Nervous System Flashcards
Nervous system
all nervous tissues in the body
Intricate network of billions of neurons and many more neuroglia
three functions of the nervous system
sensory
motor
integration
sensory function
all incoming information about the external and internal environments; transmitted as
nerve impulses to the central nervous system to be integrated
detect internal and external stimuli; carried to the brain and spinal cord through cranial
and spinal nerves
motor function
initiates all voluntary movements; responds rapidly to help adjust body processes using
nerve impulses; includes all commands that control muscles and glands
once sensory information is integrated, the nervous system may elicit an appropriate
motor response by activating effectors (muscles and glands) through cranial and spinal nerves
integration/ intergrative
responsible for our perceptions, behaviors, memories, and much more; includes all
higher level thinking, processing, and the connection between sensory and motor
integrates (processes) sensory information by analyzing and storing some of it and
by making decisions for appropriate responses
neurology
the branch of medical science that deals with the normal functioning and disorders of the nervous system
2 main subdivisions
Central nervous system
peripheral nervous system
Central Nervous System
brain and spinal cord
Processes incoming sensory info and is the source of thoughts, emotions, and memories
most nerve impulses that stimulate muscles to contract and glands to secrete originate in
the CNS
Peripheral Nervous system
all nervous tissue outside the CNS
nerves
ganglion
enteric plexuses
sensory receptors
Nerve
a bundle of hundreds to thousands of axons plus associated connective tissue and
blood vessels that lies outside the brain and spinal cord
how many pairs of cranial nerves
12 pairs of cranial nerves
how many pairs of spinal nerves
31 pairs of spinal nerves
ganglion ( ganglia)
small masses of nervous tissue, consisting primarily of neuron cell bodies, that are located outside the brain and spinal cord
a cluster of neuronal cell bodies located in the PNS; closely associated with
cranial and spinal nerves
enteric plexuses
extensive networks of neurons located in the walls of organs of the gastrointestinal tract; help regulate the digestive system
sensory receptor
a structure of the nervous system that monitors changes in the external
or internal environment
The PNS is divided into
Somatic nervous system
autonomic nervous sytem
Somatic nervous system
voluntary
Sensory neurons that convey info to the CNS
Motor neurons that conduct impulses from the CNS to skeletal muscles
Autonomic nervous system
involuntary
Sensory neurons that convey info to the CNS from autonomic sensory receptors (visceral organs)
Motor neurons that conduct nerve impulses from the CNS to smooth and cardiac muscle,
and glands
Motor part of the ANS consists of two branches: sympathetic (fight or flight) and
parasympathetic (rest and digest) divisions
enteric nervous system
involuntary; “brain of the gut”
100 million neurons in enteric plexuses that extend most of the length of the
gastrointestinal tract
2 types of cells of the nervous system
neurons and neuroglia
neurons
nerve cells
excitability
stimulus
action potential (impulse)
have 3 parts
electrical excitability
the ability to respond to a stimulus and convert it into an action potential
stimulus
any change in the environment that is strong enough to initiate an action potential
action potential (impulse)
an electrical signal that propagates along the surface of the membrane of a neuron or a muscle fiber
Neurons communicate with one another by means of nerve action potentials (nerve impulses)
3 parts of neuron
cell body soma
dendrites
axon
cell body (soma)
contains a nucleus surrounded by cytoplasm that includes typical organelles; multiple dendrites and a single axon extend from the cell body
dendrites
receiving or input part of the neuron (along with the cell body); short, tapering, highly branched; tree-shaped
axon
conducts nerve impulses toward another neuron, a muscle cell, or a gland cell; long, cylindrical projection that often joins the cell body at a cone shaped
elevation called the axon hillock
nerve impulses usually arise
at the axon hillock and travel along the axon
axon collaterals
side branches
axon terminals
fine processes at the ends of the axons and axon collaterals
Synapse
the site where two neurons or a neuron and an effector cell can communicate
synaptic end bulbs
the tips of most axon terminals that contain synaptic vesicles (tiny sacs that store neurotransmitters)
structural classification of neurons
classified according to the number of processes extending from the cell body
multipolar
bipolar
unipolar
multipolar neurons
usually have several dendrites and one axon; most neurons in the brain and spinal cord are of this type
bipolar neurons
have one main dendrite and one axon; found in the retina of the eye, in the inner ear, and in the olfactory area of the brain
unipolar neurons
have dendrites and one axon that are fused together to form a continuous process that emerges from the cell body; most are sensory receptors; most are located in the ganglia of spinal and cranial nerves
