Comprehensive Notes on Neurology and Neurologic Disorders
Anatomic and Physiologic Overview of the Nervous System
The nervous system is divided into two primary components: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS consists of the brain and the spinal cord, acting as the main control and processing center responsible for the integration and interpretation of sensory input as well as the initiation of motor responses. The PNS is composed of 12 pairs of cranial nerves and 31 pairs of spinal nerves, serving to transmit information to and from the CNS. The PNS is further subdivided into the Autonomic Nervous System (ANS) and the Somatic Nervous System. The Somatic Nervous System manages voluntary control over skeletal muscles, while the ANS provides involuntary regulation to maintain internal balance. The ANS is split into the Sympathetic branch, which governs the "fight or flight" response by increasing heart rate and blood pressure and causing pupil dilation, and the Parasympathetic branch, which governs "rest and digest" functions by decreasing heart rate, stimulating digestion, and causing pupil constriction.
The functions of the nervous system are categorized into sensory, integrative, and motor functions. The sensory function detects internal and external stimuli, the integrative function processes and interprets this gathered data, and the motor function produces a response via muscles or glands. These processes collectively maintain homeostasis, consciousness, and emotional and behavioral responses.
Cells of the Nervous System and Neurotransmission
The neuron is the basic functional unit of the nervous system. Its structure includes dendrites, which receive incoming signals from other neurons; the cell body or soma, which contains the nucleus and acts as the metabolic center; and the axon, which conducts electrical impulses away from the cell body toward other cells. Neurons possess special features such as the myelin sheath, a lipid-rich covering that increases conduction speed, and the Nodes of Ranvier, which allow for saltatory conduction where impulses jump from node to node. Neurons are functionally classified into three types: Sensory (afferent) neurons, which carry signals toward the CNS; Motor (efferent) neurons, which carry signals away from the CNS to effectors like muscles; and Interneurons (relay neurone), which connect neurons within the CNS.
Glial cells, or neuroglia, provide support and protection for neurons, maintain the chemical environment, provide nutrients, and assist in repair. In the CNS, these include astrocytes for structural support, oligodendrocytes for forming myelin, microglia for immune defense, and ependymal cells to line ventricles and produce cerebrospinal fluid (CSF). The primary glial cells of the PNS are Schwann cells, which form the myelin sheath in the periphery.
Communication between neurons occurs via neurotransmitters, which are chemical messengers that transmit signals across synapses. The mechanism begins when an action potential—an electrical change in the neuron’s membrane—reaches the axon terminal. This triggers synaptic vesicles to release neurotransmitters into the synaptic cleft, where they bind to postsynaptic receptors to cause either excitation or inhibition. Signal termination occurs through enzymatic breakdown or reuptake into the presynaptic neuron. Major neurotransmitters include Acetylcholine, the primary transmitter of the parasympathetic nervous system, which is usually excitatory but can be inhibitory, such as when the vagal nerve stimulates the heart. Serotonin is inhibitory and helps control mood and sleep. Dopamine is usually inhibitory and affects behavior, emotions, and fine movement. Norepinephrine is the major transmitter of the sympathetic nervous system and is usually excitatory, affecting mood and overall activity. Gamma-aminobutyric acid (GABA) is an inhibitory transmitter that calms firing nerves. Enkephalins and endorphins are excitatory, producing pleasurable sensations and inhibiting pain transmission. Glutamate is the most common neurotransmitter, vital for learning, memory, and the creation of nerve contacts.
Brain Anatomy and Functional Dominance
The adult brain weighs approximately , while the older adult brain weighs roughly , accounting for about of total body weight. The brain is divided into the cerebrum, brainstem, and cerebellum. The cerebrum is the largest part, consisting of two hemispheres connected by the corpus callosum. Its surface features include gyri (folds) and sulci or fissures (grooves). The cerebrum is composed of gray matter, which forms the outer cortex ( thick) and contains neuron cell bodies, and white matter, the inner layer containing myelinated nerve fibers for fast conduction.
