Comprehensive Study Notes: Clinical Neurology, Neuroanatomy, and Neuronal Function

Soma (Cell Body)

The central part of a neuron that contains the nucleus, cytoplasm, and primary cellular machinery needed to maintain cell life.

Bilipid Plasma Membrane

A double layer of phospholipids embedded with protein pores and channels that strictly regulates chemical transport into and out of the neuron.

Dendrites

Short, highly branched cellular processes extending from the soma that conduct nerve impulses in an afferent direction (distal to proximal, toward the cell body).

Axon

A single long process extending away from the cell body at the axon hillock that conducts nerve impulses in an efferent direction (away from the cell body).

Myelin Sheath

A white, shiny phospholipid bilayer sheath that wraps around axons to insulate them and increase neural conduction efficiency up to $50\text{ times}$ faster.

CNS vs. PNS Myelin Formation

In the Central Nervous System (CNS), myelin is formed by Oligodendrocytes; in the Peripheral Nervous System (PNS), it is formed by Schwann cells.

Synaptic Cleft

The minute intercellular gap between the presynaptic membrane and the postsynaptic membrane across which neurotransmitters diffuse.

Resting Membrane Potential

The steady electrical state of an inactive neuron, measured at $-70\text{ mV}$, maintained by passive leakage channels and the active $\text{Na}^+/\text{K}^+$ pump ($3\text{ Na}^+$ out for every $2\text{ K}^+$ in).

Action Potential

An all-or-nothing rapid depolarization and repolarization cycle generated when a stimulus depolarizes the axon hillock to a critical threshold ($-55\text{ mV}$).

Saltatory Conduction

The rapid propagation of an action potential along a myelinated axon, where the electrical impulse "hops" from one Node of Ranvier to the next.

Temporal vs. Spatial Summation

Temporal summation occurs when multiple impulses arrive in rapid succession at a single location; spatial summation occurs when impulses arrive simultaneously at adjacent locations.

Dura Mater

The tough, fibrous outer layer of the meninges composed of Periosteal and Meningeal layers, forming dural folds like the Falx Cerebri and Tentorium Cerebelli.

Cerebrospinal Fluid (CSF)

Clear fluid produced by the Choroid Plexus in the ventricles that cushions the CNS, regulates intracranial pressure, maintains chemical homeostasis, and removes waste.

Central Sulcus (Fissure of Rolando)

A major vertical fissure on the lateral surface of the brain that separates the Frontal Lobe from the Parietal Lobe.

Lateral Sulcus (Fissure of Sylvius)

A major horizontal fissure that separates the Frontal and Parietal Lobes superiorly from the Temporal Lobe inferiorly.

Frontal Lobe Primary Motor Area (Brodmann Area 4)

Located on the Precentral Gyrus; controls voluntary movements of contralateral skeletal muscles. Damage causes paresis or paralysis.

Broca's Area (Brodmann Area 44)

Located in the inferior frontal gyrus of the dominant hemisphere; responsible for motor planning and speech programming. Damage causes Broca's expressive aphasia or apraxia.

Wernicke's Area (Brodmann Area 22)

Located in the superior temporal gyrus of the dominant hemisphere; responsible for auditory language comprehension. Damage causes Wernicke's receptive aphasia.

Angular Gyrus (Brodmann Area 39)

Located in the parietal lobe; involved in cross-modal integration for reading and writing. Damage causes alexia, agraphia, anomia, acalculia, and left-right disorientation.

White Matter Fiber Types

Projection fibers connect cortex to lower CNS structures; Association fibers connect cortical areas within the same hemisphere; Commissural fibers connect homologous areas between hemispheres.

Limbic System & Short-Term Memory

Ring of structures (including Hippocampus and Amygdala) processing emotion and consolidating short-term memory (STM); bilateral lesions impair new STM formation while preserving long-term memory.

Basal Ganglia

Subcortical gray matter structures (Caudate Nucleus, Putamen, Globus Pallidus, Subthalamic Nucleus, Substantia Nigra) that regulate complex motor activity, posture, and muscle tone via inhibitory control.

Parkinson's Disease

A hypokinetic movement disorder caused by dopamine depletion in the Substantia Nigra, characterized by resting tremors, rigidity, bradykinesia, akinesia, and masked facies.

Thalamus

The central sensory relay center ("switchboard") of the diencephalon, housing the Medial Geniculate Body (auditory relay) and Lateral Geniculate Body (visual relay).

Brainstem Divisions

Composed of the Midbrain (visual/auditory colliculi, cerebral peduncles), Pons (CN V, VII, VIII nuclei), and Medulla Oblongata (CN IX-XII nuclei, cardiac/respiratory centers).

Cerebellum Function & Lesions

Integrates motor control by comparing intended movements with real-time feedback; lesions cause ataxia, dysmetria, intention tremor, equilibrium loss, and dysdiadochokinesia.

Final Common Pathway

Term coined by Sir Charles Sherrington for motor neurons in the ventral horn of the spinal cord, representing the final path for all neural impulses acting on muscles.

Cervical & Brachial Plexuses in SLP

The Cervical Plexus (C1-C5) includes C4 which innervates the pharynx and larynx; the Brachial Plexus (C4-T1) includes T1 which innervates the trachea, esophagus, and esophageal sphincter.

Dermatome vs. Myotome

A dermatome is an area of skin innervated by sensory fibers of a single spinal nerve root; a myotome is a group of muscles innervated by motor fibers of a single spinal nerve root.

Autonomic Nervous System (ANS) Divisions

Consists of the Sympathetic division ("fight or flight"), Parasympathetic division ("rest and digest"), Enteric division (gastrointestinal control), and the Endocrine system.