Chapter 12 part 2 Flashcards
each synaptic terminal is part of a _______
synapse
what is a synapse?
a specialized site where a neuron communicates with another cell
every synapse involves ____ cells:
2 CELLS
presynaptic cell – sends a message. INCLUDES the synaptic terminal
postsynaptic cell – receives the message
what separates the 2 cells involved in a synapse?
the synaptic cleft
in communication between 2 cells, the synaptic terminal of the ____ cell most commonly releases _____ into the ___
the synaptic terminal of the PRESYNAPTIC CELL releases chemicals called NEUROTRANSMITTERS into the SYNAPTIC CLEFT
neurotransmitter release is triggered by what?
electrical events, such as the arrival of an action potential
neurotransmitters released by the presynaptic cell flood the ___ and affect the activity of the ____
flood the SYNAPTIC CLEFT and affect the activity of the POSTSYNAPTIC CELL
The presynaptic cell is usually a ____
the postsynaptic cell is usually a ____
the presynaptic cell is usually a NEURON
the postsynaptic cell can either be a neuron or another type of cell
what is a neuromuscular junction?
a synapse between a neuron and a muscle cell
what is a secretory cell
a gland cell
what is the site called where a neuron controls or regulates the activity of a secretory cell?
a neuroglandular junction
do neurons only innervate secretory cells and muscles?
no – also a variety of other cells, such as adipocytes (fat cells)
does the structure of the synaptic terminal vary?
yes – varies with the type of postynaptic cell
a relatively simple, round synaptic terminal occurs when….
the postynaptic cell is another neuron
at a synapse, what separates the presynaptic membrane from the postsynaptic membrane?
the narrow synaptic cleft
neurotransmitters are released from the ______synaptic membrane
pre
the ____synaptic membrane bears receptors for neurotransmitters
postsynaptic
each synaptic terminal contains….
mitochondria, portions of the endoplasmic reticulum, and thousands of vesicles filled with neurotransmitter molecules
explain what a synaptic terminal does that improves efficiency
a synaptic terminal reabsorbs breakdown products of neurotransmitters formed at the synapse and reassembles them.
explain the supply of neurotransmitters to the synaptic terminal
the synaptic terminal receives a continuous supply of neurotransmitters synthesized in the cell body, along with enzymes and lysosomes
explain the travel of the materials previously mentioned (neurotransmitters, enzymes, and lysosomes) to the synaptic terminal
these materials come from the cell body (neurotransmitters are synthesized there) and travel along the length of the axon on NEUROTUBULES. they are pulled along by MOLECULAR MOTORS — kinesin and dynein – both are ATP dependent
the movement of materials between the cell body and synaptic terminals is called…..
axoplasmic transport
do vesicles containing neurotransmitters move fast or slow compared to vesicles with other materials?
vesicles containing neurotransmitters move FAST (called “fast stream” — 5-10mm per hour)
is axoplasmic transport unidirectional?
NO – it occurs in both directions
from the cell body to the synaptic terminal is called anterograde flow
substances moving TOWARD the cell body is termed retrograde flow
in ANTEROGRADE flow, the substances are carried by ______
kinesin
in RETROGRADE FLOW, the substances are carried by ______
dynein
what happens if debris or unusual chemicals appear in the synaptic terminal?
retrograde flow delivers them to the cell body
there, they may alter the activity of the cell by turning certain genes on or off
do kinesin and dynein require ATP?
YES
Name the STRUCTURAL classifications of neurons
anaxonic
bipolar
unipolar
multipolar
describe the structural neuron anaxonic
and where they are located
small. all the cell processes look alike (axons cannot be distinguished from dendrites)
located in the brain and special sense organs
Describe a bipolar neuron and where they are located
bipolar neurons have 2 distinct processes — one dendrite that branches into dendritic branches, and one axon. cell body is between the 2
they are in special sense organs where they relay information about sight, smell, or hearing from receptor cells to other neurons
RARE
describe a unipolar neuron and where it is located
the dendrites and axon are CONTIUOUS with the cell body in the middle, but off to the side.
where the dendrites converge is considered the initial segment.
the rest of the length is considered to be an axon
most sensory neurons of the peripheral nervous system are unipolar.
most sensory neurons of the PNS are _______
unipolar
the longest unipolar neurons carry sensations from ____ to _____
the tips of the toes to the spinal cord
explain multipolar neurons and where they are found
multipolar neurons have 2 or more dendrites and a single axon.
MOST COMMON NEURONS IN THE CNS
what are the 2 longest structural neurons
multipolar and unipolar
what are the most common structural neurons in the CNS?
multipolar neurons
all the motor neurons that control skeletal muscles are __ neurons
multipolar
classify neurons by their function
-sensory neurons
-interneurons
-motor neurons
sensory neurons could also be called __ neurons
motor neurons can also be called ____ neurons
sensory neurons — afferent neurons
motor neurons — efferent neurons
what is a ganglion?
a collection of neuron cell bodies in the PNS
the cell bodies of sensory neurons are located in…..
peripheral sensory ganglia
sensory neurons are _____ neurons whose processes are known as……
UNIPOLAR neurons, whose processes are known as afferent fibers
afferent fibers extend between…..
a sensory receptor and the CNS
what do sensory neurons do?
collect information about the internal or external environment
what are 2 categories of sensory neurons?
contrast their function
somatic sensory neurons and visceral sensory neurons
somatic sensory neurons – monitor the OUTSIDE world
visceral sensory neurons – monitor internal conditions and the status of other organ systems
categorize the sensory receptors and differentiate them
interoreceptors, exteroreceptors, proprioreceptors
interoreceptors – monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems
exteroreceptors – provide information about the external environment in the form of touch, temperature, or pressure sensations.
