Nervous System and Special Senses: Core Concepts

Overview: This document provides a briefing on the main themes and important concepts related to the nervous system and special senses as presented in the provided lecture notes. The notes cover the basic anatomy and physiology of the central and peripheral nervous systems, common neurological and sensory disorders, and relevant medical terminology.

Main Themes and Important Ideas:

1. Organization of the Nervous System:

•The nervous system is broadly divided into the Central Nervous System (CNS), comprising the brain and spinal cord, and the Peripheral Nervous System (PNS), which includes all other nerves.

•CNS - Brain: The brain is further subdivided into key areas:

◦Cerebrum: Consists of four lobes: frontal, temporal, parietal, and occipital.

◦Cerebellum: Responsible for learned body movement and equilibrium ("The development of learnt body movement and maintenance of equilibrium").

◦Diencephalon: Contains the thalamus and hypothalamus, processing sensory information ("process sensory information(taste, touch, sight and direction to certain parts of the brain").

◦Brain Stem: Includes the midbrain (mesencephalon), pons, and medulla oblongata, involved in processing sensory information and vital functions. The medulla is crucial for the contralateral control of the body by the brain ("The transition from right to left occurs at the medulla."). This is clinically significant in conditions like stroke: "When dealing with a CVA(stroke) that presents with left or right sided paralysis will determine what side of the brain is affected by the stroke. (i.e. Right sided facial droop will be accompanied by left sided weakness/paralysis)". The term for this crossed paralysis in stroke is "Decussation" ("“Decussation” the term for paralysis from a stroke that presents with Lt. facial paralysis and Rt. Sided body (arms & legs) paralysis").

•CNS - Spinal Cord: Serves as a pathway for communication between the brain and the body, involved in both incoming and outgoing messages. It is also responsible for reflexes ("Reflexs are un-thought responses to stimulus, these are transmitted from the spinal column. An example would be withdrawal from flame to a finger."). Spinal cord injuries at different levels result in varying degrees of paralysis ("Above C-5 =Quadriplegia, can affect respiratory drive. Below C-5=paraplegia.").

•PNS: Divided into the somatic nervous system (voluntary control - "Conscious and voluntary body movements") and the autonomic nervous system (involuntary control).

◦Somatic Nervous System: Includes 12 pairs of cranial nerves and 31 pairs of spinal nerves, involved in conscious movement and senses like touch.

◦Autonomic Nervous System: Has two branches: the sympathetic nervous system ("Sympathetic nerves(fight or flight)") and the parasympathetic nervous system ("Para-sympathetic (return to normal state)"). These systems maintain homeostasis by counterbalancing each other.

2. Protection of the CNS:

•The brain and spinal cord are protected by the meninges, a three-layered membrane consisting of the dura mater, arachnoid, and pia mater.

•Cerebral Spinal Fluid (CSF), approximately 100 ml, provides further protection from minor physical shocks.

3. Nervous System Disorders:

•Traumatic Brain Injuries (TBI): Range from mild concussions (graded 1-3 based on severity) to more severe injuries like subdural hematomas (bleeding between dura and arachnoid due to blunt trauma) and epidural hematomas (bleeding between dura and skull often due to skull fracture from blunt force).

•Vascular Disorders:

◦Transient Ischemic Attack (TIA): A temporary interruption of blood supply to the brain.

◦Cerebrovascular Accident (CVA) / Stroke: Deprivation of oxygen to an area of the brain due to blockage (clot) or rupture of a blood vessel. Manifestations can include hemiparesis (weakness), hemiplegia (paralysis), aphasia (loss of speech), or dysphasia (impaired speech).

◦Aneurysm: Localized dilation/bleeding of an artery in the brain.

•Tumors (Systemic Disorders): Can cause localized dysfunctions and increase intracranial pressure (ICP). Normal ICP is 5-15 mm/hg; pressures above 15 mm/hg are considered elevated. Tumors can be benign or malignant.

•Systemic Degenerative Diseases: Include multiple sclerosis (demyelination), Parkinson's disease (decreased dopamine), Alzheimer's/Dementia (possibly micro-embolic strokes, brain atrophy), ALS (Lou Gehrig's), and Huntington's chorea. These are often linked to genetic anomalies.

