Neuron Form & Function

Neuron Structure: Dendrites

receive signals and carry them toward the cell body.

Neuron Structure: Cell body (soma)

contains the nucleus and supports cell function.

Neuron Structure: Nucleus

genetic control center of the cell.

Neuron Structure: Axon

conducts signals away from the cell body.

Neuron Structure: Neurites

collective term for axons and dendrites.

Neuron Structure: Myelin sheath

lipid/fat-rich membrane wrapping around axons that supports efficient conduction.

Neuron Structure: Nodes of Ranvier

gaps between consecutive myelin sheaths where action potentials are regenerated.

Glia & Cytoskeleton: Astrocytes

support/nourish neurons, fill spaces, influence neurite growth, and support synapse formation.

Glia & Cytoskeleton: Oligodendroglia/oligodendrocytes

myelinate axons in the CNS.

Glia & Cytoskeleton: Schwann cells

myelinate axons in the PNS.

Glia & Cytoskeleton: Microglia

remove debris left by dead or degenerating neurons and glia.

Glia & Cytoskeleton: Tau protein

helps stabilize microtubules; Alzheimer's disease is presented as a "tauopathy" in lecture, with abnormal tau tangles disrupting normal organization.

Synapse:

junction where a presynaptic axon terminal communicates chemically with a postsynaptic neuron, muscle, or organ.

Neurotransmitters

can excite, inhibit, or modulate postsynaptic activity

Neurotransmitter: Acetylcholine (ACh)

PNS: activates muscle; CNS: alertness, attention, memory, learning.

Neurotransmitter: Glutamate

Major CNS excitatory transmitter; learning, memory, neuroplasticity.

Neurotransmitter: GABA

Major CNS inhibitory transmitter; controls information flow and sleep-wake activity

Neurotransmitter: Dopamine

Motor control, reward, addiction

Neurotransmitter: Epinephrine

Sympathetic fight-or-flight functions such as heart rate/BP/breathing

Neurotransmitter: Norepinephrine

Attention, mood, sleep-wake, and fight-or-flight.

Neurotransmitter: Serotonin

Regulation of mood, sleep, appetite, arousal.

Neurotransmitter: Substance P

Transmission of pain information

Types of Neurons: Multipolar

Many dendrites + one axon; includes motor neurons and pyramidal cells.

Types of Neurons: Bipolar

One dendrite + one axon; examples include retinal and olfactory neurons.

Types of Neurons: Pseudounipolar

One process arising from soma and splitting in two directions; common sensory-neuron arrangement.

The Action Potential: 1. Resting potential

About -70 mV; more Na+ outside, more K+ inside, outside more positive, inside more negative

The Action Potential: 2. Depolarization

Stimulus opens sodium channels; Na+ enters. At about -55 mV threshold, an action potential is triggered.

The Action Potential: All-or-none principle

An individual neuron either reaches threshold and fires a full action potential, or it does not.

The Action Potential: Signal direction

The electrical signal moves in ONE direction along the axon

The Action Potential: 3. Repolarization

K+ exits and ionic gradients are restored; membrane returns toward resting potential.

The Action Potential: 4. Refractory periods

Absolute: cannot fire; relative: can fire only with stronger-than-normal stimulation.

The Action Potential: Myelinated conduction

Action potentials are regenerated at Nodes of Ranvier, supporting faster conduction

Chemical Synaptic Transmission

1. Neurotransmitters are synthesized/prepared.

2. Neurotransmitters are loaded into synaptic vesicles.

3. Neurotransmitters are released into the synaptic cleft.

4. They bind to postsynaptic receptors and produce an excitatory or inhibitory response.

5. Neurotransmitter is removed from the synaptic cleft (e.g., uptake/reuptake, post synaptic cell acceptance, or diffusion).

Clinical Connections: Multiple sclerosis (MS):

autoimmune disorder in which CNS myelin is damaged; lesions/scarring can occur at multiple sites.

Clinical Connections: Neuromuscular junction (NMJ)

synapse between a lower motor neuron and muscle fiber.

Clinical Connections: Myasthenia gravis (MG)

autoimmune disorder with weakness/fatigability of voluntary muscles; antibodies block ACh receptors at the NMJ, impairing neurotransmission.