Chapter 6

A presynaptic location where neurotransmitter molecules are stored.

Synaptic vesicles

Receptor desensitization

Temporary inability of a receptor to respond to its ligand due to prior ligand binding

Large nuclei just below the cerebrum that serve as synaptic relay stations for inputs to the cerebral cortex

Thalamus

You are studying a cross-sectional tissue slice of a nerve using a transmission electron microscope. You find an area where there appears to be a small amount of cytoplasm surrounded by about 100 layers of stacked cell membranes. You conclude that you have found

a myelinated axon

During the action potential, a second stimulus, no matter how strong, will not produce a second action potential because the membrane is in its __ period.

absolute refractory

The central nervous system (CNS) is composed of the __ in the skull and the __ in the vertebral column.

brain, spinal cord

During this time, some of the voltage-gated Na⁺ channels have returned to their __ state, and could therefore open again.

closed

The movement of electrical charge is called __ and the charge carriers in biological systems is/are __.

current, ions

The net movement of ions causes a slight ___ of the membrane.

depolarization

In most neurons, generation of a/an __ causes the release of __ which communicate with other cells.

electrical signal, neurotransmitters

At the resting membrane potential of -70 mV, the __ gradient for K⁺ favors flux into the cell, while the __ gradient favors flux __ cell.

electrical, concentration, out of the

However, in cells that do not actively transport Cl-, the ECl is __ to the resting membrane potential.

equal

The equilibrium potential for an ion is the membrane potential at which the flux from the ion concentration gradient and the flux from the electrical gradient are ___ in magnitude but ___ in direction.

equal, opposite

The resting membrane potential is not at the ___ for either Na+ or K+.

equilibrium potential

This is called a/an ___, and its function is to bring the membrane potential of the postsynaptic cell closer to ___.

excitatory postsynaptic potential, threshold

At a/an ___ chemical synapse, activated receptors on the postsynaptic membrane is/are ___.

excitatory, non-selective cation channels

When the membrane potential is at the equilibrium potential for a particular ion, there is ___ of the ion through open ion channels, but no ___.

flux, net flux

Therefore, as Cl- channels open, Cl- enters the cell, producing a/an __ called a/an __.

hyperpolarization, inhibitory postsynaptic potential

At a/an __ chemical synapse, activated receptors on the postsynaptic membrane allow influx of __ or efflux of __ through channels specific for those ions.

inhibitory, Cl⁻, K⁺

At the resting membrane potential of -70 mV, both the electrical and concentration gradients for Na⁺ favor flux __ the cell.

into

The magnitude of the resting membrane potential depends on two factors: differences in specific __ in the intracellular and extracellular fluids and the membrane __ to those ions.

ion concentrations, permeabilities

The difference in electrical charge between two points

is called the potential difference between those points

During this time, a second action potential can be produced, but only if the stimulus strength is __ than usual.

larger

Finally, with increased K+ permeability, more K+ ions __ the cell and the membrane moves closer to the EK, causing an IPSP.

leave

Alternatively, activated receptors may act indirectly on separate ion channels through a G protein and/or second messenger, a type referred to as __ receptors.

metabotropic

In biological systems, membrane potential is measured in the units, __.

millivolts

Action potential propagation occurs rapidly in the axons of neurons covered by __.

myelin

In cells that actively transport Cl- out of the cell, the ECl is more __ than the resting membrane potential.

negative

The resting membrane potential exists because of a tiny excess of __ ions inside the cell and an excess of __ ions outside that are electrically attracted to each other across the __ of the cell.

negative, positive, plasma membrane

The basic unit of the nervous system is the individual nerve cell, or __.

neuron

The bulk of the intracellular and extracellular fluids remain __.

neutral

The spaces between adjacent sections of myelin where the axon's plasma membrane is exposed to the extracellular fluid are the __.

nodes of Ranvier

Opening these channels that are permeable to small positively charged ions therefore results in the simultaneous movement of a small number of potassium ions ___ the cell and a larger number of sodium ions ___ the cell.

out of, into

The __ consists of the nerves that connect the CNS with the body's __, glands, and sense organs.

peripheral nervous system (PNS), muscles

The difference in the amount of charge between two locations is called a/an __.

potential

Eventually, the action potential reaches the terminal of the __ neuron.

presynaptic

This is the __ period, which coincides roughly with the period of hyperpolarization.

relative refractory

All cells under resting conditions have a potential difference across their plasma membranes called the __, with the inside of the cell __ charged with respect to the outside.

