Neuroscience third edition notes and summary
Exons: are sequences of DNA that make up a gene. Between the Exons, inactive segments of DNA are
called Introns. Exons are translated into messenger RNA in order to be transcribed, they are flanked by
5’ (upstream) or 3’ (downstream) regulatory sequences. These sequences control gene expression.
Neurons have the same DNA makeup of other cells, however, they behave much differently thn other
cells, and thus, the difference must e in the regulatory sequences that determine which of the DNA
segments are expressed and how.
Sherrington and Cajal identified the discreteness of neurons in the CNS and Cajal coined the term
“synapse” which was confirmed by electron microscopy in the 1950s.
They identified the neuron, which is specialized for electrical signaling over long distances, and glial cells
which are not capable of signal conduction.
Neurons are different than other cells in that they are structurally specialized for intercellular
communication; they have many dendrites which have the primary function of being the target of
intercellular or synaptic communication. Dendrites have a high content of ribosomes and specific
cytoskeletal proteins. Neurons also differ in their cytoskeleton and the specific organization of their
organelles in different areas of the CNS.
Tubulin proteins are present all within the neuron somas and their dendrites. Tau proteins are found
only in axons. The ends of axons and dendrites contain a protein called actin.
The axon is a specialized part of the neuron, its length is specific to humans as most animals have axons
that are only a few microns in lngth whereas human axons can travel up to meters. Local circuit neuron
systems and interneurons have short axons, whereas projectio n neurons have much longer axons.
There are two types of synapses in the CNS; chemical (common) and electrical (rare).
Glia are more numerous than neurons (3 to 1), they serve many functions but binding the cns together
as their name suggests is not onr of them. Astrocytes have many branches and serve aminly to maintain
the ionic environment for signal transduction, oligodendrocytes myelinate the CNS axons and microglia,
which some classify as macrophages of the CNS are derived mainly from hematopetic precursor cells
and a smaller portion are immediately derived from neuronal precursor cells, microglia act as
scavengers of debris and dead neurons and secrete hemotactic cytokines that attract other microglia to
the site of neuronal injury.
Neural circuits:
Neural circuits are defined as a group of neural components that are organized by function within the
CNS and can also include components in the PNS.
The neuropil is the aggregation of nerve cell bodies, axond and dendrites that fuse together forming a
large tangle. The neuropil is the functional unit of the neural circuit.
, The myotatic reflex )knee-jerk reflex) is an example of a neural circuit. There are three main components
to this reflex. Afferent fibers from the peripheral sensory receptors (here, the muscle stretch receptors)
that take the information from the muscle through afferent fibers and relays it into the CNS dorsal root
ganglia and then to the dorsal root neurons.
The second component occurs when the dorsal horn neurons communicate with the ventral horn
(motor) neurons to activate two distinct groups of neurons. The first is the efferent fibers that
communicate with the extensor muscles to get them to contract and produce the desired movement.
The second is a group of interneurons that act to inhibit the opposing group of flexor muscles in order
for the extensor muscles to contract.
There are two methods to measure electrical activity of a cell; 1- extracelluar, single unit recording by
placing an electrode near thre cell to record its electrical activity and this provides a crude measurement
of action potential. Single unit extracellular recording is also used to map out the sensory field of specific
areas or nerves. 2- intracellular recording by placing an electrode inside the cell in question and this
enables us to measure the finer action potential gradients within the components of a neural circuit and
how these components behave relative to one another during firing and activity.
There are two separate potential that occur in a reflex; receptor potential and this refers to the actiona
potential generated at the post synaptic receptor specialization and synaptic potential which refers to
the action potential in the synapse.
Organization of the nervous system:
Inside the CNS, collections of cell bodies are called neurons, whereas in the PNS, collections of cell
bodies are clumped together in ganglia.
The visceral motor division of the autonomic nervous system:
The visceral pre-ganglionoic neurons in the brainstem and spine communicate with sympathetic
autonomic ganglia that lie alongside pr in front of the spinal cord. The parasympathetic ganglia ie within
the target organs themselves. There is a third component called eteric sytem which is made up of small
ganglia and individual neurons that lie in the walls os of the gut and control gastric secretions and
motility.
Electrical signals of nerve cells:
The neuron is negatively charged across its cell membrane in a resting state. If an electrode is placed
inside the cell, the first thing it records is a baseline negative resting membrane potential. If a negative
current is oassed through the cell, it’s said to hyperpolarize it which produces a passive electrical
response. If a positive current is passed, it depolarizes the cell membrane and results in generation of an
action potential.
