Block 1 - Physiology - 8/31/06

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What does nerve tissue respond to the environment by doing?: Mainly, by letting in or moving out ions of the cytoplasm, and this changes the electrical potential across the membrane
Do all cells have the ability to do this, not just nerve tissue?: Yes, all can, but nerve tissues have it to a very high degree
What are the two functions of the nervous system, and what are examples of each?: Communication is when the brain is informed about changes in the environment by sensory receptors, and this is taken by the brain, and control is when the brain controls things like muscular contractions by sending impulses
What are the two major divisions of the nervous system, and what are the comprised of?: The central nervous system is the brain and spinal cord
The peripheral nervous system is?: Everything not in the central nervous system
What two things is nervous tissue made of?: Cells and intracellular material
Does nerve tissue has intracellular material?: Very little intracellular material
The nerve and cell can be divided into two broad categories, what are the two categories?: True nerve cells, and supporting cells
What do supporting cells do?: They support the neuron metabolically
One large subset of neuronal supportative cells are neuroglia. What do they do as a general statement, and what are the 4 types: Neuroglia hold the system together, and they include astrocytes, oligodendroglia, microglia, and ependyma
What are neuroglia derived from?: They are derived from ectoderm or neuronal tissue except for microglia
What are astrocytes, and what are there 2 types?: They are star-like cells, and there two types are fibrous and protoplasmic
What are oligodendroglia?: They are cells with few processes that within the central nervous system are responsible for forming myelin.
Do oligodendroglia form myelin in the peripheral nervous system?: No
What are microglia derived from, and what do they do?: They are mesodermally derived, and they are phagocytic cells of the central nervous system
What do ependyma form?: They form the epithelial like lining of the central canal and ventricles of the brain
What are the two major parts of the neuron?: They can be divided into a cell body (neuron soma), and long processes
Which contains the nucleus?: Cell body
What are processes?: Long extensions of the cytoplasm
What are processes covered by?: They are covered by a plasma membrane, which is continuous with the plasma membrane surrounding the nerve cell body
The processes can be divided into two kinds?: Axons, and dendrites
How many axons do most neurons have?: Almost always they will have only 1 neuron
What are axons responsible for?: They are responsible for carrying the nerve impulses away from the cell body
How many dendrites do most neurons have?: They have anywhere between one to hundreds
What do dendrites serve as?: They serve as a receptive part that receives the nerve impulses
Neurons may be classified according to what?: The number of processes they have
If a cell has one process, what is it known as?: Unipolar cell
How many unipolar cells are there?: There aren't many true unipolar cells in the adult nervous system
Instead of unipolar, what are many?: Pseudo-unipolar
What are pseudo-unipolar versus unipolar?
How many processes to bipolar cells have?: They have 2, with an axon and dendrite
What are the processes and number of process in a multipolar neuron?: A multipolar neuron has anywhere between 3 and up to hundreds of dendrites, but it has one axon
What is the general rule of axons and branching?: They dont branch very much, but as they reach their termination, like a neuron innervating a muscle, it may branch many times. One nerve cell may innervate hundreds of cellular muscle cells
What is an anterior horn cell?: It is a motor neuron, that innervates skeletal muscle, and is multipolar
Gray matter contains what?: Cell bodies of dendrites
What is white matter?: Almost entirely axons
What else to have besides axons in the white matter?: Neuroglia too
Does the dorsal or ventral side contain the anterior horn, and what is the anterior horn also known as?: The ventral side contains the anterior horn, which is also known as the ventral horn
Do anterior horn cells have much heterochromatin?: No, they are mostly euchromatin
Does the cell body contain any organelles, and if yes what are the major ones?: They contain mitochondrias and fibrils, and Nissl bodies
What are Nissl bodies?: They clump cytoplasm in the cells, are contain rough ER and free ribosomes
What do they stain?: Basophilically red
Why is this?: Because they have lots of RNA, and ribosomal RNA
Where the dendrites makes synapic contact with axons, what is occuring?: These are accumulations of neurotransmitters, which are released from the presynaptic and head to postsynaptic
What is the purpose of neurtransmitters?: They cause electrical polarities to increase or decrease
If they are increasing, what is occuring?: They are inhibiting the process
If they are decreasing what are they doing?: They are stimulating the process
What is the area free of Nissl substance on the cell body?: This is the axon hillock
What occurs here?: This is where the axon arises
What does this area functionally detemine?: Once the neurotransmitters cause depolarization or hyperpolarization, and when it gets to this area, a decision is made as to whether or not to send out an action potential
What is this area sometimes known as?: Trigger area
What is the insulating sheath of the plasma membrane of the axon?: The myelin sheath
Around the myelin is another element, cytoplasm arising from another cell. What is this cell?: This cell is the Schwann cell
Where two myelin sheaths contact is called what?: It is called the Node of Ranvier
Do dendrites have Nissl substance?: Yes, they do
Does the axon and axon hillock have Nissl substance?: No, they do not.
