Lecture 2 Flashcards
endocrine system
-endocrine cells = all glands that secret hormones
-release chemical messengers (hormones) into circulatory system and carried to target cells
nervous system
-electrical signal travel in neuron
-release chemicals (neurotransmitters) into space between neuron and target cell
neuron communication strategy
electrical signal releases neurotransmitters into synapse to communicate with target (postsynaptic) cell
neurosecretory cell communication strategy
release neurohormones into circulation in response to electrical signals and interface between systems
endocrine cell communication strategy
release hormones into circulation
soma
cell body
dendrites
typically receive incoming signal (result in change in membrane potential)
axon hillock
-initiate action potentials
-travels along axon to axon terminals and triggers neurotransmitter release
-axon myelinated or unmyelinated
ion channel types
-open under different conditions
-ligand-gated channels open when ligands (neurotransmitter) bind
-voltage-gated (VG) channels open when there is a specific change in membrane potential (open at specific stages of an action potential)
signal transmission
-signal travels down the axon to the terminals to communicate with other neurons, muscles or other target cells
-the transmitting neuron is presynaptic and the receiving neuron is postsynaptic
-two types of membrane potentials: graded potentials, action potentials
graded potentials
-activated by ligand-gated Na+ channel, cause changes in membrane potential
-synaptic potential
-spatially restricted response
-conduction with decrement
electrical signals
-graded changes in membrane potential occur in dendrites and cell body
-are spatially and temporally summated
-if combined depolarization exceeds threshold, an action potential is generated
-spacial summation of Ca+ also prevent generation of APs
electrical signalling
-when net change in membrane potential at the axon hillock reaches or exceeds threshold (suprathreshold graded potential)
-an action potential is triggered and travels down the axon (non-graded, all-or-none signal transmission)
stages of action potentials
-membrane potential depolarized past threshold potential (-55mV)
-rapid depolarization until 30mV
-membrane potential repolarizes
-membrane potential undershoots resting potential
-resting potential is restored
two voltage regulated gates:
- activation gate: opens at threshold
- inactivation gate: closes at 30mV
also VG K+ channels triggered at threshold (-55mV) but open more slowly than Na+ channels
conduction of APs
-Na+ comes in
-induces local depolarization
-opens Na+ channels close by
-Na+ comes in, etc.
-Aps travel down the axon
-only in one direction (absolute refractory period)
absolute refractory period
the inactivation gate of the Na ion channel closes at 30mV, and remains closed until resting potential is reistablished - impossible to generate AP at an area where an AP has just occured
relative refractory period
during hyperpolarization - possible, but harder to generate AP
myelin sheath
a (mostly) vertebrate feature; a highly compacted, fatty substance
PNS
Schwann cells wrap axon
CNS
oligodendrocytes (OLs) wrap axons
Schwann cells/OLs
-produce myelin - acts as insulation, preserving electrical potential
-increases resistance, reduces capacitance - like insulation on an electrical wire
signal transmission
increases speed and efficiency of electrical transmission
nodes of ranvier
lots of voltage-gated Na+ channels
saltatory conduction
APs jump from node to node along the axon
graded potentials
-vary in magnitude
-vary in duration
-decay with distance
-occur in dendrites and cell body
-caused by opening and closing of many kinds of ion channels
action potentials
-always the same magnitude (in a given cell type)
-always the same duration (in a given cell type)
-can be transmitted across long distances
-occur in axons
-caused by opening and closing of voltage-gated ion channels
cell to cell communication types
- electrical
- chemical (ionotrophic and metabotrophic)
electrical synapses
gap junctions composed of connexin proteins connect presynaptic and postsynaptic cell membranes (pore allows fast chemical and ionic transmission)
ionotrophic receptors
-ligand-gated channels
-rapid changes in post synaptic membrane potential
metabolic receptors
-signaling cascade opens ion channels
-activates intracellular transduction pathway
-slower changes in postsynaptic membrane potential
-can also modify proteins and gene expression (learning and memory)
simple neural networks
sensory information detected by receptor –> signal transmitted from a sensory neuron –> efferent neuron –> effector organ (response)
reflex arc
-simple neural circuits that do not involve the conscious centers of the brain
-involuntary
-simple (2 neurons) or complex (many neurons)
-autonomic (e.g. reflex of control of blood pressure)
-somatic (e.g. knee-jerk reflex)
ancestral form neural network
receptor cell directly innervates an effector cell (little processing, no CNS)
monosynaptic neural network
sensory neuron synapses with efferent neuron (e.g. knee-jerk reflex)
polysynaptic neural network
at least one interneuron between sensory and efferent neuron (increases processing capacity)
convergence
many afferent neurons synapse with one efferent neuron
divergence
one afferent neuron synapses with many efferent neurons (allows a single signal to control many independent processes, and it is a way to apmplify the signal)
sensitization
an increase in the response to a gentle stimulus after exposure to a strong stimulus
-electric shock to tail sensitizes response to siphon stimulation
-occurs via facilitating interneurons
