Transcript nervous system

PowerPoint® Lecture Slides
prepared by
Betsy C. Brantley
Valencia College
CHAPTER
8
The Nervous
System
Organ Systems That Coordinate (Introduction)
• Two organ systems coordinate all activities to
maintain homeostasis
• Nervous system
• fast and brief
• Endocrine system
• slower but last longer
• Nervous system is the most complex organ system
Nervous System Functions (8-1)
• Three main functions of the nervous system
1. Monitors the body’s internal and external environments
2. Integrates sensory information
3. Coordinates voluntary and involuntary responses
Nervous System Anatomical Divisions (8-1)
• Central nervous system (CNS)
• Includes the brain and spinal cord
• Integrates and coordinates sensory processing and
motor transmission
• Location of higher functions (intelligence, memory,
emotion)
• Peripheral nervous system (PNS)
• All the neural tissues outside of the CNS
• Communication connection between the CNS and the
rest of the body
Figure 8-1a A Functional Overview of the Nervous System.
PNS Functional Divisions (8-1)
• Afferent division
• Brings information to the CNS from receptors in body
tissues and organs
• Receptors
• Sensory structures that detect changes in the environment
or respond to specific stimuli
• Efferent division
• Carries information away from the CNS to effectors
(muscles and glands that respond to motor commands)
Efferent Division Subdivisions (8-1)
• Somatic nervous system (SNS)
• Controls skeletal muscle
• Autonomic nervous system (ANS)
• Controls smooth and cardiac muscle, and glands
• Includes two parts
1.
Sympathetic division
2.
Parasympathetic division
Figure 8-1b A Functional Overview of the Nervous System.
Neural Tissue (8-2)
• Neural tissue includes two types of cells
1. Neurons
• Basic functional units of nervous system
• Communicate with one another and with other cells
2. Neuroglia
• Regulate environment around and support neurons
• Much more numerous than neurons
• Are able to divide (unlike most neurons)
General Structure of Neurons (8-2)
• Cell body
• Dendrites
• Receive signals coming into the cell body
• Axon
• Carries signals away from the cell body
• Axon terminals
• Bulb-shaped axon endings that form a synapse, or site of
connection with the next cell
• Axon hillock
• Thickened region marking the beginning of the axon
• Originating point for electrical impulses (action potentials)
Figure 8-2 The Anatomy of a Representative Neuron.
Functional Classification of Neurons (8-2)
1. Sensory neurons, or afferent neurons
• Receive information from sensory receptors
• Relay that information to the CNS
2. Motor neurons, or efferent neurons
• Carry instructions away from CNS
• Peripheral targets of these instructions called effectors
3. Interneurons, or association neurons
• Located entirely within the CNS
• Interconnect other neurons
Sensory Neurons (8-2)
• Number about 10 million
• Two types of somatic sensory receptors
• External receptors that monitor the external
environment
• Proprioceptors that monitor position and movement of
skeletal muscles and joints
• Visceral receptors
• Monitor activities of internal organs and provide
sensations of distention, deep pressure, and pain
Motor Neurons (8-2)
• Total about half a million in number
• Somatic motor neurons
• Innervate skeletal muscle
• Visceral motor neurons
• Innervate cardiac muscle, smooth muscle, and glands
Interneurons (8-2)
• By far the most numerous type at about 20 billion
• Located entirely in brain and spinal cord
• Function as links between sensory and motor
neurons
• Play a role in all higher functions
• Examples: memory, planning, and learning
Neuroglial Cells (8-2)
• Make up about half of all neural tissue
• Four types are found in the CNS
1. Astrocytes
2. Oligodendrocytes
3. Microglia
4. Ependymal cells
• Two types are found in the PNS
1. Satellite cells
2. Schwann cells
Astrocytes (8-2)
• Star-shaped cells in the CNS
• Largest and most numerous neuroglia
• Maintain the blood–brain barrier
• Isolates CNS from general circulation
Oligodendrocytes (8-2)
• Produce an insulating membranous wrapping
around CNS axons
• Wrapping is called myelin
• Areas covered in myelin are called internodes
• Small gaps between wrappings are called nodes, or
nodes of Ranvier
White Matter and Gray Matter (8-2)
• Myelin is lipid-rich, appearing glossy white
• White matter of the CNS
• Areas dominated by myelinated axons
• Gray matter of the CNS
• Areas containing neuron cell bodies, dendrites, and
unmyelinated axons
Microglia (8-2)
• The smallest and least numerous CNS neuroglial
cells
• Phagocytic cells derived from white blood cells
• Perform essential protective functions such as
engulfing pathogens and cellular waste
Ependymal Cells (8-2)
• Line cavities in the CNS filled with cerebrospinal
fluid including:
• Central canal of the spinal cord
• Chambers, or ventricles, of the brain
• Involved in producing and circulating cerebrospinal
fluid around the CNS
Neuroglial Cells in PNS (8-2)
• Satellite cells
• Surround and support neuron
cell bodies
• Schwann cells
• Cover every axon in PNS
• Myelinated axons have one
Schwann cell per segment
Figure 8-5 Schwann Cells and Peripheral Axons.
