Main Topics Notes
1. Nerve Cells & Impulses
Cells of the N. S. - individual, separate cells: neurons and glia (Santiago Ramón y Cajal)
- membrane: surface layer, where proteins control the traffic of chemicals
- nucleus: where chromosomes are
- mitochondrion: aerobic energy metabolism
- ribosomes: sites for synthesis of protein
neurons = receive, transmit info; (some lack axons/ defined dendrites)
- dendrites: branching fibers, synaptic receptors; + surface, + info; dendritic spines
- soma: sometimes also covered w/ synapses on its surface, cell body
- axon: only 1, may have branches; vertebrates: myelin sheath & nodes of Ranvier
- presynaptic terminal: end bulb
- motor neuron: soma in spinal cord, send signal to muscle
- sensory neuron: sensitive to particular stimulation, soma is off main trunk of axon
- afferent axon: brings info into structure (sensory); depends on point of view
- efferent axon: (exit) brings info away from structure (motor)
- interneuron or intrinsic neuron: has its own body within a structure (e.g. thalamus)
- shape, size and function varies
glia = (neuroglia): smaller and + numerous; varied functions
- astrocytes: wraps around terminals, shields from chemicals (hygiene), synchronizes
activity; control blood flow, formation and elimination of synapses
- microglia: tiny, part of immune system, remove toxins and weak synapses (learning)
- oligodendrocytes (brain + spine) & Schwann cells (periphery of body): build myelin
sheath and supply w/ nutrients
- radial glia: guide migration of neurons during prenatal development, differentiate
into neurons, oligodendrocytes or astrocytes
blood-brain barrier - endothelial cells around blood vessels blocks most chemicals from brain + spine
- because the immune system kills infected cell, and neurons are mostly irreplaceable
- microglia fights viruses that enter (syphilis) without killing, stays long in the body!
- small, uncharged molecules (CO2, O2) and fat-dissoluble (vit A, drugs) can cross
- active transport: protein uses energy to pump into the brain (glucose, amino acids)
- also blocks anti-cancer drugs, Alzheimer shrinks endothelial cells
nourishment of neurons - glucose (and thus oxygen) → crosses barrier numerously
- needs thiamine (vit B1) to use glucose
Nerve Impulse - generates an impulse at each point (conduction would lose intensity); corrects for
delay in arrival to the brain w/ different speed of impulse
resting potential → electrical gradient (polarization, -70mV, -charged proteins inside); ready to fire
- measure by inserting thin microelectrode within cell body, voltmeter and reference
- membrane of phospholipid molecules: selectively permeable (H2O, O2 pass freely)
- sodium-potassium pump: 3Na+ out, 2K+ in; active (energy) transport; 10x more Na+
outside, more K+ inside
- both the concentration gradient and electrical gradient would push Na+ into cell
- concentration gradient would be stronger for pushing K+ out (but almost in balance)
action potential - messages sent by axons; peak (e.g. +30mV) varies across axons, but is consistent!
- if stimulation is beyond threshold, produces massive depolarization: opens Na+ in
- voltage-gated channels: control Na+ and K+ (depend on voltage ≠ across membrane)
(1) Na+ and K+ gates open: a lot of Na+ in → reversed polarity (peak)
(2) close Na+ gate → concentration & electrical ≠ drives K+ out → hyperpolarization
(3) sodium-potassium pump restores original distribution of Na+ and K+ (too slow)
- local anesthetic drugs: block Na+ from passing through gate: stop action potential)
- starts in axon, but also back-propagates into dendrites and soma (for learning)
- all-or-none law: amplitude & speed is same for ≠ intensities (if reaches threshold);
, varies across neurons (+think, +speed); ≠ rhythm of response for ≠ stimuli
- refractory period: a er action potential (Na+ gate closed and K+ flowing out fast);
absolute (impossible to fire) → relative (fires if stimulus is stronger than usual)
propagation of action p. - Na+ spreads arounds → depolarizes next area→ action potential there
- does not go back because of refractory period
myelin sheath - fat and protein, insulates: increase speed; only vertebrates; saves energy:
- from node to node (where next gate is to be opened): saltatory conduction
- multiple sclerosis: immune system attacks myelin sheath → lack of nodes + myelin!
local neurons - exchange info w/ closest neighbor, no axon → graded potential: maybe be
depolarization (excitatory) or hyperpolarization (inhibitory), no all-or-none law, loses
intensity as it travels
2. Synapses
properties of synapses - Sherrington: behavioral experiment (dog, pinch, cut spine-brain): inhibition!
- reflex: automatic muscular response
- reflex arc: sensory neuron → interneuron (spine) → motor neuron → muscle response
(1) conduction speed of reflex arc is slower than that of along an axon: synapse
delays speed of reflex
(2) temporal summation: repeated stimuli have cumulative effect to exceed
threshold of postsynaptic neuron (decays quickly otherwise): graded
depolarization (excitatory postsynaptic potential, EPSP), flow of Na+ in
(3) spatial summation: EPSPs from 2+ ≠ points at once weakly stimulate same
postsynaptic interneuron
- summation depends on order of stimuli (greater depolarization?)
