Nervous Tissue Flashcards
What two body systems provide the regulation and control of all other body systems that is necessary for homeostasis? What is the basic mechanism of action used by each?
Nervous system - communicates through rapid action potentials (nerve impulses)
Endocrine system - Uses hormones (takes place over hours and days)
What are the three basic functions of the nervous system?
SIM
- sensory function - using millions of sensory receptors to monitor changes (stimulus) occurring inside and outside the body
- integrative function- interpreting the sensory input and deciding what should be done at each moment (also helps create memories)
- motor function - motor output activates effector organs (muscles contract and glands secrete hormones)
Identify the two major divisions of the nervous system.
Central Nervous System
- control center of nervous system
- interprets sensory input and dictates the motor output based on : reflexes, current conditions, and past experiences
Peripheral Nervous System
- links all parts of the body back to the brain and spinal (CNS) carry impulses too and from
What are the anatomical components of each of these divisions (#3)?
Central Nervous System-
brain and spinal cord
Peripheral Nervous System -
nerves and ganglia
nerves:
- spinal nerves (carries impulses to and from spinal cord)
- cranial nerves (carries impulses too and from the brain)
Distinguish between cranial nerves and spinal nerves.
- spinal nerves (carries impulses to and from spinal cord)
- cranial nerves (carries impulses too and from the brain)
Distinguish between the afferent and efferent functions of the PNS.
sensory division (afferent) TOWARD CNS from sensory receptors
- — somatic sensory fibers
- impulses from skin, skeletal muscles and joints
- —visceral sensory fibers
- impulses from organs within ventral body cavity
motor division (efferent)
AWAY FROM CVS to muscles and glands (causes muscles and glands to activate)
—somatic nervous system
*somatic motor nerve fibers activate the voluntary nervous system (skeletal muscles)
—-automatic nervous system
two subdivisions: sympathetic nervous system (mobilizes body systems during activity) & parasympathetic nervous system (promotes housekeeping functioning rest)
**work against each other to maintain homeostasis)
What is the function of the somatic sensory neurons?
- — somatic sensory fibers
* impulses from skin, skeletal muscles and joints to the CNS
What is the function of the visceral sensory neurons?
- —visceral sensory fibers
* impulses from organs within ventral body cavity to the CNS
Why is the motor portion of the somatic nervous system called the voluntary nervous system?
because it activates skeletal muscle and joints which is part fo the skeletal system which is voluntary
Identify the divisions of the Automatic Nervous System
—-automatic nervous system
two subdivisions: sympathetic nervous system (mobilizes body systems during activity) & parasympathetic nervous system (promotes housekeeping functioning rest)
**work against each other to maintain homeostasis)
What division of the PNS is considered involuntary?
automatic nervous system
What are the two basic cell types found in nervous tissue? Which of these basic cell types is most numerous?
neurological cells (supporting cells of the nervous system) and neurons (nerve cells that are excitable) ; astrocytes are most abundant
Name and describe (structure and function) the four types of supporting cells of the CNS.
Microglial cells - defensive cells , when invading microorganisms are present, they transform into a special type of macrophage that phagocytizes
*SMALL, OVOID W/ LONG THRONY PROCESSES
Astrocytes- Support and brace the neurons and anchor them to their nutrient supply lines (most abundant) make exchanges w/ capillaries
* STAR CELLS
Ependymal cells- line central cavities of the brain and spine. The beating of their cilia helps circulate the cerebrospinal fluid that cushions the brain and spinal cord.
*SQUAMOUS TO COLUMNAR, MANY ARE CILIATED
Oligodendrocytes- line up along the thicker nerve fibers in the CNS and wrap their processes tightly around the fibers, producing an insulating covering called myelin sheath.
*BRANCHED but not as much as astrocytes
Name and describe (structure and function) the two types of supporting cells of the PNS.
Satellite cells -
similar to astrocytes
*SHAPED LIKE SATELLITES
Schwann cells-
vital to regeneration of damage peripheral nerve fibers
* around all nerve fibers in PNS and form myelin sheaths like oligodendrocytes
What cell produces myelin in the PNS? in the CNS?
Schwann cells, oligodendrocytes
What cell serves as a phagocyte in the CNS?
microglial cells
What is the largest glial cell in the CNS? the most numerous?
Astrocytes
What glial cell participates in forming the blood-brain barrier?
Astrocytes
Identify the 3 special characteristics of neurons.
- response to stimuli by changing their membrane potential & transmit electrical signals
- amitotic (hard to regenerate)
- a long lived high metabolic rate
NO ANEROBIC METABOLISM (no oxygen, they’ll die quickly)
Identify the three parts of a neuron.
