Nervous System and Neurons

Nerve impulses travel unidirectionally from dendrites (receiving end) to cell body (integration center) to axon (transmission end). This direction is fundamental to neuronal function. Other sequences contradict the physiological flow of information through a neuron.

The vertebral column (spine) consists of stacked vertebrae that form a protective bony canal around the spinal cord. Meninges are membranes covering the brain and cord, while cranium and skull protect only the brain, not the spinal cord.

Correct Answer: peripheral nervous system

Synapses ensure unidirectional transmission because neurotransmitters are released only from the presynaptic neuron and bind only to postsynaptic receptors. This chemical one-way mechanism prevents backward signal flow. Nodes of Ranvier speed conduction, sodium pumps maintain resting potential, and nephrons are kidney structures.

Sensory neurons (afferent neurons) transmit signals FROM sensory organs TO the central nervous system. Motor neurons carry signals away from CNS to effectors. Relay neurons connect within CNS. Nerve impulse is the signal itself, not the structure carrying it.

Dendrites are the receptive endings of neurons that detect and receive information from the environment through sensory receptors. They transmit these signals toward the cell body, unlike axons which carry signals away from the neuron. Nerve endings and cytons serve different functions in neural transmission.

A synapse is the functional junction where an axon terminal of one neuron communicates with dendrites or cell body of another neuron. This is where neurotransmitters are released to continue the neural signal. Neuromuscular junctions are specialized synapses between neurons and muscles, while nodes of Ranvier are gaps in myelin sheath along axons.

The synapse is the critical junction where neural impulses are transmitted from neurons to target cells like muscle fibers or gland cells. At this specialized connection, neurotransmitters are released from axon terminals and bind to receptors on the target cell, completing the signal transmission. The cyton contains the nucleus, dendrites receive signals, and axons carry them, but the synapse enables final delivery.

The autonomic nervous system has two main divisions: sympathetic and parasympathetic. The sympathetic system prepares the body for 'fight or flight' responses during stress or emergencies, increasing heart rate and alertness. The parasympathetic system promotes 'rest and digest' functions during calm states, conserving energy and supporting digestion. These two systems work in balance to maintain homeostasis.

The central nervous system consists of two primary components: the brain and spinal cord. The brain processes information and coordinates activities, while the spinal cord transmits signals between the brain and peripheral nerves. Cranial and spinal nerves belong to the peripheral nervous system, connecting the CNS to the rest of the body.

Cerebrospinal fluid (CSF) acts as a transport medium, exchanging nutrients, oxygen, and waste products between blood vessels in the brain's ventricles and neural tissues. It provides mechanical cushioning, removes metabolic waste, and maintains chemical balance. Meninges are protective membranes, the vertebral column is bone, and aqueous humor is in the eye.

A neuron has three basic parts: dendrites (which receive signals), cell body or cyton (which contains the nucleus and processes signals), and axon (which transmits signals). Axon is clearly one of these three fundamental components. Myelin is a protective sheath around axons, pons is a brain region, and dura mater is a protective membrane - none are basic neuron parts.

The myelin sheath is a fatty layer that wraps around axons, providing electrical insulation and protection. Nodes of Ranvier are gaps in the myelin sheath, synapses are junctions between neurons, and axon terminals transmit signals to other cells - none of these insulate and protect the axon.

A relay neuron (interneuron) connects sensory neurons to motor neurons, processing and transmitting information in reflex arcs and neural pathways. Dendrites receive signals, axons transmit them, and cyton is the cell body - none of these directly pass information from sensory to motor neurons.

The cell body (also called cyton or soma) contains the nucleus and most of the cell's organelles. Dendrites and axons are extensions from the cell body, and nodes of Ranvier are gaps in the myelin sheath - none of these contain the nucleus.