Since this is the central nervous system, what is the cell called that forms the myelin here?: Oligodendrocyte
What makes myelin in the peripheral nervous system?: Schwann cells
What is the line of demarcation between central and peripheral nervous systems?: The line is where the dorsal and ventral roots go on the spinal cord
What are the major organelles neurons have?: Rough ER, free ribosomes, mitochondria, microtubules, neurofilaments, and Golgi complex
What are neurofilaments packed with?: Intermediate filaments
What is a synapse?: Where one nueron contacts another
What is passed from one cell to another here?: A nerve impulse
What is at the presynaptic terminal end?: Vesicles with neurotransmitters of various kinds
When the nerve impulse comes down, what happens pertaining to these vesicles?: They attach to the pre-synaptic membrane, and then apoptosis causes these neurotransmitters to exocytize and move across the synaptic cleft, and they hook up with synaptic receptors on the other side
What do these neurotransmitters do when they meet these receptors?: They can make the membranes either more polarized or less polarized
More polarized is ________, while less polarized is ________.: Inhibitory, excited
Does this go in both directions or one direction?: One direction only
What is the newer idea of calcium selective channels?: The idea is that these channels can cause contacts with a neurotransmitter vesicle, and then a very small pore will open up about 1nm across, and this will cause the neurotransmitters to pass through this temporary opening in the plasma membrane
What are electrical synapsis?: They occur in gap junctions
How does this occur in gap junctions?: Gap junctions form a channel across plasma membranes, so an ion passes directly from the cytoplasm of this cell to the cytoplasm of this cell, and this converts electrical polarity
Why is it electrical rather than chemical?: It's electrical because no neurotransmitter is involved
What is axonal transport?: It is movement on an axon from either the terminal end to the cell body side, or vice-versa via a molecular motor
What are the two kinds of movement?: Fast axonal transport, and slow axonal transport
How does fast axonal transport work?: It can move both directions, and if they move toward the termination of the axon, this is called anterograde, but if it moves to the cell body end, it is called retrograde
How does this work?: The microtubules in the axon serve as a railroad track for movement by molecular motors
How many motors per retrograde versus anterograde?: There is one motor for retrograde, and one motor for anterograde
How does slow axonal transport work?: It can move in one direction, from the cell body toward the termination of the axon
Is it much slower than fast?: Yes, it moves 0.2-4.0 mm per day, and fast can move up to 400mm per day
How does the axon / Schwann cell interaction occur in the peripheral nervous system?: The axon will contact a Schwann cell, and this cell will wrap itself around the axon, and it will leave behind layers of plasma membrane, so there's nothing but layer upon layer upon layer of plasma membrane
Between two successive nodes of Ranvier, what do we have?: An internode segment
So what is the internode segment comprised of?: Mostly the layer of cytoplasm released by the Schwann cells
Are all axons myelinated?: Not all are myelinated
Is there any rhyme or reason as to which are myelinated and which are not?: Nope. You can have some in the peripheral system that are heavily myelinated, and you have others with less, and then you have some axons with no myelin at all
Where are these axons with no myelin emedded?: They are embedded within the trench of cytoplasm with the Schwann cells
If an axon is myelinated, one segment is associated with _______ Schwann cell(s).: 1
If an axon in unmyelinated, one segment is associated with __________ Schwann cell(s): multiple
Does the central nervous system have regeneration?: No
Does the peripheral nervous system have regernation?: Yes
How does regeneration occur in peripheral nervous system?: If it gets severed, myelin will regenerate and then it will send out sprouts, and the Schwann cells along this length will move and connect