Neuron Organization in the PNS (8-2)
• Collections of neuron cell bodies (gray matter)
located in ganglia
• Neuron cell bodies surrounded by satellite cells
• Bundles of axons are called nerves
• May contain both sensory and motor components
• Two categories based on location
• Spinal nerves connected to the spinal cord
• Cranial nerves connected to the brain
Figure 8-6 Anatomical Organization of the Nervous System.
The Membrane Potential (8-3)
• Living cells have a polarized plasma membrane
• Excessive positive charges on the outside of the cell
• Excessive negative charges on the inside of the cell
• Difference between the two charges is called a
membrane potential
• Membrane potential of undisturbed cell is called
resting membrane potential
• Measured in millivolts
• Resting membrane potential of neurons is –70 mV
(negative on inside relative to outside)
Factors Influencing Membrane Potential (8-3)
• Imbalance in electrical charges
• Differing composition of fluids
• Extracellular fluid (ECF) is high in Na+ and CI–
• Intracellular fluid (ICF) is high in K+ and negatively
charged proteins (Pr–)
• Proteins are non-permeating, staying in the ICF
• Ions enter or leave the cell via channels and/or carrier
proteins
• Leak channels are always open
• Gated channels open or close under specific
circumstances
Passive Ion Movement across Membrane (8-3)
• Both chemical and electrical gradients influence
passive movement
• Sodium moves into the cell
• Higher chemical concentration outside
• Attracted to negative charge inside the cell
• Potassium moves out of the cell
• Higher chemical concentration inside the cell
• Chemical gradient much stronger than the electrical force
• Potassium diffuses out of cell faster than sodium enters
Maintaining Resting Membrane Potential (8-3)
• Active process required to maintain potential
difference
• Sodium–potassium exchange pump
• Pumps (exchanges) 3 Na+ out for every 2 K+ in
• Moves Na+ out as fast as it leaks in
• Cell experiences a net loss of positive ions
• Resulting in a resting membrane potential of –70 mV
Figure 8-7 The Resting Membrane Potential.
Changes in Membrane Potential (8-3)
• Resting membrane potential of a cell disturbed by:
• Stimuli altering membrane permeability to Na+ or K+ or
• Stimuli altering activity of the exchange pump
• Examples include:
• Cellular exposure to chemicals, mechanical pressure, or
temperature changes
• Changes in the ECF ion concentration
• Usual response is opening of a gated channel
• Increases movement of ions across the membrane
Changes in Membrane Potential cont. (8-3)
• Opening Na+ channels speeds up entry of Na+
• Shifts the membrane potential in a positive direction
(toward 0 mV)
• Shift in that direction called depolarization
• Opening K+ channels allows more K+ to leave
• Shifts the membrane in a negative direction (further
away from 0 mV)
• Movement to more negative from resting (i.e., –70 mV to
–80 mV) called hyperpolarization
Action Potentials (8-3)
• Propagated change in membrane potential of
excitable cells
• Cells that have an excitable membrane contain voltagegated channels that open or close in response to
changes in membrane potential
• Change in membrane potential travels the entire
length of cell
• In a neuron, called a nerve impulse
• Threshold
• Level of depolarization required to initiate an action
potential
Characteristics of an Action Potential (8-3)
• All-or-none principle
• Every stimulus that brings membrane to threshold will
result in an identical action potential
• Action potential will propagate down the length of the
neuron
• Refractory period
• Time from voltage-gated sodium channels opening until
repolarization is complete
• Repolarization is the return to resting potential
• Membrane cannot respond to further stimulation
Generation of an Action Potential (8-3)
1. Membrane depolarizes to threshold (–60 mV)
2. Sodium channels open and membrane rapidly
depolarizes up to +30 mV
3. Sodium channels close and potassium channels
open, repolarizing the membrane
4. Potassium channels close and membrane returns
to resting potential
Figure 8-8 The Generation of an Action Potential.
