NERVOUS SYSTEM
What is Guillain-Barre sydrome?
- a PNS disorder in which inflammation causes loss of myelin that surrounds peripheral neurons - characterized by muscle weakness that begins in distal limbs and advances to proximal muscles - most function recovered with little medication intervention
What are some general characteristics of glial cells?
- capable of mitosis (producing new glial cells through cell division) - smaller than neurons, but far outnumber them (account for about half the volume of nervous system) - they do not transmit electrical signals, but they do assist neurons with their functions - they physically protect and help nourish neurons and provide an organized, supporting scaffolding for all the nervous tissue (guide migrating neurons during development) - critical for normal function at neural synapses, both maintaining the anatomic structure of synapses and modifying transmission that occurs there
What are five functions of astrocytes?
- help form blood-brain barrier by wrapping feet around brain capillaries (controls which substances have access to brain) - regulate tissue fluid composition (chemical environment around neurons) --- can regulate potassium concentration - form structural support for nearby neurons - assist neuronal development - occupy the space of dying neurons
Explain the process of myelinating a PNS axon
- neurolemmocyte starts to encircle a 1-mm portion of an neuron axon. As the neurolemmocyte continues to wrap around the axon, the cytoplasm and nucleus of the neurolemmocyte are squeezed to the periphery of the neurolemmocyte. The overlapping inner layers of the plasma membrane form the myelin sheath. - the periphery of the neurolemmocyte contains the cytoplasm and nucleus and is called the neurilemma - a neurolemmocyte can myelinate only 1 mm portion of a single axon. So, if an axon is longer than 1 mm, it takes many neurolemmocyte to myelinate the entire axon.
After traumatic injuries, PNS axons can regenerate if: (2 factors)
- neuron cell body is intact - enough neurilemma remains
Events of synaptic communication
- neurotransmitter molecules released from vesicles of synaptic knob into cleft - neurotransmitter diffuses across cleft and binds to postsynaptic receptors - binding of neurotransmitter to receptor initiates postsynaptic potential (a graded potential)
Why is CNS axon regeneration extremely limited?
- oligodendrocytes secrete growth-inhibiting molecules; not growth factors - large number of axons crowd the CNS (tends to complicate regrowth activities) - regrowth obstructed by scars from astrocytes and connective tissue
What are 2 specific types of ganglia?
- posterior (dorsal) root ganglia associated with sensory neurons that extend into the spinal cord - ganglia associated with motor neurons that extend to autonomic effectors for the parasympathetic division and the sympathetic division
What is multiple sclerosis?
- progressive demyelination of neurons in CNS - autoimmune disorder: oligodendrocytes attacked by immune cells - repeated inflammatory events causing scarring and permanent loss of function
Slow axonal transport occurs at approximately ________ to _______ millimeters per day
0.1 to 3
A neurolemmocyte can myelinate only ______ millimeter portion of a single axon
1
What are the basic structural features for all neurons?
1) cell body 2) dendrites 3) an axon
What are the three connective tissue wrappings in a nerve, and what specific structure does each ensheathe?
1) epineurium - ensheathes the entire nerve to protect and support it 2) perineurium - ensheathes each fascicle 3) endoneurium - ensheathes each axon
What are 5 special characteristics about neurons?
1) excitability 2) conductivity 3) secretion 4) extreme longevity 5) amitotic
Describe the three general functions of the nervous system
1. Collect information - receptors are specialized nervous system structures that monitor changes in both the internal and external environment called stimuli. For example, receptors in the skin detect stimuli associated with touch - this sensory information then is relayed along neurons to the spinal cord and brain. 2. Process and evaluate information - after processing sensory information, the brain and spinal cord determine what response, if any, is required 3. Initiate response to information - the brain and spinal cord initiate a response as motor information is relayed along neurons to structures called effectors. Effectors include all three types of muscle tissue and glands. The effect may be either muscle contraction (or relaxation) or a change in gland secretion activity.