- cell body (soma) - most are in the CNS (surrounded by the skull for protection)
- cluster of cell bodies is called a nucleus in CNS and ganglia in PNS - dendrites - the neurons afferent processes; create large surface area for receiving signals and carrying it towards the cell body
- axon - neurons efferent process (carry action potential away from the body to the muscle or glands) connected to cell body at axon hillock
Long axon = nerve fiber
Bundles = tract in CNS & nerve in PNS
- myelin - white fatty substance that protects and electrically insulates nerve fibers
What organelles are typically present in the neuron cell body? are any noticeably absent
- nucleus, cytoplasm, ribosomes, rough ER, golgi apparatus, mitochondria, microtubules, neurofibrils
- no
What is the function of the neurofibrils?
bundles of intermediate filaments (neurofilaments) that maintain cell shape and integrity. Form a network throughout the cell body and its processes
What are Nissl bodies (sometimes called chromatophilic substance)? Why are they so prominent in the soma of neurons?
a color loving substance in the rough EF , stains darkly with basic dyes
Which neuron process conducts impulses toward the cell body? away from the cell body?
dendrites ; axon
What is the axon hillock?
connects the axon to the cell body (initial cone-shaped region of the axon)
Where are the synaptic vesicles located?
in the synaptic knob at the end of the terminal branches
What is axonal transport? Why is it important?
the task of moving molecules along their length away from the cell body (anterograde movement) or towards cel body (retrograde movement)
What is myelin? What is its function?
myelin - white fatty substance that protects and electrically insulates nerve fibers
Describe the process of myelination in both the PNS and the CNS.
PNS:
- formed by Schwann cells: indent to receive an axon and then wrap themselves around it
- concentric layers of Schwann cell plasma membrane enclose the axon, the tight coiling is the myelin sheath, thickness depends of number of spirals
- the nucleus and most of the cytoplasm of the Schwann cell bulges: outer collar of perinuclear cytoplasm
- forms one segment of the myelin sheath
CNS:
- contains both myelinated and nonmyelinated axons
- formed by oligodendrocytes, has multiple flat processes that can coil around as many as 60 axons at once
- like PNS, myelin sheath gaps separate adjacent sections of an axon’s myelin sheath
- lacks an outer collar of perinuclear cytoplasm b/c cell extensions do the coiling and squeezed out cytoplasm is force back in centrally
- like the PNS, the smallest-diameter axons are nonmyelinated, covered by the long extensions of adjacent glial cells
- gray and white matter are dense regions of myelinated fibers
What are the nodes of Ranvier?
gaps in the myelin sheath of the PNS
AP can only occur here in myelinated fiber
What is the neurilemma? Do all myelinated nerve fibers have a neurilemma?
the nucleus and most of the cytoplasm of the Schwann cell , next to the exposed part of the plasma membrane, no
Describe the association between Schwann cells and unmyelinated fibers of the PNS.
in unmyelinated fibers it enfolds several axons and forms a remake bundle instead of individual axons to make them myelinated
they don’t wrap but give support and cushioning.
What is the composition of gray matter? of white matter? (This information is easily found in the glossary of the Marieb textbook.)
Grey matter - contains neuronal cell bodies and their dendrites (where processing is done)
*mainly in brain
White matter - white substance of the central nervous system (myelinated nerve fibers) responsible for communication between gray fibers
*in brain and spinal cord
Compare and contrast nerves and tracts. (This information is easily found in the glossary of the Marieb textbook.)
tract - bundles of nerve fibers in the CNS
nerves - bundles pf nerve fibers in the PNS
Differentiate between a nucleus and a ganglion. (This information is easily found in the glossary of the Marieb textbook.)
Nucleus- a cluster of neuron cell bodies in the CNS
Ganglion- singular collection of neuron cell bodies in the PNS
Describe the structure and function of bipolar, unipolar, and multipolar neurons.
Unipolar - one process extends from the cell body and divides like a T into a PNS and CNS process
***Sensory in function
Bipolar- two processes (an axon and an dendrite) RARE
Multipolar- have 3 or more processes (one axon and all the reset are dendrites)
MOST COMMON
Which of the above types of neuron (#36) is most prevalent in the nervous system as a whole?
Multipolar neurons
What is the function of afferent, efferent, and association neurons?
Afferent- towards CNS (sensory receptor)
Efferent- away from CNS towards muscle and glands
Association - located in-between motor and sensory neurons (in CNS) shuttle signals through CNS pathways where integration occurs.
