Exam 3: Chapter 12 Nervous Tissue Flashcards
The nervous system detects _______ changes.
environmental changes
These environmental chanegs impact the body and works in tandem with what other system?
endocrine
What is hte nervous system responsible for?
-responsible for all our behaviors, memories, and movement
How does the nervous system accomplish everything it is responsible for?
able to accomplish this because of the excitable characteristics of nervous tissue which allow for the generation of nerve impulses
What are the two divisions of the nervous system?
central nervous system and the peripheral nervous system
What are the three fundamnetal steps of the nervous tissue?
sensory, interpretation, motor response occurs
what is happening in the sensory step?
detecting internal and external stimuli
What are the two functional divisions of the nervous system?
sensory (afferent) divisions and motor (efferent) division
Which fibers are used in the afferent division?
somativ afferent fibers and visceral afferent fibers
What does the somatic afferent fibers function to do?
convey impulses from skin, skeletal musces, and joints
What do the visceral afferent fibers to do?
convey impulses from visceral organs
What does the motor (efferent) division function do?
transmits impulses from the CNS to the effector organs
What are the two motor systems within the peripheral nervous system?
somatic (voluntary) motor system and the autonomic (involuntary) motor system (ANS)
What is the function of the voluntary motor system?
conscious control of skeletal muscles
What is the function of the autonomic (involuntary) motor system>
control visceral motor nerve fibers regulate smooth muscle, cardiac muscle, and glands
What are the two functional subdivisions of the autonomic motor system?
sympathetic and parasympathetic
What are neurons?
functional units of the nervous system, fomring complex processing networks within the brain and spinal cord that bring all regions of the body under the CNS control
Neuroglia are?
smaller than neurons, however, they greatly outnumber nuerons. They act to support and maintains the neuronal networks
What are the special characteristics of neurons?
long-lived cells
amitotic
high metabolic rate
plasma membrane functions in electrical signaling and cell to cell interactions during development
What does amitotic mean?
cannot divide
What does the high metabolic rate depend on?
depends on continuus supply of oxygen and glucose
What does the plamsa membrane function in doing for neurons?
electrical signaling and cell to cell interactions during developments
Most neurons contain…
dnedrites
cell body
axon
axon terminals
there are several types of neurons, what are some of the differences?
some lack dendrites
some lack axons
synapses that connect an axon to another axon or a dendrite to another dendrite
What do dendrites look like?
short, tapering, and diffused branches
Dendrites are what part of the of the neruon/
receptive, input region of the nueruon
What do the dendrites do?
convey electrical signals toward the cell body as graded potentials
The cell body is the ________ center of a neuron
biosynthetic
What does the cell body look like?
- a spherical nucleus with nucleolus
- well-developed Golgi -apparatus
- Rough ER
- contains the axon hillock
What is the Rough ER of a neuron called?
Nissil bodies
What is the axon hillock?
cone-shaped area from whcih axon arises
Axons conduct impulses _____ from the cell body toward another _____ or _____ _____?
away, toward, neuron or effectory cell
What is the initial segment?
beginning of the axon
What is the trigger zone?
junction between the axon hillock and the initial segment
Axons contain numerous _____ ______.
terminal branches
What are the terminal branches known as?
telodendria
axons contain knoblike ___ ________
axon terminals
axon terminals are the?
secretory region of the neuron that releases neurotransmitters to excite or inhibit other cells
what are the spaces in between Schwann cells?
nodes of Ranvier
What are the types of axon movement?
slow axon transport, and fast axon transport
Slow axonal transport functions in
- supplying new axoplasm to developing or regenerating axons
- replenishes axoplasm in growing and mature axons
Fast axonal transport has two types of axonal transport, what are they?
anterograde (forward) and retrograde (backward)
Anterograde (forward) transport is what
the direction that moves organelles and synaptic vesicles from the cell body to the axon terminal
Retrograde (backward) transport is
the direction that moves membrane vesicsles and other cellular materials from the axon terminals to the cell body to be degraded or recycled
What are the 3 types of fucntional classifications of neurons
sensory (afferent)
- interneurons (association neruons)
- motor neurons (efferent)
What are sensory (afferent) neurons function?
transmits impulses from sensroy receptors Toward the CNS
What are the functions of internuerons (association neurons)?
shuttle signals through CNS pathways
Internuerons are most entirely within what division of the nervous system?
