Download Spinal nerves

The cells of the nervous
system
LESSON N.9 - PSYCHOBIOLOGY
because of the location and volume as compared to our
body, the brain has always been a matter of conjecture
about its fundamental role in the control of our behavior.
However it is only in the last two centuries, with a sudden
acceleration in the last 20 years, thanks to the advent of
modern neuroscience that we have begun to understand
more deeply the basics of its and then our, functioning.
Neurons
Synapses and Ionic channel
The peripheral nervous system consists of
the:
Nerves: Set of axons bundled together
which extend for the whole body and
transmit the information to the muscles or
sensory surfaces.
These are in turn divided into:
cranial nerves
spinal nerves
autonomic nervous system
Cranial nerves
The 12 pairs of cranial nerves are
sensory systems and head engines
and are directly connected to the
brain.
3 (I II VIII) are sensory pathways to
the brain
5 (III IV VI XI XII) are motor
pathways from the brain
4 (V VII IX X) are both sensory and
motor
Spinal nerves
For the whole length of the spinal
cord there are 31 pairs of spinal
nerves that are combined to the
spinal cord at regular intervals
through the openings in the spine.
Every nerve is formed by the fusion of
two distinct branches (roots).
The ventral root consists of motor
projections ranging from the spinal
cord to the muscles
The dorsal root consists of sensory
projections ranging from the body to
the spinal cord
The spinal nerves are named
according to the vertebra to which
are connected: 8 cervical, 12 thoracic,
5 lumbar, 5 sacral, coccygeal 1
THE ANS
Clusters of neurons called autonomic ganglia are located in various parts of
the body. Their name comes from the belief that they could act
independently from the brain, but we now know that they are still regulated
by the CNS through the called preganglionic neurons. By contrast the
ganglion neurons that innervate the rest of the body are called
postganglionic.
THE ANS is formed by three main sections:
The sympathetic: the ganglionic projections are contained in the spinal cord
and innervate the sympathetic chain that through postganglionic. Performs
an action of activation on the entire body (increases blood pressure, dilated
pupils, increased heart rate)
The parasympathetic: its preganglionic are located above and below the
sympathetic, while the postganglionic are scattered throughout the body,
usually near the organ controlled. Generally it acts as opposed to the
sympathetic system
The enteric: is similar to a crosslinked system in the walls of the digestive
organs, and is controlled both by the sympathetic and parasympathetic, but
also indirectly from the CNS
The central nervous system is formed by:
BRAIN
SPINAL CORD
Exploring the brain
Exploring the brain
Brain development
The role of pruning
At birth, the neurons in the visual and motor cortices have connections to the superior colliculus, spinal cord, and pons. The neurons in each
cortex are selectively pruned, leaving connections that are made with the functionally appropriate processing centers. Therefore, the neurons in
the visual cortex prune the synapses with neurons in the spinal cord, and the motor cortex severs connections with the superior colliculus. This
variation of pruning is known as large-scaled stereotyped axon pruning. Neurons send long axon branches to appropriate and inappropriate target
areas, and the inappropriate connections are eventually pruned away.
Regressive events refine the abundance of connections, seen in neurogenesis, to create a specific and mature circuitry. Apoptosis and pruning are
the two main methods of severing the undesired connections. In apoptosis, the neuron is killed and all connections associated with the neuron
are also eliminated.
It is believed that the purpose of synaptic pruning is to remove unnecessary neuronal structures from the brain; as the human brain develops, the
need to understand more complex structures becomes much more pertinent, and simpler associations formed at childhood are thought to be
replaced by complex structures.
Important subcortical structures
White matter fibers
Diffusion Tension Imaging (DTI) is used to study
the white matter fibers in the brain
http://www.wesapiens.org/file/1876131/
Comparison+between+Nissl+and+Golgi+t
echniques
The Brodmann areas
Brodmann areas have been discussed, debated, refined, and renamed exhaustively for nearly a century and remain the most widely known and
frequently cited cytoarchitectural organization of the human cortex.
Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions.
For example, Brodmann areas 1, 2 and 3 are the primary somatosensory cortex; area 4 is the primary motor cortex; area 17 is the primary visual
cortex; and areas 41 and 42 correspond closely to primary auditory cortex. Higher order functions of the association cortical areas are also
consistently localized to the same Brodmann areas by neurophysiological, functional imaging, and other methods (e.g., the consistent localization
of Broca's speech and language area to the left Brodmann areas 44 and 45). However, functional imaging can only identify the approximate
localization of brain activations in terms of Brodmann areas since their actual boundaries in any individual brain requires its histological
examination.