(4) stimulated interneuron excites motor neuron of flexor muscle (1 leg) + extensor
muscles (3 legs); AND inhibits of extensor (1 leg) + flexor (3 legs): temporary
hyperpolarization, decay over time & distance (inhibitory postsynaptic potential,
IPSP), Cl- in/ K+ out
- spontaneous firing rate: periodic action p. without input (EPSP, IPSP act on rate)
chemical events - most synapses rely on chemical processes; most drugs act on synaptic transmission
- Loewi: frog hearts: stimulate vagus nerve (reduces beat) transfer fluid (it’s chemical!)
(1) Synthesis of neurotransmitters (NT):
- amino acids (acid w/ NH2: glutamate, GABA)
- monoamines: indoleamines (tryptophan → serotonin), catecholamines
(phenylalanine → dopamine → norepinephrine → epinephrine)
- acetylcholine (altered amino acid); neuropeptides (amino acid chains: endorphins),
purines (ATP); gases (NO: dilates blood vessels, + blood flow to active brain area)
- carbs → insulin takes competing amino acids (to enter brain) out of bloodstream →
+tryptophan in the brain → +serotonin
- drug L-dopa (precursor of dopamine) helps increase supply of dopamine
- storage: produced in terminals (neuropeptides in soma), stored in vesicles (spheres);
enzyme MAO breaks down;
(2) Action potential→ opens calcium gates, enters presynaptic terminal→
exocytosis: release of 2+ NT into synaptic cle
(3) NT diffuse→ attach to receptors→ alter activity of postsynaptic neuron
(depends on ionotropic/ metabotropic receptor):
- ionotropic effect: transmitter-gated/ ligand gated (opens channel when NT
attaches), quick; excitatory: glutamate, inhibitory:GABA (opens for chloride) → visual..
- metabotropic effect: slower, last longer; dopamine, norepinephrine, serotonin,
GABA, glutamate… attaches → receptor bends → release protein G → activates second
messenger → alters metabolic pathway/ acts on ion channels, etc → taste, pleasure, <3
- neuropeptides: neuromodulators; released by soma, dendrites, sides of axon; needs
repeated depolarization; trigger other dendrites to release too (like hormones); last
long, minutes! (alters gene activity) → hunger, thirst; diffuse only within the brain
- receptors vary: chemical properties, responses, roles in behavior, ≠effects in ≠people
1. Nerve Cells & Impulses
Cells of the N. S. - individual, separate cells: neurons and glia (Santiago Ramón y Cajal)
- membrane: surface layer, where proteins control the traffic of chemicals
- nucleus: where chromosomes are
- mitochondrion: aerobic energy metabolism
- ribosomes: sites for synthesis of protein
neurons = receive, transmit info; (some lack axons/ defined dendrites)
- dendrites: branching fibers, synaptic receptors; + surface, + info; dendritic spines
- soma: sometimes also covered w/ synapses on its surface, cell body
- axon: only 1, may have branches; vertebrates: myelin sheath & nodes of Ranvier
- presynaptic terminal: end bulb
- motor neuron: soma in spinal cord, send signal to muscle
- sensory neuron: sensitive to particular stimulation, soma is off main trunk of axon
- afferent axon: brings info into structure (sensory); depends on point of view
- efferent axon: (exit) brings info away from structure (motor)
- interneuron or intrinsic neuron: has its own body within a structure (e.g. thalamus)
- shape, size and function varies
glia = (neuroglia): smaller and + numerous; varied functions
- astrocytes: wraps around terminals, shields from chemicals (hygiene), synchronizes
activity; control blood flow, formation and elimination of synapses
- microglia: tiny, part of immune system, remove toxins and weak synapses (learning)
- oligodendrocytes (brain + spine) & Schwann cells (periphery of body): build myelin
sheath and supply w/ nutrients
- radial glia: guide migration of neurons during prenatal development, differentiate
into neurons, oligodendrocytes or astrocytes
blood-brain barrier - endothelial cells around blood vessels blocks most chemicals from brain + spine
- because the immune system kills infected cell, and neurons are mostly irreplaceable
- microglia fights viruses that enter (syphilis) without killing, stays long in the body!
- small, uncharged molecules (CO2, O2) and fat-dissoluble (vit A, drugs) can cross
- active transport: protein uses energy to pump into the brain (glucose, amino acids)
- also blocks anti-cancer drugs, Alzheimer shrinks endothelial cells
nourishment of neurons - glucose (and thus oxygen) → crosses barrier numerously
- needs thiamine (vit B1) to use glucose
Nerve Impulse - generates an impulse at each point (conduction would lose intensity); corrects for
delay in arrival to the brain w/ different speed of impulse
resting potential → electrical gradient (polarization, -70mV, -charged proteins inside); ready to fire
- measure by inserting thin microelectrode within cell body, voltmeter and reference
- membrane of phospholipid molecules: selectively permeable (H2O, O2 pass freely)
- sodium-potassium pump: 3Na+ out, 2K+ in; active (energy) transport; 10x more Na+
outside, more K+ inside
- both the concentration gradient and electrical gradient would push Na+ into cell
- concentration gradient would be stronger for pushing K+ out (but almost in balance)
action potential - messages sent by axons; peak (e.g. +30mV) varies across axons, but is consistent!
