Final answer:
The third order neuron lies in the brain, often in the thalamus, and it carries sensory information to the sensory cortex. Neuron A is part of the CNS that forms a chemical synapse with neuron B in the spinal cord, and the nerve carrying impulses from neuron B to skeletal muscle is part of the PNS and functions as an efferent nerve.
Step-by-step explanation:
The third order neuron resides in the brain. Specifically, it is part of the pathway in sensory systems where three neurons are generally involved in transmitting information from the sensory receptors to the brain. The first order neuron conducts the sensations from the periphery to the spinal cord, where it synapses with the second order neuron. This second order neuron then transmits the signals to various parts of the brain, including the thalamus. The third order neuron, which lies within the brain, particularly in the thalamus, then carries the sensory information to the sensory cortex for perception.
Answering parts of the given information:
- c. The part of neuron A that travels to the spinal cord to meet neuron B is the axon of neuron A.
- d. The signal from neuron A is transmitted to neuron B through a chemical synapse, which involves the release of neurotransmitters that cross the synaptic cleft to bind to receptors on the post-synaptic neuron's membrane.
- e. Neuron A is in the central nervous system (CNS) before it reaches the synapse at the spinal cord.
- f. The axon of neuron B travels in a nerve to a skeletal muscle cell, and the nerve is part of the peripheral nervous system (PNS). This would be an efferent nerve because it is carrying motor commands from the CNS to the skeletal muscle.
The central nervous system consists of the brain and spinal cord, while the peripheral nervous system connects the CNS to the rest of the body, and includes both the autonomic and sensory-somatic nervous systems.