Chapter 1: Nerve Cells and Nerve Impulses (unfinished)

Question 1

The nervous system is composed of two types of cells:

Answer 1

Neurons and glia

Question 2

Neurons:

Answer 2

Receive information and transmit it to other cells. 


- The human brain contains approximately 100 billion neurone (varies from person to person)

Question 3

Glia:

Answer 3

Serve many functions that are difficult to summarize. 


Question 4

2. Santiago Ramón y Cajal (1852-1934)

Answer 4

a Pioneer of Neuroscience (one of the main founders)

• Used staining techniques to reveal that small gaps separate the tips of one neuron from another.
• This discovery showed that the brain—like the rest of the body—is composed of individual cells.

Question 5

The Structure of an Animal Cell

Answer 5

• Membrane (plasma membrane)
• Nucleus
• Mitochondrion
• Ribosomes
• Endoplasmic reticulum

Question 6

Membrane (plasma membrane):

Answer 6

Composed of two layers of fat molecules, 
this membrane allows some small, uncharged chemicals to flow both into and out of the cell.

• Protein channels allow a few charged ions to cross the membrane (water, oxygen, sodium, potassium, calcium, chloride and other important chemicals), but most chemicals are unable to cross.
• Membrane separates the inside of the cell from the outside environment

Question 7

Nucleus:

Answer 7

The structure that contains the chromosomes.

- All animal cells have this except for mammalian red blood cells

Question 8

Mitochondrion:

Answer 8

The structure that provides the cell with energy. It requires 
fuel and oxygen to function.

Question 9

Ribosomes:

Answer 9

Site of new protein molecule synthesis in the cell. 


- Proteins provide building materials for the cell and facilitate chemical reactions

Question 10

Endoplasmic reticulum:

Answer 10

A network of thin tubes that transports newly 
synthesized proteins to other locations

Question 11

Larger neutron components (4):

Answer 11

dendrites, cell body (soma), axon, and 
presynaptic terminal

- The tiniest neurons may lack axons and well-defined dendrites

Question 12

Dendrites:

Answer 12

Branching fibers that extend from the cell body and get narrower at their end. The dendrite’s surface is lined with specialized synaptic receptors, at which the dendrite receives information from other neurons.
o The greater the surface areas of dendrite, more information it can receive

Question 13

Dendritic spines:

Answer 13

Short outgrowths found on some dendritic branches (increase surface area)

Question 14

Cell body (soma):

Answer 14

Contains the nucleus, ribosomes, mitochondria, and 
other structures found in most cells. 

o Covered with synapses on its surface

Question 15

Axon:

Answer 15

A long, thin fiber (usually longer than dendrites), which is the 
information-sending part of the neuron, sending an electrical impulse 
toward other neurons, glands, or muscles. 

o A neuron can only have one axon, however, an axon may have branches

Question 16

Myelin sheath:

Answer 16

Insulating covering found on some vertebrate axons. 


o Invertebrate axons do not have myelin sheaths

Question 17

Nodes of Ranvier:

Answer 17

Interruptions along the myelin sheath. 


Question 18

Presynaptic terminal (end bulb):

Answer 18

Swelling at the tip of the axon. The 
part of the neuron that releases chemicals that cross the junction between one neuron and the next. 


Question 19

Afferent axons:

Answer 19

Brings information into a structure. Every sensory neuron is an afferent to the rest of the nervous system.

Question 20

Efferent axons:

Answer 20

Sends information away from a structure. Every motor neuron is an efferent from the nervous system

Question 21

Interneurons (intrinsic neurons):

Answer 21

If a cell’s dendrites and axon are entirely located within a single 
structure of the nervous system. 


Question 22

Variations among Neurons

Answer 22

a. Neurons vary enormously in size, shape, and function. 

b. A neuron’s function is closely related to its shape. 

c. A neuron’s shape is plastic (changeable) as new experiences can modify the 
shape of a neuron. 


Question 23

Glia (neuroglia)

Answer 23

are the other major component of the nervous system.

• Glia have many different functions but they do not transmit information like neurone
• Glia are smaller and more numerous than neurons

Question 24

Types of Glia:

Answer 24

Atrocytes
Microglia
Oligodendrocytes
Schwann cells
Radial glia

Question 25

Astrocytes:

Answer 25

A type of glia that absorbs chemicals released by axons and later returns those chemicals back to the axon to help synchronize the activity of neurons.

• Astrocytes remove waste products as well, particularly those created after neurons die.
• Astrocytes also cause blood vessels to dilate to bring in more nutrients at times of increased brain activity.
• They act as a recycling system for glutamate released by neurons (absorbing excess glutamate then converting it to glutamine and passing it back into the neurons). 


Question 26

Microglia:

Answer 26

Very small cells that remove waste material as well as viruses, fungi, and other microorganisms. 


• Act as part of the immune system
• They proliferate after brain damage and in most brain diseases
• They are necessary for the survival of certain neurons early in life
• Also contribute to learning by removing the weakest synapse

Question 27

Oligodendrocytes:

Answer 27

A type of glia that builds the myelin sheaths around certain neurons in the brain and spinal cord.

