Neuron Anatomy Part 1 Flashcards
the physical structural features of a neuron
1) Cell body (soma)
2) Dendrites
3) Axon
4) Presynaptic terminal
Neuron
*Communicating/information processing cells
*‘Primary’
- vital to the life of a cell
-excitation and inhibition
-regulation of sensorimotor and higher functions (cognition and language)
Neurons are Composed of Gray & White Matter
Synapse:
* Point of contact between two neurons
Information-processing cells:
1) Sense changes in the environment and
these sensations, generating behaviors and actions and communicate these changes to other neurons
2) Commands the body’s response to
*essentially electrical responses that send/receive messages
Glial cells
*90% of CNS cells
*Supporting structures/cells of the nervous system
*Association
-protection of nerve cells and tissue repair
*provide insulation, support, structure, protection and nourishment to neighboring neurons
–can be divided into microglia (sanitation) or macroglia^(healing injury/infection)
types of Glial/Neuroglia cells
- Ependymal cells (CNS)
- Astrocytes (CNS)
- Microglia (CNS)
- Oligodendrocytes (CNS)
- Satellite cells (PNS)
- Schwaan Cells (PNS)
Oligodendrocyte (CNS)
Primary Glial Cell
- Small cells
- Provide support to axons of neurons
- Produce fatty substance called myelin
Astrocyte (CNS)
Primary Glial Cell
- Characterized by their star like shape.
- ‘End foot’ connects to capillaries
- Thought to have a role in nutritive function.
Schwann Cell (PNS)
Primary Glial Cell
- Similar to oligodendrocytes in CNS, Schwann cells myelinated neurons in the peripheral nervous system.
what composes gray and white matter of a neuron
- Gray matter = cell body and dendrites
- White matter = axon
cell body (soma)
*process information
* Spherical central part of the neuron
* Also known as the cell body
* Filled with cytoplasm, which contains:
– Cytosol: gel-like substances composed of salt and potassium
– Organelles: sub structures with various functions
* Organelles are protected by the neuronal membrane that prevents substances from the surrounding fluid from entering the cell
* Processing center of the neuron
Dendrites
Carries impulses toward the cell body
- Dendrites receive information
- Some types of neurons have single dendrite others have multiple branches or dendritic tree.
- Dendrites are designed with special receptor sites to receive chemical signals or respond to
sensory inputs. - Receptors: specialized protein
molecules in the dendritic
membrane which receive
neurotransmitters.
Axon
Carries impulses away from the cell body (some covered with myelin)
- Distinct function is action potential
- Axon is made up of white matter
- Neurons contain just 1 axon
- Carries electrical signal away from soma to axon terminal (i.e., sends out information to other cells)
- Can be less than a millimeter to over a meter long
- Variable diameter too: less than 1mm to 25mm in humans
- Diameter is important for the speed of the nerve impulse sent by the axon.
- Thicker = Faster!
Axon Terminals
- Also known as presynaptic terminals
- One component of synapse, or the point of communication between neuron
- Axons separate into a number of small fibers that have terminals
- Each of these axon terminals have a functional connection to another cell
- This is called a synapse
- This is where the axon terminals from one neuron meets the dendrite from another neuron.
Myelin Sheath of Axons
- Axons are covered in a myelin sheath
- Myelin is a multilayered lipid (fat) material that insulates and protects the nerve fiber.
- This insulation prevents the escape of electrical energy during impulse transmission and regulates the speed of nerve impulses.
- The myelin sheath is interrupted by nodes of ranvier (These are important for enhancing the rapid propagation of the electrical impulse (action potential) down the action)
Saltatory Conduction
- Action potential (electrical impulses) jumps from one node of Ranvier to the next, known as saltatory conduction.
- This facilitates rapid conduction inside the axon, up to 120 m/sec.
Myelination
- The production of myelin
*enhance the speed of the conduction of electrical impulses along the neuron, thereby improving the efficiency of neurotransmission and connectivity of the brain - The incomplete or impaired maturation of myelination has implications for the development of sensorimotor functions and speech-language-cognitive skills.
- Damaged myelin in the CNS impairs nerve impulse conduction and is found in demyelinating disorders such as multiple sclerosis.
Types of Neurons
- Sensory neurons, transmit impulses towards the CNS
- Motor neurons, transmit impulses away from the CNS
- Interneurons, connect cells within the CNS.
Micro vs Macro glia cells
Size plays a role with the
*macroglia (larger glial cells) insulating, protecting, and helping neurons to develop and migrate. (healing infection)
*microglia (smaller types of glia) have phagocytic properties, digesting foreign particles. (immunity)
Ependymal cells
Glial Cell
*creates CSF
*lines the ventricles of the brain and central canal of the spinal cord
What is the resting membrane potential and why is it important?