What two primary factors does the degree of success of PNS axon regeneration depend upon:
1. the amount of damage 2. the distance between the site of the damaged axon and the structure it innervates
Explain the 5 steps of PNS axon regeneration
1. the axon is severed by some type of trauma 2. the proximal portion of each severed axon seals off by membrane fusion and swells. the distal portion of the axon and myelin sheath (surrounding the axon) degenerates (Wallerian degeneration) but the neurilemma survives 3. neurilemma and endoneurium form a regeneration tube 4. axon regenerates (and remyelination occurs) guided by nerve growth factors released by neurolemmocytes 5. axon reinnervates original effector or sensory receptor
How many connective tissue wrappings does a nerve have?
3
Fast axonal transport occurs at approximately _________ millimeters per day
400
What shape do astrocytes exhibit?
A starlike shape due to projections from their surface. These numerous cell processes have contact with both neurons and blood capillaries.
Define a synapse
A synapse is the specific location where a neuron is functionally connected to either another neuron or an effector (muscle or gland).
Primary tumors
A tumor that originates within the organ where it is found
What glial cell is the most abundant in the CNS and constitute over 90% of the nervous tissue in some areas of the brain.
Astrocyte
Which neuroglial cell of the CNS connects to a blood supply?
Astrocytes
Describe the parts of an axon (its specialized terminology for its cytoplasm and plasma membrane)
Axoplasm: the cytoplasm within an axon Axolemma: the plasma membrane of an axon unlike the cell body, the axon lacks any chromatophilic substance.
How are neurons structurally classified?
Based upon the number of neuron processes (axon or dendrites) emanating directly from their cell body. Thus, they may be classified as multipolar, bipolar, unipolar, or anaxonic neurons.
In the process of myelination by oligodendrocytes, why does a neurilemma not form?
Because the axons of CNS neurons are myelinated
Multiple Sclerosis: PNS or CNS?
CNS
Which type of synapse is more common in humans?
Chemical synapses
What is amitotic in a neuron?
During fetal development, most neurons lose their ability to form new cells through cell division (mitotic activity). Specific exceptions include the neurons in certain areas of the brain and in the olfactory epithelium of the nose.
What are the different types of effectors controlled by the nervous system?
Effectors include all three types of muscle and glands.
What is the difference between excitability and conductivity?
Excitability refers to the ability to initiate a local electrical change (a graded potential), conductivity refers to the ability to propagate (or move) an electrical change along the plasma membrane (an action potential).
Explain the neuron characteristics of excitability, conductivity, and secretion.
Excitability refers to the ability to initiate a local electrical change (a graded potential), conductivity refers to the ability to propagate (or move) an electrical change along the plasma membrane (an action potential). In response to conductive activity, neurons release neurotransmitters (secretion).
Which type of axonal transport is both anterograde and retrograde? Give examples of substances transported by this method.
Fast axonal transport. Cellular structures formed in the cell body are moved by anterograde transport toward the synaptic knobs and include vesicles, organelles, and glycoproteins required at the synapse. Used vesicles to be broken down and recycled, and potentially harmful agents are moved via retrograde transport from the synaptic knob toward the cell body.
What are gliomas, and explain them.
Glial cell tumors - may either be relatively benign and slow-growing or malignant (capable of metastasizing)
If a person has a brain tumor, is it more likely to have developed from neurons or from glial cells? Why?
Glial cells because they have the ability to multiply and divide, unlike neurons.
What is found in the neuron's cell body (or soma) ?
Houses both the nucleus and the cytoplasm - nucleus: contains chromatin and a prominent nucleolus, which synthesizes the cell body's large number of ribosomes. - cytoplasm: specifically called the perikaryon is composed of the typical cellular organelles such as the endoplasmic reticulum, Golgi apparatus, ribosomes, and mitochondria. Distinctive feature of a neuron cell body is that it contains a large number of ribosomes - either attached to the ER as part of an extensive rough ER or are free ribosomes within the cytosol. - collectively, they readily absorb basic dyes when a nervous tissue sample is stained for viewing with a microscope; thus, they appear as dark-staining bodies and are referred to as chromatophilic substance (Nissl bodies). - axon hillcock is the only portion of the cell body that lacks chromatophilic substance.
