Download Nervous System

The Nervous System
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Functions of the Nervous System
 Sensory input – gathering information
 To monitor changes occurring inside and
outside the body
 Changes = stimuli
 Integration
 To process and interpret sensory input and
decide if action is needed
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Functions of the Nervous System
 Motor output
 A response to integrated stimuli
 The response activates muscles or glands
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Structural Classification of the Nervous
System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerve outside the brain and spinal cord
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Functional Classification of Neurons
 Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
Figure 7.1
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Functional Classification of Neurons
 Motor (efferent) division
 Nerve fibers that carry impulses away
from the central nervous system
Figure 7.1
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Functional Classification of Neurons
 Motor (efferent) division
 Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
Figure 7.1
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Functional Classification of Neurons
 Interneurons (association neurons)
 Found in neural pathways in the central
nervous system
 Connect sensory and motor neurons
 99% of neurons in body
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Organization of the Nervous System
Figure 7.2
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Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages
 Amitotic but extreme longevity (100 yrs. with
proper nutrition)
 High metabolic rate (require large amounts of O2
& C6H12O6)
 Major regions of neurons
 Cell body – nucleus and metabolic center of the cell
 Processes – fibers that extend from the cell body
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Neuron Anatomy
 Cell body (soma)
 Nucleus
 Large nucleolus
Figure 7.4a–b
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Neuron Anatomy
 Extensions outside
the cell body –
increase surface area
 Dendrites –
conduct impulses
toward the cell
body
 Axons – conduct
impulses away
from the cell
body
Figure 7.4a
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Axons and Nerve Impulses
 Axons end in axonal terminals
 Axonal terminals contain vesicles with
neurotransmitters
 Axonal terminals are separated from the next
neuron by a gap
 Synaptic cleft – gap between adjacent
neurons
 Synapse – junction between nerves
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Nerve Fiber Coverings
 Myelin sheath – fatty
husk surrounding nerve
fibers (insulator)
 Schwann cells –
produce myelin
sheaths in jelly-roll
like fashion
 Nodes of Ranvier – gaps
in myelin sheath along
the axon (increases speed
of a nerve impulse)
Figure 7.5
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Neuron Cell Body Location
 Most are found in the central nervous system
 Gray matter – cell bodies and unmylenated
fibers
 Nuclei – clusters of cell bodies within the
white matter of the central nervous system
 Ganglia – collections of cell bodies outside
the central nervous system
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Neuron Classification
Figure 7.6
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Starting a Nerve Impulse (Action Potential)
 Depolarization – a
stimulus depolarizes the
neuron’s membrane
(inside membrane
becomes more +)
 A deploarized membrane
allows Na+ to flow inside
the membrane
 The exchange of ions
initiates an action
potential in the neuron
Figure 7.9a–c
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The Action Potential
 If the action potential (nerve impulse) starts, it is
propagated over the entire axon
 Eventually the concentration gradient resists more
Na+ and Na+ gates close
 K+ gates open and K+ ions rush out of the neuron
after Na+ ions rush in, which repolarizes the
membrane
 The Na+/K+ pump restores the original configuration
– Na+ out, K+ in (3Na+:2K+)
 This action requires ATP
***Whole process takes a few milliseconds***
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Nerve Impulse Propagation
 The impulse
continues to move
away from the cell
body
 Impulses travel faster
when fibers have a
myelin sheath
Figure 7.9d–f
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Continuation of the Nerve Impulse
between Neurons
 Impulses are able to cross the synapse to
another nerve
 Neurotransmitter is released from a
nerve’s axon terminal (ie. ACh)
 The dendrite of the next neuron has
receptors that are stimulated by the
neurotransmitter
 An action potential is started in the
dendrite
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How Neurons Communicate at Synapses
Figure 7.10
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The Nervous System
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Reflex Arc
 Reflex – rapid, predictable, and involuntary
responses to stimuli
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
Figure 7.11a
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Simple Reflex Arc
Figure 7.11b–c
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The Brain
 Intricate mass of soft,
highly developed,
complex nervous tissue
 Females = 3 lbs.
(1450g)
 Males = 3.5 lbs.
