Glossary of Human Anatomy Chapter 12

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STUPID FACT (Just in case): What is ENIAC?
the first computer created (weighing 3 tons)
the study of the nervous system
What are the two divisions of the Nervous system?
Central Nervous System- the brain and spinal cord

Peripheral Nervous system- the nervous system that functions outside the CNS.
What three kinds of cells are common in the Peripheral nervous sytem
Cranial and spinal nerves (communicate messeges to and from the brain and spine). Also, ganglia (areas where cell bodies are clustered).
What are the three overlapping functions of the Nervous system.
Sensory- recieve sensory information

Integration- must be able to percieve the sensation and formulate a plan of action.

Motor output- executes a motor response according to the plan created in the integration phase.
What does afferent mean? what signals are sent by afferent transport?
"Carrying toward" the CNS.

Sensory information is sent to toward the CNS to be integrated.
What does efferent mean? what signals are sent by efferent transport?
"away from" the CNS.

Motor output is carried away from the CNS to act on the appropriate muscles.
The PNS is divided into two classes of signals. What are they?
Sensory (afferent) division and Motor (efferent) division
Each division of the peripheral nervous system is further subdivided into two classes. What are the four?
Somatic Sensory
Somatic Visceral
Motor Sensory
Motor Visceral
Both sensory and motor classes of the PNS are subdivided into either somatic or visceral, according to what?
the body regions they serve.

Somatic- Skin, skeletal muscle, bones

Visceral- organs in the ventral body.
Somatic senory division of the PNS.

- recieves what signal
- in what direction is it travelling
- from what two classes does it recieve information.

Afferent (Toward CNS)

*General Somatic senses- those stimuli that can be felt on all of the body.
(touch, pain, pressure, temperture, proprioception)

*Special somatic senses- these senses are localized and sensed in a small region of the body (vision, hearing, smelling, balance)
Visceral Sensory division of the PNS.

-Recieves what information
- In what direction is it traveling
- from what two classes of sesnses?

Afferent (Toward the CNS)

*general visceral senses-
stretch, pain, and temperature felt in the viscera. (Nausea and hunger)

*special visceral senses-
sensory information recieved from the localized organs of the body. (TASTE)
Somatic Motor division of the PNS.

-Recieves what information
- In what direction is it traveling
- from what two classes of sesnses?

Efferent (Away from the CNS)

Trick question there is only one class.
*General Somatic motor- part of the PNS that signals contraction of skelletal muscles (they are widely found in the body).
Visceral motor division of the PNS.

-Recieves what information
- In what direction is it traveling
- from what two classes of sesnses?

Efferent (Away from the CNS)

Only one class.
*General visceral motor-
part of the nervous system that regulates contraction of smooth and cardiac muscle. (AUTOnomic NS).
Nervous tissue, despite its complexity, is made up of just two types of cells. What are they?
Neurons and supporting cells.

-how many
-how are signals produced
the basic structural units of the nervous system. highly-specialized cells that propogate electrical signals from one part of their body to another.

1 billion

Action potentials
Besides a neurons ability to propogate action potentials, what are 3 special characteristics of neurons?
1.) they have EXTREME LONGEVITY (over 100 years)

2.) they DO NOT DIVIDE. (some exceptions- CNS stem cells)

Neuronal cell bodies

-consist of
also called a soma, it consists of a single nucleus surrounded by cytoplasm.
The Cell body also contains chromatophilic bodies (NIssl) and Neurofibrils. What are their functions?
Chromatophillic bodies- "color loving" clusters of rough ER which produce proteins that renew membrane.

Neurofibrils- bundles of intermediate filaments that keep the cell body from being pulled apart from tensile forces.
While MOST cell bodies (Soma) are in the CNS, some do lie outside the CNS such as...
Ganglion- clusters of cell bodies outside the CNS.
What are the two NEURONAL PROCESSES (projections off cell body).

What are their functions
Dendrites- function as receptive sites to recieve signals from other neurons. Dendrites then by definition produce AFFERENT SIGNALS ONLY!

