Topic 5 Flashcards
is the development of the specific tissues and organs of the body.
Organogenesis
Organs that perform related functions are grouped into a - .
system
How many organ are there in
systems of the body
11 organ
is composed of the brain & spinal cord
Central Nervous System (CNS)
are the basic functional units of the CNS. It is a cell specialized to receive
stimuli from the environment and transmit impulses to the spinal cord and brain where
these impulses are interpreted; and then to the effector organs (e.g. muscle, stomach,
etc.) for response.
The neurons
(nerve cells)
The connective tissue cells of the CNS are the
(oligodendrocytes, astrocytes, microgliocytes and ependymal cells).
gliocytes
A neuron consists of:
nerve cell body
axon
dendrites
which contains cytoplasm and nucleus
nerve cell body
which conducts impulses away from the cell body. The axon presents at its
end many tiny branches called telodendria, where impulses leave the neuron. Several
axons may be grouped/ bundled together to form nerve tracts in the CNS or nerve
trunks in the peripheral nervous system (PNS). Number of axon in all neurons is constant
and is always one.
axon
which receive stimuli from the environment and convert these stimuli into
impulses. Number of dendrites in the neuron varies from none to many.
dendrites
Classification of neurons based on the number of dendrites present:
Unipolar neuron
Bipolar neuron
Multipolar neuron
> neuron w/ only one process (axon only)
Unipolar neuron
> neuron w/ two processes (axon & dendrite)
Bipolar neuron
> neuron w/ many processes (one axon & many
dendrites)
Multipolar neuron
Enlarged cranial portion of the neural tube becomes the
brain
The slender middle and caudal portions become the
spinal cord
Neural canal becomes the of the brain and the central canal of the
spinal cord
ventricles
Neural crest cells become (1) of the PNS that have their cell bodies in
ganglia, (2) neurolemocytes (Schwann cells) of the PNS, (3) adrenal medulla
cells, (4) melanocytes of skin and (5) a variety of structures in the face
neurons
Neural crest cells become (1) of the PNS that have their cell bodies in
ganglia, (2) (Schwann cells) of the PNS, (3) adrenal medulla
cells, (4) melanocytes of skin and (5) a variety of structures in the face
neurolemocytes
Neural crest cells become (1) of the PNS that have their cell bodies in
ganglia, (2) (Schwann cells) of the PNS, (3) , (4) melanocytes of skin and (5) a variety of structures in the face
adrenal medulla
cells
Neural crest cells become (1)neurolemocytes of the PNS that have their cell bodies in
ganglia, (2) (Schwann cells) of the PNS, (3) adrenal medulla
cells, (4) of skin and (5) a variety of structures in the face
melanocytes
Neuroepithelium gives rise to neurons, (astrocytes and oligodendrocytes) and
gliocytes and ependymal cells of the CNS
Layers of the Neural Tube Wall
- Germinal layer or ventricular zone
- Mantle layer or intermediate zone
- Marginal layer
inner layer; composed of neuroepithelial
cells that remain lining the central canal and designated as ependymal cells
Germinal layer or ventricular zone –
– middle layer; zone of high cell density,
formed by accumulation of neuroblasts and glioblasts; becomes the gray matter of
the CNS w/c contains cell bodies of neurons & several gliocytes.
Mantle layer or intermediate zone
– the outer layer surrounding the mantle layer; cell-sparse zone
where axons of neurons & some gliocytes are present; becomes the white matter
of the CNS which contains mainly myelinated axons of neurons
Marginal layer
The lateral wall of the neural tube is divided into 2 plates:
Alar or dorsal plate and
basal or ventral plate,
, a indentation in the neural cavity
that serves as a landmark to divide the wall.
bilateral
The contains cell bodies of
efferent or motor neurons that send axons into the PNS.
basal plate
contains neurons that
receive afferent or sensory input from the PNS.
Alar plate
Midline region of the wall dorsal to the neural canal constitutes the
roof plate
counterpart wall ventral to the neural canal is the
floor plate.
By of incubaton of chick embryo the enlarged cranial end of the neural
tube forms 3 brain vesicles:
27 hours
- occupies the rostral part of the head
Prosencephalon(forebrain)
is prosocoele; presents a depression on its floor, the infundibulum
Neural canal
) - located posterior to and marked off from the
prosencephalon by constriction; Neural canal is mesocoele.
Mesencephalon (midbrain
- located posteriorly and marked off from the
mesencephalon by a slight constriction. Neural canal is rhombocoele;
continuous posteriorly w/ the spinal cord.
Rhombencephalon (hindbrain)
The cranial neural tube that will develop into brain presents 11 enlargements
called
neuromeres separated by constrictions.
are a sign of metamerism or segmentation in the embryo.
Neuromeres
– occurs at the level of the midbrain; concave ventrally.
Midbrain flexure
– occurs between the midbrain and the hindbrain; concave
dorsally.
Pontine flexure
– appears at the junction of the hindbrain and spinal cord;
persists slightly in domestic animals; concave ventrally
Cervical flexure
Rhombocoele of metencephalon is ;
metacoele
the myelencephalon is the
.
myelocoele
, the latter being composed of the
optic vesicles and part of prosencephalon lying between the optic vesicles.
cephalic telencephalon and caudal diencephalon
telencephalon presents a median portion called
median telencephalon
2 lateral evagination called
lateral telencephalic vesicles.
The paired ganglia of cranial nerves w/
sensory components have developed from cephalic neural crests. These are:
Semilunar ganglion
Geniculate ganglion
Superior ganglion
Jugular ganglion
Neural canal becomes the
central canal.
Malformations of the Brain
Cerebellar hypoplasia and atrophy
Cerebellar abiotrophy
Hydrocephalus
Hydranencephaly
- failure of cerebellum to develop due to
destruction of cerebellar cortex.
Cerebellar hypoplasia and atrophy
- premature degeneration of Purkinje cell layer of
cerebellar cortex.
Cerebellar abiotrophy
– accumulation of excessive amount of cerebrospinal fluid in the
cranial cavity.
Hydrocephalus
– thin walled and greatly enlarged lateral ventricle filled with
CSF.
Hydranencephaly
Malformations of the Spinal Cord
Myelodysplasia
Myeloschisis
Meningocoele
Meningomyelocoele
Types of Myelodysplasia
Hypoplasia (aplasia)
Hydromyelia
Syrinomyelia
Diplomyelia
Diastematomyelia
– general term for a malformation of the spinal cord. Originates
during neurula.
Myelodysplasia
– reduced or absence of development of one or
more segments of spinal cord.
Hypoplasia (aplasia)
– dilation of central canal due to excess accumulation of
CSF.
Hydromyelia
– abnormal cavitation of the spinal cord.
Syrinomyelia
– 2 spinal cords develop beside each other usually in one set
or meninges and in one vertebral canal.
Diplomyelia
- 2 spinal cords develop w/ a partition between them.
Usually in separate vertebral canals and have separate meninges.
Diastematomyelia
– cleft in the neural tube brought about by the failure of this part to close
during neurulation.
Myeloschisis
– protrusion of the meninges through an opening in the vertebral
arches to form a cyst beneath the skin
Meningocoele
– similar to meningocoele except that both meninges and
spinal cord protrudes.
Meningomyelocoele
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- are associated with
Meningocoele
Myeloschisis
– the failure of vertebral arches to close dorsal to spinal cord.
Spina bifida