resting membrane potential, negatively

Finally, neurotransmitters are removed from the synaptic cleft by __ into the presynaptic axon terminal, by diffusion away from the receptor site, or by destruction by __.

reuptake, diffusion, enzymes

As action potentials propagate along a myelinated fiber, they jump from one node of Ranvier to the next, and for this reason such propagation is called ___.

saltatory conduction

Therefore, a rise in Cl⁻ permeability does not change the membrane potential, but it makes it more difficult for other ion types to change the potential by __ the membrane at the resting level.

stabilizing

An experimentor uses an electrical stimulator to inject a resting neuron with 3 different currents: 5, 10, and 25 microamps. No action potential occurs at 5 and 10 microamps, so those are called __.

subthreshold stimuli

Neurotransmitters diffuse across the __ and bind to receptors within the membrane of the __ neuron that are ion channels, which designates them as __ receptors.

synaptic cleft, postsynaptic, ionotropic

Ca²⁺ entering during depolarization binds to a family of proteins known as __ that are associated with __ located within the axon terminal.

synaptotagmins, vesicles

An action potential does occur at 25 microamps, so it is called a/an __.

threshold stimulus

Depolarization in the terminal induces the opening of __.

voltage-gated Ca²⁺ channels

General regions of the CNS where myelinated axons are found

white matter

If the neuron was stimulated with a 50 microamp current, an action potential __ occur, and it would be __ in size to the 25 microamp-induced action potential.

would, similar

Area between the brain and spinal cord involved with motor functions, cardiovascular and respiratory control, regulation of sleep and wakefulness, and containing nuclei for processing information from most of the cranial nerves

Brainstem

In the __, the __ form myelin sheaths around multiple axons.

CNS, oligodendrocytes

The electrochemical gradient for __ favors the flux of this ion __ the axon terminal.

Ca²⁺, into

Highly branched lobular structure found behind the brainstem that is an important center for coordinating movements, posture, and balance

Cerebellum

Highly folded structure developed most extensively in humans; functions in perception, generation of skilled movements, reasoning, learning, and memory

Cerebrum

A location where neurotransmitter signals link the electrical activity of two cells.

Chemical synapse

A group of neuronal axons that connect the right and left sides of the CNS

Commissure

Multiple presynaptic neurons synapse on a single postsynaptic neuron.

Convergence

A single presynaptic neuron branches to synapse on multiple postsynaptic neurons.

Divergence

A location where gap junctions provide a low-resistance electrical connection between two cells.

Electrical Synapse

Presynaptic facilitation

Excitatory input to neurons through synapses at the presynaptic nerve terminal

An event at this location brings a postsynaptic cell's membrane potential closer to threshold.

Excitatory synapse

T or F? A neuron receives information on it's axons and delivers it to other neurons through its dendrites.

False

T or F? As the distance between oppositely charged particles becomes greater, the force of attraction between them also becomes greater.

False

T or F? Electrical potential is defined as the movement of electrical charge.

False

T or F? Glucose freely diffuses through the lipid bilayer of cell membranes, so is not inhibited from entering the brain.

False

T or F? Materials that have a low resistance to the flow of electrical current are known as insulators.

False

T or F? Morphine readily crosses the blood brain barrier, while the drug heroin does not.

False

T or F? The blood brain barrier consists of three membranes: the dura, arachnoid, and pia mater

False

T or F? The units of electrical current flow are volts.

False

Groups of neuronal cell bodies outside the CNS

Ganglia

The greater permeability of __ through leak channels maintains the resting membrane potential at a value near the equilibrium potential for this ion.

K⁺

While for ___, the electrical gradient opposes the concentration gradient.

K⁺

Immediately after an action potential, some of the voltage-gated __ channels that repolarized the membrane are still __.

K⁺, open

Temporal summation

Membrane potential produced when two or more inputs from a single source occur closely enough in time to add together; the potential change is greater than that caused by a single input

At rest, the ___ establishes and maintains the concentration gradients for these ions across the plasma membrane.

Na+/K+-ATPase pump

There are both electrical and concentration gradients driving ___ into the cell.

Na⁺

This occurs because the voltage-gated __ channels are either already open or have proceeded to the __ state.

Na⁺, inactivated

A group of neuronal axons traveling together in the PNS

Nerve

Groups of neuronal cell bodies within the CNS

Nuclei

A location where neurotransmitter receptors are clustered.