(1600g)
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Regions of the Brain
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Cerebellum
Figure 7.12b
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Cerebral Hemispheres (Cerebrum)
 Paired (left and
right) superior
parts of the brain
 Approx 83% of
brain mass
 Most conscious
behavior
 “Executive Suite”
Figure 7.13a
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Cerebral Hemispheres (Cerebrum)
 The surface is
made of ridges
(gyri “twisters”)
and grooves
(sulci “furrows”)
Figure 7.13a
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Lobes of the Cerebrum
 Fissures (deep grooves) divide the cerebrum into
lobes
 ie. longitudinal & transverse
 Surface lobes of the cerebrum
 Frontal lobe – controls voluntary motor
functions (right controls left)
 Parietal lobe – receives/interprets impulses for
pain, touch, heat, cold, distances, size & shapes
 Occipital lobe – controls eye sight
 Temporal lobe – auditory & olfaction area
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Lobes of the Cerebrum
Figure 7.15a
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Specialized Areas of the Cerebrum
 Somatic sensory area – receives impulses
from the body’s sensory receptors
 Primary motor area – sends impulses to
skeletal muscles
 Broca’s area – involved in our ability to speak
 Directs muscles of tongue, throat & lips to
articulate words
 Recognition of words, interpret meaning
(spoken or written)
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Sensory and Motor Areas of the Cerebral
Cortex
Figure 7.14
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Specialized Areas of the Cerebrum
 Cerebral areas involved in special senses
 Gustatory area (taste)
 Visual area
 Auditory area
 Olfactory area
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Specialized Areas of the Cerebrum
 Interpretation areas of the cerebrum
 Speech/language region
 Language comprehension region
 General interpretation area
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Specialized Areas of the Cerebrum
Figure 7.13c
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Layers of the Cerebrum
 Gray matter
 Outer layer, 2-4
mm thick
 Composed
mostly of neuron
cell bodies
Figure 7.13a
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Layers of the Cerebrum
 White matter
 Myelinated
fibers inside the
gray matter
 Example:
corpus
callosum connects
hemispheres
Figure 7.13a
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Diencephalon
 Sits on top of the brain stem – central core
 Enclosed by the cerebral hemispheres
 Made of three parts
 Thalamus
 Hypothalamus
 Epithalamus
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Diencephalon
Figure 7.15
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Thalamus
 Egg-shaped mass of gray matter that
surrounds the third ventricle
 Makes up 80% of diencephalon
 The relay station for sensory impulses
 Transfers impulses to the correct part of the
cortex for localization and interpretation
 “Gateway to the cerebral cortex”
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Hypothalamus
 Below the thalamus
 Forms the lateral walls & floor of 3rd ventricle
 Important autonomic nervous system (bp, heart rate
peristalsis, respiratory rate, pupil size, etc) center
 Helps regulate body temperature
 Controls water balance (thirst)
 Regulates metabolism
 Appetite control
 Biological clock
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Hypothalamus
 An important part of the limbic system
(emotions)
 The pituitary gland is attached to the
hypothalamus
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Epithalamus
 Forms the roof of the third ventricle
 Houses the pineal body (an endocrine gland
that secretes melatonin)
 Includes the choroid plexus – forms
cerebrospinal fluid
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Brain Stem
 Attaches to the spinal cord
 Parts of the brain stem
 Midbrain
 Pons
 Medulla oblongata
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Brain Stem
Figure 7.15a
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Midbrain
 Mostly composed of tracts of motor nerve
fibers
 Reflex centers for vision and hearing (startle
reflex)
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Pons
 The bulging center part of the brain stem
 Bridge between medulla oblongata &
midbrain
 Forms wall of 4th ventricle
 Mostly composed of two-way fiber tracts
 Includes nuclei involved in the respiratory
center
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Medulla Oblongata
 The most inferior part of the brain stem
 Merges into the spinal cord