Question 28

Schwann cells:

Answer 28

A type of glia that builds the myelin sheaths around certain neurons in the periphery of the body. 
They surround and insulate certain vertebrate axons
- Also supply axon with nutrients necessary for its functioning

Question 29

Radial glia:

Answer 29

Guides the migration of neurons and the growth of axons and dendrites during embryonic development. 


Question 30

The blood-brain barrier:

Why is it necessary?

Answer 30

The mechanism that keeps most chemicals out of the vertebrate brain

a. The blood-brain barrier is needed because the brain lacks the type of immune 
system present in the rest of the body. 

b. Because neurons cannot be replicated and replaced, the barrier is in place to 
minimize the risk of irreparable brain damage. 

c. A wall is formed that keeps out most viruses, bacteria, and harmful chemicals. 

d. When viruses do enter, like the rabies virus, it can infect the brain and lead to 
death. 

e. A virus that enters your nervous system probably stays with you for life (e.g., 
chicken pox and shingles). 


Question 31

c. An active transport system

Answer 31

(a protein-mediated process that uses energy) exists to pump necessary chemicals, such as glucose, amino acids, purines, choline, some vitamins, iron and certain hormones through the blood-brain barrier. 


Question 32

a. Endothelial cells

Answer 32

cells form walls of the capillaries in the brain. These cells are tightly joined in the brain, blocking most molecules from passing.
- In the rest of the body, the endothelial cells are separated by large gaps. 


Question 33

Nourishment of Vertebrate Neurons

Answer 33

1. Almost all neurons depend on glucose (a simple sugar) for their nutrition. 

2. Neurons rely on glucose so heavily because glucose is practically the only nutrient 
that crosses the blood-brain barrier in adults. Ketones (a kind of fat) can also cross but are in short 
supply. 

3. A thiamine (vitamin B1) deficiency leads to an inability to use glucose, which 
could lead to neuron death and a condition called Korsakoff’s syndrome (a disorder marked by severe memory impairment). 

   - Caused by an inability to use glucose, common in chronic alcoholism

Question 34

A thiamine (vitamin B1) deficiency

Answer 34

leads to an inability to use glucose, which 
could lead to neuron death and a condition called Korsakoff’s syndrome (a disorder marked by severe memory impairment). 

- Caused by an inability to use glucose, common in chronic alcoholism

Question 35

The Resting Potential of the Neuron

- Electrical gradient/ polarisation

Answer 35

When at rest the membrane of a neuron maintains an electrical gradient (a difference in electrical charge between the inside and outside of the cell), also known as polarization. 


Question 36

resting potential of the neuron

Answer 36

In the absence of any outside disturbance (i.e., at rest), the membrane maintains an electrical polarization (i.e., a difference in electrical charge between two locations) that is slightly more negative on the inside relative to the outside. This difference in electrical potential or voltage is known as the resting potential. 

- A typical resting membrane potential is -70 millivolts (mV). This may vary from one neuron to another. 


Question 37

Forces Acting on Sodium and Potassium Ions (p. 10):

Answer 37

a. The neuron membrane is selectively permeable, which allows some molecules 
to pass freely (e.g., water, carbon dioxide, oxygen) while restricting others. Most large molecules and ions cannot cross the membrane. A few important ions cross through protein channels.
b. During the resting potential, chloride channels (or gates) remain open along the membrane, which allows ions to pass through. Potassium channels are mostly closed, causing potassium to cross the membrane slowly. Sodium gates remain closed, restricting the passage of sodium ions. 

c. Sodium-potassium pump: a protein complex found along the neuron membrane that transports three sodium ions outside of the cell while also drawing two potassium ions into the cell; this is an active transport mechanism (requires energy to function).
- The sodium-potassium pump causes sodium ions to be more than 10X more concentrated outside than inside. 

- Potassium ions more concentrated inside than out
d. When the membrane is at rest, two forces work on sodium ions (push into the cell):
- The electrical gradient: opposite electrical charges attract, so sodium 
(which is positively charged) is attracted to the negative charge inside 
the cell. 

- The concentration gradient (difference in distribution of ions between the inside and the outside of the membrane): Sodium is more concentrated outside the membrane than inside and is thus more likely to enter the cell than to leave it. 

o Given that both the electrical and concentration gradients tend to move sodium into the cell, sodium would be expected to quickly enter the cell. However, when the membrane is at rest, sodium channels are closed. 

e. Potassium ions are subject to the same two forces; however, the forces are in opposition to each other. Potassium ions are positively charged, so the electrical gradient tends to move potassium in, but since potassium is concentrated on the inside of the cell, the concentration gradient causes potassium to flow out of the cell. 


Question 38

Why a Resting Potential?

Answer 38

a. The advantage of the resting potential is to allow the neuron to respond quickly to a stimulus.
- Because the membrane did its work in advance by maintaining the concentration gradient for sodium, the cell is prepared to respond vigorously to a stimulus

Question 39

Action potential:

Answer 39

Messages sent by axons. 


Question 40

Hyperpolarization (increased polarization):

Answer 40

Occurs when the negative charge 
inside the axon increases (e.g., -70 mV becomes -80 mV).

Question 41

Depolarization (reduce polarization towards zero):

Answer 41

Occurs when the negative 
charge inside the axon decreases (e.g., -70 mV becomes -55 mV). 


Question 42

Threshold of excitation:

Answer 42

The level that a depolarization must reach for an action 
potential to occur.