Download A&P Ch 8 PowerPoint(Nervous System)

8
The Nervous
System
The Nervous System
Two Organ Systems Control All the
Other Organ Systems:
• Nervous System characteristics
• Rapid response
• Brief duration
• Endocrine System characteristics
• Slower response
• Long duration
The Nervous System
Two Anatomical Divisions:
•
Central Nervous System (CNS)
•
•
•
Brain
Spinal cord
Peripheral Nervous System (PNS)
•
•
•
All the neural tissue outside CNS
Afferent division (sensory input)
Efferent division (motor output)
• Somatic nervous system (controls
skeletal muscle)
• Autonomic nervous system
(controls smooth & cardiac muscle)
CENTRAL NERVOUS SYSTEM
Information
Processing
PERIPHERAL Sensory information
NERVOUS
within
SYSTEM
afferent division
Motor commands
within
efferent division
includes
Somatic
nervous
system
Autonomic
nervous system
Parasympathetic
division
Receptors
Somatic sensory
receptors (monitor
the outside world
and our position
in it)
Sympathetic
division
Effectors
Visceral sensory
receptors (monitor
internal conditions
and the status
of other organ
systems)
Smooth
muscle
Skeletal
muscle
Cardiac
muscle
Glands
Adipose
tissue
Neural Tissue Organization
Two Classes of Neural Cells:
• Neurons
• For information transfer, processing,
and storage
• Neuroglia
• Supporting framework for neurons
• Contain imbedded phagocytes
Neural Tissue Organization
Three Classes of Neurons:
• Sensory neurons
• Deliver information to CNS
• Motor neurons
• Stimulate or inhibit peripheral tissues
• Interneurons (association neurons)
• Located between sensory and motor
neurons
• Analyze inputs, coordinate outputs
Neural Tissue Organization
Neuron Anatomy:
• Cell body
• Nucleus
• Mitochondria, RoughER, other organelles
• Dendrites
• Several branches
• Signal receptors (inward)
• Axon
• Signal propagation (outward)
Anatomy of a Typical Neuron
Neural Tissue Organization
Structural Classes of Neurons:
• Unipolar
• Dendrite, axon continuous, cell body
off to one side
• Sensory neurons
• Multipolar
• Many dendrites, one axon
• Most common class of neuron
• Motor Neurons
• Bipolar
• One dendrite, one axon
• Very rare, found in sense organs
Structural Classification of Neurons
Neural Tissue Organization
Types of Neuroglia (glia):
• Astrocytes
• Part of blood-brain barrier
• Oligodendrocytes
• Responsible for myelination(protective
covering) around axons
• Microglia
• Phagocytic defense cells
• Ependymal cells
• Lining of brain, spinal cord cavities
• Source of cerebrospinal fluid
Neuroglia in the CNS
Neural Tissue Organization
Two Types of Neuroglia in the PNS:
• Satellite cells
• Surround cell bodies
• Schwann cells
• Surround all peripheral axons
• Form myelin sheath on myelinated axons
Schwann Cells & Peripheral Axons
Neural Tissue Organization
Key Note:
Neurons perform all of the communication,
information processing, and control
functions of the nervous system.
Neuroglia outnumber neurons and have
functions essential to preserving the
physical and biochemical structure of
neural tissue and the survival of neurons.
Neural Tissue Organization
Anatomic Organization of CNS Neurons:
• Center—Collection of neurons with a
shared function
• Nucleus—A center with a discrete
anatomical boundary
• Neural cortex—Gray matter covering of
brain portions
• White matter—Bundles of axons (tracts)
that share origins, destinations, and
functions
Neural Tissue Organization
Anatomic Organization of PNS Neurons:
• Ganglia—Groupings of neuron cell bodies
• Nerve—Bundle of axons supported by
connective tissue
• Spinal nerves
• To/from spinal cord
• Cranial nerves
• To/from brain
Neural Tissue Organization
Neural Tissue Organization
Pathways in the CNS:
• Ascending pathways
- Carry information from sensory receptors
to processing centers in the brain
• Descending pathways
- Carry commands from specialized CNS
centers to skeletal muscles
Neuron Function
The Membrane Potential
• Resting potential
• Excess negative charge inside the
neuron
• Created and maintained by Na-K ion
pump
• Negative voltage (potential) inside
• -70 mV (0.07 Volts)
Cell Membrane at the Resting Potential
Neuron Function
A membrane potential exists across the cell
membrane because:
(1) the cytosol and the extracellular fluid
differ in their ionic composition, and
(2) the cell membrane is selectively
permeable to these ions.
