Lecture #5 Flashcards
what does the PNS include?
sensory and motor neurons
what are the two divisions of the motor portion?
somatic motor division and the visceral motor division
describe the somatic motor division:
motor axons leave the CNS to enter in contact with skeletal muscles → voluntary
describe the visceral motor division:
autonomic nervous system which is involuntary and divided into two branches → these neurons can innervate smooth muscle, cardiac muscle, and glands (effectors)
what are the two branches of the visceral motor division?
orthosympathetic and parasympathetic
what is the role of the CNS?
the integration of the information coming from the sensory branch and the interaction with the motor components that control the effectors
where are all the PNS neurons generated from?
the neural crest
what are the glial cells that support the functionality of the PNS?
Schwann cells (derive from neural crest cells)
visually, what are the two parts of the CNS?
grey matter and white matter
what is the grey matter of the brain?
region in which there’s a tight accumulation of neuronal cell bodies with nuclei
what is the white matter in the brain?
region where we have bundles of myelinated axons that often surround the grey matter
what are the three subdomains of a neuron?
dendrite, cell body, axon
what is the role of the dendrite?
receive the information from other cells
what is the role of the cell body?
region containing the nucleus which tells the cells what to do
describe the structure of the axon:
characterized by the presence of a sheath of cells called myelin: cytoplasmic bundles derived from oligodendrocytes in the CNS and Schwann cells in the PNS → constitute an insulating layer for the salatory conduction of the action potential
what is located in the gaps between the myelin?
Nodes of Ranvier → where the axon is naked and where an additional action potential is generated
what are the three types of neurons?
sensory, motor, and interneurons
describe sensory neurons:
located near specific receptors or organs that receive signals from the environment and send them to the CNS
describe motor neurons:
located inside of the CNS and send messages along he axons to effector cells (muscles and glands) → carry impulses to effectors to initiate a response
describe interneurons:
relay messages between other neurons such as sensory and motor → elaborate the signals
most often found in the brain and spinal cord
what is the name of the membrane that wraps a nerve?
epineurium
inside the neuron, what groups and wraps the fascicles?
perineurium
what are the individual axons covered by?
endometrium + the glial cells producing the myelin (Schwann cells)
what does the simplest neural network consist of?
a sensory neuron connected to a motor neuron connected to a muscle cell
what is a synapse?
a region in which a presynaptic neuron (sending cell) makes a functional interaction with the dendrite (rarely in the soma) of a postsynaptic cell (receiving cell)
what is the presynaptic terminal characterized by?
a huge number of mitochondria and cytoplasmic vesicles containing the neurotransmitters, which are released in the thin space that spears the membranes of the two neurons
describe the system at the synapses:
electrochemical: on one side we have electrical signals coming from the presynaptic axon, and on the other hand we have the release of neurotransmitters in the cleft, which are then recognized by receptors on the postsynaptic cells
receptors at the post synaptic level are in most cases ion channels
what happens when neurons are electrically paired?
two membranes are fused together, so the cytoplasm of the presynaptic neuron is in connection with the cytoplasm of the post synaptic one → gap junction
which type of synapse (electrochemical or electrical) is most common in the CNS?
chemical synapses
in a chemical synapse, the presynaptic axon terminal comes very close to the post-synaptic neuron, leaving a tiny gap called what?
synaptic cleft → here there is the release of the neurotransmitter
describe the path of an action potential:
action potential arrives at the synapses and triggers a complex chain of bio-chemical processing steps that leads to the release of neurotransmitters from the presynaptic terminal into the synaptic cleft
these molecules will be detected by specialized receptors in the post-synaptic cell membrane and will open specific channels so that ions from the extracellular fluid flow into the cell
in ion influx leads to a change in membrane potential at the post-synaptic site, so that the chemical signal is translated into an electrical response
what is the voltage response of the post-synaptic neuron to the pre-synatpic action potential called?
post-synaptic potential
describe a pre-synaptic terminal:
there is a huge accumulation of vesicles which are electron dense because they are filled with neurotransmitters
describe a post-synaptic terminal:
a dense accumulation of proteins that are located below the cell membrane called post synaptic density (PSD)
contain scaffold proteins, receptors, and many other regulatory elects allowing the post-synaptic terminal to work
what is the pre-synaptic terminal referred to as?
the button
what is the post-synaptic terminal referred to as?
the spine
as we know, at the synaptic level, the neurons never work alone - what cells help with the function of the synapses?
