Neural transmission depends on reliable electrical conduction within neurons and chemical signalling at synapses. When these steps are disrupted, messages become slowed, weakened, mistimed, or blocked, producing characteristic cognitive, sensory, or motor symptoms.

What “disrupted neural transmission” means

Neural communication can fail at two main points: signal conduction along the neuron and signal transfer between neurons (or between neuron and muscle). Disruption is often due to disease processes that alter the neuron’s insulation, synaptic chemistry, or receptor functioning.

Common disruption points

• Axon conduction problems

  • Damaged insulation slows or prevents action potential propagation.

  • Signals may “leak” or fail to reach terminals consistently.

• Synaptic transmission problems

  • Too little neurotransmitter released, excessive breakdown, or impaired vesicle release.

  • Receptors blocked, reduced in number, or structurally altered.

• Neuromuscular junction problems

  • The synapse between a motor neuron and skeletal muscle can fail, weakening movement.

Multiple sclerosis (MS): disrupted conduction in the CNS

MS is a major example of transmission failure caused by damage to myelin, the fatty insulation that increases the speed and reliability of neural signalling in the central nervous system (CNS).

Sagittal FLAIR brain MRI illustrating periventricular demyelinating lesions, with arrows marking white-matter plaques typical of multiple sclerosis. These plaques reflect areas where myelin has been damaged, which can disrupt efficient conduction across CNS pathways and contribute to variable sensory, motor, and cognitive symptoms. Source

With MS, demyelination makes action potentials less efficient. Depending on which CNS pathways are affected, symptoms can include muscle weakness, numbness/tingling, visual problems, fatigue, balance/coordination difficulties, and cognitive changes. Symptoms often fluctuate because inflammation and damage can occur in episodes.

Why myelin damage matters for transmission

Labeled drawing of a myelinated axon segment showing the node of Ranvier (a gap between myelin segments) and adjacent sheath structures. Nodes are where action potentials are regenerated in myelinated fibers; when myelin is lost, current leaks and conduction becomes slower and less reliable. Source

• Myelin normally supports rapid, energy-efficient conduction.

• When myelin is lost:

  • Signals slow, become unreliable, or stop.

  • Neurons may struggle to coordinate timing across networks, affecting complex behaviour and mental processes.

• The behavioural outcome depends on lesion location (e.g., motor pathways vs. sensory pathways).

Myasthenia gravis (MG): disrupted signalling to muscles

MG shows how neural transmission can be disrupted primarily at the neuromuscular junction, where motor neurons communicate with skeletal muscle fibres.

MG reduces the muscle’s ability to respond to the motor neuron’s signal. Because acetylcholine (ACh) is crucial for muscle contraction, blocking or reducing functional ACh receptors means that normal neural firing produces an abnormally weak muscle response.

Schematic of the neuromuscular junction (NMJ), highlighting the motor neuron terminal, synaptic vesicles, and postsynaptic acetylcholine (ACh) receptors on the muscle fiber. In myasthenia gravis, antibodies reduce effective ACh receptor function, so the same presynaptic signal produces a smaller postsynaptic response and weaker muscle contraction. Source

Typical effects linked to disrupted transmission in MG

• Weakness that worsens with use (fatigability), often improving with rest

• Difficulty with facial/eye muscles (e.g., drooping eyelids), swallowing, speaking, or limb movement

• Symptoms vary in severity depending on receptor impairment and muscle group demands

Connecting disruption to behaviour and mental processes

Disrupted neural transmission changes what the nervous system can do moment-to-moment:

• Motor effects: slowed movement, weakness, poor coordination, tremors, or paralysis (depending on pathway affected)

• Sensory effects: altered touch, pain, or vision due to unreliable sensory signalling

• Cognitive/affective effects: attention, processing speed, and mood can shift when communication across brain networks is less efficient

Key takeaway for AP Psychology

In both MS and MG, the core mechanism is the same syllabus idea: when neural transmission is disrupted, functioning changes. MS primarily disrupts CNS conduction (often via myelin loss), while MG primarily disrupts synaptic signalling to muscle (often via receptor interference).