Nervous System

Transcription

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
Functions of the Nervous System
 Motor output
 A response to integrated stimuli
 The response activates muscles or glands
Structural Classification of the Nervous
System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerve outside the brain and spinal cord
Functional Classification of Neurons
 Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
Figure 7.1
 Motor (efferent) division
 Nerve fibers that carry impulses away
from the central nervous system
Figure 7.1
 Motor (efferent) division
 Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
Figure 7.1
 Interneurons (association neurons)
 Found in neural pathways in the central
nervous system
 Connect sensory and motor neurons
 99% of neurons in body
Organization of the Nervous System
Figure 7.2
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
Neuron Anatomy
 Cell body (soma)
 Nucleus
 Large nucleolus
Figure 7.4a–b
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
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
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
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
Neuron Classification
Figure 7.6
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
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***
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
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
How Neurons Communicate at Synapses
Figure 7.10
The Nervous System
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
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
Simple Reflex Arc
Figure 7.11b–c
The Brain
 Intricate mass of soft,
highly developed,
complex nervous tissue
 Females = 3 lbs.
(1450g)
 Males = 3.5 lbs.
(1600g)
Regions of the Brain
 Cerebral hemispheres
 Diencephalon
 Brain stem
 Cerebellum
Figure 7.12b
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
Cerebral Hemispheres (Cerebrum)
 The surface is
made of ridges
(gyri “twisters”)
and grooves
(sulci “furrows”)
Figure 7.13a
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
Lobes of the Cerebrum
Figure 7.15a
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)
Sensory and Motor Areas of the Cerebral
Cortex
Figure 7.14
 Cerebral areas involved in special senses
 Gustatory area (taste)
 Visual area
 Auditory area
 Olfactory area
 Interpretation areas of the cerebrum
 Speech/language region
 Language comprehension region
 General interpretation area
Figure 7.13c
Layers of the Cerebrum
 Gray matter
 Outer layer, 2-4
mm thick
 Composed
mostly of neuron
cell bodies
Figure 7.13a
Layers of the Cerebrum
 White matter
 Myelinated
fibers inside the
gray matter
 Example:
corpus
callosum connects
hemispheres
Figure 7.13a
Diencephalon
 Sits on top of the brain stem – central core
 Enclosed by the cerebral hemispheres
 Made of three parts
 Thalamus
 Hypothalamus
 Epithalamus
Diencephalon
Figure 7.15
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”
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
Hypothalamus
 An important part of the limbic system
(emotions)
 The pituitary gland is attached to the
hypothalamus
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
Brain Stem
 Attaches to the spinal cord
 Parts of the brain stem
 Midbrain
 Pons
 Medulla oblongata
Brain Stem
Figure 7.15a
Midbrain
 Mostly composed of tracts of motor nerve
fibers
 Reflex centers for vision and hearing (startle
reflex)
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
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
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
Cerebellum
Figure 7.15a
The Nervous System
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
Protection of the Central Nervous System
 Scalp and skin
 Cranial/facial bones and vertebral column
 Meninges – forms partitions in skull
Figure 7.16a
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
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
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
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
Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17a–b
Ventricles and Location of the
Cerebrospinal Fluid
Figure 7.17c
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
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
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
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
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
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
 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
 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
 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
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
 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
 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
 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
The Nervous System
ESSENTIALS
OF HUMAN
ANATOMY
& PHYSIOLOGY
EIGHTH EDITION
ELAINE N. MARIEB
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
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
Spinal Cord Anatomy
 Meninges cover the spinal cord
 Nerves leave at the level of each vertebrae
Peripheral Nervous System
 Nerves and ganglia outside the central
nervous system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by connective
tissue
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
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
Distribution of Cranial Nerves
Figure 7.21
Spinal Nerves
Figure 7.22a
Examples of Nerve Distribution
Figure 7.23
Autonomic Nervous System
 The involuntary branch of the nervous system
 Consists of only motor nerves
 Divided into two divisions
 Sympathetic division
 Parasympathetic division
Comparison of Somatic and Autonomic
Nervous Systems
Figure 7.24
Anatomy of the Autonomic Nervous
System
Figure 7.25
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
Autonomic Functioning
 Parasympathetic – housekeeping activities
 Conserves energy
 Maintains daily necessary body functions
 Remember as the “D” division - digestion,
defecation, and diuresis
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
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

Nervous System

Transcription

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