What is meant by the term “membrane potential”? by the term “resting membrane potential”?
membrane potential- The separation of electrical charge across a plasma membrane
resting membrane potential - the transmembrane potential in a resting neuron
What causes the voltage difference across the plasma membrane?
the amount of potential energy (the separation and slight difference of numbers of positive and negative charges on the opposite sides of the plasma membrane)
In the resting state, where (what region) is K+ in the highest concentration? Where is Na+ in the highest concentration?
Inside the cell ; outside the cell
What is meant by the term “equilibrium potential” (E)? Is the resting membrane potential closer to the EK+ or ENa+? Explain why no neuron could ever depolarize to a voltage > +65mV.
the membrane potential at which the electrical force of repulsion/attraction of an ion equals the chemical force of the concentration gradient for the ion (DETERMINES RMP) ; RMP is -70 so its closer to EK+ because that is hyperpolarization which makes the plasma membrane more negative
In the resting state, is the membrane more permeable to Na+ or K+?
K+ because some non-gated or leak ion channels are opens on there is a higher amount of potassium in the cell than outside so it moves along the concentration gradient
Identify the types of ion leakage channels that help to create the resting membrane potential in nerve and muscle cells.
k+ and na+ leakage channels
Which of the channels identified above (#44) is most numerous?
more k+ leakage channels
Describe the operation of the different types of gated channels.
ligand-gated ion channels- the neurotransmitter binds to the channel, opening it
voltage-gated ion channels- open/close in direct response to a voltage change in the membrane potential
mechanically gated channels-open/close in response to physical stimulation (like you press your hand against something, triggering a reaction)
What prevents the resting cell from reaching equilibrium with respect to the diffusion of Na+ and K+ across the membrane?
the sodium potassium pump ; it ejects 3 NA+ from the cell and transports 2 K+ back into the cell to stabilize the RMP
Describe the operation of the sodium-potassium pump.
it ejects 3 NA+ from the cell and transports 2 K+ back into the cell to stabilize the RMP
What is the term which describes a decrease in the membrane potential?
depolarization (the charge becomes more positive) increased inflow of Na+
What three factors are at work to establish and maintain the resting membrane potential?
- unequal distribution of ions across the plasma membrane
- differential permeability o the plasma membrane to K+ and Na+ (K+ is more permeable)
- Na+ / K+ pump
What is the term which describes a membrane potential which is greater (i.e., more negative) than the resting membrane potential?
hyperpolarization - increased K= OUTFLOW
causing regions inside the plasma membrane to be more negative (AP goes down (-) )
Does an inflow of Na+ promote depolarization or hyperpolarization? Does an outflow of K+ promote depolarization or hyperpolarization?
depolarization ; hyperpolarization
What is a graded potential?
short-lived, local changes in the membrane potential that may be either depolarizations or hyperpolarizations
What is the functional significance of graded potentials?
- triggered by a stimulus that causes gated ion channels to open
- the local currents die out with the increasing distance from the site of the original stimulus
- the magnitude of a graded potential varies on the strength of the stimulus which produces it
- essential for initiating action potential
What is an action potential?
sequence of rapidly occurring events that produces a brief, large depolarization and subsequent depolarization of the plasma
- main way that neurons transmit information through the body
What is a threshold stimulus? What will be the result of threshold stimulation?
where the neuron will fire an action potential
in order to generate an AP , the membrane must depolarize to a critical level
At threshold, the opening of voltage gated Na+ channels increase inflow of Na+ into the cell (exceeding the outflow of K+) this establishes a positive feedback causing depolarization
At what membrane potential (i.e., voltage) does the action potential of a neuron become all or none?
threshold (-55 to -50 mV) when the depolarization reached that, the neuron will fire an action potential.
How does depolarization influence membrane permeability to Na+?
At threshold, the opening of voltage gated Na+ channels increase inflow of Na+ into the cell (exceeding the outflow of K+) this establishes a positive feedback causing depolarization
Why is the depolarization phase an example of positive feedback?
depolarization becomes self-generating
it causes more Na+ channels to open, resulting in a greater influx of positive charge which accelerates the polarization
What happens to the membrane potential when Na+ rushes into the cell?
- becomes more positive
- overshoots about 30mV as Na+ rushes in along its electrochemical gradient
What stops the flow of Na+ into the cell?
inactivation gates of the Na+ channels begin to close and Na+ decreases
Explain why there is an absolute refractory period in excitable cells, such as neurons.
it ensures that each AP is zero or a hundred and that it only moves in one direction on the axon
this period occurs due to the depolarization phase, the sodium channels are already open
What causes the voltage-gated K+ channels to open?
