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What are the two primary functional divisions/organization of the nervous system? How do they differ? Peripheral nervous system

The PNS sensory division detects stimuli and transmit information from receptors to the CNS.
The PNS motor division initiates and transmit information from the CNS to effectors.


What are the two anatomical divisions/structural organization of the nervous system?

The central nervous system consists of the brain and spinal cord. The peripheral nervous system consists of the spinal nerves and their branches/ganglia.


What three functions does the nervous system have?

Sensory, integrative, and motor.


Function of the NS that involves gathering information about the internal and external environment of the body.

Sensory functions
Afferent PNS


Functions of the NS that analyze and interpret the incoming sensory information and determine and appropriate response.

Integrative functions
Performed entirely by the CNS, mostly the brain


Functions of the NS that are the actions performed in response to integration.

Motor functions
Efferent division of the PNS


How many pairs of cranial and spinal nerves?

12 cranial
31 spinal


Division of the PNS that consists of neurons that carry general sensory signals from muscles, bones, joints, and the skin, as well as special sensory signals. 5 senses

Somatic sensory division
Consciously perceived


Division of the PNS that carries signals from viscera such as the heart, lungs, stomach, etc.

Visceral sensory division
Not consciously perceived


Division of the PNS that consists of neurons that transmit signals to skeletal muscles.

Somatic motor division Voluntary


Division of the PNS that consists of neurons that carry signals primarily to thoracic and abdominal viscera. Regulates secretion from certain glands, contraction of smooth/cardiac muscles. Homeostasis.

Visceral motor division
Autonomic nervous system


Neurons have these five features?

Excitability, conductivity, secretion, extreme longevity, amitotic


Meaning that at a certain point in a cell's development, they lose their centrioles and after that lack ability to undergo mitosis.



The excitable cell type responsible for sending and receiving signals in the form of action potentials. Consist of three parts.

Cell body, axon, dendrites


Neurons control center, enclosed by a plasma membrane with cytoplasm surrounding a nucleus with prominent nucleolus. Free and bound ribosomes. no centrioles.

Cell body of the neuron


Provide structural support for that extends out into the dendrites and axon of the neuron as well.



Receive input from other neurons, which they transmit in the form of electrical impulses to the cell body. The cell may have one or many.



These are termed either chromatophilic or Nissl bodies due to their dark color under a microscope.

Clusters of free and bound ribosomes in the cell body.


Cytoplasm within cell body



Process emanating from the cell body that makes contact with other neurons, muscle cells, or glands. Generates and conducts action potentials. Nerve fiber.



Branches extending at right angles from the axon. Both the axon and these split at the ends to produce multiple fine telodendria (axon terminals).

Axon collaterals


Telodendria terminate in these, which communicate with a target cell. Each axon generally splits into 1000 or more of these.

Axon terminals
Synaptic knobs


The plasma membrane and cytoplasm of the neuron.



Type of transport that relies on motor proteins in the axoplasm that consume Atp and move substances along the microtubules in what two ways?

Fast axonal/bidirectional transport
Retrograde (toward the cell body)
Anterograde (away from the cell body)


Neurons that have a single axon and typically multiple highly branched dendrites. Over 99% of neurons in the body. Widest variability in terms of shape and size. What division?

Multipolar neurons
Motor (efferent) neurons, interneurons


Neurons that have only two processes: one axon and one dendrite. Located in special sense organs in the PNS, such as the retina. What division?

Bipolar neurons
Sensory (afferent) neurons


Neurons that begin developmentally as bipolar, but their two processes fuse to give rise to a single axon which splits into the peripheral and central axons. Sensory neurons in the PNS, touch, pressure, etc. What does each axon do? What division?

Pseudo unipolar axons
Peripheral axon brings information from sensory receptors to the cell body
Central axon travels to the spinal cord away from the cell body.
Sensory (afferent neurons)


Association neurons. Relay messages within the CNS, primarily between sensory and motor neurons. Location of most information processing. Vast majority of neurons are these. Multipolar.



Clusters of cell bodies of neurons, most of which are in the CNS where they are called what? Within the PNS they are called what?

Nuclei in the CNS, tracts
Ganglia in the PNS, nerves


Nonexcitable cells that maintain the environment between neurons, protecting them, assisting in their functioning. Retain their ability to divide and fill in gaps when neurons die.

10 times more abundant in the CNS than neurons, make up half the mass of the brain.


Four types of glial cells in the CNS?



Two types of microglia in the PNS?

