Chapter 2: The Brain

Question 1

cerebrum

Answer 1

Also referred to as the forebrain, the cerebrum is the anterior-most part of the brain, and largest in volume. Deriving from the embryonic telencephalon, it comprises the thalamus plus all the tissue that is rostral to it. Major elements include the five lobes of cerebral cortex, basal ganglia, hippocampus, thalamus, and all the white matter connecting these structures

Question 2

diencephalon (thalamus)

Answer 2

Large collection of nuclei located near the center of the cerebrum, straddling the midline and immediately rostral (see Figure 1.2) to the midbrain. Many thalamic nuclei serve as relay points between peripheral sensory information and the cerebral cortex.

Question 3

cortex

Answer 3

Refers to the layer of tissue containing cell bodies, and thus is often synonymous with “gray matter.” Cortex is the Latin name for “rind,” and thus the name references the outer covering of many types of fruit, such as melons or citrus fruit. The cerebrum and cerebellum each have a cortex.

Question 4

hippocampus

Answer 4

A subcortical structure of the cerebrum that, in the primate, is surrounded by the cortex of the temporal lobe, and lies parallel to this lobe’s long axis. The term is Latin for seahorse, of which its shape is suggestive.

Question 5

gray matter

Answer 5

Informal, but widely used, term for the cortex. Derives from fact that the cortex lacks myelin, and thus appears darker to the naked eye than does the myelin-rich white matter.

Question 6

white matter

Answer 6

Made up of billions of myelin-sheathed axons, the white matter makes up the majority of the volume of the crebrum.

Question 7

axons

Answer 7

The branches through which a neuron sends signals to other neurons. Most axons have many “collateral” arms splitting off from the main branch, thereby enabling a single neuron to influence hundreds, thousands, and in some cases tens of thousands of other neurons.

Question 8

myelin

Answer 8

The cholesterol-laden sheath that insulates axons. Myelin is formed by branches from a type of glial cell, called oligodendrocytes, that wraps the axon in several layers.

Question 9

gyri

Answer 9

From the Latin for “circles”, convex ridges on the surface of the cerebral cortex. Each gyrus is bounded by sulci on each side.

Question 10

sulci

Answer 10

Latin for “furrows,” fissures on the cortical surface.

Question 11

synapses

Answer 11

Name introduced by Nobel Laureate Charles Sherringotn (1857-1952) for the location at which one neuron passes a signal to another cell (within the CNS, it’s typically to the dendrite of another neuron

Question 12

peripheral nervous system

Answer 12

The peripheral nervous system (sometimes abbreviated PNS) is made up of all neurons in the body whose cell bodies are located outside of the central nervous system. These include somatosensory (i.e., “touch”) neurons whose cell bodies are in the skin and that send signals via axons that project into the spinal cord, and neurons that control autonomic functions of many organ systems of the body.

Question 13

synapses

Answer 13

Name introduced by Nobel Laureate Charles Sherringotn (1857-1952) for the location at which one neuron passes a signal to another cell (within the CNS, it’s typically to the dendrite of another neuron; at the neuromuscular junction, it’s to a muscle cell), The name is derived from the Greek for “to clasp.”

Question 14

nucleus

Answer 14

In the context of the cell, the nucleus is the central structure containing DNA. In the context of gross anatomy, a nucleus is a subcortical group of neurons, often visible to the naked eye, that typically all perform the same function.

Question 15

ventricles

Answer 15

A hollow chamber inside the brain through which cerebrospinal fluid (CSF) circulates. L:ike a chain of lakes connected by canals, the ventricles are part of a continuous system of CSF that extends to the caudal end of the spinal cord.

Question 16

cerebrospinal fluid (CSF)

Answer 16

The fluid that circulates through the ventricles (thereby inflating the brain) and also along the exterior surface of the CNS (therebyu providing a medium in which the brain floats).

Question 17

pyramidal cells

Answer 17

Glutamate-releasing neurons with pyramid-shaped cell bodies that are the most common excitatory neuron in the neocortex and hippocampus.

Question 18

cortical columns

Answer 18

A group of neurons that are stacked, as though in an imaginary tube that is oriented orthogonal to the cortical surface. Neurons within a cortical column are more strongly interconnected, and, therefore, share more functional properties, than are physically adjacent neurons that are not within the same column.

Question 19

diffusion tensor imagining

Answer 19

A type of MRI that measures the diffusion of water to infer information about white-matter tracts.