Axon- thin long projections. At the meeting between soma and axon is the axon hillock where action potentials are generated. Thus by definition axons produce EFFERENT SIGNALS ONLY!
Although axons branch far less than dendrites, they do branch into segments called...
axon collaterals.
What is the diffrence between a neuron, nerve fiber and nerve?
Neuron- the smallest cellular unit of the nervous system.

Nerve fiber- long extension from the cell body (AXON)

Nerve- bundles of nerve fibers outside the CNS (ganglia?)
The sie at which neurons communicate is called a...
Most synapses in the nervous system tramsit messages by what process?
Still others use?
Because signals pass across most synapses in one direction only, synapses determine...
Chemical transmission

electrical transmission across gap junctions.

the direction of information through the nervous system
The neuron that conducts signals toward a synapse is called the...
the neuron that transmits signal away from the synapse is called the...
presynaptic neuron; postsynaptic neuron
types of synapses

Axodendritic- most common from the axon of one neuron to the dendrite of the other.

Axosomatic- many synapses have these neurons.

The rest are far less common and far less understood.
Presynaptic neurons have _________ which are membrane-bound sacs filled with NT.
Synaptic vesicles
What is the NT released at a neuromuscular junction to cause flexion of a muscle.
What is the function of Cholinesterase?
Cholinesterase serves to break down choline and control against unnecessarily long flexion.
Why do we say "action potentials on the axon" and not action potentials in the neuron.
While the whole neuron can become depolarized, only depolarization (strong enough) at the axon can cause an action potential down the length of the entire axon.
graded potentials are recieved where... they are spatially summed up where...
the dendrites and the cell body recieve graded depolarizations that cause mild depolarizations these signals are spatially summed at the axon hillock where there either there is enough depolarization to warrant an action potential (ALL OR NONE)
What is the purpose of the Sodium potassium pump? what does it actually pump in and out and in what amounts?
The purpose of the Sodium potassium pump is to mantain the resting potential of the neuron by pumping out 3 sodium ions (cations) and while pumping in 2 Potassium ions.
At resting potential, what forces from the following three ions are acting on the membrane.

-Concentration gradient- IN
- Electrochemical- IN

-Concentration- OUT
- Electrochemical- IN

-Concentration- IN
-Electrochemical- OUT
What then keeps the Sodium ions out of the membrane?
The neuronal membrane is impermeable to sodium.
What two major effects control the speed of neuronal transmission?
-Myelination- makes transmission faster

- diameter of the axon- the wider the axon the faster transmission can take place down its axon.
According to Dr. Tillman why are axons with larger diameters able to transmit more quickly?
because neurons with larger axons can have more negative charge surrounding the axon (???)
Mathematically how does the speed of conduction increase if the number of myelinated fibers doubles? unmyelinated fibers doubles?
As one doubles the other doubles.

As on doubles the other will increase by the square root of 2.
What is the weak buffalo theory of Alcohol use?
Alcohol kills off only the weak neurons (NOT TRUE)
what is the so-called "HOMER THEORY" of alcohol and marijuana use?
they simply destroy connections between neurons.
What are the two realities of using marijuana?
1.) Marijuana users have deficits in short term memory.

2.) Marijuana users' brains age quicker than non-users' brains.
What are the three STRUCTURAL classes of neurons.
Which is the most common?
What function does each normally serve?
Multipolar (99% of all neurons)- have the cell bodies between the dendrites and axon. (MOTOR NEURONS AND INTERNEURONS)

Unipolar- cell body out to the side of axon (Sensory neurons)

Bipolar- cell body in the center of the axon (sensory neurons).
Where do the names mutipolar, unipolar and bipolar come from?
Multipolars have "multi processes" or multiple projections from the soma.

Bipolar neurons have 2 projections from the soma.