CNS
Moro neurons (efferent) carry…
impulses from CNS to efferent cells and organs
What are neuroglia?
support cells that dont generate or conduct nerve impulses
how do neuroglia support neurons?
forming the blood brain barrier (BBB)
- forms myelin sheaths (nerve insulation) around neuronal axons
- making cerebral spinal fluid that circulates around the brain and spinal cord
- participates in phagocytosis
What are teh different types of neuroglia cells?
astrocytes, microglia, satellite, Schwann cells,
what are astrocytes?
most abundant and maintian chemical environement
microglia function to
migrate to injured tissue and phagocytize
satellite cells function to
maintian the chemical envirnement in the CNS
Schwann cells are
vital to regeneration of damaged PNS nerve fibers
What is myelination?
process of forming myelin sheath which insulates and increases nerve impulse speed
Myelin sheaths are a ______-_____ sheath
protein-lipid
Myelin sheaths are large in ______
diameter
In the CNS, what are the myelin sheaths made by?
oligodendrocytes
in the PNS, what cells form the myelin sheaths?
Schwann cells
Myelin sheaths in the PNS are made by…
schwann cells wraping many times around the axon
the myelin sheath is _____ layers of the schwann cell _______
concentric, membrane
Neruolemma is the
peripheral bulge of schwann cell cytoplasm
What is the process for Schwann cells forming the myelin sheath
- schwann cell envelops an axon
- schwann cell rotate aroudn axon wrapping its plasma membrane loosely around in its successive layers
- schwann cell cytoplasm is forced from between membranes. The tiht memrbane wrappings surrounding the axon from the myelin sheath
What are the nodes of ranvier?
Gaps in the myelin sheath
For every schwann cell that wraps around a portion of the axon, there are _____ nodes of ranvier formed
Two
When does myelin increase?
Increases from birth to maturity
What is multiple sclerosis?
Destruction of myelin sheaths
Why is an infnats response to stimuli niether rapid or as corrdinated as an adult?
Because mylein sheaths are still forming
Thin nerve fibers are_____
Unmyelinated
One ______ ______ may ___________ enclose ____ or more unmyelinated axons
Schwann cell, incompletely, 15
How are the myelin sheaths formed in the CNS?
Fomred by processes of oligodendroytes, not the whole cells
In the myelin sheaths of the CNS what are still present?
Nodes of ranvier
What is not present in the myelin sheaths of the CNS?
Neurolemma
The thinnest fibers are __________.
unmyelinated
What is gray matter?
Mostly neruon cell bodies with unmyeoinated fibers and houses the densdrite portions of neurons
What is white matter?
Dense collections of myelinated axons from many neuorns
Cell body clusters are called what in the CNS and what in the PNS?
CNS-> nuclie
PNS -> ganglia
Axons and dendrite bundles are called what in the CNS and what in the PNS?
Tracts in the CNS an
Nerves in the PNS
The cell bodies lose their mitotic function at?
Birth
The cell bodies can only be repaired through ________ after injury
Regneration
The regeneration of neurons depends largely upon …?
The Schwann cells in the PNS
Regeneration essentially doesn’t happen at all in the?
Why does this occur?
CNS;
Becuaes the astrocytes form scar tissue when they neurons are injured
When an axon is injured, the _________ aids in the regeneration
Neuronlemma
How does the neurolemma assist in the regneration of the axon?
By formaing a regeneration tube that guides and stimulates regrowth of the axon
What is demyelination?
Loss/destrution of sheaths
What causes demyelination?
May result from disease, radiation, chemotherapy
What can be a result of demyelination?
May cause nerve deteriation
What is the neruolemma?
Outermost layer of nerve fibers in the PNS
How is the neurolemma different from the axon or myelin sheath?
It doesn’t degenerate after a nerve has been cut or crushed.
The neurolemma forms what in the nerve regeneration process?
The regenration tube
In the CNS, axons are myleinated by __________ which is why they lack _________.
Oligodendrocytes, neurolemma
Wrapping of Schwann cells allows for …?