Exons: are sequences of DNA that make up a gene. Between the Exons, inactive segments of DNA are
called Introns. Exons are translated into messenger RNA in order to be transcribed, they are flanked by
5’ (upstream) or 3’ (downstream) regulatory sequences. These sequences control gene expression.
Neurons have the same DNA makeup of other cells, however, they behave much differently thn other
cells, and thus, the difference must e in the regulatory sequences that determine which of the DNA
segments are expressed and how.
Sherrington and Cajal identified the discreteness of neurons in the CNS and Cajal coined the term
“synapse” which was confirmed by electron microscopy in the 1950s.
They identified the neuron, which is specialized for electrical signaling over long distances, and glial cells
which are not capable of signal conduction.
Neurons are different than other cells in that they are structurally specialized for intercellular
communication; they have many dendrites which have the primary function of being the target of
intercellular or synaptic communication. Dendrites have a high content of ribosomes and specific
cytoskeletal proteins. Neurons also differ in their cytoskeleton and the specific organization of their
organelles in different areas of the CNS.
Tubulin proteins are present all within the neuron somas and their dendrites. Tau proteins are found
only in axons. The ends of axons and dendrites contain a protein called actin.
The axon is a specialized part of the neuron, its length is specific to humans as most animals have axons
that are only a few microns in lngth whereas human axons can travel up to meters. Local circuit neuron
systems and interneurons have short axons, whereas projectio n neurons have much longer axons.
There are two types of synapses in the CNS; chemical (common) and electrical (rare).
Glia are more numerous than neurons (3 to 1), they serve many functions but binding the cns together
as their name suggests is not onr of them. Astrocytes have many branches and serve aminly to maintain
the ionic environment for signal transduction, oligodendrocytes myelinate the CNS axons and microglia,
which some classify as macrophages of the CNS are derived mainly from hematopetic precursor cells
and a smaller portion are immediately derived from neuronal precursor cells, microglia act as
scavengers of debris and dead neurons and secrete hemotactic cytokines that attract other microglia to
the site of neuronal injury.
Neural circuits:
Neural circuits are defined as a group of neural components that are organized by function within the
CNS and can also include components in the PNS.
The neuropil is the aggregation of nerve cell bodies, axond and dendrites that fuse together forming a
large tangle. The neuropil is the functional unit of the neural circuit.
, The myotatic reflex )knee-jerk reflex) is an example of a neural circuit. There are three main components
to this reflex. Afferent fibers from the peripheral sensory receptors (here, the muscle stretch receptors)
that take the information from the muscle through afferent fibers and relays it into the CNS dorsal root
ganglia and then to the dorsal root neurons.
The second component occurs when the dorsal horn neurons communicate with the ventral horn
(motor) neurons to activate two distinct groups of neurons. The first is the efferent fibers that
communicate with the extensor muscles to get them to contract and produce the desired movement.
The second is a group of interneurons that act to inhibit the opposing group of flexor muscles in order
for the extensor muscles to contract.
There are two methods to measure electrical activity of a cell; 1- extracelluar, single unit recording by
placing an electrode near thre cell to record its electrical activity and this provides a crude measurement
of action potential. Single unit extracellular recording is also used to map out the sensory field of specific
areas or nerves. 2- intracellular recording by placing an electrode inside the cell in question and this
enables us to measure the finer action potential gradients within the components of a neural circuit and
how these components behave relative to one another during firing and activity.
There are two separate potential that occur in a reflex; receptor potential and this refers to the actiona
potential generated at the post synaptic receptor specialization and synaptic potential which refers to
the action potential in the synapse.
Organization of the nervous system:
Inside the CNS, collections of cell bodies are called neurons, whereas in the PNS, collections of cell
bodies are clumped together in ganglia.
The visceral motor division of the autonomic nervous system:
The visceral pre-ganglionoic neurons in the brainstem and spine communicate with sympathetic
autonomic ganglia that lie alongside pr in front of the spinal cord. The parasympathetic ganglia ie within
the target organs themselves. There is a third component called eteric sytem which is made up of small
ganglia and individual neurons that lie in the walls os of the gut and control gastric secretions and
motility.
Electrical signals of nerve cells:
The neuron is negatively charged across its cell membrane in a resting state. If an electrode is placed
inside the cell, the first thing it records is a baseline negative resting membrane potential. If a negative
current is oassed through the cell, it’s said to hyperpolarize it which produces a passive electrical
response. If a positive current is passed, it depolarizes the cell membrane and results in generation of an
action potential.
