neurons Flashcards
nerves
Cells called neurons bundled together in a sheath of connective tissue
neurons
fits form to function
cells that transmit impulses
neuron structure
Dendrites : fine branches that receive signals
Cell body : nucleus & organelles
Axon : transmits signal
Synaptic terminal : passes signal to next cell
Synapse / synaptic cleft
Interstitial space between synaptic terminal and next cell
Signaling neuron
is the presynaptic cell
receiving cell is the
Postsynaptic cell
neurotransmitters
signaling molecules (chemical messengers) Carry signal from synaptic terminal to receptors on postsynaptic cell
Glia
cells that support neurons
nourish
regulate surrounding interstitial fluid
schwann cells
make myelin in PNS
(peripheral nervous system)
glia cells
information processing three stages
sensory input
integration
motor output
external Sensory neurons
detect things from outside a. mechanoreceptors (tough and pressure)
b. chemoreceptors (chemicals, smell, taste)
c. photoreceptors (light, picture)
internal sensory neurons
detect things from Inside
a. baroreceptors (blood pressure)
b. pain receptors
CNS
central nervous system…spinal cord and brain
somatic- controls voluntary movement of skeletal muscle
PNS
PNS = peripheral nervous system.. All other nerves
AUTONOMIC- CONTROLS SELF REGULATED ORGANS AND GLANDS
integrators
Found in CNS : central nervous system
called interneurons-connect neurons in brain & longitudinal nerve cord (spinal cord)
process info sent in by
sensory neurons
motor neurons
transmit signal from CNS to effector cells
muscle cells
endocrine cells
simple diffusion
very small, not charged
ex water
facilitated diffusion
protein channel
active transport
against conc. Grad
protein pump or co-transporter (pump two things one in one out)
Resting potential
Sodium potassium pump (co transporter) active transport. 3Na put, 2K into cell creates concentrated gradient K channels leak ions back out more positive out than in cell -70 mV potential energy…voltage in cell
how much potassium and sodium go in and out of the cell
2 K+ in for every 3 Na+ out
more K+ leaks out than Na+ leaks in
Equilibrium Potential
magnitude of voltage across membrane
Hyper polarization
resetting cell
inside even
more negative…increase K diffusing out
Depolarization
sends signal
inside becomes less negative…open Na channels
graded potentials
different levels of depolarization
a. different neuron responses
b. no response or action potential
c. depolarization signals are summative
low grade potential
Low grade: small stimulus, depolarization does not reach trigger zone with high enough energy = no action potential sent down axon
high grade potential
High grade: intense or long lasting
Signal reaches trigger zone at or above threshold level
Action potential send down axon
Action Potential: massive depolarization process
A. Sum of depolarization (from dendrites)signals causes depolarization level to reach threshold
B. voltage-gated Na channels open (floods Na)
C. positive feed back opens more
D. Na flow brings voltage closer to 0mV then above 0mV to be positive
E. voltage gated K channels open (because overshoot)
F. restore negative cytoplasm
G. undershoot = too much negative charge inside (close all gates, restraining period)
H. resting potential
restored by NaK pumps (resets back to -70)
Action potential:quick reversal of polarity
A. Action potential is all or nothing
B. Na+ flow in as fast as possible for .5ms
C. Then Na+ gates shut and K+ gates open
passing action potential on
. One patch of membrane activates the Na+ gates next to it by becoming positive inside…..causes more Na+ gates to open
Propagation is 1 way due to gate inactivation. refractory period
refractory period =
Na gated channels are inactivated
Saltatory conduction (leap)
Nerve impulse
jumps between
Nodes=faster
transmission
myelin
insulator
nodes of ranvier
space between schwann cells
Electrical synapse
direct transmission
of electric charge via gap junctions
=rapid unvarying response (brain)
cant be modified or stopped
Chemical Synapse
Depolarization opens Ca+ channels
Ca+ causes synaptic vesicles to release neurotransmitters by exocytosis
Neurotransmitters diffuse to postsynaptic cell & bind to receptors
two types of neurotransmitters
excitatory and inhibitory
excitatory neurotransmitters
causes depolarization (encourages signal transmission)
inhibitory neurotransmitters
causes hyperpolarization (discourages signal transmission)
Ach neurotransmitter
acetylcholine (muscle) both excitatory and inhibitory
serotonin
mood/ memory/sleep
epinephrine/norepinephrine
(called adrenalin & noradrenalin in endocrine function)
transduction
passing action potential to next cell
ligand
any molecule that binds to a receptor
receptors
Most = ligand-gated ion channels
a. neurotransmitter = the ligand
b. binding of ligand opens the gate
excitatory receptors
some let K+ & Na+ pass to depolarize
excitatory
inhibitory receptors
some let in Cl- to hyperpolarize (inhibitory)
receptors activating second messenger
slower longer lastingresponse
b) binding n.t. activates G protein
c) G protein activates enzyme to make ATP into cAMP
d) cAMPs activate protein kinase As
e) Kinase As phosphorolate many channels = open them
f) many kinase As = amplified signal
EPSP
excitatory postsynaptic potential encourages ps cell response
IPSP
inhibitory pulls the cell back from threshold (restores resting polarization)
Integration
summation of EPSP & IPSP determines response of cell
Spatial summation
multiple synapses of same cell receive signal
Temporal summation
rapidly repeated signal
Clearing synaptic clefts: Neurotransmitters cleared by…
- diffusion
- re-uptake into pre-synaptic cell
- enzyme mediated breakdown
