N245: Alterations in Somatosensory Function

Neurons

Individual cells in the nervous system that receive, integrate, and transmit information though electrical signals

Sensory (afferent) neurons

Neurons that carry incoming information from the sensory receptors to the brain and spinal cord

Motor (efferent) neurons

Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands

Interneurons

Neurons within the brain and spinal cord that connect sensory neurons to motor neurons

Central nervous system (CNS)

Consists of the brain and spinal cord

CNS function

Take in sensory signals, process information, and send out motor signals

Peripheral nervous system (PNS)

The sensory and motor neurons outside of the CNS

PNS function

Connect the CNS to the rest of the body and the external environment

Somatic nervous system

Part of the PNS that controls voluntary movements of skeletal muscles

Cranial nerves (12 pairs)

These nerves emerge from the brainstem; transmit information directly to or from the brain

Spinal nerves (31 pairs)

These nerves emerge from the spinal cord; carry impulses to the spinal cord and to muscles, organs, and glands

White matter

Myelinated neurons in the CNS

Gray matter

Unmyelinated neurons in the CNS

Dorsal roots of spinal cord

Contain sensory neurons entering the cord

Ventral roots of spinal cord

Convey motor outputs from CNS to PNS

Where are the cell bodies of sensory neurons located?

Outside the CNS in ganglia

Where are the cell bodies of motor neurons located?

In the CNS (brain and spinal cord)

Autonomic nervous system

Part of the PNS that controls involuntary movements such as cardiac and smooth muscle contractions

Sympathetic nervous system

Stimulates involuntary body processes (fight or flight)

Parasympathetic nervous system

Inhibits involuntary body processes (rest and digest)

Enteric nervous system

Regulates involuntary activities in the GI tract

Submucosal (Meissner) plexus

In GI submucosa; controls glandular secretion of mucosa and movements of muscularis

Myenteric (Auerbach) plexus

Between the two layers of the GI muscularis;

controls peristalsis and other contractions of muscularis

Glial cells

Cells in the nervous system that support, nourish, and protect neurons

Oligodendrocytes

Cells in the CNS that produce myelin --> ensures efficient transmission of action potentials

Astrocytes

Cells in the CNS that support neurons --> provide nutrients and insulation

Microglial cells

Cells in the CNS --> remove debris from injured or dead cells

Schwann cells

Cells in the PNS that produce myelin --> ensures efficient transmission of action potentials

Somatosensory System Function

Relays sensory information from the body tissues to the CNS

General Somatic Afferent Neurons

Convey sensations of pain, touch & temperature; located all over the body

Special Somatic Afferent Neurons

Convey information about sight, sound, and balance; located in eyes and ears

General Visceral Afferent Neurons

Convey sensations of fullness and discomfort; located in organs

Special Visceral Afferent Neurons

Convey sensations of taste and smell; located in taste buds and olfactory mucosa

First-order neurons

Detect stimulus and transmit signal to spinal cord or brainstem; form sensory units

Second-order neurons

Transmit impulses from the spinal cord/brainstem to the thalamus or cerebellum; form ascending pathways

Third-order neurons

Transmit impulses from the thalamus to the primary somatosensory area of the cortex; form central processing center

Sensory unit

A single afferent neuron plus all of the receptors it innervates

Cell body of sensory neuron

Part of the neuron that contains the nucleus; located in the dorsal root ganglia of spinal cord

Peripheral branch

Axon that extends from the cell body to the sensory receptor

Central branch

Axon that extends from the cell body to the dorsal horn of spinal cord

Six types of tactile receptors in skin

Touch, temp, pressure, movement, vibration, stretching

Dermatome

Area of skin supplied by a single spinal nerve

Ascending pathways

Conveys sensory information from the spinal cord to the thalamus

Discriminative pathway

Communicates sensory information about discriminative touch and spatial orientation; contains dorsal root ganglia (1st order), dorsal column neurons (2nd order), and thalamic neurons (3rd order)

Spinothalamic pathway

Communicates information about skin temperature, non-discriminative touch and pain from the spinal cord to the brain

Neospinothalamic tract

3 neurons --> fast impulses; communicates acute pain

Paleospinothalamic tract

Many neurons --> slow impulses; communicates chronic/dull pain

Primary somatosensory cortex

Receives raw sensory information from the thalamus

Secondary somatosensory cortex

Stores and transforms the raw sensory input into meaningful information

Pain

An unpleasant sensory and emotional experience associated with actual or potential tissue damage

Pain threshold

The point at which someone perceives a stimulus as painful; consistent between individuals

Pain tolerance

Maximum intensity or duration of pain that someone is willing to endure before seeking relief; varies among individuals