 Forms wall of 4th ventricle
 Contains important control centers
 Cardiac center
 Vasomotor center
 Respiratory center
 Swallowing, vomiting, hiccupping , coughing,
sneezing
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Cerebellum
 Two hemispheres with convoluted surfaces “Small
brain”
 11% of brain’s mass
 Provides involuntary coordination of body
movements
 Balance
 Muscle tone
 Muscle coordination (speaking, walking,
writing)
 Thin outer gray matter & internal “arbor vitae”
white matter
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Cerebellum
Figure 7.15a
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The Nervous System
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Protection of the Central Nervous System
 Scalp and skin
 Cranial/facial bones and vertebral column
 Meninges – forms partitions in skull
Figure 7.16a
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Protection of the Central Nervous System
 Cerebrospinal fluid (CSF) – liquid cushion (reduces
weight by 97%)
 Blood brain barrier – inhibits passage of materials
from blood into brain
Figure 7.16a
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Meninges
 Dura mater – “tough mother”
 Double-layered external covering
 Periosteum – attached to surface of the skull
 Meningeal layer – outer covering of the brain
 Folds inward in several areas
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Meninges
 Arachnoid layer – “spider layer”
 Middle layer
 Loose brain covering with large blood vessels
 Filled with CSF
 Pia mater – “gentle mother”
 Internal layer
 Clings to the surface of the brain
 Delicate connective tissue
 Richly vascularized
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Cerebrospinal Fluid
 Similar to blood plasma composition
 Formed by the choroid plexus – capillary
knot that protrudes into ventricles
 Forms a watery cushion to protect & nourish
the brain
 Circulated in arachnoid space, ventricles, and
central canal of the spinal cord
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Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17a–b
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Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17c
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Blood Brain Barrier
 Includes the least permeable capillaries of the body
 Excludes many potentially harmful substances
 Useless against some substances
 Fats and fat soluble molecules
 Respiratory gases
 Alcohol
 Nicotine
 Anesthesia
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Traumatic Brain Injuries
 Concussion
 Slight brain injury – “seeing stars”
 No permanent brain damage
 Contusion
 Nervous tissue destruction occurs
 Nervous tissue does not regenerate
 Cerebral edema
 Swelling from the inflammatory response
 May compress and kill brain tissue
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Cerebrovascular Accident (CVA)
 Commonly called a stroke
 Most common NS disorder – 3rd leading
cause of death in U.S.
 The result of a ruptured/blocked blood vessel
supplying a region of the brain
 Brain tissue supplied with oxygen from that
blood source dies
 Loss of some functions or death may result
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Alzheimer’s Disease
 Progressive degenerative brain disease
resulting in dementia
 Mostly seen in the elderly, but may begin in
middle age
 Structural changes (shrinking gyri) in the
brain include abnormal protein deposits and
twisted fibers within neurons
 Victims experience memory loss, irritability,
confusion and ultimately, hallucinations and
death
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Developmental Disorders
 Cerebral Palsy – caused by a difficult birth
with a temporary lack of oxygen
 Volunatry muscles are poorly controlled or
paralyzed
 Results in seizures, mental retardation,
deafness & visual impairments
 Does not worsen over time
 Affects 6 out of 1000 births
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Nervous System Disorders
 Meningitis- inflammation of meninges
 Bacterial or viral
 Mild symptoms include headache, fever & stiff
neck
 Severe symptoms include paralysis, coma &
death
 Encephalitis – inflammation of brain
 Caused by chemicals or virus
 Symptoms include fever, lethargy, extreme
weakness & visual difficulties
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Nervous System Disorders
 Epilepsy – excessive discharge of neurons
 Cause is unknown
 Symptoms include convulsions, hallucinations &
loss of consciousness
 Poliomyelitis – disease of neural pathways in sc that
causes paralysis
 Vaccine has almost eliminated disease in U.S.