Figure 8-8 The Generation of an Action Potential.
Figure 8-8 The Generation of an Action Potential
Propagation of an Action Potential (8-3)
• Begins with local changes in the membrane in one
site
• Local current of moving sodium ions spreads in all
directions
• Results in the activation of voltage-gated channels in the
next adjacent site of the membrane
• Causes a wave of membrane potential changes
• Continuous propagation
• Occurs in unmyelinated fibers and is relatively slow
(about 1 meter per second)
• Saltatory propagation
• Occurs in myelinated axons and is much faster (from
18–140 meters per second)
Figure 8-9b Propagation of an Action Potential
The Synapse (8-4)
• Site where neuron communicates with another cell
• Information transferred through release of chemical
messengers called neurotransmitters
• Communication happens in one direction only
Figure 8-10 The Structure of a Typical Synapse.
Structure of a Synapse (8-4)
• Presynaptic neuron
• Neuron on sending side of synapse
• Axon terminal holds vesicles containing
neurotransmitters
• Neurotransmitters are released and diffuse across
synaptic cleft
• Postsynaptic neuron
• Neuron on receiving side of synapse
• Has receptors for neurotransmitters
The Neurotransmitter Acetylcholine (8-4)
• Acetylcholine, or ACh
• Activates cholinergic synapses in four steps
1. Action potential arrives and depolarizes the axon
terminal
2. ACh is released and diffuses across synaptic cleft
3. ACh binds to receptors and triggers depolarization of
the postsynaptic membrane
4. ACh is removed by AChE (acetylcholinesterase)
Figure 8-11 The Events at a Cholinergic Synapse.
Other Important Neurotransmitters (8-4)
• Norepinephrine (NE), or noradrenaline
• Common neurotransmitter
• Important in the brain and part of the ANS
• Dopamine, GABA, and serotonin
• Function as CNS neurotransmitters
• At least 50 less-understood neurotransmitters
• Nitric oxide (NO) and carbon monoxide (CO)
• Gases that act as neurotransmitters
The Meninges (8-5)
• Three layers of specialized membranes
1. Dura mater
2. Arachnoid
3. Pia mater
• Surround the brain and spinal cord
• Cranial meninges (covering brain) are continuous with
spinal meninges (surrounding spinal cord)
• Provide physical stability and shock absorption
The Dura Mater (8-5)
• Tough, fibrous outermost covering
• Two fibrous layers around the brain
• Outer layer fused to the periosteum of the skull
• Dural folds
• Folded membranes formed by extensions of inner layer of
dura mater into cranial cavity
• Contain large collecting veins, the dural sinuses
• Spinal cord dura mater separated from the vertebrae by
the epidural space
The Arachnoid
• Layer of squamous epithelial cells
• Separated from dura mater by subdural space
• Contains small amounts of lymphatic fluid
• Reduces friction between layers
• Subarachnoid space
• Deep to arachnoid epithelial layer
• Filled with cerebrospinal fluid (CSF)
The Pia Mater
• Innermost meningeal layer
• Firmly bound to the neural tissue underneath
• Highly vascularized
• Provides needed oxygen and nutrients to superficial
areas of neural cortex
Figure 8-13 The Meninges of the Brain and Spinal Cord.
Spinal Cord (8-6)
• Major neural pathway between brain and the PNS
• About 45 cm (18 in.) long and 14 mm (0.54 in.)
wide
• Two regions with slightly wider diameter where nerves
supplying limbs branch
• Cervical enlargement
• Lumbar enlargement
• Distal end tapers to a point
Spinal Segments (8-6)
• Spinal cord consists of 31 segments, each giving
rise to pair of spinal nerves
• Identified by a letter and number relating to the nearby
vertebrae
• 8 cervical
• 12 thoracic
• 5 lumbar
• 5 sacral
• 1 coccygeal
Figure 8-14a Gross Anatomy of the Spinal Cord.
