Nervous System Organization & Signaling

What are the two main divisions of the nervous system?

Central nervous system (CNS) and peripheral nervous system (PNS)

What does the CNS include?

The brain and spinal cord

What does the PNS include?

All nerves and ganglia outside the CNS

What are the two functional divisions of the PNS?

Somatic (voluntary) and autonomic (involuntary) systems

What are the two branches of the autonomic nervous system?

Sympathetic and parasympathetic divisions

What is the sympathetic nervous system responsible for?

Fight-or-flight responses such as increased heart rate and dilated pupils

What is the parasympathetic nervous system responsible for?

Rest-and-digest responses like slowing heart rate and promoting digestion

What is a neuron?

An excitable cell that transmits electrical and chemical signals

What are glial cells?

Supporting cells that protect

What are the main types of glial cells in the CNS?

Astrocytes

What are the main glial cells in the PNS?

Schwann cells and satellite cells

What is the function of astrocytes?

Provide structural support

What is the function of oligodendrocytes?

Form myelin sheaths in the CNS

What is the function of Schwann cells?

Form myelin sheaths around axons in the PNS

What is the function of microglia?

Act as immune cells that remove waste and debris

What is the function of ependymal cells?

Line brain ventricles and produce cerebrospinal fluid (CSF)

What is white matter?

Areas with myelinated axons

What is gray matter?

Areas with neuron cell bodies

What is the resting membrane potential?

The electrical difference across a neuron’s membrane at rest (~ -70 mV)

What causes the resting potential?

Uneven ion distribution maintained by Na⁺/K⁺ pumps and leak channels

What does the Na⁺/K⁺ pump do?

Moves 3 sodium ions out and 2 potassium ions in using ATP

What are leak channels?

Passive ion channels allowing ions to diffuse according to gradients

What causes depolarization?

Opening of Na⁺ channels allowing sodium to enter the cell

What causes repolarization?

K⁺ channels open

What is hyperpolarization?

When the membrane potential becomes more negative than the resting potential

What is threshold potential?

The voltage at which an action potential is triggered (around -55 mV)

What is an action potential?

A rapid

What is the refractory period?

Time after an action potential when another cannot easily occur

What is the absolute refractory period?

Na⁺ channels are inactivated; no new action potential can form

What is the relative refractory period?

K⁺ channels remain open; a stronger stimulus can trigger an action potential

What is continuous conduction?

Action potentials moving smoothly along unmyelinated axons

What is saltatory conduction?

Action potentials jumping between nodes of Ranvier in myelinated axons

What are nodes of Ranvier?

Gaps between myelin segments where ion exchange occurs

How does myelination affect conduction speed?

It increases signal velocity and reduces ion leakage

What is a graded potential?

A small

How do graded potentials differ from action potentials?

Graded potentials are variable and decremental; action potentials are all-or-none

What are excitatory graded potentials?

Depolarizations that move the neuron closer to threshold

What are inhibitory graded potentials?

Hyperpolarizations that move the neuron farther from threshold

Where do graded potentials occur?

In dendrites and cell bodies

Where are action potentials initiated?

At the axon hillock

What determines the strength of a stimulus?

The frequency of action potentials (frequency coding)

What is temporal summation?

Multiple signals over time from one neuron combine to reach threshold

What is spatial summation?

Inputs from multiple neurons combine to reach threshold

What is the all-or-none principle?

Once threshold is reached

What are afferent neurons?

Neurons that carry sensory information to the CNS

What are efferent neurons?

Neurons that carry motor commands away from the CNS

What are interneurons?

Neurons that connect sensory and motor pathways within the CNS

What is a reflex arc?

A simple neural pathway that triggers an automatic response to a stimulus

What are the five components of a reflex arc?

Receptor

What determines conduction velocity?

Axon diameter and degree of myelination

What is the role of calcium in neural signaling?

Triggers neurotransmitter release at synaptic terminals

What is the synaptic cleft?

The space between presynaptic and postsynaptic neurons where transmission occurs

What are synaptic vesicles?

Small sacs in the presynaptic terminal that store neurotransmitters

What is the function of the axon hillock?

Integration site where graded potentials are summed to initiate action potentials

What are inhibitory neurons?

Neurons that release neurotransmitters causing hyperpolarization in postsynaptic cells

What are excitatory neurons?

Neurons that release neurotransmitters causing depolarization in postsynaptic cells