 Hydrocephalus – increased volume of CSF in
ventricles
 Caused by blockage of 3rd/4th ventricle
 Enlarged head at birth
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Nervous System Disorders
 Parkinson’s Disease – characterized by tremors,
shuffling gait, pin-rolling & muscular rigidity
 Causes decrease in dopamine (neurotransmitter)
 Multiple Sclerosis – chronic inflammation of CNS
where WBC’s attach to sheaths of myelin (creates
scar tissue)
 Scar tissue delays/blocks nerve impulses
 Cause of inflammation is unknown
 Symptoms include weakness in extremities,
numbness, double-vision, tremors in eyes,
speech problems, loss of coordination &
paralysis
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Nervous System Disorders
 Dementia – loss of at least 2 complex
behaviors (ie. language, memory, visual &
spatial abilities or judgment)
 Brain tumors – overproduction of cells in the
brain
 Hematoma – localized mass of blood
 Caused by head trauma
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Diagnostic Procedures
 Lumbar puncture – a long needle is inserted
between L3 & L4 & CSF is removed
 Knee-jerk response
 Pneumoencephalography – X-ray of
ventricles
 Used for hydroencephaly
 CSF is withdrawn & air is injected into
subarachnoid space to float upward into
ventricles
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Diagnostic Procedures
 Cerebral angiogram – views arteries
 Injected dye, X-ray given to see blood
clots & arteriosclerosis
 CT Scan (computed tomography) aka
CAT Scan (computerized axial tomography)
 X-ray projects beams in all directions
 Images are slices the thickness of a dime
 Used to find tumors, lesions & dead tissue
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Diagnostic Procedures
 PET Scan (Positron Emission Tomography)
 Injection of a radioisotope tagged for
biological molecules (ie. glucose)
 High E rays are produced as the body
metabolizes the molecule
 Scanner provides a picture of brain’s
biochemical activities
 Used for seizures, Alzheimer’s & brain
illnesses
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Diagnostic Procedures
 MRI (Magnetic Resonance Imaging)
 Uses a magnetic field 60,000x stronger than the
Earth’s
 Patient lays in a large chamber with a huge magnet
 H+ molecules spin in the magnetic field & their E is
enhanced by radio waves
 Radio waves are turned off and the remaining E is
released into an image
 Detects degenerative diseases & can easily
distinguish soft tissues
 Problems include removal of dental fillings,
pacemakers & shrapnel & large room to contain
machine
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
The Nervous System
PowerPoint® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Spinal Cord
 Extends from the
medulla oblongata to
the region of T12
 42 cm (17 in) long;
1.8 cm (.75 in) thick
 Below T12 is the
cauda equina (a
collection of spinal
nerves)
 Enlargements occur
in the cervical and
lumbar regions
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Figure 7.18
Spinal Cord Anatomy
 Exterior white mater – conduction tracts
 Internal gray matter - mostly cell bodies
 Central canal filled with cerebrospinal fluid
Figure 7.19
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Spinal Cord Anatomy
 Meninges cover the spinal cord
 Nerves leave at the level of each vertebrae
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Peripheral Nervous System
 Nerves and ganglia outside the central
nervous system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by connective
tissue
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Structure of a Nerve
 Endoneurium surrounds
each fiber
 Groups of fibers are
bound into fascicles by
perineurium
 Fascicles are bound
together by epineurium
Figure 7.20
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Classification of Nerves
 Mixed nerves – both sensory and motor fibers
 Afferent (sensory) nerves – carry impulses
toward the CNS
 Efferent (motor) nerves – carry impulses
away from the CNS
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Distribution of Cranial Nerves
Figure 7.21
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Spinal Nerves
Figure 7.22a
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Examples of Nerve Distribution
Figure 7.23
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Autonomic Nervous System
 The involuntary branch of the nervous system
 Consists of only motor nerves
 Divided into two divisions
 Sympathetic division
 Parasympathetic division
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Comparison of Somatic and Autonomic
Nervous Systems
Figure 7.24
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Anatomy of the Autonomic Nervous
System
Figure 7.25
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Autonomic Functioning
 Sympathetic – “fight-or-flight”
 Response to unusual stimulus
 Takes over to increase activities
 Remember as the “E” division = exercise,
excitement, emergency, and
embarrassment
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Autonomic Functioning
 Parasympathetic – housekeeping activities
 Conserves energy
 Maintains daily necessary body functions
 Remember as the “D” division - digestion,
defecation, and diuresis
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Development Aspects of the Nervous
System
 The nervous system is formed during the first
month of embryonic development
 Any maternal infection can have extremely
harmful effects
 The hypothalamus is one of the last areas of
the brain to develop
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Development Aspects of the Nervous
System
 No more neurons are formed after birth, but
growth and maturation continues for several
years
 The brain reaches maximum weight as a
young adult
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