What is conductivity in a neuron?
It involves an electrical change that is quickly propagated along the plasma membrane as voltage-gated channels open sequentially during an action potential. Conductivity refers to the ability to propagate (or move) an electrical change across the plasma membrane (an action potential).
What is excitability in a neuron?
It is a responsiveness to a stimulus that causes a local electrical change in the resting membrane potential in the excitable cell by initiating the movement of ions across the plasma membrane of the excitable cell. These local electrical changes are called graded potentials
The entire neuron has an extensive cytoskeleton, explain it.
It is composed of microtubules, microfilaments (actin), and a type of intermediate filament called a neurofilament. These proteins are within the cell body and extend into the dendrites and axon. They function in maintaining neuron shape and providing structural support. The neurofilaments aggregate to form parallel bundles called neurofibrils. They also provide tensile strength. Microtubules, which are embedded in parallel clusters with the neurofibrils of an axon, participate in cellular transport within axons (axonal transport).
What is the choroid plexus?
It is made up of ependymal cells and nearby blood capillaries. It helps produce cerebrospinal fluid, a clear liquid that bathes the external surfaces of the CNS and fills its internal cavities. The cilia of ependymal cells help circulate the CSF.
What is myelin?
It is the insulating covering around an axon that consists of repeating concentric layers of plasma membrane of glial cells.
What is myelination?
It is the process by which part of an axon is wrapped with myelin.
What is the role of the postsynaptic neuron in a chemical synapse?
It is the signal receiver, or target (binds neurotransmitter)
In slow axonal transport, the materials are only moved in what direction? Anterograde or retrograde?
Materials are moved toward the cell body toward the synaptic knob (anterograde).
Which neuroglial cell of the CNS has an immune function?
Microglial cells
If a person suffers from meningitis (an inflammation of the meningeal coverings around the brain), which type of glial cell usually replicates in response to the infection?
Microglial cells (macrophages) engulf infectious agents and remove them.
What is extreme longevity in a neuron?
Most neurons formed during fetal development are still functional in very elderly individuals
How are the different processes that extend from a cell body used to structurally classify neurons?
Multipolar = multiple processes Bipolar = two processes Unipolar = single process Anaxonic = processes are only dendrites; no axon present
What are the most common type of neurons in the human body?
Multipolar neurons
Which specific type of glial cell forms a myelin sheath associated with axons in the PNS?
Neurolemmocytes (Schwann cells)
What is secretion in a neuron?
Neurons release neurotransmitters in response to conductive activity
Which neuroglial cell of the CNS creates a myelin sheath?
Oligodendrocyte
How is myelination by an oligodendrocyte in the CNS different from a neurolemmocyte?
One oligodendrocyte can myelinate a 1 mm portion of several axons, not just one, each at multiple portions of the different axons. No neurilemma is formed. Neurofibril nodes are located between adjacent oligodendrocyte "wraps."
Guillain-Barre syndrome: PNS or CNS?
PNS
Where do primary tumors typically originate?
Primary CNS tumors typically originate in supporting tissues within the brain or spinal cord that have retained the capacity to undergo mitosis: the meninges (protective membranes of the CNS) or the glial cells
What is the general function of receptors?
Receptors are specialized nervous system structures that monitor changes in both the internal and external environment called stimuli. They detect stimuli and then relay the information along neurons to the spinal cord and brain.
What are the three categories of neurons?
Sensory neurons, motor neurons, and interneurons
What are microglial cells, and what is their function?
Small cells that wander CNS and replicate in infection. They are classified as phagocytic cells (macrophages) of the immune system. They protect the CNS against microorganisms and other potentially harmful substances by engulfing and destroying them through phagocytosis. They also function in removing debris from dead or damaged nervous tissue that results from infections, inflammation, trauma, and brain tumors.
Describe how transmission works between a presynaptic and a postsynaptic neuron.
