Download The NERVOUS SYSTEM

THE NERVOUS SYSTEM
*THE NERVOUS SYSTEM:
OVERVIEW
 Swift, brief response to stimuli
 Monitors internal & external environment
 Integrates sensory information
 Coordinates voluntary & involuntary
responses of other systems
ORGANIZATION
 Central Nervous System (CNS)
 Processes data and transmits commands
 Intelligence, memory, emotion
 Consists of:
 Brain
 Spinal cord
 Peripheral Nervous System (PNS)
 All neural tissue outside of the CNS
 “the highway” of communication
ORGANIZATION, CTD.
 PNS
 Afferent division
 Carries info from receptors to CNS
 Efferent division
 Carries commands from CNS to muscles, glands, adipose tissue
in body
 Divided into:
 Somatic Nervous System (SNS) – skel musc. contraxns
 Autonomic Nervous System (ANS) – automatic stuff like smooth &
cardiac muscle, glandular secretion, and adipose tissue…divided into:
 Sympathetic Nervous System
 Parasympathetic Nervous System
Peripheral nervous system (PNS)
Central nervous system (CNS)
Cranial nerves and spinal nerves
Communication lines between the
CNS and the rest of the body
Brain and spinal cord
Integrative and control centers
Sensory (afferent) division
Somatic and visceral sensory
nerve fibers
Conducts impulses from
receptors to the CNS
Somatic sensory
fiber
Motor (efferent) division
Motor nerve fibers
Conducts impulses from the CNS
to effectors (muscles and glands)
Somatic nervous
system
Somatic motor
(voluntary)
Conducts impulses
from the CNS to
skeletal muscles
Skin
Visceral sensory fiber
Stomach
Skeletal
muscle
Motor fiber of somatic nervous system
Sympathetic division
Mobilizes body
systems during activity
Sympathetic motor fiber of ANS
Structure
Function
Sensory (afferent)
division of PNS
Motor (efferent)
division of PNS
Parasympathetic motor fiber of ANS
Autonomic nervous
system (ANS)
Visceral motor
(involuntary)
Conducts impulses
from the CNS to
cardiac muscles,
smooth muscles,
and glands
Parasympathetic
division
Conserves energy
Promotes housekeeping functions
during rest
Heart
Bladder
Figure 11.2
FIGURE 8.2
Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Nucleolus
Axon
(impulse generating
and conducting region)
Nucleus
Nissl bodies
Axon hillock
(b)
Impulse
direction
Node of Ranvier
Schwann cell
Neurilemma (one interTerminal
node)
branches
Axon
terminals
(secretory
region)
Figure 11.4b
FIGURE 8.3
*CELLULAR ORGANIZATION
 Neurons (carry electrical impulses)
 Cannot divide (lack centrioles)
 Neuroglia (supportive cells)
 Regulate environment
 Provide framework
 Phagocytic
 Smaller but more numerous
 Can divide
*CLASSIFICATION OF NEURONS
Structural
 Pyrimidal Cell
found in brain
 Multipolar
 Motor neurons
 Unipolar
 Most sensory neurons
 Bipolar
 Some special sensory organs –
sight, smell, hearing
Functional
 Sensory neurons
 ~10 mil.
 Motor neurons
 ~500,000
 Interneurons
 ~20 billion!
*SENSORY NEURONS
 Form afferent division of PNS
 Receive info from sensory receptors
 Monitor external and internal envts, then
relay to CNS
 Somatic sensory receptors
 External receptors: touch, temp, pressure, sight, etc.
