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Flashcards in Nerve Tissue Deck (128):

Nerve Tissue function

-provides rapid and specific communication between organs and body




-highly speacialized cells. Similar to muscle cells they are electrically excitable

-support cells, also called glial cells


Number of Neurons in the body

100,000,000 neurons


Sensory neurons

-gather information from receptors



-form a communicating network between neurons


Motor neurons

-convey impulses from the nervous system to the effector cells


Neuron nucleus

-large, rounded usually euchromatic nucleus with prominent nucleolus(i)



-cell body
-varies in size between 5-135 micrometers


Rough ER of neurons

-extremely well developed
-forms dense structure, visible in the light microscope called Nissl bodies.


Nissl bodies

-parallel arrays of RER cisternae


Golgi complex of Neurons

-well developed RER and Golgi reflect the need for the neuron to produce membrane and neurotransmitter in large quantities.



Neurons have many mitochondria



-usually present in the cytoplasm of neurons


Neurons and centrioles

-neurons usually lack the centrioles
-mature cell is not capable of cellular division
-some neurons retain the centrosome, which may play a role in nucleation of microtubules



-few neuroblasts that are able to divide and reproduce in small numbers.
-only neurons that are replaced in an adult body on a regular basis are the olfactory neurons


Neuron cytoskeleton

-very well developed and consists of neurofilaments (type of intermediate filaments), microfilaments (composed of actin), and microtubules


Two processes of neurons

Axon and dendrite
-neurons form synapses, which are used for communication with other neurons, muscle cells, and glandular cells



-one axon per cell
-convey signals from the perikaryon to the next neuron or to the effector cell.
-end with an axon terminal


Size of axon

-usually fairly long (up to 1 meter), and have more or less constant diameter throughout their length


Axon Hillock

-begin from an elevated platform on the perikaryon.
-Nissl bodies are absent from the axon hillock


Myelin sheath

-insulation sheath that covers axons
-allows electric impulse to travel rapidly through the axons.
-abnormalities in the formation of the myelin sheath result in severe disorders



-continuation of the plasma membrane that encloses the axon



-cytoplasm of the axon
-does not contain Nissl bodies or ribosomes, but has well developed SER.


Axon cytoskeleton

-formed by numerous microtubules and neurofilaments


Axonal transport

-presence of microtubules indicates intense transport of material through the axon.


Anterograde flow

-perikaryon to the periphery of the axon
-transport of actin filaments, proteins, organelles (Such as mitochondria), and vesicles.
-motor protein is kinesin


Slow axonal transport (anterograde flow type)

~1-6 mm/day
-move tubulin molecules, actin molecules, and proteins that form neurofilaments, from the perikaryon to the end of the axon


Fast axonal transport (type of anterograde flow)

~100-400 mm/day
-used to move membrane-bound organelles, such as RER compartments, synaptic vesicles, and mitochondria


Retrograde flow
Fast retrograde flow

Retrograde- transport from the distal part of the axon towards the perikaryon

Fast- transport of material taken up by endocytosis at axon terminal back to perikaryon
-used by some viruses (herpes, rabies) to travel through NS
-Toxins (tetanus) can be taken up to the perikaryon by the retrograde flow as well
-protein motor is dynein



-most neurons have several dendrites per cell.
-deliver the signal from the cell periphery to the perikaryon


Dendrite characteristics

-typically numerous thick, short, and tapered processes of nerve cells
-not myelinated
-cytoplasmic composition is similar to that of the perikaryon
-contain ribosomes and RER, but not Golgi apparatus


Dendritic Tree

-branch profusely which increases the area for synaptic contacts
-up to 200,000 synapses in one dendritic tree


Dendritic spines

-on the surface of dendrites
-synapses with axonal processes of other neurons
-have a "mushroom" shape and the "head" is where most postsynaptic receptors are located



-primarily sensory neurons that have a single large process that begins from the perikaryon
-single cellular process branches into the peripheral and central processes.


Peripheral process and Central process of pseudounipolar

-PP-reaches the sensory area and collects the information, which is delivered to the central nervous system through the central process (CP)
-conduct like one axon


Location of pseudounipolar neurons

Dorsal root ganglia and some cranial nerve ganglia


Why is it called pseudounipolar?

