Chapter 12.1 : Nervous Tissue Flashcards
What two systems regulate homeostasis?
endocrine system and nervous system
Endocrine system
communicates by means of chemical messengers (hormones) secreted into to the blood // slow
Nervous system
employs electrical (action potentials) and
chemicals (neuro-transmitters) to send
messages between cell to cell // fast
The nervous system carries out its task in what three steps?
– sense organs (receptor) [1. receive information] about
changes in the body and the external environment then
transmits coded messages to the spinal cord and the
brain
– brain and spinal cord [2. processes this information],
relates it to past experiences, and determine what
response is appropriate to the circumstances
– brain and spinal cord [3. issue commands] to muscles and
gland cells to carry out such a response
What are the two anatomical divisions of the nervous system?
Central nervous system and peripheral nervous system
Central nervous system (CNS)
– brain and spinal cord enclosed in bony coverings
– enclosed by cranium and vertebral column
– nuclei – isolated “islands” of grey matter within CNS
nuclei
isolated “islands” of grey matter within CNS
Peripheral nervous system (PNS)
– all the nervous system except the brain and spinal cord
– composed of nerves and ganglia
* nerve – a bundle of nerve fibers (axons) wrapped in fibrous connective tissue
* ganglion – isolated “islands” of grey matter within PNS // soma outside CNS // a knot-like swelling in a nerve where neuron cell bodies are concentrated
nerve
a bundle of nerve fibers (axons) wrapped in fibrous connective
tissue
ganglion
isolated “islands” of grey matter within PNS // soma outside
CNS // a knot-like swelling in a nerve where neuron cell bodies are concentrated
How is the peripheral nervous system subdivided?
Somatic Nervous System, Autonomic Nervous System, and Enteric Nervous System.
Somatic refers to which parts of the body?
muscles, bones, joints, and the skin
Visceral refers to which parts of the body?
Internal organs
What is the target tissue of the somatic nervous system?
Skeletal muscle
What is the target tissue of the autonomic nervous system?
smooth muscle, cardiac muscle, and glands
What is the target tissue of the enteric nervous system?
Smooth muscle, glands, and endocrine cells of GI tract
Sensory division neurons
– carries sensory signals from receptors located in skeletal muscles and other tissues to the CNS
– informs the CNS of stimuli thoughout the body
somatic sensory neurons (division)
carries signals from receptors in the skin, muscles, bones,
and joints
visceral sensory neurons (division)
carries signals from the viscera of the thoracic and
abdominal cavities /// heart, lungs, stomach, blood
vessels, and urinary bladder
Motor Division Neurons
These signals originate in CNS and flow out to the
effectors
What are the two types of Motor division neurons?
somatic and visceral
Visceral motor neurons
by way of the Autonomic Nervous System = to glands, smooth muscle, and cardiac
Effectors
tissues that respond to commands
from the CNS
Somatic Motor Division (efferent fibers) signal originates from brain’s ________ ______
precentral gyrus
Visceral motor division (autonomic nervous system)
– carries signals to glands, cardiac muscle, and smooth muscle
– involuntary reflexes regulated by two division // also called
visceral reflexes (e.g. salavation, voiding urinary bladder)
What are the two divisions of the Visceral motor division (autonomic nervous system)
sympathetic division and parasympathetic division
sympathetic division
– tends to arouse body for action
– accelerating heart beat and respiration, while inhibiting
digestive and urinary systems
parasympathetic division
– tends to have calming effect
– slows heart rate and breathing
– stimulates digestive and urinary systems
Universal Properties of a Neuron
- Excitability (irritability) /// respond to environmental
changes called stimuli - Conductivity /// neurons respond to stimuli by
producing electrical signals that are quickly
conducted to other cells at distant locations - Secretion /// when electrical signal reaches end of
nerve fiber, a chemical neurotransmitter is secreted
that crosses the gap and stimulates the next cell - Note: The neuron’s function requires an electro-chemical
form of communication! // its not just an electrical signal
and not just a chemical signal but both which occurs at the
synapse
neuron’s function requires an _______
form of communication!
electro-chemical
Neurons are defined by using either _______ or ______ criteria
structural ; functional
Soma
Control center of the neuron
also called neurosoma, cell body, or perikaryon
has a single, centrally located nucleus with large nucleolus
cytoplasm contains mitochondria, lysosomes, a Golgi complex, numerous inclusions, extensive rough endoplasmic reticulum, and a cytoskeleton.