Postsynaptic density

Axo-axonic synapse

Presynaptic synapse where an axon stimulates the presynaptic terminal of another axon

Autoreceptors

Receptors on a cell affected by a chemical messenger released from the same cell

What would occur if the concentration of ATP were depleted in a typical nerve cell?

Resting membrane potential would become less negative

This binding triggers a conformational change in the __ complex that leads to membrane fusion and the release of __.

SNARE, neurotransmitters

In the PNS, cells called __ form individual myelin sheaths at regular intervals along the axons.

Schwann cells

Action potential

- all or none - initiated by a graded potential - is conducted without decrement - is only a depolarization - threshold is usually about 15 mV depolarized relative to the resting potential - cannot be summed - has a refectory period - mechanism depends on the voltage-gated channels

Both CNS and PNS

- axons of efferent neurons - axons of afferent neurons

CNS

- axons of interneurons - axon terminals of interneurons - dendrites of interneurons - cell body of somatic efferent neurons - cell body of interneurons - dendrites of somatic efferent neurons

Graded potential

- can be summed - mechanism depends on ligand-gated channels or other chemical or physical changes - has no refectory period - amplitude varies with size of the initiating event - has no threshold - is conducted decremental; amplitude decreases with distance

PNS

- cell body of afferent neurons - peripheral processes of afferent neurons - axon terminals of efferent neurons - sensory receptors of afferent neurons

Oligodendrocytes

- form myelin

interneuron characteristics

- function as integrators and signal changers - have wide range of physiological properties, shapes, and functions - lie entirely within the CNS, account for 99% of all neurons

autonomic nervous system characteristics

- has two-neuron chain between the CNS and effectors - neurons release norepinephrine that binds to adrenergic receptors located on the effector organs - receptors on effector organs are also responsive to epinephrine that is released into the blood by the adrenal medulla - can lead to excitation or inhibition of the effectors - innervates smooth and cardiac muscle, glands, and GI neurons - neurons release acetylcholine that binds to muscarinic acetylcholine receptors located on the effector organs

Microglia

- provide immune functions

Ependymal Cells

- regulate production and flow of cerebrospinal fluid

Astrocytes

- remove K⁺ and neurotransmitters from ECF near synapses - help create blood-brain barrier - sustain the neurons metabolically - serve as guides for developing neurons

somatic nervous system characteristics

- single neuron between the ins and effectors - neurons are also called motor neurons - activates skeletal muscles - can lead only to excitation of the effectors - neurons release acetylcholine that binds to nicotinic acetylcholine receptors located on the effector organs

Efferent neuron characteristics

- transmit info away from CNS - second most abundant type of neuron - axons terminate on muscles, glands, or other neurons - cell body, dendrites, and small segment of axon are in the CNS

Afferent neuron characteristics

- transmits info toward CNS - least abundant type of neuron - contain sensory receptors at their peripheral endings - cell body and long peripheral process of the axon are in the PNS

The resting membrane potential of a typical neuron is ___ mV.

-70

With an extracellular concentration of 5 mmol/L and an intracellular concentration of 150 mmol/L, the equilibrium potential for K⁺ in a typical neuron is __ mV.

-90

Spatial summation

Adding together effects of simultaneous inputs to different places on a neuron to produce potential change greater than that caused by a single input

General regions of the CNS where cell bodies are found

Gray Matter

Cluster of nuclei at the base of the forebrain that is the master command center for integration of neural and hormonal regulation of homeostasis

Hypothalamus

Presynaptic inhibition

Inhibitory input to neurons through synapses at the presynaptic nerve terminal

An event at this location can either stabilize or hyperpolarize a postsynaptic cell's membrane potential.

Inhibitory synapse

A group of neuronal axons traveling together within the CNS

Tract

T or F? According to Ohm's law, if resistance stays the same and electrical potential increases, the electrical current will increase.

True

T or F? Alcohol has rapid effects on the brain because it is highly soluble in lipid membranes of the blood-brain barrier.

True

T or F? Electrical forces increases as the quantity of charged particles increases.

True

T or F? Membranes that form the blood-brain barrier contain physiological transporters that allow permeation of some hydrophilic substances.

True

T or F? Negatively charged particles will tend to be attracted to move in the direction of positively charged particles.

True

T or F? Ohm's law states that current is proportional to voltage and inversely proportional to resistance.

True

T or F? The blood-brain barrier dresses the access of some therapeutic substances to the brain.

True

T or F? The permeability of the plasma membrane to potassium ions is much greater than its permeability to sodium ions.

True