Cerebral dominance dictates that the left hemisphere typically controls the right side of the body and governs language, logic, math, reasoning, and spoken/written communication. The right hemisphere controls the left side of the body and is associated with spatial awareness, music, creativity, facial recognition, and non-literal thinking. Deep within the brain are the basal ganglia, which are nuclei responsible for coordination of movement and fine motor control. The thalamus acts as a relay station for all sensory input except smell, processing pain, temperature, and touch. The hypothalamus is the chief control center for the endocrine and autonomic systems, regulating temperature, hunger, thirst, sleep-wake cycles, blood pressure, and emotional responses like rage or pleasure via its influence on the pituitary gland.
The brainstem connects the brain to the spinal cord and includes the midbrain, pons, and medulla oblongata. The midbrain contains centers for visual and auditory reflexes and cranial nerves (CN) III and IV. The pons acts as a bridge between brain regions, containing CN V through VIII and regulating breathing. The medulla oblongata contains vital centers for heart rate, breathing, and blood pressure, as well as reflex centers for coughing and swallowing; it is also the site of decussation, where nerve fibers cross. The cerebellum, located below the cerebrum and behind the brainstem, is responsible for balance, coordination, posture, and smooth movement.
Protection and Fluids of the Central Nervous System
The brain is protected by the rigid skull, which features indentations called fossae: the anterior fossa for the frontal lobe, the middle fossa for the temporal lobe, and the posterior fossa for the cerebellum and brainstem. Beneath the bone lie the meninges, consisting of three layers: the tough outer dura mater; the middle web-like arachnoid mater, which contains the subarachnoid space; and the thin pia mater, which adheres directly to the brain tissue.
Cerebrospinal fluid (CSF) is a clear, colorless fluid produced in the choroid plexus of the ventricles at a rate of approximately , with a normal total volume of about . It provides protection, nutrition, and waste removal. The circulation pattern flows from the lateral ventricles through the Interventricular foramen (of Monro) to the third ventricle, then through the Aqueduct of Sylvius to the fourth ventricle, and into the subarachnoid space before being absorbed by arachnoid villi into the venous system. A blockage in this system leads to obstructive hydrocephalus. A clinical indicator of a CSF leak is the "Halo Sign," where blood-tinged fluid from the nose or ear creates a double-ring pattern on absorbent material.
Cerebral circulation receives about of cardiac output. Arterial supply is provided by the internal carotid and vertebral arteries, which form the Circle of Willis to provide collateral circulation. Venous drainage occurs via dural sinuses and the internal jugular vein; notably, these veins lack valves, making flow dependent on pressure.
Spinal Cord Anatomy and Peripheral Nervous System
The spinal cord extends from the foramen magnum to the L1 vertebra, measuring roughly (). It ends in a tapered point called the conus medullaris, followed by a bundle of nerve roots called the cauda equina. The internal structure features H-shaped gray matter in the center, containing neuron cell bodies, and outer white matter consisting of ascending (sensory) and descending (motor) tracts. The anterior (ventral) horns contain motor neurons for voluntary muscle activity, while the posterior (dorsal) horns contain sensory neurons. Lateral horns in the thoracic and lumbar regions contain sympathetic neurons. Spinal tracts include the posterior columns (touch, pressure, vibration), which cross in the medulla; spinocerebellar tracts (muscle coordination), which do not cross; and spinothalamic tracts (pain, temperature), which cross in the spinal cord. This crossing results in contralateral control, where the left hemisphere interprets stimuli from the right side of the body.
The vertebral column consists of 7 cervical, 12 thoracic, 5 lumbar, sacrum, and coccyx segments. Each vertebra has a body and an arch, with intervertebral foramina that allow spinal nerves to exit and discs that act as shock absorbers. The PNS includes 12 pairs of cranial nerves and 31 pairs of spinal nerves (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal). Cranial nerves are categorized as sensory (I, II, VIII), motor (III, IV, VI, XI, XII), or mixed (V, VII, IX, X). Spinal nerves connect to the cord via dorsal (sensory) and ventral (motor) roots. Dermatomes are specific areas of skin supplied by single spinal nerves; they are critical for assessing spinal injuries and diagnosing conditions like shingles or "saddle anesthesia" (S2-S4), which suggests cauda equina syndrome.
