Nervous Tissue
Epithelium
Classifications
of Tissues
• lines and covers
surfaces
Connective • protect, support, and
bind together
tissue
Muscular
tissue
• produces movement
Nervous
tissue
• receive stimuli and
conduct impulses
Nervous System Overview
• The nervous system detects environmental changes that
impact the body, then works in tandem with the
endocrine system to respond to such events.
• It is responsible for all our behaviors, memories, and
movement.
• It is able to accomplish all these functions because of the excitable
characteristic of nervous tissue, which allows for the generation of
nerve impulses (called action potentials).
Nervous System Overview
• Everything done in the nervous
system involves 3 fundamental
steps:
1. A sensory function detects
internal and external stimuli.
2. An interpretation is made
(analysis).
3. A motor response occurs
(reaction).
Nervous System Overview
Nervous System Overview
• Over 100 billion neurons and 10–50 times that number
of support cells (called neuroglia) are organized into two
main subdivisions:
• The central nevous
system (CNS)
• The peripheral nervous
system (PNS)
Nervous System Overview
• A “typical neuron is shown in this graphic.
• The Schwann cell depicted in red/purple is one of 6
types of neuroglia that we will
study shortly.
Photomicrograph showing neurons in
a network.
blue: neuron
red/purple: glial cell
Nervous System Overview
• As the “thinking” cells of the brain, each neuron does, in
miniature, what the entire nervous system does as an
organ: Receive, process and transmit information by
manipulating the flow of charge across their
membranes.
• Neuroglia (glial cells) play a major role in support and
nutrition of the brain, but they do not manipulate
information.
• They maintain the internal environment so that neurons can
do their jobs.
Divisions of the Nervous System
• The central nervous system (CNS) consists of the brain
and spinal cord.
• The peripheral nervous
system (PNS) consists of
all nervous tissue outside
the CNS, including
nerves, ganglia,
enteric plexuses, and
sensory receptors.
Divisions of the Nervous System
• Most signals that stimulate muscles to contract and
glands to secrete originate in the CNS.
• The PNS is further divided into:
• A somatic nervous
system (SNS)
• An autonomic
nervous system
(ANS)
• An enteric nervous
system (ENS)
Divisions of the Nervous System
• The SNS consists of:
• Somatic sensory (afferent) neurons that convey information
from sensory receptors in the head, body wall and limbs
towards the CNS.
• Somatic motor (efferent) neurons that conduct impulses away
from the CNS towards the skeletal muscles under voluntary
control in the periphery.
• Interneurons are any neurons that conduct impulses between
afferent and efferent neurons within the CNS.
Divisions of the Nervous System
• The ANS consists of:
1. Sensory neurons that convey information from autonomic
sensory receptors located primarily in
visceral organs like the stomach or lungs to the CNS.
2. Motor neurons under involuntary control conduct nerve
impulses from the CNS to smooth muscle, cardiac muscle, and
glands. The motor part of the ANS consists of two branches
which usually have opposing actions:
• the sympathetic division
• the parasympathetic division
Divisions of the Nervous System
• The operation of the ENS, the “brain of the gut”,
involuntarily controls GI propulsion, and acid and
hormonal secretions.
• Once considered part
of the ANS, the ENS
consists of over 100
million neurons in
enteric plexuses that
extend most of the
length of the GI tract.
Divisions of the Nervous System
Divisions of the Nervous System
• Ganglia are small masses of neuronal cell bodies located
outside the brain and spinal cord, usually closely
associated with cranial and
spinal nerves.
• There are ganglia which
are somatic, autonomic,
and enteric (that is, they
contain those types
of neurons.)
Neurons and Neuroglia
• Neurons and neuroglia combine in a variety of ways in
different regions of the nervous system.
• Neurons are the real “functional unit” of the nervous system,
forming complex processing networks within the brain and
spinal cord that bring all regions of the body under CNS
control.
Neurons and Neuroglia
• Neurons and neuroglia combine in a variety of ways in
different regions of the nervous system.
• Neuroglia, though smaller than neurons, greatly
outnumber them.