Starts when neurotransmitter molecules stored in synaptic vesicles are released from the synaptic knob of a presynaptic neuron into the synaptic cleft. Some of the neurotransmitter diffuses across the synaptic cleft to bind to receptors within the plasma membrane of the postsynaptic neuron to initiate a graded potential.
The nervous system consists of two anatomic divisions, what are they?
The central nervous system (CNS) and the peripheral nervous system (PNS)
Describe the structure of a unipolar neuron.
The short, multi-branched receptive endings are dendrites. The other portion is the axon because it generates and conducts action potentials. These axons are composed of the combined peripheral processes (from dendrites to the cell body) and central process (from the cell body into the CNS).
What is the axon hillcock?
The triangular, cone-shaped region of the cell body
What are neurolemmocytes (Schwann cells), and what is their function?
These elongated and flattened cells wrap around and insulate axons within the PNS to form a myelin sheath through myelination. As with myelin sheaths formed by oligodendrocytes in the CNS, this allows for faster propagation of action potentials along the axon.
What are capillaries associated with and how do they function?
They are associated with the endoneurium and function as the site of exchange of substances (oxygen, glucose, waste products) between axons of neurons and the blood.
What are satellites, and what is their function?
They are flattened cells arranged around neuronal cell bodies in a ganglion. They physically separate cell bodies from their surrounding interstitial fluid. They function to electrically insulate the cell body and regulate the continuous exchange of nutrients and waste products between neuron cell bodies and their environment.
What are oligodendrocytes, and what is their function
They are large cells with a bulbous (round) body and slender cytoplasmic extensions or processes. The extensions of oligodendrocytes wrap around and insulate axons within the CNS to form a myelin sheath through a process called myelination. This insulation allows for faster propagation of action potentials along the axon.
What are neurotransmitters?
They are molecules stored in vesicles and when released bind to an excitable cell to cause either an excitatory or inhibitory effect on these target cells (other neurons or effectors).
What are neoplasms and what do they result from?
They are tumors that sometimes occur within the CNS. They result from unregulated cell growth.
How do axons function at synaptic knobs?
They function in the initiation and propagation of action potentials (relatively large electrical changes, which are due to voltage-gated channels open sequentially) along their axolemma. Action potentials trigger synaptic vesicles to release neurotransmitter from synaptic knobs.
Describe unipolar neurons.
They have a single, short neuron process that emerges from the cell body and branches like a T. These neurons are also called pseudounipolar because they start out as bipolar neurons during development, but their two processes fuse into a single process.
Describe bipolar neurons
They have two processes that extend from the cell body - one dendrite and one axon. The location of these neurons is relatively limited in humans.
Where are interneurons located, and what is their function?
They lie entirely within the CNS. They receive stimulation from many other neurons, process the information, and "decide" how the body responds to stimuli.
What is a fascicle?
a bundle of axons within a nerve
What is a ganglion?
a cluster of neuron cell bodies within the PNS
What is the endoneurium?
a delicate layer of areolar CT that surrounds each axon.
What is the perineurium?
a layer of dense irregular CT that wraps each fascicle.
What do ependymal cells and nearby blood capillaries form?
a network called the choroid plexus
What is an electrical synapse composed of?
a presynaptic neuron and a postsynaptic neuron physically bound together by gap junctions
What is an axon?
a single axon is typically a longer process emanating from the cell body to make contact with other neurons, muscle cells, or gland cells.
What is the epineurium?
a thick layer of dense irregular CT that encloses the nerve.
How are neurons functionally classified?
according to the direction in which action potentials are propagated relative to the CNS.