(in repolarization phase)
- the decrease in Na+ permeability
What happens to the membrane potential when K+ rushes out of the cell?
voltage becomes more negative and restores the internal negativity of the neuron (repolarization phase)
What causes after-hyperpolarization (i.e., the undershoot of the AP)?
the voltage-gated K+ channels close slowly so K+ permeability still continues so theres excess k+ from the cell
the sodium potassium pump restores the ionic distribution of the resting state and Na+ channels are resting to their original positions
What restores the resting membrane potential following an action potential?
the sodium potassium pump
Describe the absolute refractory period and tell why it is important.
when a second AP cannot be generated, even if its a strong stimulus
it gives our neurons a chance to catch their breath
Describe the relative refractory period and identify the phase of the action potential to which it corresponds.
the time during which a second AP can be generated, but only by a larger than-threshold stimulus
during the refractory period
Explain why the generation of an action potential is said to be an all-or-none phenomenon.
- if depolarization reached threshold (-55 to -50), voltage gated Na+ channels open and an AP arises
- every time an AP arises, it has a maximum strength and docent decay (makes it different from graded potentials)
Describe the process of impulse propagation in unmyelinated fibers.
called CONTINUOUS CONDUCTION
action potential has to be regenerated at each point
the process of impulse traveling down the axon to the axon terminals
AP generated in the axon hillock (cause there are sodium ion channels there)
as the impulse travels, it depolarizes nearby patches of the membrane causing the impulse to self-propagate along the membrane (from the axon hillock to the axon terminals)
Describe the process of impulse propagation in myelinated fibers.
SALUTATORY CONDUCTION (is faster)
same as with unmyelinated fibers but the myelin serves as an insulator so to prevent leakage of the ions, the depolarization can only move from node to node
Why is propagation faster in myelinated fibers?
because the Melin keeps the current in the axons (voltage doesnt decay as much)
What factors influence the speed of impulse conduction in nerve fibers?
- diameter of the fiber (the larger the diameter the faster it’ll conduct AP)
- presence/absense of a myelin sheath
the presence of one will make it travel faster
Describe the three types of nerve fibers with respect to their relative diameters, degree of myelination, and speed of impulse conduction.
Greatest—least
A fibers -
largest, heavily myelinated
*Mostly somatic sensory and motor fibers serving in the skin, skeletal muscle and joints
B fibers -
intermediate, lightly myelinated
*afferent & efferent ANS fibers serving visceral efferent fibers
C- fibers-
smallest, unmyelinated
*poorly localized pain, touch, pressure and visceral (ANS) efferent fibers
What is the function of synaptic vesicles?
to hold the neurotransmitter
What is the function of neurotransmitters?
carries the impulse from the pre to the post synaptic neuron or the dendrites/cell body
Describe the process of impulse transmission across a synapse.
- AP reaches the synaptic knob, depolarization causes opening of the voltage-gates Ca2+ channels
- Ca2+ flows into the synaptic knob, the increase of calcium inside triggers the exocytosis of the Neurotransmitter from the synaptic vesicles
- NT diffuses across the synaptic cleft and binds to the receptor in the postsynaptic membrane , causing graded potentials
4 NT effects are terminated
What ion triggers exocytosis of neurotransmitter from the synaptic vesicles?
calcium
By what process does the neurotransmitter get across the synaptic cleft?
diffusion
What effect does neurotransmitter have on the postsynaptic membrane?
the receptor it binds to is ligand gated which causes the channel to open and create graded potentials
(postynaptic potentials)
In what way is the postsynaptic membrane specialized to receive communication from presynaptic neurons?
the have a high density of NT receptors
What is synaptic delay?
the time required for the processes which occur in a chemical synapse (NT to re released, diffuse across synaptic cleft and bind to its receptor)
What is a postsynaptic potential?
production of graded potentials
Describe and identify the functional importance of an excitatory postsynaptic potential (EPSP).
- NT binding depolarizes the postsynaptic membrane
- chemically gated ion channels open (instead of voltage-gated)
- Na+ and K+ diffuse through the membrane simultaneously but in opposite directions
- electrochemical gradient for Na+ is much steeper= net depolarization/more Na+ influx than K+ efflux
- reach 0mV, well above an axon’s threshold, but postsynaptic membranes generally do no generate AP- instead EPSP
- each EPSP last for a few ms, then membrane returns to resting potential
- helps trigger an AP distally at the axon hillock of the postsynaptic neuron
- often spread all the way to the axon hillock
- if current at hillock is strong enough, axonal voltage-gated channels will open and fire an AP
Describe and identify the functional importance of an inhibitory postsynaptic potential (IPSP)?
