Chapter 12: Neurons

Question 1

neurons

Answer 1

functional unit of the nervous system

• generate, transmit, recieve action potentials

Question 2

parts of a neuron

Answer 2

cell body, dendrites, axon

Question 3

cell body contains

Answer 3

• nucleus, nucleoli
• lysosomes
• mitochondria
• golgi complex
• lipofuscin pigment
• residues of undigested lysosomal material
• nissal bodies and neurofibrils

Question 4

nissal bodies

Answer 4

clusters of dark staining granules

Question 5

neurofibrils are found where?

Answer 5

abundant in cell body, dendrites and axon

Question 6

dendrites

function

characteristics, for what purpose?

Answer 6

• recieves + relays impulses twd cell body
• many
• contain little spines called gemmules on tips that increase surface area to recieve more axon surfaces

Question 7

axon conducts impulses away from ________ towards _______ (6)

function

how many per neuron

Answer 7

conducts impulses away from the cell body twds dendrites, axon, or cell body of another neuron, muscle or gland (effector)

• one

Question 8

parts of axon (6)

Answer 8

• axon hillock: pryamid shaped part on soma
• initial segment: region of axon btwn hillock and begining of myelin sheath, AP is generated
• axolemma: plasma membrane of axon
• axoplasm: cytoplasm of axon
• axon terminal: branches at terminal end of axon
• synaptic buttons: bulbs at terminal, have ACh

Question 9

how are neurons classified?

Answer 9

according to the # and arrangement of axons and dendrites extending from the soma

Question 10

monopolar neuron

Answer 10

has 1 process extending from the cell body

• 1 branch serves as an axon
• 1 as a dendrite

Question 11

bipolar

Answer 11

has 2 processes extending from the cell body

• 1 is an axon
• other is dendrite

Question 12

multipolar

Answer 12

• most common
• has many processes extending from the cell body
• one is axon
• one is dendrite

Question 13

can neurons reproduce?

Answer 13

no, they dont have centrioles

Question 14

% of all neurons in the nervous system are interneurons

Answer 14

90%

Question 15

types of neuroglia

Answer 15

astrocytes, oligodendrocytes, microglia, ependymal cells, scwann cells, satellite cells

Question 16

astrocyte

description

Answer 16

associated with blood vessels in the CNS

• irregularly shaped
• many cytoplasmic extensions

Question 17

oligodendrocytes

function

description

Answer 17

• produce the myelin sheath in the CNS
• controls movement
• smaller than astrocytes
• myelin sheath covers + insulates axons
• can myelinate more than 1 cell

Question 18

microglia

where does it originate from?

Answer 18

• phagocytes in the CNS thought to have come from macrophages
• comes from monocyte

Question 19

ependymal cells

function

where is it found

Answer 19

• produce cerebrospinal fluidin CNS
• cuboidal or columnar cells that line ventricles of brain + central canal

Question 20

schwann cells

function

description

Answer 20

• produce the neurolemma sheath in the PNS
• wraps body around axon 20-30 times
• cytoplasm and nucleus is squeezed into periphery
• outermost layer represents the neurolemma

Question 21

neurolemma

Answer 21

• noncontinuous
• nodes of ranvier aka sheath of shwann

Question 22

satellite cells

Answer 22

in PNS ganglia (collection of cell bodies of neurons that lie outside the CNS)

Question 23

neuroglia in CNS

Answer 23

astrocytes, oligodedrocytes, microglia, ependymal cells

Question 24

neuroglia in PNS

Answer 24

schwann cells, satellite cells

Question 25

neuropil represents

Answer 25

neurofilaments, neurfibrils, all cytoplasmic extensions of neuroglia

Question 26

myelin sheath description can have?

Answer 26

multilayered lipoprotein casing that covers the axons of most neurons * can have unmyelinated axons

Question 27

what does sheath of schwann do? (2)

Answer 27

insulates the axon and increases the speed of nerve impulse conduction

Question 28

schwann cells produce\_\_\_\_ in the \_\_\_\_\_

Answer 28

myelin sheath, PNS

Question 29

outer layer of the schwann cell is called the _____ and is found only around axons in the \_\_\_\_

Answer 29

neurolemma, PNS

Question 30

what does the neurolemma aid in?

Answer 30

regeneration in an injured axon

Question 31

what are the gaps in the myelin sheath called?

Answer 31

nodes of ranvier

Question 32

what happens when there is damage or death to a neurons cell body?

Answer 32

degeneration of attached dendrites + axons * if nerve fiber is cut, regeneration is only possible if it is covered by schwann cell or neurolemma * closer damage to CNS, the less likely it will repair * distal to cute regenerates, leaving and empty meurolemma tube

Question 33

do spinal cord injuries regenerate?

Answer 33

no

Question 34

oligodendrocytes form ____ for CNS axons

Answer 34

myelin sheaths * no neurolemma or regrowth after injury

Question 35

white matter

Answer 35

aggregations of myelinated axons * brain: inner * spinal cord: outer

Question 36

gray matter

Answer 36

neuron cell bodies, dendrites, bundles of unmyelinated axons and neuroglia * brain: outer * spinal cord: inner

Question 37

spinal cord

Answer 37

gray matter forms an H shaped inner core surrounded by white matter

Question 38

brain

Answer 38

an outer shell of gray matter covers the cerebral hemispheres

Question 39

nucleus

Answer 39

mass of nerve cell bodies and dendrites inside the CNS