What are sensory neurons also referred to as?
afferent neurons
What are the two neurons separated by in a chemical synapse?
an extremely narrow, fluid-filled gap (of about 30 nanometers) called the synaptic cleft
What is a synaptic cleft?
an extremely, narrow fluid-filled gap between two neurons in a synapse
What is a nerve?
an organ composed of cablelike bundle of axons, connective tissue layers, and blood vessels, and it is a component of the PNS
Cellular structures formed in the cell body are moved by _____________ transport toward the synaptic knobs and include vesicles, organelles, and glycoproteins required at the synapse.
anterograde
What are interneurons also referred to as?
association neurons
Several subpopulations of __________ have been identified
astrocytes
What are the four types of glial cells found in the CNS?
astrocytes, ependymal cells, microglia, and oligodendrocytes
What are the side branches of an axon called?
axon collaterals
Astrocytes connect _____________ to ______________
blood vessels to neurons
Substances are moved in ________ directions through an axon.
both
What do mixed nerves contain?
both sensory and motor neurons
Cranial nerves extend from the ____________ and spinal nerves extend from the __________.
brain; spinal cord
An extensive network of blood vessels, branch and extend through both the epineurium and perineurium to become ______________
capillaries
What are the types of effectors that can only be involuntarily controlled?
cardiac muscle, smooth muscle, and glands
Most synapses within the nervous system are __________ synapses
chemical
What are the two types of synapses in the human body?
chemical synapses and electrical synapses
What are ependymal cells?
ciliated simple cuboidal or simple columnar epithelial cells that line the internal cavities (ventricles) of the brain and the central canal of the spinal cord. They have slender processes that branch extensively to make contact with other glial cells in the surrounding nervous tissue.
What do interneurons facilitate?
communication between sensory and motor neurons.
What are motor neurons responsible for?
conducting motor output away from the CNS to both somatic effectors (skeletal muscle) and autonomic effectors (cardiac muscle, smooth muscle, and glands).
What are sensory neurons responsible for?
conducting sensory input from both somatic sensory (touch receptors) and visceral sensory receptors (stretch receptors within the urinary bladder) toward the CNS.
Graded potentials are both received from the ____________ and initiated at the ________________________
dendrites; cell body
What are motor neurons also referred to as?
efferent neurons
Substances can be moved via fast axonal transport in ___________ direction
either (anterograde or retrograde)
List the connective tissue wrappings around a nerve from deep to superficial
endoneurium, perineurium, and epineurium
What kind of substances are moved by slow axonal transport (anterograde)?
enzymes, cytoskeletal components, and new axoplasm for regenerating axons
The transport processes are classified as either _________ axonal transport or _________ axonal transport, depending upon the relative speed of movement.
fast; slow
What does myelination in both the CNS and PNS allow for?
faster propagation of action potentials
What is important about mixed nerves
in mixed nerves, individual sensory or motor neurons still transmit only one type of information (even though they contain both sensory and motor neurons)
How do gap junctions work in electrical synapses?
in the plasma membranes of both neurons and facilitate the flow of ions between the cells. The cells act as though they share a plasma membrane. Thus, the electrical signal passes between the cells with essentially no synaptic delay (fast). Electrical synapses are located within limited regions of the brain and the eyes.
What does the somatic motor component do?
initiates and transmits motor output from the CNS to the only type of effector that can be voluntarily controlled - skeletal muscles. For example, you exert voluntary control over your leg muscles as you press on the accelerator of your car.
What does the autonomic motor (or visceral motor) component do?
innervates and regulates the other types of effectors that can only be involuntarily controlled - cardiac muscle, smooth muscle, and glands. These effectors function without our conscious control. We can neither voluntarily make our heart stop beating nor prevent our stomachs from growling.
Located within CNS 99% of our neurons are __________
interneurons
What is the main difference between the somatic motor component and the autonomic (visceral) motor component?
it is based upon whether the stimulated effector can be controlled consciously (voluntarily).
What is the role of the presynaptic neuron in a chemical synapse?
it is the signal producer (it releases neurotransmitter)
What is the importance of the cell body in a neuron?
it serves as the neuron's control center because: - it contains both the nucleus and the cytoplasm - it functions in many of the cell's metabolic activities - it transmits graded potentials (local electrical changes in membrane potential that vary in size) along its plasma membrane to the axon
What glial cell represents the smallest percentage of CNS glial cells, with some estimates of their prevalence as low as 5%?
microglia
Fast axonal transport involves movement along _______________
microtubules
What is the neuron's cytoskeleton composed of?
microtubules, microfilaments (actin), and a neurofilament
Most named nerves (including all spinal nerves and most cranial nerves) are __________ nerves.