 Proprioceptors: monitor position and movement
 Visceral (internal) receptors
 Monitor digestion, respiration, CV, etc. and taste, deep
pressure, and pain
*MOTOR NEURONS
 Form efferent division of PNS
 Send messages to effectors (which DO
something)
 Somatic motor neurons (SNS)
 Visceral motor neurons (ANS)
*INTERNEURONS
 Located in CNS only
 Connect other neurons
 Distribute info and coordinate
activity
 Also play a role in planning,
memory, and learning
FIGURE 8.4
NEUROGLIA -- CNS CELL TYPES:
 Astrocytes
 lg., numerous, maintain blood-brain barrier,
repairs
 Oligodendrocytes
 Insulate axons (white matter/gray matter)
 Microglia
 small, rare phagocytes
 Ependymal
 line CNS cavities
NEUROGLIA
 PNS Cell types:
 Satellite cells
 Surround and support
cell bodies
 Schwann cells
 Myelinate axons
outside of CNS
 Demyelination
neural
Schwann cell
plasma membrane
Schwann cell
cytoplasm
Axon
1
A Schwann cell
envelopes an axon.
Schwann cell
nucleus
2
The Schwann cell then
rotates around the axon,
wrapping its plasma
membrane loosely around
it in successive layers.
Neurilemma
Myelin sheath
(a) Myelination of a nerve
fiber (axon)
3
The Schwann cell
cytoplasm is forced from
between the membranes.
The tight membrane
wrappings surrounding
the axon form the myelin
sheath.
Figure 11.5a
ANATOMICAL ORGANIZATION
 PNS
 Cell bodies (gray matter) located in ganglia
 Axons (white matter) bundled together into nerves
 CNS
 Collection of cell bodies with common function = center
 Center with discrete boundary = nucleus
 Neural Cortex: thick layer of gray matter
 Columns  made of tracts (bundles of axons of CNS)
 Pathways link centers to rest of body
*MEMBRANE POTENTIAL
 All undisturbed cells are polarized
 Outside of cell has + charge, inside has –
 This is a potential difference, called membrane potential
 Unit = Volt (V) [cell membrane potential usu. measured in
millivolts, or mV
 “Normal,” or undisturbed cell’s membrane potential
= resting potential
 In neurons, resting potential is approximately -70mV
 Why is there a potential in resting cells?
*
 https://www.youtube.com/watch?v=_bPFKDdWlCg
Sodium Potassium Pump
https://www.youtube.com/watch?v=OZG8M_ldA1M
Crash Course Action Potential
https://www.youtube.com/watch?v=HYLyhXRp298
Action Potential Bozeman
FIGURE 8.7
 The sodium-potassium pump
ACTIVE TRANSPORT
 Is one type of active transport system
1Cytoplasmic Na+ binds to
the sodium-potassium pump.
Na+ binding stimulates
phosphorylation by ATP.
EXTRACELLULAR
FLUID
[Na+] high
[K+] low
2
Na+
Na+
Na+
Na+
Na+
[Na+] low
[K+] high
Na+
CYTOPLASM
ATP
P
ADP
Na+
Na+
Na+
K+ is released and Na+
3
sites are receptive again;
the cycle repeats.
K+
P
K+
Phosphorylation causes the
4
protein to change its
conformation, expelling Na+ to
the outside.
K+
K+
Loss of the phosphate
5
restores the protein’s
original conformation.
P
K+
K+ P i
6
Extracellular K+ binds to the
protein, triggering release of
23the
Phosphate group.
*WHAT HAPPENS WHEN IT CHANGES?
