nervous system academic anatomy & physiology. the function to act as the master controlling and...
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Nervous System
Academic Anatomy & Physiology
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The Function To act as the
master controlling and communicating system for the body
Subdivided into CNS & PNS
http://www.agen.ufl.edu/~chyn/age2062/lect/lect_20/nervsys.gif
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Cells of the Nervous System 1. Neuroglia
Acts to support neurons Makes up ~ 90% of brain and spinal cord (s.c.) There are 5 different types of
neuroglial cells
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Types of Neuroglia A. Astrocytes B. Oligodendrocytes C. Microglial cell D. Ependymal Cells E. Schwann Cells
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Assignment Using page 225 in your text, draw
the different types of neuroglia and list their location and function within the nervous system below each drawing
DO NOT draw Schwann cells but do list its location and function
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Cells of the Nervous System 2. Neurons
The conducting nerve cell Senses changes in environment,
integrates information, carries out motor responses
Structure: each neuron varies in shape and size, but all have 3 main parts (dendrite, axon and cell body)
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Neuron
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Neuron Anatomy
A. Dendrite: a process off of the cell body; receives impulses from adjacent neurons & conducts electrical impulses TOWARD the cell body; ~1000/neuron
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Neuron Anatomy
B. Axon: aka nerve fiber; acts to transmit impulses AWAY from the cell body; 1 axon/neuron
C. Cell Body: contains the nucleus and metabolic center of the cell
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Neuron Anatomy
D. Myelin sheath: made by schwann cells in PNS and oligodendrocytes in CNS; encloses the axon & speeds up the rate of nervous conduction
i. Gray matter: non-myelinated nerve fiber
ii. White matter: myelinated nerve fiber
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Neuron Anatomy
E. Nodes of Ranvier: gaps in myelin sheath @ regular intervals; aids in increasing speed of nervous conduction
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3 Types of Neurons
1. Afferent (sensory) Neurons: transmit impulses from PNS to CNSi.e. pain receptors and proprioceptors
2. Efferent (motor) Neurons: transmit impulses from CNS to muscles or glands
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Motor Neuron
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3 Types of Neurons
3. Interneurons (association neurons): located within CNS and conducts impulses between sensory and motor neurons
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Nerve Conduction: Distribution of Ions
More Na+ on outside than inside a neuron
More K+ on inside than outside + negatively charged particles
K+ ions permeate through lipid bi-layer more easily than Na+ ions do
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Nerve Conduction: Resting Potential Describes a polarized, resting nerve K+ and Na+ follow laws of diffusion Na+/K+ pump maintains the unequal
distribution of these ions across membrane Cell uses energy to keep Na+ out and K+ in
despite natural diffusion Inside of cell is more negative than outside
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Nerve Conduction: Depolarization An activated nerve cell; has been
stimulated Na+ specific channels in the
membrane open and Na+ floods into the cell
The charge on the inside of the cell is now LESS negative (more positive)
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Nerve Conduction: Repolarization Returning to a resting state K+ specific channels in the membrane
open and K+ floods the outside of the cell This returns the inside of the cell to a
MORE negative (less positive) state Depolarization + Repolarization of a nerve
cell = An Action Potential
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Impulse Conduction A wave of bioelectric action potentials
travels the length of a neuron, stimulating adjacent neurons as it goes
Unmyelinated neurons slower than myelinated
Impulses on myelinated neurons seem to jump from one node of Ranvier to the next
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The Synapse An action potential is electrical
across the neuron and chemical once it reaches the synaptic cleft
Presynaptic Neurons Have synaptic knobs sensitive to Ca+
When Ca+ is present allow synaptic vesicles within them to release neurotransmitters
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The Synapse Neurotransmitters cross the synaptic cleft
and bind to postsynaptic neurons Excitatory Neurotransmitters:
triggers action potential to continue in postsynaptic neuron
Inhibitory Neurotransmitters: lessens the chance of a continuing neurotransmitter
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Impaired Conduction The following block nervous
impulses by reducing the membrane permeability to sodium ions Alcohol Sedatives Anesthetics Cold and pressure (slows, does not
impair)
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Structural Classifications of Nervous System Central Nervous
System (CNS) Includes brain and
spinal cord Acts as integrating
and command center
Peripheral Nervous System (PNS) Includes nerves
outside of CNS• Spinal nerves• Cranial nerves
Links all parts of body by carrying impulses
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Subdivisions of PNS 1.) Somatic system: voluntary
nervous system Contains sensory and motor nerves Makes you aware of the world around
you & allows you conscious control
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Subdivisions of PNS 2.) Autonomic System:
involuntary nervous system Consists of motor nerves that carry
impulses to organs, blood vessels and glands
