integration and coordination of nervous system

anatomy notes summarised

1. ANATOMY AND PHYSIOLOGY INTEGRATION AND COORDINATION LECTURER:DORCAS T. ASAN

2. Functional Organization of the Nervous System Divisions of the Nervous System Learning Objectives By the end of this lesson, students should be able to: Identify and describe the main divisions of the nervous system and their functions. Explain the structure and role of neurons and neuroglial cells. Describe the structure and function of the synapse and neurotransmitters. Explain how an action potential is generated and conducted along a neuron. Differentiate between continuous and saltatory conduction. Describe how nerve impulses are integrated and processed in neuronal circuits. Relate basic nervous system functions to common clinical conditions.

3. INTRODUCTION The nervous system is one of the body’s main control and communication systems. It works with the endocrine system to maintain homeostasis — the stable internal environment of the body. It detects changes inside or outside the body, interprets them, and responds appropriately through muscular or glandular activity. 1. Structural Divisions The nervous system is divided structurally into two main parts: A. Central Nervous System (CNS) Components: Brain and spinal cord. Function: Acts as the control center for the entire body. Receives sensory information, interprets it, and initiates motor responses. Responsible for intelligence, memory, learning, and emotion. The brain processes and stores information, while the spinal cord conducts signals and coordinates reflexes.

4. B. Peripheral Nervous System (PNS) Components: All nerves outside the CNS — cranial nerves (12 pairs) and spinal nerves (31 pairs). Function: Connects the CNS to the limbs, organs, and body surfaces. Serves as the communication link between the CNS and the rest of the body.

5. 2. Functional Division Functionally, the nervous system is divided into three major parts A. Sensory (Afferent) Division Carries information from sensory receptors to the CNS. Receptors detect stimuli such as temperature, touch, light, sound, or chemical changes. Afferent neurons transmit this input to the brain and spinal cord. Example: Touching a hot object → receptors in the skin send impulses to the brain. B. Motor (Efferent) Division Carries commands from the CNS to effectors — muscles or glands. Divided into two subsystems: Somatic Nervous System (SNS): Controls voluntary movements (skeletal muscles). Example: Deciding to walk or write. Also includes reflex actions that occur automatically for protection.

6. 2. Functional Division cont ’ Autonomic Nervous System (ANS): Regulates involuntary body activities (smooth muscles, cardiac muscles, glands). Subdivided into: Sympathetic Division (fight or flight): Prepares body for stress — increases heart rate, dilates pupils, inhibits digestion. Parasympathetic Division (rest and digest): Conserves energy, promotes digestion and rest. Enteric Nervous System (ENS): Sometimes called the brain of the gut. Network of neurons in the gastrointestinal tract that controls digestion independently but also communicates with the CNS via the ANS.

7. integration Function The CNS integrates sensory input and makes decisions. It processes incoming information, compares it with stored memories or experiences, and generates appropriate responses. Example: Sensory input → You feel heat. Integration → Brain decides to withdraw hand. Motor output → Muscles contract to pull hand away. Clinical Connection Multiple Sclerosis (MS): Damage to myelin sheaths in CNS disrupts communication. Diabetic neuropathy: PNS nerve damage due to high glucose affects sensory and motor pathways. Autonomic disorders: Abnormal regulation of blood pressure or digestion due to ANS malfunction.

8. Nervous System Cells The nervous system is made up of two main types of cells: Neurons (nerve cells) The functional units of the nervous system. Specialized to generate and transmit nerve impulses (action potentials). Neuroglia (glial cells) The supporting cells of the nervous system. They protect, nourish, and assist neurons but do not conduct impulses. .Neurons Neurons are electrically excitable cells that carry information as nerve impulses throughout the body.Each neuron has three basic parts:

9. Neuron structure

10. Parts of a Neuron Part Structure / Description Function Cell body (Soma) Contains the nucleus, organelles, and cytoplasm (perikaryon). Controls cell metabolism; integrates incoming signals. Dendrites Short, branched extensions of the cell body. Receive impulses from other neurons or sensory receptors. Axon Long, single fiber extending from the cell body; may be myelinated. Transmits impulses away from the cell body to other neurons, muscles, or glands. Axon terminals (synaptic end bulbs) Fine branches at the end of the axon. Release neurotransmitters into the synapse to communicate with other cells.