• They are the “glue” that supports and maintains the
neuronal networks.
Neurons
• Though there are several different types of neurons,
most have:
• A cell body
• An axon
• Dendrites
• Axon
terminals
Neurons
• Neurons gather information at dendrites and
process it in the
dendritic tree and
cell body.
• Then they transmit
the information
down their axon to
the axon terminals.
Neurons
• Dendrites (little trees) are the receiving end of the
neuron.
• They are short, highly branched structures that conduct
impulses toward the cell body.
• They also contain
organelles.
Neurons
• The cell body has a nucleus surrounded by cytoplasm.
• Like all cells, neurons contain organelles such as lysosomes,
mitochondria, Golgi complexes, and rough
ER for protein production (in neurons, RER is called
Nissl bodies) – it imparts
a striped “tiger
appearance”.
Neurons
• The cell body has a nucleus surrounded by cytoplasm.
• Like all cells, neurons contain organelles such as lysosomes,
mitochondria, Golgi complexes, and rough
ER for protein production (in neurons, RER is called
Nissl bodies) – it imparts
a striped “tiger
appearance”.
Neurons
• Axons conduct impulses away from the cell body toward
another neuron or effector cell.
• The “axon hillock” is where the axon joins the cell body.
• The “initial segment”
is the beginning of
the axon.
• The “trigger zone” is
the junction between
the axon hillock and
the initial segment.
Neurons
• The axon and its collaterals end by dividing into many
fine processes called axon terminals (telodendria). Like
the dendrites, telodendria may also be highly
branched as they interact with the dendritic
tree of neurons “downstream”.
• The tips of some axon terminals swell into
bulb-shaped structures called
synaptic end bulbs.
Neurons
• The site of communication between two neurons or
between a neuron and another effector cell is called a
synapse.
 The synaptic cleft is the
gap between the pre and
post-synaptic cells.
Neurons
• Synaptic end bulbs and other varicosities on the axon
terminals of presynaptic neurons contain many tiny
membrane-enclosed sacs called
synaptic vesicles that store packets
of neurotransmitter chemicals.
• Many neurons contain two or
even three types of neurotransmitters, each with
different effects on the
postsynaptic cell.
Neurons
• Electrical impulses or action potentials (AP) cannot
propagate across a synaptic cleft. Instead,
neurotransmitters are used to communicate
at the synapse, and
re-establish the AP in
the postsynaptic cell.
Neurons
• Axons conduct impulses away from the cell body toward
another neuron or effector cell.
• The “axon hillock” is where the axon joins the cell body.
• The “initial segment”
is the beginning of
the axon.
• The “trigger zone” is
the junction between
the axon hillock and
the initial segment.
Neurons
• The axon and its collaterals end by dividing into many
fine processes called axon terminals (telodendria). Like
the dendrites, telodendria may also be highly
branched as they interact with the dendritic
tree of neurons “downstream”.
• The tips of some axon terminals swell into
bulb-shaped structures called
synaptic end bulbs.
Neurons
• The site of communication between two neurons or
between a neuron and another effector cell is called a
synapse.
 The synaptic cleft is the
gap between the pre and
post-synaptic cells.
Neurons
• Synaptic end bulbs and other varicosities on the axon
terminals of presynaptic neurons contain many tiny
membrane-enclosed sacs called
synaptic vesicles that store packets
of neurotransmitter chemicals.
Neurons
• Electrical impulses or action potentials (AP) cannot
propagate across a synaptic cleft. Instead,
neurotransmitters are used to communicate
at the synapse, and
re-establish the AP in
the postsynaptic cell.
Classifying Neurons
• Neurons display great diversity in size and shape - the
longest of them are almost as long as a person is tall,
extending from the toes to the lowest part of the brain.
• The pattern of dendritic branching is varied and distinctive
for neurons in different parts of the NS.
• Some have very short axons or lack axons altogether.
• Both structural and functional features are used to
classify the various neurons in the body.
Classifying Neurons
• Multipolar neurons have several dendrites and only one
axon and are located throughout
the brain and spinal cord.