Schwann cells
Satellite cells


Macroscopic cable-like bundle of parallel axons



Layer of dense irregular connective tissue that wraps bundles of axons, fascicles and support the blood vessels.



Delicate layer of areolar connective tissue that separates and electrically insulates each axon. Has capillaries that supply the axon.



The most numerous and largest neuroglia in the CNS. Anchors neurons and blood vessels, regulates the extracellular environment, facilitates the blood-brain barrier, and repairs damaged tissue.



Astrocyte-ensheathed capillaries that are rendered impermeable to most proteins and polar compounds. Only non-polar, lipid-soluble, or facilitated diffusion can pass. Maintains a stable environment for the brain.

Blood-brain barrier


What is the blood-brain barrier made of?

Continuous epithelium of capillary walls
Basal lamina
Feet of astrocytes (provide signal to endothelium for formation of tight junctions)


Neuroglia that myelinated certain axons in the CNS. Concentric layers of plasma membrane.



The least numerous neuroglia cells in the CNS. Activated by injury in the brain and become wandering phagocytes that ingest pathogens, dead neurons, and other debris.



Ciliated neuroglia that line fluid-filled cavities. Circulates fluid around the brain and spinal cord, and some secrete this fluid.

Ependymal cells


Neuroglial cells that create the myelin sheath in the PNS. Play a vital role in the repair of damaged axons in the PNS.

Schwann cells


Neuroglial cells that are flat and enclose and support the cell bodies. Have intertwined processes that link them with other parts of the neuron, Schwann cells, and other cells of their same type.

Satellite cells


Tumors originating from the brain. Typically form in supporting tissues that have the ability to undergo mitosis, meninges, or glial cells.

Primary brain tumors


Glial cells tumors that may be relatively benign. May be malignant, capable of metastasizing.



Whitish, fatty (protein-lipoid), segmented sheath around most long or large-diameter axons. Protects the axon, electrically insulates fibers from one another, increases the speed of nerve impulse transmission.

Myelin sheath
Myelinated axons conduct impulses 15-150 times faster than unmyelinated axons


The nucleus and the bulk of the cytoplasm and organelles of the Schwann cell, on the outer surface of a myelinated axon in the PNS



White matter vs gray matter of the CNS?

White matter is composed of myelinated axons.
Gray matter is made up primarily of cell bodies and dendrites which are never myelinated, as well as unmyelinated axons


Why might axons fail to regenerate (Wallerian degeneration)?

Oligodendrocytes might inhibit the process of neuronal growth
Growth factors that trigger mitosis are largely absent in the CNS
Astrocytes create space-filling scar tissue, release chemicals


PNS axons are vulnerable to cuts and trauma. Explain their chances of regeneration?

It's possible if the cell body remains intact and enough neurilemma remains. Success is more likely if the damage isn't extensive and there's a smaller distance between the site of damage and the structure it innervates.


Autoimmune disorder that involved progressive demyelination of neurons in the CNS. Oligodendrocytes attacked by immune cells. Repeated inflammatory events cousin scarring and loss of function.

Multiple scleroisis
Vision problems, muscle weakness and spasms, urinary and bladder problems, mood problems


Loss of myelin from peripheral nerves due to inflammation. Muscle weakness that begins distal limbs and advances to include proximal muscles. No specific infectious agent identified.

Guillain-Barre syndrome
Most function recovered with little medical intervention


Channels in the plasma membrane that are always open and continually allow ions to follow their concentration gradient.

Leak channels
K+ channels diffuse it out of the cell
Na+ channels diffuse it into the cell


Channels in the plasma membrane the are closed at rest and only open in response to certain stimuli.

Gated channels


Gated channel that opens in response to a certain chemical binding to the channel or to an associated receptor.

Ligand-gated channel


Gated channel that opens or closes in response to changes in voltage across the membrane.

Voltage-gated channel


Gated channel that opens or closes in response to mechanical stimulation such as stretch, pressure, or vibration.

Mechanically gated channel


How does the Na+/K+ pump move ions?

Two potassium ions into the cytosol as it moves three sodium into the ECF. Maintains stable resting potential, primarily causes the transmembrane potential.


States that greater current is possible with larger voltage and smaller resistance. Current=voltage/resistance

Ohm's Law


Potential where ECF has high concentrations of Na+ and Cl-. Cytosol has high concentrations of K+ and -proteins that cannot cross the membrane. 0.07 volts or -70 millivolts. Slightly negative inside.

Resting potential


Opening of chemically or voltage gated channels, cation and voltage Na+ channels. Inside of cell becomes more positive, to -60mV. Movement of Na+ into neuron.



