Neurogenesis and Neuroplasticity

neurogenesis

the development of new neurons from neuronal stem cells, most occurs during fetal development

chemotaxis

axons and dendrites grow in response to molecular cues (from astrocytes) (either attractive or repulsive), these molecular cues attach to cell surface receptors of the axon/dendrites, cues can cause: growth, lack of growth, branching, changes in sensitivity

growth cone

mobile sensitive structure at ends of dendrites and axons that respond to chemical cues in environment

acetylcholine

excites neurons, excites skeletal muscle, inhibits cardiac muscle, excites or inhibits smooth muscles and glands (depends on location)

GABA

most common inhibitory NT, critical for regulation of excitatory impulses throughout CNS

epinephrine and norepinephrine

AKA adrenaline and nonadrenaline, generally excitatory (but depends on receptors), important in sleep/wake cycles, mood

serotonin

involved in sleep/wake cycles, mood

dopamine

involved in elevation of mood, control of skeletal muscles, involved in reward and craving → many addictive drugs tap into dopamine NT system in the brain (e.g., cocaine), prevent reuptake of dopamine

parkinson’s

neurodegenerative disease that affects nervous system, particularly dopamine-producing neurons in the brain, dopamine is absent so not able to smooth out muscle movements → tremors

neural integration

ability of neurons to process information, store it, and make decisions about if signal should be continued or not

synapses

where does “decision making” about whether to generate an AP or not occur?

EPSP

excitatory postsynaptic potentials, depolarizing → neuron more likely to fire and create AP

IPSP

inhibitory postsynaptic potentials, hyperpolarizing → neuron less likely to fire and create AP

synaptic plasticity

ability of synapses to change in response to use/disuse, controlled by neurotransmitters, synapses can be created or removed in as little as 1-2 hours, brain is highly plastic from birth to about age 25

synaptic potentiation

ability to make transmission across synapses easier (increase strength between synapses)

epinephrine and ACh

what two neurotransmitters are necessary to enhance memory/learning by exciting postsynaptic neurons?

short-term memory

lasts a few seconds to a few hours, due to elevated Ca⁺² levels

long-term memory

can last a lifetime, can involve physical remodeling of synapses

lack of synapses

what can short-term memories vanish due to?

long-term depression

long-term memories can be lost through this process, low-frequency stimulation of synapses causes depressed Ca⁺² levels, proteins that make up dendrites degrade, synapses removed from circuits

alzheimer’s disease

neurodegenerative disease associated with deficiencies in ACh and nerve growth factor, plasma membranes of neurons begin to break down first in hippocampus (memory) then in cerebral cortex (language, reasoning, social behavior), protein released due to break down of plasma membranes from plaques and further interferes with neuron communication/function