• The vast majority of the
neurons in the human body
are multipolar.
Classifying Neurons
• Bipolar neurons have one main dendrite and one axon.
• They are used to convey the special senses of sight, smell,
hearing and balance.
As such, they are found
in the retina of the eye, the
inner ear, and the olfactory
(olfact = to smell) area of
the brain.
Classifying Neurons
• Unipolar (pseudounipolar) neurons contain one process
which extends from the body
and divides into a central
branch that functions as an axon
and as a dendritic root.
• Unipolar structure is often
employed for sensory
neurons that convey touch
and stretching information
from the extremities.
Classifying Neurons
• The functional classification of neurons is based on
electrophysiological properties (excitatory or inhibitory)
and the direction in which the AP is conveyed with
respect to the CNS.
• Sensory or afferent neurons convey APs into the CNS through
cranial or spinal nerves. Most are unipolar.
• Motor or efferent neurons convey APs away from the CNS to
effectors (muscles and glands) in the periphery through cranial
or spinal nerves. Most are multipolar.
Classifying Neurons
• The functional classification continued…
• Interneurons or association neurons are mainly located
within the CNS between sensory and motor neurons.
• Interneurons integrate (process) incoming sensory information from
sensory neurons and then elicit a motor response by activating the
appropriate motor neurons. Most interneurons are multipolar in
structure.
Neuroglia
• Neuroglia do not generate or conduct nerve
impulses.
• They support neurons by:
• Forming the Blood Brain Barrier (BBB)
• Forming the myelin sheath (nerve insulation) around neuronal
axons
• Making the CSF that circulates around the brain and spinal cord
• Participating in phagocytosis
Neuroglia
• There are 4 types of neuroglia in the CNS:
• Astrocytes - support neurons in the CNS
• Maintain the chemical environment (Ca2+ & K+)
• Oligodendrocytes - produce myelin in CNS
• Microglia - participate in phagocytosis
• Ependymal cells - form and circulate CSF
• There are 2 types of neuroglia in the PNS:
• Satellite cells - support neurons in PNS
• Schwann cells - produce myelin in PNS
Neuroglia
Neuroglia
• In the CNS:
Neuroglia
• In the PNS:
Neuroglia
• Myelination is the process of forming a myelin sheath
which insulates and increases nerve impulse speed.
• It is formed by
Oligodendrocytes
in the CNS and by
Schwann cells in
the PNS.
Neuroglia
• Nodes of Ranvier are the gaps in the myelin sheath.
• Each Schwann cell wraps one axon segment between two nodes of
Ranvier. Myelinated nodes are about 1 mm in length and have up to
100 layers.
• The amount of myelin increases from birth
to maturity, and its presence greatly increases
the speed of nerve conduction.
•
Diseases like Multiple Sclerosis
result from autoimmune
destruction of myelin.
Neuronal Regeneration
• To do any regeneration, neurons must be located in the
PNS, have an intact cell body, and be myelinated by
functional Schwann cells having a neurolemma.
• Demyelination refers to the loss or destruction of myelin
sheaths around axons. It may result from disease, or from
medical treatments such as radiation therapy and
chemotherapy.
• Any single episode of demyelination may cause deterioration of
affected nerves.
Gray and White Matter
• White matter of the brain and spinal cord is formed from
aggregations of myelinated axons from many neurons.
• The lipid part of myelin imparts the white appearance.
• Gray matter (gray because it lacks myelin) of the brain and
spinal cord is formed from neuronal cell bodies
and dendrites.
External Cord Anatomy
 Each posterior root has a swelling, the posterior
(dorsal) root ganglion, which contains the cell bodies of
sensory neurons. The anterior (ventral) root and
rootlets contain axons of motor neurons, which conduct
nerve impulses from the CNS to
effectors (muscles
and glands).
Internal Cord Anatomy
 In the spinal cord, the white matter is on the outside,
and the gray matter is on the inside. In the brain the
white matter is on the inside, and the gray matter is on
the outside.
Internal Cord Anatomy
The white matter of the cord consists of millions of
nerve fibers which transmit electrical information
between the limbs, trunk and organs of the body, and
the brain.
