Unit 3 pt 1

Terminology, Aging, and the Neurological System Overview

Nervous System:

• Divided into two parts:

  • Central Nervous System (CNS):

    • Comprises the brain and spinal cord.

    • Responsible for processing and transmitting neural signals throughout the body, controlling mental functions such as thought, emotion, memory, and voluntary muscle movements.

    • Disease, injury, or trauma impacting the CNS can lead to dysfunction in various tissues and can manifest as motor deficits, sensory changes, or cognitive impairments.

  • Peripheral Nervous System (PNS):

    • Includes all neural tissues that lie outside the CNS, such as cranial and spinal nerves.

    • Facilitates communication between the CNS and the rest of the body, coordinating involuntary functions and responses associated with the autonomic nervous system (ANS).

Upper and Lower Motor Neuron Lesions

• Upper Motor Neuron (UMN) Lesions:

  • Indicate issues within the CNS.

  • Characterized by increased muscle tone, clonus, and spasticity.

  • Common symptoms include heightened deep tendon reflexes and the presence of pathological reflexes such as the Babinski sign.

• Lower Motor Neuron (LMN) Lesions:

  • Occur in the PNS and lead to flaccid paralysis.

  • Exhibits reduced or absent muscle tone and deep tendon reflexes.

  • Damage may be localized to specific muscles innervated by affected nerves, leading to muscle atrophy and weakness.

Aging and the CNS:

• Common changes associated with aging in the CNS include:

  • Simple loss of nerve cells leading to a decline in cognitive functions and memory.

  • Shrinkage of remaining nerve cells, contributing to a decreased conduction velocity of myelinated fibers, which can impact sensory and motor functions.

  • Decreased blood supply to CNS tissues, resulting in ischemia and reduced metabolic support for neurons.

  • Other aging-related changes in the CNS are still under investigation and may include alterations in neurotransmitter levels and receptor sensitivity.

Changes in the Peripheral Nervous System with Aging:

• Structural Changes:

  • The fascicles of peripheral nerves are largely unaffected; however, the perineurium and epineurium layers may thicken, contributing to nerve compression conditions such as carpal tunnel syndrome.

  • The endoneurium may become fibrosed, limiting healing post-injury.

  • Alterations in the vascular supply to nerves can lead to impaired regenerative capabilities.

  • Diminished sympathetically controlled vascular responses can affect wound healing efficiency and overall peripheral circulation.

  • Autonomic Nervous System (ANS) dysfunction becomes more prevalent compared to CNS dysfunction, resulting in issues such as orthostatic hypotension and diminished thermoregulation.

• Functional Changes:

  • Altered axonal myelination with aging leads to a loss of myelinated fibers, causing sensory alterations, including increased neuropathic pain or numbness.

  • Symptoms of peripheral neuropathy may present, including diffuse weakness and motor control issues which affect mobility and balance.

Overview of Cranial Nerves:

• There are 12 pairs of cranial nerves that emerge from the brain and are involved in numerous sensory and motor functions.

• The numbering of cranial nerves reflects their order of emergence, with the notable exceptions being CN XI (Accessory) and CN XII (Hypoglossal).

• List of Selected Cranial Nerves:

  • CN I: Olfactory (S) - Sense of smell

  • CN II: Optic (M) - Vision

  • CN III: Oculomotor (M) - Eye movement, pupil constriction

  • CN IV: Trochlear (B) - Eye movement (downward, inward)

  • CN V: Trigeminal (M) - Facial sensation, mastication

  • CN VI: Abducens (B) - Eye movement (lateral)

  • CN VII: Facial (B) - Facial expressions, taste (anterior 2/3 of tongue)

  • CN VIII: Vestibulocochlear (B) - Hearing and balance

  • CN IX: Glossopharyngeal (B) - Taste (posterior 1/3 of tongue), swallowing

  • CN X: Vagus (M) - Autonomic functions, heart, and digestive system control

  • CN XI: Accessory (M) - Shoulder and neck movement, swallowing

  • CN XII: Hypoglossal (M) - Tongue movement

• Mnemonics for memorizing cranial nerves:

  • "On Old Olympus' Towering Top, A Finn Van German Viewed A Hop"

  • "Some Say Marry Money, But My Brother Says Big Brains Matter More"

CNS Lesions and Symptoms:

• Critical findings associated with cranial nerve lesions often reveal significant clinical implications:

  • CN I: Anosmia (loss of smell), can indicate neurological conditions or head trauma.

  • CN II: Visual field defects, loss of pupillary constriction, can signify increased intracranial pressure or optic nerve damage.

  • CN III: Ptosis (drooping eyelid) and inability to move the eye inward or upward may suggest a lesion affecting the oculomotor nerve.

  • CN IV: Difficulty looking down when the eye is adducted can indicate trochlear nerve impairment.

  • CN V: Loss of sensation in the face and difficulty with jaw movement is characteristic of trigeminal nerve dysfunction, and can also relate to conditions like trigeminal neuralgia.

  • CN VI: Diplopia (double vision) during lateral gaze can imply abducens nerve injury.

• Additional cranial nerves exhibit specific signs based on functions affected by respective lesions or injuries.

Nerve Injury Classifications:

• Types of Nerve Damage:

  • Neuropraxia:

    • Represents a temporary disruption of nerve function without structural damage, allowing for normal conduction across the nerve with no axonal loss. Recovery typically occurs within minutes to days with conservative treatment.

  • Axonotmesis:

    • More severe damage that affects nerve fibers and surrounding connective tissue, leading to infarction and necrosis. Surgical intervention is often necessary for full recovery, which may take weeks to months depending on the extent of damage.

  • Neurotmesis:

    • The most severe type of nerve injury, involving complete severing of nerve fibers and surrounding tissues. Surgical repair is essential, and recovery can take a significant amount of time, often involving rehabilitation.

• Wallerian Degeneration:

  • Refers to the process of degeneration that follows the cut or crush of an axon. The distal portion of the axon undergoes degeneration while the proximal segment may regenerate if the nerve is partially injured, which is critical for nerve repair processes.