Removal of chemical stimulus, when membrane returns to resting potential. Voltage Na+ channels close and voltage-gated K+ channels open. K+ pumped out of cell.



Occurs when gated K+ channels open and allow K+ to move out of the neuron, or when gated Cl- channels open and allow Cl- to move into the cell.



How does a graded potential differ from an action potential in terms of the types of channels involved and where it occurs?

Action potentials involved voltage-gated channels at the axon.
Graded potentials involve chemically gated channels at dendrites and the cell body.


When after an action potential, no additional stimulus, no matter how strong, is able to produce an additional action potential.

Absolute refractory period
Ensures action potential moves in one direction only


After an action potential, when only a strong stimulus will produce another.

Relative refractory period


States that in the case of an action potential it either happens completely or it doesn't at all.

All-or-none principal


Potential that occurs in the receptive segment of a neuron due to opening of chemically gated channels. Temporary, reversible, decremental. Dendrites and cell bodies.

Graded/local potentials
Can cause depolarization or hyperpolarization


Potential with rapid depolarization and repolarization. Due to the opening of voltage gated channels, generated by the axons.

Action potential


Conduction wherein the axon is myelinated. Where it isn't

Saltatory conduction
Continuous conduction


What is the sequence of events from the arrival of an action potential at the synaptic knob until the release of neurotransmitter into the synaptic cleft?

Voltage-gated calcium ion channels are triggered to open by an action potential. Calcium ions move into the synaptic knob. They bind to proteins of synaptic vesicles, resulting in fusion of vesicles with neuron plasma membrane. Neurotransmitter is released.


How does conduction of an action potential in an unmyelinated axon and myelinated axon differ?

In an unmyelinated axon action potentials occur down the whole length of the axon. In an unmyelinated axon, action potentials only occur at neurofibril nodes. In myelinated regions Na+ quickly diffuses through axoplasm, initiating action potentials at the next neurofibril node.


Electrical synaptic transmission is these two things? Either neuron may act as the presynaptic or postsynaptic neuron, current may flow either direction. And this.

Nearly instantaneous


Synapse that occurs between cells that are electrically coupled via gap junctions. The axolemmas of two neurons are nearly touching and the junctions contain channels that form pores.

Electrical synapse
Found in the brain and areas that are automated. Developing tissue in embryo/fetus.


Synapse that converts an electrical signal into a chemical signal and back again once in the postsynaptic neuron, with no loss of strength. Vast majority synapses. More efficient.

Chemical synapse


What are the general characteristics of group A nerve fibers, and what functions do they normally serve?

Group A nerve fibers have the fastest conduction velocity. This is due to their large diameter and their myelination.


Local potentials that occur in the membrane of the neuron that can move the membrane either closer to or further from threshold. After the release of neurotransmitter, opening of gated channels after binding of transmitters

Postsynaptic potentials


Result from the opening of ion channels for Na or Ca ions and the entrance of positive charges into the postsynaptic. Inside of the cell becomes slightly more positive.

Excitatory postsynaptic potentials (EPSP)
Each successive one makes the membrane more depolarized and more likely to reach threshold


Result from the opening of K ion channels, which causes a loss of positive charges. Or the opening of Cl anion channels.

Inhibitory postsynaptic potential
Moves farther away from threshold


How can neurotransmitters be degraded?

Diffusion and absorption
Degradation in the synaptic cleft
Reuptake into the presynaptic neuron


The phenomenon of adding the input from several postsynaptic potentials to affect the membrane potential at the trigger zone.



Summation that occurs when the neurotransmitter is released repeatedly for the axon terminal of a single presynaptic neuron.

Temporal summation


Summation that involves the simultaneous release of neurotransmitters from the axon terminals of multiple presynaptic neurons.

Spatial summation


What are the four types of neurotransmitters?

Biogenic amines
Amino acid neurotransmitters


Groups of interneurons in the CNS. Tangled mat of neuroglial cells, dendrites, and axons in the brain, while their cell bodies may lie in other parts of the CNS.

Neuronal pools
The patterns of synaptic connection between these are called neural circuits.


Circuit that begins with one axon of an input neuron that branch so make contacts with multiple postsynaptic neurons. The axons of these then branch into more neurons, and so on.

Diverging circuit
Allows a single neuron to communicate with multiple parts of the brain/and or body.


Circuit in which axon terminals from multiple input neurons converge onto a single postsynaptic neuron, allowing for spatial summation of synapses.

Converging circuits
Input from sense receptors converge onto a neuron in the brain.