Chapter 12: Nervous Tissue (Part 1) Flashcards
What systems maintain the internal coordination? (2)
endocrine & nervous system
Which system communicates using chemical messengers secreted into the blood?
endocrine
Which system employs electrical & chemical means to send messages?
nervous
3 basic tasks of the nervous system
- Receive info about changes in the body & transmit info to spinal cord & brain
- Brain & spinal cord process the info and determine response
- Brain & spinal cord issue commands to muscles & glands to carry out response
What are the 2 subdivisions of the nervous system?
- central nervous system (CNS)
- peripheral nervous system (PNS)
What is included in the CNS?
spinal cord & brain
What is the PNS composed of?
ganglia & nerves
nerves
a bundle of nerve fibers wrapped in fibrous connective tissue
ganglion
a knotlike swelling in a nerve where neuron cell bodies are concentrated
What are the 2 subdivisions of the PNS?
sensory & motor
sensory afferent division
carries sensory signals from various receptors to the CNS
somatic sensory division
carries signals from receptors in the skin, muscles, bones, & joints
visceral sensory division
carries signals from the viscera of the thoracic and abdominal cavities
afferent
towards the CNS
efferent
away from the CNS
motor efferent division
carries signals from the CNS to gland and muscle cells that carry out body responses
effectors
cells and organs that respond to commands from CNS
somatic motor division
carries signals to skeletal muscles
visceral motor division is also known as_____
autonomic nervous system
involuntary that carries signals to glands, smooth muscle
visceral motor division is divided into
sympathetic & parasympathetic system
sympathetic division
“fight or flight” response
tends to arouse body for action
parasympathetic division
“rest or digest”
tends to have calming effect
excitability
respond to environmental changes called stimuli
properties of neurons (3)
- excitability
- conductivity
- secretion
conductivity
neurons respond to stimuli by producing electrical signals
secretion
when electrical signal reaches end of nerve fiber and a chemical is secreted
______->________->________
afferent; interneurons; efferent
interneurons (3)
- lie entirely within the CNS
- carry out the integration function of the CNS
- 90% of neurons
integrative function
ability to process, store, and retrieve info to make decisions
soma (4)
- the control center of the neuron
- made of microtubules & neurofibrils
- no centrioles = no cell division
- inclusions
dendrites
vast number of branches that come from thick branches of the soma that receive signals from other neurons
axon?=______
nerve fiber
originates from mound on one side of the soma
branches of the axon?
axon collaterals
extensive complex of fine branches?
terminal arborization
axoplasm
cytoplasm of axon
axolemma
plasma membrane of axon
bipolar neuron
one axon and one dendrite
unipolar neuron
single process leading away from the soma
anaxonic neuron
many dendrites but no axon
axonal transport
two way passage of proteins, organelles, and other material along an axon
What are the 2 types of axonal transport? describe?
anterograde: movement down the axon from soma
retrograde: movement up the axon toward the soma
What helps guide materials along axon
microtubules
Motor proteins used to carry material along microtubules?
kinesin(anterograde) & dynein(retrograde)
fast anterograde vs fast retrograde transport
anterograde: for small particles, organelles, enzymes, synaptic vesicles (immediate)
retrograde: for recycled materials and pathogens
slow axonal transport (2)
- always anterograde
- damaged nerve fibers regenerate at a speed governed by this
neuroglia (4)
- outnumber neurons 50 to 1
- support & protect the neurons
- bind neurons together & form framework for nervous tissue
- allow signals to move fast
Neuroglial cells in CNS? (4)
- oligodendrocytes
- astrocytes
- ependymal cells
- microglia
Neuroglial cells in PNS? (2)
- schwann cells
- satellites cells
oligodendrocytes
form myelin sheath in CNS
ependymal cells
secrete & circulates cerebrospinal fluid
microglia
- immune system
- small macrophages formed WBC (monocytes)
astrocytes (2)
- busy (multiple functions)
- most abundant glial cell in CNS
functions of astrocytes (5)
- form supportive framework
- have perivascular feet to form blood brain barrier
- convert blood glu to lactate (generate energy)
- promote nerve growth factors
- regulate chemical composition (absorb excess neurotransmitter)
astrocytosis
when neuron is damaged, astrocytes form hardened scar tissue & fill space formerly occupied by the neuron
compartmentalized rough ER in soma
nissal bodies
schwann cells
produce myelin sheath in PNS
satellite cells (2)
- surround the neurosomas in ganglia
- provide electrical insulation around the soma
tumors
masses of rapidly dividing cells
brain tumors arise from ____
meninges & metastasis from nonneuronal tumors
gliomas (3)
- grow rapidly & highly malignant
- blood brain barrier decreases effectiveness of chemotherapy
- treatment with surgery or radiation
_______- can regenerate unlike neurons
neuroglia
myelin sheath
an insulating layer around the nerve fiber; consists of 20% protein & 80% lipid
The myelin sheath is created by the ______ in the CNS and the ______ in the PNS
oligodendrocytes; Schwann cells
myelination
production of the myelin sheath begins at week 14 of fetal development
How is the myelin sheath added to nerve fibers in the PNS?