More readily conducting impulses
Like muscle fibers, nerve fibers are ________ _________.
Electrically excitable
What are the two types of electrical signals used for communication?
Graded potentials and action potentials
Graded potentials are?
Used for short distance communication ONLY
Has varying degrees of impusle
Action potentials allows for?
Communication over long distances within the body
The impulse of action potentials are always…?
The same regardless of impulse
In the neurons, the RMP is about _____
-70mV
How is the resting membrane potential generated?
Differences in ionic makeup of intercellular fluid and extracellular fluid
Differential permeability of the plasma membrane
The differences in the ionic make up of ICE and ECF is referring to..?
ICF having a lower concentration of Na+ and Cl- than ECF
ICF having higher concentation of K+
The differential in permeability of the plasma membrane refers to?
Membrane Freely permeable to Cl-
Large negatively charged proteins (A-) that always remain in the cytosol
Leakage channels favor a gradient where more K+ leaks out than Na+ leaks in
The memrbane is 75x more permeable to K+
What are the types of membrane channels?
Passive (leak) channels
Active (gated) channels
Passive channels are always_____
Open
Active channels may be…
Closed but are capable of opening
For active channels, open means ________ and closed means _______ and is incapable of ______.
Activated, inactive, opening
What are some examples of membrane channels?
Chemical gated,
Voltage gated
Mechanical gated
When do graded potentials occur?
When a stimulus causes gated ion channels to open
What is this graded potential also known as?
Receptor potentials, generator potential, postsynaptic potential
The magnitude of graded potentials are…?
Variable with stimulus strength
When does the magnitude decrease?
Magnitude will decrease with distance as ions flow and diffuse through leakage channels
Graded potentials travel only
Short distances
When the cell is having a depolarizing graded potential occur the
Cell becomes more positive
Hyperpolarized graded potentials are when the cell becomes
More negative
Graded potentials can ______ or ______ each other out
Summate or cancel
Wehre do graded potentials occur?
In dendrites and cell bodies
Don’t travel to axons
What are action potentials (AP)?
t
Signal which travels the length of the neuron
The action potential is where the membrane potential…?
Reverses and then eventually is restored to its resting state
What is the amplitude of the action potential?
About –100 mV
If a neuron receives a threshold stimuuls, this means?
A full strength nerve impulse is produced
When the neruon recevies a threshold stimulus and the full strength nerve impulse is produced it will…?
Spread down the axon of the neuron to the axon terminals
If a stimulus is not strong enough (subthreshold), no nerve impulse will resul
duh
WHAT HAPPENS DURING AN ACTION POTENTIAL?
- Sodium ions arrive at the axon hillock
- Threshold voltage is reached
- Voltage-regulated Na+ (fast) gates open and slow voltage gated K+ gates open
- Propogation of signal (sending down neuron)
- Na+ gated close (inactive) above 0mV
- K+ gates are finally fully open
- K+ gates close more slowly than Na+ gates
What is causing the action potential?
Permiablility changes in the plasma membrane
All action potentials are _____ and are _______ of stimulus ________.
Alike, independent, intensity
What is a strong stimuli?
Generate AP more often than weaker stimuli but it will not cause a larger impulse
CNS determines stimulus intensity by…
The frequency of impulses
What is the absolute refractory period?
STUDY THE IMAGE ON NOTES
- The time when a cell cnt generate an AP no matter the stimulus. This is the time where opening of Na+ channels to resetting.
What does the relative refractory period ensure?
That an AP is all or nothing and enforces one-way transmission or nerve impulses
The relative refractory period follows the?
Absolute refactory period
What may generate another AP after the refractory period?
An exceptionally strong stimulus
What is happening in the relative refractory period?
The membrane can respond only to a larger-than-normal stimulus
At the relative refractory period, what is happeining to the cell?
Na+ channels have returned to their resting state
SOme K+ channels are still open
Repolarization is occuring
Threshold for AP generation is _________.
Elevated because of hyperpolarization
Conduction velocities of neurons vary _____.
Widely
What are the things that affect conduction velocity?
Axon diameter, effect of myelin
What is the effect of axon diameter?