-beginning of the development of the neuron two processes are formed, a dendrite and an axon, but they fuse later on to form one larger process that begins from the perikaryon


Bipolar neurons

-sensory neurons that are rather limited in their distribution
-found primarily within the major sense organs, such as eye retina, olfactory mucosa, and cochlea, and semicircular canals of the inner ear.


2 processes of bipolar neurons

-axon and dendrite
-dendrite branches in the sensory area and acts as a receptor
-axon delivers the impulse to the CNS


Multipolar neurons

-most common type of neurons
-both motor and interneurons belong to this type.
-have one axon and many dendrites


Golgi type I cells

-type of multipolar neuron
-have a long axon
-large motor neurons found in the motor nuclei of the CNS


Golgi type II cells

-type of multipolar
-short axon
-these are smaller interneurons found in the CNS


Electrophysiology of the nerve

-similar to muscle cells, plasma membrane of a nerve cell is an electric capacitor, like the sarcolemma of a muscle cell


Negative membrane potential in resting cell

-voltage on the inner side of the plasma membrane is negative (-70mV) relative to the outer side
--possible b/c the Na+ ions are actively pumped outside of the cell, so the concentration of Na+ is ten times greater outside of the cell than inside


Action potentials

-brief positive going changes in the membrane potential that ate propagated along the length of the membrane at speed up to 120m/sec.



-as action potential travel along the membrane they open the voltage-sensitive channels and let the NA+ diffuse into the cell, which decreases the membrane potential



-the membrane potential becomes even more negative, which makes the membrane more difficult to depolarize



How nerve cells communicate with each other and with other cells (muscles)
-electrical and chemical


Electrical synapses

-represented by gap junctions, which allow direct passage of ions from one cell to another to transmit the wave of depolarization


Chemical synapses

-principal type of synapses found in mammals
-no protoplasmic continuity between the two cells and the signal is transmitted by release of a chemical (neurotransmitter) by one cell.
-binding of the neurotransmitter to the receptors of the other cell results in either depolarization or hyperpolarization of the membrane


Excitatory synapses

-depolarize the membrane of the postsynaptic cell making the generation of an action potential more likely


Inhibitory synapses

-increase the negative potential, which hyperpolarizes the postsynaptic membrane, thus making it less likely to generate the action potential


Presynaptic knob

-contains vesicles that are 40-60nm in diameter and contain the neurotransmitter



-diverse group of chemicals (over 100 known) that are capable of binding to receptors to generate the wave of depolarization of hyperpolarization in the postsynaptic cell


Synaptic cleft

-narrow space (~20 nm) b/t the plasma membranes of the presynaptic and postsynaptic cells


Postsynaptic membrane

-contains receptor sites for the neurotransmitter


Action potential propagation

-usually propagated along the membrane of the presynaptic cell from the perikaryon towards the axon terminal
-as it reaches the presynaptic terminal it opens the Ca++ channels briefly
-influx of Ca++ into the cytoplasm causes the synaptic vesicles to migrate to the membrane and fuse with it.
-neurotransmitter diffuses across the cleft.
-when the neurotransmitter is bound by the receptors on the membrane, it starts the local depolarization of the membrane of the postsynaptic cell.
-extra plasma membrane that was formed as a result of fusion of synaptic vesicles with the plasma membrane is removed by endocytosis using clathrin-coated vesicles


2 ways s Neurotransmitter that was released into synaptic cleft gets deactivated

1. Recapture
2. Degradation


High-affinity reuptake

-up to 80% of the neurotransmitters, such as catecholamines (dopamine, norepinephrine) that has been released into the cleft can be recaptures.
-neurotransmitter is reincorporated by endocytosis into vesicles that are ready for repackaging


Degradation (break down)

-enzymes, associated with the synaptic membrane, breakdown the remaining neurotransmitter that is left in the synaptic cleft.
-such neurotransmitters as acetylcholine are broken down into acetate and choline in the cleft


