Nervous System Flashcards
nervous system
master control and communication
functions of nervous system
sensory input
integration
motor output
sensory input
monitoring stimuli
dendrites/PNS
integratation
interpretation of sensory input
cell body/CNS
motor output
response to stimuli
axon/PNS
central nervous system CNS
form- brain and spinal cord
function- integration and control center
peripheral nervous system PNS
form- paired spinal and cranial nerves
function- carries messages to and from spinal cord and brain, link body to CNS
division of PNS
sensory (afferent)
motor (efferent)
sensory (afferent) division- inputs
somatic afferent fibers- from skin, skeletal muscles, and joints to brain
visceral afferent fibers- from visceral organs to brain
motor (efferent) division- outputs
transmits impulses from CNS to effector organs
motor division organization
somatic nervous system
autonomic nervous system
somatic nervous system
conscious control of skeletal muscles
autonomic nervous system
regulates involuntary muscle (cardiac and smooth) and glands
sympathetic and parasympathetic
sympathetic
part of autonomic nervous system
stress and stimulation
fight or flight
parasympathetic
part of autonomic nervous system
relax and conservation
same organs, separates nerves for opposite effects of sympathetic
neurons
transmit electrical signals
neuroglia
nerve glue
supporting cells
location of neuroglia in CNS
astrocytes
microglia
ependymal cells
oligodendrocytes
location of neuroglia in PNS
satellite cells
schwann cells
characteristics of neurons
excitable
long lived (+100 years)
amitotic- no centrioles to divide
high metabolic rate- uses lots of glucose and oxygen
development of neurons
ectoderm forms neural tube
neuroblasts- embryonic precursors
migrated and guided
how do neuroblasts migrate during development?
move throughout embryo using growth cone with filopodia
crawl through embryo
how are neuroblasts guided during development?
genetic signals guide to correct spot for final destination
inhibitory, attractive, goal cues
cell adhesion molecules for migration (synapses)
apoptosis for 2/3 of neuroblasts that do not find spot
soma
nerve cell body
contains nucleus and other organelles
focal point for outgrowth of neuronal processes (dendrites and axons)
axon hillock
where axons arise
ramp off cell body that leads to axon
nuclei
clusters of cell bodies in CNS
ganglia
bundles of cell bodies in PNS
dendrites
processes out of soma that receives information
numerous, short, tapering, diffusely branched
contain spines where synapses form
large surface area for input
graded potentials travel toward soma
axons
generate and conduct nerve impulses
form synapses and release neurotransmitters
characteristics of axons
one per neuron
long
lacks golgi and rough ER
anterograde and retrograde transport
tracts
CNS bundles of axons
nerves
PNS bundles of axons
characteristics of neuroglia
- provide supportive scaffolding for neurons
- segregate and insulate neurons
- guide young neurons to proper connections
- promote health and growth
- help regulate neurotransmitter levels
- phagocytosis
astrocytes
most abundant and versatile neuroglia
cling to neurons and synaptic endings
cover capillaries and link neurons
supporta nd brace neurons
guide young neurons and synapse formation
control chemical environment around neuron
microglia
immune function
monitor health of neurons
transfer into macrophages to remove cellular debris, microbes, or dead neurons
ependymal cells
circulate cerebrospinal fluid
line the central cavities of brain and spinal column
squamous/columnar shaped (often ciliated)
oligodendrocytes
wrap CNS axons like jelly roll
form insulating myelin sheath for electrical impulses
up to 60 axons each
schwann cells
surrounds axons of PNS (like oligodendrocytes)
form insulating myelin sheath, essential support, help injured nerves regenerate
satellite cells
surround neuron cell bodies of PNS
function like astrocytes
myelin sheath
white fatty sheath protects long axons
electrically insulates fibers
increases speed of nerve impulses
outer collar of cytoplasm
nodes of ranvier
gaps between schwann cells
white matter
dense collections of myelinated fibers
gray matter
mostly soma and un-myelinated fibers
action potentials definiton
electrical impulses carried along length of axon
always same regardless of stimuli
