2: Anatomy of Neurons Flashcards
(19 cards)
How can neurons be categorized?
- Neurons can be categorized based on their shape (stellate, pyramidal)
- -neurochemical characteristics (dopamine, serotonin),
- location (visual cortex, auditory cortex) and
- connectivity (frontal-amygdala)
What is the difference between macrocircuits and microcircuits?
– Macrocircuits involve a population of neurons that project from one brain region to another (frontal-amygdala) while microcircuits reflect local cell-cell interactions within a particular brain region (visual cortex)
What is the process of distinguishing/classifying neurons?
- Anatomical classes are defined first by the location of the neuron in the nervous system
- further distinguished from each other by features which include dendritic and axon morphology
- Anatomical features also include synaptic connectivity (inputs and outputs) and molecular phenotype (the particular neurotransmitters, receptors, and ion channels expressed by a neuron).
- Neurons can be classified by general function (Sensory, motor, interneuron); Functions can also include whether the neuron is a relay neuron or a local interneuron or whether it is involved in sensory processing or correction of motor responses.
- Physiological actions can also include the firing properties of the neuron (bursting, tonic, quiescent).
What are the broad functional classification of neurons?
- sensory neurons
- motor neurons
- principal neurons (pyramidal/non-pyramidal)
- interneurons (pyramidal/non-pyramidal)
What are sensory neurons?
– also known as afferent neurons
– responsible for transforming a specific type of input or stimulus (chemical, physical, pressure) from sensory organs into electrical and chemical signals to inform the nervous system of internal or external environmental
events (called sensory transduction)
What are motor neurons?
- A motor neuron is responsible for the direct or indirect control of effector organs such as muscles and glands
- The axons of the motor neurons are efferent nerve fibers that carry signals away from the CNS to produce movements
What are principal neurons?
- Principal cells are the main neurons in the CNS (usually make up the macrocircuits of the brain and are typically excitatory)
- responsible for a lot of the output and communication between cells
- can be pyramidal or non-pyramidal
What are pyramidal neurons?
- pyramidal neurons have longer axons so they can reach further
- Have a pyramidal-shaped cell body (soma) and two distinct dendritic trees (apical and basal)
- All cortical output (consciousness) and activity of the cortex is mediated by pyramidal cells
What are interneurons?
- Interneurons typically make up the microcircuits and are inhibitory and they typically work with principal cells to help control their activity
- Interneurons operate between other neurons, so they mediate neuron-neuron interactions. They regulate how neurons communicate with each other
- pyramidal and non-pyramidal interneurons: Functionally, both types of interneurons are almost always inhibitory, but because of the length of their axons and the difference in dendritic arborization, they can perform different kind of inhibitory control
- -> ex. non-pyramidal interneurons are shorter, so they might hold inhibitory control between different cell types close by (proper functioning between neuronal pathways) while pyramidal cells might hold inhibitory control through different layers (thalamo-corticol)
- synapses from pyramidal cells is much lower than synapses onto pyramidal cells which are much higher
What is the cell membrane?
– Regulates movement of substances into and out of the cell: most cannot pass
– Proteins embedded within membrane allow substances into and out of cell
– Phospholipid bilayer
> Hydrophilic head: glycerol/ phosphorous/electrically charged molecule (choline)
> Hydrophobic tail: lipids (fatty acid molecules)
What is the nucleus?
- Contain genetic material
- Maintains the integrity of genes and controls the activities of the cell by regulating gene expression
- Nuclear envelope: a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm
- Nuclear pores are required to regulate nuclear transport of molecules across the envelope (rRNA and proteins that exit to make ribosomes); Transcription factors enter the nuclear pores and bind to DNA and then mRNA leaves
- Nuclear matrix that adds mechanical support
What is the mitochondria?
- Organelles that convert energy to forms that cells can use for work (cellular respiration, the catabolic process that generates ATP)
- Number of mitochondria is based upon the cells level of metabolic activity
- intracellular Ca2+ signaling, and generation of reactive oxygen species; neurons critically depend on mitochondrial function to establish membrane excitability and to execute the complex processes of neurotransmission and plasticity
What is the rough endoplasmic reticulum?
- Made of a series of membranes
- Attached ribosomes to its exterior make the membranes appear rough.
- Majority of the RER lies directly adjacent to the nucleus
- Ribosomes attach to mRNA and translate them by synthesizing proteins
What are ribosomes?
- The ribosomes on the RER help make proteins, along with RNA, during protein synthesis. Therefore, the RER is associated with protein production.
- Local protein synthesis in neurons plays a major role in neuronal development and synaptic plasticity
What is the Golgi apparatus?
- Made of a series of flat membrane sacs that are unconnected and known as cisternae.
- The Golgi apparatus packages, ships, and delivers proteins.
- As the proteins travel through the cisternae, sugars are added.
- It is these sugars that act as directions to determine where they should be delivered in the cell.
What is the Smooth Endoplasmic Reticulum?
- SER delivers the proteins created by the ribosomes of the RER.
- The SER releases calcium ions that are needed to help the muscles contract.
- detoxification of drugs and poisons by adding a hydroxyl group
- After a great influx of calcium into the cell during excitation, the smooth ER can act as a sink, allowing the cells to recover from the effects of membrane depolarization
- In a cell of the endocrine system, the SER synthesizes and releases steroids/hormones (lipids)
What are dendrites?
- Receiving portion of the nerve cell
- Signal collecting
- Electrical and biochemical signals channeled to cell body
- Surface area of dendrites is many times greater than that of cell body
What are dendritic spines and the different types?
– Expand the area of dendrites
– Points where inputs from other cells are directed
> Head region (point where connection to another cell is made)
> Shaft or neck
1) thin 2) mushroom 3) stubby
What are axons?
- Only one axon emanates from cell body
- May branch to give off collaterals
- Specialized to carry info (action potentials) away from cell body to other cells
- 0.2 to 20 um in diameter
- May extend up to 1 meter
