Download Nervous System

PowerPoint® Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
The Nervous
System
7
PART A
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Nervous System Medical Terms
 Ax – axle
 Peri – around
 Dendr – tree
 Plex – interweaving
 Gangli – swelling
 Sens – feeling
 Mening – membrane
 Soma - body
 Moto – moving
 Syn - together
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The Nervous System allows the body to:
 Think
 Feel
 Remember
 Move
 Be aware of the world
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Nervous tissue is composed of neurons.
 Neurons transmit information in the form of
electrochemical changes called nerve impulses
from cell to cell.
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Anatomy of a Neuron
 Neurons = nerve cells
 Cell body
 Processes—fibers that extend from the cell
body
 Dendrites—receive messages
 Axons—send messages
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Nervous Tissue: Neurons
Figure 7.4
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Nerves are bundles of axons
 Neuroglial cells support nerves like connective
tissues
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Nervous System Organs are in two groups
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerves outside the brain and spinal cord
 Cranial nerves
 Spinal nerves
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Three major functions of the Nervous System
 Sensory Function - using receptors at the ends of
peripheral neurons
 Detect changes inside and outside the body
 Convert environmental information into nerve
impulses
 Send information to CNS – signals are
“integrated”
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Three major functions of the Nervous System
 Integrated Function – allows us to make
conscious and unconscious decisions, use motor
function to act on them
 Signals are brought together
 Create sensations
 Added to memory
 Produce perceptions
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Three major functions of the Nervous System
 Motor Function – uses peripheral neurons to carry
impulses to effectors
 Effectors are muscles or glands
 Muscles contract
 Glands secrete
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Functions of the Nervous System
Figure 7.1
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Motor Functions are divided into two categories.
 Somatic nervous system = voluntary
 Consciously controlled
 Skeletal Muscles
 Autonomic nervous system = involuntary
 Unconsciously controlled
 Heart, smooth muscle contractions and
glands
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More about nerves
 Mature neurons do not divide.
 Some nervous stem cells do.
 Myelin – protein covering around axons
 “Myelin Sheath”
 Gray Matter = myelinated axons
 White Matter = Unmyelinated axons
 Peripheral nerves regenerate axons when
damaged
 CNS neurons do not regenerate.
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Relative Size of a Neuron
 If the cell body was the size of a tennis ball,
 The dendrites would fill a large bedroom,
 And the axon would be 1 mile long and ½ inch
thick!!!
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Nerve Impulses – “threshold potential”
 Na+ and K+ ions flow into and out of the cell as
the Na+/K+ pump tries to maintain normal
concentrations
 The flow of ions transmits the signals down the
axons
 All-or-None response – if there is a response, it is
complete
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Nerve Impulses
Figure 7.9a–b
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Nerve Impulses
Figure 7.9c–d
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Nerve Impulses
Figure 7.9e–f
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The Synapse
 Nerve impulses travel along nerve pathways
 Neurons do not touch
 Synapse—junction between nerves
 Synaptic cleft—gap between adjacent neurons
 Synaptic transmission – the process of crossing a
synapse
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Transmission of a Signal at Synapses
Axon of
transmitting
neuron
Axon
terminal
Action
potential
arrives
Vesicles
Synaptic
cleft
Receiving
neuron
Synapse
Figure 7.10, step 1
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Sensory  Dendrite  Cell Body  Axon 
Synapse  Dendrite Receptor
Figure 7.6
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Transmission of a Signal at Synapses
 When the impulse reaches the synapse, vesicles
in the “knob” release a neurotransmitter, which
binds to specific receptors on the next neuron.
 Neurotransmitters
 Excitatory
 Inhibitory
 Thousands of presynaptic neurons may
communicate with one postsynaptic neuron
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Neurotransmitters
 50+ have been identified
 Acetylcholine – Ach – Skeletal muscles
“excitatory”
 Epinephrine, dopamine, serotonin – inhibitory
 Neurotransmitters bind and allow Ca+2 to flow
sending the message
 Caffeine lowers thresholds – neurons more easily
excited
 Antidepressants – keep serotonin in synapses
longer
 Prozac, Paxil, Zoloft
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Nerve Fibers – aka “axons”
 Nerve – bundle of fibers
 Sensory fibers – brain and spinal cord
 Motor fibers – muscles or glands
 Mixed nerves – carry both
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Nerve Anatomy
 Fibers are bundled into bundles surrounded by
endoneurium
 Bundles are covered in perineurium and form
fascicles
 Fascicles are surrounded by epineurium
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Structure of a Nerve
Figure 7.23
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Reflexes
 Reflex—rapid, predictable,
and involuntary response to
a stimulus
 Knee-jerk, heart rate,
digestion
 Reflex arc—direct route
from a sensory neuron, to
an interneuron, to an
effector
 Swallowing, sneezing,
coughing, vomiting
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Simple Reflex Arc
Sensory receptors
(stretch receptors
in the quadriceps
muscle)
Sensory (afferent)
neuron
Spinal cord
Sensory receptors
(pain receptors in
the skin)
Sensory (afferent)
neuron
Synapse in
ventral horn
gray matter
Interneuron
Motor
(efferent)
neuron
Motor
(efferent)
neuron
(b)
Effector
(quadriceps
muscle of
thigh)
Effector
(biceps
brachii
muscle)
(c)
Figure 7.11b–c
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Protection of the Central Nervous System
 Scalp and skin
 Skull and vertebral column
 Meninges
 Cerebrospinal fluid (CSF)
 Blood-brain barrier
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Protection of the Central Nervous System
Figure 7.17a
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Meninges
Figure 7.17b
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Meninges
 Membranes between bones and nerves for
protection
 Three layers
 Dura mater
 Arachnoid mater
 Pia mater
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Meninges
 Made of connective tissue
 Contain blood vessels and nerves
 Separated from the bones by an “epidural space”
 Loose connective and adipose tissues
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Spinal Cord Anatomy
Figure 7.21
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Spinal Cord
 Slender nerve column from brain into vertebral
canal ends at L1
 31 pairs of spinal nerves arise from the spinal
cord
 Thickens at the cervical and lumbar regions for
service to the arms and legs
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Spinal Cord Anatomy
Figure 7.20 (1 of 2)
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Spinal Cord Anatomy
Figure 7.20 (2 of 2)
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Cross Section of the Spinal Cord
 Gray Matter – Interneurons
 White matter—Cell bodies – axons extend out
 Central canal - filled with cerebrospinal fluid
 Spinal nerves – extend to effectors
 Vertebrae – bone covering
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Two functions of the Spinal Cord
1. To conduct nerve impulses
2. Serve as a center for spinal reflexes
Axons can extend from the spinal cord to your toe.
