Ch 12 pt 1- Overview, Neurons & Glial Cells

Function of the Nervous System

Sensory input, integration, and motor output.

Sensory Input

Gathering information from sensory receptors to monitor internal and external changes.

Integration

Processing and interpreting sensory input to decide an appropriate response.

Motor Output

Activation of effector organs (muscles/glands) to cause a response.

Central Nervous System (CNS)

The part of the nervous system that includes the brain and spinal cord; it processes information and coordinates responses.

what are part of the central nervous stytem

the brain and the spinal cord

Peripheral Nervous System (PNS)

The part of the nervous system outside the brain and spinal cord; it connects the CNS to the rest of the body through nerves that carry sensory and motor signals.

2 divions of the peripheral nervous system

motor neurons, sensory neurons

Motor Neuron divisions

Somatic nervous system and Autonomic nevous system

Autonomic Nervous System divisions

sympathetic division and parasympathetic division

Sensory (Afferent) Division of PNS

Carries impulses from sensory receptors to the CNS.

Motor (Efferent) Division of PNS

Transmits impulses from the CNS to effector organs (muscles and glands).

Neuron

The primary cell of the nervous system that conducts electrical impulses.

Three Properties of Neurons

Excitability (input), conductivity (action potentials), and secretion (transmission).

Glial Cells (Neuroglia)

Support, protect, and nourish neurons; do not transmit impulses.

Parts of a Neuron

Soma (cell body), dendrite, axon, and synapse.

Soma (Cell Body)

The main part of a neuron that contains the nucleus and organelles; it integrates incoming signals and maintains the cell’s health.

Dendrite

Branch-like extensions of a neuron that receive signals from other neurons and transmit them toward the cell body.

Axon

A long, thin projection that carries electrical impulses (action potentials) away from the cell body toward other neurons or effectors.

Synapse

The junction between two neurons (or a neuron and another cell) where signals are transmitted through neurotransmitters.

primary cell of the nervous system

Input, Conductivity, Transmission

Input

The process by which a neuron receives signals, usually through dendrites, from other neurons or sensory receptors.

Conductivity

The ability of a neuron to transmit an electrical impulse (action potential) along its axon.

Transmission

The process of passing a signal from one neuron to another (or to a muscle/gland) across a synapse using neurotransmitters.

Multipolar Neurons

Neurons that have one axon and multiple dendrites; the most common type in the CNS, specialized for integrating a large amount of information from other neurons.

Bipolar Neurons

Have two processes; rare, found in eye, ear, and olfactory mucosa.

Unipolar Neurons

Have a single process; mostly sensory neurons in the PNS.

Four Types of Glia in the CNS

Astrocytes, microglia, ependymal cells, oligodendrocytes.

Two Types of Glia in the PNS

Schwann cells and satellite cells.

Astrocytes

Most abundant CNS glia; support neurons and maintain chemical environment.

Microglia

CNS immune cells; remove debris and pathogens via phagocytosis.

Ependymal Cells

Line brain ventricles and spinal cord; circulate cerebrospinal fluid (CSF).

Oligodendrocytes

Form myelin sheaths around CNS axons for insulation and speed.

Schwann Cells

Form myelin sheaths around PNS axons; enable saltatory conduction.

Satellite Cells

Surround neuron cell bodies in the PNS; regulate environment.

Myelin Sheath Function

Protects, insulates axons, and speeds up nerve impulse transmission.

Nodes of Ranvier

Gaps in the myelin sheath; enable saltatory (jumping) conduction.

White Matter

The region of the nervous system composed mainly of myelinated axons; it’s responsible for transmitting nerve signals between different parts of the brain and spinal cord.

Gray Matter

The region of the nervous system made up mostly of neuron cell bodies, dendrites, and unmyelinated axons; it’s where information processing and integration occur.

Synapse

Junction between two neurons or a neuron and an effector cell.

➡ Action Potentials – Rapid electrical impulses that travel along the axon due to the movement of ions through voltage-gated channels.

what makes the electricity flow in the axon?

➡ Integration of Signals – Dendrites receive excitatory and inhibitory inputs from other neurons; if the combined (summed) signals reach threshold at the axon hillock, an action potential is triggered.

how does dendrites govern wether an axon will fire

➡ Synaptic Transmission – The action potential reaches the axon terminal, triggering neurotransmitter release into the synapse, which can excite, inhibit, or modulate the next cell’s activity.

what happens at the end so you get different outcome

Presynaptic Neuron

Conducts impulses toward the synapse.

Postsynaptic Neuron

Receives and transmits impulses away from the synapse.

Voltage

The electrical potential difference between two points; it represents the energy needed to move a charge and drives the flow of ions across the membrane.

Current

The flow of electrical charge, carried by ions or electrons, from one point to another. In neurons, it’s the movement of ions across the membrane.

Resistance

The opposition to the flow of electrical current; higher resistance makes it harder for ions or electricity to move across a material or membrane.

insulator

A material that resists the flow of electrical current because it lacks free-moving charged particles (e.g., rubber, fat, myelin sheath).

conductor

A material that allows electrical current to flow easily because it has many free-moving charged particles (e.g., metals, body fluids).

Sodium-Potassium Pump

Maintains resting potential by pumping 3 Na⁺ out and 2 K⁺ in; keeps inside negative.

Ion Channels

Pathways for ions to move across membranes; can be gated or always open.

passive/ leakage channels

always open, allowing continuous movement of ions (like Na⁺ and K⁺) down their concentration gradients to help maintain the resting membrane potential.

Ligand-Gated Channel

opens when a specific chemical messenger (ligand), such as a neurotransmitter, binds to it—allowing certain ions to move across the membrane and change the cell’s electrical potential.

Voltage-Gated Channel

opens or closes in response to changes in the membrane potential, allowing specific ions (like Na⁺, K⁺, or Ca²⁺) to flow across the membrane and generate electrical signals.

Mechanically Gated Channel

Opens in response to physical deformation of the membrane, such as pressure, touch, or vibration, allowing ions to flow across the membrane.

When gated channels are open

1. Ions move quickly across the membrane

2. Movement is along their electrochemical gradients

3. An electrical current is created

4. Voltage changes across the membrane

Chemical Diffusion

Movement of ions from an area of high concentration to low concentration across the membrane (Concentration gradient)

Electrical Diffusion

Movement of ions due to attraction or repulsion between positive and negative electrical charges across the membrane (Electrical gradient or electrostatic force)

Resting Membrane Potential (RMP)

-70 mV; maintained by Na⁺/K⁺ pump and differential ion permeability.

graded potential

small, variable-strength signals that decrease in magnitude as they travel, and can be either excitatory or inhibitory

Action potention

all-or-nothing signals that are triggered only when the sum of graded potentials reaches a threshold and are conducted without decrement, meaning they travel long distances without losing strength

Depolarization

Inside of the membrane becomes less negative (moves toward +).

Repolarization

The membrane returns to its resting membrane potential (moves back down)

Hyperpolarization

The inside of the membrane becomes more negative than the resting potential (below resting potential)