The Spinal Cord Structure and Function

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Questions and Answers

Where does the spinal cord originate from?

Cerebellum

Brain stem

Medulla oblongata (correct)

Cerebrum

What type of neurons have their cell bodies in the ventral horn of the spinal cord and use acetylcholine as their neurotransmitter?

Lower Motor Neurons (correct)

Sensory neurons

Upper Motor Neurons

Interneurons

What is the name of the nerve fibers that project from the end of the spinal cord beyond L1?

Cauda Equina (correct)

Ventral Roots

Conus Medullaris

Dorsal Roots

What is the primary function of the dorsal horn of the gray matter in the spinal cord?

Processing sensory information from the body Signup and view all the answers

What is the level of the vertebral column where the spinal cord terminates in adults?

L1 Signup and view all the answers

What type of neurotransmitter is used by Upper Motor Neurons?

Glutamate Signup and view all the answers

Which type of reflex arc is responsible for maintaining posture?

Stretch reflex Signup and view all the answers

In the Golgi Tendon Reflex, what is the primary function of the sensory receptors?

To sense if there is too much muscle tension Signup and view all the answers

Which of the following is NOT a part of the stretch reflex arc?

Dorsal Column pathway Signup and view all the answers

What is the primary function of the ascending information pathway in the stretch reflex arc?

To send afferent messages to the brain Signup and view all the answers

What is the clinical correlation of the stretch reflex?

It operates as a protective mechanism to prevent strain/tear of muscles and tendon Signup and view all the answers

Which of the following tracts is responsible for transmitting pain and temperature sensations?

Spinothalamic pathway Signup and view all the answers

What is the function of the Dermatomes in the spinal cord organization?

They are responsible for transmitting sensory information Signup and view all the answers

Which of the following tracts contains upper motor neurons?

Corticospinal tract Signup and view all the answers

Which of the following tracts carries information about pain and temperature?

Spinothalamic tract Signup and view all the answers

What is the primary difference between a complete and incomplete spinal cord injury?

The number of tracts affected Signup and view all the answers

Which of the following is a characteristic of a cord concussion?

Transient dysfunction of the spinal cord with rapid changes in velocity Signup and view all the answers

What is the most common location of cord contusions?

Cervical cord Signup and view all the answers

What is the primary cause of cord infarction?

Atherosclerosis Signup and view all the answers

What is the primary difference between primary and secondary cord injuries?

Timing of the injury Signup and view all the answers

Which of the following tracts is most lateral in the corticospinal tract?

Sacral neurons Signup and view all the answers

What is the most common location of spinal cord injuries?

C1-L2 Signup and view all the answers

What is the primary mechanism by which autoimmune diseases originate?

An initiating event in a genetically predisposed individual Signup and view all the answers

What is the characteristic of autoantibodies in Systemic Lupus Erythematosus?

They are primarily against nucleic acids, histones, ribonucleoproteins, and other nuclear materials Signup and view all the answers

What is the consequence of DNA deposition in the renal tubular basement membranes in Systemic Lupus Erythematosus?

It results in the deposition of immune complexes, causing inflammatory lesions Signup and view all the answers

What is the most common complication of hematologic abnormalities in Systemic Lupus Erythematosus?

Anemia Signup and view all the answers

What is the percentage of Systemic Lupus Erythematosus patients who develop cardiovascular diseases?

30-50% Signup and view all the answers

What is the frequency of arthralgias or arthritis in Systemic Lupus Erythematosus patients?

90% or more Signup and view all the answers

What is the hallmark of the osteoarthritic process?

Loss of proteoglycans from articular cartilage Signup and view all the answers

Which joint disease is characterized by the presence of monosodium urate crystals in connective tissues throughout the body?

Gout Signup and view all the answers

What is the primary pathogenesis in Osteoarthritis?

Degeneration, loss, and disordered repair of articular cartilage Signup and view all the answers

What is the leading cause of disability in middle-aged and older populations in the US?

Osteoarthritis Signup and view all the answers

Which of the following is a characteristic of Osteoarthritis?

Local areas of loss and damage of articular cartilage Signup and view all the answers

What is the effect of the loss of proteoglycans from articular cartilage in Osteoarthritis?

