Cells of the Nervous Tissue (4) Flashcards
Central Nervous System (CNS)
Brain and spinal cord
Peripheral nervous system (PNS)
cranial nerves, spinal nerves, ganglia
Divisions of PNS
somatic and autonomic nervous systems
Divisions of Autonomic nervous system (within PNS)
sympathetic and parasympathetic
sympathetic division
fight or flight; stress response; sickness, exercise, fear, etc.
parasympathetic division
calm and relaxed; rest and digest
nervous tissue
consists of neurons and their supporting cells
neurons
electrically excitable cells that transmit electric signals
- high metabolic rate
- conductive
- secretory
- long lived, amitotic
neuroglia (glial cells)
“helper cells”
surround and wrap neurons, scaffolding for neurons, segregate, insulate, guide new neurons to their connections, promote neuron health and growth
Astrocytes
star shapped body with projections; most abundant, cover capillaries; support, brace, anchor neurons to nutrient supply; guide migration; control chemical environment
Microglia
gobbles up everything that shouldn’t be there; small, ovoid cells with spiny processes; phagocytes, monitor neuron health; primary immunity in brain
Ependymal cells
line central brain and spinal cavities; produce cerebrospinal fluid
oligodendrocytes
branched cells, wrap around neuron axons in CNS - myelin sheath
schwann cells
maintain myeline sheath around PNS nerve cells
satellite cells
surround neuron cell bodies with ganglia
Types of neuroglia
astrocytes, microglia, ependymal cells, oligodendrocytes, schwann cells, satellite cells
Sensory (afferent) neurons
detect changes in body and environment; transmit info to CNS
Interneurons
between sensory and motor pathways in CNS; 90% of neurons; process, store, and retrieve info
motor (efferent) neurons
send signals to muscles and gland cells; organs that carry out responses are effectors (can remember bc efferent are carrying to effectors)
dendrites
receptive region - first stimulation processed here
soma
cell body, biosynthetic, receptive region
nissl bodies
similar to rough ER; clumps of ribosomes
Axon hillock
summing center of impulse
axon
long conducting process
process
any arm like extensions
- tracts in CNS
- nerves in PNS
axon terminals
secretion of NT
resting membrane potential
potential difference across the plasma membrane
chemical gradient
ions flow high to low
electrical gradient
move to area of opposite charge
electrochemical gradient
electrical + chemical gradients
Passive or leakage ion channel
always open; move in direction would like to
chemically (ligand) gated ion channel
open with binding of specific neurotransmitter
mechanically gated ion channel
open and close due to physical deformation
i.e. if stretch then open
volatage-gated ion channel
open and close in response to membrane potential
-like have an internal voltmeter
-in axon and axon hillock
graded potentials
only in sensory region (dendrites); short-lived localized changes on membrane potential; decrease with distance from site; magnitude varies with strength; can initiate action potential
excitatory postsynaptic potential (EPSP)
causes local depolarization (more +); inc membrane potential; in favor action potential
inhibitory postsynaptic potential (IPSP)
causes local membrane hyperpolarization (more -); dec membrane potential; inhibits action potential
subthreshold
no summation
threshold charge
-55 mV
temporal summation
time based; small charges will add up if more frequent
spatial summation
close together in space
EPSP and IPSP
if together can cancel each other other
Action potential
short reversal of membrane potential; only generated by muscle cells and neurons; NO decrease in strength over distance
-all or nothing response
What would cause an action potential to be propagated down an axon?
threshold of -55mV reached
nerve impulse
action potential in the axon
What are the phases of an action potential?
Stimulus, depolarization, repolarization, hyperpolarization, return to rest potential
AP: resting state
Na+ activation gate closed and K+ channels closed
some leakage
AP: depolarization phase (cells more +)
Na+ gates open, K+ gates still closed
becomes self generating as Na+ ions flowing in trigger next voltage gated channels
AP: repolarization phase (becoming more negative again)
Na+ inactivation gates close, K+ gates open
AP: hyperpolarization (too negative)
K+ gates remain open, excessive efflux of K+
Neuron insensitive to stimulus and depolarization to help keep nerve signals independent
After hyperpolarization…
sodium potasium pumps and ATPase work to get cell back to resting state (-70mV)
Absolute refractory period
time from opening of Na+ activation gates until closing of inactivation gates - prevents generation of AP
ensures each AP separate
enforces one-way transmission of nerve impulses
Relative refractory period
interval following absolute refractory period when:
-Na+ gates closed
-K+ gates open
-repolarization is occurring
threshold level elevated allowing strong stimuli to increase frequency of AP events
all-or-nothing phenomenon
AP occur completely or not at all
What can rate of impulse propagation be determined by?
Axon diameter
myelin sheath presence
Rate of impulse will ______ with myelination
increase
myelination
fatty, white, segmented sheath around many long axons
function of myelination
protection,
electrical insulation,
increase speed of electrical impulse
nodes of ranvier
gaps in myelin sheath between adjacent Schwann cells
Schwann cells in unmyelineated axons
Schwann cells still associate with unmyelineated nerve fibers
- surround but don’t coil
- protective coating
Saltatory conduction
myelinated axon
current only passes at nodes of ranvier where voltate-gated Na+ channels are very concentrated
AP triggered only at nodes and jump from node to node
saltatory conduction is ______ than conduction along unmyelinated axons
faster
what makes saltatory conduction fast?
densely packed Na+ channels at nodes of ranvier
-Na+ really wants to rush in very quickly
presynaptic neuron
conducts impulses toward synapse
postsynaptic neuron
transmits impulses ways from synapse
Steps to the release of neurotransmitter
- AP at axon terminal
- AP opens voltage gared Ca++ channels
- Ca++ enters cell
- Ca++ binds calmodulin
- Ca++-calmodulin activate PKA
- PKA phosphorylates synapsin proteins
- synapsin release vesicles from cytoskeleton
synaptic cleft
gap between axon of one neuron and dendrite of another
SNARE proteins
on vesicle and plasma membrane
- entangle each other
- force fusion
- NT released
Synaptic delay
rate-limiting step of neural transmission (0.3-0.5 ms)
Neurotransmiter released, diffuses across synapse, binds to receptors
Neurotransmitter fate
diffusion
reuptake
enzyme degradation
Why can’t the neurotransmitter just stay forever?
so that it is possible to differentiate between signals
