BIO 360 - Exam 2 - Chapter 8 Outline

Question 1

Information flow through the nervous system follows the basic pattern of a reflex…

Answer 1

Stimulus - Sensor - Input signal - Integrating center - Output signal - Target - Response.

Question 2

It is important to note that the CNS can initiate activity without sensory input, such as when you decide to text a friend. Also, the CNS need not create any measurable output to the efferent divisions. For example, thinking and dreaming are complex higher-brain functions that can take place totally within the CNS.

Question 3

______ ______ carry information about temperature, pressure, light, and other stimuli from sensory receptors to the CNS.

______ ______ ______ are pseudounipolar, with cell bodies located close to the CNS and very long processes that extend out to receptors in the limbs and internal organs. In these sensory neurons, the cell body is out of the direct path of signals passing along the axon (Fig. 8.2a). In contrast, sensory neurons in the nose and eye are much smaller bipolar neurons. Signals that begin at the dendrites travel through the cell body to the axon (Fig. 8.2b).

Answer 3

Sensory neurons / Peripheral sensory neurons

Question 4

The axons may divide several times into branches called?

Answer 4

Collaterals

Question 5

Efferent neurons have enlarged endings called ______ ______. Many autonomic neurons also have enlarged regions along the axon called ______. Both ______ ______ and ______ store and release neurotransmitter.

Answer 5

axon terminals / varicosities / axon terminals / varicosities

Question 6

______ increase the surface area of a neuron, allowing it to receive communication from multiple other neurons.

Answer 6

Dendrites

Question 7

Most peripheral neurons have a single axon that originates from a specialized region of the cell body called?

Answer 7

Axon hillock - The primary function of an axon is to transmit outgoing electrical signals from the integrating center of the neuron to target cells at the end of the axon.

Question 8

______ (or ______) transport moves vesicles and mitochondria from the cell body to the axon terminal.
______ (or______) transport returns old cellular components from the axon terminal to the cell body for recycling.

Answer 8

Forward (anterograde) / Backward (retrograde)

Question 9

The motor proteins ______ and ______ are the major motor proteins for axonal transport.

Answer 9

kinesin-1 / dynein

Question 10

______ ______ ______ goes in both directions and can move material at rates of up to 400 mm (about 15.75 in.) per day.

______ ______ ______ moves soluble proteins and cytoskeleton proteins from the cell body to the axon terminal at a rate of 0.2–8 mm/day.

______ ______ ______ can be used only for components that are not consumed rapidly by the cell, such as cytoskeleton proteins.

Answer 10

Fast axonal transport / Slow axonal transport / Slow axonal transport

Question 11

______ are highly branchedCNS glial cells that by some estimates make up about half of all cells in the brain.

Answer 11

Astrocytes

Question 12

Most gated channels fall into one of three categories:

(1) ______ gated ion channels are found in sensory neurons and open in response to physical forces such as pressure or stretch.

(2) ______ gated ion channels in most neurons respond to a variety of ligands, such as extracellular neurotransmitters and neuromodulators or intracellular signal molecules.

(3) ______ ion channels respond to changes in the cell’s membrane potential. Voltage-gated Na+ and K+ channels play an important role in the initiation and conduction of electrical signals along the axon.

Answer 12

Mechanically / Chemically / Voltage-gated

Question 13

Internal resistance ______ as cell diameter ______, so larger diameter neurons have _____ resistance.

Answer 13

decreases / increases / lower

Question 14

Why do graded potentials lose strength as they move through the cytoplasm? Two factors play a role:

Answer 14

(1) Current leak. The membrane of the neuron cell body has open leak channels that allow positive charge to leak out into the extracellular fluid. Some positive ions leak out of the cell across the membrane as the depolarization wave moves through the cytoplasm, decreasing the strength of the signal moving down the cell.

(2) Cytoplasmic resistance. The cytoplasm provides resistance to the flow of electricity, just as water creates resistance that diminishes the waves from the stone. The combination of current leak and cytoplasmic resistance means that the strength of the signal inside the cell decreases over distance.