Posterior median sulcus
Dorsal root
Dorsal root
ganglion
White matter
Gray
matter
Central
canal
Spinal
nerve
Ventral
root
C3
Anterior median fissure
b This cross section through the cervical region of the
spinal cord shows some prominent features and the
arrangement of gray matter and white matter.
Figure 8-14b Gross Anatomy of the Spinal Cord.
The Brain (8-7)
• Contains almost 97 percent of the body’s neural
tissue
• Typical brain weighs 3 lb
• Brain size varies among individuals
• No correlation between brain size and intelligence
Six Major Regions of the Brain (8-7)
1. Cerebrum
2. Diencephalon
3. Midbrain
4. Pons
5. Medulla oblongata
6. Cerebellum
Brain Structure Overview (8-7)
• The cerebrum
• Divided into paired cerebral hemispheres
• Functions: conscious thoughts, sensations, intellectual
functions, memory storage and processing
• Deep to the cerebrum is the diencephalon
• Divided into thalamus, hypothalamus, and
epithalamus
• The brain stem
• Contains the midbrain, pons, and medulla oblongata
• The cerebellum
• Most inferior/posterior portion of the brain
Figure 8-16a The Brain.
Cerebrum
Longitudinal
fissure
A
N
T
E
R
I
O
R
Cerebral veins
and arteries
below
arachnoid mater
a Superior view
Right cerebral
hemisphere
Left cerebral
hemisphere
Cerebellum
P
O
S
T
E
R
I
O
R
Figure 8-16b The Brain.
Figure 8-16c The Brain.
The Ventricles of the Brain (8-7)
• Internal cavities filled with cerebrospinal fluid and
lined with ependymal cells
Figure 8-17 The Ventricles of the Brain.
Cerebrospinal Fluid (8-7)
• Cerebrospinal fluid, or CSF
• Surrounds and bathes the exposed surfaces of the CNS
• Cushions brain and spinal cord against physical trauma
• Supports the brain by “floating” it in fluid
• Transports nutrients, chemicals, and wastes
The Cerebrum (8-7)
• Largest region of the brain
• Includes gray matter and white matter
• Superficial layer of gray matter called cerebral cortex
• Gray matter also found in deeper areas called basal
nuclei
• White matter is deep to the cortex and surrounds basal
nuclei
• Outer surface of cerebrum forms series of folds
(gyri) that increase surface area
• Separated by shallow depressions, or sulci
• Deeper grooves called fissures
The Cerebral Hemispheres (8-7)
• Divided into regions, or lobes
• Named after overlying bones of the skull
• Frontal lobe, parietal lobe, temporal lobe, and occipital
lobe
• Each lobe has sensory regions and motor regions
• Each hemisphere sends and receives information
from the opposite side of the body
Features of the Cerebral Hemispheres (8-7)
• Separated by the longitudinal fissure
• Central sulcus
• Divides frontal lobe from parietal lobe
• Lateral sulcus
• Separates frontal lobe from temporal lobe
• Parieto-occipital sulcus
• Separates parietal lobe from occipital lobe
Motor and Sensory Areas of the Cortex (8-7)
• Primary areas divided by the central sulcus
• Precentral gyrus of the frontal lobe
• Contains the primary motor cortex
• Postcentral gyrus of the parietal lobe
• Contains the primary sensory cortex
Other Sensory Areas of the Cortex (8-7)
• Visual cortex in the occipital lobe
• Receives visual information
• Gustatory cortex in the frontal lobe
• Receives taste sensations
• Auditory cortex and olfactory cortex in the
temporal lobe
• Auditory receives information about hearing
• Olfactory receives information about smell
Association Areas (8-7)
• Integrate sensory and motor cortexes
• Interpret incoming information
• Coordinate a motor response
• Somatic sensory association area
• Monitors activity in primary sensory cortex
• Helps to recognize a touch
• Somatic motor association area, or premotor
cortex
• Responsible for coordinating learned movements
• Example: picking up a glass
Figure 8-19 Motor and Sensory Regions of the Cerebral Hemispheres.