The unconscious or “automatic control”
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Subdivisions of Autonomic System A. Sympathetic
division Active during stress heart rate,
respiratory rate and rate of ATP breakdown
B. Parasympa-thetic Division Active during
conditions of normal organ functioning
These 2 divisions often work antagonistically to one another
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CNS: The Brain 4 major portions:
Cerebrum: largest; sensory & motor function, higher thought, memory & reasoning
Cerebellum: coordination of skeletal muscles
Diencephalon: sensory information Brain stem: connects parts of nervous
system; controls visceral activities
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CNS: Cerebrum Cerebral
Hemispheres Cerebral Cortex Corpus Callosum Gyri Sulci Fissures
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CNS: Cerebral Lobes Frontal Lobe: anterior portion
Primary motor area Concentration, planning, problem solving Broca’s Area: motor speech
Temporal Lobe: lateral lobe Interpretation of sensory impulses, memory,
visual & auditory patterns Auditory area Olfactory area
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CNS: Cerebral Lobes Parietal Lobe: superior, lateral
lobe Sensory area Understanding speech; using words
Occipital Lobe: posterior lobe Vision Combining visual images; visual
recognition
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CNS: Hemisphere Dominance Equal participation in receiving and
analyzing sensory information, controlling skeletal muscles and storing memory
Dominant Hemisphere: ability to understand language 90% of people dominant left side
Nondominant Hemisphere: nonverbal functions, orientation in space, musical patterns, nonverbal visual experiences
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CNS: Cerebellum Located inferior to
occipital lobes and posterior to brain stem
Functions in: positioning of limbs, coordinating skeletal movements, maintanance of posture
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CNS: Diencephalon Located between cerebral hemispheres;
superior to midbrain Thalamus: central relay center for sensory
impulses; allows awareness of pain, touch & temperature
Hypothalamus: regulates visceral activities; links nervous and endocrine systems
Also holds: optic chiasma, posterior pituitary gland, pineal gland, infundibulum
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CNS: Brainstem Connects cerebrum to spinal cord Midbrain: b/n diencephalon and
pons Visual, auditory reflex centers; head
movement for hearing Pons: rounded bulge b/n midbrain
and medulla Relays sensory impulses; helps regulate
breathing
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CNS: Brainstem Medulla
Oblongata: from pons to spinal cord Cardiac center,
vasomotor center, respiratory center
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CNS: Spinal Cord A continuation of the brain running
from base of brain to 1st or 2nd lumbar vertebrae
Is enclosed within spinal column Is ~ size of thumb except at
enlarged cervical and lumbar plexuses (spinal nerve distribution to upper and lower limbs)
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CNS: Spinal Cord Provides a 2-way pathway to and from the
brain Serves as a reflex center Has 31 linear segments giving way to 31
spinal nerves (relay info. from PNS to CNS and vice versa)
Cauda Equina: collection of spinal nerves at the inferior end of the vertebral column
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Spinal Cord in Column
http://www.latrobe.edu.au/podiatry/Images/1%20Biomech%20pics/SPINALMECHpics/Spinal%20cord%20diag.GIF
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Spinal Cord Cross Section
http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/CNS_Histology/Spinal_Cord/sp_cd_jpgs/Spinal_Cord_PC271478md.JPG
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Spinal Cord Cross-Section Gray Matter: unmyelinated
Located in center of cord forming an “H”: divided into horns
Each horn runs a different fiber tract• Posterior Horn: sensory neurons• Anterior Horn: motor neurons• Lateral Horn: motor neurons in autonomic
system
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Spinal Cord Cross-Section White Matter: myelinated fibers
Surrounds central gray matter Divided into anterior, posterior and
lateral columns Each column holds longitudinal nerve
tracts•Ascending tracts: carry sensory info to
brain•Descending tracts: carry motor info.
away from brain
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Reflex Center Reflex: an extremely rapid response to an
emergency situation Occurs in spinal cord or lower brain; does
not require thinking The Reflex Arc:
Receptor: at end of sensory neuron; can generate an action potential to CNS
Association neurons: receive info. from sensory neuron and routes response to motor neuron
Motor neurons: conduct impulses to effectors
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Reflex Arc
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Protections of CNS Bone: skull and
vertebral column
Cerebrospinal Fluid (CSF): Made from the blood Forms a watery cushion
that protects tissue from trauma
Changes in composition indicates brain pathology
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Protections of CNS Meninges: connective tissue
membranesA. Dura mater: tough outer covering of
brain and s.c.B. Arachnoid mater: middle layerC. Pia mater: inner surface which clings
tightly to surface of brain and s.c.• Subarachnoid space: separates the
arachnoid and pia maters; filled with CSF
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Protections of CNS Blood-Brain Barrier
Composed of least permeable capillaries in body
Brain depends on a very constant internal environment
• Allows: water, glucose, and essential amino acids• Disallows: urea, protein and most drugs• Cannot block: fats, respiratory gases and fat soluble
molecules (alcohol, nicotine and anesthetics)
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