both terminals are wrapped by glial cells, in particular macroglial cells like astrocytes → fundamental for the function of the synapse since they are rich in receptors and work with neurons for draining the neurotransmitters from the cleft
what does the pre-synaptic terminal contain besides vesicles to support the release of neurotransmitters from an energetic point of view?
mitochondria
what flank the regions where the neurotransmitters are released?
calcium channels
what specific role do the calcium channels play
voltage-sensitivie activation: fundamental for the synaptic electrochemical transmission → Ca entry though these channels evokes an increase of the intracellular Ca concentration which is a factor required for triggering the exocytosis of synaptic vesicles
no Ca = no transmission
describe the neurons-muscule junction:
post-synaptic terminal is organized in the crustal and the cleft, where you have the receptor for the neurotransmitter
in the cleft there is also acetylcholine esterase, an enzyme that degrades the neurotransmitter to avoid acetylcholine staying too long in the region
what is the synaptic connections that underlie neural circuits made of?
a dense tangle of dendrites, axon terminals, and glial cell processes, that altogether make up the neuropil wh
what are tripartite synapses?
glial cells that wrap neuropils → three entities working together: pre + post synaptic terminals and astrocytes
which neurons carry Info from the periphery towards the brain or spinal cord?
afferent neurons
which neurons carry info from the brain to the periphery?
efferent neurons
what is the function of interneurons?
participate only in local aspect of a circuit and are the huge number of neurons that we have in between → belong to the most complex part of the story because they contain the coding portion in which no one understands
what is the simplest circuit in the body?
myotatic reflex → knee jerk reaction
describe the myotatic reflex:
when the hammer tap stretches the tendon the sensory neuron sense this alteration and sends the signal toward the spinal cord contacting other neurons, that lead o the contraction of the extensor muscle and inhibition of the flexor muscle
what is electrophysiology?
the ability to perform recordings of the electrical activity of a neuron using very thin electrodes
what are the two electrophysiology methods?
extracellular recording and intracellular recording
describe extracellular recording:
you can only sense variations of the electric field occurring in a region that is outside the cell
what is extracellular recording particularly useful for?
the detection of temporal patterns of action potential activity and relating those patterns to stimulation by other inputs
what can intracellular recording detect?
can detect the smallest graded changes in electrical potential that trigger action potentials, and this allowing a more detailed analysis of communication among neurons within a circuit
why is the concept of a negative MP very important for the understanding the mechanism of an ion channel?
most important channel is the sodium / potassium pump (electrogenic) → it displaces 3+ charges outside and 2+ charges inside, displacing a single + charge outside than inside causing the negative potential
living cells always have a negative MP
what is depolarization?
influx of positive charges the moves the MP to a more positive value
what is hyperpolarization?
a further reduction of MP
what does hyperpolarization prevent?
the formation of an action potential
when are the voltage gated Ca channels activated?
only the the action potential arrives and induces depolarization of the membrane, allowing calcium influx and consequently the neurotransmitter release
what are active zones in voltage-gates Ca channels in the pre-synaptic regions?
highly ordered cytoskeleton formations were the membrane lipids are organized in “rafts” in which the channels are located
how does Botulinic toxin affect the pre-synaptic terminals?
most potent venom
affects transmembrane proteins hampering the ability of the docked vesicles to fuse with the PM
how does Latratoxin affect the pre-synaptic terminals?
induces the release of all neurotransmitters in docked vesicles without any stimulation (uncontrolled fusion)
how do ionotropic receptors work?
can be activation by a variation of membrane potential - express specific domains that undergo conformational changes in response to action potential variations
what are metabotropic receptors?
coupled with G proteins that perform the intracellular signaling
once the ligand interacts with the protein, it induces a conformational change, and this transmembrane protein activates the G protein that divides itself into subunits
how many different types of neurotransmitters are in our body?
over 100
what are the two broad categories of neurotransmitters?
neuropeptides and individual amino acids
describe the size of neuropeptides:
relatively large neurotransmitters composed of 3-36 aa
what do more than 80% of excitatory neurons in the cerebral cortex rely on?
the release of glutamate
but uncontrolled glutamate waves stimulate neurons in a toxic way
what do the vast majority of inhibitory neurons in the CNS rely on?
GABA
what are some examples of biogenic amines?
dopamine, norepinephrine, serotonin, and histamine
what was the first substance identified as a neurotransmitter and is fundament for muscles?
acetylcholine
