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95 Cards in this Set

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The nervous system has two major anatomical subdivisions:
central nervous system (CNS)
peripheral nervous system (PNS)
consists of the brain and spinal cord
central nervous system (CNS)
consists of all the nervous system except the brain and spinal cord. It is composed of nerves and ganglia
peripheral nervous system (PNS)
fibers always conduct signals away from the CNS
Motor (efferent)
fibers always conduct signals toward the CNS
Sensory (afferent)
fibers innervate skeletal muscle, the skin, bones, and joints.
Somatic
fibers innervate cardiac muscle, smooth muscle, and glands.
Visceral
There are three general classes of neurons;
Sensory (afferent) neurons, Interneurons (association neurons), and motor (efferent) neurons
About 90% of our neurons are
interneurons
The control center of the neuron is the
soma
also called the neurosoma, cell body, or perikaryon
soma
There are six kinds of neuroglia (glial cells)
Four types occur only in the CNS, and two occur only in the PNS.
Oligodendrocytes produce the myelin in the CNS, and Schwann cells produce the myelin in the PNS
two occur only in the PNS
Since the myelin consists of the plasma membranes of these glial cells, its composition is like that of plasma membranes in general
It is 80% lipid and 20% protein
They resemble a cuboidal epithelium, line the internal cavities of the brain and spinal cord, and are responsible for the production of cerebrospinal fluid (CSF)
Ependymal cells are found only in the CNS
They are the most abundant glial cells in the CNS
Astrocytes
are also found only in the CNS and are responsible for formation of the blood-brain barrier
are the macrophages of the CNS
Microglia
have one axon and multiple dendrites
Multipolar neurons
have one axon and one dendrite
Bipolar neurons
have only a single process leading away from the soma
Unipolar neurons
Conduction speed of nerve fibers depends on two factors:
the diameter of the fiber and the presence or absence of myelin
Large diameter fibers conduct signals
more rapidly than small diameter fibers
Myelinated fibers conduct signals
more rapidly than unmyelinated fibers
the fastest signal-conducting fibers in our nervous system are large
myelinated fibers
The myelin covering a nerve fiber is
segmented
The myelinated segments are called
internodes
the unmyelinated gaps in between the myelinated segments are called
nodes of Ranvier
In order for a peripheral nerve fiber to regenerate it must have an
intact soma and at least some neurilemma intact
Damaged nerve fibers in the CNS cannot
regenerate
Potassium ions have the greatest influence on the resting membrane potential (RMP)
because the plasma membrane is more permeable to potassium than any other ion
the opening of sodium gates causes sodium ions to come into the cell, which leads to depolarization of the plasma membrane
During an action potential
Chloride ions, being negatively charged, cause the membrane potential to become more negative when they enter the cell. When a cell is at its RMP, any decrease in voltage that causes the voltage to become more negative than the RMP is called
hyperpolarization
At threshold
both sodium and potassium gates are opening
___________ of an action potential no stimulus of any strength will trigger a new action potential
During the absolute refractory period
____________ it is possible to trigger a new action potential, but only with an unusually strong stimulus
During the relative refractory period
____________ each action potential at the current node has the same strength as the one at the previous node
saltatory conduction
Synapses that employ acetylcholine as the neurotransmitter are called
cholinergic synapses
Amino acid neurotransmitters include,
glycine, glutamate, aspartate, and gamma-aminobutyric acid (GABA)
There are four major classes of neurotransmitters
Acetylcholine is in a class by itself
GABA is considered an inhibitory neurotransmitter
because the binding of GABA to its receptor opens chloride(Cl-) gates that hyperpolarize the membrane
The monoamines include
norepinephrine, epinephrine, dopamine, and others
The monoamines act through second-messenger systems such as
cyclic AMP.
The neuropeptides are
chains of 2 to 40 amino acids. Some examples are beta-endorphin and substance P
Even though all action potentials are the same, the brain can differentiate a variety of stimuli by source and intensity. The mechanism by which the nervous system converts these action potentials into meaningful information is called
neural coding
Synapses are not fixed for life; in response to experience, they can be added, taken away, or modified to make transmission easier or harder. This ability of synapses to change is called
synaptic plasticity
________ is the ability to hold something in mind for just a few seconds
Immediate memory
________ lasts from a few seconds to a few hours
Short-term memory
lasts up to a lifetime
Long-term memory
The meninges of the spinal cord from superficial to deep
dura mater (dural sheath), arachnoid mater, and pia mater
The spinal cord is divided into
cervical, thoracic, lumbar, and sacral regions
The space between the dura mater and vertebral bones is called the
epidural space
_______ is introduced into this space to block pain signals during pregnancy
Epidural anesthesia
The space between the arachnoid mater and pia mater is the
subarachnoid space
The subarachnoid space is filled with
cerebrospinal fluid (CSF)
The spinal cord has a central core of gray matter surrounded by
white matter.
