neural control mechanism Flashcards
neurons
The basic unit of the nervous system is the individual
nerve cell, or neuron .
Neurons operate by generating electrical signals that
move from one part of the cell to another part of the same
cell or to neighboring cells.
cell body
Cell body (Soma): contains the nucleus and ribosomes and
thus has the genetic information and machinery necessary for
protein synthesis.
-involved in grated potetials
-involved in protein synthases of Neurotransmitters, Enzymes, membrane proteins
dendrites
series of highly branched outgrowths of the cell
body
Branching dendrites increase a cell’s surface area—some
neurons may have as many as 400,000 dendrites
Knoblike outgrowths called dendritic spines increase the
surface area
ligand gated channels
- neurotransitters bind to pocet of LG channel which allows positive charge to come in causing depolarization (EPSP)
- or N.T makes negative charge come in causing repolariation (IPSP)
Axon
a long process that extends from the cell body and carries outgoing signals
to its target cells
segment or axon hillock also
termed as “trigger zone”
Region of the axon that arises from the cell body (initial segment or axon hillock ) also
termed as “trigger zone”
collaterals
The axon may have branches, called collaterals . The greater the degree of branching of the
axon and axon collaterals, the greater the cell’s sphere of influence
axon terminal
Each branch ends in an axon terminal , which is responsible for releasing neurotransmitters
from the axon
varicosities
Alternatively, some neurons release their chemical messengers from a series of bulging areas
along the axon known as varicosities
myelin
The axons of many neurons are covered by sheaths of myelin, usually consists of 20 to 200
layers of highly modified plasma membrane
schwann cells
In the PNS, cells called Schwann cells form individual myelin sheaths surrounding 1- to
1.5-mm-long segments at regular intervals along some axons
oligondendrocytes
In the brain and spinal cord, these myelin-forming cells are the oligodendrocytes . Each
oligodendrocyte may branch to form myelin on as many as 40 axons
nodes of ranvier
The spaces between adjacent sections of myelin where the axon’s plasma membrane is
exposed to extracellular fluid are called the nodes of Ranvier
maintenance of the structure and function of cell axon
Various organelles and other materials must move as far as 1 meter between the cell
body and the axon terminals. This movement, termed axonal transport , depends
on a scaffolding of microtubule “rails” running the length of the axon and
specialized types of motor proteins known as kinesins and dyneins ( Figure 6.3 ).
At one end, these double-headed motor proteins bind to their cellular cargo, and the
other end uses energy derived from the hydrolysis of ATP to “walk” along the
microtubules.
kinesin
Kinesin transport mainly occurs from the cell body toward the axon terminals (
anterograde ) and is important in moving nutrient molecules, enzymes,
mitochondria, neurotransmitter-filled vesicles, and other organelles.
dynein
Dynein movement is in the other direction ( retrograde ), carrying recycled membrane
vesicles, growth factors, and other chemical signals that can affect the neuron’s
morphology, biochemistry, and connectivity. Retrograde transport is also the route
by which some harmful agents invade the CNS, including tetanus toxin and the
herpes simplex, rabies, and polio viruses.
afferent neurons
convey information from the tissues and organs
of the body toward the CNS
At their peripheral ends have sensory receptors , which respond to
various physical or chemical changes in their environment by
generating electrical signals in the neuron
Structurally different, two branched axon, one is peripheral process,
begins where the dendritic branches converge from the receptor
endings. The other branch, central process, enters the CNS to form
junctions with other neurons
Cell body and the long axon are outside the CNS
Efferent neurons
convey information away from the CNS to
effector cells like muscle, gland, or other cell types
Conventional neuronal structure (refer to figure) Their cell bodies and
dendrites are within the CNS
interneurons
Interneurons: connect neurons within the CNS
Lie entirely within the CNS
They account for over 99% of all neurons and have a wide range
of physiological properties, shapes, and functions.
The number of interneurons interposed between specific afferent
and efferent neurons varies according to the complexity of the
action they control.
Example: The knee-jerk reflex elicited by tapping below the
kneecap activates thigh muscles without interneurons. In
contrast, to hear a song or smell a certain perfume that evokes
memories of someone you know, millions of interneurons may
be involved
divisions of the nervous system
-central NS
-Peripheral NS
Central NS
-includes brain and spinal cord and supporting cells called neuroglia
-strcutures of brain and spinal cord are arrranged into two layers, gray and white matter
