BSC 228 MU Chapter 6

Which is generally true regarding how postsynaptic potentials initiate action potentials at synapses between neurons?

Individual EPSPs are small, so initiating an action potential requires the summation of multiple excitatory inputs within a short time period.

Which of the following is true of spatial summation within the nervous system?

It is due to the convergence of neural pathways. It occurs when signals from several presynaptic neurons summate within one postsynaptic neuron.

The ANS has two main efferent subdivisions. The _______ nervous system exits the CNS from the thoracic and lumbar regions of the spinal cord, and the _______ nervous system exits the CNS from the brainstem and sacral region of the spinal cord.

sympathetic; parasympathetic

Neurotransmitter molecules within the presynaptic neuron endings are contained within many small membrane-enclosed sacks called

synaptic vesicles.

While K+ ions move through both leakage and voltage-gated channels, Na+ ions move predominantly through ________ during an action potential.

voltage-gated channels

Threshold stimuli

elevate the membrane potential sufficiently to generate an action potential.

About 80% of hormonal secretion of the adrenal medulla is _______, and about 20% is _______.

epinephrine; norepinephrine

Removal of neurotransmitters from synapses occurs by

-active transport back into the presynaptic terminal. -enzymatic transformation into inactive substances. -diffusion away from the synapse. -active transport into nearby cells, such as glial cells.

A subthreshold stimulus to a neuron

-does not generate an action potential. -depolarizers the local membrane potential briefly before it returns to the resting potential.

The myelin sheath that covers some axons

-is formed by Schwann cells in the PNS. -is formed by oligodendrocytes in the CNS.

Chemical synapses

-may contain more than one neurotransmitter at a time. -have a synaptic cleft between pre- and postsynaptic cells. -use neurotransmitters released by the presynaptic cell to transmit signals across the postsynaptic cell.

An action potential

-occurs very rapidly. -is an all-or-none event. -is conducted without decrement.

The magnitude of the resting membrane potential depends upon

-the differences in ion concentration between ICF and ECF -the electronegative effect of the Na+/K+-ATPase pump -the permeability of the membrane to each type of ion

Which best describes the process of repolarization?

A neuron is returning from the peak of its action potential toward its resting potential.

Which of these explains why an action potential is able to propagate along the full length of an axon?

Action potentials are regenerated in each patch of membrane by depolarizing local currents arriving from previously-depolarized patches of membrane.

Which of the following changes in postsynaptic cell ionic permeability commonly mediate inhibitory postsynaptic potentials?

An increase in permeability to Cl- and K+

With regard to the ANS, what is meant by dual innervation?

An organ receives input from both the sympathetic and parasympathetic systems.

Which of the following structures are part of the central nervous system?

Brain and spinal cord

What are the two major divisions of the forebrain?

Cerebrum and diencephalon

What are the branches of an axon called?

Collaterals

Which of the following are catecholamines?

Dopamine (DA), norepinephrine (NE), and epinephrine

Agonists

Drugs that bind to and activate receptor proteins

True or False: The number of anions floating freely in the bulk solution inside of excitable cells is greater than the number of cations in the bulk of the solution, which is why the resting membrane potential is negative.

False: There is a slight excess of negative particles inside the cell and slight excess of positive particles outside the cell. These particles attractive each to the plasma membrane, creating an electrical neutrality of the fluid as a whole.

True or False: if an action potential was started in the middle of an axon it could only propagate in one direction--away from the cell body.

False; It would propagate in both directions away from the middle; action potentials generally move "one-way" because they generally start at one end of the axon.

Which physiological state is associated with activation of the sympathies division of the autonomic nervous system?

Fight-or-flight repsonse

Glutamate binds to ______ receptors.

N-methyl-D-aspartate (NMDA) and alpha-amino-3 hydroxy-5 methyl-4 isoxazole propionic acid (AMPA)

The ions that enter a neuron and cause the depolarization phase of a typical action potential are _______ ions.

Na+

Which ion species are in high concentration in the ICF than in the ECF?

Phosphate ions and potassium ions

The hind brain develops into these three major parts:

Pons, medulla oblongata, and cerebellum

Which is true about the anatomy of efferent autonomic pathways of the ANS?

Postganglionic neurons originating in the ganglia in the PNS synapse onto smooth muscle, cardiac and gland cells. Preganglionic neurons originating in the CNS synapse onto postganglionic neurons in a ganglion in the PNS.

Place the following structures in the order they would be penetrated by a surgeon accessing the brain to remove a tumor, with the first structure at the top and the last at the bottom.

