Neurons, Synapses, and Signaling

What are the three stages of information processing in the nervous system?

Sensory input → Integration → Motor output

What does a sensory neuron do?

Carries information from sensory receptors to the CNS

What does an interneuron do?

Processes information within the CNS

What does a motor neuron do?

Carries signals from the CNS to muscles or glands

What is the function of dendrites?

Receive incoming signals

What is the function of the axon?

Conducts electrical signals away from the cell body

What is the axon hillock?

Site where action potentials are initiated

What is the myelin sheath?

Insulates axon and speeds up signal transmission

What are nodes of Ranvier?

Gaps in myelin where action potentials 'jump'

What is membrane potential?

Voltage difference across a cell membrane

What is resting potential?

Membrane potential of a neuron at rest (~ -70 mV)

What creates membrane potential?

Ion concentration gradients + selective permeability

Why is the inside of a neuron negative at rest?

More K⁺ leaves than Na⁺ enters + negatively charged proteins inside

What does the sodium-potassium pump do?

Pumps 3 Na⁺ out and 2 K⁺ in (uses ATP)

Why is resting potential around -60 to -80 mV?

High K⁺ permeability + Na⁺/K⁺ pump maintaining gradients

What is the difference between gated and ungated channels?

Gated open/close in response to stimuli; ungated are always open

What is the difference between ligand-gated and voltage-gated channels?

Ligand-gated open via chemical signal; voltage-gated respond to membrane potential

What is a graded potential?

Small, local change in membrane potential

How is a graded potential different from an action potential?

Graded = varies in size; Action = all-or-nothing

What happens during depolarization?

Na⁺ channels open → Na⁺ rushes in

What happens during repolarization?

K⁺ channels open → K⁺ leaves cell

What are the two factors causing repolarization?

Na⁺ channel inactivation + K⁺ channel opening

What is the refractory period?

Time when neuron cannot fire another AP

How does an action potential move down an axon?

Local depolarization triggers next segment

What increases conduction speed?

Larger axon diameter + myelination

What is saltatory conduction?

AP 'jumps' between nodes of Ranvier

What is the difference between electrical and chemical synapses?

Electrical = direct ion flow; Chemical = neurotransmitters

What are the parts of a chemical synapse?

Presynaptic terminal, synaptic cleft, postsynaptic membrane

How is signal transmitted at a synapse?

AP → Ca²⁺ influx → neurotransmitter release → receptor binding

What is an EPSP?

Depolarizes neuron (more likely to fire)

What is an IPSP?

Hyperpolarizes neuron (less likely to fire)

What is summation?

Adding multiple signals together

What is the difference between temporal and spatial summation?

Temporal = rapid signals from one neuron; Spatial = signals from multiple neurons

What does acetylcholine do?

Usually excitatory; triggers muscle contraction

What are biogenic amines?

Neurotransmitters like dopamine, serotonin (affect mood, etc.)

Name 4 amino acid neurotransmitters.

Glutamate, GABA, glycine, aspartate

What are neuropeptides?

Small protein-like neurotransmitters (e.g., endorphins)

How does nitric oxide act as a neurotransmitter?

Diffuses directly across membranes (no vesicles)

What is unique about CO as a signaling molecule?

Acts locally and diffuses like NO

Why does myelination increase conduction speed?

It prevents ion leakage and allows APs to jump node-to-node

What would happen if Na⁺ channels didn't close?

Neuron couldn't repolarize → no new AP

Why are EPSPs and IPSPs important together?

They determine whether neuron reaches threshold