11. Myelin Sheath A fatty covering around axons that speeds up nerve impulse transmission. Formed by: Oligodendrocytes in the CNS Schwann cells in the PNS. The gaps between myelin segments are called Nodes of Ranvier — they allow impulses to “jump” from node to node (saltatory conduction), increasing speed. Clinical Connection Multiple Sclerosis : Demyelination of CNS axons → slow or lost conduction → muscle weakness and poor coordination. Guillain–Barré Syndrome: Autoimmune attack on PNS myelin → temporary paralysis.

12. Axonal Transport Movement of materials (neurotransmitters, enzymes) along the axon. Slow axonal transport: Moves substances 1–5 mm/day (used for structural proteins). Fast axonal transport: Moves materials up to 400 mm/day (used for vesicles and neurotransmitters). Important for neuron maintenance and regeneration.

13. Classification of Neurons Neurons are classified in two ways: 1. By Structure (based on the number of processes) 2. By Function (based on the direction of impulse)

14. 1. By Structure (based on the number of processes) Type Description Example / Location Multipolar neurons One axon, many dendrites Most neurons in brain and spinal cord Bipolar neurons One axon, one dendrite Retina of the eye, inner ear, olfactory area Unipolar (pseudounipolar) neurons Single process that branches into axon and dendrite Sensory neurons in dorsal root ganglia

15. 2. By Function (based on the direction of impulse) 1. Sensory Neurons Found in peripheral nervous system.  Find out external stimuli ( eg : touch, temperature, pain) and send signals to the central nervous system (CNS)  Example: Nerve endings in the  skin  which is a feeling of heat. 2. Motor Neurons Control muscle movements by transmitting signals from the CNS to muscles or glands  Essential for voluntary and involuntary movements 3. Interneurons  Found in the CNS (brain and spinal cord) Act as connectors, relaying signals between sensory and motor neurons

16. Neuroglia (Supporting Cells) Neuroglia are smaller but more numerous than neurons (about 10 times more). They can multiply and divide, unlike neurons. Their role is to protect, nourish, and support neurons.

17. Neuroglia of the Central Nervous System Type Description / Function Astrocytes Star-shaped; provide structural support, regulate ion balance, form blood–brain barrier (BBB). Oligodendrocytes Produce myelin sheath around CNS axons. Microglia Small phagocytic cells; remove cellular debris, microbes, and damaged tissue. Ependymal cells Line brain ventricles and central canal of spinal cord; produce and circulate cerebrospinal fluid (CSF).

18. Neuroglia of the Peripheral Nervous System Schwann cells Form myelin sheath around PNS axons; assist in regeneration after injury. Satellite cells Surround neuron cell bodies in ganglia; regulate exchange of materials between neurons and interstitial fluid.

19. The Synapse The functional junction between one neuron and another, or between a neuron and an effector cell (muscle or gland) It is the site of information transfer — converting electrical impulses (action potentials) into chemical or electrical signals NB: In the neuromuscular junction, the postsynaptic cell is a muscle fiber;in neuron-to-neuron communication, it is another neuron.

20. components of synapse Component Description Function Presynaptic neuron The neuron that sends the signal. Transmits impulses toward the synapse. Synaptic cleft A tiny space (about 20–50 nm wide) between two neurons. Separates the presynaptic and postsynaptic membranes; neurotransmitters diffuse across it. Postsynaptic neuron or effector The neuron, muscle, or gland cell that receives the signal. Has receptor sites that bind neurotransmitters to generate a response.

21. Types of Synapses Electrical Synapses Structure: Gap junctions connect the cytoplasm of adjacent neurons. Signal Type: Direct transmission of ionic current. Features: Faster communication — impulses pass directly from one cell to another. Allow synchronization of activity in groups of neurons or muscle fibers (e.g. cardiac muscle, smooth muscle). Can transmit in both directions. Example: Found in visceral smooth muscles, cardiac muscle fibers , and some areas of the brain.

22. Types of Synapses cont ’ Chemical Synapses Structure: Separated by a synaptic cleft (no physical continuity). Signal Type: Involves neurotransmitters — chemicals released from presynaptic vesicles. Features: Most common type in the human body. One-way communication: presynaptic → postsynaptic. Slight delay due to neurotransmitter diffusion and receptor binding. Example: Neuromuscular junction (acetylcholine-mediated), and neuron-to-neuron transmission in CNS.

