Anatomy & Physiology
Nervous Tissue &
Homeostasis
 excitable characteristic of nervous tissue allows for
generation of nerve impulses (action potentials) that
provide communication & regulation of most body
tissue.
 together with endocrine system: responsible for
maintaining homeostasis
Differences in Nervous &
Endocrine Control of
Homeostasis
NERVOUS
ENDOCRINE
 rapid responder
 slow, prolonged
response
 action potentials
 releases hormones
Structures of the Nervous
System
 total mass of 2 kg (~3% of total body mass)
 Skull
 Spinal Cord
 Spinal Nerves
 Cranial Nerves
 Ganglia
 Enteric Plexus
 Special Senses & other Sensory Receptors
Major Structures of the
Nervous System
Functions of the Nervous
System
 3 basic functions:
1. Sensory
2. Integrative
3. Motor
Sensory Function
 sensory receptors detect internal & external
stimuli
 sensory (afferent) neurons carry this sensory
information to spinal cord & brain thru cranial
& spinal nerves
Integrative Function
 integrate: process
 nervous system takes information from sensory
neurons & processes that information, analyzes
it, stores some of it & makes decisions for
appropriate responses
 served by interneurons (connect 1 neuron to
another neuron
 Perception:
 conscious awareness of sensory stimuli
 occurs in brain
Motor Function
 served by motor (efferent) neurons
 carry info from brain/spinal cord  effectors
(muscle or gland) thru cranial or spinal nerves
 results in muscles contraction or gland
secreting
Quick Quiz
 What terms are given to neurons that carry
input  spinal cord & brain?
 What terms are given to neurons that carry
output out of the brain & spinal cord?
Organization of the Nervous
System
Histology of the Nervous
System
 2 cell types
1. Neurons
2. Neuroglia
Neurons
 nerve cells that possess electrical excitability:
 ability to respond to a stimulus & convert
it into an action potential
 stimulus: any change in environment that
is strong enough to initiate an action
potential
Direction Action Potential
Travels
Action Potential
 electrical signal that propagates along surface
of neurolema (membrane)
 begins & travels due to movement of ions
between interstitial fluid & inside of
neuron thru specific ion channels
 once begun it travels rapidly @ constant
strength
Parts of a Neuron
Parts of Neuron: Cell Body
 contains nucleus,
cytoplasm, typical
organelles,
 + Nissl bodies
clusters of RER
 make materials
for:


growth of neuron
regenerate
damaged axons in
PNS
Dendrites
 “little trees”
 input portion of
neuron
 usually, short,
tapering, highly
branched
 their cytoplasm
contains Nissl bodies,
mitochondria
Axon
 propagates action potentials 
 another neuron
 muscle fiber
 gland cell
Parts of an Axon
 joins cell body @ cone-shaped elevation: axon
hillock
 part of axon closest to hillock = initial segment
 jct of axon hillock & initial segment where
action potential arises so is called the trigger
zone
Parts of an Axon
 axoplasm: cytoplasm of an axon
 axolemma: plasma membrane of axon
 axon collaterals: side branches along length of
axon (most @ 90°)
 axon terminals: axon divides into many fine
processes
Synapse
 site of communication between 2 neurons or
between a neuron & effector cell
 synaptic end bulbs: tips of some axon terminals
swell into bulb-shaped structures
 synaptic vesicles: store neurotransmitter
 many neurons have >1 neurotransmitter,
each with different effects on postsynaptic
cell
Types of Neurons
Functional
Classification
Structural Classification
 Sensory
 use # processes
extending from cell
 Interneurons
 Motor
body
1. Multipolar neurons
2. Bipolar neurons
3. Unipolar neurons
Multipolar Neurons
 several dendrites with 1 axon
 includes most neurons in brain & spinal cord
Bipolar Neuron
 1 main dendrite & 1 axon
 retina, inner ear, olfactory area of brain
Unipolar Neuron
 are sensory neurons that begin in embryo as




bipolar
during development axon & dendrite fuse then
divide into 2 branches (both have characteristic
structure & function of an axon)
1 branch ends with dendrites (out of CNS)
2nd branch ends in axon terminal (in CNS)
cell bodies of most found in ganglia
Unipolar Neuron
Purkinje Cells
 found in cerebellum
Pyramidal Cells
 in cerebral cortex of brain
Neuroglia (Glia)
 ~50% vol of CNS
 “glue”
 do not generate or propagate action potentials
 multiply & divide in mature nervous systems
 glioma:
 brain tumors derived from glial cells
 very malignant, grow rapidly
Glial Cells of the CNS
1. ASTROCYTES
2. OLIGODENDROCYTES
3. MICROGLIA
4. EPENDYMAL CELLS
Astrocytes
 star-shaped
 largest & most numerous of glial cells
 functions:
1. physically support neurons
2. assist in blood-brain-barrier (bbb)
3. in embryo: regulate growth, migration,
&interconnections between neurons
4. help maintain appropriate chemical
environment for propagation of action
potentials
Oligodendrocytes
 “few trees”
 smaller & fewer branches than astrocytes
 Functions:
1. form & maintain myelin sheath on axons in
CNS
2. 1 oligo. myelinates many axons
Microglia
 small cells with slender processes giving off
many spine-like projections
 function:
1. phagocytes


remove cellular debris made during normal
development
remove microbes & damaged nervous tissue
Ependymal Cells
 single layer of cuboidal to columnar cells
 ciliated & have microvilli
 function:
1. line ventricles of brain & central canal of
spinal cord
2. produce, monitor, & assist in circulation of
cerebrospinal fluid (CSF)
3. form bbb
Neuroglial Cells of the PNS
 Schwann cells
 Satellite cells
Schwann Cells
 functions:
1. myelinate axons in PNS
 1 Schwann cell myelinates 1 axon
2. participate in axon regeneration
Satellite Cells
 flat cells that surround cell bodies of neurons
in PNS ganglia
 functions:
1. structural support
2. regulate exchange of materials between
neuronal cell bodies & interstitial fluid
Myelination
 myelin sheath: made up of multilayered lipid &
protein (plasma membrane) covering
 function:
1. electrically insulates axon
2. increases speed of nerve impulses
Myelinated & Unmyelinated
Axons
Nodes of Ranvier
 gaps in myelin sheath
 1 Schwann cell wraps axon between nodes of
Ranvier
Myelin
 amount increases from birth to maturity
 infant‘s responses slower & less coordinated as
older child or adult in part because myelination
is a work in progress thru infancy
Demyelination
 loss of myelin sheath
 see in disorders:
 multiple sclerosis
 Tay-Sachs
 side effect of radiation therapy & chemotherapy
Gray Matter of the Nervous
System
 contains:
 neuronal cell bodies
 dendrites
 unmyelinated axons
 axon terminals
 neuroglia
White Matter of the Nervous
System
 composed of:
 myelinated axons