by schwann cells repeatedly spiraling a single nerve fiber; no cytoplasm between the membrane
neurilemma (2)
- thick outermost coil of myelin sheath
- contains nucleus & most of cytoplasm
endoneurium
external to the neurilemma made of a fibrous connective tissue
How is the myelin sheath added to nerve fiber in the CNS?
oligodendrocytes reach out to myelinate several nerve fibers in its immediate vicinity
T or F nerve fibers in the CNS have neurilemma or endoneurium
FALSE
node of ranvier
gap between segments of myelin sheath
internodes
myelin-covered segments from one gap to the next
initial segment
short section of nerve fiber between the axon hillock and the first glial cell
trigger zone
the axon hillock & the initial segment (play a role in initiating a nerve signal)
multiple sclerosis
- oligodendrocytes & myelin sheath in the CNS deteriorate
- myelin sheath is hardened by scar tissue
- nerve conduction disrupted
- fatal 25-30 years after diagnosis
tay-sachs disease
a hereditary disorder of infants with an abnormal accumulation of glycolipid called ganglioside(GM2) in the myelin sheath
mesaxon
neurilemma wrapping of unmyelinated nerve fibers
The speed at which a nerve signal travels along a nerve fiber depends on what 2 factors?
- diameter of fiber
- presence or absence of myelin
Where is the signal conduction occur in a nerve fiber
along the surface
Which signal conduction is the fastest?
large & myelinated
denervation atrophy
due to loss of nerve contact by damaged nerve
When can regeneration of a damaged peripheral fiber occur?
- its soma is intact
- at least some of the neurilemma remains
axon hillock contains ___ & ____
trigger zone & initial segment
When cant fibers be regenerated?
if they are distal to the injury because macrophages clean up tissue debris
During regeneration of a never fiber what happens?
soma swells, ER break up, and the nucleus moves off center
regeneration tube is produced by what? (3)
schwann cells
basal lamina
neurilemma near injury
Can regeneration of damaged fibers in the CNS occur?
NO
nerve growth factor
a protein secreted by a gland, muscle, & glial cell and picked up by the axon terminals of the neuron that prevents cell apoptosis
resting membrane potential
-70mV (negative means more negatively charge particles on the inside)
charge difference across the plasma membrane
What maintains the resting membrane potential?
Na/K pump (3 Na for 2 K)
What is the greatest influence on the RMP?
K because the membrane is more permeable to it & its more concentrated in the ICF
_____ is concentrated in the ICF & _____ is concentrated in the ECF when a membrane is at resting membrane potential?
K inside and Na outside
local potentials
(short range change)
disturbance in membrane potential when a neuron is stimulated; when a short current is produced by Na diffusing in that travels toward the cell trigger zone
process of neuron response (4)
- begins at the dendrites
- spreads through the soma
- travels down the axon
- ends at the synaptic knobs
what causes a membrane to depolarize?
when a neuron is stimulated by chemical, light or heat that causes Na channels to open and Na rushes in which results in the cell becoming less negative
action potential
more dramatic change produced by a voltage regulated ion gates in the plasma membrane; can not be regenerated by a soma
threshold
- 55mV
- critical voltage to which local potential must rise to open the voltage-regulated gates
- once reached a neuron fires and produces an action potential
spike (2)
when more and more Na+ channels open in a positive feedback cycle at the trigger zone that creates a rapid rise in the membrane voltage
-often called an action potential
hyperpolarization
the effect of leaving K+ gates open longer than Na+
What is affected during an action potential?
a thin layer of the cytoplasm next to cell membrane
action potential vs. local potential
action: all or nothing; nondecremential (do not get weaker with distance); irreversible
local: graded (vary in magnitude w/ stimulus strength);decremential ;reversible; either excitatory or inhibitory