23. Steps of Synaptic Transmission at a Chemical Synapse Step 1: Nerve Impulse Arrives at the Axon Terminal An action potential (nerve impulse) travels along the axon of the presynaptic neuron. When it reaches the axon terminal, the membrane depolarizes (becomes more positive). Key point : Depolarization triggers changes that open voltage-gated calcium channels. Step 2: Calcium Ion (Ca²⁺) Channels Open The depolarized membrane opens voltage-gated Ca²⁺ channels in the synaptic knob. Calcium ions move into the presynaptic terminal from the extracellular fluid. Why important: Calcium acts as the trigger for neurotransmitter release.

24. Step 3: Neurotransmitter Release The increase in Ca²⁺ concentration causes synaptic vesicles to move toward and fuse with the presynaptic membrane. Through exocytosis, vesicles release their neurotransmitter molecules into the synaptic cleft. Examples of neurotransmitters : Acetylcholine ( ACh ) – at neuromuscular junctions Dopamine , Serotonin , GABA , Norepinephrine , Glutamate Step 4: Neurotransmitter Diffusion and Binding The neurotransmitter molecules diffuse across the synaptic cleft (very short distance). They bind to specific receptor proteins on the postsynaptic membrane (often ligand-gated ion channels). This binding is like a key fitting into a lock.

25. Step 5: Postsynaptic Response (Generation of Graded Potential) Binding of neurotransmitters causes ion channels in the postsynaptic membrane to open. Depending on the type of neurotransmitter and receptor: Excitatory postsynaptic potential (EPSP): Na⁺ channels open → depolarization → neuron closer to firing an action potential. Inhibitory postsynaptic potential (IPSP): K⁺ or Cl⁻ channels open → hyperpolarization → neuron less likely to fire. Example: Glutamate produces EPSPs (excitation). GABA and glycine produce IPSPs (inhibition).

26. Step 6 : Neurotransmitter Removal (Termination of Signal) The signal must be stopped quickly to prevent continuous stimulation. Neurotransmitters are removed from the synaptic cleft by diffusion, enzyme breakdown, or reuptake

27. Action potential An action potential is a sequence of rapidly occurring events that decrease and then reverse the membrane potential and restore it to the resting state. It allows neurons to transmit information quickly over long distances. Resting membrane potential-The charge difference across the membrane of a resting neuron (about –70 mV). Inside = negative; outside = positive. Depolarization-Inside becomes less negative (more positive) as Na⁺ enters the cell Repolarization-Membrane potential returns to resting level as K⁺ leaves the cell. Hyperpolarization-Membrane becomes more negative than resting potential. Threshold-The critical voltage (≈ –55 mV) required to trigger an action potential.

28. 2. Types of Ion Channels Channel Type Opens in Response To Location / Function Leak channels Always open Maintain resting membrane potential Voltage-gated channels Change in membrane potential Responsible for action potential generation Ligand-gated channels Binding of neurotransmitter (e.g., ACh) Found at synapses Mechanically-gated channels Mechanical stimulation (touch, pressure) Found in sensory receptors

29. Steps of an Action Potential I. Resting Membrane Potential (Before stimulation ) The neuron membrane is polarized: Inside: –70 mV (negative) Outside: positive Ion distribution: Na⁺ (sodium) higher outside K⁺ (potassium) higher inside Maintained by the sodium–potassium pump (Na⁺/K⁺ ATPase) which moves: → 3 Na⁺ out and 2 K⁺ in per cycle. Result : Neuron is ready to fire but stable until stimulated.

30. Generation of the Action Potential: Step-by-Step Step 1: Stimulus and Threshold A stimulus (e.g., neurotransmitter, touch, or electrical change) depolarizes the membrane slightly. If depolarization reaches threshold (≈ –55 mV), voltage-gated channels open → action potential begins. If threshold is not reached → no action potential. Step 2: Depolarization Phase Threshold reached → Voltage-gated Na⁺ channels open. Na⁺ ions rush into the neuron (down concentration and electrical gradients). The inside of the membrane becomes positive relative to outside. Membrane potential rises from –55 mV → 0 → +30 mV. Result: The neuron is depolarized; the inside is now positive.

31. Step 3: Repolarization Phase At +30 mV → Na⁺ channels close, K⁺ channels open. K⁺ ions leave the neuron, moving out of the cell. The loss of positive charges restores the negative potential inside. Membrane potential returns toward –70 mV. Result: The neuron begins to recover to its resting state. Step 4: Hyperpolarization (Afterpotential) K⁺ channels remain open slightly longer than needed. Too many K⁺ ions leave → membrane becomes more negative than resting (≈ –80 mV). Na⁺/K⁺ pump then restores ions to original positions and brings potential back to –70 mV. Result: Brief undershoot before full recovery.