Norepinephrine clinical application

-inhibition of the enzyme that breaks down the neurotransmitter norepinephrine, or inhibition of high-affinity reuptake, has beneficial effect in the treatment of depression



-synapse where the connection is between an axon and a dendrite



-if the connection of the synapse is between an axon and a perikaryon (soma)



Synapse where the connection is between an axon and another axon


Motor end-plate is the neuromuscular junction and specialized type of synapse. Consists of:

1. Axon terminal that contains presynaptic vesicles with the neurotransmitter acetylcholine
2. Synaptic cleft is the space b/t the plasma membranes of the nerve cell and the muscle cell
3. Sarcolemma of a muscle cell forms multiple junctional folds in the area of the motor end-plate. The receptor sites for acetylcholine are located within the junctional folds


Which toxins disable the chemical synapses including motor end-plates and do not allow the depolarization of the sarcolemma.

Curare toxin and botulinum toxin


Curare toxin

-used by the South American Indians to hunt prey.
-it binds to the acetylcholine receptors and acts as a muscle relaxer


Botulinum toxin

-a neurotoxin protein produced by the bacterium Clostridium botulinum.
-the toxin prevents release of acetylcholine from the synaptic vesicles
-Botox (brand name for the botulinum neurotoxin) is used in cosmetic surgery to relax the facial musculature


Myasthenia gravis

- autoimmune disease characterized by extreme muscle weakness
1. Auto-antibodies to the acetylcholine receptor protein are produced
2. Auto-antibodies bind to the receptor sites, which weakens the muscle response to the nerve stimuli


Rabies (carried most often by skunks, bats, and raccoons)
-old name: hydrophobia

1. Muscle fibers are broken during bite, the virus gets into muscle and starts replication. Replication takes place for 1-2 weeks and this in when vaccine can still help.
2. After replication the virus finds a motor-end plate and gets into the cleft
3. Virus enters the synaptic terminal and via retrograde axonal transport it reaches the body of the motor neuron in the CNS and is ready to spread to other neurons.
4. Very soon most of the CNS is affected, which causes severe inflammation. Any change in the light intensity or any sounds, like the running water, cause seizures.
5. The virus spreads into the salivary glands and that is how it is transmitted from animal to animal with a bite.
6. After the symptoms have shown up, generally there is no cure


Support cells
PNS support cells?
CNS support cells?

-nourish and protect neurons
-far out number the neurons.

PNS: Schwann cells and satellite cells

CNS:astrocytes, oligodendrites, microglial cells, and ependymal cells


Schwann cells

-form a lipid layer called the myelin sheath that surrounds axons in the peripheral nerves.
-"envelope" the unmyelinated axons


Myelin sheath

-isolate the axon from the surrounding tissue and provides electrical insulation for the nerve fibers.
-necessary for rapid conduction of electrical impulses


Nodes of Ranvier

-open gaps in myelin sheath
-the axolemma of myelinated nerve fibers in the areas at the nodes of Ranvier has high concentration of Na+ channels.


Nodes of Ranvier action potential

-action potential in myelinated nerve fibers travels via saltatory conduction, which means that the membrane is only depolarized at the nodes of Ranvier.
-presence of electrical insulation in the form of the myelin sheath there is no charge leakage through the membrane, so depolarization of the membrane at one node is sufficient to elevate the voltage at the next node to the level necessary to generate an action potential


Nodes of Ranvier branching

-allow axons to form synapses with each other and to form branches.
-branching is usually best expressed in the vicinity of the target group of cells.


Schwann cell myelinated

-a single axon is sheathed by a Schwann cell that wraps around it several times.
-plasma membrane layers fuse together to form the myelin sheath, a lipoprotein complex
-action potential travels through myelinated nerve fibers using saltatory conduction (fast)


Schwann cells unmyelinated

-in unmyelinated fibers of the PNS several axons are enveloped into simple clefts in the Schwann cell.
-is located in the middle of the nerve bundle
-action potential in unmyelinated fibers is wave-like


Satellite cells

-support cells found primarily in the ganglia of the peripheral nervous system, where they surround bodies of individual neurons.
-create micro environment around individual neurons and provide electrical insulation for the bodies of neurons.
-act similar to Schwann cells, but they do not have myelin
-provide a pathway for metabolic exchange necessary for the neurons



-Amon the largest neuroglial cells (8-10 microns) and provide support for neurons and vascular structures of the CNS
-granular cytoplasm and large nuclei
-mitochondria are numerous in the cytoplasm
-processes extend between neurons and blood vessels.
-stain positive for glial fibrillary acidic protein (GFAP), which forms the intermediate filament cytoskeleton of these cells.


