Download • Nervous System Cells

Nervous System Cells
• Neurons = functional cellular unit of nervous
system; action potentials
• Neuroglial cells = support, nourish, or
protect neurons
Oligodendroglial & Schwann cells =
insulate neurons with myelin
(Gnathostomes)
Astrocytes = transport nutrients (& signal
neurons at synapse); CNS only
Microglia = engulf bacteria; CNS only
Ependymal cells = cilliated cells that line
central canal & ventricles; CNS only
Neural Tissue
Motor Neuron
cell
body
axon
myelin under
a Schwann cell
dendrite
axon
hillock
synaptic
terminal
node of
Ranvier
Neuron Function
• Signal propagates down
an axon as ion channels
open along the axon
(changing voltage) –
electrical signal
• At the end of the axon
vessicles containing
neurotransmitter
release– chemical
signal
Schwann Cells & Oligodendroglia
Subphylum Vertebrata
myelin (Schwann cells &
oligodendrocytes)
brain
Nervous System Development
• Three ectodermal sources.
• Neural tube – becomes C.N.S., optic “nerve,”
retina, and pre-ganglionic motor nerves.
CNS derived only from neural tube.
• Neural crest – becomes post-ganglionic
nerves and peripheral glia.
• Neurogenic placodes – become postganglionic cranial nerve (V, VII, IX, X) AND
olfactory, vestibular, and lateralis sensory
receptor cells.
Vertebrate Neurula (section)
somite
notochord
coelom
gut
intermediate
mesoderm
lateral
plate mesoderm
Vertebrate Embryo (section)
neural
crest
cells
sclerotome
dermatome
myotome
splanchnic
mesoderm
somatic
mesoderm
gut
coelom
Vertebrate Embryo (section)
neural
crest
cells
sclerotome
dermatome
myotome
gut
coelom
Vertebrate Embryo (section)
neural
crest
cells
vertebra
dermatome
myotome
gut
coelom
Vertebrate Embryo (section)
will form
dorsal root
ganglion
vertebra
dermatome
myotome
developing
skin
gut
will form
other
ganglia
coelom
Neurogenic Placodes
(post-ganglionic cranial nerves V, VII, IX, & X)
Brain Development
• Neurons migrate from the
ependymal layer more
superficially; 1st migrate least.
• The anterior neural tube forms:
-Prosencephalon (Forebrain)
-Mesencephalon (Midbrain)
-Rhombencephalon
(Hindbrain)
rhombomeres = segmental
divisions
Brain Developmental Regions
• Prosencephalon = FOREBRAIN
Telencephalon cerebrum & olfactory lobes
Diencephalon thalamus, hypothalamus
• Mesencephalon = MIDBRAIN
optic lobes / superior colliculi & tegmentum
• Rhombencephalon = HINDBRAIN
Metencephalon cerebellum & pons
Myelencephalon medulla oblongata
Spinal Nerves Development
sensory
inter-
motor
notochord
Amniote Embryo (section)
Nervous System Overview
• Central Nervous System (CNS) = brain and
spinal cord; myelin from oligodendroglia
(astrocytes in synapse)
Tract= region of axons;
Nucleus or Cortex = region of cell bodies
• Peripheral Nervous System (PNS) = nerves
and ganglia; myelin from Schwann cells (also
can cover synapse)
Nerve = bundle of axons
Ganglion = bundle of cell bodies
PNS Overview
• Cranial Nerves =
attached to brain; many
have ganglia; numbered
with Roman numerals
from anterior to posterior
• Spinal Nerves =
attached to spinal cord;
most have ganglia;
distinctly segmental
dorsal root
ventral root
Peripheral Nervous System
• Sensory (Afferent) = brings info. to CNS
• Motor (Efferent) = takes info. from CNS
• Visceral = innervates smooth muscle or
organs in the coelom
• Somatic = innervates skel. muscle and skin
• Pre-ganglionic = cell bodies in the CNS;
between CNS & a ganglion
• Post-ganglionic Nerves = cell bodies in a
ganglion; between a ganglion & another
ganglion or a non-neural tissue
Nervous System Overview
Spinal nerves
• Spinal Nerves = segmental
from spinal cord
• Dorsal Root = afferent
(sensory) nerve
• Dorsal Root Ganglion =
afferent (sensory) neuron
cell bodies
• Ventral Root = efferent
(motor) nerve
• Sypathetic chain = chain of
ganglia ventral to spinal cord
Human Spinal Nerves
• Cervical Plexus (C1-C5) also
innervates diaphragm
(Phrenic nerves)
• Brachial Plexus (C5-T1)
innervates arm
• Intercostal / Thoracic Nerves
(T2-T12)
• Lumbar Plexus (T12-L5)
• Sacral Plexus (L5-Co2) also
innervates legs
(Sciatic nerves)
Human Thoracic Spinal Nerve
Human Thoracic Spinal Nerves
dorsal root
ventral root
dorsal root
ganglion
spinal
nerve
sypathetic ganglion
Human Thoracic Spinal Nerves
Sensory Neurons
Human Thoracic Spinal Nerves
Motor Neurons
Shingles
Herpes/chicken pox virus dormant in
spinal or cranial nerve
Cranial Nerves
• 10-13 nerves arising from the brain;
numbered anterior to posterior.