 Any substance that alters permeability of
membrane or alters the activity of pumps in
the membrane
 Exposure to chemicals
 Mechanical changes
 Temperature changes
 Change in extracellular fluid
 Change in resting potential can have an
immediate effect
VOCAB
 Depolarization
 Polarization
 Graded potential
 Ex: goblet/gland cell
 Action potential
 Skeletal muscles
 Axons of neurons
 Threshold
 Trigger analogy
 All – or – none principle
*NEURAL COMMUNICATION
 Info travels thru action potentials
(=electrical or nerve impulses)
 At end of axon, info (neurotransmitters)
is passed to another neuron or to an
effector
 https://www.youtube.com/watch?v=VitFvNvRIIY
The Synapse Bozeman
*NEUROTRANSMITTERS
 A single neurotransmitter may bind specifically to
more than a dozen different receptors
 Receptor activation and postsynaptic response
cease when neurotransmitters are cleared from the
synaptic cleft
 Neurotransmitters are removed by simple diffusion,
inactivation by enzymes, or recapture
(reabsorption) into the presynaptic neuron
PRESYNAPTIC NEURON
Neurotransmitter
FIGURE 48.18
Neurotransmitter
receptor
Inactivating enzyme
POSTSYNAPTIC NEURON
(a) Enzymatic breakdown of neurotransmitter in the
synaptic cleft
Neurotransmitter
Neurotransmitter
receptor
Neurotransmitter
transport
channel
(b) Reuptake of neurotransmitter by presynaptic neuron
*THE SYNAPSE
 Presynaptic neuron—conducts
impulses toward the synapse
 Postsynaptic neuron—transmits
impulses away from the synapse
PRESYNAPTIC NEURON
FIGURE 48.18A
Neurotransmitter
Neurotransmitter
receptor
Inactivating enzyme
POSTSYNAPTIC NEURON
(a) Enzymatic breakdown of neurotransmitter in the
synaptic cleft
FIGURE 48.18B
Neurotransmitter
Neurotransmitter
receptor
Neurotransmitter
transport
channel
(b) Reuptake of neurotransmitter by presynaptic neuron
ACETYLCHOLINE
 Acetylcholine is a common neurotransmitter in
vertebrates and invertebrates
 It is involved in muscle stimulation, memory
formation, and learning
 Vertebrates have two major classes of acetylcholine
receptor, one that is ligand gated and one that is
metabotropic
 A number of toxins disrupt acetylcholine
neurotransmission
 These include the nerve gas, sarin, and the botulism
toxin produced by certain bacteria
 Acetylcholine is just one of more than 100 known
neurotransmitters
 The remainder fall into four classes: amino acids,
biogenic amines, neuropeptides, and gases
TABLE 48.2
TABLE 48.2A
TABLE 48.2B
TABLE 48.2C
AMINO ACIDS
 Amino acid neurotransmitters are active in the
CNS and PNS
 Known to function in the CNS are
 Glutamate
 Gamma-aminobutyric acid (GABA)
 Glycine
BIOGENIC AMINES
 Biogenic amines include
 Epinephrine
 Norepinephrine
 Dopamine
 Serotonin
 They are active in the CNS and PNS
NEUROPEPTIDES
 Several neuropeptides, relatively short chains of
amino acids, also function as neurotransmitters
 Neuropeptides include substance P and
endorphins, which both affect our perception of
pain
 Opiates bind to the same receptors as endorphins
and can be used as painkillers
GASES
 Gases such as nitric oxide (NO) and carbon monoxide
(CO) are local regulators in the PNS
 Unlike most neurotransmitters, NO is not stored in
cytoplasmic vesicles, but is synthesized on demand
 It is broken down within a few seconds of production
 Although inhaling CO can be deadly, the vertebrate
body synthesizes small amounts of it, some of which is
used as a neurotransmitter
NEUROTRANSMITTER OVERVIEW
 https://www.youtube.com/watch?v=Ths
T8HOeOtQ
FIGURE 8.15
PNS: ANATOMY
 Peripheral Nerves,
ctd
 Spinal Nerves
 Connect to the spinal
cord
 31 pairs, ea monitors a
dermatome
*REFLEXES
 Reflex arc
 Wiring of a single reflex
 Is this an example of positive or negative feedback?
 Types of reflexes
 Monosynaptic – sensory neuron synapses directly on motor neuron
 Ex: stretch reflex used by docs to test general condition of spinal cord,
peripheral nerves, and muscles.
 Polysynaptic reflexes – contain interneurons, so longer delay between
stimulus and response
 Withdrawal reflex
 Flexor reflex
*REFLEX ARC*

Components of a reflex arc (neural path)
1.
Receptor—site of stimulus action
2.
Sensory neuron—transmits afferent impulses to the CNS
3.
Integration center—either monosynaptic or polysynaptic
region within the CNS
4.
Motor neuron—conducts efferent impulses from the
integration center to an effector organ
5.