based on changes in ion concentrations across membrane
voltage V
potential energy from separation of charges
measured in millivolts from flow of ions
current I
flow of electrical charge between two points
plasma membrane resists
insulator
substance with high electrical resistance
myelin sheath
4 types of ion channels
passive
voltage gated
ligand gated
mechanically gated
passive channels
leakage
always open
voltage gated channels
open and close in response to membrane potential
important for action potential
ligand gated channels
chemically gated
open when specific neurotransmitter binds
mechanically gated channels
open and close in response to physical forces
not used in neurons
electrochemical gradient
ions will move from high to low concentration
ions will move toward the opposite charge
creates electrical current when ions move, and changes voltage across membrane
resting membrane potential
-70 mV
inside of cell membrane has more negative charges than outside
Na/K ATPase pump maintains resting potential
Na and K voltage gates are closed
depolarization
inside of membrane becomes less negative
Na gates opened, K closed
threshold- critical level -55 mV, action potential fires
positive feedback loop causes more channels to open
hyperpolarization
inside of membrane becomes more negative than resting potential
K gates still open and leave cell
neuron less sensitive to stimuli until resting restored
repolarization
membrane returns to its resting membrane potential
Na inactivation gates close, K opens and leaves
graded potentials
short lived localized changes in membrane potential
spread is determined by strength of stimulus
action potential characteristics
brief reversal of membrane polarity (-70 to +30)
all or nothing event
maintain strength over distance
generated only by muscle cells and neurons
phases of action potential
- resting state
- depolarization
- repolarization
- hyperpolarization
- return to resting potential
two voltage regulated gates of sodium
activation gate
inactivation gate
how are ionic conditions restored?
Na/K ATPase pumps NA out and K in
repolarization restores electrical differences across membrane (not ionic)
absolute refractory period
neuron cannot generate action potential
ensures each action potential is separate events
one way transmission of nerve impulses
relative refractory period
threshold is elevated
only strong stimuli can generate action potentials
propagation of action potential
self propagating
constant velocity
refractory period causes unidirectional propagation
action potential frequency
stronger stimuli generate more frequent potentials
all potentials are same strength, more stimuli gives stronger result
2 factors that determine velocity of signal
axon diameter
presence of myelin sheath
axon diameter
larger the diameter, faster the impulse
presence of myelin sheath
faster impulses
saltatory conduction- node jumping
action potentials only generated in gaps and jump faster from gap to gap
somatic sensory and motor nerves
skin, muscles, joints
have axons with largest diameters and lots of thick myelin
autonomic sensory nerves
axons with smaller diameters
lightly myelinated or not at all
multiple sclerosis MS
autoimmune disease where immune system attacks myelin sheath
sheath turned into scleroses
conduction decreases or misfires
axons make more Na+ channels to compensate
treated with corticosteroids and drugs to reduce immune response
synapse
junction for cell - cell communication
neuron to neuron
neuron to effector cell
presynaptic neuron
conducts impulses toward synapse
post synaptic neuron/cell
receives signal
may or may no act on signal
axosomatic synapses
axons attached to somatic body of cell
axodendritic synapses
axons attached to dendrites
axoaxonal synapses
axons attached to axon hillock
electrical synapse
gaps right next to each other
like gap junctions- direct ion flow from cell to cell
less common- important in CNS for neural development, synchronization of activity, and emotions and memory
chemical synapse
excitatory or inhibitory
communication via neurotransmitters
action potential causes flood of calcium, presynaptic cell releases neurotransmitter, synaptic cleft if fluid filled, post synaptic cell has membrane bound receptors for neurotransmitter to bind
neurotransmitters recycled, removed, or degraded after release
what type of gate is present in chemical synapses?