The membrane potential can quickly
change, as the ionic permeability of the
cell membrane changes, in response to
chemical or physical stimuli.
Depolarization to threshold
Activation of voltageregulated sodium channels
and rapid depolarization
Sodium ions
Local
current
Potassium ions
Inactivation of sodium
channels and activation of
voltage-regulated
potassium channels
Transmembrane potential (mV)
+30
DEPOLARIZATION
3
REPOLARIZATION
0
2
_ 60
_ 70
The return to normal
permeability and resting state
Threshold
1
4
Resting
potential
REFRACTORY PERIOD
0
1
2
Time (msec)
3
Neuron Function
Key Note:
“Information” travels within the nervous
system primarily in the form of
propagated electrical signals known as
action potentials. The most important
information (e.g., vision, balance,
movement), is carried by myelinated
axons.
Neural Communication
Synapse Basics
• Intercellular communication
• Axon terminal receives
electrical signal from cell
body
• Input to next cell
• Chemical signaling to cross
synapse
• Neurotransmitter release
Neural Communication
Structure of a Synapse:
• Presynaptic components
• Axon terminal
• Synaptic knob
• Synaptic vesicles
• Synaptic cleft
• Postsynaptic components
• Neurotransmitter receptors
Neural Communication
The Structure of a Typical Synapse
Neural Communication
Synaptic Function and Neurotransmitters
• Cholinergic synapses
• Release neurotransmitter acetylcholine
• Enzyme in synaptic cleft
(acetylcholinesterase) breaks it down
• Adrenergic synapses
• Release neurotransmitter norepinephrine
• Dopaminergic synapses
• Release neurotransmitter dopamine
Neural Communication
Extracellular Ca2+ enters the synaptic
cleft triggering the exocytosis of ACh
An action potential arrives and
depolarizes the synaptic knob
PRESYNAPTIC
NEURON
Synaptic vesicles
Action potential
EXTRACELLULAR
FLUID
ACh
ER
Synaptic
knob
Ca2+
Synaptic
cleft
Ca2+
AChE
CYTOSOL
Chemically regulated
sodium channels
POSTSYNAPTIC
NEURON
ACh is removed by AChE
(acetylcholinesterase)
ACh binds to receptors and depolarizes
the postsynaptic membrane
Initiation of
action potential
if threshold
is reached
Propagation of
action potential
(if generated)
Na2+ Na2+
Na2+
Na2+ Receptor
Na2+
Neural Communication
• Neuronal pools
Groups of interconnected neurons with
specific functions
• Divergence
Spread of information from one neuron
to several others
• Convergence
Several neurons send information to
one other
Neural Communication
Two Common Types of Neuronal Pools
Neural Communication
Key Note:
A synaptic terminal releases a neurotransmitter that binds to the postsynaptic
cell membrane. The result is a brief, local
change in the permeability of the
postsynaptic cell.
Many drugs affect the nervous system by
stimulating neurotransmitter receptors
and thus produce complex effects on
perception, motor control, and emotions.
The Central Nervous System
Meninges—Layers that surround and
protect the brain and spinal cord (CNS)
• Dura mater (“tough mother”)
• Tough, fibrous outer layer
• Epidural space above dura of spinal cord
• Arachnoid (“spidery”)
• Subarchnoid space
• Cerebrospinal fluid
• Pia mater (“delicate mother”)
• Thin inner layer
The Meninges
The Meninges
The Central Nervous System
Spinal Cord Basics:
• Relays information to/from brain
• Processes some information on its
own (reflexes)
• Divided into 31 segments
• Each segment has a pair of:
• Dorsal root ganglia
• Dorsal roots
• Ventral roots
• Gray matter appears as horns
• White matter organized into columns
Anatomy of the Spinal Cord
Anatomy of the Spinal Cord
Sectional Anatomy of the Spinal Cord
Sectional Anatomy of the Spinal Cord
The Central Nervous System
Key Note:
The sensory and motor nuclei (gray matter)
of the spinal cord surround the central canal.
Sensory nuclei are dorsal, motor nuclei are
ventral. A thick layer of white matter
consisting of ascending and descending
axons covers the gray matter. These axons
are organized into columns of axon bundles
with specific functions. This highly organized
structure often enables predicting the impact
of particular injuries.
