The Neuron and the Synapse Flashcards
What are the divisions of the CNS
spinal cord and brain
What are the divisions of the PNS
somatic nervous system and autonomic nervous system
Somatic Nervous System
voluntary controls
What are the divisions of the autonomic nervous system?
sympathetic and parasympathetic nervous system
Sympathetic Nervous System
fight or flight
Parasympathetic Nervous System
rest and digest
Parts of the Brain
forebrain, cerebellum, brain stem
Forebrain
higher function, contains thalamus and hypothalamus
Cerebellum
fine motor movements
Brain Stem
extension of the spinal cord
Parts of the brain stem
pons, medulla oblongata, midbrain
Afferent
sensory info into CNS
Efferent
motor- exits CNS
Somatic (afferent)
from skin, retina, and membranous labyrinth
Visceral (afferent)
from thoracic and abdominal organs, olfactory epithelium, and taste buds
Somatic (efferent)
to skeletal muscle; voluntary control
Visceral (efferent)
to cardiac and smooth muscle and glands
Information Flow in a Neuron
- dendrites
- soma
- axon
- pre-synaptic terminal
Dendrites
branch-like extensions from the soma. Receive signals from other neurons. Multiple inputs to a single neuron. Electrical signals summate at the soma
Soma Components
nucleus, ribosomes, rER, Golgi
Axon
signal from initial segment to pre-synaptic terminal. Bi-direction
What is the charge on the interior of the neuron?
negative
Na K Pump
3 Na out, 2 K in
Depolarized
more positive than resting membrane potential. Inward flow of positive charge
Hyperpolarized
more negative than resting membrane potential, outward flow of positive charge or inward flow of (-) ions
Excitatory Post-Synaptic Potential
resting membrane potential more positive. Closer to reaching action potential. Usual influx of Na
Inhibitory Post-Synaptic Potential
resting membrane potential more negative. less likely for an action potential. Cl influx or K effux
Inhibitory Post-Synaptic Potential
resting membrane potential more negative. less likely for an action potential. Cl influx or K effux
Summation
single discharge of presynaptic terminal onto dendrite does not initiate action potential. Requires Summation: spatial summation and temporal summation
Action Potential
Initiation of AP when stimulus reaches threshold. Fixed in amplitude, uniform shape, not graded. A regenerative signal that begins at an axon’s initial segment and rapidly spreads down axon
Stages of Action Potential
- Resting Stage
- Depolarization Stage
- Repolarization Stage
Resting Stage
cell is polarized- negative inside cell
Depolarization Stage
depolarization above threshold triggers all or nothing response. Opening of voltage-gated ion channels
Repolarization Stage
Na channels close and voltage-gated K channels open. Rapid diffusion of K out of cell
Axonal Conduction
axons carry electrical signals rapidly, efficiently, and reliably.
How to increase conduction speed
larger diameter, myelination
Saltatory Conduction
Jumping from Node of Ranvier to Node of Ranvier
Node or Ranvier
junction between Schwann cells. There is increased density of Na channels at nodes. Actions potential occurs at nodes
What happens between the nodes of Ranvier?
ions flow in and out
Types of Synapse
chemical and electrical
Chemical Synapse
majority in CNS and at NMJ. Release of neurotransmitters. Propagate current from presynaptic cell to postsynaptic cell
Electrical Synapse
smooth muscle and cardiac muscle. Self-propagating.
Basic Process of Transmission
- NT packages into synaptic vesicles
- AP arrives at presynaptic terminal
- Opening of voltage-gated ion channels
- Fusion of vesicles with membrane and release of NT
- NT diffuses across synapse and binds receptor
- Activation of postsynaptic cell
Neurotransmitter Release
- Presynaptic membrane contains voltage-gated Ca channels
- AP at presynaptic terminal causes Ca channels to open
- Ca facilitates fusion of synaptic vesicles with membrane
- NT binds to receptor on postsynaptic cell
Consequences of NT Binding
Excitation, Inhibition
Excitation
Opening of Na channels. Decreased diffusion of Cl into cell of K out of cell. Changes in internal metabolism
Inhibition
Opening of Cl channels, increased diffusion of K out of cell. Enzymes that inhibit cellular metabolism.
Innervation of Muscle
one nerve can innervate several muscle fibers. Each muscle cell can only have 1 neuron. Transmission from nerve to muscle
What is the excitatory neurotransmitter at the NMJ?
acetylcholine
Post Synaptic Membrane
Junctional folds or subneural clefts. Increase surface area
Breakdown of Acetylcholine
- made of choline and acetyl CoA
- In the synapse acetylcholine is rapidly broken down by the enzyme acetylcholinesterase
- choline is transported back into the axon terminal and used to make more acetylcholine
Consequence at Nerve-Nerve Junction
May be excitatory or inhibitory. Uses a variety of neurotransmitters. Can be bi-directional transmission. Variety of receptor types. AP often have to summate for post-synaptic AP. Relies on Ca influx for neurotransmitter release
Consequence at NMJ
NMJ produces excitation. Uses acetylcholine. One-way signal transduction
Nicotinic Receptor. AP leads to muscle contraction. Relies on Ca influx for neurotransmitter release.
What is the only similarity between nerve-nerve junction and NMJ?
both rely on Ca influx for neurotransmitter release
Myasthenia Gravis
auto-antibody binds to acetylcholine receptors inhibiting muscle activation, leading to weakness and paralysis. To treat, inhibit acetylcholinesterase so there is more acetylcholine available
Tick Paralysis
toxin binds to Ca receptors, preventing the release of acetylcholine. Open Ca channels by removing tick or give preventatives
Snake Envenomation
toxin binds to acetylcholine receptors. Acute quadriplegia, absent reflexes, muscle tremors
Organophosphate Toxicity
Irreversibly bind acetylcholinesterases. Causes excessive acetylcholine (nicotinic crisis), muscarinic crisis (excessive parasympathetic). Treatment: supportive care
Characteristics of Nerve-Nerve Junction
- Influx of Calcium
- Requires Summation
- Can be excitatory or Inhibitory
- Multiple neurotransmitters
- Multiple receptors
- Can be bi-directional