Disrupts the regulation of water and synovial fluid movement into and out of the cartilage Signup and view all the answers

What is the clinical manifestation of Gout in the great toe metatarsophalangeal joint?

Severe pain, swelling, tenderness, and erythema Signup and view all the answers

What is the effect of increased water content in cartilage with normal aging?

Affects the strength of the cartilage Signup and view all the answers

What is the composition of the matrix in cartilage?

Collagen and proteoglycans Signup and view all the answers

What is the primary function of Chondrocytes in the articular cartilage?

To maintain the structure of the articular cartilage Signup and view all the answers

Study Notes

The Spinal Cord

Lies within the vertebral column and is covered by the meninges
Originates in the medulla oblongata and carries two types of information: efferent motor neuron outputs from the brain and afferent sensory neural inputs to the brain from the body
In the adult, the spinal cord extends to the lower border of L1, with the conus medullaris located at L1/L2 and the cauda equina consisting of nerve fibers projecting from the end of the spinal cord to S5

Gray Matter Horns

Dorsal horn: contains axons and interneurons of sensory (afferent) neurons, with sensory fibers traveling through the dorsal roots to the posterior horn of the gray matter
Ventral horn: contains cell bodies for motor (efferent) pathways leaving the spinal cord, with motor fibers traveling out through the ventral roots from the anterior horn of the gray matter

Upper and Lower Motor Neurons

Upper motor neurons: cell bodies located in the motor cortex of the brain, with axons reaching down to a certain vertebral level in the corticospinal tract, crossing from one side of the body to the other at the level of the brain stem, and using glutamate as their neurotransmitter
Lower motor neurons: cell bodies located in the ventral horn of the spinal cord, with axons reaching out into the peripheral nervous system (PNS) and using acetylcholine as their neurotransmitter at the neuromuscular junction

Spinal Reflexes

Definition: involuntary, near-instant response to a stimulus that does not involve input from the brain
Types of reflex arcs:
- Autonomic - visceral organs
- Somatic
- Stretch - plays a major role in maintaining posture, including the deep tendon reflex (e.g., patellar tendon reflex) and the Golgi tendon reflex
- Crossed extensor - helps the body compensate for a stimulus on one side of the body
- Flexor/Withdrawal - withdrawal in response to a noxious stimulus

Stretch Reflex Arc

Four processes:
- Monosynaptic response: information only goes through one synapse, involving the stretch of a muscle, sending an afferent message to the spinal cord, and receiving an efferent message to contract the muscle
- Reciprocal innervation: opposing muscle groups receive an efferent message to relax
- Synergistic muscle recruitment: accessory muscle groups receive an efferent message to help with the extension of the leg
- Ascending information: afferent fibers travel from the spinal cord up to the brain to process the event

Clinical Correlation - Stretch Reflex

Operates as a protective mechanism to prevent strain or tear of muscles and tendons
Clinically, reflexes can provide information about the spinal cord, peripheral nerves, and muscle tone/strength

Spinal Cord Organization

Dermatomes and myotomes:
- Sensory: dermatomes
- Motor: myotomes
We can predict deficits someone will have from an injury using dermatomes and myotomes
Ascending and descending tracts:
- Ascending tracts: afferent/sensory
- Descending tracts: efferent/motor

Ascending and Descending Tracts

Afferent pathways (ascending):
- Spinothalamic: vague touch, pain, temperature, with fibers decussating immediately at their level of entry into the spinal cord
- Dorsal columns: basic perception of touch, proprioception, vibration, with fibers crossing at the medulla
Efferent pathways (descending):
- Corticospinal tracts: efferent/motor control below the head, containing upper motor neurons, with some fibers staying ipsilateral and traveling in the anterior corticospinal tract, and most fibers crossing at the medulla to travel down the lateral corticospinal tract

