Nervous System PDF

Nervous System A. General Functions of the Nervous System 1. Sensory Input: Detects internal and external stimuli via sensory receptors. 2. Integration: Processes and interprets sensory information to make decisions. 3. Motor Output: Initiates responses by activating muscles or glands. B. Centr...

Nervous System A. General Functions of the Nervous System 1. Sensory Input: Detects internal and external stimuli via sensory receptors. 2. Integration: Processes and interprets sensory information to make decisions. 3. Motor Output: Initiates responses by activating muscles or glands. B. Central Nervous System (CNS) vs. Peripheral Nervous System (PNS) - CNS: Composed of the brain and spinal cord; functions in processing and integrating information. - PNS: Includes cranial and spinal nerves; relays information to and from the CNS. C. Motor (Efferent) vs. Sensory (Afferent) - Motor (Efferent): Sends signals from the CNS to muscles or glands to trigger action. - Sensory (Afferent): Transmits sensory information from receptors to the CNS. D. Nervous System as a Control System - Sensory Receptors detect changes, which are sent through afferent pathways to the control center (CNS). The CNS processes this information and sends instructions via efferent pathways to effector organs (muscles or glands) to elicit a response. E. Somatic Motor vs. Autonomic Motor Division - Somatic Motor: Controls voluntary movements (skeletal muscles). - Autonomic Motor: Controls involuntary functions (smooth muscles, glands). F. Somatic Sensory vs. Visceral Sensory - Somatic Sensory: Detects external stimuli (skin, skeletal muscles). - Visceral Sensory: Detects internal stimuli (organs). G. Major Components of a Neuron - Cell Body: Contains the nucleus and cytoplasm; integrates information. - Dendrites: Receive incoming signals. - Axon: Transmits outgoing signals. - Axon Hillock: The origin of action potentials. - Chromatophilic Substance: Involved in protein synthesis. H. Three Structural Types of Neurons - Unipolar: Single process; sensory neurons in the PNS. - Bipolar: One axon, one dendrite; found in sensory organs (retina). - Multipolar: Several dendrites, one axon; most common in CNS. I. Three Functional Types of Neurons - Sensory Neurons (Afferent): Transmit sensory information to CNS. - Interneurons (Association): Process information within the CNS. - Motor Neurons (Efferent): Carry signals from CNS to effectors. J. Six Types of Neuroglial Cells - CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells. - PNS: Schwann cells, satellite cells. Each type has a specific role in support, protection, and myelination. K. Myelination Myelination involves wrapping the axon in myelin sheaths to speed up electrical conduction. In the CNS, this is done by oligodendrocytes, and in the PNS, by Schwann cells. L. Depolarization, Repolarization, Hyperpolarization, and Threshold - Depolarization: Na+ influx causing the inside of the membrane to become less negative. - Repolarization: K+ efflux restores the negative internal charge. - Hyperpolarization: Membrane potential becomes more negative than resting potential. - Threshold: Minimum voltage required to trigger an action potential. M. Sodium-Potassium Pump The pump maintains resting membrane potential by actively transporting 3 Na+ out and 2 K+ into the cell, keeping the inside of the neuron negatively charged. N. Major Ion Channels - Leak Channels: Always open, maintain resting potential. - Voltage-Gated Channels: Open in response to changes in membrane potential. - Ligand-Gated Channels: Open in response to neurotransmitters. - Mechanically Gated Channels: Open in response to mechanical force. O. Resting Membrane Potential The RMP is established by the differential distribution of Na+ and K+ ions, maintained by leak channels and the sodium-potassium pump. P. Graded Potentials vs. Action Potentials** - Graded Potentials: Local changes in membrane potential; can summate. - Action Potentials: All-or-nothing events that travel along the axon. Q. Absolute vs. Relative Refractory Periods - Absolute: No new action potential can be initiated. - Relative: A stronger-than-normal stimulus can initiate another action potential. R. Action Potential Conduction Action potentials propagate as voltage-gated Na+ and K+ channels open along the axon. S. Myelinated vs. Unmyelinated Axons - Myelinated: Saltatory conduction between nodes of Ranvier increases speed. - Unmyelinated: Continuous conduction, slower. T. Synapse - Electrical Synapse: Direct transmission via gap junctions. - Chemical Synapse: Neurotransmitters cross synaptic clefts. U. Synaptic Transmission 1. Action potential arrives at the axon terminal. 2. Ca2+ channels open. 3. Neurotransmitter release. 4. Neurotransmitter binds to receptors on the postsynaptic cell. V. Termination of Neurotransmitter Activity - Reuptake, enzymatic breakdown, or diffusionends the signal. W. Common Neurotransmitters - Excitatory: Glutamate, acetylcholine. - Inhibitory: GABA, glycine. X. Single Neurotransmitter Responses Neurotransmitters can have different effects depending on the type of receptor on the postsynaptic cell. Y. Gray vs. White Matter - Gray Matter: Neuron cell bodies, dendrites, and unmyelinated axons. - White Matter: Myelinated axons. Z. Tracts vs. Nerves / Nuclei vs. Ganglia - Tracts: Bundles of CNS axons. - Nerves: Bundles of PNS axons. - Nuclei: Clusters of neuron cell bodies in the CNS. - Ganglia: Clusters of neuron cell bodies in the PNS. 1. Layers of the Meninges The meninges are protective membranes surrounding the CNS (brain and spinal cord) and consist of three layers: - Dura Mater: The tough outermost layer, which is a thick, durable membrane. - Arachnoid Mater: The middle layer, a web-like membrane that provides a cushioning effect. - Pia Mater: The thin, delicate innermost layer, which is closely adhered to the surface of the brain and spinal cord. Functionally, these layers protect the CNS, contain cerebrospinal fluid (CSF), and support blood vessels. 