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central nervous system consists of
brain and spinal cord
peripheral nervous system consists of
cranial and spinal nerves
the peripheral nervous system is divided into
afferent division and efferent division
afferent division
brings sensory information to the CNS from receptors in body tissues and organs
efferent division
carries information away from the CNS to effectors
effectors
muscles and glands that respond to motor commands
the efferent division is divided into 2 parts
somatic nervous system autonomic nervous system
somatic nervous system (SNS)
voluntary controls skeletal muscle
autonomic nervous system (ANS)
involuntary controls smooth and cardiac muscle, glands and adipose tissue
autonomic nervous system is also called
visceral motor system
autonomic nervous system includes 2 parts
sympathetic division parasympathetic division
sympathetic division
increases heart rate
parasympathetic division
decreases heart rate
neural tissue consists of two kinds of cells
neurons and neuroglia
neurons
the basic units of the nervous system communication of neurons with one another and with other cells
neuroglia act as
phagocytes
phagocytes
clean up waste
neuroglia
regulate environment around neurons provide a supporting framework for neural tissue
neuroglia are much
smaller cells and outnumber neurons
neuroglia retain the ability to
divide
a multipolar neuron consists of
cell body dendrites axon axon terminals
dendrites
receive incoming signals into the cell body
axon terminals
form a synapse with the next cell
free ribosomes and RER form
nissl bodies giving a gray color to areas with many cell bodies
most neurons lack centrioles, as a result
typical CNS neurons cannot divide
CNS neurons cannot
be replaced if lost to injury or disease
neural stem cells
are present in the adult nervous system, but are typically inactive
multipolar neuron
all motor neurons that control skeletal muscles efferent
unipolar neuron
most sensory neurons of the PNS afferent
bipolar neurons
small and rare, occur in special sense organs afferent
sensory neurons are
afferent unipolar and bipolar
sensory neurons
receive information from sensory receptors monitoring the external and internal environment
somatic sensory receptors are divided into
external receptors and proprioceptors
external receptors
monitor the external environment
proprioceptors
monitor the position and movement of skeletal muscles and joints
visceral receptors are also called
internal receptors
visceral receptors
monitor activities of internal organs and provide sensations of distension, deep pressure and pain
motor neurons are
efferent multipolar
motor neurons
total about half a million carry instructions away from CNS
somatic motor neurons
innervate skeletal muscles
visceral motor neurons
innervate cardiac muscle, smooth muscle, and glands
interneurons are
association neurons most numerous about 20 billion
interneurons
function as links between sensory and motor neurons
interneurons are located
entirely within the CNS
interneurons play a role
in all higher functions
neuroglia make up
about half of all neural tissue
4 types of neuroglia
astrocytes, oligodendrocytes, microglia, ependymal cells
astrocytes are
the largest and most numerous
astrocytes maintain
the blood brain barrier that isolates the CNS from the bodys general circulation
astrocytes secrete
chemicals that cause the capillaries to become impermeable to many compounds
astrocytes create
structural framework for CNS neurons and perform repairs in damaged neural tissues (scabs)
oligodendrocytes
produce an insulating membranous wrapping around CNS axons called myelin
myelin
increases speed of action potential
internodes
areas covered in myelin
Nodes of Ranvier
gaps in the myelin sheath
white matter
regions inside the CNS that are dominated by myelinated axons
gray matter
areas in CNS dominated by neuron bodies, glial cells, and unmyelinated axons
Oligodendrocytes can wrap
around multiple axons
microglia size
smallest and least numerous of neuroglia
microglia
perform protective functions such as engulfing cellular waste and pathogens
microglia act as
phagocytic cells
phagocytic cells
derived from white blood cells that migrated into the CNS as the nervous system formed
ependymal cells are
simple cuboidal epithelial that have microvilli
ependymal cells
line cavities in the CNS filled with cerebrospinal fluid
ependymal lines
central canal of the spinal cord ventricles of the brain
Ependyma
involved in producing and circulating cerebrospinal fluid around the CNS
ependyma lacks
basement membrane
2 types of neuroglia found in PNS
satellite cells schwann cells
satellite cells
surround and support neuron cell bodies in PNS
schwann cells cover
every axon in the PNS
outer surface of schwann cells is called
neurilemma
neurilemma
outer surface of schwann cells
myelinated axons in PNS have one
schwann cell per segment
one schwann cell can encircle
several unmyelinated axons
gray matter consists of
neuron cell bodies
white matter consists of
bundles of axons
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