Astrocytes functions

-play an important role in moving metabolic substances between blood and nerve cells.
-together with the endothelial cells of blood capillaries astrocytes form the blood-brain barrier


Protoplasmic astrocytes

-found in gray matter of the brain
-numerous short, branching processes that form structures called perivascular feet along blood capillaries


Fibrous astrocytes

-more prominent cytoskeleton, than protoplasmic astrocytes, and are primarily found in white matter of the brain.
-have fewer processes with less expressed branching



-tumors derived from astrocytes
-some of the most common tumors in the brain and represent 20% of all brain tumors (including ones that were formed elsewhere and metastasized into the brain)
-astrocytes give rise to 80% of all tumors that originate in the brain


Glial scar

-local damage to the brain astrocytes are responsible for the process called gliosis, which results in the formation of a glial scar



-most common neuroglial cells of the CNS
-smaller than astrocytes (6-8 microns)
-small nuclei, abundant SER, and prominent Golgi apparatus
-few tongue-like cell processes that extend from the oligodendrocyte cell body to wrap around the axons of the neurons of the CNS forming segments of myelin sheath.
-gaps b/t individual segments of oligodendrocytes in the CNS represent the node of Ranvier. Oligodendrocytes of the CNS are similar to the Schwann cells of the PNS, different in the way they form the myelin sheath


Multiple Sclerosis

-disease that is caused by damage to the myelin sheath of the axons in the CNS done by cells of the immune system.
-results in the partial loss of the myelin sheath
-symptoms may include loss of sensitivity, partial paralysis (depending on the area that is damaged)


Microglial cells

-distinctive phagocytic properties
-derived from monocytes and are part of the mononuclear phagocytic system
-smallest cells of the neuralgia (5-7 microns)
-dark indented nuclei and limited cytoplasm


Microglial cell characteristics

-have few twisted processes that are covered with spike, which may be equivalent to the ruffled border seen in other phagocytic cells.
-cytoplasm of microglial cells contains many lysosomes
-numbers of microglial cells in the brain increase with injury, so microglial cells are believed to remove the debris from the CNS


Alzheimer's and Parkinson's diseases

-microglial cells are abundant in patients.
-possible that they are partially responsible for the plaque formation, demyelination and destructions of nerve fibers in the CNS of pt's with these disorders


Ependymal cells

-lining the ventricles of the brain and cavities of the spinal cord
-production and absorption of CSF
-arranged in a form of simple cuboidal epithelium, but unlike the true epithelia there is no basal lamina


Ependymal cell functions

-tightly bound by junctional complexes and often possess microvilli, which are responsible for absorbing CSF
-few cilia attached to the luminal surface of some ependymal cells
- basal processes of ependymal cells interdigitate with astrocyte processes allowing exchange of metabolite b/t these cells.
-glial fibrillary acidic protein is also present in ependymal cells


Peripheral nervous system consists of:

-cranial, spinal, and peripheral nerves, ganglia, and special nerve endings


Nerves of the PNS are made of:

-many nerve fibers that carry sensory and motor information between the organs and tissues of the body
-composed of myelinated and non-myelinated axons


Sheets of connective tissue that hold PNS nerve fibers together:




-surrounds individual nerve fibers



-surrounds nerve fascicles



-surrounds individual nerves and extends into the spaces between the fascicles



-clusters of neuron cell bodies outside the CNS.
-covered by a connective tissue capsule and usually have satellite cells associated with them