2. Epidural, Subdural, and Subarachnoid Spaces - Epidural Space: Located between the dura mater and the skull/spinal column; in the spinal cord, it contains fat and blood vessels. - Subdural Space: Between the dura mater and the arachnoid mater; normally a potential space, it may fill with blood during injury (subdural hematoma). - Subarachnoid Space: Located between the arachnoid and pia mater; it contains cerebrospinal fluid (CSF) and blood vessels. 3. Dural Venous Sinuses Dural venous sinuses are channels located between layers of the dura mater, primarily found around the brain. These sinuses collect venous blood from the brain and direct it to the internal jugular veins for drainage. Major sinuses include the superior sagittal sinus, transverse sinus, and straight sinus. 4. Cranial Dural Septa The dura mater forms folds (septa) within the cranial cavity that provide stabilization and compartmentalization of the brain: - Falx Cerebri: Separates the two cerebral hemispheres. - Tentorium Cerebelli: Separates the cerebellum from the occipital lobes. - Falx Cerebelli: Separates the two halves of the cerebellum. 5. Cranial Bones and Vertebral Column in CNS Protection - Cranial Bones: The skull encloses the brain and acts as a hard protective casing. - Vertebral Column: Surrounds and protects the spinal cord, composed of vertebrae, and provides structural support. 6. Production, Flow, and Reabsorption of CSF** - Production: CSF is produced by the choroid plexus in the ventricles of the brain. - Flow: It flows through the ventricles, into the subarachnoid space, and around the brain and spinal cord. - Reabsorption: CSF is reabsorbed into the blood via arachnoid granulations into the dural venous sinuses. 7. General Functions of Cerebrospinal Fluid (CSF) - Cushioning and Protection: CSF acts as a shock absorber for the CNS. - Nutrient and Waste Transport: Helps in nutrient delivery and waste removal. - *Buoyancy: Reduces the effective weight of the brain, preventing compression. 8. Dura Mater Surrounding the Brain vs. Spinal Cord - Brain: Dura mater has two layers (periosteal and meningeal), forming sinuses in between. - Spinal Cord: Dura mater consists of a single layer and is separated from the vertebrae by the epidural space. 9. Major Parts of the Adult Brain - Cerebrum: Responsible for higher cognitive functions like thinking, sensation, and voluntary movements. - Diencephalon: Contains the thalamus and hypothalamus, responsible for sensory relay and homeostatic control. - Brainstem: Includes the midbrain, pons, and medulla, controlling vital functions such as heart rate and breathing. - Cerebellum: Coordinates movement and balance. 10. Cerebral Hemispheres and Lobes - Frontal Lobe: Involved in reasoning, motor control, and language. - Parietal Lobe: Processes sensory information. - Temporal Lobe: Responsible for hearing and memory. - Occipital Lobe: Processes visual information. - Insula: Involved in emotions and homeostasis. 11. Motor Speech Area (Broca's Area) vs. Wernicke's Area - Broca's Area: Located in the frontal lobe, responsible for speech production. - Wernicke's Area: Located in the temporal lobe, involved in language comprehension. 12. Autonomic Nervous System (ANS) vs. Somatic Nervous System (SNS) - Site of Origination: ANS originates from the brainstem and spinal cord; SNS originates in the motor cortex. - Number of Neurons: ANS involves two neurons (preganglionic and postganglionic); SNS involves one neuron directly innervating muscles. - Effectors: ANS affects smooth muscle, cardiac muscle, and glands; SNS affects skeletal muscles. - Receptors/Neurotransmitters: ANS uses acetylcholine and norepinephrine; SNS uses acetylcholine. 13. Divisions of the ANS - Sympathetic Division: Activates the "fight or flight" response, uses norepinephrine, has short preganglionic and long postganglionic fibers, originates in the thoracolumbar region. - Parasympathetic Division: Promotes "rest and digest" functions, uses acetylcholine, has long preganglionic and short postganglionic fibers, originates in the craniosacral region. 14. Components of the Sympathetic and Parasympathetic Divisions - Sympathetic: Includes the sympathetic trunk (chain ganglia), splanchnic nerves, and prevertebral ganglia. - Parasympathetic: Includes cranial nerves III, VII, IX, X, and pelvic splanchnic nerves, with terminal ganglia close to target organs. 15. Visceral Reflex Arcs - Sensory Component: Detects stimuli from internal organs and transmits to the CNS. - Motor Component: Involves two neurons (preganglionic and postganglionic) that modulate the function of visceral organs. 16. Role of the Nervous System in Homeostasis The nervous system regulates bodily functions to maintain homeostasis through mechanisms such as body temperature regulation and blood pressure control, in coordination with systems like the endocrine system. 17. Sympathetic vs. Parasympathetic Effects on Effectors - Heart: Sympathetic increases heart rate; parasympathetic decreases it. - Airways: Sympathetic dilates airways; parasympathetic constricts them. - Gastrointestinal Tract: Sympathetic inhibits digestion; parasympathetic promotes it. 18. Autonomic Tone Autonomic tone refers to the balance of sympathetic and parasympathetic activity in maintaining homeostasis, like regulating resting heart rate. 19. ANS and Stress Response The ANS mediates the body's response to stress. Chronic stress can lead to overactivation of the sympathetic division, contributing to health issues like hypertension, anxiety, and immune suppression.