The cytoskeleton consists of dense mesh of microtubules
and neurofibrils
compartmentalizes rough ER into dark staining Nissl
bodies
neurofibrils
bundles of actin filaments
Nissl bodies
compartmentalizes rough ER into dark staining
cytoskeleton of soma consists of dense mesh of microtubules
and neurofibrils
Do soma have centrioles?
no
Inclusions bodies
glycogen granules, lipid droplets,
melanin
Lipofuscin / inclusion bodies
(golden brown pigment
produced when lysosomes digest worn-out organelles)
* lipofuscin accumulates with age
* wear-and-tear granules
* most abundant in old neurons
Dendrites
Primary site for receiving signals from
other neurons = “the receptors”
* Transducers = receptors
* Stimulus creates local potential ///
graded potentials
* the more dendrites the neuron has, the
more information it can receive and
incorporate into decision making
* provide precise pathway for the reception
and processing of neural information
Axon is commonly called
nerve fiber
axon originates from a mound on one side of
the soma called the
axon hillock or trigger zone
axoplasm
cytoplasm of axon
axolemma
plasma membrane of axon
only ___ axon per neuron
1
axon collaterals
branches of axon
Schwann cells
myelin sheath enclose axon
terminal “arborization”
distal end of axon, complex of fine branches / like in a tree!
synaptic knob (terminal button)
little swelling that forms a junction (synapse) with the next cell. neuron to muscle or neuron to glandular tissue
Stores neurotransmitters
There are many types of neurotransmitters. Some are _________ others ________
stimulatory ; inhibitory
Neurotransmitters made in _____ and transported down ___ in
vesicles
soma ; axon
Neurotransmitters released from synaptic knob via ________
exocytosis
Synaptic knob forms part of the ______ // the presynaptic
membrane
synapse
Explain the events at a chemical synapse:
synaptic transmission.
- An action potential in the presynaptic neuron triggers Ca2+ channels in the axon terminal to open.
- Influx of Ca2+ causes synaptic vesicles to release neurotransmitters into the synaptic cleft.
- Neurotransmitters bind to receptors on the postsynaptic neuron.
- Ion channels open, leading to a local potential and possibly an action
Interneurons (association neurons)
are confined to the CNS.
receive signals from many neurons and carry
out the integrative function
90% of all neurons are
interneurons
multipolar neuron
– one axon and multiple dendrites
– most common
– most neurons in the brain and
spinal cord
bipolar neuron
– one axon and one dendrite
– olfactory cells, retina, inner ear
unipolar neuron
– single process
– sensory from skin and organs to
spinal cord
anaxonic neuron
– many dendrites but no axon
– help in visual processes
How many neurons are in the nervous system?
a trillion (10 to the 12th power) neurons
How many neurons are in an organism?
50 trillion
Neuroglia outnumber the neurons by as much as
50 to 1
Neuroglia (also called glial cells)
– Support, protect, and enhance function of neurons
– Bind neurons together and form framework for nervous
tissue
– In fetus, guide migrating neurons to their destination
– If the surface of a mature neuron is not in synaptic contact
with another neuron then non-synaptic surface is covered
by glial cells /// prevents neurons from touching each
other /// gives precision to conduction pathways
The CNS has how many types of glial cells? What are they?
4
oligodendrocytes
ependymal cells
microglia
astrocytes
oligodendrocytes form _______ _______ in CNS
myelin sheaths
each arm-like process on an oligodendrocytes wraps around a ______ ______, forming an insulating layer that ______ ___ signal conduction
nerve fiber ; speeds up
ependymal cells ____ internal cavities of the brain
line
ependymal cells are ______ epithelium with ___ on apical surface
cuboidal ; cilia
ependymal cells ______ and _______ cerebrospinal fluid (CSF)
secrete ; circulate
cerebrospinal fluid (CSF)
clear liquid that bathes the CNS
microglia are
small, wandering macrophages
microglia are formed by white blood cell called __________
monocytes
microglia are thought to perform a complete ______ on the brain tissue several times a day
checkup
microglia wander in search of cellular debris to _________
phagocytize
Astrocytes are the most _______ glial cell in CNS
abundant
What covers entire brain’s surface and most nonsynaptic
regions of the neurons in the gray matter of the CNS?