Dorsal root is sensory or ________: afferent
Ventral root is motor or _______: efferent
A collection of nerve cell bodies outside the CNS is called what?: Ganglia
A collection of nerve cell bodies within the CNS are called?: A nucleus
What types of neurons are there in the dorsal root ganglion, and how many processes do they have?: They are peudo-unipolar neurons, and they have two processes
What are the locations of where the two processes lead?: One goes through the dorsal root and into the ventral horn cells, and the other process goes away from the spinal cord
In addition to Schwann cells, what else is covering nerve bundles?: In addition to Schwann cells, we have loose connective tissue, called endoneurium
Around each bundle of fibers is a layer of cells called the __________: perineurium
So the perineurium is external to the endoneurium?: Yes, it is
How many layers thick is the perineurium?: Maybe 4-5 or more layers thick
What is the perineurium composed of?: It is composed of flattened epithelial like squamous cells, and they form a sheath around this bundle of axons
What is the function of the perineurium?: Their primary function is to serve as a protective sleeve around these axons, and so we have a perioneurium
Holding these bundles together, and surrounding the groups of fibers, we have what?: Dense irregular connective tissue called the epineurium
What do they have around them?: Tight junctions
What is a fascicle?: It means a bundle, and it could mean a bundle of anything
The longer the axon, the more heavily myelinated it is, and the longer the internodes are, the (faster / slower) it will conduct a nerve impulse: faster
Does an unmyelinated axon conduct nerve impulses slower?: Much slower
What color does osmium stain lipid?: Black
What is an example of a sensory ganglia?: Dorsal root ganglia
What kind of neurons do sensory ganglia have?: They have pseudo-unipolar neurons
What is another name for motor ganglia?: Autonomic ganglia
From the central nervous system, axons pass out into the motor ganglia and make active contact with what, and where?: They make contact with a neuron inside the motor ganglia
Then what do they do?: These neurons innervate something like the gut if its an autonomic motor ganglia versus a somatic motor ganglia which would be a muscle
Are there synapses in sensory ganglia?: There are no synapses in sensory ganglia
Are there synapses in motor ganglia?: They have many synapses
What is the size difference in motor ganglia versus sensory ganglia?: Motor ganglia not as large, and not as round
How are the nuclei arranged in motor ganglia?: The nuclei are located eccentrically
What type of neurons are in motor ganglia?: They are multi-polar
How do you classify sensory receptors?: You classify them based on their structure
What is the simplest kind of afferent receptor?: A free nerve ending receptor
What is a free nerve ending receptor in the epidermis for example?: At the junction between the dermis and epidermis, the myelin looses its myelin sheath, and the branches of this free nerve go out into the epidermis
What is Meissner's corpuscle?: It is a type of nerve ending that is encapsulated
What does it contain?: In Meissner's corpuscle, it has a capsule, and some cells are located at right angles to it, and axons will come in and penetrate the capsule and it will settle up at this area, with many cells
What are Meissner's corpuscles used in?: They are related to touch
What are Pacinian corpuscles?: It is a nerve ending that is encapsulated, that responds to pressure and in particular vibration
What is a neuromuscular spindle?: It is found among skeletal muscle, and what this sensory nerve ending senses is muscle stress, so it is a muscle stress receptor
What does it consist of?: It consists of a capsule surrounding some modified skeletal muscle cells, and these cells are inside this connective tissue capsule