Unipolar neurons have 1.
What are the three functional classifications of neurons? What structural class of neurons make them up? what direction do they transmit messges.
1.) Sensory neurons are nearly all Unipolar neurons that transmit afferent messages (toward the CNS) from the PNS.
Sensory neurons do not have dendrites. WHY?
Because the central process caries a signal to the CNS (therefore it is an axon b/c it transmits a signal and toward the CNS). The peripheral process is also considered axonal as it transmits a signal eventhough it is toward the cell body (characteristically of dendrites)
what are the three functional classification s of neurons?
Sensory neurons, Motor neurons, and inter neurons (mixed neurons.)
Motor neurons

-carry afferent/efferent messages.
-motor neurons are made up of what structural class of neurons.
-Motor neurons from junctions with effector cells in order to...
Efferent (Away from the CNS)

Multipolar neurons

junctions with effector cells stimulate mucsles to contract or glands to secrete.
Interneurons (Mixed neurons)

-lie between
- confound only to
- function to
- made up of what structural class of neurons
-interesting fact.
-Sensory and motor neurons

- the CNS

- link together sensory and motor neurons to form complex neuropathways.

- almost all are made up of multipolar neurons.

-Makeup 99% of all the neurons in the body.
Sensory neurons

-afferent/efferent transmission
-structural type

Transmit toward the CNS (afferent)


-afferent/efferent transmission
-structural class of neuron
CNS exclusively.


Motor neurons

-afferent/efferent transmission
-structural class of neuron

effrerent (away from the CNS)

Supporting cells are also called neuroglia. There are six classes of neuroglia. What are their names and where can they be found?
-Ependmal cells

PNS support cells
-Schwann cells
-Satelite cells


bind several neurons to nearby capilaries to supply it with glucose, oxygen, nutrients and removal of wastes.
Microglial cells


Phagocytize any pathogens or debris.
Ependymal cells


Move CSF by ciliary action.


Provide myelination for neurons in the CNS.
Satelite cells


Physically support cell bodies in ganglia (OUTSIDE THE CNS)
Schwann cells


myelinate the neurons of the perioheral nervous system.
How does myelinaion increase the speed at which a neuron can propogate signal?
Myelination insluates the neuron from losing electrical potential down its axon. Electrical signal actually occurs only in the NODES OF RANVIER and causes what is called saltatory conduction.
What is gray mater vs. white mater?
White mater refers to nerves that are myelinated, wheras gray mater refers to unmyelinated nerves.
Recall that a neuron is a single cell and several neurons form a fassicle. Several fassicles form a nerve in the PNS.

Each neuron is surrounded by...
Each fassicle is surrounded by...
Each nerve is surrounded by...


simple chains of neurons that explain out simplest, relexive behaviors and determine the basic structural plan of the nervous system.
Reflex arcs.

it should be mentioned these reactions are unleraned, unpremeditated, and involuntary (NO BRAIN USAGE)
The five essentaial components of a reflex arc.
1.) receptor- where the stimulus acts
2.) Sensory neuron-transmits the afferent impulses to the CNS
3.) integration center- synapses in the CNS that integrate signal and send back signals
4.) Motor neuron- conducts efferent impulses
5.) Effector- the muscle or gland that reacts to the efferent message.
Monosynaptic (stretch reflex)

- how many neurons are required
- Fast/slow
Only 2 neurons (Sensory and motor)~ NO INTERNEURON REQD



Knee-jerk response.
Polysynaptic (Withdrawal) reflex

-requires how many neurons
polysynaptic (w/ interneurons)

Slower than monosynaptic


touching hot stove
Crossed Extensor reflex

-requires how many neurons?

slower than monosynaptic

contralateral and ipsilateral

stepping on a nail.
In crossed extensor reflex arcs what key process occurs at the interneuron?
The crossing over of information to the conralateral side of the body.
What information enters the dorsal spine. What information exits the ventral spine.
Afferent sensory information enters the dorsal spines of the spinal column and reaches the brain then exits the ventral spine of the spinal column out to effector cells.
Sensory neurons develop from the...
neural crest and hence are found OUTSIDE THE CNS.
Motor neurons develop from...
ventral neuroblasts of the basal plate.
Interneurons develop from...
dorsally the neuroblasts of the alar plate.
Does neural regeneration exist?
IF AXONS ONLY are destroyed in the PNS the immune system phagocytically eats distal to the injury and new innervations are made.

In the CNS the neural glial cells never form bands to help guide reinnervation as they do in the PNS. Therefore essentially CNS regeneration is NOT possible.

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