Module 10: Altered Somatic & Sensory Function

Pain is subjective and unique to every individual.
Involves the somatosensory system, including sensations of pain, touch, temperature, and body position.
Composed of 1st, 2nd, and 3rd order neurons.
Focuses on pain and itch via free nerve endings.

First-Order Neurons:
- Carry receptive endings to the spinal cord (dorsal horn).
- Detect stimuli threatening tissue integrity.
- Transmit sensory information from the periphery to the central nervous system (CNS).
Second-Order Neurons:
- Carry sensory impulses to the brain (specifically, the thalamus).
- Relay information from the spinal cord to the thalamus.
- Two distinct tracts: medial lemniscus, neospinothalamic and paleospinothalamic.
Third-Order Neurons:
- Carry sensory impulses from the thalamus to the cortex.
- Process pain information, giving a subjective feeling of pain.

A Fibers:
- Large and myelinated.
- Fast conduction.
- Associated with discriminative touch and spatial orientation.
C Fibers:
- Small and unmyelinated.
- Slow conduction.
- Associated with slow, chronic pain.

Discriminative Pathway:
- Transmission of sensory information for discriminative touch.
- Used for spatial orientation.
Anterolateral Pathway:
- Involves anterior and lateral spinothalamic tracts.
- Transmits pain, thermal sensations, and crude touch.
Paleospinothalamic Pathway:
- Slower, diffuse, aching, unpleasant sensations.
- Seen with chronic visceral pain.

Gate Control Theory:
- Peripheral receptors generate impulses along afferent neurons, entering the spinal cord.
- The spinal cord acts as a gate, regulating the transmission of impulses.
- Pain is influenced by stress, attention, and expectations.
Neuromatrix Theory:
- The brain identifies pain, with multiple dimensions and determinants including mood, genetics.

A-Delta Fibers:
- Large diameter, myelinated, fast conducting.
- Respond to mechanical stimuli over a certain intensity.
- Cause well-localized, sharp, stinging pain (fast pain).
C-Fibers:
- Small diameter, unmyelinated, slow conducting.
- Respond to mechanical, thermal, and chemical stimuli.
- Cause diffuse, dull, burning, aching pain (slow pain).

Sensory region of the body innervated by a single pair of dorsal ganglia.
Neighboring dermatomes can overlap, so loss of one dorsal root may only decrease, not eliminate, sensory innervation.

Acute Pain:
- Sudden onset, resolves quickly with diagnosis and treatment.
- Results from disease, inflammation, or injury.
Chronic Pain:
- Lasts a long time (months or longer).
- May be associated with a disease.
- More difficult to treat than acute pain.
Nociceptive Pain:
- Arises from activation of nociceptors.
  - Somatic Pain:
    - Cutaneous, deep (muscle, tendon, ligament, bone).
  - Visceral Pain:
    - Originates from organs; often difficult to treat.
Referred Pain:
- Perceived at a site different from the origin due to interconnecting sensory nerves.
Phantom Limb Pain:
- Painful sensations from a limb that is no longer there.
- Treatment: TENS, hypnosis, relaxation, sympathetic blocks.

Pharmacologic:
- Anesthetics cause unconsciousness, but don't cure underlying disease; long-term use requires increased dosage due to tolerance.
- Non-narcotic analgesics (OTC meds) for mild to moderate pain; aspirin, NSAIDs (anti-inflammatory).
  - Acetaminophen: Not anti-inflammatory.

Components: Cornea, retina, pupil, iris, lens, aqueous humor, vitreous humor, ciliary muscles, photoreceptors (rods and cones).
Rods: Vision in dim light (rhodopsin).
Cones: Vision in bright light and color.
Color vision results from combinations of cones; absence of cones leads to color blindness.

Light is reflected into the cornea.
Rods and cones convert light into electrical impulses, transmitted to bipolar neurons, then ganglion neurons.
Axons of ganglion neurons form the optic nerve, exit at the optic disk.
Impulses cross over at the optic chiasm, travel to the optic tract, thalamus, and occipital lobe for visual processing.

Caused by damage to eye structures, motor dysfunction, or impaired neural conduction.
Consequences range from mild visual impairment to blindness.

Increased pressure in the eye.
Second leading cause of blindness in the elderly.
Leading cause of preventable blindness in the US.
Caused by increased aqueous humor production or decreased outflow.
- Normal: $14-16 mmHg$
- Abnormal: >22 mmHg
Types:
- Primary Open Angle Glaucoma: Gradual onset, often asymptomatic.
- Angle-Closure Glaucoma: Rapid onset, more severe, common in hyperopia.
Risk Factors: Age (over 60), family history, diabetes, hypertension, sickle-cell anemia, eye trauma, long-term steroid use.
Clinical Manifestations: Eye pain, headache, nausea, blurred vision, rainbows around lights (acute).

Affects the macula, leading to distortion or loss of central vision.
Leading cause of blindness among older Americans.
Types:
- Dry Macular Degeneration: Thins over time.
- Wet Macular Degeneration: More severe, blood vessels grow under the retina, causing leakage.
Risk Factors: Age (over 60), smoking, hypertension, obesity, family history.

The labyrinth contains the cochlea, important for hearing.
Within the cochlea, the organ of Corti contains hair cells, the receptors responsible for the neural impulse that allows hearing
Mechanical energy from the ossicles forces the oval window into the cochlea.
The motion of the cochlea's fluid stimulates hair cells.
Stereocilia on each hair cell respond to unique sound frequencies, or pitches.
Movement of stereocilia leads to hyperpolarization or depolarization

Three semicircular canals and vestibule (containing the utricle and saccule, connected membranous sacs) are also located in the bony labyrinth and are important for balance and equilibrium
Semicircular canals and vestibule (vestibular apparatus) detect head position and acceleration, maintaining body position and stable visual fields

The ear canal are frequently caused by inflammation, drainage, or obstruction->cerumen, tumor

Most common infection of the middle ear.
Hearing loss may result from immobility of the tympanic
membrane, fluid accumulation of the middle ear, and
scarring from rupture of the tympanic membrane, altering
function.
Can be acute or recurrent, and it is associated with
effusion (fluid) in the middle ear and seen across all age
groups but has greatest prevalence in infants and children.
-Antibiotics
Clinical Manifestations: Pain, loss of balance, pressure, hearing difficulties, tinnitus, irritability, difficulty sleeping, fever, fluid drainage

Chronic infection affecting the inner ear; usually unilateral.
Clinical Manifestations: Vertigo, a feeling of spinning, is a
hallmark of Ménière disease and is often associated with
nausea and vomiting, Nystagmus and tinnitus may also develop

Recurrent, moderate to severe
headaches that last 1-2 days
Clinical Manifestations: Often associated with nausea
vomiting, and sensitivity to noise and
light