 Internal to this peripheral region, and surrounding the
central canal, is the

butterfly-shaped
central region made
up of nerve cell
bodies (gray matter –
here stained brown).
Internal Cord Anatomy
 Anterior (ventral) gray horns consist of somatic motor
neurons.
 Posterior (dorsal) gray horns consist of somatic and
autonomic sensory nuclei.
 The posterior gray horn is the site of synapse between firstorder sensory neurons coming in from the periphery, and
second-order neurons which either ascend in the cord or exit
back out as parts of reflex arcs.
Internal Cord Anatomy
 Other notable features visualized on a transected cord
are the anterior median fissure, the posterior median
sulcus, the gray and white commissures, and the central
canal.
 The central canal extends the entire length of the spinal cord
and
is filled
with CSF.
Internal Cord Anatomy
 A tract is a bundle of
neuronal axons that are
all located in a specific
area of the cord and all
traveling to the same
place (higher or lower in
the brain or cord).
Senses
Olfaction: Sense of Smell
• Smell is a chemical sense
• The human nose contains 10 million to 100 million
receptors for smell (olfaction) in the olfactory
epithelium of the superior part of the nasal cavity
• The olfactory epithelium covers the inferior surface of
the cribriform plate (of the ethmoid bone of the skull)
and extends along the superior nasal concha
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Olfaction: Sense of Smell (3 of 9)
There are 3 types of cells:
1. Olfactory receptor cells
2. Supporting cells
3. Basal cells
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Olfaction: Sense of Smell (5 of 9)
• Supporting cells (columnar epithelium): located in the
mucous membrane lining the nose
 Used for physical support, nourishment and
electrical insulation for olfactory receptor cells
• Basal stem cells undergo mitosis to replace olfactory
receptor cells
• Olfactory glands (Bowman’s glands) produce mucus
that is used to dissolve odor molecules so that
transduction may occur
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Gustation: Sense of Taste (1 of 8)
• Taste is a chemical sense, but it is much simpler than
olfaction
• There are only 5 primary tastes:
 Sour
 Sweet
 Bitter
 Salt
 Umami (meaty, savory)
• Flavors other than umami are combinations of the
other four primary tastes
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Gustation: Sense of Taste
• Taste buds contain receptors for the sensation of taste
 Approximately 10,000 taste buds are found on the
tongue of a young adult and on the soft palate,
pharynx, and epiglottis
• Taste buds contain 3 kinds of epithelial cells:
 Supporting cells
 Gustatory receptor cells
 Basal stem cells
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Gustation: Sense of Taste (4 of 8)
• Taste buds are located in elevations on the tongue
called papillae
• 3 types of papillae that contain taste buds:
 Vallate papillae - about 12 that contain 100–300
taste buds
 Fungiform papillae - scattered over the tongue with
about 5 taste buds each
 Foliate papillae - located in lateral trenches of the
tongue (most of their taste buds degenerate in early
childhood)
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Gustation: Sense of Taste
Filiform papillae cover the entire surface of the tongue
 Contain tactile receptors but no taste buds
 Increase friction to make it easier for the tongue to
move food within the mouth
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Vision (
• The lacrimal apparatus produces and drains tears
• The pathway for tears is:
 The lacrimal glands
 The lacrimal ducts
 The lacrimal puncta
 The lacrimal canaliculi
 The lacrimal sac
 The nasolacrimal ducts that carry the tears into the
nasal cavity
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Vision (7 of 42)
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Lacrimal glands
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Vision (
• Six extrinsic eye muscles move the eyes in almost any
direction
 These muscles include the superior rectus, inferior
rectus, lateral rectus, medial rectus, superior oblique
and inferior oblique
• The eyeball contains two tunics (coats):
 Fibrous tunic (the cornea and sclera)
 Vascular tunic (the choroid, ciliary body and iris)
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Vision (13 of 42)
• The retina contains sensors (photoreceptors) known as rods and
cones
 Rods to see in dim light
 Cones produce color vision
• From these sensors, information flows through the outer synaptic
layer to bipolar cells through the inner synaptic layer to ganglion cells
 Axons of these exit as the optic (II) nerve
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Vision (15 of 42)
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Vision (16 of 42)
• The eye is divided into an anterior chamber and a
posterior chamber by the iris (colored portion of the
eyeball)
• The anterior chamber (between the iris and cornea) is
filled with aqueous humor (a clear, watery liquid)
• The posterior chamber lies behind the iris and in front
of the lens and is also filled with aqueous humor
• Behind this is the posterior cavity (vitreous chamber)
filled with a transparent, gelatinous substance, the
vitreous humor
.