Astrocytes
Astrocytes form a supportive _______ of nervous tissue
framework
Astrocytes have extensions (perivascular feet) that
contact blood capillaries that stimulate them to
form a tight seal called the
blood-brain barrier
Astrocytes convert blood glucose to ______ and supply this to the neurons for _______
lactate ; nourishment
Nerve growth factors secreted by astrocytes promote
______ ______ and _______ _______
neuron growth ; synapse formation
Astrocytes communicate electrically with neurons and may
influence ______ ______ // role in memory not
understood
synaptic signaling
Astrocytes regulate chemical composition of tissue fluid by
absorbing excess ______________ and ____
neurotransmitters ; ions
astrocytosis or sclerosis
when neuron is damaged, astrocytes form hardened scar tissue and fill space formerly occupied by the neuron
Two types of glial cells occur in PNS. What are they?
Schwann cells and satellite cells
Schwann cells
- envelope nerve fibers in PNS
- wind repeatedly around a nerve fiber
- produces a myelin sheath similar to the ones
produced by oligodendrocytes in CNS - assist in the regeneration of damaged fibers
Satellite cells
- surround the neurosomas in ganglia of the PNS
- provide electrical insulation around the soma
- regulate the chemical environment of the neurons
an insulating layer around a nerve fiber
Myelin sheath
– formed by [oligodendrocytes] in CNS
– formed by [Schwann cells] in PNS
– consists of the plasma membrane of glial cells (20%
protein and 80 % lipid)
production of the myelin sheath
Myelination
Myelination begins the ____ week of fetal development
14th
- proceeds rapidly during infancy
- completed in late adolescence
- dietary fat is important to nervous system
development (Danger! Trans Fat!)
Schwann cell
spirals repeatedly around a single nerve fiber
lays down as many as a hundred layers of its own membrane
no cytoplasm between the membranes
neurilemma
thick outermost coil of myelin sheath ///
contains nucleus and most of its cytoplasm
external to neurilemma is basal lamina and a thin layer of
fibrous connective tissue
endoneurium
oligodendrocytes cannot ______ around nerve fibers like
Schwann cells
migrate
nerve fibers in CNS have no _______ or
_______
neurilemma ; endoneurium
Many Schwann cells and oligodendrocytes are needed to cover one ____
nerve fiber
mesaxon
neurilemma wrapping of unmyelinated nerve fibers
Speed at which a nerve signal travels along a nerve fiber depends on two factors
Diameter of fiber
- larger fibers have more surface area and conduct signals
more rapidly
Presence or absence of myelin / amount of myelination
- myelin further speeds signal conduction
Temperature (lower speed when cooled)
-
slow signals supply
the stomach and dilate pupil where speed is less of an issue
fast signals of the nerve fiber supply
skeletal muscles and transport sensory signals for vision and balance
regeneration of a damaged peripheral nerve fiber can occur only if ….
– The soma is not damaged but intact
– Neurilemma must be intact
axon distal to the injury cannot survive and they
degenerate
macrophages engulf tissue debris inside tubular Schwan cells
distal to point of damage
due to loss of nerve growth factor from neuron’s
target cell,
the soma swells, ER breaks up, and nucleus
moves off center
Peripheral Motor Nerves are not able to regenerate their
cell bodies
axon stump sprouts multiple ________ _______
growth processes
regeneration tube
formed by Schwann cells, basal lamina, and the neurilemma
near the injury
regeneration tube guides the growing sprout back to the original target cells and
re-establishes synaptic contact
In regeneration of peripheral motor nerve axons, the nucleus
returns to normal shape
regeneration of damaged nerve fibers in the CNS may
not occur
Denervation Atrophy
Atrophy of muscle due to loss of nerve contact by damaged nerve
nervous pathway are a series of cells separated by
gaps called ________.
synapses
nerve growth factor (NGF) are what and do what 2 things?
a protein secreted by a gland, muscle, and glial cells and picked up by the axon terminals of the neurons.
– prevents apoptosis (programmed cell death) in growing neurons
– enables growing neurons to make contact with their target cells
many proteins made in soma must be transported to
axon terminal
axonal transport
two-way passage of proteins, organelles,
and other material along an axon
anterograde transport and retrograde transport
microtubules
guide materials along axon
motor proteins
carry materials “on their backs” while
they “crawl” along microtubules
kinesin
motor proteins in anterograde transport
dynein
motor proteins in retrograde transport
fast axonal transport
rabies, herpes simplex, tetanus, polio viruses
slow axonal transport
damaged nerve fibers regenerate at a speed governed by slow axonal transport
tumors
mature neurons have little or no capacity for mitosis and seldom form tumors
current science tells us certain neurons do have the capacity to
undergo mitosis however
most neurons are in G zero
brain tumors arise from:
