Spinal Cord Injury Quiz

Alterations in Motor Function

• Definition: The study covers various disorders affecting the motor system, from its organization and control to specific diseases affecting the nervous system and muscles
• Overview: The motor system is a functional hierarchy with high levels (motor cortex) for planning movements and lower levels (spinal cord) to execute them; the cerebellum and basal ganglia contribute to coordination, timing, and accuracy.
• Motor System Organization: The brain's motor cortex, brainstem, cerebellum, and basal ganglia work together to plan and execute bodily movements, maintain posture, and respond to the environment.

Motor Cortex

• Function: Controls precise, skillful, and intentional movements (examples like typing and skillful actions).
• Components: Primarily, premotor, and supplementary motor areas found within the frontal lobe.
• Role in Movement: Involved in the planning and execution of intended activities.

Cerebellum & Basal Ganglia

• Function: The cerebellum refines movements and helps with timing, coordination, and accuracy. The basal ganglia control the initiation, execution, and termination of complex movement sequences in a smooth, graceful manner.
• Interactions: Together these structures ensure precise, coordinated movements.

Brainstem

• Function: Connects the cerebrum and cerebellum to the spinal cord; relays motor information.

Spinal Cord

• Function: Contains motor neurons that send efferent signals (motor commands) to muscles.
• Organization: Includes dorsal (sensory) roots and ventral (motor) roots.
• Action Potential: Provides pathways for neural signaling.

Descending Pathways

• Overview: Upper Motor Neurons (UMNs) project from the brain down to the lower motor neurons, facilitating motor control.
• Two Categories:
  • Pyramidal Tracts: Responsible for conscious, voluntary control of movements (head, face, and body muscles); these initiate voluntary movements.
  • Extrapyramidal Tracts: Control unconscious and automatic movements; these regulate posture and balance.
• Function of Pathways: UMNs send signals to LMNs for detailed movement.

Neuromuscular Junctions

• Function: LMN axons connect and initiate signals to the muscle fibers.
• Motor Unit: A motor neuron and all the muscle fibers it controls.
• Endplate Region: The axon terminal of a motor neuron and its receptors where signals are transmitted to contract the muscle.

Spinal Reflexes

• Action: Simple, involuntary responses to stimuli, occurring quickly and automatically
• Components:
  • Sensory receptors: Detect stimuli affecting body functions.
  • Sensory neurons: Relay information about stimuli to the spinal cord.
  • Integrating center: Interneurons in the spinal cord form a processing station; they interpret and analyze the data from the sensors.
  • Motor neurons: Send signals to muscles to initiate the response.
  • Effectors (muscles): Carry out the reflex movement.
• Types:
  • Monosynaptic: Only one synapse; quickly contracts muscle (eg, knee-jerk).
  • Polysynaptic: Multiple synapses; involves interneurons (eg, withdrawal reflex).
• Roles: Protective mechanisms, maintain posture and balance swiftly.

Upper Motor Neuron Disorders (UMN)

• Signs: Spasticity, clonus, hypertonia, and hyperreflexia can occur; babinski sign or fanning of toes occurs.
• Common Disorders: Multiple sclerosis, amyotrophic lateral sclerosis (ALS), and spinal cord injuries.
• Impact: Damage to UMNs impairs voluntary movement control, causing stiffness and overactive reflexes.

Multiple Sclerosis (MS)

• Definition: Autoimmune disorder that damages myelin in the CNS, particularly UMNs, affecting speed and transmission.
• Cause: Precise cause is unknown, but likely related to genetic predisposition and environmental factors.
• Pathophysiology: Destruction of myelin in the UMNs results in slowing or blocking nerve impulses.
• Symptoms: General symptoms (fatigue, dizziness, weakness); more specific symptoms such as brief, shocking sensations and difficulties moving, coordinating, or speaking can also arise.
• Complications: Leads to impairments in balance and coordination.

Amyotrophic Lateral Sclerosis (ALS)

• Definition: Progressive, neurodegenerative disease affecting the motor neurons (both UMN and LMN) of the brain and spinal cord, that causes muscle wasting and weakness.
• Cause: Exact cause is still debated, potentially stemming from multiple genetic or environmental factors (but 90-95% of cases are sporadic and not inherited.
• Pathophysiology: Degeneration of motor neurons in the spinal cord and brain; particularly the UMNs, and the degeneration of axons in the corticospinal tracts leads to progressive muscle weakness.
• Symptoms: Early symptoms include muscle stiffness, weakness and cramping; later symptoms arise such as slowed or slurred speech and swallowing difficulties (dysphagia).