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Vision (32 of 42)
Rods and cones, the
photoreceptors in the
retina that convert light
energy into neural
impulses, were named for
the appearance of their
outer segments
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Vision (21 of 42)
Structure
Function
Lens
Refracts light.
Anterior cavity
Contains aqueous humor that helps
maintain shape of eyeball and
supplies oxygen and nutrients to lens
and cornea.
Vitreous chamber
Contains vitreous body that helps
maintain shape of eyeball and keeps
retina attached to choroid.
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Vision
Summary of the Structures of the Eyeball
Structure
Function
Fibrous tunic
Cornea: Admits and refracts
(bends) light.
Sclera: Provides shape and protects
inner parts.
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Vision (20 of 42)
Structure
Function
Vascular tunk
Iris: Regulates amount of light that
enters eyeball.
Ciliary body: Secretes aqueous
humor and alters shape of lens for
near or far vision (accommodation).
Choroid: Provides blood supply and
absorbs scattered light.
Retina
Receives light and converts it into
receptor potentials and nerve
impulses. Output to brain via axons
of ganglion cells, which form optic
(II) nerve.
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Hearing and Equilibrium
• The transduction of sound vibrations by the ear’s
sensory receptors into electrical signals is 1000 times
faster than the response to light by the eye’s
photoreceptors
• The ear also contains receptors for equilibrium
• The ear is divided into 3 regions: the external ear,
middle ear and internal ear
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The external (outer) ear contains the auricle (pinna),
external auditory canal, and the tympanic membrane
(eardrum)
 The auricle captures sound
 The external auditory canal transmits sound to the
eardrum
 Ceruminous glands secrete cerumen (earwax) to
protect the canal and eardrum
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• The middle ear contains 3 auditory ossicles (smallest
bones in the body)
 Malleus, incus, and stapes
 Sound vibrations are transmitted from the eardrum
through these 3 bones to the oval window
• The auditory tube (pharyngotympanic tube, eustachian
tube) extends from the middle ear into the
nasopharynx to regulate air pressure in the middle ear
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• Pressure waves travel from the scala vestibuli to the
vestibular membrane to the endolymph of the cochlear
duct.
• The basilar membrane vibrates. This moves the hair
cells of the spiral organ (organ of Corti) against the
tectorial membrane. These cells generate nerve
impulses in cochlear nerve fibers.
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Hearing and Equilibrium
• Equilibrium (balance) exists in two forms:
 Static equilibrium: maintenance of the body’s position
relative to the force of gravity
 Dynamic equilibrium: the maintenance of the body’s
position in response to sudden movements.
• Vestibular apparatus: The organs that maintain equilibrium.
Includes saccule, utricle (both otolithic organs), and
semicircular canals.
• Otoliths are calcium carbonate crystals. The walls of the
utricle and saccule contain a macula. The two maculae are
receptors for static equilibrium.
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The otolithic membrane sits on top of the macula.
Movement of the head causes gravity to move it down
over hair cells. The hair cells synapse with neurons in the
vestibular branch of the vestibulocochlear (VIII) nerve.
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• Three semicircular canals are responsible for dynamic
equilibrium
 The ducts lie at right angles to each other which allows
for rotational acceleration or deceleration
• An ampulla in each canal contains the crista with a group of
hair cells
 Movement of the head affects the endolymph and hair
cells
 This generates a potential leading to nerve impulses that
travel along the vestibular branch of the
vestibulocochlear (VIII) nerve
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