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Chapter 13

BISC 3221 Chapter 13: Chapter 13 Notes- The Nervous System

Biological Sciences
Course Code
BISC 3221
Craig Frank

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Chapter 13: The Nervous System
13.1 An Overview of the Nervous System
Nervous system: includes all neural tissue in body
o Central Nervous System: brain and spinal cord; integrating, processing, coordinating
sensory input/motor output, intelligence, memory, emotion, learning
Central canal: narrow canal that persists in spinal cord
Cerebrospinal fluid fills central canal and ventricles
o Peripheral Nervous System: all neural tissues outside of CNS, provides sensory info to
CNS, carries motor commands to peripheral tissues/systems
Afferent division: brings sensory information to CNS; begins at receptors
(dendrite, specialized cell/cluster of cells, or complex sense organ)
Efferent division: carries motor commands to muscles/glands; begins at effector
(muscle cell, gland cell, other cell specialized to perform specific function)
Afferent division carries info from somatic sensory receptors (monitor skeletal
muscles, joints, skin) and visceral sensory receptors (monitor internal structures)
Somatic Nervous System (SNS) controls skeletal muscle contractions;
Autonomic Nervous System (ANS) controls smooth muscle, cardiac muscle,
gland activity (these are subdivisions of efferent division)
Activity of somatic nervous system can be voluntary or involuntary
Autonomic nervous system activities are typically outside our awareness/control
13.2 Cellular Organization in Neural Tissue
Neurons: cells responsible for transfer and processing of info in nervous sytem
o Soma: cell body
o Perikaryon: region around nucleus
o Dendrites: branch from cell body, each with dendritic spines, receive info from other
o Axon: elongated section that ends at synaptic terminals, used to communicate with
another cell
Neuroglia: supporting cells; isolate the neurons, provide supporting framework for neural tissue,
maintain intercellular environment, act as phagocytes; 5 times as many glia as neurons
o Retain ability to divide
o Half volume of nervous system
13.3 Neuroglia
Neuroglia of the CNS
4 types found in CNS
o Largest, most numerous glial cells
o Control interstitial environment: have many cytoplasmic processes (high SA), control
chemical content of interstitial environment; processes can enclose other neurons,
isolating them from changes in chemical composition of interstitial space
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o Maintain blood brain barrier: cells that isolate CNS from general circulation; cytoplasmic
processes (pedicels) cover most of surface of capillaries within CNS, interrupted only
where other glial cells contact capillary surfaces; chemicals secreted by astrocytes
maintain blood brain barrier
o Creating a 3d framework for CNS: contain many microfilaments, provides mech strength
o Repairs in damaged tissue: make structural repairs to stabilize tissue, produce scar tissue
o Guide neuron development: in developing brain, secrete neurotropic factors to direct
growth/connection of neurons
o Thinner and fewer cytoplasmic processes, smaller cell body
o Processes contact axons or cell bodies of neurons
o Tie clusters of axons together, wrap axons in myelin
Internodes: large areas of axon wrapped in myelin
Myelin sheath gaps = nodes
White matter: regions of CNS dominated by myelinated axons
Gray matter: regions of CNS dominated by unmyelinated axons
o Smallest glial cells, thing processes with fine branches
o Originate from stem cells that are related to those that produce tissue macrophages and
monocytes of blood
o Phagocytic cells of CNS, engulf cellular debris/waste
Ependymal Cells
o Ependyma: cellular layer lining ventricles of brain, central canal of spinal cord
These chambers contain cerebrospinal fluid (surrounds brain and spinal cord,
provides cushion, transports gases/nutrients/wastes/etc.)
o Ependymal cells: cuboidal or columnar, have processes that contact glial cells in neural
tissue; may act as receptors that monitor composition of CSF
Neuroglia of the PNS
Clustered into ganglia (masses), axons bundled and wrapped in CT to form peripheral nerves
All axons/soma are completely isolated from surroundings by processes of glial cells
Satellite Cells
o Regulate exchange of nutrients/waste between cell body and extracellular fluid
o Isolate neuron from stimuli other than those at synapses
Schwann Cells
o All peripheral axons (myelinated or not) are covered by these cells
o Axolemma: plasmalemma of axon
o Neurolemma: cytoplasmic covering provided by Schwann cells around axon
13.4 Neurons
Perikaryon: cytoplasm surrounding nucleus in soma
o Cytoskeleton contains neurofilaments, neurotubules
o Neurofibrils: bundles of neurofilaments, extend into dendrites/axon
o Contains organelles like mitochondria, free/fixed ribosomes, ER
o Chromatophilic substance: clusters of ribosomes AKA Nissl bodies (accounts for grey
color of areas of brain)
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