Cortical Connections (8-7)
• Regions of the cortex are linked by the deeper
white matter
• The left and right hemispheres are interconnected
across the corpus callosum
• Other axons link the cortex with:
• The diencephalon, brain stem, cerebellum, and
spinal cord
Cerebral Processing Centers (8-7)
• Receive information from many association areas
• Direct extremely complex motor activities
• Often lateralized or restricted to one hemisphere
• General interpretive area, or Wernicke’s area
• Integrates sensory information and visual and auditory
memory
• Damage affects ability to interpret what is read or heard
• Speech center, or Broca’s area
• Regulates breathing and vocalization required for
speech
• Damage affects ability to form words
The Prefrontal Cortex (8-7)
• Located in the frontal lobe
• Coordinates information from association areas of
the entire cortex
• Performs abstract intellectual functions
• Example: predicting consequences of actions or events
• Damage affects ability to estimate time relationships
• Generates feelings of frustration, tension, and anxiety as
events are interpreted and predictions made
Hemispheric Lateralization (8-7)
• Each hemisphere is responsible for specific
functions not ordinarily performed by opposite
hemisphere
• Left hemisphere tends to be involved in language skills,
analytical tasks, and logical decision making
• Right hemisphere tends to be involved in spatial
analysis, analyzing sensory input and relating it to the
body, and analyzing emotional context
Figure 8-20 Hemisphere Lateralization.
Left Cerebral Hemisphere
Right Cerebral Hemisphere
LEFT HAND
RIGHT HAND
Prefrontal
cortex
Prefrontal
cortex
Speech center
Writing
Auditory cortex
(right ear)
General interpretive center
(language and mathematical
calculation)
Visual cortex
(right visual field)
C
O
R
P
U
S
C
A
L
L
O
S
U
M
Anterior commissure
Analysis by touch
Auditory cortex
(left ear)
Spatial visualization
and analysis
Visual cortex
(left visual field)
The Electroencephalogram (8-7)
• Electroencephalogram (EEG)
• Printed record of electrical activity in the brain
• Electrical patterns called brain waves
• Brain waves correlated with level of consciousness
• Can also provide diagnostic information regarding brain
disorders
• Other methods of mapping brain activity
• Brain imaging using PET scan and MRI scan
Figure 8-21 Brain Waves.
a Alpha waves are
characteristic of
normal resting adults
b Beta waves typically
accompany intense
concentration
Patient being wired
for EEG monitoring
c Theta waves are
seen in children and
in frustrated adults
d Delta waves occur in
deep sleep and in
certain pathological
conditions
0 Seconds
1
2
3
4
Memory (8-7)
• Fact memories
• Specific bits of information (like your social security number)
• Skill memories
• Learned motor skill that can become incorporated into
unconscious memory (like playing the violin)
• Short-term memories
• Do not last long but can be recalled immediately
• Converting into long-term memory through memory
consolidation
• Long-term memories
• Remain for long periods, sometimes an entire lifetime
• Amnesia
• Memory loss as a result of disease or trauma
The Basal Nuclei (8-7)
• Masses of gray matter that lie beneath the lateral
ventricles
• Function in subconscious control of skeletal
muscle tone and coordination of learned
movements
• Contains the amygdala
• Component of the limbic system
Figure 8-22 The Basal Nuclei.
The Limbic System (8-7)
• A functional grouping, rather than an anatomical
one
• Functions
• Establishes the emotional states
• Links the conscious with the unconscious functions
• Aids in long-term memory storage and retrieval with help
of the hippocampus
Figure 8-23 The Limbic System.
