Transcript Nervous System PNS

NERVOUS SYSTEM
PNS
NEURONS
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Nervous tissue contains masses of nerve cells called
neurons.
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Specialized to react to physical and chemical changes.
Transmit info in the form of electrochemical changes called
nerve impulses.
Bundles of axons make nerves.
Also contains neuroglial cells that provide physical support,
insulation, and nutrients for neurons.
THE TYPICAL NEURON
NS FUNCTIONS
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SENSORY
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Neurons contain sensory receptors at their ends.
Detect changes inside and outside the body
 Convert information into nerve impulses that travel through the
PNS to the CNS
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INTEGRATIVE
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In the CNS, impulses are brought together creating
sensations, adding memory, producing thoughts, etc.
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Making conscious and subconscious decisions
MOTOR
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Impulses are carried from the CNS to effectors (muscles
and glands).
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2 categories
 Somatic Nervous System
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Consciously controlled; skeletal muscle
Automatic Nervous system
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Involuntary; heart, smooth muscle, glands
CLASSIFICATION OF NEURONS
Vary in structure, size, shape, and the number of
connections they make with other neurons.
 3 major structural groups (pg. 218)
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Bipolar: found in eyes, ears, nose
Multipolar: found in brain and spinal cord
Unipolar: lead to PNS and CNS, can form ganglia
CLASSIFICATION CONT..
3
major functional groups
Sensory neurons
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Carry impulses from PNS to CNS
Receptor cells found at end of dendrites or in skin or
sensory organs
Most are unipolar
Interneurons
2)
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In brain and spinal cord
Transmit impulses from one part of the brain or spinal cord
to another
multipolar
Motor neurons
3)
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Carry impulses out of brain or spinal cord to effectors
multipolar
NEUROGLIAL CELLS (PG. 215)
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Outnumber neurons in CNS
Can divide (neurons do not normally divide)
4 TYPES
1) Microglial cells
Support neurons and phagocytize bacterial cells and cellular debris
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Oligodendrites
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Align along nerve fibers
Provide insulating layers of myelin
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Astrocytes
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Found b/w neurons and blood vessels
Provide structural support
Regulate nutrient and ion concentration within tissue
Form scar tissue that fill spaces following an injury in the CNS
“blood-brain barrier”
Sheilds delicate tissue from chemical fluctuations
Some drugs can get in some can’t
4.) Ependymal cells
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Forms an epithelia-like membrane that covers specialized
brain parts
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Forms inner linings that enclose spaces within the brain
and spinal cord
*Schwann Cells: are neuroglial cells that form a myelin
sheath around
axons.
THE SYNAPSE
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The junction between two communicating neurons
Synaptic cleft: the gap between
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Synaptic transmission:
-process of the impulse crossing
the cleft
-one-way process carried out by
neurotransmitters
-n.t. can be excitatory or inhibitory
-about 50 neurotransmittersin n.s
-pg. 226 chart
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NERVE IMPULSES –ACTION POTENTIAL
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The surface of a cell membrane is polarized (electrically charged)
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At rest, membrane potential is negative, membrane is polarized.
Na+++++++++++++
K+++++++++++
K+++++++++++
Na++++++++++++++
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When the membrane reached its threshold stimulus, Na/K channels open, ions
diffuse, and membrane is depolarized.
K+K+Na+Na+
N+Na+ K+K+
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Na/K channels open again, ions diffuse, and the membrane repolarizes.
Na+++++++
K++++++
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A wave of action potentials is occurring
throughout the membrane of a neuron.
*This is an ALL-OR-NOTHING response*
SYNAPSE AFFECTORS/OTHER PROBLEMS
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Caffeine: stimulates the nervous system by lowering the
threshold at the synapse so neurons are more easily
excited.
Antidepressants: keeps the neurotransmitter, serotonin,
in the synapse longer.
Epileptic seizures: caused when nerve impulses reach
the synaptic knob to fast, exhausting the
neurotransmitter.
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Multiple sclerosis (MS): is a disease in which the
fatty myelin sheaths around the axons of the brain
and spinal cord are damaged, leading to
demyelinization and scarring. The body’s immune
system attacks and damages the myelin. Axons can
no longer effectively conduct signals. Symptoms
include muscle weakness, spasms, difficulty in
moving, coordination,
balance, speech, or
swallowing, visual
problems, fatigue, and
bladder and bowel
difficulties.
NERVE PATHWAYS (PG. 229)
Are routes nerve impulses follow as they travel
through the nervous system.
 The simplest of these pathways includes only a few
neurons called a reflex arc.
 Reflexes are automatic responses to stimuli that
help maintain homeostasis.
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Heart rate
Coughing
Breathing
blood pressure
vomiting
sneezing
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Patellar reflex: uses only 2 neurons, helps
maintain upright posture
Withdrawal reflex: aids in limiting tissue
damage caused by touching something
harmful.