Nervous Tissue Flashcards
What are the 3 function of the nervous system?
- Sensory input- afferent neurons
- Integration- mostly interneurons
- Motor output- efferent neurons
What is the CNS composed of?
Brain and Spinal cord
Name a few structures that the PNS is composed of.
Cranial Nerves
Spinal Nerves
Ganglia
Plexuses (intermingling of neuron cell process from ventral rami of different cord levels)
*Nerve is collection of axons outside of CNS
What two cell types are found in nervous tissue?
- Nerve cells or Neurons
2. Neuroglia, Glia, or Supporting cells
Describe the characteristics of neurons.
They are the main functional cells of the nervous system. They can produce and transmit action potentials. But, they can not multiply and divide.
Describe the characteristics of Neuroglia or supporting cells.
- much small than neurons but outnumber them greatly.
- support neurons so they can function effectively and efficiently.
- do NOT generate action potentials
- can multiply and divide (few exceptions)
- structural support, electrical insulation, metabolic exchange from vasculature and neurons
What are the 3 special characteristics of neurons.
- Extreme longevity (~100yrs)
- Most are Amitotic (lose ability to divide as they become communicating links in the nervous system)
- High Metabolic rate (need large and continuos supple of glucose and oxygen, will die in few min. without)
Describe function and characteristics of the Neuronal cell body/ Perikaryon.
- biosynthetic center of neuron
- always unmyelinated, no action potentials
- basophilic, contain nissl bodies which are clumps of RER and free ribosomes
- No centrioles, b/c they are amitotic
- range from 4-150 micrometers in diameter
- microtubules and golgi aparatus
Describe function and characteristics of the dendrites.
- main receptive or input regions of neurons
- always unmyelinated, no action potentials
- can be multiple on a single neuron
- No golgi aparatus
- have small “dendritic spines” that branch off and are 1-3 micrometers in length
What is the signal called while in the dendrites and cell body before it reaches the axon hillock?
Graded Potential
Where is the initial action potential generated?
Axon hillock (has no organelles but is still part of the cell body?)
Describe the structure of axons/nerve fibers.
- conducting region of neuron, can generate and transmit AP’s
- can be myelinated, only one axon per neuron
- Axon terminals to relase chemicals (NT’s)
- no nissl bodies or golgi apparatus
What are the 2 types of transportation for axons?
- Anterograde: Cell body to Axon terminal
- Retrograde: Axon terminal to Cell body
- Transport via microtubules*
What is the secretory portion of a neuron?
Axon terminal (Boutons)
What is the function of dendritic spines?
Increase surface area for reception
Describe the change of channels as you travel along a neuron.
- Ligand, mechanical, chemical gated channels in the dendrites and cell body
- Voltage-gated Na+/K+ channels in axon
- Voltage-gated Ca+ channels in axon terminal
What are the 3 types of neurons based on structure?
- Multipolar- 3 or more processes
- Bipolar- 2 processes (1 axon/1dendrite)
- Unipolar- 1 process (no synapse @ cell body)
Which type of neuron is found the least in the human body?
Bipolar neurons
What type of neuron is most common in the brain and spinal cord?
Multipolar neuron
What type of neurons are typically multipolar? Bipolar? Unipolar?
Mulitpolar- Motor or Interneurons
Bipolar- Special sensory (retinal/olfaction)
Unipolar- General sensory
What are the 5 types of synapses?
*1. Axodendritic- axon terminal and dendrite
2. Axosomatic- Axon terminal and cell body
3. Axoaxonic- between axons
4. Dendrodendritic- between dendrites
5. Dendrosomatic- dendrite and cell body
() denotes most common in human body
What can a postsynaptic neuron also be?
An effector cell
Describe a chemical synapse.
Action potentials directly between adjacent cells via Gap Junctions. They are fast and direct signals, can synchronize cells. EX: Cardiac Cells
What are the 6 steps involved in transfer across a chemical synapse?
