Download Functions of the Nervous System

CHAPTER
SEVEN
The
Nervous
System
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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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Functions of the Nervous System
Figure 7.1
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Structural Classification
of the Nervous System
 Central nervous system (CNS)
 Brain
 Spinal cord
 Peripheral nervous system (PNS)
 Nerves outside the brain and spinal cord
 Spinal nerves
 Cranial nerves
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Functional Classification of
the Peripheral Nervous System
 Sensory (afferent) division
 Nerve fibers that carry information to the
central nervous system
 Motor (efferent) division
 Nerve fibers that carry impulses away from the
central nervous system
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Organization of the Nervous System
Figure 7.2
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Central
Nervous System
CNS
Spinal cord
Brain
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Functions
 Integrates Information
 Processes changes in the internal and
external environments
 Initiates Responses
 Responds (with the endocrine system) to
coordinate and regulate body systems
functions to maintain homeostasis
 body's ability to physiologically
regulate its inner environment to
ensure its stability in response to
changes in the outside environment
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Major parts of the brain
 Brain Stem
 Cerebellum-coordination
 Cerebrum
 Frontal-processing
 Parietal-movement
 Occipital-vision
 Temporal-hearing
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Frontal View
 Corpus
Callosum
 connector
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Cerebrum
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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
 Dura mater
 Double-layered external covering
 Periosteum—attached to inner surface of
the skull
 Meningeal layer—outer covering of the
brain
 Folds inward in several areas
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Meninges
Dura
 Arachnoid
 Pia

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Meninges
 Arachnoid layer
 Middle layer
 Web-like
 Pia mater
 Internal layer
 Clings to the surface of the brain
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Meninges
Figure 7.17b
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Cerebrospinal Fluid (CSF)
 Similar to blood plasma composition
 Formed by the choroid plexus
 Forms a watery cushion to protect 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
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Ventricles and Location of
the Cerebrospinal Fluid
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Cerebrospinal Fluid (CSF)
 bring nutrients to nerves and to remove waste
products
 Similar to Lymph Fluid
 act as a cushion for CNS
 made in choroid plexus in the brain sinuses or
Ventricles
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Pathology - Hydrocephalus
 buildup of too much cerebrospinal fluid in the
brain
 too much fluid puts harmful pressure on your
brain – intracranial pressure
 can permanently damage the brain
 problems with physical and mental development
 Place shunt in brain to drain excess fluid
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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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―Water on the Brain‖
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Blood-Brain Barrier
 Includes the least permeable capillaries of the
body
 Excludes many potentially harmful substances
 Useless as a barrier against some substances
 Fats and fat soluble molecules
 Respiratory gases
 Alcohol
 Nicotine
 Anesthesia
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Traumatic Brain Injuries
 Concussion
 Slight brain injury
 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
 The result of a ruptured 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
 Mostly seen in the elderly, but may begin in
middle age
 Structural changes 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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Pathology - Meningitis
 Swelling & inflammation of membranes covering
the brain affecting Cerebrospinal Fluid (CSF)
 Usually caused by an infection does have
meningitis, the cerebrospinal fluid will be
 Major reason for a spinal tap or lumbar puncture
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Spinal Tap or Lumbar
Puncture
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Bacteria in CSF
Cerebrospinal fluid from a patient with
meningitis. The bacteria are streptococci,
found in pairs.
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Multiple Sclerosis - MS
 Scleroses = scars; plaques or lesions that form in the
nervous system.
 most commonly involves white matter areas close to
the ventricles, cerebellum, brain stem, optic nerve.
 function of white matter cells is to carry signals
between grey matter areas, where the processing is
done.
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Myelin Sheath – nerve covering
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MRI of MS Patient
 Typically
white females
between 20
and 40
 Acute and
Progressive
stages
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Nerve damage can cause:
 Weakness or Numbness
 Weakness in an arm or leg
 Loss of balance
 Muscle spasms
 leads to frequent tripping or difficulty walking
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– inflammation of the optic nerve
 many times the
first sign
 blurred vision,
loss of color
vision, eye pain,
or blindness,
usually in one eye
 usually temporary
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The toll MS takes …….
 Mental difficulties
 mild memory loss or trouble concentrating
 Loss of bladder control
 Fatigue
 tired even after a good night‘s sleep.