functional classification of neurons
classified according to the direction in which the nerve impulse is conveyed with respect to the CNS
sensory
motor
interneurons
sensory ( afferent ) neurons
either contain sensory receptors at their distal ends (dendrites) or are located just after sensory receptors that are separate cells; action potential is generated and conveyed into the CNS; most are unipolar
motor ( efferent) neurons
convey action potentials away from the CNS to effectors (muscles and glands) in the PNS; most are multipolar
interneurons ( associate neurons)
located within the CNS between sensory and motor neurons; integrate incoming sensory information from sensory neurons and then elicit a motor response by activating the appropriate motor neurons; most are multipolar
neuroglia
support nourish, and protect the neurons and maintain homeostasis in the interstitial
fluid that bathes them
neuroglia= glia
Make up about half the volume of the CNS
Actively participate in the activities of nervous tissue
Smaller than neurons, but are 5-25 times more numerous
Do not generate or conduct nerve impulses, can multiply and divide in the mature
nervous system
6 types
types of neuroglia in CNS
astrocytes, oligodendrocytes, microglia, and ependymal cells
types of neuroglia in PNS
Schwann cells and satellite cells
myelination
axons with a myelin sheath are said to be myelinated, those without are unmyelinated
Neuroglia cells produce myelin sheaths by wrapping themselves around and around axons (sometimes 100 layers on one axon)
myelin sheath
a many-layered covering composed of lipid and protein that surrounds the axons
of most neurons; insulates the axon of a neuron and increases the speed of nerve impulse conduction
Myelination in PNS
schwann cells
Myelination in CNS
Oligodendrocytes
Nodes of Ranvier
gaps in the myelin sheath at intervals along the axon
Collections of Nervous tissue
ganglion
nucleus
nerve
tract
Nucleus
a cluster of neuronal cell bodies located in the CNS
Nerve
a bundle of axons that is located in the PNS
cranial nerves connect to the brain to the periphery
spinal nerves connect the spinal cord to the periphery
tract
a bundle of axons that is located in the CNS; interconnect neurons in the spinal cord and
brain
widespread regions of nervous tissue are grouped together as
gray or white matter
in brain and spinal cord, some are white and glistening, others appear gray
white matter
composed primarily of myelinated axons; whitish color of myelin makes it
appear white
blood vessels
gray matter
contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and
neuroglia; appears grayish because the cellular organelles impart a gray color and little or no myelin
blood vessels
In spinal cord, the outer white matter
surrounds an inner core of gray matter
in the brain, a thin shell of gray matter ( cortex)
covers the surface of the largest portions of the brain, the cerebrum, and cerebellum
Generation of action potentials in muscle cells and neurons depends on 2 basic features of the plasma membrane
the existence of a resting membrane potential
the presence os specific types of ion channels
existence of a resting membrane potential
a difference in the amount of electrical
charge on the inside of the plasma membrane as compared to the outside; like voltage stored in a battery
A cell that has a membrane potential is said to be polarized
presence of specific types of ion channels
the flow of ions in living tissues
constitutes electrical currents
ion channels
When they are open, ion channels allow specific ions to diffuse across the plasma
membrane from where the ions are more concentrated to where they are less
concentrated
Positively charged ions will move toward a negatively charged area and vice
versa
The flow of current can change the membrane potential
leak channels
type of ion channel that allows a small but steady stream of ions to leak across the membrane
gated channels
type of ion channel that opens and closes on command
voltage- gated channels
type of ion channel that opens in response to a change in membrane potential; used to generate and conduct action potentials
resting membrane potential
In a resting neuron, the outside surface of the plasma membrane has a positive
charge and the inside surface has a negative charge
The separation of positive and negative electrical charges is a form of potential
energy
Most negatively charged ions inside the cell are not free to leave, which
contributes to the negativity inside the cell
Arises from the unequal distributions of various ions in cytosol and extracellular
fluid
action potential (impulse)
a sequence of rapidly occurring events that decrease and reverse the membrane potential and then eventually restore it to the resting state
threshold
a critical level of depolarization caused by a stimulus that leads to the generation of
an action potential
2 main phases of action potential
depolarizing
repolarzing
all-or-none principle
as long as a stimulus is strong enough to cause depolarization to
threshold, an action potential occurs; a stronger stimulus will generate the same action potential; a weak stimulus that fails to cause a threshold-level depolarization does not elicit an action potential
