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Organizations of the Nervous System
Bryon Curletto
Overview
This video provides a hierarchical overview of the nervous system's organization, dividing it into the Central Nervous System (CNS) and Peripheral Nervous System (PNS) based on anatomy. It further categorizes the PNS into sensory and motor divisions, with the motor division including the autonomic nervous system (sympathetic and parasympathetic). The video also touches upon the types of neurons found in each division (multipolar, bipolar, unipolar/pseudounipolar) and their respective functions in integration and signal transmission, emphasizing how this structure aids in understanding neurological concepts.
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Chapters
- The nervous system is divided into the Central Nervous System (CNS) and the Peripheral Nervous System (PNS) based on anatomical location.
- The CNS consists of the brain and spinal cord, serving as the primary integration center.
- The PNS includes all nerves extending from the brain and spinal cord, such as cranial and spinal nerves.
Understanding this fundamental anatomical split is crucial for differentiating between the processing center of the nervous system and the communication pathways that connect it to the rest of the body.
The brain and spinal cord form the CNS, while nerves branching out to your limbs and organs constitute the PNS.
- The CNS exclusively contains multipolar neurons, characterized by a single axon and multiple dendrites extending from the cell body.
- These multipolar neurons in the CNS function as integration neurons, processing incoming signals to make decisions.
- The CNS acts like the 'computer' in a system, making sense of sensory input before sending out commands.
Knowing that only multipolar neurons exist in the CNS helps clarify their role in processing and decision-making, distinguishing them from neurons involved in signal transmission to or from the CNS.
Similar to how a thermostat's computer processes temperature data and decides whether to activate the heater or air conditioner, CNS neurons integrate various signals.
- The PNS contains multipolar neurons, as well as bipolar and unipolar (or pseudounipolar) neurons.
- Bipolar neurons, often found in special senses, have two extensions from the cell body.
- Unipolar/pseudounipolar neurons, typically involved in general senses, have one main extension that splits, with the cell body off to the side.
- These PNS neurons transmit signals either into the CNS (sensory) or out of the CNS (motor).
The presence of different neuron types in the PNS highlights its role in both receiving information from the environment and carrying commands to the body, utilizing specialized structures for efficient signal conduction.
Sensory receptors in your skin sending a 'hot' signal via a unipolar neuron to the spinal cord, and motor neurons then carrying a 'move away' command back via multipolar neurons.
- The sensory (afferent) division of the PNS carries information towards the CNS.
- It's further divided into somatic sensory (body wall sensations like touch, pain, position) and visceral sensory (sensations from internal organs).
- Special senses (sight, sound, taste, smell) are also part of the sensory division, often utilizing bipolar neurons.
- General senses typically involve unipolar/pseudounipolar neurons, with their cell bodies often located in dorsal root ganglia.
This breakdown clarifies how the body gathers information from both external and internal sources, distinguishing between general bodily feelings and specialized sensory inputs.
Feeling the texture of a surface (somatic sensory) or sensing hunger pangs (visceral sensory).
- The motor (efferent) division of the PNS carries commands away from the CNS to effectors (muscles and glands).
- Somatic motor pathways control skeletal muscles, responsible for voluntary movements.
- The autonomic nervous system (ANS) controls involuntary effectors: cardiac muscle, smooth muscle, and glands.
- The ANS is further divided into the sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) branches.
Understanding the motor division explains how the CNS directs bodily actions, from conscious muscle movements to the automatic regulation of internal organs and responses to stress or relaxation.
Consciously deciding to lift your arm (somatic motor) versus your heart rate increasing during exercise (sympathetic autonomic).
- The ANS is a subdivision of the PNS motor output, specifically controlling involuntary functions.
- It regulates cardiac muscle, smooth muscle (found in organs and blood vessels), and glands.
- The sympathetic division prepares the body for action ('fight or flight') by increasing heart rate, diverting blood flow, etc.
- The parasympathetic division promotes 'rest and digest' activities, conserving energy and facilitating digestion.
This distinction is vital for understanding how the body manages internal states automatically, responding to environmental demands and maintaining homeostasis without conscious thought.
The sympathetic system causing your pupils to dilate when startled, while the parasympathetic system slows your heart rate after a meal.
Key takeaways
- The nervous system is organized anatomically into the CNS (brain, spinal cord) for processing and the PNS (nerves) for communication.
- Different neuron types (multipolar, bipolar, unipolar) are specialized for specific roles within the CNS and PNS.
- The PNS is functionally divided into sensory input (afferent) and motor output (efferent) pathways.
- The motor division includes voluntary control of skeletal muscles (somatic) and involuntary control of organs and glands (autonomic).
- The autonomic nervous system has two opposing branches: sympathetic (activation) and parasympathetic (calming).
- Understanding this organizational framework is key to comprehending how the nervous system processes information and controls bodily functions.
Key terms
Central Nervous System (CNS)Peripheral Nervous System (PNS)Multipolar NeuronBipolar NeuronUnipolar Neuron (Pseudounipolar)Somatic SensoryVisceral SensorySomatic MotorAutonomic Nervous System (ANS)Sympathetic Nervous SystemParasympathetic Nervous SystemAfferentEfferent
Test your understanding
- What are the two main anatomical divisions of the nervous system and what structures comprise each?
- How do the functions of the CNS and PNS differ, and what types of neurons are primarily found in each?
- What is the difference between the somatic motor system and the autonomic nervous system?
- Explain the distinct roles of the sympathetic and parasympathetic divisions of the autonomic nervous system.
- How does the organization of sensory neurons (e.g., unipolar vs. bipolar) relate to their function in transmitting different types of information?