patrick yerkes. the nervous system carries information from one part of the body to another the...
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Nervous SystemPatrick Yerkes
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Introduction
The nervous system carries information from one part of the body to another
The nervous system transmit information by nerve impulses to communicate with other parts of the body
Main parts of the nervous system are the: Brain, Spinal Cord, and Nerves Regulate homeostasis and responds to
disease
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Organs and Divisions of the Nervous System
Central Nervous System (CNS) Occupies the midline or
central part of the body Peripheral Nervous
System (PNS) Nerves extend to the
outlying or peripheral part of the body▪ Autonomic Nervous
System (ANS)▪ Regulate the body’s
involuntary functions
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Cells of the Nervous System
•Two types of cell:•Neurons
•Nerve cells•Conduct nerve impulses
•Gila•Specialized connective tissue cells•Support neurons
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Neurons
Neurons consist of three parts Cell body- main part of
the neuron Dendrites- branching
projections of the neuron▪ Processes that transmits
impulses to the cell bodies
Axon- elongated projection▪ Transmits impulses away
from the cell body
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Transmitted Impulses
3 main types of neurons Sensory- Transmits impulses to the spinal
cord and brain from all parts of the body. Also called Afferent.
Motor- Transmits impulses away from the brain or spinal cord. Only conduct impulses to two kinds of tissues (muscle and glandular epithelial). Also call Efferent.
Interneuron- conduct impulses from the sensory neurons to motor neurons. Also call Central or Connective Neurons
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Neurons continued
Myelin is a white fatty substance formed by a Schwann Cells that wrap the axons around the CNS
The fibers are called Myelinated Fibers Nodes of Ranvier are indentations
between nearby Schwann Cells The outer cell membrane is the
Neurilemma Axons in the brain and spinal cord do not have
Neurilemma and decreases healing or regeneration
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Gila
Also called- Neuroglia Do not specialize in transmitting
nerve impulses Are support cells
Greek word Gila means “glue” Holds the functions neurons together
and protect them Regulates nerve function Common brain tumor is called Glioma
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Gila continued
Gila can be different in size Large cells that look
somewhat like star from their thread like extensions are called- Astrocytes
Microglia- are the smaller cells, they remain stationary▪ When inflamed or
degenerating brain tissue they will enlarge and act as micro scavengers
▪ Eat other micros
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Gila continued
Oligodenrocytes- hold nerve fibers together and serve a more important function which is to produce fatty myelin sheath that envelops nerve fibers located in the brain or spinal cord
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Nerves
Nerve- is a group of peripheral nerve fibers bundles together
Peripheral nerve fibers usually have myelin sheath Often look white
Bundles of axons in the CNS are called tracts
The axons could be myelinated and forming white matter
Unmyelinated axons and dendrites are called grey matter for being grey
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Nerves End
Each axon in a nerve is surrounded by thin wrapping fibrous connective tissue called ‘endoneurium’
Groups of endoneurium are called ‘fascicles’
Each fascicle is surrounded by a thin fibrous ‘perineurium’
A tough fibrous sheath is called a ‘epineurium’ which covers the whole nerve
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Stop
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Reflex Arcs
Some nerve impulses are called ‘Action Potentials’ Can travel over trillions of routes Neurons create the paths Routes named Neuron Pathways
Reflex Arcs are one way streets, the impulse can only go one way
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Reflex Neurons
A specialized type of neuron pathway is called the ‘reflex arc’ The simplest kind of reflex arc is a two-
neuron arc▪ Consist on only 2 types of neurons: Sensory
and Motor neurons Three- neuron arc is the next simplest
arc▪ Consist of all 3 neurons: Interneurons, Motor,
and Sensory
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Reflex Arc: Receptors
Are the beginnings of dendrites of sensory neurons
Often away from the spinal cord mostly located in; (in tendons, skin, or mucous membranes)
Sensory receptors are located in the quadriceps and the patellar tendon
Reflex response for the patellar tendon which is the rubber hammer and creates a knee- jerk Example of a two-
neuron arc
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Reflex Arc: Ganglion
A group of nerve- cell bodies located in t he PNS
Near the Spinal cord Each spinal ganglion contains no
sensory neuron The axon of the sensory neuron
travels from the cell body in the dorsal root ganglion Ends in the dendrites of another neuron
in the grey matter
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Reflex Arc: Continued
A microscopic space that separates the axon ending with one neuron from the dendrites to another This is called a Synapse
Nerve impulse stops at the synapse
The neuron axon forms a synapse called the ‘effectors’
Organs put the nerve signals to effect
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Reflex Arc: Effectors
Effectors are the muscles and glands Muscles contract The glands secretion
Only kind of reflexes by these effectors
A response to impulse conduction on the reflex arc is called a reflex
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Reflex Arc: Interneuron
Some neurons need 3 neurons More complex involves one more
sensory and motor neuron In the 3 neuron reflex
End of the sensory neurons’ axon synapses first with a interneuron
Before chemical signals are sent to a second synapse
Ending up with a conduction motor neuron
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Reflex Arc: Example
Applying an irritating stimulus to the skin of the thigh
It creates a 3- neuron reflex response
Causes contractions of the muscles to pull away from the leg away from the irritant
3 neuron contraction is also called a - withdrawal reflex
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Reflex Arc: Interneurons Continued
All interneuron's’ lie entirely within gray matter of the brain or spinal cord Grey matter forms the ‘H’ shaped inner
core of the spinal cord 3 neuron reflex has 2 synapses 2 neuron reflexes has 1 synapses
between a sensory neuron and the motor neuron
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Reflex Arc: Identify
•ID motor neuron
•Look at its dendrites and cell body•Located in spinal cord•Dies in the muscles
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Stop
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Nerve impulse: Introduction
A nerve impulse is a self- propagation wave of electrical disturbance that travels along the surface of a neuron’s plasma membrane.