- if stimulation is beyond threshold, produces massive depolarization: opens Na+ in
- voltage-gated channels: control Na+ and K+ (depend on voltage ≠ across membrane)
(1) Na+ and K+ gates open: a lot of Na+ in → reversed polarity (peak)
(2) close Na+ gate → concentration & electrical ≠ drives K+ out → hyperpolarization
(3) sodium-potassium pump restores original distribution of Na+ and K+ (too slow)
- local anesthetic drugs: block Na+ from passing through gate: stop action potential)
- starts in axon, but also back-propagates into dendrites and soma (for learning)
- all-or-none law: amplitude & speed is same for ≠ intensities (if reaches threshold);
, varies across neurons (+think, +speed); ≠ rhythm of response for ≠ stimuli
- refractory period: a er action potential (Na+ gate closed and K+ flowing out fast);
absolute (impossible to fire) → relative (fires if stimulus is stronger than usual)
propagation of action p. - Na+ spreads arounds → depolarizes next area→ action potential there
- does not go back because of refractory period
myelin sheath - fat and protein, insulates: increase speed; only vertebrates; saves energy:
- from node to node (where next gate is to be opened): saltatory conduction
- multiple sclerosis: immune system attacks myelin sheath → lack of nodes + myelin!
local neurons - exchange info w/ closest neighbor, no axon → graded potential: maybe be
depolarization (excitatory) or hyperpolarization (inhibitory), no all-or-none law, loses
intensity as it travels
2. Synapses
properties of synapses - Sherrington: behavioral experiment (dog, pinch, cut spine-brain): inhibition!
- reflex: automatic muscular response
- reflex arc: sensory neuron → interneuron (spine) → motor neuron → muscle response
(1) conduction speed of reflex arc is slower than that of along an axon: synapse
delays speed of reflex
(2) temporal summation: repeated stimuli have cumulative effect to exceed
threshold of postsynaptic neuron (decays quickly otherwise): graded
depolarization (excitatory postsynaptic potential, EPSP), flow of Na+ in
(3) spatial summation: EPSPs from 2+ ≠ points at once weakly stimulate same
postsynaptic interneuron
- summation depends on order of stimuli (greater depolarization?)
(4) stimulated interneuron excites motor neuron of flexor muscle (1 leg) + extensor
muscles (3 legs); AND inhibits of extensor (1 leg) + flexor (3 legs): temporary
hyperpolarization, decay over time & distance (inhibitory postsynaptic potential,
IPSP), Cl- in/ K+ out
- spontaneous firing rate: periodic action p. without input (EPSP, IPSP act on rate)
chemical events - most synapses rely on chemical processes; most drugs act on synaptic transmission
- Loewi: frog hearts: stimulate vagus nerve (reduces beat) transfer fluid (it’s chemical!)
(1) Synthesis of neurotransmitters (NT):
- amino acids (acid w/ NH2: glutamate, GABA)
- monoamines: indoleamines (tryptophan → serotonin), catecholamines
(phenylalanine → dopamine → norepinephrine → epinephrine)
- acetylcholine (altered amino acid); neuropeptides (amino acid chains: endorphins),
purines (ATP); gases (NO: dilates blood vessels, + blood flow to active brain area)
- carbs → insulin takes competing amino acids (to enter brain) out of bloodstream →
+tryptophan in the brain → +serotonin
- drug L-dopa (precursor of dopamine) helps increase supply of dopamine
- storage: produced in terminals (neuropeptides in soma), stored in vesicles (spheres);
enzyme MAO breaks down;
(2) Action potential→ opens calcium gates, enters presynaptic terminal→
exocytosis: release of 2+ NT into synaptic cle
(3) NT diffuse→ attach to receptors→ alter activity of postsynaptic neuron
(depends on ionotropic/ metabotropic receptor):
- ionotropic effect: transmitter-gated/ ligand gated (opens channel when NT
attaches), quick; excitatory: glutamate, inhibitory:GABA (opens for chloride) → visual..
- metabotropic effect: slower, last longer; dopamine, norepinephrine, serotonin,
GABA, glutamate… attaches → receptor bends → release protein G → activates second
messenger → alters metabolic pathway/ acts on ion channels, etc → taste, pleasure, <3
- neuropeptides: neuromodulators; released by soma, dendrites, sides of axon; needs
repeated depolarization; trigger other dendrites to release too (like hormones); last
long, minutes! (alters gene activity) → hunger, thirst; diffuse only within the brain
- receptors vary: chemical properties, responses, roles in behavior, ≠effects in ≠people
