Tema 7 Flashcards
what is an excitable cell
Those that can modify their membrane potential in response to various stimuli.
They generate electrical responses (action potentials) that serve as signals that trigger other events.
The most important are neurons and muscle cells
There are several secretory cells that have voltage-dependent channels and excitability, such as:
Hypophysis
β-cells of the pancreas
Adrenal medulla cells
what is a membrane potential
Its the imbalance of electrical charges across cell membranes
All the cells are more electronegative in their interior than in their exterior.
The membrane potential is around -60 to -100 mV.
what is an action potential
Excitable cells trigger them
Its the rapid change of the membrane potential, from negative to slightly positive values (depolarization).
Its produced by a rapid change in membrane permeability for Na+ –> it enters the cell.
It requires the opening of ion channels operated by voltage (have to be abundant).
If the depolarization is sufficiently intense, it will produce a change in the membrane potential and cause an action potential.
which are the cellular elements of the NS
- neurons or nerve cells
- glial cells or glia
in CNS
-oligodendroglia
-astroglia
-microglia
in PNS
-schwann cells
-satellite cells
NEURONS characteristics
Excitable cells specialized in conducting electrical impulses (action potentials).
Characteristics that differentiate them from other cells:
-They are very long-lived cells, which in principle last a lifetime.
-They are amitotic, or postmitotic cells: they do not divide.
-Its metabolism is markedly aerobic and dependent on the consumption of oxygen and glucose.
morphology of neutrons
1) Body or soma
2) Dendritas
3) Axon
describe the soma
It contains the nucleus and cellular organelles.
It has a variable size (~ 5-140 μm Ø).
Functionally, it is the metabolic center of the neuron and it receives and transmits information in the form of electrical signals.
It can receive numerous projections (dendrites).
The neuronal soma emits a unique projection –> AXON
describe the dendrites
They tend to be very numerous in each neuron.
* Branched formations that increase the area capable of receiving information from other neurons.
* They contain receptors (ligand-dependent channels) for neurotransmitters.
* They send their electrical signals to the soma.
describe the axon
Single projection that leaves the neuronal soma towards the target cells.
Tubular structure of ~ 0.2 to 20 μm, can measure > 1 m.
Main structure of information conduction, in the form of action potentials.
First portion: axonic cone
–>where the local potentials are integrated and the action potential is triggered (or not) thanks to its high density of voltage- dependent channels.
It can branch (axonal collaterals)
Neuron diversity
-morphological
Morphological types
1) Anaxonic neurons:
– Neurons with dendrites but without axons.
2)Monopolar neurons:
– From the soma emerges a single process that quickly branches off.
3) Bipolar neurons:
– Only two processes, dendrite and axon, emerge from the soma.
4) Multipolar neurons:
– They have an axon and one or more dendritic trees that emerge from all the neuronal
soma.
– They represent the largest part of vertebrate neurons.
– Infinity of sizes and shapes, depending on the number of synapses they receive.
Neuron diversity
-functional types
1) Sensory or afferent neurons:
– Located in the ganglia of the PNS
– They are usually monopolar , without dendrites.
– They send information of an internal or external stimulus to the CNS
2) Motor or efferent neurons:
– They carry information from the CNS to other parts of the body .
– The somatic motor neurons innervate skeletal muscle of voluntary control.
– Neurons of the autonomic nervous system innervate glands and smooth
muscle.
– They are usually multipolar neurons
Interneurons or association neurons
– The most abundant of the nervous system.
– Located completely in CNS.
– All are multipolar neurons.
– Their main functions are:
* Distribute information through the CNS
* Integrate sensory information.
* Coordinate motor activity.
GLIAL CELLS description
Classically considered support cells for neurons, they surround somas and axons.
Smaller size than neurons
They divide themselves.
Between 10 and 50 times more numerous than neurons in the central NS.
GLIAL CELLS distribution
in CNS
-oligodendrocytes
-astrocytes
-microglia
in PNS
-schwann cells
-satellite cells
GLIAL CELLS functions
- They serve as support elements, providing firmness and structure to the brain. Sometimes, they isolate functional groups of neurons.
- The oligodendrocytes and the Schwann cells FORM the MYELIN that isolates axons.
- Some eliminate traces of injured or dead neurons.
- They maintain the extracellular environment, regulating the K+ conc. and eliminating neurotransmitters.
- During embryonic development some glial cells guide the migration of neurons and direct the growth of axons.
- Astrocytes form the blood-brain barrier.
- They participate in the nutrition of neurons.