The Autonomic Nervous System Functions
The ANS regulates involuntary functions of the heart, lungs, vessels, and glands. The Sympathetic Nervous System, or "fight-or-flight" system, is activated by stress and primarily uses norepinephrine and epinephrine. Its effects include bronchodilation, increased heart rate, vasoconstriction in the skin (leading to cool, pale skin), pupil dilation (mydriasis), and glucose release from the liver. Conversely, the Parasympathetic Nervous System, or "rest-and-digest" system, uses acetylcholine to conserve energy. Its effects include decreased heart rate, bronchoconstriction, pupil constriction (miosis), increased peristalsis, and stimulation of salivary, lacrimal, and mucus secretions. The two systems work in opposition to maintain homeostasis. Specific effects include the relaxation of the bladder wall in the sympathetic state and contraction in the parasympathetic state, and thick versus thin salivary secretions, respectively.
Neurologic Diagnostic Procedures
Diagnostic tests are essential for identifying tumors, strokes, and infections. Computed Tomography (CT) scans use X-rays to create cross-sectional images; without contrast, they are best for detecting acute bleeding (which appears bright), while contrast enhances tumors and infections. Nursing care for CT involves checking for iodine/shellfish allergies and monitoring kidney function. Magnetic Resonance Imaging (MRI) uses magnetic fields to detect soft tissue changes and early-stage strokes. Safety is paramount with MRI; all metal must be removed, and implants must be screened. Positron Emission Tomography (PET) measures brain metabolism using a radioactive glucose tracer, detecting decreased metabolism in Alzheimer’s or increased metabolism in tumors. Single-Photon Emission Computed Tomography (SPECT) focuses on cerebral perfusion and blood flow. Cerebral Angiography is an invasive procedure involving contrast injection into the arterial system to evaluate aneurysms or occlusions. Myelography involves injecting contrast into the spinal subarachnoid space to detect herniated discs. Electroencephalography (EEG) records brain electrical activity for seizure or coma evaluation, sometimes requiring patient sleep deprivation to enhance detection of abnormal activity.
Lumbar Puncture and Cerebrospinal Fluid Analysis
A lumbar puncture (spinal tap) involves inserting a needle into the subarachnoid space between L3-L4 or L4-L5, safely below the end of the spinal cord at L1. It is used to measure CSF pressure, obtain samples for analysis, or administer intrathecal medications. Normal CSF pressure is () in the lateral recumbent position. Normal fluid is clear and colorless with minimal cells, protein levels of , and glucose between . Abnormal findings include bloody fluid (hemorrhage), high protein (infection), or low glucose (bacterial infection). Contraindications include intracranial mass lesions due to the risk of brain herniation (uncal, tonsillar, or central).
Nursing care for the procedure includes obtaining informed consent, positioning the patient in a "fetal position" to open intervertebral spaces, and maintaining the patient in a prone or supine position for post-procedure. A common complication is the post-lumbar puncture headache, caused by CSF leakage through the puncture site, which leads the brain to sag and compress pain-sensitive structures. This is managed with bed rest, hydration, and caffeine.
Altered Level of Consciousness (LOC)
Altered LOC is a continuum ranging from alert and confused to lethargic, stuporous, and comatose. Specific states include akinetic mutism (awake but no movement/speech), persistent vegetative state (sleep-wake cycles but no awareness), minimally conscious state (inconsistent awareness), and locked-in syndrome (conscious but paralyzed except for eye movements). Pathophysiology involves neuronal dysfunction, cerebral edema, and disruption of the reticular activating system. The Glasgow Coma Scale (GCS) measures eye opening (), verbal response (), and motor response (); a score of indicates deep coma, while is alert. Abnormal motor patterns include decorticate posturing (flexion toward the core, indicating cerebral damage) and decerebrate posturing (extension and outward rotation, indicating severe brainstem or pons damage).
