Nerve Cell Physiology

Question 1

Cell body

Answer 1

Consists of two major components:
nucleus
cytoplasm

Question 2

Cytoplasm

Answer 2

protein molecules and an aqueous (watery) sub-
stance enclosed within the cell membrane

Contains many microscopic subcellular units called organelles which include mitochondria, ribosomes, lysosomes, rough and smooth endoplasmic reticulum (ER), and the Golgi apparatus.

Question 3

Axon

Answer 3

cytoplasmic extensions that extend from the cell body and mediate nerve impulses.

efferent - transmit information away from the cell body to other neurons, muscles or glands

do not produce their own protein

usually synapse with dendrites (axodendritic synapse)

Question 4

Dendrites

Answer 4

cytoplasmic extensions that extend from the cell body and mediate nerve impulses.

afferent (receptive)

transmit information to the cell body from other cells via synaptic sites

short and have many branches; sometimes have small spines that add to their arborization increasing the surface available for synapses with other nerve cells

Question 5

Nerve Cell

Answer 5

A nerve cell consists of three primary elements:
cell body (soma)
dendrites
axon

Question 6

organelles

Answer 6

microscopic subcellular units

include:
mitochondria
ribosomes
lysosomes
rough and smooth endoplasmic reticulum (ER)
golgi apparatus

Primary function to metabolize protein essential for growth and function of the cell body

Question 7

cylindrical microtubules

Answer 7

transportation network for cellular proteins

Question 8

cellular cytoskeleton

Answer 8

composed of long strands of proteins

microtubules - largest
neurofilaments
microfilaments - smallest

Question 9

nerve fiber

Answer 9

the axon and its myelin sheath covering

Question 10

axon hillock

Answer 10

the initial segment of the axon

Question 11

oligodendroglial cells

Answer 11

produce the myelin sheath in the CNS

Question 12

Schwann cells

Answer 12

produce the myelin sheath in the PNS

Question 13

nodes of Ranvier

Answer 13

intervals in the myelin sheath

action potentials jump from one NOR to the next (saltatory conduction)

Question 14

internode

Answer 14

a segment of myelin sheath between two nodes of Ranvier

Question 15

synapse

Answer 15

the space between the presynaptic terminal and the postsynaptic cell

includes three parts:

• presynaptic terminal - may be a clearly defined button or simply close proximity of cells
• synaptic cleft
• postsynaptic cell

Question 16

depolarization

Answer 16

changes in membrane potentials in which the cellular interior changes from negative (resting potential) to positive

Question 17

hyperpolarization

Answer 17

increased internal negativity across a cell membrane causing changes in voltage

Question 18

electrical synapse

Answer 18

present where extremely fast communication must occur; no neurotransmitters involved

Question 19

multipolar

Answer 19

many dendrites, one axon

most common

motor neuron; primary motor cortex; communicates w/ muscles to move

Question 20

bipolar

Answer 20

one dendrite, one axon

interneuron; in spinal cord; connect sensory info to brain

found in the retina and inner ear

Question 21

unipolar

Answer 21

T-shaped; one axon that divides in half

sensory neuron; only receive info

Question 22

neuroglia cells (glial cells)

Answer 22

located in gray matter; support and protect neurons

40 - 50x more neuroglia than neurons; develop into adolescence

Four types in the CNS:
astrocytes
oligodendroglia
ependymal
microglia

Two types in the PNS:
schwann
satellite

Question 23

astrocytes

Answer 23

glial cell of the CNS

function as connective tissue and provide skeletal support

protect the brain by forming external/internal limiting membranes; manage fluid

contribute to the blood-brain barrier by regulating transmission of substances across blood vessels

regulate extracellular concentration of ions

can degrade released neurotransmitters

seal a lesion with a cyst (large) or glial scar

Question 24

microglia

Answer 24

glial cell of the CNS

no normal function; only utilized after brain injury; phagocytose (engulf and digest) dead tissue, debris and pathogens

Question 25

ependymal cell

Answer 25

glial cell of the CNS

line the inner surface of the ventricles

form the internal limiting membrane with astrocytes

contribute the circulation of cerebrospinal fluid

Question 26

oligodendroglia

Answer 26

glial cell of the CNS

create the myelin sheath of axons in the CNS

Question 27

schwann cells

Answer 27

glial cell of the PNS

create the myelin sheath of axons in the PNS

Question 28

satellite cells

Answer 28

glial cell of the PNS

guiding cells, unsure of purpose, seem to be active in early development in guiding neural cells to proper locations

Question 29

nerve impulse

Answer 29

communication between nerve cells

have a chemical component underlying the electrical component

activate the release of a neurotransmitter in presynaptic neuron; the transmitter causes the adjacent post-synaptic receptors to open an ion channel; By selectively opening or closing an ion channel, the released neurotransmitter controls the excitability of next neuron

Question 30

action potential

Answer 30

electrical impulse representing a transient fluctuation in membrane potentials, which are propagated along axonal processes to activate postsynaptic terminals

results from charged particles (ions) moving through cell membranes

builds up in axon hillock – when enough stimuli is received, the axon can fire

Sodium (Na) and Potassium (K) ions pass through cell membranes – when cell becomes more positive (even if still negative) charge begins to build – at -50 (threshold) ions flow quickly until reach -20; then resets to -70 or resting potential; domino or wave effect; open/close cycle down the length of the axon, until the telodondria reached and neurotransmitter is released

Once the electrical voltage hit’s the 20+ range, it will automatically begin to shut down and start to repolarize (K+ will leave cell) - end result is hyperpolarization (resting potential)….the cycle will repeat.

Question 31

resting potential/state

Answer 31

the neuron is not excited or conducting an impulse

polarized state, unequal ion distribution inside/outside cell

Question 32

Sodium/Potassium pump

Answer 32

Transports Na out and K into the cell (typical cell has low Na and high K concentration inside cell)

Usually closed – only opens when brain needs fuel – neuron will break down ATP from mitochondria – the energy opens the pump gate

leak channels - open at rest - more permeable to K than Na

Question 33

Barriers to strong action potential

Answer 33

not enough charge
poorly functioning cell membrane
unhealthy dendrites
malfunctioning cell body parts
damaged myelin

Question 34

excitability

Answer 34

the cell’s response to various stimuli (chemical/temperature changes, electrical pulses, and mechanical stimulation) and conversion of response to nerve impulse or action potential

Question 35

absolute refractive period

Answer 35

a brief period following an action potential in which a cell is incapable of producing a second action potential

Question 36

Neural Regeneration

Answer 36

Neural cells can repair themselves, but they do not repair well or quickly; less capable of cell division and regeneration than other types of cells

Injured cells may not be able to transmit nutritive (trophic) substances to other cells

Axotomy affects not only the injured neuron but the postsynaptic neurons and neurons that innervate the injured neuron

Question 37

telodendria

Answer 37

fibers at the end of an axon; end with terminal button

Question 38

terminal button

Answer 38

establishes connection with another neuron, gland or muscle