Nervous, Muscular & Endocrine Systems – Lecture Vocabulary Review

Spinal Cord, Spinal Nerves, and Protective Structures

• Formation of a spinal nerve
  • Dorsal (posterior) and ventral (anterior) roots from each spinal segment unite → one mixed (sensory + motor) spinal nerve.
• Meninges & meningitis
  • Meninges = protective membranes (dura mater, arachnoid mater, pia mater).
  • Meningitis = inflammation/infection of these membranes → ↑ intracranial pressure, headache, stiff neck, photophobia, potential neurological damage.
• Cerebrospinal fluid (CSF) sampling
  • Diagnostic lumbar puncture needle inserted into the \text{subarachnoid space} (typically between L3–L4 or L4–L5) where CSF circulates around cauda equina.
• High cervical (C3–C5) crush injury
  • Regions house the phrenic nerve nucleus → damage compromises diaphragm → respiratory failure + quadriplegia (loss/impairment of motor and sensory function in arms, trunk, legs).

Brain Anatomy: Key Regions & Functions

• Medulla oblongata
  • Autonomic centers for blood pressure, heart rate, respiration, digestion (cardiovascular & respiratory rhythmicity centers).
  • Damage → life-threatening dysautonomia.
• Blood supply to brain
  • Internal carotid arteries (anterior circulation) + vertebral arteries (posterior circulation) = \text{Circle of Willis} anastomosis ensuring constant cerebral perfusion.
• Cerebellum
  • Oversees postural / axial muscles, coordinates rapid automatic adjustments to maintain balance & equilibrium.
  • Integrates proprioceptive input + vestibular, visual, cortical, and basal ganglia signals.
  • Lesion → ataxia, intention tremor, dysmetria ("jerky, uncoordinated" movements).
• Basal nuclei & substantia nigra
  • Substantia nigra pars compacta supplies dopamine to striatum.
  • Degeneration ↓ dopamine → excess basal-nuclei inhibitory output → generalized ↑ muscle tone, resting tremor → hallmark of Parkinson’s disease.
• Cerebral cortex functional areas
  • Primary motor cortex = precentral gyrus → voluntary movement initiation (somatotopically arranged motor homunculus).
  • Occipital lobe → primary & association visual cortices; trauma (posterior blow) → cortical blindness or visual field defects.
  • Left superior temporal lobe (Wernicke’s area) → language comprehension. Lesion: receptive aphasia (can hear words, cannot derive meaning).

Muscular System & Fiber Types

• Thyroid hormone & skeletal muscle
  • Thyroxine (T4)/Tri-iodothyronine (T3) ↑ basal metabolic rate → stimulates ATP consumption & heat production in muscle fibers.
• Fiber distribution
  • Most human muscles mix slow oxidative (Type I) + fast glycolytic (Type II).
  • Calf (soleus) rich in slow fibers for postural endurance.
  • Extraocular muscles ≈ entirely fast fibers → rapid eye movements (saccades).
• Surgical / clinical muscle highlights
  • Rectus abdominis is cut when incision is made lateral & close to linea alba in abdominal surgery.
  • Quiet breathing relies primarily on diaphragm; damage → ventilatory compromise.
  • Preferred large-volume intramuscular injection in adult posterior thigh = gluteus maximus (upper outer quadrant to avoid sciatic nerve).

Somatic vs Autonomic Divisions

• Overall nervous system functions
  • Sensory input, integration, motor output, short-term rapid regulation.
  • NOT responsible for direct long-term processes like growth (endocrine handles that).
• Somatic nervous system (SNS)
  • Voluntary control of skeletal muscle via lower motor neurons.
• Autonomic nervous system (ANS)
  • Sympathetic activation effects: ↑ HR, ↑ BP, bronchodilation, sweating, glycogenolysis → ↑ blood glucose.

Neurophysiology Fundamentals

• Synapse
  • Specialized site of neuron-to-cell communication (chemical or electrical). determines directionality & modulation.
• Neuroglia
  • Microglia = CNS phagocytes; migrate to mediate immune defense & debris removal.
• Blood–brain barrier (BBB)
  • Tight-junctioned endothelial cells of CNS capillaries restrict passage of many drugs/toxins; lipophilic & actively transported molecules cross.
• Membrane potential events
  • Opening Na^+ channels → rapid Na^+ influx → membrane depolarization toward +30\,mV (rising phase action potential).
• Cholinergic receptor (nicotinic) activation
  • Ligand-gated cation channel opens → Na^+ influx (NOT efflux) depolarizes postsynaptic membrane.
• Neuronal repair limits
  • Mature CNS neurons are post-mitotic; lose regenerative capacity during development (lack of neurilemma, inhibitory environment).

Cranial Nerves & Specialized Receptors

• Vestibulocochlear nerve (CN VIII)
  • Afferent for hearing & equilibrium from cochlea + vestibular apparatus.
• Trigeminal nerve (CN V) dental anesthesia
  • Inferior alveolar branch (mandibular division V3) blocked to numb mandibular teeth.
• Baroreceptors
  • Stretch receptors (e.g., aortic arch, carotid sinus) monitor arterial BP; relay via glossopharyngeal & vagus nerves to medulla.
• Reticular Activating System (RAS)
  • Brainstem network (midbrain → thalamus) maintaining consciousness & arousal; damage → coma.

Vision

• Lens accommodation
  • Ciliary muscle contraction loosens zonular fibers → lens rounds → focus near; relaxation flattens lens → focus far.
• Fovea centralis
  • Cone-only pit within macula lutea → highest acuity, color discrimination; requires precise ocular alignment.
• Iris
  • Pigmented diaphragm; pupillary dilator & sphincter muscles adjust aperture → regulate retinal illumination.
• Optic disc (blind spot)
  • Site where optic nerve exits; lacks photoreceptors; brain normally “fills in” missing visual info.

Hearing

• External → middle → inner ear pathway
  • Auricle & external acoustic meatus collect waves.
  • Tympanic membrane converts acoustic → mechanical vibration.
  • Auditory ossicles (malleus, incus, stapes) in middle ear transmit to oval window.
  • Middle ear connects to nasopharynx via auditory (Eustachian) tube equalizing pressure.

Endocrine System Highlights

• Posterior pituitary hormones
  • Antidiuretic hormone (ADH/vasopressin) → kidney collecting ducts ↑ aquaporin insertion → water reabsorption; deficiency → diabetes insipidus.
  • Oxytocin → uterine smooth muscle contraction (labor), milk ejection, prostate contraction; synthesized in hypothalamic supraoptic & paraventricular nuclei, released from neurohypophysis.
• Thymosin
  • Secreted by thymus; promotes T-lymphocyte maturation & immune competence.
• Erythropoietin (EPO)
  • Glycoprotein from renal peritubular fibroblasts (and liver); hypoxia-induced; stimulates bone-marrow erythrocyte production.
• Diabetes mellitus (untreated)
  • Chronic hyperglycemia (>200\,mg\,dL), glucosuria, osmotic diuresis → polyuria, polydipsia, weight loss; risk ketoacidosis (type 1) or HHS (type 2).

Clinical Integration & Ethical Considerations

• Neurological deficits following trauma (e.g., C3–C5 injury, occipital impact, Wernicke’s aphasia) highlight necessity of standardized acute care & rapid imaging. Ethical imperative to ensure rehabilitation access.
• Parkinson’s disease underscores translational research importance from neurochemical pathway insights to therapies (L-DOPA, deep-brain stimulation). Ethical issues: experimental treatments, quality of life.
• Endocrine disorders (DM, ADH imbalance) illustrate interplay between lifestyle, chronic management, and health-care equity.