Brain ventricles
The four cavities of the human brain are called ventricles. The two largest are the lateral ventricles in the cerebrum; the third
ventricle is in the diencephalon of the forebrain between the right and left thalamus; and the fourth ventricle is located at the
back of the pons and upper half of the medulla oblongata of the hindbrain. The ventricles are concerned with the production and
circulation of cerebrospinal fluid. Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spine. It is
produced in the choroid plexuses of the ventricles of the brain. It acts as a cushion or buffer for the brain's cortex, providing basic
mechanical and immunological protection to the brain inside the skull. The CSF also serves a vital function in cerebral
autoregulation of cerebral blood flow.
Blood supply in the brain
Blood supply to the brain is normally
divided into anterior and posterior
segments, relating to the different arteries
that supply the brain. The two main pairs
of arteries are the Internal carotid arteries
(supply the anterior brain) and vertebral
arteries (supplying the brainstem and
posterior brain).
The anterior and posterior cerebral
circulations are interconnected via
bilateral posterior communicating
arteries. They are part of the Circle of
Willis, which provides backup circulation
to the brain. In case one of the supply
arteries is occluded, the Circle of Willis
provides interconnections between the
anterior and the posterior cerebral
circulation along the floor of the cerebral
vault, providing blood to tissues that
would otherwise become ischemic
Brain meninges
The meninges are the three membranes that envelop the brain
and spinal cord. In mammals, the meninges are the dura mater,
the arachnoid mater, and the pia mater. Cerebrospinal fluid is
located in the subarachnoid space between the arachnoid
mater and the pia mater.The primary function of the meninges
is to protect the central nervous system
History:
Fathers of modern
Neuroscience
Camillo Golgi
Black reaction
Santiago Ramon Y Cajal
Neuron doctrine vs.
reticular theory
Charles Sherrington
Synapses
Nervous cells
• The soma or cell body
incoming information is
processed through spatial
and temporal summation
processes
• The dendrites (dendritic
spines)
• Axon hillock numerator
role
• The axon
• synapses
Flusso dell’informazione nervosa
Primary information
Secondary information
Classification of the neuron
The neurons can be classified according to their
function:
sensory neurons
interneurons
motoneurons
All of these types can in turn be classified in
accordance with their morphology (no. Of
neurites in the output from the soma) in:
multipolar neurons
bipolar neurons
monopolar neurons
Neuroglia
In addition to neurons, the nervous system is
formed by a second type of cells, called neuroglia
or glia. Glia has a smaller morphological and
functional complexity and includes only four
types of cells:
astrocytes
microglia
oligodendrocytes
Schwann cells
Initially it was believed that the glia had only
structural support functions, but recently has
emerged that this is just one of many functions.
It has been demonstrated that the Glia can send
signals to each other and to the neurons, altering
the neural transmission mechanisms.
Astrocytes
Are cells with a star-shape, with numerous
ramifications that go in all directions, at the
same time interweaving with neurons and
blood vessels.
Their functions range from support and
communication between the blood vessels
and neurons. They are also responsible for
the formation of new synapses and dynamic
control of local blood flow. Finally they can
directly interact with neurotransmitters at
post-synaptic level.
They receive electrical impulses directly
from neurons, but are unable to generate
their own impulses.
Microglia
Microglia has primarily a role of macrophages and nervous environmental protection.
During development of the nervous system, through the phagocytosis of dead cells and waste material, it
contributes to the modeling of neural structures.
In the adult nervous system contributes to the maintenance of homeostasis in response to activating pathogens
present at the level of the central nervous system.
Oligodendrocytes and Schwann
cells
They are cells that perform the same
function, respectively in the CNS and in the
PNS.
These glial cells wrap their extended plasma
membrane in several coils around the axons
forming a layer of myelin that has the
function of acting as an insulating sheath,
preventing the dispersion of electric fields
related to nerve impulses that travel along
axons.
In particular, the longer axons that have to
carry nerve signals over long distances
compared to the soma are wrapped with
myelin, ensuring in these cases an efficient
and fast transmission
Myelination takes about 15-20 years in
humans.
Oligodendrocytes and Schwann
cells
Since glial cells have a limited length compared to the length of an axon, axon myelination along the entire length
will be discontinuous, formed by myelinated sections (internodes) and short sections devoid of myelin (nodes of
Ranvier).
Multiple sclerosis is a disease that affects the myelin, slowing down and preventing the transmission of nerve
impulses.