• 0 - nervus terminalis
sensory for blood vessels of olfactory epithelium
• I - olfactory “nerve”
(ethmoid foramina)
sensory fibers that innervate the olfactory epithelium
• II - optic nerve
(optic canal)
sensory “nerve;” innervates retina
not a true nerve; an extension of brain
Cranial Nerves
• III - oculomotor nerve (superior orbital fiss.)
motor nerve for 4 of the 6 extrinsic eye muscles
• IV - trochlear nerve (superior orbital fissure)
motor nerve for 1 of the 6 extrinsic eye muscles
• V - trigeminal nerve (3 branches) (foramina
ovale and spinosum & superior orbital fissure)
sensory for skin of head; motor for 1st arch muscles
(mandibular branch) Trigeminal/Gasserion Ganglion
• VI - abducens nerve (superior orbital fissure)
motor nerve for 1 of the 6 extrinsic eye muscles
Cranial Nerves
• VII - facial nerve (3 branches) (stylomastoid
foramen) - Facial/Geniculate Ganglion
sensory for taste buds and head lateralis system;
motor for 2nd arch muscles (hyomandibular branch)
• VIII - auditory nerve (Vestibulocochlear)
sensory for inner ear/vestibule (internal aud. meatus)
• IX - glossopharyngeal nerve (jugular for.)
sensory for taste and pharynx; motor for 3rd arch
muscles (1st branchial arch branch) – Superior &
Inferior Glossopharyngeal Ganglia
• IX - vagus nerve (jugular foramen)
sensory and motor for mouth, pharynx, outer ear, and
most viscera – Superior & Inferior Vagus Ganglia
Posterior-Most Cranial Nerves
• XI - spinal accessory nerve (amniotes
only)
(foramen magnum)
sensory & motor for branchiomeric muscles (e.g.,
trapezius, sternomastoid)
= branch of vagus in non-amniotes
• XII - hypoglossal nerve (amniotes only)
(hypoglossal canal)
motor & sensory for tongue muscles
= occipital nerves in non-amniotes
Shark-like Vertebrate
somitomeres
1-7
mandibular
arch
hyoid
arch
somites
1-4
1st branchial
arch
Special Sensory Cranial Nerves
optic
II
olfactory
I
terminal
0
mandibular
arch
auditory
VIII
hyoid
arch
1st branchial
arch
Segmental Cranial Nerves
III
IV
V VI VII IX
X
XII
XI
mandibular
arch
hyoid
arch
1st branchial
arch
Segmental Cranial Nerves
IV
III
V VI VII IX
II
VIII
X
XII
XI
0 I
mandibular
arch
hyoid
arch
1st branchial
arch
Suprabranchial Placodes
• Form ganglia for the
trigeminal, facial,
glossopharyngeal, &
vagus cranial
nerves.
