A&P Chapter 12

Nervous Tissue. For Test #3.

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What is the nervous system
About 3% of total body weight, one of the smallest but most complex systems.
What are some structures of the nervous system?
Brain, cranial nerves and their branches, ganglia, enteric plexuses, sensory receptors.
The brain is...
enclosed by the skull, contains 100 billion neurons, and 12 pairs (rgt and lft) of cranial nerves.
What is a nerve?
A bundle of hundreds to thousands of axons w/ associated tissue and blood vessels that lies outside of the brain and spinal cord.
What is the function of the spinal cord?
Connects the brain through the foramen magnum of the skull and is encircled by the bones of the vertebral colum, contains 100 million neurons.
Spinal nerves
31 prs, that emerge from the spinal cord, each serving a specific region on the right and left side of the body.
small masses of nervous tissue, consisting mostly of neuron cell bodies, located outside of brain and spinal cord
enteric plexuses
extensive neurons that help regulate the digestive system
sensory receptor
used to refer to dendrites of sensory neurons as well as separate, specialized cells that monitor changes in internal or external enviroment
Function of the nervous system
carries out a complex array of tasks, grouped into 3 basic functions: sensory, integrative, motor
Sensory function
detect internal stimuli. Info carried to brain/spinal cord through spinal & cranial nerves
Integrative function
nervous system integrates information by analyzing & storing. Connects Sensory and motor functions.Important function, perception
the conscious awareness of sensory stimuli
Motor function
activates effectors (muscles and glands) through cranial and spinal nerves. Stimulation of the effectors causes contraction and secretion.
What are the two subdivisions of the nervous system?
Central nervous system (CNS), Peripheral nervous sytem (PNS).
CNS consists of...
brain and spinal cord
PNS includes...
all nevous tissue outside of the CNS
What are neurons
also known as nerve cells, possess electrical excitability.
Electrical excitability
the ability to respond to a stimulus and convert it into AP
any change in the environment that is strong enough to initiate an AP
An AP or nerve impulse is a....
electrical signal that propagates (travels) along the surface of the membrane neuron, it begins and travels due to K+ and Na+ ions.
In what manner does the electrical signal travel?
once begun they travel at a rapid and constant strength
What are the three parts of a neuron
cell body, dendrites, and axons
cell body
known as the periaryon or soma, contains nucleus and cytoplasm with organelles.
What are the three unique features of the cell body
-there are nissil bodies located in the rough ER -hypofusion/lipofuscion the yellow pigment -neurofibrils (maintains shape and support)
structures that receive stimulus and send info to cell body, tree-shaped
takes all info from cell body and it is a strong enough stimulus it will send out information, long thin cylindrical w/ branches
Where are the places an Axon will send a stimulus?
Towards/Away from: neuron along the path, the brain, the spinal cord, glands, muscles, cells, organs
Parts of an Axon:
Hillock, initial segment, trigger zone, axon collateral, axolemma, axoplasm, axon terminal, myelin sheath
cone-shaped, cell body of axon
Initial segment
first part of the axon closest to the axon hillock
Trigger Zone
junction of hillock and initial segment
plasma membrane of the axon
cytoplasm of the axon
axon terminal
the many fine processes at the end of the axon
myelin sheath
only on myelinated axons/ Ex: PNS
stands for neurotransmitters
What are neurolgia and how large is it?
also known as glial, smaller than neurons, 5 to 50X more, take up 1/2 volume of CNS
What do neurolgia do?
They do not generate AP's, can divide, nourish/insulate/support/protect neurons
How many types or neurolgia are there?
6 types. 4 in CNS, 2 in PNS
4 types of neurolgia in CNS
Astrocytes, Oligodendrocytes,Microbial cells, ependymal cells
takes up the excess NTS's and maintains the K+ balance, star shaped cells, largest and most numerous
produces and secretes myelin, which increases the speed of AP's
microbial/ microglia
small phagocytic with spinelike projections, eats microbes and cell debris
ependymal cells
possess cilia and microvilli, lines the surface, secretes CSF (cerebrealspinal fluid)
2 types of neurolgia
schwann cells and satellite cells
schwann cells
myelin sheath (speeds up AP)
satellite cells
supports neuron cell bodies in the ganglion
Nerve Repair
-occurs only in PNS -neurolemma repairs damadged axon (schwann cells)
nodes of ranvier
"sausages" gaps in the myelin sheath, appear in intervals along the axon
resting membrane potential
electrochemical gradient
a concentration (chemical) difference plus an electrical difference
what happens when ion channels open?
they allow specific ions to move across the plasma membrane
how to ions move
from a higher concentration to a lower concentration, postively charged cations move toward a neg. charged area
ion charges open and close due to...
leakage channels
randomly alternate b/w open and closed. Permeabililty to K+ much higher than to NA+
ligand-gated channel
opens and closes in response to a specific chemical stimulus, a wide variety of chemical ligands can open and close channels
What are some examples of chemical ligands
neurotransmitters and hormones
What does the neurotransmitter acetylcholine do?
opens cation channels that allow Na+ and Ca+ to diffuse inward and K+ to diffuse outward