Question 20

axon hillock

Answer 20

Region of the cell body from which the axon emerges. The membrane of the hillock is dense with voltage-gated Na⁺ channels, such that it can powerfully initiate action potentials.

Question 21

depolarize

Answer 21

To make the membrane potential of a cell more positive. Typically, because the resting state of neurons is negative, this is equivalent to making the membrane potential less negative.

Question 22

synaptic cleft

Answer 22

The gap between the presynaptic and postsynaptic terminals, across which neurotransmitter diffuses from pre- to post-.

Question 23

ligand

Answer 23

A substance, typically a molecule, that binds to a specific site on a protein, thereby triggering msome process. In the context of neurotransmission, the ligand is the neurotransmitter that binds witha binding site on the postsynaptic receptor.

Question 24

excitatory neurotransmitter

Answer 24

A neurotransmitter whose effect on the postsynaptic membrane is to depolarize it.

Question 25

glutamate

Answer 25

Also referred to as “glutamic acid,” glutamate is the excitatory neurotransmitter released by cortical pyramidal cells, and thus the primary chemical currency for information transmission in the brain.

Question 26

inhibitory neurotransmission

Answer 26

Of a neurotransmitter whose effect on the postsynamptic membrane potential is to hyperpolarize it, i.e., to make it more negative.

Question 27

GABA

Answer 27

The abbreviated name of y-aminobutyric acid, the most common inhibitory neurotransmitter in the CNS.

Question 28

inhibitory interneurons

Answer 28

Along with pyramidal cells, the second major class of neurons in the cerebral cortex. Although there are many types of inhibitory interneuron, this book will primarily refer to the generic internueron: a GABAergic cell with only local projections to nearby pyramidal cells.

Question 29

hyperpolarize

Answer 29

To make the membrane potential of a cell more negative (i.e. the opposite of depolarize).

Question 30

cations

Answer 30

A general term for positively charged ions.

Question 31

anions

Answer 31

A general term for negatively charged ions.

Question 32

reuptake

Answer 32

The active process of removing molecules of neurotransmitter from the synamptic cleft by transporting them into a cell, either the presynaptic neuron or an adjacent astrocyte.

Question 33

Na⁺/K⁺ pump

Answer 33

Also known as “ATPase,” because it’s an enzyme that requires ATP for its operation. The Na⁺/K⁺ pump is a membrane-sanning complex that actively restores the electrochemical gradients of Na⁺ and K⁺ that are decreased by the mechanisms of the action potential and of neurotransmitter reuptake.

Question 34

functional magnetic resonance imaging (fMRI)

Answer 34

The application of MRI that is sensitive to physiological signals (as opposed to anatomical structure).

Question 35

cotransport

Answer 35

Process whereby more than one molecule is simultaneously carried across a cell membrane, as with reuptake.

Question 36

laminar

Answer 36

“Lamina” is another word for layer; although derived from Latin, the plural form is “laminas” or “laminae.” It is often used as an adjective when referring to layer-specific (i.e. “laminar”) organization within cortex.

Question 37

axonal transport

Answer 37

Intracellular mechanisms for transporting proteins from the cell body to synapses.

Question 38

local field potential (LFP)

Answer 38

The oscillating electrica potential recorded from extracellular space that reflects the moment-to-moment aggregation of fluctuating voltages from all dendritic trees in the vicinity of the electrode.

Question 39

gamma frequency band

Answer 39

Neural oscillations in the range of 30-80 Hz.

Question 40

intracellular recordings

Answer 40

Electrical recordings made with a hollow-tube electrode that punctures the membrane of a cell (and forms a tight seal between membrane and electrode) so that fluctuations of voltage within a that individual neuron can be measured.

Question 41

extracellular recordings

Answer 41

Electrical recordings made from an electrode located in extracellular space. Such recordings can be sensitive to action potentials and/or LFPs.

Question 42

electrocorticography (ECoG)

Answer 42

Electrical recordings made from the surface of the cortex.

Question 43

ensembles

Answer 43

From the French for “together,” this term is often used to refer to a group of neurons that are “working together” as a functional unit. The analogy is to a musical ensemble, such as a string quartet.

Question 44

phase synchronization

Answer 44

The phase of a sine wave refers to the location within the cycle (e.g., the peak, or the trough). To synchronize the phase of two oscillators is to adjust them such that, whenever one is at a particular phase in its cycle (say, the peak) the other will always be at the same phase in its (this could also be the peak, or it could be any other phase, so long as its predictable).