelin sheath

Sheathing on Dendrites

ranging from practically nonexistent to several meters long

Length of Axons

often much shorter than axons

Length of Dendrites

axonal transport

the transport of materials between the neuronal cell body and axon terminals

anterograde transport

moves materials toward the axon terminals; same direction as electrical signal

retrograde transport

moves materials back to the cell body

1. The rapid transmission of electrical signals along the outside of the axon (like a wire)

2. The much slower transportation of substances through the inside of the axon, to and from the axon terminals

2 Main Functions of the Axon

astrocyte

a star-shaped glial cell with numerous processes that extend in all directions; monitor neuronal activity and regulate blood flow to meet neural demand

end feet

some astrocytes form these sucker-like things on blood vessels, regulating blood flow to provide more supplies to neurons when they are active

microglial cell/microglia

extremely small glial cells that remove cellular debris from injured or dead cells

oligodendrocytes

a type of glial cell that forms myelin in the central nervous system; each cell myelinates several nearby axons

Schwann cells

a glial cell that forms myelin in the peripheral nervous system; each cell ensheathes a limited length of a single axon

myelination

the process of ensheathing axons in myelin

myelin

the fatty insulation around an axon, formed by glial cells, that speeds the conduction of action potentials

nodes of Ranvier

a gap between successive segments of the myelin sheath where the axon membrane is exposed needed to propagate electrical signals

edema

the swelling of tissue, such as in the brain, in response to injury

multiple sclerosis

literally, “many scars.” A disorder characterized by widespread degeneration of myelin; demyelinating disease

within, between

Information flows …. a neuron via electrical signals. Information passes …. neurons through (most often) chemical signals

1. Input zone - where neurons collect and process information, either from the environment or from other cells

2. Integration zone - where the decision to produce a neural signal is made

3. Conduction zone - where information can be electrically transmitted over great distances

4. Output zone - where the neuron transfers information to other cells

5. Axon terminals

6. Axon collaterals

7. Axon

8. Dendritic spines

9. Cell body

10. Dendrites

1. Multipolar neuron

2. Bipolar neuron

3. Unipolar neuron

4. Input zone

5. Integration zone

6. Conduction zone

7. Output zone

8. Dendrites

9. Dendritic branches

10. Cell body

11. Axon

12. Axon terminals

axon hillock

Action potential generation is initiated at the ….

myelinated

insulated, fast-conducting

unmyelinated

non-insulated, slow conducting

1. Presynaptic axon terminal

2. Mitochondrion

3. Synaptic vesicles

4. Presynaptic membrane

5. Neurotransmitter molecules

6. Synaptic cleft

7. Postsynaptic membrane

8. Dendritic spine

axodendritic synapse

most synapses are formed here, between a presynaptic axon and a postsynaptic dendrite

A) Axodendritic

B) Axosomatic

C) Axoaxonic

D) Dendrodendritic

nondirected synapses

like drip irrigation; neurotransmitters released along large sections of tissue from axonal swellings called varicosities

neurophysiology

the study of electrical and chemical processes in neurons

microelectrode

an especially small electrode used to record electrical potentials from living cells

resting membrane potential

a difference in electrical potential across the membrane of a nerve cell during an inactive period; about -50 to -80 mV

negative polarity

a negative electrical-potential difference relative to a reference electrode

1. Electrostatic pressure - the force that causes oppositely charged particles to come together and causes particles with the same electrical charge to repel one another
2. Diffusion - the tendency of molecules of a substance to spread away from regions of high concentrations to regions of low concentration
3. Selectively permeable membranes - allows certain ions (like K+) to cross freely, but normally prevents other ions (like Na+) from passing through

Why do neurons have a resting membrane potential of about -65 mV?

concentration gradient

variation of the concentration of a substance within a region

ion channels

a pore in the cell membrane (protein) that permits the passage of certain ions through the membrane when the channel is open

K+, Na+

…. is allowed to freely enter or exit the neuron, while …. are impeded by the cell membrane

equilibrium

in a neuron, when the concentration of K+ ions stays the same on both sides of the cell membrane because of constant diffusion of K+ into and out of the cell; voltage is about -58 mV

sodium-potassium pump

the energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in; for every 2 K+ ions pumped in, 3 Na+ ions are pumped out

Nernst equation

an equation predicting the equilibrium potential for a given ion based on the concentrations of the ion on opposite sides of a permeable membrane

equilibrium potential

the voltage across a permeable membrane that exactly counteracts the movement of ions from the side with a high concentration to the side with a low concentration

Goldman equation

an equation predicting the potential difference across a membrane based on the concentrations of multiple ions on opposite sides of the membrane, as well as its relative permeability to each ion

action potentials

the propagated electrical message a neuron sends along its axon to the presynaptic axon terminals

hyperpolarization

an increase in membrane potential (the interior of the neuron becomes even more negative); more negative than resting potential

depolarization

a reduction in membrane potential (the interior of the neuron becomes less negative); less negative than resting potential

capacitance

the membrane’s ability to store electrical charge causing the distortions at the beginning and end of the neuron’s response

graded response

the greater the stimulus, the greater the response, so the neuron’s change in potential is called… IPSP and EPSP responses add up to determine the membrane potential

local potentials

an electrical potential that is initiated by stimulation at a specific site, which is a graded response that spreads passively across the cell membrane, decreasing in strength with time and distance

threshold

the stimulus intensity that is just adequate to trigger an action potential; varies among neurons but near -40 mV

overshoot

the brief period when the neuron interior is positive

all-or-none property

the fact that the amplitude of the action potential is independent of the magnitude of the stimulus

afterpotentials

the positive or negative change in membrane potential that may follow an action potential

voltage-gated Na+ channel

an Na+-selective channel that opens or closes in response to changes in the voltage of the local membrane potential. It mediates the action potential.

refractory

referring to transiently inactivated or exhausted axonal membrane

absolute refractory phase

a brief period of complete insensitivity to stimuli; no amount of stimulation can induce another action potential because the voltage-gated Na+ channels are unresponsive

relative refractory phase

a period of reduced sensitivity during which only strong stimulation produces an action potential because the flow of K+ ions out has temporarily hyperpolarized the neuron, so a stronger stimulus would be needed to reach threshold

conduction velocity

the speed at which an action potential is propagated along the length of an axon (or section of peripheral nerve); larger axons allow the depolarization to spread faster through the interior; varies with diameter and myelination

saltatory conduction

the form of conduction that is characteristic of myelinated axons, in which the action potential jumps from one node of Ranvier to the next

neurotransmitter

the chemical released from the presynaptic axon that serves as the basis of communication between neurons

postsynaptic potentials

a local potential that is initiated by stimulation at a synapse, can vary in amplitude, and spreads passively across the cell membrane, decreasing in strength with time and distance

excitatory postsynaptic potential (epsp)

a depolarizing potential in the postsynaptic neuron that is caused by excitatory connections. These increase the probability that the postsynaptic neuron will fire an action potential