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Treatment
 Treat symptoms – no ‗cure‘
 Support patient functioning
 Physical therapy
 Massage therapy
 Chiropractic
 Medications
 Interferon
 corticosteroids
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Trephination
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Functional Classification of
the Peripheral Nervous System
 Motor (efferent) division (continued)
 Two subdivisions
 Somatic nervous system = voluntary
 Autonomic nervous system = involuntary
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Nervous Tissue: Support Cells
Figure 7.3e
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Nervous Tissue: Neurons
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Nervous Tissue: Neurons
 Cell body
 Nucleus
 Large nucleolus
 Processes outside the cell body
 Dendrites—conduct impulses toward the cell
body
 Axons—conduct impulses away from the cell
body
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Nervous Tissue: Neurons
 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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Nervous Tissue: Neurons
 Myelin sheath—whitish, fatty material covering
axons
 Schwann cells—produce myelin sheaths in jelly
roll–like fashion
 Nodes of Ranvier—gaps in myelin sheath along
the axon
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Functional Classification of Neurons
 Sensory (afferent) neurons
 Carry impulses from the sensory receptors to
the CNS
 Cutaneous sense organs
 Proprioceptors—detect stretch or tension
 Motor (efferent) neurons
 Carry impulses from the central nervous
system to viscera, muscles, or glands
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Neuron Classification
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Structural Classification of Neurons
 Multipolar neurons—many extensions from the
cell body
Figure 7.8a
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Structural Classification of Neurons
 Bipolar neurons—one axon and one dendrite
Figure 7.8b
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Structural Classification of Neurons
 Unipolar neurons—have a short single process
leaving the cell body
Figure 7.8c
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Functional Properties of Neurons
 Irritability
 Ability to respond to stimuli
 Conductivity
 Ability to transmit an impulse
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The Reflex Arc
 Reflex—rapid, predictable, and involuntary
response to a stimulus
 Occurs over pathways called reflex arcs
 Reflex arc—direct route from a sensory neuron, to
an interneuron, to an effector
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Simple Reflex Arc
Sensory receptors
(stretch receptors
in the quadriceps
muscle)
Sensory (afferent)
neuron
Sensory receptors
(pain receptors in
the skin)
Spinal cord
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)
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Types of Reflexes and Regulation
 Somatic reflexes
 Activation of skeletal muscles
 Example: When you move your hand away
from a hot stove
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Types of Reflexes and Regulation
 Autonomic reflexes
 Smooth muscle regulation
 Heart and blood pressure regulation
 Regulation of glands
 Digestive system regulation
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Types of Reflexes and Regulation
 Patellar, or knee-jerk, reflex is an example of a
two-neuron reflex arc
Figure 7.11d
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Spinal Cord
 Extends from the foramen magnum of the skull to
the first or second lumbar vertebra
 31 pairs of spinal nerves arise from the spinal
cord
 Cauda equina is a collection of spinal nerves at
the inferior end
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Spinal Cord Anatomy
Figure 7.20 (1 of 2)
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Spinal Cord Anatomy
Figure 7.21
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Pathways Between Brain and Spinal Cord
Figure 7.22
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Peripheral Nervous System (PNS)
 Nerves and ganglia outside the central nervous
system
 Nerve = bundle of neuron fibers
 Neuron fibers are bundled by connective tissue
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PNS: Structure of a Nerve
Figure 7.23
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PNS: Classification of Nerves
 Mixed nerves
 Both sensory and motor fibers
 Sensory (afferent) nerves
 Carry impulses toward the CNS
 Motor (efferent) nerves
 Carry impulses away from the CNS
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PNS: Cranial Nerves
 12 pairs of nerves that mostly serve the head and
neck
 Only the pair of vagus nerves extend to thoracic
and abdominal cavities
 Most are mixed nerves, but three are sensory only
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PNS: Cranial Nerves
 I Olfactory nerve—sensory for smell
 II Optic nerve—sensory for vision
 III Oculomotor nerve—motor fibers to eye
muscles
 IV Trochlear—motor fiber to eye muscles
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PNS: Cranial Nerves
 V Trigeminal nerve—sensory for the face; motor
fibers to chewing muscles
 VI Abducens nerve—motor fibers to 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
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PNS: Differences Between Somatic
and Autonomic Nervous Systems
 Nerves
 Somatic: one motor neuron
 Autonomic: preganglionic and postganglionic
nerves
 Effector organs
 Somatic: skeletal muscle
 Autonomic: smooth muscle, cardiac muscle,
and glands
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PNS: Autonomic Nervous System
 Motor subdivision of the PNS
 Consists only of motor nerves
 Also known as the involuntary nervous system
 Regulates activities of cardiac and smooth
muscles and glands
 Two subdivisions
 Sympathetic division
 Parasympathetic division
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PNS: Anatomy of the
Autonomic Nervous System
Figure 7.28
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PNS: 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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PNS: Autonomic Functioning
 Parasympathetic—―housekeeping‖ activites
 Conserves energy
 Maintains daily necessary body functions
 Remember as the ―D‖ division
 digestion, defecation, and diuresis
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