Week 2: Excitable Cells and Neuroanatomy

Vocabulary practice flashcards covering excitable cell physiology, neuroanatomy, glial cell classifications, and action potential mechanics.

Corpus Callosum

The major nerve fiber bundle connecting the left and right cerebral hemispheres, which is severed during surgical split-brain procedures.

Microglia

Small, dynamic glial cells of the central nervous system (CNS) that survey brain tissue, engulf foreign materials, remove cellular debris, digest dead neurons, and eliminate unused synapses.

Medulla

A lower brainstem structure controlling vital involuntary functions such as breathing, blood pressure, swallowing, and heart rate; it is also where corticospinal tract motor fibers cross over to innervate the opposite side of the body.

Pons

A brainstem structure that serves as a relay station transferring information between the cerebellum and cerebral cortex, and coordinates breathing in conjunction with respiratory centers in the medulla.

Midbrain

The brainstem region that bridges the lower brainstem with the diencephalon; its primary functions include controlling eye movements and mediating auditory and visual motor reflexes.

Pituitary Gland (Hypophysis)

An endocrine organ controlled by the hypothalamus that secretes signaling hormones into the bloodstream to regulate lactation, growth, development, reproduction, and the stress response.

Hormones

Chemical messengers released into the bloodstream that cells utilize to communicate over long distances with other target tissues and organs.

Cerebellum

A brain structure situated in the posterior region beneath the occipital lobe and above the brainstem that coordinates voluntary movement, processes sensory input, and contains the highest number of neurons in the body.

Frontal Lobe

The cerebral lobe housing the primary motor cortex that receives input from skeletal muscles and coordinates voluntary motor output.

Temporal Lobe

The cerebral lobe containing the primary auditory cortex, specialized in processing olfactory information and storing short-term memories.

Parietal Lobe

The cerebral lobe housing the primary somatosensory cortex that integrates sensory information originating from the body's major senses.

Occipital Lobe

The posterior cerebral lobe containing the primary visual cortex that integrates visual stimuli with other sensory inputs.

Sulci

The anatomical grooves, dips, or valleys located on the cerebral surface that enlarge brain surface area and serve as landmarks to demarcate lobes.

Gyri

The raised ridges or bumps on the surface of the cerebral cortex that maximize cortical surface area.

Multiple Sclerosis (MS)

A chronic, progressive autoimmune pathology of the central nervous system in which inflammatory attacks destroy axonal myelin sheaths, leading to slowed, disrupted, or completely blocked nerve impulse conduction.

Schwann Cells

Glial cells of the peripheral nervous system (PNS) that enclose axons, synthesize myelin sheaths, and support peripheral nerve function, survival, and regeneration.

Satellite Cells

Peripheral glial cells that ensheath neuronal cell bodies within ganglia, providing essential nutrients and structural support comparable to central nervous system astrocytes.

Astrocytes

The most abundant glial cells in the central nervous system; they anchor neurons in place, transport nutrients, clear extracellular debris, regulate extracellular fluid composition, digest dead neurons, and support injury responses.

Oligodendrocytes

Myelin-producing glial cells restricted to the central nervous system (CNS), each capable of wrapping myelin membranes around segments of multiple axons; they cannot replicate after injury.

Ependymal Cells

Ciliated cuboidal glial cells that line the cerebral ventricles and central canal of the spinal cord to produce, circulate, and reabsorb cerebrospinal fluid (CSF), while assisting in osmotic regulation.

Multipolar Neuron

The most common structural type of neuron in the central nervous system, characterized by having multiple branching dendrites and a single axon extending from the soma to link the CNS with effector organs.

Unipolar Neuron

A sensory neuron predominantly found in the peripheral nervous system with one process projecting from a cell body situated off to the side, transmitting sensory signals to and from the spinal cord.

Bipolar Neuron

A specialized neuron possessing two distinct processes—one dendrite branch and one axon—extending from opposite poles of the soma, typically located in sensory structures such as the retina.

Central Nervous System (CNS)

The anatomical division of the nervous system consisting exclusively of the brain and the spinal cord.

Peripheral Nervous System (PNS)

The nervous system division consisting of all cranial and spinal nerves branching outside the CNS to supply muscles and organs; it comprises somatomotor and autonomic subdivisions.

Saltatory Conduction

The rapid transmission of an action potential along a myelinated axon, where the impulse jumps from one node of Ranvier to the next, accelerating conduction velocity by $10\text{--}15\text{ fold}$ compared to unmyelinated fibers.

Nodes of Ranvier

Unmyelinated, periodic gaps along a myelinated axon membrane that are highly enriched in voltage-gated ion channels to enable rapid impulse regeneration.

Myelin Sheath

A lipid-rich insulating sheath composed of layered phospholipid membranes and proteins that surrounds axons to prevent charge leakage and accelerate action potential propagation.

Axon

The long, slender projection of a neuron that propagates generated action potentials away from the soma toward target cells.

Dendrites

Branching cytoplasmic projections extending from the neuronal soma that receive neurotransmitter signals from adjacent cells and direct depolarizing graded potentials toward the soma.

Soma

The central cell body of a neuron enclosing the nucleus and main organelles, serving as the metabolic and synthetic center of the nerve cell.

Axon Terminals

The distal, branched endings of an axon that synthesize, store, and exocytose chemical neurotransmitters into the synaptic cleft to transmit signals to post-synaptic cells.

Excitable Cell

A specialized cell (including neurons, muscle fibers, and certain endocrine cells) that can use its resting membrane potential to trigger and propagate an electrochemical impulse termed an action potential.

Action Potential (AP)

A rapid, all-or-nothing electrical impulse characterized by sequential membrane potential reversal mediated by the opening and closing of voltage-gated ion channels.

Threshold Potential

The critical membrane potential level (typically $-55\,\text{mV}$) that incoming depolarizing stimuli must achieve to trigger an all-or-nothing action potential.

Depolarization

The initial rapid phase of an action potential during which voltage-gated $\text{Na}^+$ channels open, permitting an influx of $\text{Na}^+$ ions that shifts the interior membrane potential from negative toward positive values (up to $+40\,\text{mV}$).

Repolarization

The downward phase of an action potential during which voltage-gated $\text{Na}^+$ channels become inactivated and voltage-gated $\text{K}^+$ channels open, allowing $\text{K}^+$ efflux to return the cell interior toward negative potentials.

Hyperpolarization

The transient phase at the conclusion of an action potential where prolonged $\text{K}^+$ efflux causes the membrane potential to drop below the standard resting membrane potential, forming the basis of the relative refractory period.

Absolute Refractory Period

The timeframe encompassing the depolarization and repolarization phases during which voltage-gated $\text{Na}^+$ channels are either open or inactivated, making it impossible to initiate another action potential regardless of stimulus strength.

Relative Refractory Period

The timeframe coinciding with hyperpolarization where a second action potential can be fired, but requires a stronger-than-normal stimulus because the cell interior is more negative than resting level.

Resting Membrane Potential (RMP)

The stable electrical voltage maintained across an excitable cell membrane under unstimulated baseline conditions, approximately $-70\,\text{mV}$ in neurons.