Final answer:
The brachial plexus is associated with the lower cervical and first thoracic spinal nerves. The correct approach for a peripheral nerve block at the brachial plexus depends on the specific procedure. Upper motor neurons target lower motor neurons, and damage to these neurons can result in muscle movement disorders with preserved muscle tone.
Step-by-step explanation:
The brachial plexus is a nerve plexus associated primarily with the lower cervical spinal nerves and first thoracic spinal nerve. When addressing the original question, "PNB's are approached at the brachial plexus at the (lower/upper) point along its path," it refers to interventions such as peripheral nerve blocks (PNBs) that may target either proximal (upper) or distal (lower) points along the path of the nerve plexus. However, the question as it stands lacks clear context to determine the correct answer without additional information on the specific PNB procedure being referenced.
Addressing other questions: The target of an upper motor neuron is indeed the lower motor neuron, with upper motor neurons originating in the cerebral cortex and descending to synapse on lower motor neurons, which then innervate skeletal muscles. A motor disorder where the arm cannot be moved voluntarily, but muscle tone is present, likely indicates damage to the upper motor neuron, because lower motor neuron damage typically results in flaccid paralysis and a lack of muscle tone.
The right ventricle sends blood to the lungs for oxygenation.