ANAPHY-9-LEC-1 PDF - Nervous System

Major Functions of the Nervous System: 1. Receiving of sensory inputs 2. Integrating information 3. Controlling muscles and glands 4. Maintaining homeostasis 5. Establishing and maintaining mental activity Main Divisions of the Nervous System: (Refer to Figure 8.1, page 19...

Major Functions of the Nervous System: 1. Receiving of sensory inputs 2. Integrating information 3. Controlling muscles and glands 4. Maintaining homeostasis 5. Establishing and maintaining mental activity Main Divisions of the Nervous System: (Refer to Figure 8.1, page 193 of the book) 6. Central Nervous System (CNS) – consists of the brain and spinal cord. 7. Peripheral Nervous System (PNS) – consists of all the nervous tissue outside the CNS (nerves & ganglia). Sensory Division / Afferent Division – conducts action potentials from sensory receptors to CNS by sensory neurons. Motor Division / Efferent Division – conducts action potentials from the CNS to effector organs, such as muscles & glands by motor neurons. Somatic Nervous System – innervates skeletal muscles; mostly under voluntary control. Autonomic Nervous System – innervates cardiac muscle, smooth muscle, and glands; mostly under involuntary control. o Sympathetic Division o Parasympathetic Division o Enteric Nervous System (ENS) – subdivision of PNS that has both sensory and motor neurons contained wholly within the digestive tract. Cells of the Nervous System: 8. Neurons / Nerve Cells – receive stimuli, conduct action potentials, & transmit signals to other neurons or effector organs; has three parts: o Cell Body – contains a nucleus and processes stimulus. o Dendrites – extensions of the neuron cell body; receive stimulus from other neurons or from sensory receptors. o Axon – transmits stimulus to a gland, muscle, organ, or other neuron.  9. Glial Cells / Neuroglia – supportive cells of CNS & PNS; do not conduct action potentials; have other functions that enhance neuron function and maintain normal conditions. Types of Neurons & Glial Cells: (See table 8.1, page 195 and figures 8.4 & 8.5, pages 195- 196). Myelin Sheaths – fatty, protective wrapping around axons of some neurons that are formed by oligodendrocytes (CNS) and Schwann cells (PNS); serve as an excellent insulator and speeds up the propagation of action potentials. Nodes of Ranvier – gaps in the myelin sheath, where the ion movement occurs and action potential develops. Organization of Nervous Tissue: 10. Gray Matter – consists of groups of neuron cell bodies & their dendrites, where there is very little myelin. o Cortex – located on the surface of the brain. o Nuclei – clusters of gray matter located deeper within the brain. o Ganglion – a cluster of neuron cell bodies in the PNS. 11. White Matter – consists of bundles of parallel axons with their myelin sheaths, which are whitish in color. o Nerve Tracts / Conduction Pathways – found on the CNS which propagate action potential from one area of the CNS to another. o Nerves – bundles of axons located in the PNS. Electrical Signals of the Nervous System: include the resting membrane potential, action potential, synapse, and reflexes. Resting Membrane Potential – is the point of equilibrium at which the tendency for K⁺ to move down its concentration gradient out of the cell is balanced by the negative charge within the cell, which tends to attract the K⁺ back into the cell. This is generated by three main factors: 12. A higher concentration of K⁺ immediately inside the cell membrane. 13. A higher concentration of Na⁺ immediately outside the cell membrane. 14. Greater permeability of the cell membrane to K⁺ than to Na⁺. 15. A higher concentration of Na⁺ immediately outside the cell membrane.  16. Greater permeability of the cell membrane to K⁺ than to Na⁺. Sodium-Potassium Pump – is required to maintain the greater concentration of Na⁺ outside the cell membrane and K⁺ inside; occurs in order to compensate for the constant leakage of ions across the membrane. Two Basic Ion Channels: (See Process Figure 8.7, page 197 of the book) 17. Leak Channels – always open; K⁺ channels are much greater than Na⁺ channels. 