Mechanically gated channels
open or close in response to mechanical stimulation in the form of vibration, touch, pressure or tissue stretching
voltage gated channels
opens in response to a change in membrane potential (voltage)
how does resting membrane potential exist
because of a small buildup of -ions in the cytosol along the inside of the membrane and equal buildup of +ions in ECF along outer surface
potential energy is measured in...
millivolts (mv)
what is potential energy
a separation of positive and negative electrical charges
what is true about the difference in charge across the membrane
the greater the difference the larger the membrane potential (voltage)
what is graded potential
a small deviation from the membrane potential that makes the membrane more polarized or less polarized
more polarized
the inside is more negative
less polarized
the inside is less negative
when the response makes the membrane more polarized
depolarizing graded potential
when the response makes the membrane less polarized
decremental conduction
the mode of travel by which graded potentials die out as they spread along the membrane
the process by which graded potentials add together
the AP keeps its strength as it spreads along the membrane
continous conduction
involves step by step depolarization and repolarization of each adjacent segment of the plasma membrane
salatory conduction
the special mode of AP propagation that occurs along myelinated axons, occurs b/c of uneven distribution of voltage-gated channels
nodes of Ranvier (no myelin sheath)
the axolemma has many voltage-gated channels
what are the two consequences of a current crossing the membrane
AP appears to leap from node to node as each nodal area depolarized to threshold=saltatory, opening a small # of channels, energy efficient
what three things effect the speed of propagation of an AP
amount of myelination, axon diameter, and temperature
amount of myelination
AP propagates more rapidly along myelinated axons than along unmyelinated axons
axon diameter
larger-diameter axons propagate AP faster than smaller ones due to their larger surface areas
axons propagate AP's at lower speeds when cooled
presynaptic neuron
the synapse b/w neurons, it is the neuron sending the signal
postsynaptic neuron
neuron receiving the message
from axon to dendrite
from axon to axon
What are the two types of synapses
electrical and chemical
what are synapses essential for
homeostasis b/c they allow info to be filtered and integrated
what can come from the disruptions of synaptic communication
diseases and neurological disorders
electrical synapse
AP's conduct directly b/w adjacent cells through structures called gap junctions
where are gap junctions common
visceral smooth muscle, cardiac muscle, developing embryo, CNS
What are two main advantages to electrical synapses
Faster communication and Synchronization
Faster communication
faster communication, b/c AP conduct directly through gap junctions, they are faster
coordination of the activity of a group of neurons or muscle fibers, can produce AP's in unison
Chemical synapses
plasma membranes of presynaptic and postsynaptic neurons that are close but do not touch
postsynaptic potential
type of grade potential caused when postsynaptic neuron recieves chemical signal
excitatory and inhibitory posysynaptic potential (neurotransmitter deploarizes the postsynaptic membrane bringing it closer to threshold
Inhibitory postsynaptic potential
IPSP, neurotransmitter that causes hyperpolarization, membrane potential becomes more negative and farther than threshold
iontropic receptor
a type of neurotransmitter receptor that contains a NT binding site and an ion channel, are components of the same protein
what kind of channel is an iontropic receptor
ligand-gated channels
when does ESPS or IPSP occur in the postsynaptic cell
w/out the ligand, the ion channel component of ionotropic receptor is closed, when correct neurotransmitter binds ion channel opens
what do epsp's result in
opening of cation channels and allow K+, Na+, and Ca+ through the cell membrane
what do ipsp's result from
opening Cl channels, when these open chloride ions diffuse inward
spatial summation...
is the summation of postsynaptic potentials in response to stimuli that occur at different locations in membrane at the same time
temporal summation
summation of postsynaptic potentials in response to stimuli that occur at the same location in membrane at different times (gradual)
acetylcholine (ACh)
released by many PNS neurons and by some CNS neurons, when binding occurs w/ ionotropic receptors cation channels open
glutamic acids (amino acid) powerful excitatory affect
aspartic acid (amino acid) powerful excitatory affect
gamma aminobutyric acid and glycine
GABA and glycine are important inhibitory neurotransmitters, opens Cl channels
norepinephrine (NE)
plays roles in arousal (awakening from deep sleep), dreaming, regulating mood, serves as hormones
neurotransmitter, serves as hormones
are active during emotional responses, addictive behavior and pleasurable experiences, help regulate skeletal muscle tone and some mvmnt
concentrated in the neurons in a part of the brain, involved in sensory perception, temp regulation, control of mood, appetite and sleep
nitric oxide
important w/ widespread effects throughout the body
numerous and widespread in both CNS and PNS, bind to metabotropic receptors, have excitatory and inhibitory actions
200x stronger than morphine
endorphins and dynorphins
bodies natural painkillers

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