neurons

What are the 4 major functions of neurons?

Reception → integration → transmission → transfer of information

What is the soma?

The cell body of a neuron.

What is the primary function of dendrites?

Receive incoming information from other cells.

What is the primary function of an axon?

Carry electrical signals away from the soma.

Why is the axon hillock important?

Incoming signals summate here; if threshold is reached, an action potential is generated.

What does myelin do?

Insulates the axon, reduces current leakage, and increases conduction speed/efficiency.

What are Nodes of Ranvier?

Gaps in myelin with high concentrations of voltage-gated Na⁺ and K⁺ channels where the AP is regenerated.

What is afferent flow?

Information traveling toward the reference point/CNS.

What is efferent flow?

Information traveling away from the reference point/CNS.

What is the role of interneurons?

Connect neurons and help integrate information.

What 4 ions are most important for neuronal signaling?

Na⁺, K⁺, Ca²⁺, and Cl⁻.

Why do ions require channels to cross the cell membrane?

Charged ions cannot easily cross the lipid bilayer.

What are the 3 major properties of ion channels?

Conduct ions, are selective for specific ions, and open/close in response to specific signals.

What are leak channels?

Non-gated channels that are always open and allow passive ion movement.

What opens a ligand-gated ion channel?

Binding of a chemical/ligand, usually a neurotransmitter.

What opens a modality-gated channel?

A specific stimulus such as touch, photons, or chemicals.

What opens a voltage-gated channel?

A change in membrane voltage.

What is a concentration gradient?

Net movement from an area of high concentration → low concentration.

What is an electrical gradient?

Movement of charged ions based on attraction/repulsion of electrical charges.

What determines an ion’s overall direction of movement?

Its electrochemical gradient = chemical + electrical gradients.

Why can K⁺ move out of a negatively charged neuron?

Its concentration is much higher inside, so its chemical gradient can drive it outward despite the electrical gradient pulling it inward.

What is the typical resting membrane potential of a neuron?

Approximately −60 to −70 mV.

What 3 major factors maintain the RMP?

Large intracellular anions + leak channels + Na⁺/K⁺ ATPase.

What large intracellular molecules contribute to the negative interior?

DNA, RNA, and proteins.

What does the Na⁺/K⁺ ATPase do?

Pumps 3 Na⁺ OUT and 2 K⁺ IN using ATP.

Why is the Na⁺/K⁺ pump clinically important?

It requires energy/ATP; loss of ATP prevents normal ion gradients from being maintained.

What is depolarization?

Membrane becomes less negative/more positive → closer to threshold.

What is hyperpolarization?

Membrane becomes more negative → farther from threshold.

What is modulation?

A gradual, longer-lasting shift in membrane potential in either direction.

What are local potentials?

Small, short-lasting, graded changes in membrane potential.

What is a receptor potential?

A stimulus activates a receptor → ion flow → change in membrane potential.

What is a synaptic potential?

Neurotransmitter release causes a membrane potential change in another neuron.

What is an EPSP?

Excitatory postsynaptic potential; depolarizes the neuron and moves it closer to threshold.

What is an IPSP?

Inhibitory postsynaptic potential; hyperpolarizes the neuron and moves it farther from threshold.

What is spatial summation?

Multiple neurons/inputs firing at different locations combine to reach threshold.

What is temporal summation?

One input fires repeatedly in a short period so the potentials combine.

Where are incoming potentials integrated to determine whether an AP occurs?

Axon hillock.

Spatial vs temporal summation?

Spatial = multiple inputs; temporal = repeated input.

What are 3 major characteristics of an action potential?

All-or-none, requires voltage-gated Na⁺ channels, and requires threshold.

What happens when threshold is reached?

Voltage-gated Na⁺ channels open → Na⁺ rapidly enters → AP begins.

Which ion causes rapid AP depolarization?

Na⁺ entering the neuron.

Which ion causes AP repolarization?

K⁺ leaving the neuron.

What causes the hyperpolarizing afterpotential?

K⁺ continues leaving briefly after repolarization.

What is the basic AP sequence?

Threshold → Na⁺ IN → depolarization → Na⁺ channels inactivate → K⁺ OUT → repolarization → hyperpolarization → RMP.

What is the absolute refractory period?

Period when another AP is impossible regardless of stimulus strength because Na⁺ channels are inactivated.

What is the relative refractory period?

Period when another AP is possible but requires a stronger stimulus.

Why is a stronger stimulus required during the relative refractory period?

K⁺ is still leaving and the membrane remains hyperpolarized.

Why are refractory periods important?

They help prevent backward AP propagation and support one-way conduction.

What is axoplasmic resistance?

Resistance to current flow inside the axon.

How does increasing axon diameter affect conduction?

↓ internal resistance → ↑ conduction speed.

What is membrane resistance?

Resistance to current leaking through the axonal membrane.