The Central Nervous System
Brain Regions
•
•
•
•
•
•
Cerebrum
Diencephalon
Midbrain
Pons
Medulla oblongata
Cerebellum
The Brain
The Brain
The Brain
The Central Nervous System
Brain—The four hollow chambers in
the center of the brain filled with
cerebrospinal fluid (CSF)
• CSF produced by choroid plexus
• CSF circulates
• From ventricles and central canal
• To subarachoid space
• Accessible by lumbar puncture
• To blood stream
Ventricles of the Brain
Circulation of Cerebrospinal Fluid
The Central Nervous System
Functions of the Cerebrum:
•
•
•
•
Conscious thought
Intellectual activity
Memory
Origin of complex patterns of movement
Anatomy of Cerebral Cortex:
• Highly folded surface
• Elevated ridges (gyri)
• Shallow depressions (sulci)
The Central Nervous System
Functions of the Cerebral Cortex
• Hemispheres serve opposite body sides
• Primary motor cortex (precentral gyrus)
• Directs voluntary movement
• Primary sensory cortex (postcentral gyrus)
• Receives somatic sensation (touch, pain,
pressure, temperature)
• Association areas
• Interpret sensation
• Coordinate movement
Surface of Cerebral Hemispheres
The Central Nervous System
Hemispheric Lateralization
• Categorical hemisphere (usually left)
• General interpretative and speech centers
• Language-based skills
• Representational Hemisphere (usually
right)
• Spatial relationships
• Logical analysis
Hemispheric Lateralization
Brain Waves
(Electroencephalogram)
The Central Nervous System
The Basal Nuclei
• Lie deep within central white
matter of the brain
• Responsible for muscle tone
• Coordinate learned movements
• Coordinate rhythmic movements
(e.g., walking)
The Basal Nuclei
The Central Nervous System
Functions of the Limbic System
• Establish emotions and related
drives
• Link cerebral cortex intellectual
functions to brain stem autonomic
functions
• Control reflexes associated with
eating
• Store and retrieve long-term
memories
The Limbic System
The Central Nervous System
The Diencephalon
• Switching and relay center
• Integration of conscious and
unconscious motor and sensory
pathways
• Components include:
• Epithalamus
• Choroid plexus
• Pineal body
• Thalamus
• Hypothalamus
The Central Nervous System
The Diencephalon and Brain Stem
Figure 8-24(a)
The Central Nervous System
Functions of the Thalamus
• Relay and filter all ascending (sensory)
information
• Relay a small proportion to cerebral
cortex (conscious perception)
• Relay most to basal nuclei and brain
stem centers
• Coordinate voluntary and involuntary
motor behavior
The Central Nervous System
Functions of the Hypothalamus
• Produce emotions and behavioral drives
• Coordinate nervous and endocrine
systems
• Secrete hormones
• Coordinate voluntary and autonomic
functions
• Regulate body temperature
The Central Nervous System
Anatomy and Function of the Brain Stem
• Midbrain
• Process visual, auditory information
• Generate involuntary movements
• Pons
• Links to cerebellum
• Involved in control of movement
• Medulla oblongata
• Relay sensory information
• Regulate autonomic function
The Central Nervous System
Functions of the Medulla Oblongata
• Links brain and spinal cord
• Relays ascending information to cerebral
cortex
• Controls crucial organ systems by reflex
• Cardiovascular centers
• Respiratory rhythmicity centers
The Central Nervous System
Anatomy and Function of the Cerebellum
•
•
•
•
Oversees postural muscles
Stores patterns of movement
Fine tunes most movements
Links to brain stem, cerebrum, spinal cord
• Communicates over cerebellar peduncles
The Central Nervous System
Key Note:
The brain, a large mass of neural tissue,
contains internal passageways and
chambers filled with CSF. The six major
regions of the brain have specific functions.
As you ascend from the medulla oblongata
to the cerebrum, those functions become
more complex and variable. Conscious
thought and intelligence are provided by the
cerebral cortex.
The Peripheral Nervous System
PNS Basics
• Links the CNS with the body
• Carries all sensory information and motor
commands
• Axons bundled in nerves
• Cell bodies grouped into ganglia
• Includes cranial and spinal nerves
The Peripheral Nervous System
The Cranial Nerves
• 12 Pairs
• Connect to brain not the cord
• Olfactory (CN I)
• Sense of smell
• Optic (CN II)
• Sense of vision
• Oculomotor (CN III)
• Eye movement
The Peripheral Nervous System
The Cranial Nerves (continued)
• Trochlear (CN IV)
• Eye movement
• Trigeminal (CN V)
• Eye, jaws sensation/movement
• Abducens (CN VI)
• Eye movement
• Facial (CN VII)
• Face, scalp, tongue sensation/movement
• Vestibulocochlear (CN VIII)
• Hearing, balance
The Peripheral Nervous System
The Cranial Nerves (continued)
• Glossopharyngeal (CN IX)
• Taste, swallowing
• Vagus (CN X)
• Autonomic control of viscera
• Accessory (CN XI)
• Swallowing, pectoral girdle movement
• Hypoglossal (CN XII)
• Tongue movement
The Cranial Nerves
The Cranial Nerves
The Peripheral Nervous System
Key Note:
The 12 pairs of cranial nerves are
responsible for the special senses of
smell, sight, and hearing/balance, and
control movement of the eye, jaw, face,
tongue, and muscles of the neck, back,
and shoulders. They also provide
sensation from the face, neck, and
upper chest and autonomic innervation
to thoracic and abdominopelvic organs.