refractory period
the brief time after an action potential begins during which a muscle fiber or
neuron cannot generate another action potential
conduction of nerve impulses
propagation
continous conduction
saltatory conduction
propagation
a mode of conduction in which nerve impulses travel from where they arise
(usually at the axon hillock) along the axon to the axon terminals
continous conduction
the type of action potential conduction that occurs in unmyelinated axons
Each adjacent segment of the plasma membrane depolarizes to threshold and generates an action potential that depolarizes the next patch of the membrane
saltatory conduction
the type of action potential conduction that occurs in myelinated axons
Current is carried through the interstitial fluid surrounding the myelin sheath and through
the cytosol from one node to the next; impulse appears to leap from node to node; travels much farther in the same time interval
Axons with large diameters
conduct faster than small
myelinated axons conduct
faster than unmyelinated
axons with the largest diameters
are all myelinated
axons with the smallest diameters
are unmelinated
axons conduct faster when
when warmed
axons conduct lower
when cooled
synaptic transmission
a series of events by which neurons communicate with other neurons or
with effectors
presynaptic neuron
the neuron sending the signal
postsynaptic neuron
the neuron receiving the message
synaptic cleft
a tiny space filled with interstitial fluid between the pre and postsynaptic
neurons
2 types of synapses
Electrical
chemical
electrical
nerve impulses conduct directly between the plasma membranes of adjacent
neurons through gap junctions
rapid conduction and coordination
gap junctions
tunnel-like structures that connect adjacent cells and allow ions to flow through; visceral smooth muscle, cardiac muscle, and the brain
chemical
most nerve impulses; a nerve impulse in a presynaptic neuron causes the
release of neurotransmitter molecules into the synaptic cleft; neurotransmitters produce a nerve impulse in the postsynaptic neuron
events at a chemical synapse
A nerve impulse arrives at a synaptic end bulb of a presynaptic axon
The depolarizing phase of the nerve impulse causes Ca to flow into the synaptic end bulb
An increase in the concentration of Ca inside the synaptic end bulb triggers the release of
thousands of neurotransmitter molecules into the synaptic cleft
The neurotransmitter molecules diffuse across the synaptic cleft and bind to neurotransmitter receptors in the postsynaptic neuron’s plasma membrane
Binding of neurotransmitter molecules opens ion channels, which allows certain ions to flow across the membrane
As ions flow through the opened channels, the voltage across the membrane changes
If a depolarization occurs in the postsynaptic neuron and reaches threshold, then it triggers one or
more nerve impulses
3 ways neurotransmitters are removed for normal synaptic function
some of the released neurotransmitter molecules diffuse away from the synaptic cleft
some are destroyed by enzymes
many are actively transported back into the neuron that released them (reuptake) or
transported into neighboring neuroglia (uptake)
neurotransmitters
about 100 are known or suspected
most are synthesized and loaded into synaptic vesicles in the synaptic end bulbs, close to their site of release
ACh
acetycholine
one of the best-studied; released by many PNS neurons and some CNS neurons
Excitatory neurotransmitter at some synapses (neuromuscular junction); also known to be
inhibitory at other synapses (slow heart rate)
several amino acids are neurotransmitters in the CNS
glutamate and aspartate
gamma aminobutyric acid and glycine
glutamate and aspartate
powerful excitatory effects
gamma aminabutyric acid ( GABA)
important inhibitory neurotransmitters
Valium and other antianxiety drugs enhance the action of GABA
norepinephrine
plays roles in arousal (awakening from deep sleep), dreaming, and regulating mood
dopamine
active during emotional responses, addictive behaviors, and pleasurable experiences; regulates some aspects of movement
serotonin
thought to be involved in sensory perception, temperature regulation, control of mood, appetite, and the onset of sleep
endorphins
the body’s natural painkillers; linked to improved memory, and feelings of pleasure
or euphoria
nitric oxide
different because it is not synthesized in advance and packaged into synaptic
vesicles; formed on demand, diffuses out of cells that produce it and into neighboring cells and acts immediately; plays a role in learning and memory
carbon monoxide
not produced in advance and packaged into synaptic vesicles; formed as
needed and diffuses out of cells that produce it into adjacent cells; excitatory; produced in the brain; might protect against excess neuronal activity and might be related to dilation of blood vessels, memory, olfaction, vision, thermoregulation, insulin release, and anti-inflammatory activity
demyelination
loss or destruction of myelin sheaths around axons in the CNS or PNS
neuropathy
any disorder that affects the nervous system but particularly a disorder of a cranial or
spinal nerve