Sensory craniospinal ganglia in autonomic nervous system

-contain pseudounipolar neurons
-pseudonuipolar neurons have a single process, which T-branches into peripheral and central processes.
-peripheral process is long and goes to the receptor organ.
-central process is rather short and goes to the spinal cord (dorsal root ganglia) or to the brain (cranial ganglia) to form synapses with neurons of the CNS.
-satellite cells surround the pseudounipolar neurons of the craniospinal ganglia


Motor ganglia of the autonomic nervous system:

-contain multipolar neurons and satellite cells


Special ending types

1. Motor
2. Sensory


Motor nerve endings in skeletal muscle tissue:

-called motor end-plates


Sensory nerve endings: two types

1. Special-sense nerve endings
2. Somesthetic receptors


Special senses nerve endings

-sensory endings specialized for smell, sight, hearing, and equilibrium


Somesthetic receptors location

-found throughout the body in epithelial tissues, connective tissues, muscles, and joints


Free nerve endings

-branched sensory endings that mediate pain


Encapsulated nerve endings

-include Meissner's corpuscle, Pacinian corpuscle, and several others


Meissner's corpuscle

-cylindrical structure formed by the stacks of lamellae that surround one or two sensory nerve endings.
-these receptors provide the sense of touch and are most common in the skin of fingers and toes


Pacinian corpuscle

-largest of encapsulated nerve endings (up to 2mm) and is the most complex type
-spherical in shape and consists of up to 30 concentric sheets of connective tissue with fluid between the layers that surround a single nerve fiber.


Pacinian corpuscle location

-respond to vibrations and deep pressure and are found in the dermis of the skin, mesenteries, and inside Internal organs (pancreas)



-designed to collect information about the angulations of joints and muscle tension


Muscle spindle

-specialized receptor unit located in the skeletal muscle
-specialized stretch receptor
-covered with two capsules, internal and external with fluid-filled space separating them


Intrafusal fibers

-inside muscle spindle
-are thin skeletal muscle fibers that are surrounded by the nerve fibers of two types (sensory and motor)


Sensory nerve fibers in muscle spindle of proprioceptors:

-wrap around the intrafusal fibers and transmit information about the degree of stretching of the muscle.


Motor nerve fibers in the muscle spindle of proprioceptors

-thought to regulate the sensitivity of the stretch receptor


Central Nervous System

-consists of the spinal cord and the brain


Nuclei in CNS

-clusters of neurons in the CNS are called nuclei


CNS organization, support, and matter

-nerve fibers organized into tracts
-organs of the CNS are supported by accessory structures, such as meninges, choroid plexuses, ventricles
-can be divided into the white and gray matter, which are organized in a different way in the spinal cord and in the brain


Gray matter

-consists of neuron bodies and unmyelinated fibers that form dense fibrous network
-tissue has extensive vascular supply through a system of capillaries


Gray matter in the spinal cord

-gray matter is internal to the white matter (opposite of what we see in the brain)
-organized into two pairs of horns: anterior and posterior (ventral and dorsal)
-ventral horns contain large motor neurons, while the dorsal horns receive information from the dorsal root ganglia
-gray matter on the left and right sides of the spinal cord is connected via the gray commissure


Gray matter in the brain

-is external to the white matter and is often thrown into deep folds called gyri
-in the cerebellum these fold are called folia


Gray matter in cerebrum

-organized into 6 layers
-three main types of neurons found in the cerebrum are pyramidal cells, fusiform cells, and granule cells


Gray matter in the cerebellum

-organized into three layers:
1. molecular layer
2. Purkinje cell layer
3. Granular layer


Cerebellum->gray matter->molecular layer

- most external layer
-contains relatively few cell bodies of neurons called basket cells and numerous cell processes


Cerebellum->gray matter->Purkinje cell layer

-thin layer composed of very large neurons called Purkinje cells


Cerebellum->gray matter-> granular layer

-most internal layer, adjacent to the white matter
-highly cellular and is mostly compose of small neurons called granule cells


White matter

-consists of myelinated axons and glial cells
-has limited blood supply compared to the gray matter.
-tissue is rather dense with very limited extracellular space
-no synaptic contacts within the white matter
-in the spinal cord the white matter is external to the gray matter, while it is the opposite in the brain