18. Gated Channels – closed until opened by a specific signal: o Chemically Gated: opened by neurotransmitters or other chemicals. o Voltage-Gated: opened by a change in membrane potential (See Process Figure 8.8, page 198 of the book). Action Potential – occurs when a charge across the cell membrane is briefly reversed; generated by the opening of gated channels. Gated channels open due to stimulus applied resulting in Na⁺ channels open very briefly. Movement of Na⁺ inside the cell (Local Current). Inside of the cell becomes more positive (Depolarization). Once depolarization occurs, the local potential reaches the threshold value. All-or-None Action Potential is started. Voltage-gated Na⁺ channels open and depolarization continues at a much faster pace. Action potentials continue until a brief reversal of charge takes place (Na⁺ channels close, K⁺ channels open). Outward flow of K⁺ repolarizes the cell membrane to its resting membrane potential (Repolarization). Charge on cell membrane briefly becomes more negative than the resting membrane potential (Hyperpolarization). Sodium-Potassium Pump restored. Types of Action Potential Conduction: (See Process Figures 8.10 & 8.11, page 200) 19. Continuous Conduction – occurs in unmyelinated axons; an action potential in one part of a cell membrane stimulates local currents in adjacent parts. 20. Saltatory Conduction – occurs in myelinated axons; an action potential “jumps” from one node of Ranvier to the next along the length of the axon. Synapse – a junction where the axon of one neuron interacts with another neuron or with cells of an effector organ; involved in the release of neurotransmitter (ex: neuromuscular junction). Three Major Components: 21. Presynaptic Terminal – end of axon; has synaptic vesicles that store neurotransmitters. 22. Postsynaptic Membrane – membrane of the dendrite or effector cell. 23. Synaptic Cleft – space separating the presynaptic terminal & postsynaptic membrane. Action potentials arrive in presynaptic terminal: Voltage-gated Ca²⁺ channels open & Ca²⁺ moves into the cell. Influx of Ca²⁺ releases neurotransmitter by exocytosis. Neurotransmitters diffuse across the synaptic cleft & bind to specific receptor molecules in the postsynaptic membrane. Chemically gated channels (Na⁺, K⁺, or Cl⁻) open or close depending on: Type of neurotransmitter (See table 8.2, page 202). Type of receptors. Stimulation or Inhibition of action potential. Neurotransmitters (See table 8.2, page 202). Reflexes – involuntary reactions in response to a stimulus applied to the periphery & transmitted to CNS; allow a person to react to stimuli more quickly; no conscious thought is required. Reflex Arc – the neuronal pathway by which a reflex occurs; basic functional unit of the nervous system; smallest, simplest pathway capable of receiving a stimulus & yielding a response. Five Basic Components of Reflex Arc: (See Process figures 8.13, page 203) 24. Sensory Receptor – detects stimulus. 25. Sensory Neuron – afferent; sends stimulus to interneurons in spinal cord.  26. Interneurons – located in CNS and connect to motor neurons; process stimulus to some reflexes. 27. Motor Neuron – efferent; send response to effector. 28. Effector Organ – muscle or gland. Neuronal Pathways are divided into two simplest types: (See Process figures 8.14, page 203) 29. Converging Pathway – two or more neurons synapse with the same postsynaptic neuron; allows transmitted information in more than one neuronal pathway to converge into a single pathway. 30. Diverging Pathway – axon from one neuron divides & synapses with more than one other postsynaptic neuron; allows transmitted information in one neuronal pathway to diverge into two or more pathways. Summation – this allows the integration of multiple subthreshold local potentials from the signals in neuronal pathways which can bring the membrane potential to threshold & trigger action potential. Spatial Summation occurs when the local potentials originate from different locations on the postsynaptic neuron (ex: from converging pathways). Temporal Summation occurs when local action potentials overlap in time; from a single input that fires rapidly, which allows the local potentials to overlap briefly. Spinal Cord – extends from the foramen magnum at the base of the skull to the 2nd lumbar vertebra; protected by the vertebral column; its inferior end where the spinal nerves exit is called cauda equina (resembles a horse’s tail). Organization of Spinal Cord (See figure 8.16, page 205) Gray Matter – mainly collection of cell bodies at the center of spinal cord that is shaped like a butterfly or H structure; consists of four structures: a. Posterior Horns – contain axons which synapse with interneurons. b. Dorsal Root Ganglion – contains cell bodies of pseudo-unipolar sensory neurons & axons that originate in the periphery of the body; passes through spinal nerves to posterior horn of the spinal cord. c. Anterior Horns – contain somatic motor neurons. d. Lateral Horns – contain autonomic neurons. e. Central Canal – fluid-filled space in the center of the cord.  