Glial cells are the support crew of the nervous system. Neurons do the signaling, but they rely on these non-neuronal cells to keep the environment stable, supply nutrients, and shield neurons from damage. For instance, astrocytes help feed neurons and regulate the ion balance around synapses; oligodendrocytes and Schwann cells insulate axons with myelin to speed up transmission and protect them; microglia act as immune defenders and clean up debris. Ependymal cells are another type of glial cell, mainly lining brain ventricles and helping produce cerebrospinal fluid. Neurotransmitters are signaling chemicals, not cells. So the description fits glial cells.

Photoreceptors respond to light by hyperpolarizing, not by firing action potentials. In darkness they are depolarized because cGMP keeps Na+ channels open, so they continuously release the neurotransmitter glutamate. When light hits the photoreceptors, a phototransduction cascade lowers cGMP levels, closing those channels. That causes the cell to become more negative inside (hyperpolarize) and release less glutamate. This shift in neurotransmitter release alters the signaling to bipolar and ganglion cells, helping the brain detect changes in light. The key idea is that light causes hyperpolarization and a decrease in glutamate release, which is why this option is correct.

The main idea here is how signaling speed and precision differ between the nervous system and the endocrine system. The nervous system uses rapid electrical impulses that travel along neurons, with neurotransmitters released at synapses to produce effects on specific muscles or glands. These responses are fast and typically short-lived, and they act very precisely on targeted effectors. That contrasts with the endocrine system, which releases hormones into the bloodstream; these hormones can reach many tissues, generally taking longer to produce effects and often lasting longer, though they can still be specific when receptors are present. The statement that nervous signals are fast and short-lived with precise effects on specific muscles or glands best captures this contrast. The other ideas mischaracterize the systems: nervous signaling isn’t slow and hormone-based, endocrine signals aren’t limited to the brain, and the speeds of signaling aren’t the same in the two systems.

Afferent information travels from sensory receptors toward the central nervous system, and in the spinal pathway that input enters the CNS via the dorsal roots. The dorsal root contains the sensory (afferent) fibers, with their cell bodies located in the dorsal root ganglion just outside the spinal cord. In contrast, the ventral root carries motor (efferent) information from the spinal cord to muscles. The meninges are protective coverings around the CNS, not conduits for sensory signals, and the spinal cord is the processing center rather than the specific route for incoming sensory input. Therefore, the structure that carries afferent information is the dorsal root of the spinal nerve.