Stubbing your toe sends a sensory message in
1/100 second.
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Pathways Between Brain and Spinal Cord
Figure 7.22
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The Brain
 100 billion neurons
 Cerebrum – sensory and motor function, memory
and reasoning
 Cerebellum – voluntary muscle movements
 Brain stem – organ activities, connection to body
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Regions of the Brain: Cerebrum
Figure 7.12b
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Cerebrum
 Paired Left and Right halves of the brain
 Bridge – Corpus Callosum
 Four lobes - Frontal, Parietal, Temporal, Occipital
Covered by cerebral cortex – gray mater
Contains 75% of all neurons
White mater contains myelinated axons that
connect the cortex to other brain regions or the
body
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Regions of the Brain: Cerebrum
Figure 7.13b
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Regions of the Brain: Cerebrum
Figure 7.15
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Regions of the Brain: Cerebrum
Figure 7.13c
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Regions of the Brain: Cerebrum
Figure 7.14
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Regions of the Brain: Diencephalon
Figure 7.16
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Functions of the Cerebrum
 Higher brain functioning
 Interprets sensory Impulses, initiates voluntary
muscular movements
 Stores information for memory and uses it to
reason
 Intelligence and personality
 90% of people are left hemisphere dominant for
writing, speech and reading
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Ventricles contain Cerebrospinal Fluid (CSF)
 Allows organs to float in fluid
 Absorbs forces
 Spinal tap – measures pressure in fluid; can
detect infection, tumor or blood clot
 Brain blood barrier – tightly packed epithelials
and neuroglia only allow certain molecules from
blood to brain
 Keeps toxins out and prevents large
biochemical fluctuations
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Ventricles and Location of
the Cerebrospinal Fluid
Figure 7.18a–b
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Hydrocephalus in a Newborn
 Hydrocephalus
 CSF accumulates and exerts pressure on the
brain if not allowed to drain
Figure 7.19
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Blood-Brain Barrier
 Useless as a barrier against some substances
 Fats and fat soluble molecules
 Respiratory gases
 Alcohol
 Nicotine
 Anesthesia
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Diencephalon – surrounds the midbrain
 Contains
 Thalmus – channels sensory impulses to the
brain
 Hypothalmus – homeostasis, regulates organs
with hormones
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Brain Stem – attaches to the spinal cord
 Midbrain – links movement to eyesight or sound
 Pons - breathing
 Medulla oblongata – heart, vasomotor, respiratory
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Regions of the Brain: Brain Stem
Figure 7.16a
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Cerebellum
 Provides involuntary coordination of body
movements
 Posture
 Reports on positions of the limbs
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Regions of the Brain: Cerebellum
Figure 7.16a
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PNS: Cranial Nerves
 I Olfactory nerve—smell
 II Optic nerve—vision
 III Oculomotor nerve—extrinsic eye muscles
 IV Trochlear—oblique eye muscles
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PNS: Cranial Nerves
 V Trigeminal nerve—sensory for the face; motor
fibers to chewing muscles
 VI Abducens nerve—lateral rectus eye muscles
 VII Facial nerve—sensory for taste; motor fibers
to the face
 VIII Vestibulocochlear nerve—sensory for
balance and hearing
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PNS: Cranial Nerves
 IX Glossopharyngeal nerve—sensory for taste;
motor fibers to the pharynx
 X Vagus nerves—sensory and motor fibers for
pharynx, larynx, and viscera
 XI Accessory nerve—motor fibers to neck and
upper back
 XII Hypoglossal nerve—motor fibers to tongue
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PNS: Distribution of Cranial Nerves
Figure 7.24
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PNS: The Cranial Nerves
Table 7.1 (1 of 4)
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PNS: The Cranial Nerves
Table 7.1 (2 of 4)
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PNS: The Cranial Nerves
Table 7.1 (3 of 4)
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PNS: The Cranial Nerves
Table 7.1 (4 of 4)
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PNS: Spinal Nerves
Figure 7.25a
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PNS: Distribution of Major Peripheral
Nerves of the Upper and Lower Limbs
Figure 7.26a
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PNS: Distribution of Major Peripheral
Nerves of the Upper and Lower Limbs
Figure 7.26b
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PNS: Distribution of Major Peripheral
Nerves of the Upper and Lower Limbs
Figure 7.26c
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