•Seizures/Psychosis:

◦Epilepsy: Characterized by petite mal and grand mal seizures, often caused by metabolic disorders or cerebral lesions.

◦Behavioral Disorders: Include anxiety disorders, OCD, phobias, mood disorders (depression, bipolar), and psychosis (schizophrenia).

4. Special Senses:

•The ability to perceive reality is crucial for attaining wisdom ("The English words “sense” and “sentience” are from the Latin verb “sentire”, which refers to the human ability to perceive reality and thus to attain wisdom.").

•The five senses are touch (PNS), smell (Cranial nerve #1 - olfactory), taste (Cranial nerve #9 - glossopharyngeal), sight, and hearing.

5. Sense of Sight:

•The eye functions like a video camera, continuously transmitting light images to the brain via the nervous system ("The eye transmits light images to the brain via the nervous system. The eye basically works similar to a video camera continuously. The eyes take continuous video and transmit’s them to the brain.").

•Vision is controlled by Cranial nerve #2 (optic). Eye movement is controlled by Cranial nerves #3 (oculomotor), #4 (trochlear), and #6 (abducens).

•The eye has three layers: sclera, uveal tract (choroid, iris, ciliary body), and retina (containing light-sensitive rods and cones - "Retina(light sensitive cells called “rods” & ‘cones”)").

•Common disorders include presbyopia (farsightedness), myopia (nearsightedness), astigmatism (refractive error), conjunctivitis (pink eye - "Inflammation of the mucous membrane of the anterior portion of the eye(pink eye)"), keratitis (corneal inflammation), glaucoma (increased intraocular pressure), and cataract (cloudiness of the lens).

6. Sense of Hearing:

•The ear is responsible for both hearing and equilibrium.

•Hearing is controlled by Cranial nerve #8 (vestibulocochlear).

•The ear is divided into the outer ear (pinna, auditory canal, tympanic membrane), middle ear (malleus, incus, stapes - "hammer, anvil and stirrup"), and inner ear (cochlea/labyrinth - transmits hearing to the brain and maintains balance).

•Hearing disorders include deafness (unilateral or bilateral), conductive hearing loss (outer/middle ear - "inability to conduct sound vibrations"), sensorineural hearing loss (nerve involvement - "Sorineural refers to hearing loss involving the nerve"), impacted cerumen (ear wax buildup - "A build up of ear wax is defined as “Impact cerumen”"), earaches (trauma or infection), Meniere's syndrome (inner ear disorder), and tinnitus (ringing in the ears - "Ringing or buzzing in one or both ears, symptom of Meniere's").

7. Medical Terminology and Abbreviations:

•The notes provide a list of common abbreviations related to the nervous system and special senses, along with their definitions (e.g., CNS - Central nervous system, CVA - Cerebrovascular accident, ICP - Intracranial pressure, PERRLA - Pupils equal, round, reactive to light and accommodation).

•Key terms are defined (e.g., Arachnoid mater, Axon, Cerebellum, Thalamus, Aphasia, Ataxia, Cerebral thrombosis, Delirium, Dysphasia, Neuralgia, Paresthesia).

8. Questions for Further Consideration:

•The document ends with several questions, indicating areas for further learning or clarification:

◦What is Todd paralysis? ("Post seizure, transient focal neurological deficits that resembles a stroke")

◦What is the difference between “hemiparesis” and “hemiplegia”? ("Partial or incomplete paralysis" vs. "Nothing, both mean paralysis" - note the discrepancy in the provided answers)

◦What does the acronym “CVA” represent? ("Cerebral vascular accident")

◦What does the root word “paresis” mean? ("Partial or incomplete paralysis")

◦What is the Babinski reflex? (Question posed but not answered in the text)

Conclusion:

These lecture notes provide a foundational understanding of the nervous system and special senses, covering their anatomical divisions, key functions, common disorders, and relevant medical vocabulary. The inclusion of clinical examples, such as the impact of stroke on contralateral body control, highlights the practical application of this knowledge. The questions at the end indicate areas for deeper exploration and understanding.