III
IV
V
VI
VII
IX
0
X
XII
XI
II
I
VIII
CNS
• Spinal Cord = CNS dorsal to
notochord and posterior to
head
• Central canal = canal within
spinal cord
• Brain = enlarged anterior CNS
• Ventricles = cavities in brain
• Cerebrospinal fluid (CSF) =
fills ventricles & central canal
• Choroid plexus = tuft of
capillaries that secrete CSF
Meninges
• Meninges = layers of connective tissue
surrounding CNS
Non-tetrapods = 1 (primitive meninx)
Non-mammal tetrapods = 2 (dura matter
+ secondary meninx)
Mammals = 3
• Dura matter = outermost
• Arachnoid = middle
• Pia matter = innermost
CNS
• Gray matter = many cell bodies; >integration
• White matter = few cell bodies; many axons
with myelin (in Gnathostomes); >transport
• Gray matter ancestrally deep; white matter
superficial, EXCEPT superficial in forebrain
in amniotes, teleosts, hagfishes, and a few
chondrichthyans
Spinal Cord
cauda
equina
Brain Regions
• Prosencephalon = FOREBRAIN
Telencephalon cerebrum & olfactory lobes
Diencephalon thalamus, hypothalamus,
epiphysis, hypophysis, optic nerves
• Mesencephalon = MIDBRAIN;
tectum superior colliculi & inferior colliculus
tegmentum
• Rhombencephalon = HINDBRAIN
Metencephalon cerebellum & pons
Myelencephalon medulla oblongata
Brain Regions
Teleost Brain Regions
Pros-
Mes-
Rhomb-
Bird Brain Regions
Pros-
Mes-
Rhomb-
Telencephalon
• Olfactory lobes
• Cerebrum, large in mammals &
birds, lateral ventricles.
• In mammals, dorsal pallium
forms the 6 layered neocortex.
• gyri = folds of neocortex
• sulci = grooves of neocortex
• Actinopterygiians = gray matter
everts; single medial ventricle
• All other vertebrates = gray
matter inverts; 2 lateral ventricles
Diencephalon
• Thalamus, Hypothalamus, & Median
Ventricle (3rd).
• Optic nerves cross and enter brain at optic
chiasma (neurons pass through the
diencephalon, synapse in the
mesencephalon).
• Dorsal epiphysis (pineal & parietal organ)
& Ventral hypophysis (pituitary).
Mesencephalon
• Tectum (anterior = optic lobes /
superior colliculi;
posterior =
auditory tectum / inferior colliculus)
& Tegmentum.
• Optic ventricle in non-mammals,
cerebral aqueduct in mammals.
• Mammals have small paired
superior colliculi (optic tectum) and
median inferior colliculus
(auditory).
Metencephalon
• Cerebellum
& pons (only in
birds & mammals).
• Fourth ventricle.
• Actinopterygii = Cerebellum
expanded for processing lateral
line information
• Birds & Mammals = Cerebellum
expanded and folded (folds =
folia); pons present.
Myelencephalon
• Medulla oblongata.
• Fourth ventricle.
• Structurally very similar to
spinal cord.
• No complex intergration.
Human Brain Ventricles
Brain Evolution
Subphylum Vertebrata
2
meninges
1 meninx
cerebellum
cerebrum
everts;
large optic
tectum
enlarged
cerebrum
neocortex with
gyri & sulci;
small optic
lobes, 3
meninges
Sensory Receptors
• Sensory Receptor Cells = respond to a
physical property and can generate an action
potential (some are specialized neurons)
Chemoreception / Smell
• Chemoreception = reception of a chemical
stimulus; smell & taste
• Olfactory epithelium = chemo-receptive
epithelium associated with the nares (smell);
paired in Gnathostomes. Develop from…
Olfactory Placodes
that invaginate to form
the olfactory epithelium.
Olfactory Epithelium
• Olfactory neuron = sensory cell of olfactory
epithelium; cilia receptors
• Sustentacular cell = supporting cell of an
olfactory epithelium
• Basal cell = can form other cells of the
olfactory epith
Chemoreception / Smell
• Turbinates = bone that extends into the nasal
cavity of amniotes; more olfactory surface
area (well developed in mammals on maxilla
and ethmoid).
