Brain Structure: Depolarization & Neurotransmitters

Neurons: constructive unit of the nervous system; interconnected like electrical circuits
Made up of:
Soma (cell body): contains nucleus, keeps nerve cells alive (grey matter)
Dendrites: receiving portion of nerve cell- receiving end of cell
Axon: sends impulses away from the cell (white matter)
Dendrites and axons are all interconnected; vary in shape and size
Glial cells: hold neurons in place; make nutrients, absorb waste
Tripatite Synapse: synapse between dendrite , axons, synapse
Blood-brain barrier: glial cells that prevent waste from entering the brain
Neurons do two important things: generate electricity and release chemicals
Neurons= batteries; inner structure in salty solution encased in inner membrane; VERY CONDUCTIVE
Positive Na, more positive K on outside= resting potential: -70mV (polarized)
Action Potential: sudden reversal of voltage along neuron membrane to cause depolarization (-70mV – +40mV)
Graded potentials: incoming stimulation not strong enough to complete depolarize a cell
*MUST MEET ACTION POTENTIAL THRESHOLD to cause action potential -> depolarization
All-or-none law: neurons must fire at max intensities or not at all
Ion channels: graded potentials move ions through these channels (Na= +) which when done enough can depolarize the cell (action potential threshold: -55mV)

Depolarization Steps:

1) Negative charge inside of membrane (due to K ions) positive charge on outside (Na), more negative than positive.

2) Action potential causes the sodium channels to open and Na ions flow into inner membrane; K+ ions flow out.

3) Sodium-potassium pump depolarize cell during refractory period; 2:3 Na:K pumped into cell

Actions potential do not vary but the rate/ number of neuron stimulated will result in high-intensity stimulation
Axons covered by myelin sheath= insulation/ protective
Nodes of Ranvier: section of axon where myelin sheath are not present or absent. Impulses hope along these nodes to get better conductivity and speed.
Synapse: connection between neurons (axons and dendrites)
Neurotransmission occurs between axon and dendrites in synaptic cleft

5 steps

Synthesis- chemicals have made within the neuron
Storage- these chemicals are stored within the synaptic vesicles
Release- chemicals move across the synaptic cleft from presynaptic neuron (axon) to post synaptic neuron (dendrites)
Binding: the vesicle bind to the receptor sites on the neurons. These chemicals will (a) depolarize the neuron by exciting it or (b) hyperpolarize the neuron and inhibit it.
Deactivation: shuts off, is depolarized

Exciting Chemicals: Glutamate, Acetylcholine, Norepinephrine, Dopamine
Inhibiting Chemicals: GABA, Serotonin, Dopamine
Acetylcholine -> (motor movement, sleep, dreaming, muscle) Alzheimer’s disease (lack of)
Botulism: blocked Ach, paralysis
Dopamine -> Parkinson’s disease (lack of) can be treated; also treats schizophrenia (overload)/ delusions
Serotonin (5HT) -> sensitivity to it linked to depression (due to undersupply of it)
Endorphins -> reduce pain
Neuromodulators -> widespread effect
Drugs can mimic some neurotransmitters (block uptake, bind at stop TP)
Sensory Neurons: sent info the brain/ spine
Motor Neurons: send impulses from brain/ spine to muscles/ organs
Interneurons: connective neurons

CNS: brain/ spine PNS: everything else

Somatic Nervous system: voluntary movements (muscles, senses)
Autonomic Nervous system: controls glands, heart, etc.
Fight-or-Flight: Sympathetic: arousal to stress Parasympathetic: recovery from stress [HOMOEOSTATIS]