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Chapter 14-16

ANAT 100 Chapter Notes - Chapter 14-16: Posterior Cerebral Artery, Anterior Cerebral Artery, Central Nervous System

Anatomy and Cell Biology
Course Code
ANAT 100
Leslie W Mac Kenzie

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Module 5: Nervous System
The nervous system consists of the brain, spinal cord, sensory organs, and all of the nerves that connect
these organs with the rest of the body. Together, these organs are responsible for the control of the body
and communication among its parts. The brain and spinal cord form the control center known as the
central nervous system (CNS), where information is evaluated and decisions made. The sensory nerves
and sense organs of the peripheral nervous system (PNS) monitor conditions inside and outside of the
body and send this information to the CNS. Efferent nerves in the PNS carry signals from the control
center to the muscles, glands, and organs to regulate their functions.
Master controlling and communication system:
Sensory input
○ Integration
Motor output
Principal Subdivisions:
1. Central nervous system (CNS):
Brain and spinal cord (integration and command centre)
2. Peripheral nervous system (PNS):
Cranial nerves and spinal nerves (communications lines that link all parts of the body
to the CNS) and ganglia (clusters of neuron cell bodies outside of the CNS)
Functional subdivisions of PNS:
Sensory “afferent” division (input):
Convey impulses to the CNS from receptors
Somatic afferents (from skin, skeletal muscles, joints)
Visceral afferents (from organs within ventral cavity)
Motor “efferent” division:
Transmits impulses away from the CNS to effector organs
Somatic nervous system:
Somatic motor nerve fibers that conduct impulses from the CNS to
skeletal muscles
Voluntary nervous system
3. Autonomic nervous system (ANS):
Visceral motor fibers regulating smooth muscles, cardiac muscle, glands
Involuntary nervous system
Sympathetic division
Parasympathetic division
Together, the CNS and PNS perform three general functions:
collecting information: receptors detect changes in internal and external envmt
processing and evaluating information: determines what, if any, response is required
responding to information: motor output travels through structures to effectors
5.1 Histology of the Neural Tissue
Two principal cell types:
Neurons (excitable nerve cells that transmit electrical signals)
Supporting cells (smaller cells that surround and wrap the neurons)

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Neurons, also known as nerve cells, communicate within the body by transmitting
electrochemical signals.
Structural units of the nervous system
Consists of a cell body and cytoplasmic processes
Cell Body:
Also called perikaryon or soma
5-150 um in diameter
Contain usual cellular organelles except centrioles
Nissl bodies (rough endoplasmic reticulum) aka
chromatophilic substance
Most neuron cell bodies located in CNS
Nuclei: clusters of nerve cell bodies in the
Ganglia: fewer clusters of nerve cell bodies
in PNS
Cytoplasmic Processes:
Extension of the cytoplasm from the cell body
CNS contains cell bodies and processes
PNS consists mainly of neuron cell processes
Short, branching extensions of the cell body
Convey incoming messages to the cell body
One axon per neuron
Comes from the axon hillock of the cell body
Axon collaterals:
Branches along the length of the axon
Functions to generate a nerve impulse and
it away
from the
cell body
5.2 Neuron Classification
Structural Classification Description Functional Ex.
Unipolar neuron Has a single process
Very short and divides to form the axon
Found in the ganglia of PNS
Most sensory neurons
Bipolar neuron Has two processes, an axon and a dendrite Only in special sense

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organs (eye and ear)
Multipolar neuron Has three or more cellular processes
Most common type and major type in CNS
Interneurons, motor
Functional Classification Description Structural Ex.
Sensory Towards the CNS
Unipolar with cell bodies located in ganglia
of PNS
Most sensory neurons are
unipolar, a few are
Motor Away from the CNS
Multipolar with cell bodies in CNS
5.3 Supporting Cells
Neuroglia or glial cells: differ from neurons b/c smaller, capable of mitosis and do not transmit nerve
impulses. Assist neurons w/ their functions and far outnumber neurons.
Within the CNS there are four types:
Small, star shaped with numerous processes
Most abundant of the glial cells
Functions in maintaining the integrity of neural tissue
Small oval cells with processes
Accounts for 5% of glial cells in CNS
Monitor the health and welfare of the neurons (phagocytic)
Ependymal cells:
Simple cuboidal in shape with cilia that help circulate the CSF
Lines cavities of brain and spinal cord
Assists in the production, circulation and monitoring of CSF
Wrap around nerve fibers (axons) in the CNS
Myelin sheaths
A single cell can myelinate up to 60 axons
Nodes of Ranvier: spaces between the bundles
Within the PNS there are two types:
Schwann cells:
Surrounds and forms the myelin sheath around nerve fibers (axons) in the PNS
A single cell can only myelinate a portion of only one axon
Nodes of Ranvier = spaces between bundles
Satellite cells:
Surround neuronal cell bodies within ganglia
Plays a role in controlling the chemical environment of the neuron
Note: nerve axons in the CNS and PNS are embraced by either oligodendrocytes or Schwann cells but
they don’t wrap around the axons thus they are said to be unmyelinated axons: myelinate fibers in the
CNS are referred to as white matter whereas gray matter contains mostly nerve cell bodies and
unmyelinated axons
5.4 CNS: Support and Protection
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