White Matter – located at the spinal cord periphery; each half is organized into three columns: dorsal (posterior), ventral (anterior), and lateral columns. Each column contains ascending and descending tracts/pathways: o Ascending Tracts – consist of axons that conduct action potentials toward the brain. o Descending Tracts – consist of axons that conduct action potentials away from the brain. Spinal Cord Reflexes: (See Process figures 8.18 & 8.19, pages 206-207) 31. Knee-Jerk Reflex / Patellar Reflex – a classic example of stretch reflex in which the stimulus is stretching of the quadriceps femoris muscles; done when the patellar ligament is tapped. o Prevents damage from overstretching, and plays a role in maintaining posture. 32. Withdrawal Reflex / Flexor Reflex – contains pain receptors as its sensory receptors; if stimulated, reflex occurs to remove a limb or another body part from a painful stimulus. Painful Stimuli to Pain Receptors → Sensory Neuron → Dorsal Root → Interneurons → Ventral Root → Motor Neuron of Flexor Muscles → Withdrawal. Spinal Nerves – arise along spinal cord from union of dorsal & ventral roots (See figure 8.20, page 209). All contain axons from both sensory and somatic motor neurons (mixed nerves). Categorized by region of vertebral column from which they emerge – cervical (C1 to C8), thoracic (T1 to T12), lumbar (L1 to L5), sacral (S1 to S5), and coccygeal (Co) – 31 pairs in total. Dermatome – area of skin supplied with sensory innervation by a pair of spinal nerves; each spinal nerve has specific cutaneous sensory distribution (except C1). Plexus – area where neurons of spinal nerves come together & intermingle. Major Plexuses of the Spinal Nerves: (See table 8.3, page 209). Brain – consists of its major regions which are the brainstem, the cerebellum, the diencephalon, and the cerebrum. Brainstem – connects the spinal cord to the remainder of the brain (See figure 8.22, page 211). Brain stem Location Prominent Features Function Comp onent inferior Regulates heart rate, blood Medul Pyramids – two enlargements portion; vessel diameter, breathing, la at uppermost part (anterior); continuous swallowing, vomiting, Oblon involved in conscious control with spinal hiccupping, coughing, sneezing, gata of skeletal muscle. cord balance. Brain stem Location Prominent Features Function Comp onent P Superior to Aids in assisting Serves as a functional bridge between cerebrum o medulla functions of the and cerebellum, breathing, swallowing, balance, n oblongata medulla oblongata chewing, and salivation. s Mid Smallest region; Arched footbridge Coordinates eye movements, controlling bra superior to pons (anterior surface) pupil diameter and lens shape. in Involved in visual Superior Colliculi – reflexes and receive 2 mounds touch and auditory input. Major relay centers Inferior Colliculi for auditory nerve pathways in CNS. Involved in Substantia Nigra – regulating general black nuclear mass body movements. Cerebrum – largest part of the brain which is divided into right & left hemispheres by longitudinal fissure (See figure 8.24, page 213). Lobes of Cerebral Hemispheres:  33. Frontal Lobe – vital in control of voluntary motor functions, motivation, aggression, mood, & olfactory reception. 34. Parietal Lobe – principal center for receiving & consciously perceiving most sensory information, such as touch, pain, temperature, and balance. 35. Occipital Lobe – functions in receiving and perceiving visual input. 36. Temporal Lobe – involved in olfactory & auditory sensations; plays an important role in memory. o Psychic Cortex: anterior & inferior portion of temporal lobe associated with abstract thought & judgment. 37. Insula / Fifth Lobe – deep within the lateral fissure; it processes interoception – the sensory information on the physiologic condition of the body (heartbeat & blood pressure regulation & gastric motility). Cerebral Cortex – located at the surface of cerebrum that is composed of gray matter. Functions: controls thinking, communicating, remembering, understanding, & initiates involuntary movements. Prominent Features: Gyri – folds on the cerebral cortex that greatly increase the surface area. Sulci – intervening grooves; shallow indentations. o Central Sulcus – separates the frontal and parietal lobes. o Lateral Fissure – separates most of the temporal lobe from the rest of the cerebrum.