How does myelin affect membrane resistance?

↑ membrane resistance → ↓ current leakage → faster conduction.

What was the professor’s analogy for myelin?

Myelin is like duct tape covering leaks in a garden hose.

What is saltatory conduction?

AP effectively jumps from one Node of Ranvier to the next.

Why is saltatory conduction beneficial?

It increases conduction speed and decreases energy requirements.

What axons conduct signals fastest?

Large-diameter, myelinated axons.

What is convergence?

Many neurons → one neuron; integrates information.

What is divergence?

One neuron → many targets; distributes information.

What are neural stem cells capable of doing?

Self-renewing and differentiating into neurons.

Where were neural stem cells discussed as being found?

Parts of the hippocampus and lining of the lateral ventricular wall.

What major functions are associated with the hippocampus?

Learning and memory.

Why are neural stem cells relevant to rehabilitation?

They have potential for implantation/regeneration to aid rehabilitation, although natural regeneration is usually insufficient for major CNS damage.

How does tetrodotoxin affect neurons?

Blocks voltage-gated Na⁺ channels → prevents normal AP conduction.

What nervous system is primarily affected by Guillain-Barré syndrome?

PNS; demyelination slows nerve conduction.

What nervous system is primarily affected by multiple sclerosis?

CNS; demyelination slows conduction.

What is Charcot-Marie-Tooth associated with?

Peripheral neuropathy causing weakness, sensory loss, ↓ reflexes, and muscle atrophy.

What neurons are affected in ALS?

Neurons giving rise to corticospinal tracts and motor neurons in the spinal cord/brainstem.

What PT interventions should remind you of AP/conduction physiology?

Ice, electrical stimulation, and TENS.

What is a synapse?

Specialized junction between two cells that allows electrical and/or chemical communication.

What are the major components of a synapse?

Presynaptic terminal, vesicles, NTs/neuromodulators, synaptic cleft, postsynaptic membrane/receptors, and uptake transporters.

Where are postsynaptic receptors located?

Postsynaptic membrane.

Where are reuptake transporters located?

Presynaptic terminal.

What is an axosomatic synapse?

Axon → soma; often inhibitory.

What is an axodendritic synapse?

Axon → dendrite; usually excitatory.

What is an axoaxonic synapse?

Axon → axon; usually modulatory.

What is the sequence of synaptic transmission?

AP arrives → presynaptic depolarization → voltage-gated Ca²⁺ channels open → Ca²⁺ IN → vesicle fusion → NT release → receptor binding → postsynaptic response → NT removal.

What ion triggers neurotransmitter release?

Ca²⁺.

What does presynaptic Ca²⁺ influx cause?

Vesicles move/fuse with the membrane → neurotransmitter exocytosis.

Na⁺ vs Ca²⁺ in neuronal signaling?

Na⁺ drives AP depolarization; Ca²⁺ triggers NT release.

What happens during presynaptic facilitation?

Depolarization → ↑ Ca²⁺ entry → ↑ NT release.

What happens during presynaptic inhibition?

Hyperpolarization → ↓ Ca²⁺ entry → ↓ NT release.

What is the relationship between presynaptic Ca²⁺ and NT release?

More Ca²⁺ → more NT release.

What are the major neurotransmitter groups?

ACh, amino acids, amines, peptides, and gases.

What are the major amino acid NTs discussed?

Glutamate, aspartate, GABA, and glycine.

What are the major amines discussed?

Dopamine, histamine, serotonin, and norepinephrine.

What peptides were discussed?

Substance P, endorphins, enkephalins, CGRP, and galanin.

What gas neurotransmitter was discussed?

Nitric oxide.

What is the difference between a neurotransmitter and neuromodulator?

NT acts more directly at synaptic receptors; neuromodulators often act farther away, affect multiple neurons, and produce slower/prolonged effects.

Can neurotransmitters be inhibitory?

Yes. Neurotransmitters can be excitatory or inhibitory.

What ultimately determines the cellular response to a neurotransmitter?

The receptor type.

What happens if a neurotransmitter is released but the target cell lacks its receptor?

No receptor-mediated effect occurs.

What is an agonist?

Chemical that binds a receptor and mimics the neurotransmitter’s action.

What is an antagonist?

Chemical that binds a receptor and blocks the neurotransmitter’s action.

What are the major functions of ACh?

NT at NMJ and in ANS; predominantly neuromodulatory in CNS.

What are the 2 major ACh receptors?

Nicotinic and muscarinic.

What type of receptor is nicotinic ACh?

Fast ligand-gated cation channel.

What type of receptor is muscarinic ACh?

Slower G-protein coupled receptor.

What is the major excitatory NT in the CNS?

Glutamate.

What 3 major glutamate receptor groups should you know?

NMDA, AMPA/kainate, and metabotropic.

What is unique about the NMDA receptor?

It is both voltage- and ligand-gated.