mixed
The greater the number of dendrites, the ___________ input a neuron may recieve.
more
Motor neurons are neurons of the __________ nervous system
motor
In the motor nervous system, motor information is sent from the CNS to the effectors - what is this called?
motor output
Interneurons are either ____________ neurons or __________ neurons.
multipolar; anaxonic
What do Schwann cells supply for the peripheral neurons?
myelin
What do oligodendrocytes do to the axons of the CNS?
myelinate them
What does the PNS include?
nerves, which are bundles of axons of neurons and ganglia
What are the gaps between the neurolemmocytes called?
neurofibril nodes, or nodes of Ranvier
Neurofilaments aggregate to form parallel bundles called _______________
neurofibrils
What are glial cells sometimes referred to as?
neuroglia
What plays an active role in PNS axon regeneration?
neurolemmocytes
What cell in the PNS and what cell in the CNS completes myelination?
neurolemmocytes in the PNS and oligodendrocytes in the CNS
What are unmyelinated axons in the PNS associated with?
neurolemmocytes, which help to protect and support the axon. However, no myelin sheath covers them.
What two distinct cell types is nervous tissue composed of?
neurons and glial cells
Describe anaxonic neurons
neurons that have only dendrites and no axons. They are different from other types of neurons because they produce graded potentials, but they do not produce action potentials.
Are unmyelinated axons associated with oligodendrocytes in the CNS?
no
Are either the dendrites or the cell body insulated with myelin?
no, neither are
A chemical synapse between two neurons is composed of a ____________ neuron and a ___________ neuron
presynaptic; postsynaptic
What is the sensory nervous system (or afferent nervous system) responsible for?
receiving sensory information from receptors and transmitting this information to the CNS.
What are the receptors included in the somatic sensory component?
receptors associated with the 5 senses (sight, smell, taste, hearing, and touch) and proprioceptors (receptors in muscles, tendons, and joints that detect body position)
Used vesicles to be broken down and recycled, and potentially harmful agents are moved via ___________ transport from the synaptic knob toward the cell body.
retrograde
What are the two types of glial cells found in the PNS?
satellite cells and neurolemmocytes
Sensory neurons are neurons of the _____________ nervous system
sensory
In the sensory nervous system, information is sent from the receptors to the CNS - what is this called?
sensory input
How can the different glial cells in the CNS be distinguished?
size, intracellular organization, and the presence of specific cytoplasmic processes
What is the only type of effector that can be voluntarily controlled?
skeletal muscles
What are the 2 subdivisions of the motor nervous system?
somatic motor and autonomic (or visceral) motor
What is fast axonal transport powered by?
specialized motor proteins that split ATP to supply the energy needed
What do the somatic sensory components detect?
stimuli that we can consciously perceive
What do the visceral sensory components detect?
stimuli that we typically do not consciously perceive
What are the receptors included in the visceral sensory component?
structures located within internal organs (heart, stomach, kidneys) and blood vessels. Visceral receptors detect stretch of an organ wall or chemical composition of the blood.
What is the protein called that stabilizes microtubules of the neuron cytoskeleton and is associated with Alzheimers disease?
tau
What is another word for axon terminals?
telodendria
What is the structural classification of nerves based on?
the CNS component from which the nerve extends
What two primary factors determine the effectiveness of PNS axon regeneration?
the amount of damage and the distance between the site of the damaged axon and the structure it innervates
Where are unmyelinated axons in the PNS?
the axon rests in a depressed portion of the neurolemmocyte, but its plasma membrane does not form repeated layers around the axon
What causes multiple sclerosis (MS) an autoimmune disorder of the CNS?
the body's immune cells mistake the oligodendrocytes as foreign and attack them. As a result, the propagation of action potentials is disrupted, leading to impaired sensory and motor coordination.
What does the nervous system serve as?
the body's primary communication and control system
What does the CNS include?
the brain and the spinal cord
Most axons and the axon collaterals branch extensively at their distal end into an array of fine terminal extensions (telodendria) - what are the extreme tips of these fine extensions called?
the extreme tips of these fine extensions (telodendria) are slightly expanded regions called synaptic knobs (terminal boutons).
