The Nervous System

Nervous System

• Central Nervous System (CNS) comprises the brain and spinal cord.
• Peripheral Nervous System (PNS) consists of cranial nerves (12 pairs), spinal nerves (31 pairs), and the Autonomic Nervous System (ANS).
• The sympathetic nervous system excites, while the parasympathetic nervous system inhibits.

Neurons

• Dendrites receive electrochemical messages.
• The cell body contains the nucleus.
• Axons are long projections that carry electrical impulses away from the cell body.
• Myelin sheaths increase the speed of electrical impulse conduction.
• Ganglia/Nuclei: Nerve cells clustered together.

Neurotransmitters

• They communicate messages from one neuron to another or to a target cell, acting either as excitatory or inhibitory signals.
• Acetylcholine primarily serves the parasympathetic nervous system and is typically excitatory when stimulated by the sympathetic nervous system. It affects brain function and muscle contractions, becoming inhibitory when influenced by the parasympathetic system, stimulating the heart through the vagal nerve, and impacting mood and immune responses.
• Serotonin is inhibitory, aiding in controlling mood and sleep, and inhibiting pain pathways.
• Dopamine is inhibitory, affecting behavior, attention, emotion, and fine movement.
• Norepinephrine is mainly for the sympathetic nervous system and is usually excitatory, influencing mood and overall activity.
• Gamma-aminobutyric acid (GABA) is inhibitory.
• Enkephalin and endorphin are excitatory, governing pleasurable sensations and inhibiting pain transmissions.

Cerebral Circulation

• The brain gets 15% of the total cardiac output, roughly 750 ml/min of blood flow.
• Oxygen must be constantly supplied.
• The blood-brain barrier (BBB) restricts many circulating substances from entering the CNS.
• This barrier filters substances entering the cerebrospinal fluid (CSF), preventing them from entering the blood, and is vital for protection, but alters in trauma, cerebral edema, or hypoxemia.

Peripheral Nervous System Divisions

• The somatic division conveys voluntary information to the CNS from the senses and to skeletal muscles from the CNS, which the body controls.
• The autonomic division manages internal environmental activities like the heart, lungs, and gastrointestinal tract, carrying information from the CNS to bodily organs, serving as the visceral part of the PNS.
• Sympathetic NS: excitatory; flight-fight response, arousing the body
• Parasympathetic NS - inhibitory; mostly controls the visceral function; rest and digest; plays a role in homeostasis

Sympathetic Nervous System

• The sympathetic nervous system increases sympathetic responses during emotional and physical stress.
• Norepinephrine is the primary neurotransmitter, originating from the thoracolumbar division of the brain stem.
• Actions of Sympathetic NS:
  • Bronchioles dilate for gas exchange during Dyspnea on Breathing (DOB) or Shortness of Breath (SOB)
  • Heart rate increases
  • Blood vessels dilate to supply needed blood during decreased cardiac output, prioritizing major organs
  • Peripheral blood vessels constrict, redirects blood flow from less important organs like skin and GIT
  • Decreased peristalsis occurs due to GIT blood vessel constriction.
  • The liver releases glucose for quick energy.
  • Muscle contraction leads to pyloerection.
  • Glycogen conversion to glucose allows blood entry using the enzyme.
  • Excites sweat glands.

Parasympathetic Nervous System

• This system controls most visceral organs, is dominated by acetylcholine (brain stem from the craniosacral), and mainly inhibits.
• It operates during calm, non-stressful states, balancing the sympathetic NS to maintain homeostasis.

Neurological Assessment

• Exploration & observation of patient conditions is key.
• Interviewing: COLDSPA (Character, Onset, Location, Duration, Severity, Pattern, Associated Factors).

Key Symptoms

• Acute Pain: Linked to brain hemorrhage, spinal ailments & trig trigeminal neuralgia.
• Chronic Pain: Associated with disorders such as multiple sclerosis, stroke, myasthenia gravis, etc.
• Seizures: Caused by irregular electrical discharges in brain's cortex.
• Dizziness: Abnormal balance/movement sensations, 50% experience vertigo.
• Visual disturbances can stem from aging, glaucoma, cataract, tumors, or CVA/stroke lesions.
• Muscle weakness has various types affecting the muscles
• Abnormal sensations: Can entail both CNS & PNS; can lead to reduced strength & pain.

Physical Evaluation - Consciousness & Cognition

• Check appearance, behavior, dress, hygiene, orientation (time, place, personal details), recent & remote memory.
• IQ tests: Checking digit repetition, backward counting & math; average IQ can repeat 7 digits without falter (1,2,3,4,5,6,7), can recite 5 digits backwards (5,4,3,2,1), and can do simple maths such as serials of 7 (100 - 7= 93; 93 - 7 = 86...).
• Focused questioning for clarity & meaningful thoughts can indicate problems.
• Emotions assessed by observation of affect.
• Speech must have meaning.
• Language ability to respond normally.

Assessing Level of Consciousness (LOC)

• Observe wakefulness & environmental response.
• An important measure in finding increasing Intracranial Pressure (ICP).
• Glasgow Coma Scale used to scale consciousness: Scores range from alert (15) to comatose (7 or less).
• Terminology: Alert (responds quickly), Lethargic (drowsy), Stuporous (needs stim), Comatose (unresponsive).

Cranial Nerve Examination

• This assessment determines sensory and motor function.
• Sensory Nerves: I, II, VIII
• Motor Nerves: III, IV, VI, XI, XII
• Mixed Nerves: V, VII, IX, X

Assess Motor System

• Walking observations detect posture, gait & balance.
• Muscle strength & resistance checked.
• Measured via five-point scale, graded 0-5.

Deep Tendon Reflexes (DTR)

• DTR Rating Scale:
  • 4+ – Very brisk, hyperactive, with clonus
    • Clonus: Alternating muscle contraction & relaxation
  • 3+ – Brisker than average, slightly hyperreflexic
  • 2+ – Average, normal
  • 1+ – Low normal
  • 0 – Absent
• Note that grading is subjective and dependent on the examiner.
• Biceps reflex: Tests C5-C6 reflexes; normal response - elbow flexion
• Triceps reflex: Assesses C7-C8 spinal nerves; normal response - elbow extension
• Brachioradialis reflex indicates C5-C6 spinal cord issues; flexion/supination of the forearm is typical

Superficial Reflexes (Example)

• Corneal: Cotton wisp on sclera prompts blinking; absence may point to CN V issues.
• Gag: touching pharynx induces gag; absent points to CN IV or X problems
• For men only, Cremasteric: Stroking inner thigh elevates scrotum; absent with spine injury (T12, L1, L2).
• Plantar movement assessment evaluating L4, L5, S1, S2; an abnormal (+) Babinski means toes fan.

Sensory System

• Subjective, cooperation is needed.
• Dermatomes represent distribution of the peripheral nerves from the spinal nerve.
• Touch, superficial pain, temperature, vibration, proprioception assessed via stimuli.
• Tactile agnosia (astereogenesis) is tested if eyes have shut. In failure to recognize items, the parietal lobe is affected.
• Visual agnosia is tested if eyes opened. There is failure to identify with an affected occipital lobe.