proprioreceptors – monitor the position and movement of skeletal muscles and joints
do we have more motor neurons or sensory neurons?
way more sensory (10 million vs half a million)
what are efferent fibers?
axons travelling away from the CNS
the 2 major efferent systems are….
the SNS and ANS
The SNS includes which motor neurons?
somatic motor neurons – innervate skeletal muscles.
the cell body of somatic motor neurons lies ___ and extends ____
lies in the CNS and its axon extends within a peripheral nerve to innervate skeletal muscle fibers at a neuromuscular junction
___________ innervate all peripheral effectors other than skeletal muscles
visceral motor neurons
visceral motor neurons are part of…….
the ANS
name the peripheral effectors that visceral motor neurons innervate
smooth muscle, cardiac muscle, glands, and adipose tissue throughout the body
explain how visceral motor neurons innervate peripheral effectors (glands, smooth muscle, cardiac muscle, adipose tissue)
the axons of visceral motor neurons in the CNS innervate a SECOND set of visceral motor neurons in peripheral autonomic ganglia.
the neurons whose cell bodies are in that ganglia innervate and control these peripheral effectors
therefore, to get from the CNS to a peripheral effector, a signal must travel along 1 axon, be relayed across a synapse, and then travel along a SECOND axon to its final destination
the axons extending from the CNS –> autonomic ganglion are called….
pregangliolic fibers
axons connecting autonomic ganglion –> peripheral effectors are called….
postganglionic fibers
___ outnumber all other types of neurons combined
interneurons
interneurons could also be called…..
association neurons
MOST interneurons are located where?
in the CNS (brain and spinal cord)
what is the function of interneurons?
interneurons distribute sensory information and coordinate motor activity
how many interneuron(s) are located between a sensory neuron and a motor neuron?
1 or more.
the more complex the response to a given stimulus, the more interneurons are involved
give another function of interneurons BESIDES distributing sensory information and coordinating motor activity
higher functions, such as memory, planning, and learning
neuroglia account for about ___ the volume of the nervous system
half
which contains a greater variety of neuroglial cell types —— the PNS or the CNS?
the CNS
name the neuroglia found in the central nervous system
ependymal cells
astrocytes
oligodendrocytes
microglia
what are the neuroglia found in the PNS
satellite cells
Schwaan cells
give the FUNCTIONS of the neuroglia found in the CNS
ependymal cells — line ventricles (brain) and central canal (spinal cord); assist in producing, cicrulating, and monitoring cerebrospinal fluid
astrocytes — MAINTAIN THE BLOOD BRAIN BARRIER. structural support, regulate ion nutrition and dissolved gas concentrations, absorb and recycle neurotransmitters, form scar tissue after injury
Oligodendrocytes — myelinate CNS axons. provide structural framework
microglia — remove cell debris, wastes, and pathogens by phagocytosis. (type of phagocyte)
give the FUNCTIONS of the PNS neuroglia
satellite cells — surround the neuron cell bodies in the ganglia. regulate O2, CO2, nutrient, and neurotransmitter levels around neurons in the ganglia
Schwaan cells — surround all axons in the PNS. responsible for myelination of peripheral axons. participate in repair process after injury
ependymal cells form a _____
EPITHELIUM called the ependyma
what are the largest and most numerous neuroglia in the CNS?
astrocytes
what does the blood brain barrier do?
isolates the CNS from general circulation.
compounds in circulating blood do NOT have free access to the interstitial fluid of the CNS
neural tissue must be ___ and ____ isolated from general circulation. why?
physically and biochemically
hormones, amino acids, or other chemicals in the blood can alter neuron function
what controls the chemical exchange between the blood and interstitial fluid ?
endothelial cells lining CNS capillaries
these endothelial cells lining the CNS capillaries make up what?
the Blood brain barrier
explain how astrocytes maintain the blood brain barrier
the slender cytoplasmic extensions of astrocytes wrap around and form a complete blanket around the capillaries.
astrocytes secrete chemicals that maintain the selective permeability of endothelial cells
what is the function of CSF (cerebrospinal fluid) and where is it located?
CSF fills the longitudinal axis of the brain and spinal cord, this fluid circulates continuously and provides a protective cushion that transports gases, nutrients, waste, and other materials.
the “passageway” filled with CSF – explain how it is different between the brain and the spinal cord
in the spinal cord, this passageway is narrow and is called the central canal
in the brain, the passageway forms enlarged chambers called VENTRICLES
What lines the central canal and ventricles of the brain?
ependymal cells
which neuroglia myelinates CNS axons
oligodendrocytes
what is myelin?
cytoplasmic wrapping of oligodendrocytes around the axolemma of a neuron.
myelin serves as electrical insulation and increases the speed at which an action potential travels along an axon
what is an INTERNODE?
The fairly large areas of an axon that are wrapped in myelin
what are nodes?
nodes are the small gaps that separate adjacent internodes
in dissection, myelinated axons appear ____. why?
glossy white due to the lipids in the myelin
regions dominated by myelinated axons are known as WHITE MATTER
are all axons in the CNS myelinated?
no!
unmyelinated axons are common where short axons and collaterals form synapses with densely packed neuron cell bodies. this area is known as GRAY MATTER
What are the least numerous and smallest neuroglia in the CNS
microglia
microglia appear early in embryonic development. they originate from ___ Stem cells
mesodermal (also produce monocytes/macrophages)