Skin Skull bone Dura mater Arachnoid mater Subarachnoid space Pia mater

Arrange the statements in the order that most logically explains how a cell goes from having no membrane potential to having a steady negative resting membrane potential.

The Na+/K+-ATPase pump moves Na+ out of the cell and K+ into the cell, setting up concentration gradients across the membrane. Due to a permeability difference, there a greater net movement of K+ out of the cell than of Na+ into the cell. The membrane potential becomes negative, approaching the K+ equilibrium potential. Equal leaks of Na+ and K+ are offset by the continued activity of the Na+/K+-ATPase pump.

Synapse

The anatomically specialized junction between two neurons where electrical and chemical activity in one neuron influences excitability of the other

Acetylcholine (ACh)

The main neurotransmitter released into skeletal muscle cells by motor neurons

Current

The movement of electrical charge

Dendrites

The thin branching processes of neurons that provide receptive sites for incoming signals

Which two statements are true about neurons?

They operate by generating electrical signals that move from one part of the cell to another part of the cell or to a neighboring cell. They are the cells responsible for the basic functioning of the nervous system.

The neurotransmitter secreted from somatic motor neurons onto skeletal muscle cells is ______, and it always causes ________.

acetylcholine; contraction

Receptors that respond to norepinephrine and epinephrine are called ______ receptors.

adrenergic

A graded potential occurring in a postsynaptic cell that increases its likelihood of reaching the threshold voltage is called

an excitatory postsynaptic potential (EPSP).

Masses of gray matter deep within the cerebral white matter are called

basal nuclei.

The exchange of substances between blood and the extracellular fluid in the CNS is different from the exchange between blood and the ECF of other tissues; it is more restrictive in the CNS due to the

blood-brain barrier.

The extracellular liquid that circulates through brain ventricles, the spinal canal, and the subarachnoid space is called _________ _________.

cerebrospinal fluid

The left and right cerebral hemispheres are physically connected, internally, by a fiber tract called the _______ _______.

corpus callosum

Sensory fibers of a spinal nerve are found in the _______ root, and motor fibers are found in the _______ root.

dorsal; ventral

The capability of a cell to produce electrical signals through the action of actively-gated ion channels is called

excitability.

The membrane potential of a postsynaptic neuron is brought closer to threshold (depolarizer) at an

excitatory synapse.

The four lines that make up the cerebral hemispheres are

frontal, parietal, occipital, and temporal lobes.

The non-neuronal cells of the nervous system that provides physical and metabolic support to neurons are collectively called ______ cells.

glial

The surface area of the cerebrum is large due to its folding into sinuous ridges called ________ separated by grooves called ________.

gyri; sulci

When EPSPs summate, the region of the postsynaptic cell that usually reaches the action potential threshold first is the

initial segment.

The resting membrane potential of body cells

is negative, with values varying from -5 to -100mV.

A collection of axons encased in connective tissue in the PNS is called a

nerve.

The usual effect of activated receptors on postsynaptic cells at excitatory synapses is to open

no selective cation channels permeable to both Na+ and K+.

Fibers from the cerebellum connect directly or indirectly with the

pons and spinal cord, reticular formation, and primary motor cortex.

When neurotransmitters such as GABA or ACh are released from neuron A and bind to receptors embedded in the membrane of the axon terminal of neuron B, causing a decrease in the amount of an excitatory neurotransmitter released by neuron B, it is called __________.

presynaptic inhibition

A neuron that conducts a signal toward a synapse is defined as the _______ neuron, and a neuron that conducts a signal away from a synapse is defined as the _______ neuron.

presynaptic; postsynaptic

In afferent neurons, the initial depolarization to threshold that initiates action potentials is achieved by a graded potential called a _________ potential.

receptor

The _______ ________ runs throughout the core of the brain stem and consists of loosely arranged nuclei intermingled with bundles of axons. It receives and integrates information from all regions of the CNS and is involved in motor functions, respiratory control, and the mechanisms that regulate sleep and wakefulness.

reticular formation

The term used to describe the type of action potential propagation that regenerates itself at nodes in a myelinated axon is ________ conduction.

saltatory

The efferent neurons of the _______ division of the nervous system innervate skeletal muscles, whereas the efferent neurons of the ________ division of the nervous system innervate smooth and cardiac muscle, glands, neurons in the gastrointestinal tract, and other tissues.

somatic; autonomic

Autonomic ganglia of the ______ division of the nervous system are found in two chains close to the spinal column, while ganglia in the _______ division are found within or near target tissues.

sympathetic; parasympathetic