Question 15

Graded potentials that are strong enough eventually reach the region of the neuron known as the ______ ______.
In efferent neurons and interneurons, the trigger zone is the ______ ______ and the very first part of the axon, a region known as the i______ s______. The trigger zone is the integrating center of the neuron and contains a high concentration of voltage-gated ______ channels in its membrane.

Answer 15

trigger zone / axon hillock / initial segment / Na+

Question 16

Action potentials moving from trigger zone to axon terminal cannot overlap and cannot travel backward.

Question 17

The ______ ______ is a key characteristic that distinguishes action potentials from graded potentials. If two stimuli reach the dendrites of a neuron within a short time, the successive graded potentials created by those stimuli can be added to one another. If, however, two suprathreshold graded potentials reach the action potential trigger zone within the absolute refractory period, the second graded potential has no effect because the Na+ channels are inactivated and cannot open again so soon.

Refractory periods limit the rate at which signals can be transmitted down a neuron.

The ______ ______ ______ also ensures one-way travel of an action potential from cell body to axon terminal by preventing the action potential from traveling backward.

Answer 17

refractory period / absolute refractory period

Question 18

A distinguishing characteristic of action potentials is that they can travel over long distances of a meter or more without losing energy, a process known as ______.

Answer 18

conduction

Question 19

Two key physical parameters influence the speed of action potential conduction in a mammalian neuron:

Answer 19

(1) the diameter of the axon
(2) the resistance of the axon membrane to ion leakage out of the cell (the length constant).

The larger the diameter of the axon or the more leak-resistant the membrane, the faster an action potential will move.

Question 20

The conduction of action potentials down an axon is faster in axons with ______- ______ membranes so that current leak out of the cell is ______.

Answer 20

high-resistance / minimized

Question 21

The Body’s Wiring
Many aspects of electrical signaling in the body have their parallels in the physical world. The flow of electricity along an axon or through a muscle fiber is similar to the flow of electricity through wires. In both cells and wires, the flow of electrical current is influenced by the physical properties ofthe material, also known as the cable properties. In cells, two factors alter current flow: resistance (discussed in the text) and capacitance.
Capacitance refers to the ability of the cell membrane to store charge (like a battery). A system with high capacitance requires more energy for current flow because some of the energy is diverted to “storage” in the system’s capacitor. In physics, a capacitor is two plates of conducting material separated by a layer of insulator. In the body, the extracellular and intracellular fluids are the conducting materials, and the phospholipid cell membrane is the insulator.

Question 22

Electrical synapses occur mainly in neurons of the CNS. They are also found in glial cells, in cardiac and smooth muscle, and in nonexcitable cells that use electrical signals, such as the pancreatic beta cell. The primary advantage of electrical synapses is rapid and ______ ______ of signals from cell to cell to synchronize activity within a network of cells.

Gap junctions also allow chemical signal molecules to diffuse between adjacent cells.

Answer 22

bidirectional conduction

Question 23

At chemical synapses, the electrical signal of the presynaptic cell is converted into a neurocrine signal that crosses the synaptic cleft and binds to a receptor on its target cell.

Question 24

If the synaptic potential is depolarizing, it is called an
______ ______ ______ (______) because it makes the cell more likely to fire an action potential.

If the synaptic potential is hyperpolarizing, it is called an
______ ______ ______ (______) because hyperpolarization moves the membrane potential away from threshold and makes the cell less likely to fire an action potential.

Answer 24

excitatory postsynaptic potential (EPSP) / inhibitory postsynaptic potential (IPSP)

Question 25

In many situations, ______ ______ in a neuron incorporate both ______ and ______ summation. The summation of graded potentials demonstrates a key property of neurons: ______ ______.

When multiple signals reach a neuron, postsynaptic integration creates a signal based on the relative strengths and durations of the signals. If the integrated signal is above threshold, the neuron fires an action potential. If the integrated signal is below threshold, the neuron does not fire.

Answer 25

graded potentials / temporal and spatial / postsynaptic integration