Pain receptors (nociceptors)

Respond to tissue damage (mechanical, electrical, or thermal stimuli)

Unimodal nociceptors

Respond to one type of stimulus only (mechanoreceptive, thermoreceptive, OR chemoreceptive )

Polymodal nociceptors

Respond equally to all kinds of damaging stimuli

A-delta fibers

Large, myelinated axons, conduct impulses quickly (10 to 30 m/s)

C fibers

Small, unmyelinated axons, conduct impulses slowly (0.5 to 2.5 m/s)

Endogenous Pain Inhibition

The ability to inhibit the perception of pain without the use of pain meds

Endogenous opioid peptides

Chemicals produced by the brain --> bind to opioid receptors in the spinal cord --> prevent transmission of sensory pain impulses up the ascending spinothalamic pathway

Descending inhibitory pathways

Neural pathways from the brain to the dorsal horns --> activation of the pathway prevents transmission of pain impulses up the ascending spinothalamic tract --> prevents transition from acute to chronic pain

Somatic pain

What: Pain that originates from skeletal muscles, ligaments, or joints

Etiology: Stimulation of somatic nociceptors

Cutaneous pain

What: Superficial pain usually involving the skin or subcutaneous tissue

Quality: Sharp, burning, well localized

Deep pain

What: Pain that occurs in tissues below skin level

Quality: Dull, aching, poorly localized

Visceral pain

What: A poorly localized, dull, or diffuse pain that arises from the abdominal organs, or viscera

Quality: Squeezing pain, poorly localized

Etiology: Stimulation of visceral nociceptors by strong contractions, distention, or ischemia affecting the walls of organs

Acute pain

What: Pain that lasts for

Chronic pain

What: Pain that lasts for >6 months

Course: Continuous

Purpose: Nothing useful, causes physical and psychological stress

Etiology: Persistent stimulation of nociceptors in chronic disorders (e.g. arthritis, cancer)

Referred Pain

What: Pain that is perceived at a location other than its site of origin

Etiology: ??

Hyperesthesia

Increased sensitivity to tactile stimulation (touch) due to irritation of the peripheral nerves

Hypoesthesia

Decreased touch sensation

Anesthesia

Loss of feeling or sensation

Hyperalgesia

Increased sensitivity to pain

Hypoalgesia

Decreased pain sensation

Analgesia

Pain relief; inability to feel pain

Neuropathic Pain

What: Pain that occurs when nerves are affected by injury or disease

Quality: Burning, stabbing pain

Etiology: Neurotoxic drugs, nerve compression, reactivation of varicella-zoster virus, uncontrolled diabetes

Trigeminal neuralgia

Compression of the trigeminal nerve by a blood vessel --> unilateral, excruciating face pain during talking/smiling

Post-herpetic neuralgia

Reactivation of latent varicella-zoster virus in the dorsal root ganglia neurons --> unilateral, painful, rash on the neck or chest (shingles)

Allodynia

Pain following a non-noxious, often repetitive stimulus that is not usually known to provoke pain (showering or bathing, wearing clothes, touching sheets on lying down)

Dynamic Allodynia

Pain that results from an object moving across the skin

Static/Tactile Allodynia

Pain that results from gentle touch/pressure

Thermal Allodynia

Pain that results from mild changes in environmental temperature

Phantom Limb Pain

Pain in a limb (or extremity) that has been amputated

Tension Headache

What: Dull aching pain in the head, face or neck lasting for 30 minutes to 7 days

S+S: A sense of tightness/pressure around forehead

Cause: Physical/emotional stress, overexertion

Migraine Headache

What: Severe throbbing pain in the head lasting for 1 to 2 days

S+S: Nausea and vomiting, or sensitivity to light and sound, aura?

Causes: Periods, alcohol?

Aura

Temporary visual, motor, sensory, or verbal disturbances that occur during migraines

Cluster headache

What: Headaches occur in clusters over days/weeks

S+S: Excruciating pain behind the eye or cheek; occasional eyelid swelling, conjunctival redness, lacrimation, and a runny nose

Chronic daily headache

Headaches that occur 15 days or more per month

Numerical rating scale

Patient is asked to verbally rate their level of pain from 0 to 10

Visual analog scale

Patient is asked to mark an X on a scale that aligns with their level of pain

Wong-Baker faces scale

Patient is asked to point to the picture that best represents their level of pain

Non-pharmacologic pain management

Deep breathing, massage, acupressure, acupuncture

Pharmacologic pain management

Nonopioids, NSAIDs, opioids, hypnotics/sedatives

Pain Assessment

Onset, provocation/palliation, quality, region/radiation, severity, timing