Download The Human Body in Health and Illness

Nervous System: Nervous Tissue
and Brain
1
Divisions of the Nervous System
• Central nervous
system (CNS)
– Brain
– Spinal Cord
• Peripheral nervous
system
– Everything outside the
CNS
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
2
Types of Nervous Tissue
• Neurons
– Do the communicating for the nervous system
– Long shape makes them delicate
– Do NOT replicate or self-repair
• Neuroglia or glia
– Most abundant type
– Support, protect, insulate, nourish, and generally
care for neurons
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Neuroglia (Glia)
• Astrocytes
– Star shaped
– Transfer nutrients from blood
• Ependymal cells
– Produce fluid
• Microglia
– Phagocytic
• Schwann cells (PNS)
– Produce myelin sheath
• Oligodendrocytes (CNS)
– Produce myelin sheath
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Types of Neurons
• Unipolar: one process off of cell body
• Bipolar: one axon, one dendrite (2 things)
• Multipolar: one axon, several dendrites
Parts of a Neuron
• Cell body
• Dendrites (receives
info)
• Axon
– Schwann cell/Olig.
• Myelin sheath
• Nodes of
Ranvier
• Neurilemma
– Axon terminal
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Nerves and Tracts
Nerves: bundles of peripheral nerve fibers
held together

Endoneurium: delicate layer nerve fiber
(innermost)

Perineurium: tissue holding together
fascicles (middle)

Epineurium: surrounding numerous
fascicles and blood vessels to form a
complete nerve (outermost)
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Nerves and Tracts

Tracts: bundles of nerve fibers within the CNS


DO NOT have connective tissue coverings
White matter



CNS—myelinated tracts
PNS—myelinated nerves
Gray matter



Made up of cell bodies and unmyelinated fibers
CNS—referred to as nuclei
PNS—referred to as ganglia
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Functions of the Nervous System
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Types of Neurons
• Sensory (afferent) neurons
– Carry information from periphery toward the CNS
• Interneurons
– Found only in CNS; connect sensory and motor
nerves
• Motor (efferent) neurons
– Carry information from CNS toward periphery
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Nerve Impulses or Signals
• Electrical signals convey information along a
neuron
• Also called action potential
• Move along sensory or motor neurons
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The Action Potential
• Polarization: Resting
state
• Depolarization:
Stimulated state
• Repolarization:
Return to resting
Ionic Basis of the Action Potential
• Polarization
– K+ leaks from neuron.
– Determines resting
membrane potential
• Depolarization
– Na+ rushes in.
• Repolarization
– K+ rushes out.
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Why Action Potential “Moves”
• Action potential
– Forms at axon’s
beginning
– Regenerates along
axon’s length
– Enters axon terminal
– Releases ACh from
vesicles
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Increasing Action Potential’s Speed
• Myelin insulates axon.
• Action potentials jump
quickly from node to
node
– like a kangaroo.
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Communication across the Synapse
• ACh is
– Secreted from
neuron A
– Diffused across
synaptic cleft
– Bound to receptors
on neuron B
• Neuron B is
activated.
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Random thing about biology
• Suffix of –ase
– Tells reader it is an enzyme
– Inactivate/Inhibits the enzyme it’s named after.
• Acetylcholine= neurotransmitter
• Acetylochoinesterase = Inactivator
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Application
• In Multiple Scleroses the myelin sheath is
destroyed.
• The myelin sheath hardens to a tissue called
the scleroses.
• This is considered an autoimmune disease.
• Why does MS appear to affect the muscles?
Four Major Areas of the Brain
•
•
•
•
Brain stem
Cerebellum
Diencephalon
Cerebrum
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
23
Cerebellum
• Mediates
reflexes
• Coordinates
motor activity
• Evaluates
sensory input
• Rhythmic
movements
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Brain Stem
• Midbrain
• Reflex for eye and ear
• Pons
• Breathing rate and
rhythm
• REM and Sleep
Paralysis??
• Medulla
oblongata
• Vital center
• Emetic center
• Reflex center 25
Diencephalon
• Thalamus: intergrates
sensory from lower brain
• Links to a number of
Disorders
–
–
–
–
Bipolar
ADHD
Autism
Depression
• Hypothalamus:
body thermostat,
endocrine(hormones)
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Cerebrum: Four Lobes
•
•
•
•
Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
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Cerebrum: Markings
• Gyrus (convolution)
• Fissures (sulci)
– Central
– Lateral
– Longitudinal
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
28
Frontal Lobe
•
•
•
•
“ The executive”
Behavior
Personality
Motor control
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
29
Frontal Lobe: Motor Activity
• Primary motor area
– Precentral gyrus
• Frontal eye field
• Motor speech area
– Broca’s area
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
30
Frontal Lobe: Motor Homunculus
• Shows
percentages of
frontal lobe
devoted to
body’s motor
activities
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
31
Other Cerebral Lobes
• Parietal
– Somatosensory area
– Gustatory area
• Temporal
– Auditory cortex
– Gustatory area
– Olfactory area
• Occipital
– Visual cortex
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
32
Functions Spanning Cerebral Lobes
• Speech areas
– Span temporal, parietal and occipital lobes
– Usually in left hemisphere
– Wernicke’s area (helps translate thought into
speech)
• Association areas
– Helps to interpret sensory information
– Examples: Visual, auditory, somatosensory
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
33
Structures Spanning Brain Divisions
• Limbic system
– Emotional brain
• Reticular formation: Reticular activating
system; sleep-wake cycle, consciousness, gaze
center
• Memory areas
– Immediate memory
– Short-term memory
– Long-term memory
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
34
Protecting the CNS: Four Layers
•
•
•
•
Bone
Meninges
Cerebrospinal fluid
Blood-brain barrier
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
35
Protecting the CNS: Meninges
• Dura mater
• Arachnoid mater
– Subarachnoid space
• Pia mater
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
36
Protecting the CNS:
Cerebrospinal Fluid (CSF)
• Formed in ventricles
by choroid plexus
• Circulates through
subarachnoid space
– From central canal of
spinal cord
– From foramina
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Drainage of CSF
• Drainage of CSF must
equal its production.
• Arachnoid villi
project into dural
sinuses filled with
blood.
• CSF drains into blood
and leaves the brain.
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
38
Protecting the CNS:
The Blood-Brain Barrier
• Made of special cells (astrocytes) within
cerebral capillaries.
• Prevents some toxins from entering CNS from
blood
Copyright © 2011, 2007 by Saunders,
an imprint of Elsevier Inc. All rights
reserved.
39