- The resting membrane potential of a neuron refers to the charge of the fluid inside and outside of the cell when the cell is at rest.
- crucial to the proper functioning of the nervous and muscular systems.
- it allows a cell to function as a battery, providing power to operate a variety of “molecular devices” embedded in the membrane
Depolarization/Hyperpolarization
*depolarization and hyperpolarization are two key ways to produce changes in the Vm(membrane potential/the separation of charges which is a voltage) of a neuron
Hyperpolarization
- Safety mechanism for the brain because it allows for a resting state and for normal voltage to return
*Hyperpolarizing events lead to a decrease in the responsiveness and activity of a neuron, and thus reduce information transfer across a network and are characterized as inhibitory or suppressive in nature.
- A change in potential that increases the polarized state of a membrane
Action Potential
An action potential is defined as a sudden, fast, transitory, and propagating change of the resting membrane potential. Only neurons and muscle cells are capable of generating an action potential
Events leading up to an action potential
- Thumbtack enters skin (or other stimulus)
- Membrane (receptor of nerve fibers in skin is stretched)
- Sodium (Na+) permeable channels open
- Sodium enters the cell (neuron) making it more positive. Because the cell was
more negative on the inside of the cell than the outside (polarized), the rush of the sodium into the cell depolarizes the cell. - If this depolarization reaches a certain threshold, then an action potential is
triggered.
- This electrical current travels down the axon to the axon terminal
- When it reaches the axons terminal, it forms a synapse on the next neuron.
- This is where the action potential ceases and synaptic transmission begins
- Their speed depends on the size of the axon
- Can range from 1 mile per hour to 150 miles per hour
- Up to this point we have mentioned an electrical impulse that travels down an axon.
- That electrical impulse is called an action potential
- Specifically, an action potential occurs when a neuron sends information down an axon. It is an explosion of electrical activity that is created by a depolarizing current as a result of some stimulus
Events Following an Action Potential
- Stimulus causes sodium (Na+) channels to open and sodium ions rush in 2. Neuron becomes more positive and becomes depolarized 3. It takes longer for potassium (K+) channels to open. When they do open, potassium rushes out of the cell, reversing the depolarization.
- At about this time, sodium channels start to close.
- This causes the action potential to go back toward -70 mV (a depolarization). The action potential actually goes past -70 mv (a hyperpolarization) because the
potassium channels stay open a bit too long. - Gradually, the ion concentrations ago back to resting levels and the cell returns to -70 mv.
- The neuron MUST be back to resting state before another action potential can fire.
afferent
carrying toward a given point; such as the sensory neurons and nerves that carry impulses toward the CNS
efferent
carrying away from a given point such as the Motor neurons that carry impulses away from the CNS
nerve
bundle of nerve cell fibers outside the CNS
Components of a Neuron
- Nucleus: located in the cell body, and is in charge of producing energy for the cells’ functions.
- Dendrites: the “arms of the neuron”, they form branch extensions that come out of different parts of the neuron. In other words, it is the cell body; main function is the reception of stimuli from other neurons.
- Cell body: where most of the neuron molecules are synthesized or generated and the most important activities are carried out to maintain life and take care of the functions of the nerve cell.
- Glial cells: Astrocytes, oligodendrocytes, microglia, Schwann cells, ependymocyte
- Myelin: It is found forming sheaths around neuronal axons, which allows them to be protected, isolated and transmit up to 100 times more efficiently the potential for action……In the central nervous system, myelin is produced by oligodendrocytes, while in the peripheral nervous system, it is produced by Schwann cells.
- Axon Terminal: aka synaptic boutons, are found at the end of the axon of the neuron, divided into terminals whose function is to link other neurons and create a synapse. The brain’s neurotransmitters are stored in the synaptic boutons in small areas called synaptic vesicles. The transmission of these vesicles from the terminal buttons of one neuron to the dendrites of another neuron is what is known as synapses
- Node of Ranvier: a gap or space between each myelin sheath of the axon extensions necessary to optimize impulse transmission and ensure that it does not get lost. This is what is known as nerve impulse jump conduction. The main function of the Node of Ranvier is to facilitate movement and optimize energy consumption.
- Axon: responsible for transmitting the electric signals between these brain cells. As was previously mentioned, axons have nerve endings wrapped in myelin sheaths that are responsible for transmitting electrical signals from the soma of the neuron to the terminal buttons.
