Ch.3, units of the nervous system Flashcards
Cajal vs golgis idea
Golgi: nerve net hypothesis/reticular theory nervous system is interconnected network of fibers so that all pieces could easily communicate
Cajal: Neuron theory/doctrine nervous system is made up of discrete cells
Cell body of the neuron and functions
Soma: integrates info gathered from dendrites for axon to send away. May have many dendrites but only one axon
contains ribosomes and mitochondria
Dendrites
collect info from other cells; incoming info; branching extensions. Main root is the single axon (which then carries messages away); afferent
Dendritic spines
Increases dendritic area; spines are important points of contact with other neurons for information collection. The extent of a cell’s branches and its spine number correspond to its information-processing capacity.
Axon hillock, function and definition
junction of soma and axon
Axon collaterals definition and function
From there, the axon may branch out into one or many hundreds of axon collaterals, which usually emerge from it at right angles, as shown at the bottom of Figure 3-3B. These projections enable the neuron to send messages to many other neurons.
Terminal button/end foot definition an function
At the end of each telodendrion is a knob called a terminal button, or an end foot. The terminal button sits very close to, but usually does not touch, a dendritic spine or some other part of another cell SAME AS AXONTERMINALS
Synapse definition and function
includes the surfaces of the end foot and the neighboring dendritic spine as well as the space between them. The synapse is the main information transfer site between neurons.
Difference between sensory neurons, interneurons, and motor neurons
Neurons of varying shapes and sizes are structured to perform three specialized functions. Sensory neurons (Figure 3-5A) conduct information from the sensory receptors in or on the body into the spinal cord and brain. Interneurons (Figure 3-5B) associate sensory and motor activity in the central nervous system (CNS) ONLY; CONSTITUTE MOST OF THE BRAIN’S NEURONS IN MAMMALS
. Motor neurons (Figure 3-5C) carry information from the brain and spinal cord out to the body’s muscles, MUCH LARGER, RESIDE IN LOWER BRAINSTEM AND SPINAL CORD; have to be so long to carry messages across long distances
Bipolar neuron: what type, function, and definition
s. A bipolar neuron found in the retina of the eye, for example, has a single short dendrite on one side of its cell body and a single short axon on the other side. Bipolar neurons transmit afferent (incoming) sensory information from the retina’s light receptors to the neurons that carry information into the brain’s visual centers.
Somatosesnory neuron,definition and function
A bit more structurally complicated is the somatosensory neuron, which brings sensory information from the body into the spinal cord, a long distance. Structurally, the somatosensory dendrite connects directly to its axon, so the cell body sits to one side of this long pathway.
Telodendria
Branched ends of nerve cells are called telodendria, which establish the functional contact with other nerve cells.
Presynaptic membrane vs postysynaptic membrane
Axon initial segment
before each myelin sheath, signal; integration center
Pyramidal Cell
A pyramidal cell has a long axon, a pyramid-shaped cell body, and two sets of dendrites
Purkinje neuron
is a distinctive interneuron with extremely branched dendrites that form a fan shape. It carries information from the cerebellum to the rest of the brain and spinal cord.
What do longer neuronal extensions mean?
neurons with a large cell body have long extensions, whereas neurons with a small cell body, such as stellate interneurons, have short extensions.
Long extensions carry information to distant parts of the nervous system; short extensions are engaged in local processing.
How do neurons respond when there are so many excitatory and inhibitory messages coming in at the same time?
The neuron’s response to all those inputs is reasonably democratic: it sums them. A neuron is spurred into action and sends messages to other neurons if its excitatory inputs exceed its inhibitory inputs. If the reverse occurs and inhibitory inputs exceed excitatory inputs, the neuron does not communicate.
GLIAL cell, ependymal cell
Small ovoid; secretes cerebrospinal fluid
Astrocytes
glial cells; Star shaped; contributes to neuronal nutrition, support, and repair; contributes to forming the blood–brain barrier and to healing scarring after injury; contributes to information transfer between neurons
contributes to formation of “tight junctions”, preventing toxins from entering the brain”
Microglial cell (glial cell)
Small, derived from blood; defensive function is to remove dead tissue
What occurs when there is an error in glial cell replication?
Glial cells differ from neurons in that most types of glial cells are produced throughout an organism’s life, and errors in their replication are a main source of abnormal growths — namely, brain tumors.
Tripartite synapse
2 neurons plus an astrocyte; three partners in this kind of synapse
Non-myelinated axons
Nerve signal (Action potential) must continuously regenerate along the length of an axon: myelin increases resistance to electrical flow bc it is “insulation”