Management focuses on the airway (intubation if needed) and preventing complications of immobility. Nursing diagnoses include ineffective airway clearance, risk for aspiration, and impaired skin integrity. Oral care must be frequent to prevent parotitis and ventilator-associated pneumonia (VAP). For nutrition, enteral feeding should start within if oral intake is impossible. Fluid administration must be slow to avoid increasing intracranial pressure (ICP).
Increased Intracranial Pressure (ICP) and Cerebral Perfusion
ICP is the pressure within the rigid skull exerted by brain tissue (), blood (), and CSF (). The Monro-Kellie Doctrine states that because the skull's volume is fixed, an increase in any one component must be compensated for by a decrease in another. Failure of this compensation leads to increased ICP (normal is ). Cerebral Perfusion Pressure (CPP) is the pressure needed to ensure blood flow to the brain, calculated as: . A normal CPP is ; values below result in irreversible brain damage.
Cushing’s Triad is a late sign of increased ICP, characterized by systolic hypertension (widening pulse pressure), bradycardia, and irregular respirations (Cheyne-Stokes). Management includes osmotic therapy (Mannitol or hypertonic saline ) to create a gradient that pulls water from brain tissue, and corticosteroids like dexamethasone for tumor-related edema. Carbon dioxide levels () must be controlled; high causes vasodilation and increases ICP, so controlled ventilation is used to maintain levels between . Surgical options include decompressive hemicraniectomy or ventriculostomy for CSF drainage.
Ischemic Stroke Pathophysiology and Management
Ischemic stroke accounts for approximately of all strokes and occurs when a vessel occlusion reduces cerebral blood flow. Types include large artery thrombotic (atherosclerosis), small penetrating artery (lacunar), cardioembolic (clots from atrial fibrillation), and cryptogenic (unknown cause). The "ischemic cascade" begins with energy failure and anaerobic metabolism, leading to lactic acidosis, ATP depletion, and calcium influx, resulting in neuronal death. The "penumbra" is the area of low blood flow surrounding the infarct that is ischemic but potentially salvageable with rapid intervention.
Clinical manifestations involve contralateral motor deficits (hemiplegia/hemiparesis), communication disorders (aphasia, dysarthria, apraxia), and visual field deficits such as homonymous hemianopsia (loss of half the visual field). The NIH Stroke Scale (NIHSS), with scores from to , is used to assess severity. Medical management prominently features recombinant tissue plasminogen activator (t-PA). Eligibility for IV t-PA includes being over years old, having a diagnosis of ischemic stroke, and treatment within (up to in select cases). The dosage is (max or ), with given as an IV bolus and infused over . BP must be maintained below for t-PA administration. Prevention focuses on diet (DASH or Mediterranean), statin therapy, and anticoagulation for patients with atrial fibrillation.
Hemorrhagic Stroke and Vascular Malformations
Hemorrhagic stroke ( of cases) has a higher mortality rate and involves bleeding into the brain tissue (Intracerebral Hemorrhage or ICH) or subarachnoid space (Subarachnoid Hemorrhage or SAH). Causes include hypertension, intracranial aneurysms (dilations often at the Circle of Willis), and Arteriovenous Malformations (AVM). SAH is often marked by the "worst headache of one's life," nuchal rigidity, and photophobia.
Major complications include rebleeding and cerebral vasospasm, which occurs post-hemorrhage and leads to delayed ischemia. Nimodipine is the only FDA-approved medication to prevent vasospasm. ICH management requires careful BP control (lowering SBP to approximately if it is between ). For patients on anticoagulants, reversal agents like Vitamin K (for Warfarin) or Idarucizumab (for Pradaxa) are used. Surgical management includes aneurysm clipping, coiling, or craniotomy for hematoma evacuation if there is neurologic deterioration.