6: Nervous System
- Page ID
- 100006
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\dsum}{\displaystyle\sum\limits} \)
\( \newcommand{\dint}{\displaystyle\int\limits} \)
\( \newcommand{\dlim}{\displaystyle\lim\limits} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\(\newcommand{\longvect}{\overrightarrow}\)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 6.1: Functions of the Nervous System
- The nervous system functions as the body’s rapid communication and control network, continuously monitoring internal and external conditions and coordinating appropriate actions. It operates through three core functions: sensory input to detect stimuli, integration to process and interpret information, and motor output to activate muscles or glands. Together, these steps allow the body to respond quickly and effectively to changing conditions.
- 6.2: Organization of the Nervous System
- Networks of neurons transmit signals to coordinate sensation, integration, and response. The nervous system is divided structurally into the central and peripheral nervous systems, and functionally into somatic, autonomic, and visceral pathways. This organization allows information to be efficiently processed and directed to produce appropriate voluntary and involuntary responses.
- 6.3: Nervous Tissue - The Wiring of the Body
- Nervous tissue is a specialized, excitable tissue composed of neurons and neuroglia that enables rapid communication throughout the body using electrical and chemical signals. Neurons generate and transmit information, while neuroglial cells support, protect, and insulate neurons to ensure efficient signaling. Together, these cells form the wiring system that allows the body to sense its environment, process information, and respond appropriately.
- 6.4: Structural and Functional Diversity of Neurons
- Neurons show remarkable structural and functional diversity allowing them to handle many different tasks. They can be classified by their shape, based on the number of processes extending from the cell body, and by their function, based on the direction information travels relative to the central nervous system. Together, these classifications help explain how neurons are specialized to detect sensory input, integrate information, and produce appropriate motor responses.
- 6.5: Signal Speed — How Myelin Turns Nerves into Racetracks
- Myelin is a lipid-rich insulating sheath that wraps around axons and greatly increases the speed of nerve signal transmission. By restricting ion exchange to the nodes of Ranvier, action potentials travel by saltatory conduction, allowing signals to move rapidly and efficiently. Differences in myelination by oligodendrocytes in the CNS and Schwann cells in the PNS also help explain why peripheral nerves can regenerate more effectively than those in the CNS.
- 6.6: Structure of a Neuron
- Motor neurons provide a clear model for understanding neuron structure because they contain all the classic components involved in signal transmission. Information flows into the neuron through dendrites, is processed in the cell body, and is carried away by a single long axon to its target. Myelin sheaths and nodes of Ranvier along the axon increase signal speed, allowing motor neurons to transmit rapid and precise commands to muscles.
- 6.7: Gray vs. White Matter- Headquarters and Highways in the CNS
- Gray and white matter represent the two major organizational components of the CNS. Gray matter consists mainly of neuronal cell bodies and dendrites and serves as the primary site of information processing and integration, while white matter is composed of myelinated axons that form tracts for rapid communication between regions. Together, these “headquarters” and “highways” allow the CNS to efficiently process information and coordinate responses throughout the body.
- 6.8: Nerve and Ganglion Structure
- The peripheral nervous system is organized into nerves, which are bundles of axons, and ganglia, which are clusters of neuron cell bodies located outside the brain and spinal cord. Nerves, wrapped in protective connective tissue layers, transmit sensory and motor signals between the body and the CNS, while ganglia act as relay and processing sites in the PNS.
- 6.9: Inside the Brain — Your Control Tower
- The brain is organized into four major regions, with the cerebrum and its folded cerebral cortex providing expanded processing power through specialized lobes and functional areas. Overall, the functions of the cerebrum are motor initiation and coordination, processing of general and special senses, and high level functions such as judgment, reasoning, problem solving, and learning.
- 6.10: More Brain Highlights — Diencephalon and Brainstem
- Deep and inferior to the cerebrum, the diencephalon, brainstem and cerebellum make up the rest of the brain. These regions are responsible for various functions. The diencephalon acts as a major relay and homeostatic control center, the brainstem maintains life-support functions and communication with the spinal cord, and the cerebellum coordinates balance, precision, and motor learning.
- 6.11: Cortical Homunculus
- The cortical homunculus is a map of the body laid out across the brain’s primary motor and primary somatosensory cortices. It shows that body parts are represented in proportion to the amount of cortical tissue devoted to movement or sensation, not their physical size. By comparing the motor and sensory homunculi, this concept explains why areas requiring fine control or high sensitivity, such as the hands and face, occupy disproportionately large regions of the cortex.
- 6.12: Neurophysiology
- Neurophysiology explains how neurons use electrical signals to communicate by moving ions across their membranes. Differences in ion concentrations create a resting membrane potential, which can change through graded potentials or trigger rapid, all-or-none action potentials. Together, ion channels, ion pumps, and membrane potentials allow neurons to generate, transmit, and regulate fast electrical signals.
- 6.13: Synapses
- Synapses are specialized junctions that allow neurons to communicate with other neurons, muscles, or glands. Most synapses are chemical, using neurotransmitters to transmit and modulate signals across a synaptic cleft. Alternatively, the electrical synapses provide rapid, direct signal transfer through gap junctions. Disruption of synaptic communication plays a key role in neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
- 6.14: Somatic and Autonomic Reflexes
- Reflexes are rapid, automatic responses that protect the body and help maintain homeostasis without conscious control. Somatic reflexes use a direct pathway to skeletal muscle, while autonomic reflexes regulate smooth muscle, cardiac muscle, and glands through a two-neuron efferent pathway. Together, these reflex systems allow the nervous system to respond quickly to external threats and internal changes.
- 6.15: Meninges- Support and Protection of the Brain
- The meninges are three layers of protective connective tissue that surround the brain and spinal cord, providing cushioning, support, and stability for the CNS. Along with the skull, blood–brain barrier, and cerebrospinal fluid, they form a multi-level defense system that protects delicate neural tissue from injury and infection.
- 6.16: Cerebrospinal Fluid and Its Circulation
- Cerebrospinal fluid is a clear, circulating fluid that cushions the brain and spinal cord while maintaining a stable chemical environment for neural function. It is continuously produced, flows through the ventricles and subarachnoid space, and is regularly replaced to remove waste and provide buoyancy and protection. Because CSF bathes the entire CNS, analyzing it through a lumbar puncture offers valuable insight into infections, bleeding, autoimmune conditions, and neurodegenerative diseases.
- 6.17: The Autonomic Nervous Systems
- The autonomic nervous system is the involuntary branch of the PNS that regulates vital internal functions such as heart rate, digestion, and blood pressure. It is divided into the sympathetic system, which prepares the body for action, and the parasympathetic system, which promotes rest and recovery. Together, these two divisions work in balance to maintain homeostasis and adapt the body to changing demands.
- 6.18: Agonists and Antagonists of the ANS
- Agonists and antagonists are drugs that modify the NS activity by either activating or blocking its receptors. Agonists mimic natural neurotransmitters to enhance sympathetic or parasympathetic effects, while antagonists prevent neurotransmitters from binding and reduce those effects. By selectively targeting cholinergic or adrenergic receptors, these drugs allow precise control of heart rate, airway tone, blood pressure, and other vital functions.