Final answer:
Signal propagation in the nervous system is best modeled as electrochemical signal transmission. Sensory transduction converts stimuli to electrical signals that travel through the PNS to the brain. Synapses between neurons predominantly use chemical communication via neurotransmitters. Option d is the correct answer.
Step-by-step explanation:
The student's question relates to how signal propagation in the nervous system can be modeled. The nervous system uses electrochemical signal transmission to convey messages. This process involves both electrical and chemical changes. Sensory transduction is the conversion of a stimulus to an electrical signal by the sensory receptors, which is then transported through the nervous system. For example, when you touch a hot object, sensory receptors in your skin convert that thermal stimulus into an electrical signal that travels through the peripheral nervous system (PNS) to the brain.
The term chemical synapse refers to the point where two neurons meet and communication takes place with the release of neurotransmitters. These chemicals are released at the axon terminals of the neuron, which then bind to receptors on the dendrites of the next neuron, transmitting the signal across the synapse. This is distinct from an electrical synapse, where the communication is purely electrical and much faster but less common than chemical synapses.
Furthermore, in terms of sensory signal processing, after a sensory signal has undergone transduction, it travels through the brain as an electrical signal. It's important to understand that while the transmission between neurons is typically chemical at the synapses, the signal within a neuron is electrical.
The nervous system is categorized into the CNS and PNS. The CNS consists of the brain and spinal cord, while the PNS involves nerves that extend to and from the CNS to the rest of the body. Nerves in the PNS can be either afferent, carrying signals toward the CNS, or efferent, carrying instructions from the CNS to effectors such as muscles.