Larger diameter fibers have less resistance to local current flow and have faster impulse
What is the effect of myelin on conduction velocity
Continous conduction in unmyelinated axons is slower than saltatory conduction in myelinated axons
Myelin sheath prevents leakage ions
What is the differece of conduction velocity with myelination?
Saltatory conduction
What happens in saltatory conduction?
About 30x faster
Voltage gated Na+ channels are located at nodes
APs appear to “jump” from node to node
What are the classification of fibers?
Group A, B, and C
What are group A fibers?
Large diameter fibers
Fast fibers (120m/s or 268mph)
Myelinated somatic sensory and motor fibers
What are group B fibers?
Intermediate diameter
Medium speed (18m/sec; 40 mph)
Lightly myelinated visceral sensory and ANS fibers
What are group C fibers?
Smallest diameter
Slowest (1m/sec, 2mph)
Unmyelinated sensroy ANS motor fibers
The presynaptic neuron converts ______ ______ into ______ ________.
Electrical signal (nerve impulse), chemical signal (released neurotransmitter)
Post syaptic neuron reeives the _________ _______ and generates an _______ _________.
Chemical signal, electrical signal
The time needed for these processes at a chemical synpase produces a _________ _______ of about ______.
Synaptic delay; 0.5msec
The synaptic delay is known as the?
Rate limiting step of neural transmission
Within a few msec, the neurotransmitter is ______.
Terminated
What are the types of termination done to a neurotransmitters?
Degradation, reuptake, diffusion
Degradation is done by?
Enzymes
Reuptake is done by?
Astrocytes or axon terminal
Diffusion is done at?
Away from the synaptic cleft
Postsynaptic potential Strength is determined by…?
Amount of neurotransmitter released
Time the neurotransmitter is released in the area
What are the types of postsynaptic potentials?
EPSPs and IPSPs
What are EPSPs?
Excitatory postsynaptic potentials
Local depolarization of postsynaptic membrane that brings the neuron closer to AP threshold
What do EPSPs allow for?
Neurotransmitter binding opens ligand channels allowing outflow of K+ and influx of Na+
What are IPSP?
Inhibitory postsynaptic potentials
This is local hyperpolarization of postsynaptic membrane and arises the neruon away from AP threshold
What does IPSPs do?
Neurotransmitter binding opens K+ and Cl- channels which allows for K+ outflow and Cl- inlux
A single EPSP cannot…?
Induce an action potential
Howeer, EPSPs can ________ to reach ________.
Summate, threshold
IPSPs can also _______ with EPSPs _______ ____ each other
Summate, cancel out
What are the types of summation?
Temporal summation and spatial summation
What is temporal summation?
One or more presynaptic neruons transmit impulses in rapid fire order
What is spatial summation?
Postsynaptic neuron is stimulated by a large number of terminals at the same time
Most neurons make _____ or more neurotransmitters.
Two
Neurotransmitters are released at different ________ ______.
Stimulation frequencies
____ or _____ neurotransmitters have been identified.
50 or more
Neurotransmitters are classified by ______ ________ and by _______.
Chemical structure and by function
Neurotransmitters may be ________ or ________ depending on ________ on the postsynaptic neuron.
Excitatory or inhibitory, receptor
Neurotransmitter effects can be modified many ways by?
Synthesis can be stimulated or inhibited
Release can be blocked or enhaned
Removal can be stimulated or blocked
Receptor site can be blocked or activated
What is the agonist?
Chemical that enhances or stimulates the effects at. A given receptor
What is the antagonist?
Chemical that blocks or dimisnihes the effects at a given receptor
What are the two types of actions of neurotransmitters?
Direct and indirect
What does direct action of neurotransmitters do?
The neurotransmitter binds to channel linked receptor and opens channels
Promotes rapid responses
What does indirect action neurotransmitters do?
Neurotransmitters binds to a G-protein linked receptor
Promotes long lasting effects
Neurons porcess information when changes occur at the _______ _____ through _______ and ______ _______ of _____ and _____.
Trigger zone through spatial and temporal summation IPSPs and EPSPs
Integration is the…?
Process accomplished by the post-synaptic neuron when it combines all excitiatory and inhibitory inputs and responds accoridingly
These integration processes occurs over and over as interneurons are activated..?
In higher parts of the brain