The Diencephalon (8-7)
• Contains switching and relay centers
• Centers integrate conscious and unconscious
sensory information and motor commands
• Three components
1. Epithalamus
2. Thalamus
3. Hypothalamus
The Epithalamus (8-7)
• Epithalamus contains the pineal gland
• Endocrine structure that secretes melatonin
• Functions in regulating day–night cycles
• Thalamus functions as relay and processing center
for sensory information
The Hypothalamus (8-7)
• Lies inferior to the third ventricle
• Functionally associated with the limbic system
• Contains centers involved with emotions,
autonomic functions, and hormone production
• Pituitary gland connected to hypothalamus by narrow
stalk
• Primary link between nervous and endocrine systems
Hypothalamus Functions (8-7)
• Subconscious control of skeletal muscle
contractions associated with strong emotion
• Adjusts pons and medulla functions
• Coordinates the nervous and endocrine systems
• Secretes hormones including ADH and oxytocin
• Produces “drives” of thirst and hunger
• Coordinates voluntary and autonomic functions
• Regulates body temperature
• Coordinates daily cycles
The Midbrain (8-7)
• Midbrain
• Involved in visual and auditory processing, eye
movement, wakefulness and muscle tone
• Pons
• Links the cerebellum with the midbrain,
diencephalon, cerebrum, and spinal cord
• Also connected to the medulla oblongata
• Contains sensory and motor nuclei for cranial
nerves V, VI, VII, and VIII
• Other nuclei influence rate and depth of respiration
The Cerebellum (8-7)
• Automatic processing center
• Adjusts voluntary and involuntary motor activities based
on sensory input and stored memories
• Adjusts postural muscles to maintain balance
• Programs and fine-tunes movements
The Medulla Oblongata (8-7)
• Connects the brain with the spinal cord
• Contains sensory and motor nuclei for cranial
nerves VIII, IX, X, XI, and XII
• Contains reflex centers
• Cardiovascular centers
• Adjust heart rate and contraction strength (cardiac center)
and peripheral blood flow (vasomotor center)
• Respiratory rhythmicity centers
• Regulate respiratory rate
• Adjusted by respiratory centers of the pons
Figure 8-24a The Diencephalon and Brain Stem.
Peripheral Nervous System (8-8)
• Links the CNS to the rest of the body through
peripheral nerves
• Cranial nerves originate from the brain
• Spinal nerves connect to the spinal cord
• Cell bodies of sensory and motor neurons are
contained in the ganglia
Cranial Nerves (8-8)
• Twelve pairs
• Designated with Roman numerals I through XII
• Classified as:
• Primarily sensory
• Primarily motor
• Mixed (both sensory and motor)
• Often names remembered with a mnemonic
• “Oh, Once One Takes The Anatomy Final, Very Good
Vacations Are Heavenly”
The Twelve Cranial Nerves (N I–II) (8-8)
• Olfactory nerves (N I)
• Only cranial nerves connected to the cerebrum
• Carry sensory information concerning the sense of smell
• Optic nerves (N II)
• Carry sensory visual information from the eyes, through
the optic foramina of the orbits to the optic chiasm
The Twelve Cranial Nerves (N III–IV) (8-8)
• Oculomotor nerves (N III)
• Motor only, arising in the midbrain
• Innervate four of the six extrinsic eye muscles that move
the eyeball and the intrinsic eye muscles that control the
size of the pupil
• Trochlear nerves (N IV)
• Smallest cranial nerves, also arise in the midbrain
• Motor nerves
• Innervate the superior oblique muscles of the eyes
The Twelve Cranial Nerves (N V) (8-8)
• Trigeminal nerves (N V)
• Mixed nerves with nuclei in the pons
• The largest cranial nerves
• Three branches
1.
Opthalmic provides sensory input from the orbit,
sinuses, nasal cavity, skin of forehead, nose, eyebrows,
and eyelids.
2.
Maxillary provides sensory input from the lower eyelid,
upper lip, cheek, nose, upper gums, and teeth.
3.
Mandibular provides sensory input from salivary glands
and tongue and motor control to chewing muscles
The Twelve Cranial Nerves (N VI–VII) (8-8)
• Abducens nerves (N VI)
• Motor nerves
• Innervate only the lateral rectus eye muscle
• Nuclei located in the pons
• Facial nerves (N VII)
• Mixed nerves
• Emerge from the pons
• Sensory fibers monitor proprioception in the face and
provide taste information from anterior two-thirds of the
tongue
• Motor fibers provide facial expressions and control tear
and salivary glands
The Twelve Cranial Nerves (N VIII) (8-8)
• Vestibulocochlear nerves (N VIII)
• Sensory nerves
• Nuclei in the pons and medulla
• Respond to sensory receptors in the inner ear
• Two components
1.
Vestibular nerve
• Conveys information about balance and position
2.