Spinal Cord Injuries

Complete vs incomplete spinal cord injury:
- Complete spinal cord transection: interrupting all three tracts with complete loss of motor/sensory function below the level of injury
- Incomplete spinal cord injury: variable degree of dysfunction due to only part of the spinal cord being affected, with some tracts still intact and others disrupted
Types of spinal cord injuries:
- Cord concussion: transient dysfunction of the spinal cord with or without vertebral damage and no pathologic changes, resolving within 48 hours
- Cord contusion: bruise caused by crushing of the spinal cord, leading to bleeding, edema, and tissue death, with severity depending on the integrity of remaining nerve fibers
- Cord compression: pressure on the spinal cord from an external source, such as bone, ruptured/herniated vertebral disks, hematoma, abscess, or tumor
- Cord transection: tear within the spinal cord itself due to traumatic injury, compromising blood supply and CSF, with clinically complete loss of motor/sensory function below the level of injury (if complete transection)
- Hemorrhage: typically due to trauma or vascular malformation, most commonly seen in the central gray matter at the point of impact, leading to further injury due to edema and cord infarction
- Infarct: blockage of vertebral arteries due to atherosclerosis, inflammation, or blood clots, leading to tissue death
- Evolution of spinal cord injury: primary cord injury (the actual trauma/compression/transaction) and secondary cord injury (a cascade of events leading to swelling and tissue destruction)

Autoimmune Reaction and Autoimmune Diseases

Autoimmune reaction causes inflammation in areas of the body where it is not needed, leading to pain, swelling, and organ damage
Autoimmune diseases originate from an initiating event in a genetically predisposed individual, leading to an autoimmune mechanism that affects specific target tissues or cells

Systemic Lupus Erythematosus (SLE)

More common in women (10:1) and in people aged 20-40
Characterized by frequent remissions and exacerbations
A chronic, multisystem, inflammatory disease
Pathophysiology involves production of a large variety of autoantibodies, including ANA, anti-DS DNA, anti-Smith, and APLA
Autoantibodies are against nucleic acids, histones, ribonucleoproteins, and other nuclear materials
Most common clinical manifestations:
- Arthralgias or arthritis (90%)
- Vasculitis and rash (malar and discoid)
- Renal disease (40% to 50%)
- Hematologic abnormalities (50% with anemia being the most common complication)
- Cardiovascular diseases (30% to 50%)
Diagnosis is difficult due to intermittent and widespread symptoms
serial or simultaneous presence of at least four of 11 common clinical findings indicates SLE

Arthropathies

Joint diseases
Types:
- Non-inflammatory arthropathy (Osteoarthritis)
- Inflammatory Arthropathies (Rheumatoid Arthritis, Gout, Ankylosing Spondylitis)

Osteoarthritis

Most common joint disease
Leading cause of disability in middle-aged and older populations in the US
Most often affects knees, hip, neck, hands, and lower back
Characterized by:
- Local areas of loss and damage of articular cartilage
- Bone spurs (osteophytes)
- Subchondral bone changes
- Variable degrees of mild synovitis
- Thickening of the joint capsule
Susceptibility factors:
- Joint Vulnerability: systemic factors (Age, Female, Genetics, Nutritional factors)
- Joint Vulnerability: Intrinsic Factors (Previous damage, muscle weakness, malalignment, proprioception deficiency)
- Joint load factors (Obesity, Physical activities prone to injury)
Pathogenesis:
- Primary pathogenesis is degeneration, loss, and disordered repair of articular cartilage
- Higher levels of pro-inflammatory markers and cascade of cytokine, biochemical, and growth factor pathways
- Chondrocytes of the articular cartilage become damaged
- Loss of proteoglycans from articular cartilage is a hallmark of the osteoarthritic process
Cartilage composition:
- Water + Matrix
- Matrix: Collagen + Proteoglycans
Clinical manifestations:
- Joint pain and stiffness
- Stiffness in morning and usually brief

Gout

Clinical manifestations:
- Increase in serum urate concentration
- Recurrent attacks of monoarticular arthritis
- Severe pain, swelling, tenderness, erythema
- 50% of initial attacks are in great toe metatarsophalangeal joint
- Tophi: Deposits of monosodium urate in and around the joints
- Renal disease involving glomerular, tubular, and interstitial tissues and blood vessels
- Formation of renal stones
3 Clinical Stages:
- Asymptomatic Hyperuricemia
- Acute Gouty Arthritis
- Tophaceous Gout

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Description

Exploring the spinal cord's location, role in transmitting information, and anatomy, including the conus medullaris and cauda equina.