Spinal Cord Injuries

• Types: Tetraplegia/quadriplegia, Paraplegia, spinal shock.
• Causes: Trauma (fractures or dislocations of vertebrae), forceful bending or compression of neck.
• Symptoms: Vary depending on the segment of the spinal cord injured and can include weakness or paralysis.

Disorders of the Cerebellum & Basal Ganglia

• Definition: Disorders or conditions related to the cerebellum or basal ganglia.
• Cerebellar Disorders:  Cerebellar ataxia and cerebellar tremor.

Cerebellar Ataxia

• Definition: Lack of coordination, characterized by wide-based and unsteady gait; and difficulty performing coordinated movements.
• Causes: Alcohol abuse and other brain conditions.

Cerebellar Tremor

• Definition: Visible tremors that worsen when approaching a target.
• Causes: Various conditions, including alcohol overdose.

Basal Ganglia Disorders

• Function: Control of slow, sustained movements; initiation, and execution. They are crucial for coordinating smooth movements and stopping skilled movements.
• Causes: Infections, genetic mutations, or drug overdose.

Parkinson's Disease

• Definition: Progressive disorder of the basal ganglia.
• Cause: Degeneration of dopamine-producing neurons in the substantia nigra; the exact cause remains unknown.
• Symptoms: Tremors, rigidity, bradykinesia (slowed movement), postural instability.

Lower Motor Neuron Disorders (LMN)

• Definition: LMN disorders affect the LMNs impacting muscle control.
• Signs: Muscle weakness, paresis, hypotonia, hyporeflexia/areflexia.
• Broad Categories: Myopathies (affecting muscle fibers), endplate disorders (neuromuscular junctions), peripheral neuropathies (axons of the LMNs), and ventral horn cell disorders (cell bodies of the LMNs).

Myopathies

• Examples: Muscle atrophy, muscular dystrophy.

Endplate Disorders

• Example: Myasthenia gravis

Peripheral Neuropathies/PNS

• Definition:  Conditions that damage nerves outside the brain and spinal cord.
• Examples: Carpal tunnel syndrome, Guillain-Barré syndrome.

Carpal Tunnel Syndrome

• Definition: Compresses the median nerve within the wrist's carpal tunnel; causing numbness and tingling (especially thumb and index fingers, and part of the ring finger) .
• Causes: Repetitive hand movements, inflammation.

Guillain-Barré Syndrome

• Definition: Autoimmune disorder that targets the myelin sheath, impacting multiple peripheral nerves.
• Symptoms: Progressive weakness that starts in the legs and ascends to the upper body.

Spinal Muscular Atrophy

• Definition: Progressive degeneration of LMN cell bodies in the spinal cord; causing muscle weakness and atrophy, starting as a child.
• Cause: Genetic mutations, leading to reduced availability of a protein needed for muscle function.
• Symptoms: Muscle weakness that becomes more extreme over time, typically beginning as an infant.

Muscle Atrophy

• Definition: Reduction in muscle fiber size due to reduced or lack of stimulation
• Types: Disuse atrophy (due to lack of exercise), Denervation atrophy (due to loss of nerve stimulation).

Muscular Dystrophy

• Definition: Inherited muscle disorders; affecting muscle fibers and leading to progressive weakness and disability.
• Types: Duchenne and Becker Muscular Dystrophies.
• Cause: Mutations in the dystrophin gene, which encodes a protein essential for maintaining muscle structure.
• Symptoms: Gradual muscle weakness; often beginning in childhood, resulting in decreased mobility, and in some cases requiring assisted movement. 

Myasthenia Gravis

• Definition: Autoimmune neuromuscular junction disorder that impairs neuromuscular transmission; causing weakness and fatigability in skeletal muscles.
• Cause: Damage to the acetylcholine receptors on the muscle causes the muscles to not get proper stimulation; Antibodies attack and damage the acetylcholine receptors on muscles.
• Symptoms: Muscle weakness; especially in the face, eyes, and throat; muscle weakness often worsens with exertion.

Test your knowledge on spinal cord injuries, including types of paralysis and common complications. This quiz covers essential concepts related to the impairment of motor functions and management strategies for spinal cord injuries.