- NT binding reduces a postsynaptic neuron’s ability to generate an AP
- hyperpolarize the membrane by making the membrane more permeable to K+ or Cl- (Cl- in, K+ out if each channel opens)
- Na+ permeability is not effected
- as the membrane potential increases and is driven farther from the axon’s threshold, the postsynaptic neuron become less and less likely to fire an AP
When numerous EPSPs and IPSPs are occurring in a neuron at one time, what determines whether or not the neuron will fire an action potential?
- EPSPs: if effects dominate the membrane potential enough to reach threshold, the neuron will fire
- if summation yields only subthreshold depolarization or hyperpolarization, the neuron fails to generate an AP
Describe the difference between temporal and spatial summation.
- temporal: involves the accumulation of NT released from a single presynaptic neuron (or only a few presynaptic neurons) firing several impulses in rapid succession
- spatial: results from a buildup of NT released by a several presynaptic knobs close to each other on the dendrite or cell body of postsynaptic neuron, simultaneously initiates EPSPs
Distinguish between synaptic potentiation and presynaptic inhibition.
synaptic potentiation- continuous use of a synapse (even for short periods of time) enhances the presynaptic neurons ability to excite the postsynaptic neuron, producing larger-than-expected EPSPs.
presynaptic inhibition- when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axoaxonal synapse. less neurotransmitter is released forming smaller EPSPs.
At what type of synapse does presynaptic inhibition (or facilitation) occur?
axo- axonal. synapse
Identify and distinguish between the main classes of neurotransmitters.
- acetylcholine:
the first NT identified, released at NMJ, released by all neurons that stimulates skeletal muscles and some in the ANS, also in CNS
- biogenic amine:
include catcholamines, dopamine/NE synthesized from tyrosine, serotnin is synthesized from tryptophan, broadly distributed in the brain, play a role in emotional behavior and help regulate the biological clock, motor neurons can release NE, imbalances=mental illness
- amino acids:
glutamate, aspartate, glycine, GABA - peptides: neuropeptides, substance P- important mediator of pain signals, endorphins reduce our perception of pain under stressful conditions (second-wind or runner’s high)
- purines: N-containing that are breakdown products of nucleic acids, ATP in both CNS and PND, adenosine potent inhibitor of the brain
- gases and lipids: gasotransmitters: synthesized on demand and diffuse out of the cells, zoom through plasma membrane (NO, CO, HS), endocannabinoids: natural NT, clipping of the cell’s own plasma membrane lipids, with learning and memory
Identify the neurotransmitters derived from the amino acid tyrosine.
- dopamine and norepinephrine
What is the neurotransmitter at the neuromuscular junction?
ACh
Which neurotransmitters play a role in reducing pain and elevating mood?
peptides: endorphins
Identify the main inhibitory and excitatory amino acid neurotransmitters.
excitatory: glutamate
inhibitory: glycine, GABA
Explain why the number of neurons in a pathway influences the speed with which information can be transmitted?
synaptic delay
What are neuronal pools?
functional groups of neurons that integrate incoming information received from receptors or different neuronal pools and then forward the processed information to other destinations
Describe each of the four types of neuronal circuits and give an example of each.
1) diverging circuit: one input-many outputs, an amplifying circuit, single neuron in the brain activates 100 motor neurons in the spinal cord
2) converging circuit: many inputs-one output, a concentration circuit, different sensory stimuli can all elicit the same memory
3) reverberating circuit: signal travels through a chain of neurons, each feeding back to previous neurons, an osciallating circuit, controls rhythmic circuit, involved in breathing, sleep-wake cycle, and repetitive motor activities such as walking
4) parallel after discharge circuit: signal stimulates neurons arranges in parallel arrays that eventually converge on a single output cell, impulses reach output cell at different times, causing a burst of impulses call an after discharge, may be involved in exacting mental processes such as math calculations
What type of circuit concentrates information from a variety of sources?
converging circuit
What type of circuit is probably involved with rhythmic activities (e.g., breathing)?
reverberating circuit
Which type of circuit produces bursts of impulses in the output cell over a period of 15+ msec?
parallel after-discharge circuit
Describe and give an example of serial processing.
- whole system works in a all or nothing manner
- one neuron stimulates the next and so on causing an anticipated response
- spinal reflexes and straight-through sensory pathways from receptors to the brain
- reflexes: occur over neural pathways called reflex arcs: receptor, sensory neuron, CNS integration center, motor neuron, and effector
Describe and give an example of parallel processing.
- inputs are segregated into many pathways and different parts of the neural cicuitry deal simultaneously with the information delivered by each pathway
- triggers unique pathways, same stimulus promotes many responses beyond simple awarness
- not repetitious because the circuits do different things with the information
- important for higher-level mental functioning