• Vomeronasal organ (VNO)= chemoreceptive
epithelium; different innervation than olfact.
Associated with phermone response.
Chemoreception / Taste
• Taste Buds = groups of chemo-receptive
cells (gustatory cells) in the oral cavity (taste)
• Gustatory cells have microvilli (not cillia) for
picking up chemical signals.
Mechanoreception
• Mechnoreception =
response to changes in
mechanical force; hearing,
balance, lateralis
• Hair Cells =
mechanoreceptive cells with
cillia (called stereocillia) and a
long cillium (called a
kinocillium)
• Neuromast organ = cluster
of hair cells and supporting
cells
Lateralis System
• Lateralis system = neuromasts on skin
surface or in canals; sense water motion
• On head and along body (lateral line) except
in hagfishes and amniotes. (Amphibians lose
it at metamorph.)
• Lateralis Placodes = form neuromasts.
Otic Placodes – Hearing/Balance
• Otic (Labyrinth) placodes sink in and form
the Vestibules (Labyrinths)
• Vestibule = semicircular canals and portions
filled with endolymph; balance/hearing
• Vestibular System = compartments and
semicircular canals in otic region; filled with
endolymph; balance/hearing
• Neuromasts at bases of semicircular canals and in sacculus
& utriculus chambers.
• Cupula w/ otoconia or otoliths.
Vestibular System
• Hagfishes = 1 semicircular canal
• lampreys = 2 semicircular canals
• gnathostomes = 3 semicircular canals
• Actinopterygiians = large otoliths
• One region of the vestibule functions in
sound reception. (lagena)
• Cochlea = coiled lagena in most mammals
Mammalian Vestibular System
semicircular
canal
utriculus
sacculus
lagena
(cochlea)
Ear Ossicles
• Middle ear = region adjacent to vestibule
containing ossicles
• Stapes (Columella) = Hyomandibula
modified for sound transmission in
tetrapods
• Incus = Quadrate modified for sound
transmission in mammals
• malleus = Articular modified for sound
transmission in mammals
Human Ear
Inner Ear Hair Cells
Electroreception
• Modified lateralis system in aquatic veretbrates.
• Ampullae of Lorenzini = electroreceptive
organs in chondrichthyans
Photoreception / Sight
• Photoreception = sensory response to light
stimulus; sight. Vertebrate eye.
• Eye develops from neural (optic vessicle) and
generalized ectoderm (optic placode).
Optic vessicle retina, iris, & intrinsic muscles.
Optic placode lens & cornea.
• Optic “nerve” = extension of brain
Eye Development
Vertebrate Eye
Retina
Cutaneous Sensory Systems
• Free sensory receptors = “naked”
dendrites in a tissue; pain
• Encapsulated sensory receptors =
dendrites covered in connective
tissue; touch, temperature, & pressure
• Associated sensory receptors =
dendrites wrapped around another
structure (e.g., hair, feather);
movement of the structure
Cutaneous Sensory Systems
Free
Encapsulated
Associated
Proproiception
• Proprioception = sensation of muscle
position and activity.
• Tendon organ = sensory dendrite
associated with the collagen of a
tendon. tendon tension
• Intrafusal muscle cells = modified
sensory muscle cells, monitored by an
intrinsic sensory dendrite. muscle
tension
Sensory Receptors
Subphylum Vertebrata
turbinates
vomeronasal
organ
brain
paired olfactory epithelia;
myelin (Schwann cells &
oligodendrocytes)
Amniota
vomeronasal
organ
lost
turbinates
* Groups in which many subgroups
have lost the vomeronasal organ
** superficial gray matter in teleosts
Subphylum Vertebrata
**
turbinates;
c.n. XI & XII;
VNO; lateralis lost;
stapes superficial
gray matter
myelin; pair. olf. epi.; 3 semicirc. canals
2 semicircular canal; lateralis syst. & nerves
brain; 1 semicircular canal; 0-X cranial nerves
Amniota
cochlea
coiled
malleus,
incus,
curved cochlea (lagena)
turbinates
VNO
lost
elongate
lagena
(cochlear duct)