- AP arrives at axon terminal of presynaptic axon
- Depolarization causes voltage-gated Ca channels to open
- Ca signals for release of NT’s (stored in synaptic vesicles) via exocytosis into synaptic cleft
- NT diffuses across synapse and binds to receptors at postsynaptic membrane
- Binding of NT opens ligand-gated channels, allowing ions to flow across postsynaptic membrane
- This produces local changes in postsynaptic potential, a type of graded potential (depolarizing or hyperpolarizing)
Give a few examples of a Neurotransmiter.
Acetylcholine, biogenic amines, AA’s, peptides, ATP, dissolved gases (NO/CO)
3 ways the Neurotransmitter can be removed from the postsynaptic receptor?
- Degredation by enzymes
- Reuptake by astrocytes or presynaptic terminal
- Diffusion away from the synapse
What is the ratio of Neuroglia/Neurons in the brain
10/1
What 4 Neuroglia are found in the CNS?
- Astrocyte
- Microglial cells
- Ependymal cells
- Oligodendrocyte
What 2 Neuroglia are found in the PNS?
- Schwann cells
2. Satellite cells
Describe an Oligodendrocyte.
- Produce myelin in CNS for electrical insulation
- Myelinate axons of multiple neurons
- predominant in white matter
- line up in rows
- cytoplasm unstained due to Golgi
- not as many processes as others like astrocyte
What is the predominant cell is white matter?
Oligodendrocyte
Describe an Astrocyte.
- Largest of neuroglia, with lots of processes
- Connected to one another via gap junctions
- Major role to control ionic environment of neurons
- Are majority in Grey matter
What are the extensions of an astrocyte onto a capillary called?
Perivascular feet
What are some function of Perivascular feet?
- Cover endothelial cells of capillaries, help w/ BBB
- Regulate vasodilation of vessels
- Used as scaffolding during fetal development
- Form cellular scar tissue when CNS is damaged
- Can get rid of excess NT’s
Describe an Ependymal cell.
- Like low columnar/cuboidal cells that line spaces in CNS like ventricles
- Connected to each other vis tight junctions
- Have cilia to help circulate CSF
- Part of choroid plexus, help transport water/ions
Which cells predominate in gray matter?
Astrocytes
Describe a Microglia.
- evenly distributed in gray/white matter
- have short processes/spikes that cannot be seen without special staining
- Elongated nuclei that are densely stained
- Immune defense
- originate from Monocytes (act like macrophages)
Describe Schwann cells.
- AKA Neurolemmocytes
- Myelinate PNS (only 1 inter nodal segment on 1 axon)
- provide structural support for unmyelinated axons
What is the function of satellite cells?
-They surround neuronal cell bodies in a ganglion (PNS) for support
What is white matter composed of?
Primarily myelinated axons and some neuroglia (oligodendrocytes), white due to myelin (fats)
What is gray matter composed of?
Neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia. Gray due to nissl bodies and lack of myelin.
What are clusters of neuronal cell bodies in PNS? CNS?
PNS: Ganglion
CNS: Nucleus
What is a bundle of Neuronal axons in the PNS? CNS?
PNS: Nerve
CNS: Tract
What are the 5 main things a nerve contains?
- Neuron processes
- Schwann cells
- Connective tissue
- Blood vessels
- Lymphatic vessels
What is different about schwann cells with myelinated and unmyelinated axons?
They can only myelin ate 1 segment of 1 axon, BUT they can associate with multiple unmyelinated axons to provide support.
What is the function of Myelin Sheaths?
- Protect and electrically insulate axons from other axons
2. Increases speed of nerve impulse transmission
Describe the basic sequence of myelination.
The schwann cell attaches to the axon and begins wrapping its membrane multiple times around the axon. As it does this, the cytoplasm and organelles (neurilemma) are pushed to the outside. The membranes fuse to increase the lipid content.
What is myelin stained with?
Osmium Tetroxide (lipids)
What 2 things does the rate of impulse depend on?
- Axon diameter (larger=faster)
- Myelination
- Unmyelinated axons: Continuous Conduction
- Myelinated axons: Saltatory Conduction