The gray matter contains
the somas, dendrites, and proximal parts of axons of neurons
The white matter contains bundles of myelinated fibers called
tracts running up and down the spinal cord
Ascending tracts carry sensory signals
up the spinal cord
Descending tracts carry motor signals down
the brainstem and spinal cord
When the origin and destination of a tract are on opposite sides of the body we say they are
contralateral to each other
In most nerves, the nerve fibers are gathered in bundles called
fascicles, with each fascicle wrapped in a sheath called the perineurium
The connective tissue sheath surrounding the entire nerve is the
epineurium
The ventral (anterior) rami of the spinal nerves form five weblike nerve plexuses:
cervical, brachial, lumbar, sacral, and coccygeal
The most important nerve of the cervical plexus is the
phrenic nerve, which plays an essential role in breathing
The tibial and common fibular nerves travel together through a
connective tissue sheath, and are collectively referred to as the sciatic nerve
The gray matter contains
the somas, dendrites, and proximal parts of axons of neurons
The white matter contains bundles of myelinated fibers called
tracts running up and down the spinal cord
Ascending tracts carry sensory signals
up the spinal cord
Descending tracts carry motor signals down
the brainstem and spinal cord
When the origin and destination of a tract are on opposite sides of the body we say they are
contralateral to each other
In most nerves, the nerve fibers are gathered in bundles called
fascicles, with each fascicle wrapped in a sheath called the perineurium
The connective tissue sheath surrounding the entire nerve is the
epineurium
The ventral (anterior) rami of the spinal nerves form five weblike nerve plexuses:
cervical, brachial, lumbar, sacral, and coccygeal
The most important nerve of the cervical plexus is the
phrenic nerve, which plays an essential role in breathing
The tibial and common fibular nerves travel together through a
connective tissue sheath, and are collectively referred to as the sciatic nerve
The gray matter contains
the somas, dendrites, and proximal parts of axons of neurons
The white matter contains bundles of myelinated fibers called
tracts running up and down the spinal cord
Ascending tracts carry sensory signals
up the spinal cord
Descending tracts carry motor signals down
the brainstem and spinal cord
When the origin and destination of a tract are on opposite sides of the body we say they are
contralateral to each other
In most nerves, the nerve fibers are gathered in bundles called
fascicles, with each fascicle wrapped in a sheath called the perineurium
The connective tissue sheath surrounding the entire nerve is the
epineurium
The ventral (anterior) rami of the spinal nerves form five weblike nerve plexuses:
cervical, brachial, lumbar, sacral, and coccygeal
The most important nerve of the cervical plexus is the
phrenic nerve, which plays an essential role in breathing
The tibial and common fibular nerves travel together through a
connective tissue sheath, and are collectively referred to as the sciatic nerve
is a diagram of the cutaneous regions innervated by each spinal nerve. Because dermatomes overlap at their edges by as much as 50%, it is necessary to sever or anesthetize three successive spinal nerves to produce a total loss of sensation from one dermatome.
A dermatome map
Four important properties of a reflex:
1. Reflexes require stimulation and do not occur spontaneously; they are responses to sensory input.
2. Reflexes are very predictable. They occur in essentially the same way every time.
3. Reflexes are involuntary.
4. Reflexes are quick and generally involve few if any interneurons.
__________ has three principal classes of nerve fibers. A primary (group Ia) fiber, a secondary (group II) fiber, and a gamma motor neuron.
A muscle spindle
Muscle spindles are
proprioceptors that respond to stretch
Proprioceptors are sense organs which are
specialized to monitor the position and movement of body parts
A somatic reflex employs a reflex arc, in which signals travel along the following pathway:
somatic receptor >>> afferent nerve fiber >>> integrating center >>> efferent nerve fiber >>> skeletal muscle
The quickest reflex arcs involve only two neurons, thus forming
monosynaptic reflex arcs
The muscle fibers within a muscle spindle are called intrafusal fibers,
while those that make up the rest of the muscle and do its work are called extrafusal fibers.
When a muscle is stretched, it “fights back”. It contracts and feels stiffer than an unstretched muscle. This response is called the
stretch (myotatic) reflex
The tendon reflex is a response to excessive tension on the tendon.
It inhibits alpha motor neurons to the muscle so the muscle does not contract as strongly.