Nervous System, Neurons, and Neurotransmitters Flashcards
Neuron (Nerve Cell)
Neuron (Nerve Cell) is a specalized cell that conducts info. in the nervous system & neurons can vary in size & shape.
Neurons consist of 3 parts:
- Dendrites (Branch Like): Recieve info from other cells & conduct it toward the cell body.
-
Cell Body (SOMA): Contains several structures including:
- Nucleus
- Mitochondria: Site where the cell perf. metabolic acitivites.
- Ribosomes: Site where cell synthesizes new protien molecules.
- Golgi Complex: System of membrane that prep neurotransmitters & other sub for secretion.
- Axon: Then transmit info. from the cell body to other cells by releasing neurotransmitters
- Synaptic Cleft: Goes into this area which is the gap btwn the axon terminal of the presynaptic cell & receptors on the dendrite of the post-synaptic cell.
Most neurons have a single axon that divides into numerous branches & many axons are connected by a Myelin Sheath: A fatty substance that acts as an insulator & speeds up the conduction of nerve impulses.
Neuron (Action Potential)
The neuron (nerve cell) is a specialized cell that is directly involved in mental processes & behavior. Messages w/in a neuron are transmitted from a neuron’s dendrites to the end of its axon through an electrical process called conduction.
With sufficient stimulation from other cells, a cell becomes:
- Depolarized (the interior of the cell becomes less negative), which triggers an action potential- i.e. an electrical impulse that travels quickly through the cell.
Neuron (All-or-None Principle)
Predicts that an action potential will always be of the same magnitude regardless of the amount of stimulation received by a neuron as long as the minimal level of stimulation (the threshold) has been reached.
Neurotransmitters
Chemical substances that are released from axon terminals, diffuse across synapses, & excite or inhibits receptor sites on postsynaptic nerve cells.
Neurotransmitters Include:
- Acetylcholine (ACh)
- Dopamine (Catecholamine)
- Norepinepherine (Catecholamine)
- Epinepherine (Catecholamine)
- Serotonin (5-HT)
- Gamma-Amino Butyric Acid (GABA)
- Glutamate
- Endorphins
Acetylcholine
ACh is both excitatory and inhibitory and is involved in:
- voluntary movement: ACh causes muscles to contract, and myasthenia gravis is an autoimmune disorder that causes muscle weakness by destroying ACh receptors at neuromuscular junctions.
- parasympathetic arousal,
- attention
- memory: low levels of ACh in the entorhinal cortex and hippocampus have been linked to the early memory loss associated with Alzheimer’s disease.
- Too much assoc. w/Depression
- Too little (in Hippocampus) assoc w/Dementia (e.g. memory loss in Alzheimers disease)
Dopamine
Dopamine serves both excitatory and inhibitory functions. It contributes to:
- movement,
- personality,
- mood,
- sleep
-
Too Little:
- Parkinson’s Disease: A degeneration of dopamine producing cells in the substantia nigra & basal ganglia (Muscle rigidity & tremors) &
- Forms of Depression
-
Too Much linked to:
- Schizophrenia: According to Dopamine Hypothesis, schizophrenia is due to high levels of dopamine or hyperactivity of dopamine receptors.
- Tourtte’s Disorder: an excessive level in the caudate nucleus
*Cocaine, Amphetamines & other stimulant drugs elevate mood my increasing levels of dopamine in areas of the midbrain & limbic system that have been ID as part of the brains reward system.
*Alcohol increases dopamine levels & causes the pleasurable feelings related to alcohol use leading to reinforcing effects of alcohol additction.
Norepinepherine
Norepinephrine is an excitatory neurotransmitter and is involved in:
- arousal
- attention
- learning
- memory
- stress
- mood.
- Too Little: assoc. w/Depression (Catecholamine Hypothesis)
- Too Much: mania is due to excessive norepinephrine.
Epinephrine
Neurotransmitter involved in energy & glucose metabolism.
- Too little assoc. w/Depression
Serotonin (5-HT)
Neurotransmitter that has an inhibitory effect and plays a role in many functions including:
- arousal
- sleep
- sexual activity
- mood
- appetite
- pain.
-
Too Little:
- Depression
- increased risk for suicide
- Anxiety D/O’s (OCD)
- Bulimia (Antidepressant Rx that increases serotonin levels have been found useful to control binge & purge behaviors)
- Migraine headaches
-
Too much:
- Schizophrenia
- Autism spectrum disorder (ASD)
-
Anorexia: Assoc. w/an excess of serotonin which causes nervousness & anxiety. Food restriction helps lower serotonin levels which reduce thses unplesant feelings.
- Rx that increases serotonin are not useful for these indiv. but once they have reached normal weight Rx may help prevent weight loss.
*Evidence that low levels of serotonin are involved in cravings for alcohol in abusers.
Gamma Amino Butyric Acid (GABA)
GABA is a primary inhibitory neurotransmitter and is involved in:
- memory
- mood
- arousal
- sleep
- motor control
-
Too Little:
- insomnia
- seizures
- anxiety
- benzodiazepines reduce anxiety and induce sleep by amplifying the effects of GABA.
- Degeneration of GABA and ACh cells in the basal ganglia contributes to the motor symptoms of Huntington’s disease
- Affected by CNS Depressants
Glutamate
Glutamate is an excitatory neurotransmitter and contributes to:
- movement
- emotions
- learning
- memory: Long-term potentiation (LTP): Brain mechanism believed to be responsible for the formation of long-term memories.
Too much:
- Excessive levels can produce Excitotoxicity - which damages or destroys nerve cells & have been linked to stroke related brain damage, TBI, Huntington Disease & Alzhiemers Disease.
- Alcohol alters Glutamate levels in the brain & are related to memory impairment & alcohol related black outs; responsible for the harmful effects alcohol has on memory.
Endorphins
(Endogenous Morphines) Inhibitory neuromodulator that lowers the sensitivity of postsynaptic neurons & neurotransmitters.
Have analgesic properties & involved in:
- Pain Relief: Prevents release of substance P, involved in transmission of pain impulses.
- Feelings of pleasure & contentedness, emotions, sexual behaviors, memory & learning.
