Chapter 2: Flashcards
Peripheral Nervous System
Grey Matter is in the middle: Cell bodies, the somas
Dorsal: Sensory
White matter: Neuron axons, the tracts.
Ventral root: Motor
31 pairs of spinal nerves
Spinal Reflexes
Spinal cord has two parallel pathways
Sensory Nerves: Dorsal Root
Motor Nerves: Ventral Root
Bell-Megendie Law of Neural Specialization
Sensory / Motor information segregated at level of PNS and CNS
Afferent:
projections to CNS, brain region, or neuron
Efferent
projections from CNS, brain region, or neuron
Autonomic Nervous System
Two divisions:
Sympathetic
Parasympathetic
Regulate 4 critical bodily states related to survival—i.e., the 4 Fs: Fighting Fleeing Feeding sex
FIGHT-or-FLIGHT
Sympathetic Autonomic Nervous System
REST-and-DIGEST
Parasympathetic Autonomic Nervous System
Neuron facts
Human brain ~ 100 billion neurons
More than 100 types of neurons
5,000 to 80,000 synapses per neuron
1,500 TRILLION synapses/human brain
Dendrites
Dendritic tree
Collection of dendrites from single neuron
Dendritic spines
Contact point between axon and dendrite
Low dendritic spine number is correlated with mental retardation
Elevated spine density correlated with autism
TYPICALLY synapses form at the spines
Spine Density in the Hippocampus Impacted by External & Internal Factors
Enriched environment leads to denser spines
High expression of dendrites during estrous.
Rodents learn better when they are ovulating.
More spines: more synaptic synapses, better for learning
The Soma
Cytoplasm: cytosol & organelles
Nucleus: contained in nuclear envelope
Gene expression
~23000 human genes
Transcription: mRNA assembly
Translation: Assembly of proteins from 20 amino acids
Some animals and plants have more genes than we do.
Cell Membrane segregates ions inside cell from ions in extracellular fluid
Channels provide a path for ions to cross back and forth across membrane
Ionic movement is influenced by:
Diffusion
An ion’s concentration gradient across the membrane
Electricity
The separation of ionic charge across the membrane
Seeking Equilibrium
Sodium
Na+
Higher concentration OUTSIDE of cell
Both Diffusion and Electrical Force attract Sodium INTO the cell
Depolarize
Potassium
K+
Higher Concentration on the INSIDE.
Diffusion pushes Potassium out; electrical force sucks Potassium in.
Hyperpolarize
Calcium
Ca2+
Higher concentration OUTSIDE of cell
Chloride
Cl-
Higher concentration OUTSIDE of cell
Diffusion pushes chlorine in; electrical force pushes chlorine out
In the case of chloride,
Diffusion is much stronger than the electrical force.
So Chlorine goes INTO the cell
Hyperpolarized
The inside of the cell is _____ charged.
The inside of the cell is negatively charged.
depolarization
As the sodium rushes back into the cell the positive sodium ions raise the charge inside of the cell from negative to positive.
Once the interior of the cell becomes positively charged, depolarization of the cell is complete.
MORE POSTIVE
Hyperpolarization
Hyperpolarization is a change in a cell’s membrane potential that makes it more negative.
Inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.
Resting membrane potential
The difference in charge between the inside and outside of the membrane of a neuron at rest
AT REST, THE INSIDE OF THE NEURON IS AT______
AT REST, THE INSIDE OF THE NEURON IS AT -70 MV
The Axon
Axon hillock (beginning), Axon proper (middle) and Axon terminal (end) Relays action potentials when membrane potential depolarizes past threshold
All-or-none
Action potentials
All-or-nothing.
A binary event.
Rising phase:
Na+ enters neuron
Depolarization
Overshoot:
Neuron positive inside. Up to about 40 MV
Falling phase:
K+ exits neuron
Repolarization
Falling phase is due to opening of potassium channels that are opened but delayed just for a moment (enough to reach peak) and then potassium flows out.
The potassium channels are a bit delayed in closing, which gives us the after hyperpolarization period where another spike is impossible unless an incredibly strong stimulus is given.
AHP: After hyperpolarization. Needs a much stronger stimulus to activate it. Essentially a limit on temporal excitability.
STEP 1 of Action Potential
Rising phase
Na+ enters neuron
Depolarization
STEP 2 of Action Potential
Overshoot
Neuron becomes so depolarized that it’s positive inside
STEP 3 of Action Potential
Falling phase
K+ exits neuron, making cell more negative, hyperpolarizing the cell
Repolarization
Potential is just another word for ______
Potential is just another word for voltage
The membrane at the _____ depolarizes, then we reach _____, then we initiate an ____
The membrane at the axon hillock depolarizes, then we reach threshold, then we initiate an action potential
Action Potentials
Communication
Convey information over distance in nervous system
Neural information code:
Pattern (temporal code)
Frequency (rate code)
Saltatory conduction
From the Latin “saltare,” to hop or leap.
The propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.
Synapse
point of contact between presynaptic axon terminal and another (postsynaptic) neuron
Information is passed directionally from presynaptic to postsynaptic cell
1897: Charles Sherrington coined term “Synapse”
Soups vs. Sparks Debate
Physical nature of synaptic transmission
Chemical vs. Electrical transmission
It is a chemical signal that is released at the presynaptic terminal.
At gap junctions, the signals are electrical and bidirectional.
These form a minority of the communication methods in the brain.
Chemical Synapses
Presynaptic terminals release
chemical signals.
Neurotransmitters regulate information transfer
Neurotransmitter Cycle
- Synthesis/Packaging of Neurotransmitter into Vesicles
- Exocytosis: fuse with membrane and spill contents
- Receptor Binding: neurobind to postsynaptic receptors.
What happens after the Neurotransmitter release? There are several possibilities:
Inactivation
Reuptake
Diffusion
Neurotransmitters:
Amino acids
GABA (inhibitory)
glutamate (excitatory)
Neurotransmitter Types
Small molecules, often called neuromodulators:
serotonin, norepinephrine, epinephrine, dopamine, acetylcholine
Amino acids:
GABA (inhibitory), glutamate (excitatory)
Neuropeptides (small protein):
secretin, oxytocin
*Soluble gases:
nitric oxide, carbon monoxide
*Typically, these Gases are Retrograde messengers: typically released from the postsynaptic terminal to the presynaptic.
Neurotransmitters:
Neuropeptides
small proteins
secretin, oxytocin
Neurotransmitters:
Soluble gases
nitric oxide, carbon monoxide
Typically, these Gases are Retrograde messengers:
typically released from the postsynaptic terminal to the presynaptic.