What does slow axonal transport result from?
the flow of the axoplasm (an axon's cytoplasm), it is also called axoplasmic flow
What is the functional classification of nerves based on?
the functional type of neuron (sensory neuron or motor neuron) a nerve contains
What is retrograde transport?
the movement of materials from synaptic knows toward the cell body
What is anterograde transport?
the movement of materials from the cell body toward synaptic knobs
What forms a regeneration tube in PNS axon regeneration?
the neurilemma and endoneurium
What is the basic structural unit of the nervous system?
the neuron
What does myelin consist of?
the plasma membrane of these glial cells and contains a large proportion of lipids and a smaller amount of proteins. The high lipid content of the myelin gives an axon a distinct, glossy-white appearance and effectively insulates an axon
What are the two functional divisions of the nervous system?
the sensory nervous system and the motor nervous system
What encloses and protects the brain?
the skull
What are the 2 subdivisions of the sensory nervous system?
the somatic sensory component and the visceral sensory component
What are the 2 subdivisions of the autonomic motor (or visceral motor) component?
the sympathetic and parasympathetic divisions
What houses and protects the spinal cord?
the vertebral canal
What is synaptic delay in the transmission process?
there is a synaptic delay associated with neurotransmitter release at chemical synapses. The delay is the time between the neurotransmitter release from the presynaptic cell, its diffusion across the synaptic cleft, and neurotransmitter binding to receptors in the postsynaptic neuron plasma membrane. This delay is usually between 0.3 and 0.5 millisecond.
What is the function of the endoneurium?
these more delicate coverings function to separate and electrically insulate each axon.
What is the function of the perineurium?
these tough, fibrous CT sleeves also provide protection and support, but to each bundle of axons. This layer supports blood vessels.
What are neurons?
they are excitable cells that initiate and transmit electrical signals
What are glial cells?
they are non-excitable cells that primarily support and protect the neurons
Describe multipolar neurons.
they have many dendrites and a single axon that extends from the cell body. These are the most common type of neurons in the human body.
What do synaptic knobs house?
they house numerous synaptic vesicles containing neurotransmitters.
Where are interneurons located?
they lie entirely within the CNS
What are interneurons responsible for?
they receive stimulation from other neurons, process it, and store information and "decide" how the body responds to stimuli.
What are dendrites and why are they important to a neuron?
they tend to be relatively short, small, tapering processes that branch off the cell body. Some neurons have many dendrites; others only have one. Dendrites transmit graded potentials along their plasma membrane toward the cell body.
What is the function of the epineurium?
this fibrous tissue ensheathes the entire nerve to protect and support it like a tough leather sleeve.
What is the motor nervous system (or efferent nervous system) responsible for?
this system controls effectors (muscles and glands). It is responsible for initiating and transmitting motor information from the CNS to the effectors.
Sensory nerves contain only neurons that relay information _____________ the CNS (called sensory neurons), and motor nerves contain neurons that relay information ___________ the CNS (called motor neurons).
toward; away from
All motor neurons are __________
unipolar
Most sensory neurons are ____________. What are the exceptions?
unipolar. However, a few somatic sensory neurons are bipolar, such as those in the retina of the eye and olfactory epithelium of the nose.
What is a significant difference between the cell body and the axon?
unlike the cell body, the axon lacks any chromatophilic substance. This distinctive difference allows the cell body to be distinguished from the axon when nervous tissue is viewed with a microscope.
Nerves are ________________ by an extensive network of blood vessels
vascularized
When does transmission occur between a presynaptic and postsynaptic neuron?
when neurotransmitter molecules stored in synaptic vesicles are released from the synaptic knob of a presynaptic neuron into the synaptic cleft.
Where is a synapse commonly located?
with a dendrite of the postsynaptic neuron. The synaptic knob of the presynaptic neuron does not quite make contact with the postsynaptic neron.
Where are glial cells found
within both the CNS and the PNS