The Peripheral Nervous System
The Spinal Nerves
• 31 Pairs
• 8 Cervical
• 12 Thoracic
• 5 Lumbar
• 5 Sacral
• Dermatome—Region of the
body surface monitored by a
pair of spinal nerves
The Peripheral Nervous System
Nerve Plexus—A complex, interwoven
network of nerves
• Four Large Plexuses
• Cervical plexus
• Brachial plexus
• Lumbar plexus
• Sacral plexus
The Peripheral Nervous System
Reflex—An automatic involuntary motor
response to a specific stimulus
• The 5 steps in a reflex arc
• Arrival of stimulus and activation of
receptor
• Activation of sensory neuron
• CNS processing of information
• Activation of motor neuron
• Response by effector (muscle or gland)
Arrival of
stimulus and
activation of
receptor
Activation of a
sensory neuron
Receptor
Sensation
relayed to
the brain by
collateral
Dorsal
root
REFLEX
ARC
Stimulus
Effector
Ventral
root
Activation of a
motor neuron
Response
by effector
Reflex Action
Information
processing
in CNS
KEY
Sensory neuron
(stimulated)
Excitatory
interneuron
Motor neuron
(stimulated)
The Peripheral Nervous System
Examples of Reflexes
• Monosynaptic reflex—Simplest reflex arc;
sensory neuron synapses directly on motor
neuron
• Stretch reflex—Monosynaptic reflex to
regulate muscle length and tension
(example: patellar reflex)
• Muscle spindle—Sensory receptor in a
muscle that stimulates the stretch reflex
Stretching of muscle tendon
stimulates muscle spindles
Muscle spindle
(stretch receptor)
Stretch
Spinal
cord
REFLEX
ARC
Contraction
Activation of motor
neuron produces reflex
muscle contraction
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings
The Peripheral Nervous System
Polysynaptic reflex—A reflex arc with
at least one interneuron between the
sensory afferent and motor efferent
• Has a longer delay than a
monosynaptic reflex (more synapses)
• Can produce more complex response
• Example: flexor reflex, a withdrawal
reflex
• Brain can modify spinal reflexes
The Flexor Reflex
The Peripheral Nervous System
Key Note:
Reflexes are rapid, automatic responses
to stimuli that “buy time” for the planning
and execution of more complex
responses that are often consciously
directed.
The Peripheral Nervous System
The Autonomic Nervous System
Autonomic Nervous System
Branch of nervous system that
coordinates cardiovascular,
digestive, excretory, and
reproductive functions
The Autonomic Nervous System
Divisions of the ANS
• Sympathetic division
• Preganglionic neurons in the thoracic and
lumbar segments of the spinal cord
• “Fight or flight” system
• Parasympathetic division
• Preganglionic neurons in the brain and
sacral segments
• “Rest and digest” system
The Autonomic Nervous System
Key Note:
The two divisions of the ANS operate
largely without our awareness. The
sympathetic division increases
alertness, metabolic rate, and
muscular abilities;
The parasympathetic division reduces
metabolic rate and promotes visceral
activities such as digestion.
The Sympathetic Division
The Autonomic Nervous System
Effects of Sympathetic Activation
•
•
•
•
•
•
Generalized response in crises
Increased alertness
Feeling of euphoria and energy
Increased cardiovascular activity
Increased respiratory activity
Increased muscle tone
The Parasympathetic Division
The Autonomic Nervous System
Effects of Parasympathetic Activation
•
•
•
•
Relaxation
Food processing
Energy absorption
Brief effects at specific sites
The Autonomic Nervous System
Relationship between the Two Divisions:
• Sympathetic division reaches visceral and
somatic structures throughout the body
• Parasympathetic division reaches only
visceral structures via cranial nerves or in
the abdominopelvic cavity
• Many organs receive dual innervation
• In general, the two divisions produce
opposite effects on the their target organs
Aging and the Nervous System
Age-Related Changes
•
•
•
•
Reduction in brain size and weight
Loss of neurons
Decreased brain blood flow
Changes in synaptic organization of the
brain
• Intracellular and extracellular changes in
CNS neurons