Inside a neuromuscular spindle, the muscles are peculiar. Explain the two kinds of muscle cells within, and describe each of their functions: Skeletal muscle cells have many nuclei in one cell, like 100 in one cell, and these nuclei are located just under the fiber membrane of this skeletal muscle cell, but these modified skeletal muscle cells have an area with most of the nuclei, and this is called a nuclear bagged muscle cell. The second modified muscle cell is located adjacent to the nuclear bagged and they are nuclear chain muscle cells
Primary sensory fibers are?: Afferent and Efferent
Secondary sensory fibers are what?: Afferent and efferent
Which are responsible for the stretch reception of these muscle cells?: Both are responsible
What are gamma afferent fibers?: They are the motor innervations responsible for this
What's the purpose of having a motor fiber related to these modified cells: Motor innervation of these muscle fibers tends to adjust the sensitivity of it
How does this relate functionally?: If they are relatively contracted, they will be more sensitive to stress. If they are less contracted they will be less sensitive to stress
What is a golgi tendon organ?: It is made up of dense fibers, surrounding a tissue capsule
What kind of fibers are in a golgi tendon organ?: You will have afferent fibers and efferent fibers
How do these fibers work, and what do they sense off of?: They sense off of the tendons they receive input from, and when pressure is put on a tendon, it squeezes the fibers, and this is sensed as a nerve impulse to the central nervous system
What is the point of golgi tendon organs?: They are a sensory mechanism to sense how much tension is placed on the tendon
Describe taste buds, what is inside them, and how they work: We have them in the mouth, and these are related to sensory fibers, we have basal cells, sensory cells, which are innervated by sensory fibers, and then we have supporting cells
Basal cells are what?: Sensory cells are constantly needing ot be replaced, and basal cells can divide and replace supporting cells and sensory cells
Taste buds are responsive to what?: Chemicals
The dura surrounding which, the brain or the spinal cord, consists of two layers? (External to dura mater): The brain has two layers
What are these two layers called?: The layer immediately adjacent to the bone is the periosteal layer, and the other inner layer is the meningeal layer
What is the ventricle of the brain?: It is the space inside the brain with the CSF
What is an ependyma?: It lines the ventricle
What is exterior to the ependyma?: Externally, we have the pia
In areas where the periosteal and meningeal spaces we have a venous space, and in these venous spaces we have what?: Evaginations of the arachnoid
What do the evaginations provide?: They serve as one-way valves allowing the subarachnoid space to move to the venous space
What is this space continuous with?: It is continuous with the internal jugular vein, and then into the heart
What are the evaginations called?: They are called an arachnoid villus
Where are astrocytes located?: In the white matter if they are fibrous, and if they are protoplasmic they are in the gray matter
What do astrocytes do?: They send out process that surround blood vessels, and they form a network of proceses under the epindyma as well as another network of processes under the pia
What do astrocytes surround?: They tend to surround just about everything not surrounded by something else
What do protoplasmic astrocytes have?: They have little feet that connect to blood vessels and axons
What do these astrocytes do?: They take up excess neurotransmitters and buffer the ion by taking out excess ions
Do protoplasmic astrocytes have long or short processes in relation to fibrous astrocytes?: Protoplasmic have much shorter processes, but they have more. Fibrous astrocytes have fewer but longer processes
When protoplasmic astrocytes surround blood vessels, what do they accomplish?: They induce formation of tight junctions between the endothelial cells lining the blood vessels
What type of epithelium do ependyma form?: They form a simple columnar or pseudo-stratified layer
White matter has _______ axons, and gray matter has _________ axons: myelinated, unmyelinated

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