Cochlear nerve
• Conveys information related to sense of hearing
The Twelve Cranial Nerves (N IX) (8-8)
• Glossopharyngeal nerves (N IX)
• Mixed nerves innervating the tongue and pharynx
• Nuclei in the medulla oblongata
• Sensory portion
• Provides taste sensations from posterior third of the
tongue
• Monitors blood pressure and blood gases
• Motor portion controls pharyngeal muscles used in
swallowing and parotid salivary gland secretion
The Twelve Cranial Nerves (N X) (8-8)
• Vagus nerves (N X)
• Nuclei located in the medulla oblongata
• Mixed nerves
• Sensory input
• From ears, diaphragm, taste receptors, visceral receptors
• Information provided is vital to autonomic control of
visceral function
• Motor components
• Control skeletal muscles of the soft palate, pharynx, and
esophagus
• Also a major pathway for ANS output to cardiac muscle,
smooth muscle, and digestive glands
The Twelve Cranial Nerves (N XI–XII) (8-8)
• Accessory nerves (N XI), or spinal accessory
nerves
• Motor nerves innervating structures in neck and back
• Some fibers originate in the medulla oblongata
• Other fibers come from the spinal cord
• Hypoglossal nerves (N XII)
• Nuclei located in medulla oblongata
• Provide voluntary motor control over the tongue
a
Figure 8-25a The Cranial Nerves.
Figure 8-25b The Cranial Nerves.
Nerve Plexuses (8-8)
• Networks of major nerve
trunks
• Cervical plexus
• Innervates the muscles of
the neck and the diaphragm
• Brachial plexus
• Innervates the pectoral
girdles and upper limbs
• Lumbar plexus and the sacral
plexus
• Innervate the pelvic girdle
and lower limbs
Figure 8-26 Peripheral Nerves and Nerve Plexuses.
Figure 8-26 Peripheral Nerves and Nerve Plexuses.
Figure 8-26 Peripheral Nerves and Nerve Plexuses.
Dermatome (8-8)
• Specific region of the body
surface monitored by a pair
of spinal nerves
• Clinically important in
determining location of
damage or infection of a
spinal nerve
Figure 8-27 Dermatomes.
Reflexes (8-9)
• Reflex
• Rapid, automatic response to a specific stimulus
• Monosynaptic reflexes
• Simplest type of reflex
• Only involve one synapse
• Example: the stretch reflex
• Muscle spindles detect stretch of muscle fibers
• Best known stretch reflex is the patellar reflex, or kneejerk reflex
Simple Reflexes (8-9)
• Wired in a reflex arc
• A stimulus activates a sensory receptor
• An action potential travels down a sensory neuron
• Information processing occurs with the interneuron
• An action potential travels down a motor neuron
• The effector organ responds
• Usual response removes or opposes original stimulus,
an example of negative feedback
Figure 8-29 A Stretch Reflex.
Figure 8-28 Events in a Reflex Arc.
Two Divisions of the ANS (8-11)
• Sympathetic division
• Parasympathetic division
Sympathetic Division Functions (8-11)
• Called the “fight-or-flight” division
• Effects
• Increase in alertness, metabolic rate, sweating, heart
rate, blood flow to skeletal muscle
• Dilates the respiratory bronchioles and the pupils
• Blood flow to the digestive organs is decreased
• Epinephrine and Norepinephrine from the adrenal
medulla support and prolong the effect
The Parasympathetic Division (8-11)
• Preganglionic neurons arise from the brain stem
and sacral spinal cord
• Fibers travel within cranial nerves III, VII, IX, and X
• The vagus nerve (N X) provides about 75 percent of all
parasympathetic outflow
• Ganglia very close to or within the target organ
• Preganglionic fibers of the sacral areas form the
pelvic nerves
Parasympathetic Division Functions (8-11)
• Called the “rest-and-digest” division
• Effects
• Constricts pupils, increases digestive secretions,
increases digestive tract smooth muscle activity
• Stimulates urination and defecation
• Constricts bronchioles, decreases heart rate
Aging and the Nervous System (8-12)
• Age-related changes begin by age 30 and
accumulate over time and include:
• Reduction in brain size and weight
• Reduction in number of neurons
• Decrease in blood flow to the brain
• Change in synaptic organization of the brain
• Decreased synaptic connections and neurotransmitter
production
• Increase in intracellular deposits and extracellular
plaques
• Dementia can be a result of all these changes