Ch. 1 - Nerve Cells & Nerve Impulses

Question 1

Neurons

Answer 1

• Neurons receive information and transmit it to other cells

- Approximately 86 billion neurons in adult human brain

Question 2

Membrane

Answer 2

-The surface of a cell which separates the inside of the cell from the outside environment

Question 3

Nucleus

Answer 3

-Structure that contains the chromosomes

Question 4

Mitochondria

Answer 4

• The structure that performs metabolic activities, providing the energy that the cell uses for all activities
• Mitochondria have genes separate from those in the nucleus of the cell, and mitochondria differ from one another genetically

Question 5

Ribosomes

Answer 5

• The sites within a cell that synthesize new protein molecules
• Some ribosomes float freely in the cell, but some are attached to the endoplasmic reticulum (ER)

Question 6

Endoplasmic Reticulum (ER)

Answer 6

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

Question 7

Motor neuron

Answer 7

-A motor neuron has it’s soma (cell body) in the spinal cord, and receives excitation though its dendrites and conducts impulses along its axon to a muscle

Question 8

Sensory neuron

Answer 8

• Is specialized at one end to be highly sensitive to a particular type of stimulation, such as light, sound, or touch.
• Tiny branches lead directly from the receptors into the axon, and the cell’s soma is located on a little stalk off the main trunk

Question 9

Dendrites

Answer 9

-Are branching fibers that get narrower near their ends
-The dendrites surface is lined with specialized
synaptic receptors”, at which the dendrite receives information from other neurons.
-The greater the surface area of a dendrite, the more information it can receive
-Many dendrites contain DENDRITIC SPINES

Question 10

Dendritic spines

Answer 10

-Short outgrowths on dendrites that increase the surface area available for synapses

Question 11

Cell body (soma)

Answer 11

• Contains the nucleus, ribosomes, and mitochondria
• Most of a neuron’s metabolic work occurs here
• The cell body is also covered with synapses on its surface, similar to the dendrites

Question 12

Axon

Answer 12

• Is a thin fiber of constant diameter
• The axon conveys an impulse toward other neurons, an organ, or a muscle.
• Axons can be more than a meter long
• A neuron can have many dendrites, but only ONE axon, but the axon may have branches
• The end of each branch has a swelling, called a PRESYNAPTIC TERMINAL

Question 13

Myelin sheath

Answer 13

-Many vertebrate axons are covered with an insulating material called a myelin sheath, with interruptions (spaces) known as NODES OF RANVIER

Question 14

Presynaptic terminal

Answer 14

• A swelling at the end of axon branches

- At that point the axon releases chemicals that cross through the junction between that neuron and another cell

Question 15

Afferent axon

Answer 15

• Brings information INTO a structure

- Every sensory neuron is an afferent to the rest of the nervous system

Question 16

Efferent axon

Answer 16

• Carries information AWAY from a structure

- Every motor neuron is an efferent from the nervous system

Question 17

Interneuron (or intrinsic neuron)

Answer 17

-If a cell’s dendrites and axon are entirely contained within a single structure, the cell is an interneuron or intrinsic neuron

Question 18

Astrocytes

Answer 18

• A star-shaped glia cell, which wraps around the synapses of functionally related axons
• Astrocytes are important for generating rhythms , such as your rhythm of breathing
• They alose dilate the blood vessels to bring more nutrients into brain areas that have heightened activity

Question 19

Microglia

Answer 19

• Tiny cells that act as part of the immune system, removing viruses and fungi from the brain
• They also contribute to learning by removing the weakest synapses

Question 20

Oligodendrocytes and Schwann cells

Answer 20

• Oligodendrocytes in the brain and spinal cord and Schwann cells in the periphery of the body build the myelin sheaths that surround and insulate certain vertebrate axons
• They also supply an axon with nutrients necessary for proper functioning

Question 21

Radial glia

Answer 21

• Guide the migration of neurons and their axons and dendrites during embryonic development
• When embryological development finishes, most radial glia differentiate into neurons, and a smaller number differentiate into astrocytes and oligodendrocytes

Question 22

Blood brain barrier

Answer 22

• The mechanism that excludes most chemicals from the vertebrate brain
• Endothelial cells form the walls of the capillaries. In the brain, they are joined so tightly that they block viruses, bacteria, and other harmful chemicals from passage
• Oxygen and carbon dioxide are small, uncharged molecules that can pass through the cell walls freely
• Molecules that dissolve in the fats of the membrane also cross easily (ex. vitamins A and D, drugs such as antidepressants and even heroin)

Question 23

Active transport

Answer 23

-A protein-mediated process that expends energy to pump chemicals from the blood into the brain

Question 24

Electrical gradient (AKA polarization)

Answer 24

-A difference in electrical charge between the inside and outside of the cell

Question 25

Resting potential

Answer 25

- The electrical potential inside the membrane is slightly negative with respect to the outside, mainly because of negatively charged proteins inside the cell. This difference in voltage is called the resting potential - The resting potential prepares the neuron to respond rapidly

Question 26

Selective permeability

Answer 26

- Some chemicals pass through the membrane more freely than others do - Oxygen, carbon dioxide, urea, and water cross freely through channels that are always open

Question 27

Sodium-potassium pump

Answer 27

- A protein complex, repeatedly transports three sodium ions out of the cell while drawing two potassium ions into it - The sodium-potassium pump is an active transport that requires energy

Question 28

Concentration gradient

Answer 28

-The difference in distribution of ions across the membrane

Question 29

Action potentials

Answer 29

-Messages sent by axons

Question 30

All-or-none law

Answer 30

-The amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold

Question 31

Propagation of the action potential

Answer 31

- During an action potential, sodium ions (Na) enter a point on the axon - Temporarily, that spot is positively charged in comparison to neighbouring areas along the axon - The positive ions flow within the axon to neighbouring regions - The positive charges slightly depolarize the next area of the membrane, causing it to reach its threshold and open its voltage-gated sodium channels - Then the membrane regenerates the action potential at that point. In this manner the action potential travels along the axon

Question 32

Myelin

Answer 32

-An insulating material composed of fats and proteins

Question 33

Saltatory conduction

Answer 33

- The jumping of action potentials from node to node | - A myelinated axon admits sodium only at its nodes

Question 34

Refractory period

Answer 34

- Remember that at the peak of the action potential, the sodium gates snap shut - As a result, the cell is in a refractory period during which it resists the production of further action potentials

Question 35

Absolute refractory period

Answer 35

- The first part of the refractory period | - During this part, the membrane cannot produce another action potential, regardless of the stimulation

Question 36

Relative refractory period

Answer 36

- The second part of the refractory period | - During this part, a stronger-than-usual stimulus is necessary to initiate an action potential

Question 37

Local neurons

Answer 37

- Many small neurons have no axon. - Neurons without an axon exchange information with only their closest neighbours, therefore we call them local neurons - Because they do not have an axon, they do not follow the all-or-none law - When a local neuron receives information from other neurons, it has a graded potential

Question 38

Graded potential

Answer 38

-A membrane potential that varies in magnitude in proportion to the intensity of the stimulus