Overview
This lecture covered the structure and function of the nervous system, focusing on neural tissues, synapses, spinal cord anatomy, and key clinical concepts relevant for nurses.
Organization of the Nervous System
- The nervous system is divided into the central nervous system (CNS: brain and spinal cord) and the peripheral nervous system (PNS: cranial and spinal nerves).
- CNS includes the brain and spinal cord; PNS includes nerves that arise from the brain (cranial nerves) and spinal cord (spinal nerves).
- There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.
Neural Tissues and Cells
- Neurons (nerve cells) transmit nerve impulses and consist of dendrites, a cell body, and an axon.
- Neuroglia (glial cells) support neurons but do not transmit impulses.
- In the PNS, Schwann cells provide myelination, and satellite cells are found in ganglia (bundles of neuron cell bodies).
- Myelin is a lipid substance that insulates axons and speeds up impulse conduction by allowing impulses to jump at the nodes of Ranvier.
- In the CNS, oligodendrocytes provide myelin, astrocytes help form the blood-brain barrier, microglia act as phagocytes, and ependymal cells produce cerebrospinal fluid (CSF).
Synapses and Neurotransmitters
- A synapse is the junction between neurons or between a neuron and an effector cell.
- Synaptic vesicles at axon tips contain neurotransmitters such as dopamine, acetylcholine, serotonin, adrenaline, and GABA.
- Neurotransmitters bind to specific receptors (e.g., dopaminergic, cholinergic, adrenergic).
- Dopamine deficiency can cause Parkinson’s disease; low serotonin is linked to depression.
- SSRIs (like Prozac) increase serotonin levels by inhibiting its reuptake.
Spinal Cord and Meninges
- The spinal cord is protected by the vertebral column and three meninges: dura mater (tough outer layer), arachnoid mater (middle, spiderweb-like layer), and pia mater (inner layer on the cord surface).
- The epidural space (above the dura) contains fat and blood vessels; the subarachnoid space (below the arachnoid) contains CSF.
- Epidural anesthesia is injected into the epidural space; spinal anesthesia is injected into the subarachnoid space.
- CSF leakage after a spinal tap can cause a spinal headache; bed rest helps prevent this.
Clinical Correlations and Pathways
- Polio affects anterior horn cells (ventral horn), leading to paralysis.
- Sensory nerve tracts (ascending, afferent) carry impulses to the brain; motor tracts (descending, efferent) carry impulses from the brain.
- Sensory signals often cross sides in the medulla, so each brain hemisphere controls the opposite side of the body.
Key Terms & Definitions
- Neuron: nerve cell that transmits impulses.
- Neuroglia (glial cell): supports and protects neurons.
- Myelin: fatty sheath that speeds impulse conduction.
- Synapse: junction between neurons.
- Neurotransmitter: chemical messenger in synapses.
- Meninges: three protective layers around the CNS.
- Epidural space: area above the dura mater, site for epidural anesthesia.
- Subarachnoid space: area beneath the arachnoid mater, contains CSF.
- Afferent (sensory) tract: carries impulses toward the CNS.
- Efferent (motor) tract: carries impulses from the CNS to muscles or glands.
Action Items / Next Steps
- Review chapters 13, 14, and 15, focusing on neural tissue, synapses, and spinal cord structures.
- Complete the provided study guide and prepare for the midterm exam (chapters 1–15, excluding 12).
- Reinforce understanding by creating concept maps without using notes or textbooks.