Chapter 6 - Neuronal Signaling and The Structure of The Nervous System Flashcards
Central Nervous System (CNS)
Brain and spinal cord
Peripheral Nervous System (PNS)
Nerves that connect the brain or spinal cord with the body’s muscles, glands, and sense organs
Neurons (characteristics)
- also known as “nerve cells”
- amitotic (do not divide)
- high metabolic rate
- clusters of cell bodies in the CNS is called nuclei.
- NOT the most numerous cell in CNS. Flush Cells are
What are the 4 Glial Cells of CNS?
Astrocytes, microglia, ependymal cells, and oligodendrocytes
Astrocytes
Support cells and control extracellular environment of neurons. They remove potassium ions and neurotransmitters around synapses. It also stimulates the formation of tight gap junctions. They also provide glucose and remove the secreted metabolic waste product ammonia.
Microglia
Immune system of the CNS, contribute to synapse remodeling and plasticity
Ependymal cells
Ciliated and involved with production of CSF and CSF movement
Oligodendrocytes
Responsible for the myelin formation
What are the two types of Glial cells of the PNS?
Satellite cells and Schwann cells
Satellite cells
Surround neuron bodies located in the PNS
Schwann cells
Surround and form myelin sheaths around the large nerve fibers. This is vital to regeneration and proper never signal conduction
What are the three classes of neurons?
Afferent, efferent, and interneurons
Afferent neurons
- transmit information into the central nervous system from receptors at their peripheral endings
- cell body and the lob peripheral process of the axon are in the PNS. Only the shirt central of the axon enters the CNS
Efferent neurons
- Transmit information out of the CNS to effector cells, particularly muscles, glands, or other neurons
- cell body, dendrites, and a small segment of the axon is in the PNS
Interneurons
- Function as integrators and signal changers
- integrate groups of afferent and efferent neurons into reflex circuits
- lie entirely within the CNS
- account for >99% of all neurons
Synapses
- can use both chemical and electrical stimuli to pass information
- can be inhibitory or excitatory depending on the signal/neurotransmitter being transmitted
Neuron
individual cells that make up the nervous system
Cell Body (structure of neuron)
Contains the nucleus and ribosomes that make proteins. Contains most of the genetic information needed for the secretion of proteins,
Neurotransmitters
Chemical messengers that help communicate with other cells
Glial Cell
a non-neuronal cell. Not cell-cell communication, but functions as support for neurons.
Dendrites (structure of neuron)
receive the incoming information
-branching dendrites and dendritic spines increase the surface area
Axon
also known as nerve fiber, sends out the information (signals) to its target cells
Initiated Segment
propogated electrical signals are generated
Axon Collateral
greater the degree of branching, the greater the sphere of influence
Axon terminal
releases neurotransmitters from axon
varicosities
bulging areas in axon
kinesin
a motor neuron;transport from cell body to axin terminals mainly(ANTEROGRADE). It moves nutrient molecules, enzymes, mitochondria, neurotransmitter filled vesicles, and other organelles.
Dynein
motor neuron; (RETROGRADE) carries signals, recycled membrane vesicles, and growth factors that can affect the neruon connectivity, etc.
-Retrograde is the way in which some harmful agents can attack the CNS
Synapse
Is a junction between two neurons where one neuron alters the chemical signal and electrical activity of another
Presynaptic neuron
neuron conducting signal TOWARD a synapse
postsynaptic neuron
neuron conducting signals AWAY from a synapse
Transmission of neuronal activity
1) Afferent neurons in PNS receive input at sensory receptors
2) Efferent components of the PNS may terminate on muscle, gland, neuron, or other effector cells
Blood-brain barrier
selective filter for exchanged substances than is present between the blood and most other tissues.
Resting Membrane Potential
inside of the cell is negatively charged with respect to the outside
excitatory synapse
membrane potential of a postsynaptic neuron bought closer to threshold(hyperpolarized)
inhibitory synapse
membrane potential stabilized to resting potential
Convergence
Many presynaptic neurons affecting a single postsynaptic cell. Allows information from many sources to influence a cell’s activity.
Divergence
A single pre-synaptic neuron affects many of the post-synaptic cells. One cell affects many pathways
How do you determine the level of excitability of a post synpatic cell?
depends on the number of synapses active at any one time and the number that are ecitatory and inhibitory.
If the membrane of the post-synpatic neuron reaches threshold, it will generate action potentials that are propogated along its axon to the axon terminals, which in turn influence the excitability of other cells.
Electrical synapse
plasma membrane of the presynaptic and postsynaptic cells are joined by gap junctions
chemical synapse
specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands.
Mechanisms of signaling at a chemical synapse (6 steps)
1) action potential reaches terminal
2) volatage gated ion channels open
3) calcium enters the axon terminal
4) neurotransmitter is released and diffuses into the cleft
5) neurotransmitter binds to postsynaptic receptors
6) neurotransmitter removed from synaptic cleft
ionotropic receptors
activated receptors that are ion channels
metabotropic receptors
receptors may indirectly infleunce ion channels through a G-protein receptor and/or a second messenger
EPSP (excitatory postsynaptic potential)
temporary depolarization of postsynaptic membrane caused by the flow of positively charged ions into the postsynaptic cell as a result of the opening of ligand-sensitive channels.
The EPSP increases the neurons membrane potential.
IPSP (inhibitory postsynaptic potential)
hyperpolarzing graded potential; open to Cl and K channels. the Na permeability is not an
synaptic functions of drugs (eight of them)
1) increase leakage of neurotransmitter from vesicle to cytoplasm, exposing it to enzyme breakdown
2) increase transmitter release into the cell
3) block transmitter release
4) block cleft or intracellular enzymes that metabolize transmitter
5) bind to receptor on postsynaptic membrane to block (antagonist) or mimic(agonist) transmitter action
6) inhibit transmitter synthesis
7) block transmitter reuptake
8) inhibit or stimulate second messenger activity within postsynaptic cell