Example A Spark going to fuse
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Nerve Impulse: Neuron
First they have to be stimulated ( a change in the neuron’s environment) Temperature, Pressure, and chemical
changes are used as stimuli Membrane of a resting neuron has a
slight positive charge on the outside and a negative charge on the inside This occurs from excessive amounts of
sodium ions (NA+) on the outside of the membrane
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Nerve Impulses: Neuron continued
When the section of the neuron is stimulated and the channels open
The sodium ions (NA+) flood inside
Causing the membrane to become positive temporarily and then becomes negative
The neuron immediately recovers the electrical disturbance stimuli (Na+)
If a impulse is traveling interacts with a section of a membrane insulating myelin ‘jumps’ around the
myelin called ‘saltatory conduction’
Saltatory Conduction can travel much faster then the nonmyelinated sections
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Saltatory Conduction
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Stop
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Synapse: Introduction
By definition a synapse is a place where impulses are transmitted from one neuron called presynaptic neuron to another postsynaptic neuron.
The presynaptic and postsynaptic neuron makes up the synapse
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Synapse: Structures
Three structures of the synapse is: a synaptic knob, a synaptic cleft, and the plasma membrane of a postsynaptic
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Synapse: Synaptic Knob
Is a tiny bulge at the end of the terminal branch of a presynaptic neuron’s axon
Each synaptic knob has many small sacs or vessels
Each vessel contains a very some quantity of a chemical compound called a neurotransmitter
After the nerve impulse arrives at the synaptic knob neurotransmitters molecules are released from the vesicles into the synaptic cleft
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Synapse: Synaptic Cleft
Is the space between the plasma membrane (of the postsynaptic neuron) and the synaptic knob
About 2 millionths of a centimeters in width
Has protein molecules embedded in opposite synaptic knobs
The receptors and neurotransmitters bind The binding can cause an impulse in the
postsynaptic neuron by opening the ion channels in the postsynaptic membrane
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Synapse: Neurotransmitter Neurotransmitters -
Chemicals help neurons communicate
Around 30 different compounds have been identified as neurotransmitters
Neurotransmitters are did sent randomly They are localized in
certain types of neuron groups and released in specific pathways
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Synapse: Neurotransmitter Sub Groups
ACETYLCHOLINE
Released in certain areas in the Spinal Cord
Also in the neuromuscular junctions Also called nerve-
muscle
CATECHOLAMINE
Includes Norepinephrine Dopamine Serotonin
All three of these transmitters play a role for Sleep Motor function Mood Pleasure recognition
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Synapse: Sub Groups
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Synapse: Pain Killer (Neurotransmitters)
2 ‘morphine’ like N.transmitters are called endorphins and enkephalins
Released in multiple areas in the spine and brain in the pain conduction pathways
Are natural pain killers Endorphins are
released mainly in intense exercise
Pain is normally used as a warning sign that draws our attention to injuries
Hold back against severe pain because it can stop us from continuing an activity that is needed for survival
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Activities to help relieve pain
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Synapse: Nitric Oxide
Unlike other transmitters Nitric Oxide diffuses directly across the plasma membrane Rather then being released in the
vesicles Nitric Oxide is important for the male
sexual response to create a penile erection
Drugs like Viagra (sildenafil) treats MED or Male Erectile Dysfunction by promoting the Nitric Oxide response
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Stop