Neuroscience: Neurons, CNS, PNS, and Brain Structures

**Neuron

Basic functional cell of the nervous system that transmits electrical impulses**

**Cell Body (Soma)

Neuron region containing nucleus and organelles; integrates signals**

**Dendrites

Branching neuron extensions that receive incoming signals**

**Axon

Long projection that carries impulses away from the cell body**

**Axon Terminal

End of axon where neurotransmitters are released**

**Myelin Sheath

Fatty insulation that speeds electrical conduction**

**Node of Ranvier

Gap in myelin where ion exchange occurs during conduction**

**Central Nervous System (CNS)

Brain and spinal cord; integrates and processes information**

**Peripheral Nervous System (PNS)

All nerves outside CNS; carries sensory and motor signals**

**Astrocytes

Most abundant CNS neuroglia; regulate extracellular environment and form blood‑brain barrier**

**Oligodendrocytes

CNS cells that produce myelin sheath around axons**

**Microglia

CNS immune cells that remove debris, pathogens, and dead neurons**

**Ependymal Cells

CNS cells lining ventricles; produce and circulate cerebrospinal fluid**

**Schwann Cells

PNS cells that form myelin sheath and aid in axon regeneration**

**Satellite Cells

PNS cells surrounding neuron cell bodies; provide support and regulate environment**

**Threshold (neuron)

Critical voltage (~‑55 mV) required to trigger an action potential**

**Depolarization (neuron)

Rapid rise in membrane potential due to Na⁺ influx**

**Repolarization (neuron)

Return toward negative potential due to K⁺ efflux**

**Hyperpolarization

Membrane potential becomes more negative than resting (~‑80 mV)**

**Absolute Refractory Period

Time when no new action potential can occur**

**Relative Refractory Period

Time when a stronger‑than‑normal stimulus is needed to fire**

**Multipolar Neuron

Neuron with one axon and many dendrites; most common type**

**Bipolar Neuron

Neuron with one axon and one dendrite; found in retina and olfactory epithelium**

**Unipolar (Pseudounipolar) Neuron

Neuron with one process that splits; most sensory neurons**

**Saltatory Conduction

Fast conduction in myelinated axons where impulse jumps node to node**

**Continuous Conduction

Slow conduction in unmyelinated axons where impulse travels along entire membrane**

**Cerebrum

Largest brain region controlling thought, memory, emotion, and voluntary movement**

**Cerebral Cortex

Outer gray matter layer of cerebrum responsible for higher processing**

**Left and Right Hemispheres

Two halves of cerebrum separated by longitudinal fissure**

**Diencephalon

Deep brain region containing thalamus, hypothalamus, and epithalamus**

**Thalamus

Relay station for sensory information (except smell)**

**Hypothalamus

Autonomic and endocrine control center regulating homeostasis**

**Epithalamus

Contains pineal gland which secretes melatonin**

**Cerebellum

Brain region coordinating balance, posture, and smooth voluntary movement**

**Brainstem

Midbrain, pons, and medulla; controls vital automatic functions**

**Midbrain

Contains visual and auditory reflex centers**

**Pons

Connects cerebrum and cerebellum; regulates breathing rhythm**

**Medulla Oblongata

Controls heart rate, blood pressure, and breathing**

**Gyrus

Elevated ridge on cerebrum surface**

**Sulcus

Shallow groove separating gyri**

**Gray Matter

Unmyelinated cell bodies and dendrites where processing occurs**

**White Matter

Myelinated axons forming communication pathways**

**Cerebrum Internal Tissue

White matter with deep gray nuclei**

**Cerebrum External Tissue

Gray matter cortex**

**Cerebellum Internal Tissue

White matter (arbor vitae)**

**Cerebellum External Tissue

Gray matter cortex**

**Brainstem Tissue

Mixed gray nuclei and white tracts**

**Spinal Cord Gray Matter

Butterfly‑shaped horns**

**Spinal Cord White Matter

Surrounding columns**

**Association Fibers

Connect regions within the same cerebral hemisphere**

**Commissural Fibers

Connect left and right hemispheres**

**Projection Fibers

Connect cortex with lower CNS structures**

**Central Sulcus

Groove dividing frontal lobe (motor) from parietal lobe (sensory)**

**Longitudinal Fissure

Deep groove separating left and right cerebral hemispheres**

**Dura Mater

Tough outer meningeal layer**

**Epidural Space

Space above dura; real in spinal cord, potential in skull**

**Subdural Space

Potential space below dura; site of subdural hematoma**

**Arachnoid Mater

Middle meningeal layer with web‑like trabeculae**

**Subarachnoid Space

Real space containing CSF and major blood vessels**

**Pia Mater

Thin vascular layer tightly adhering to brain surface**

**Autonomic Nervous System Control Center

Hypothalamus**

**HEALER Functions of Hypothalamus

Homeostasis, Endocrine control, Autonomic control, Limbic integration, Energy balance, Circadian rhythms**

**Medulla Controls

Heart rate and respiration**

**Dorsal Root

Sensory root carrying afferent signals into spinal cord**

**Dorsal Root Ganglion

Contains sensory neuron cell bodies**

**Ventral Root

Motor root carrying efferent signals out of spinal cord**

**Reflex Pathway

Neural route producing rapid involuntary response**

**Reflex Receptor

Detects stimulus**

**Sensory Neuron

Carries impulse to CNS**

**Integration Center

CNS processing site (often spinal cord)**

**Motor Neuron

Carries command to effector**

**Effector

Muscle or gland producing response**

**Sympathetic Division

Fight or flight responses**

**Parasympathetic Division

Rest and digest responses**