ligand gated ion channels
steps to neurotransmitter action
- action potential reaches axon terminus
- calcium voltage gated channels let Ca enter terminus
- calcium stimulates release of neurotransmitter via exocytosis
- neurotransmitter travels across cleft, binds to its receptor and causes a graded potential
- neurotransmitter is subject to reuptake, degradation, or diffusion
acetylcholine
neuromuscular junctions
learning
biogenic amines
dopamine, norepinephrine, epinephrine, serotonin, histamine
emotional behavior, biological clock, ANS motor neurons
pleasure and mood
amino acids
glutamate, aspartate, glycine, GABA
learning
peptides
endorphines, enkephalins, substance P, somatostatin
pain levels
neurotransmitters in both CNS and PNS
purines- ATP/adenosine
gases and lipids- nitric oxide, CO, H2S
endocannabinoids- learning, memory, appetite/nausea
direct neurotransmitter receptors
channel linked receptors - ligand binding changes shape and opens
rapid response
sensory motor coordination
indirect neurotransmitter receptors
G protein linked receptors
indirect, slow, complex
receptor activates G protein which uses 2nd messangers to open ion channels
memory, learning, ANS
dopamine, serotonin, norepinephrine
postsynaptic potential
post synaptic membranes achieve graded potentials, not action potentials
at axon hillock
EPSP
excitatory postsynaptic potentials
cell depolarized by Na/K channels
Glutamate muscle contraction to do something
IPSP
inhibitory postsynaptic potentials
cell is hyperpolarized by K/Cl channels
GABA
conditions for postsynaptic cell firing
- which neurotransmitter released
- amount of neurotransmitter present
- length of time the neurotransmitter is bound to receptor
if threshold isn’t reached, no action potential
spatial summation
multiple graded potentials arrive at same time
number of IPSP vs EPSP determine if action potential generated
temporal summation
multiple graded potentials arrive at different times
time intervals determine if action potential is generated
synaptic potentiation
repeated or continuous use of synapse enhances ability to stimulate again
hippocampus- learning and memory
neuronal pools
neurons closely associated with axon more likely to be stimulated vs those further away
serial processing
system works in all or nothing, quick and predictable manner
reflex
sterotyped, automatic response to a stimulus
parallel processing
stimulus activates multiple neuronal circuits
process information very quickly for higher order thinking
memory, emotion, hunger
types of circuits
diverging
converging
reverberating
parallel after discharge
diverging circuit
one input, many outputs
amplifying circuit
converging circuit
many inputs, one output
concentrating circuit
reverberating circuit
signal travels through chain of neurons, each feeding back to previous neuron
oscillating circuit rhythmic activity
parallel after discharge circuit
signal stimulates neurons arranged in parallel arrays that eventually converge on a single output cell
impulses reach output cell at different times, cause a burst of impulses (after discharge)
BoTox
botulinum toxin
blocks acetylcholine release at neuromuscular junction
facial muscles cant contract and wrinkles disappear
local anesthesia
block sodium channels so action potentials aren’t generated
how are neurotransmitter kept in concentration in synapse?
inhibit enzymes associated with postsynaptic membrane that degrade it
inhibit reuptake of it by astrocytes or presynaptic terminal
pleasure
brains reward us with behavior necessary for survival with dopamine
involved in drug and alcohol addiction
drugs of abuse
chemically similar to neurotransmitter of reward system
amphetamine drugs
enhances release of dopamine
meth
cocaine
prevents reuptake of dopamine
dopamine continues to signal
brain stops making dopamine (less signaling)
mood, sleep, appetite
serotonin
anti-anxiety/depression drugs block reuptake
LSD- blocks activity, excites certain neurons
Ecstasy- enhances release and activity, may destroy neurons
depression
linked to altered levels of serotonin
SSRI- selective serotonin reuptake inhibitors
provides greater signal from less neurotransmitter
pain
opioids- oxycontin, fentanyl, vicodin, heroin
similar to natural opioids and mimic pain relief pathway
highly addictive