32. Refractory Periods After an action potential, a neuron needs time to recover before firing again It ensures that impulses travel in one direction and that each action potential is separate and distinct. Types: Absolute refractory period: Occurs during depolarization and early repolarization. Na⁺ channels are inactivated — no new impulse can start. Relative refractory period: Occurs during late repolarization and hyperpolarization. Some Na⁺ channels recover; a stronger stimulus can trigger another impulse. Function: Prevents overlapping impulses and maintains one-way transmission of nerve signals.

33. 5: Impulse Processing After nerve impulses are generated and transmitted, they must be processed and interpreted by the central nervous system (CNS). This processing allows the body to make appropriate responses — whether automatic (reflexes) or conscious (decision-making). Impulse processing involves the integration of incoming information within the central nervous system and the generation of appropriate responses. ➡ Sensory input → Integration (processing) → Motor output

34. 1. Integration in the CNS Integration means the CNS combines information from multiple sources, compares it with stored data, and decides how to respond. Occurs mainly in the interneurons of the spinal cord and brain. Integration may lead to: Inhibition or excitation of certain pathways. Storage of information as memory. Transmission of signals to effectors (muscles/glands). Example: You touch a hot object , the spinal cord processes the signal instantly and withdraws your hand (a reflex).

35. 2. Neuronal Pools A neuronal pool is a functional group of interconnected neurons in the CNS that process specific kinds of information. Each pool receives input from many neurons and sends output to others. They can amplify, inhibit, or redirect impulses.

36. Functional Zones within a Neuronal Pool Zone Description Function Facilitated Zone Neurons close to threshold but not yet activated. Respond only when additional input arrives. Discharge Zone Neurons with strong connections to incoming fiber . Produce immediate response. Example: In the spinal cord, neuronal pools control posture, breathing, and walking patterns.

37. 3. Patterns of Neural Processing Neurons are arranged in specific patterns called neural circuits, which determine how impulses are processed and transmitted A. Divergence One neuron → many neurons. Allows amplification of a signal. Example: One motor neuron in the brain stimulates thousands of muscle fibers for coordinated contraction. Function: Distributes a signal to multiple destinations. B. Convergence Many neurons → one neuron . Several inputs combine to influence a single output. Example: Different sensory neurons send information to one motor neuron in the spinal cord to control a single muscle. Function: Integrates different inputs for unified response.

38. C. Serial Processing Impulses pass through neurons step by step in a specific sequence. Example: Reflex arc — receptor → sensory neuron → interneuron → motor neuron → effector. Function: Produces predictable responses (e.g., reflexes). D. Parallel Processing A single stimulus activates several pathways simultaneously, leading to multiple responses. Example: Smelling food → activates hunger, salivation, and memory of taste. Function: Complex processing like problem-solving and emotion.

39. E. Reverberation (Feedback Circuit) The axon collaterals of neurons send impulses back to earlier neurons in the pathway. Produces repeated stimulation — maintains activity until inhibited. Example: Regulating breathing, sleep–wake cycles, and muscle tone. Function: Continuous rhythmic output.

40. Synaptic Facilitation and Inhibition Term Definition Effect Facilitation A condition in which a neuron receives repeated or simultaneous subthreshold stimuli, bringing it closer to threshold. Makes the neuron more likely to fire an impulse. Inhibition Occurs when a neuron receives hyperpolarizing input. Decreases the chance of impulse generation. Continuous gentle touch may facilitate sensory neurons; sudden pain triggers full activation.

41. reflex Processing (Simplest Form of Impulse Processing) Reflexes represent automatic, rapid responses to stimuli. They are processed mainly at the spinal cord level, not the brain, ensuring quick reactions. Reflex Arc Components Receptor – detects the stimulus. Sensory neuron – transmits impulse to spinal cord. Integration center (interneuron) – processes information. Motor neuron – carries response to effector. Effector – muscle or gland that carries out response. Example: Knee-jerk (patellar) reflex.

42. References Tortora, G. J., & Derrickson, B. (2014). Principles of Anatomy and Physiology (12th ed.). Hoboken, NJ: John Wiley & Sons, Inc. Marieb , E. N., & Hoehn, K. (2016). Human Anatomy & Physiology (10th ed.). Boston, MA: Pearson Education, Inc. Sherwood, L. (2016). Human Physiology: From Cells to Systems (9th ed.). Boston, MA: Cengage Learning. THANKS