Nervous System Organization and Function (3A) - Bio & Biochem

1. Which glial cells myelinate axons in the peripheral nervous system?

   Schwann cells. These PNS glial cells individually myelinate axons, aiding in nerve regeneration and signal conduction.

2. What is the functional difference between afferent and efferent neurons?

   Afferent: sensory to CNS; efferent: motor from CNS. Afferent neurons transmit signals toward the CNS for integration, while efferent carry commands away to effectors.

3. What are the two major anatomical divisions of the nervous system?

   Central nervous system and peripheral nervous system. The nervous system is anatomically divided into central components for processing and peripheral for communication with the body.

4. Which ANS division is associated with "fight-or-flight" physiology?

   Sympathetic nervous system. This division mobilizes energy resources and prepares the body for emergency responses through widespread activation.

5. What are the two divisions of the autonomic nervous system (ANS)?

   Sympathetic and parasympathetic. The ANS is subdivided into antagonistic branches that balance physiological responses to stress and relaxation.

6. What is the neurotransmitter released by all preganglionic ANS neurons?

   Acetylcholine (ACh). Preganglionic neurons in both ANS divisions use this neurotransmitter to synapse with postganglionic neurons at ganglia.

7. What structures make up the central nervous system (CNS)?

   Brain and spinal cord. The CNS integrates sensory information and coordinates responses, consisting of protected neural tissues.

8. Which ANS division is associated with "rest-and-digest" physiology?

   Parasympathetic nervous system. This division conserves energy and promotes maintenance activities like digestion during non-stressful states.

9. What is the primary immune-like phagocytic cell type in the CNS?

   Microglia. These resident macrophages of the CNS engulf debris and pathogens to protect neural tissue.

10. What is the correct ion movement that causes depolarization in a neuron?

    Voltage-gated $Na^+$ channels open; $Na^+$ influx depolarizes. Threshold depolarization triggers sodium channel opening, allowing rapid sodium entry to reverse membrane potential.

11. What is the effect of opening ligand-gated $Cl^-$ channels on membrane potential?

    Hyperpolarization (inhibitory postsynaptic potential, IPSP). Chloride influx shifts the membrane potential more negative, reducing the likelihood of action potential generation.

12. Which brain region is the primary homeostatic control center for autonomic and endocrine output?

    Hypothalamus. This diencephalic structure integrates sensory inputs and regulates vital functions through neural and hormonal mechanisms.

13. Identify the direction of neurotransmitter release across a chemical synapse.

    From presynaptic axon terminal to postsynaptic membrane. Chemical synapses transmit signals unidirectionally via neurotransmitter diffusion across the synaptic cleft to receptor sites.

14. What structures make up the peripheral nervous system (PNS)?

    Cranial nerves, spinal nerves, and ganglia. The PNS connects the CNS to the rest of the body, facilitating sensory input and motor output through neural bundles and clusters.

15. Which glial cells myelinate axons in the central nervous system?

    Oligodendrocytes. These CNS glial cells wrap multiple axons to form myelin sheaths, supporting rapid neural signaling.

16. Which receptor class is activated by NE in most sympathetic target organs?

    Adrenergic receptors (alpha and beta). These G-protein coupled receptors mediate sympathetic responses by binding catecholamines like NE in effector organs.

17. What are the two main functional divisions of the efferent PNS?

    Somatic nervous system and autonomic nervous system. Efferent PNS divisions separate voluntary control from involuntary regulation of internal functions.

18. What neurotransmitter is typically released by sympathetic postganglionic neurons?

    Norepinephrine (NE). Sympathetic postganglionic fibers primarily release this catecholamine to elicit fight-or-flight effects on target tissues.

19. What is the primary role of astrocytes in the CNS?

    Support neurons and help maintain the blood-brain barrier. Astrocytes provide metabolic and structural support to neurons while regulating the extracellular environment and barrier integrity.

20. Which receptor type binds ACh at the skeletal muscle neuromuscular junction?

    Nicotinic acetylcholine receptor (nAChR). This ionotropic receptor triggers muscle contraction by allowing cation influx upon binding at the motor end plate.

21. What ion movement is primarily responsible for repolarization of the action potential?

    Voltage-gated $K^+$ channels open; $K^+$ efflux repolarizes. Following peak depolarization, potassium channels open to restore the negative membrane potential through potassium outflow.

22. What is the key difference between somatic and autonomic motor pathways?

    Somatic: skeletal muscle; autonomic: smooth/cardiac/glands. Somatic pathways enable conscious control of movement, whereas autonomic regulate involuntary visceral functions.

23. What neurotransmitter is typically released by parasympathetic postganglionic neurons?

    Acetylcholine (ACh). Parasympathetic postganglionic neurons release this neurotransmitter to mediate rest-and-digest responses in visceral organs.

24. What is the functional role of myelin in axons?

    Increases conduction velocity by insulating the axon. Myelin sheaths prevent ion leakage and enable faster signal propagation via saltatory conduction along axons.

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