Effector—muscle fiber or gland cell that responds to the
efferent impulses by contracting or secreting
FIGURE 8.28
Stimulus
Skin
1 Receptor
Interneuron
2 Sensory neuron
3 Integration center
4 Motor neuron
5 Effector
Spinal cord
(in cross section)
Figure 13.14
The patellar (knee-jerk) reflex—a specific example of a stretch reflex
2
Quadriceps
(extensors)
1
3a
3b
3b
Patella
Muscle
spindle
Spinal cord
(L2–L4)
Hamstrings
(flexors)
Patellar
ligament
1 Tapping the patellar ligament excites
muscle spindles in the quadriceps.
2 Afferent impulses (blue) travel to the
spinal cord, where synapses occur with
motor neurons and interneurons.
3a The motor neurons (red) send
+
–
Excitatory synapse
Inhibitory synapse
activating impulses to the quadriceps
causing it to contract, extending the
knee.
3b The interneurons (green) make
inhibitory synapses with ventral horn
neurons (purple) that prevent the
antagonist muscles (hamstrings) from
resisting the contraction of the
quadriceps.
Figure 13.17 (2 of 2)
SENSORY RECEPTORS
 Specialized to respond to changes in their
environment (stimuli)
 Activation results in graded potentials that
trigger nerve impulses
 Sensation (awareness of stimulus) and
perception (interpretation of the meaning of
the stimulus) occur in the brain
*CLASSIFICATION OF RECEPTORS
 Based on:
 Stimulus type
 Location
 Structural complexity
*CLASSIFICATION BY STIMULUS TYPE
 Mechanoreceptors—respond to touch, pressure,




vibration, stretch, and itch
Thermoreceptors—sensitive to changes in temperature
Photoreceptors—respond to light energy (e.g., retina)
Chemoreceptors—respond to chemicals (e.g., smell,
taste, changes in blood chemistry)
Nociceptors—sensitive to pain-causing stimuli (e.g.
extreme heat or cold, excessive pressure, inflammatory
chemicals)
UNENCAPSULATED DENDRITIC ENDINGS
 Thermoreceptors
 Cold receptors (10–40ºC); in superficial
dermis
 Heat receptors (32–48ºC); in deeper
dermis
UNENCAPSULATED DENDRITIC ENDINGS
 Nociceptors
 Respond to:
 Pinching
 Chemicals from damaged tissue
 Temperatures outside the range of
thermoreceptors
 Capsaicin
UNENCAPSULATED DENDRITIC ENDINGS
 Light touch receptors
 Tactile (Merkel) discs
 Hair follicle receptors
Table 13.1
ENCAPSULATED DENDRITIC ENDINGS
 All are mechanoreceptors
 Meissner’s (tactile) corpuscles—discriminative touch
 Pacinian (lamellated) corpuscles—deep pressure and vibration
 Ruffini endings—deep continuous pressure
 Muscle spindles—muscle stretch
 Golgi tendon organs—stretch in tendons
 Joint kinesthetic receptors—stretch in articular capsules
Table 13.1
*CLASSIFICATION OF NERVES
 Most nerves are mixtures of afferent and efferent fibers and
somatic and autonomic (visceral) fibers
 Pure sensory (afferent) or motor (efferent) nerves are rare
 Types of fibers in mixed nerves:
 Somatic afferent and somatic efferent
 Visceral afferent and visceral efferent
 Peripheral nerves classified as cranial or spinal nerves
*GANGLIA
 Contain neuron cell bodies associated
with nerves
 Dorsal root ganglia (sensory, somatic)
 Autonomic ganglia (motor, visceral)
CRANIAL NERVES
 Twelve pairs of nerves associated with the brain
 Most are mixed in function; two pairs are purely
sensory
 Each nerve is identified by a number (I through XII)
and a name
“On occasion, our trusty truck acts funny—very
good vehicle anyhow”
 The cranial nerves are:
 I - Olfactory nerve
Old
 II - Optic nerve
Opie
 III - Occulomotor nerve
Occassionally
 IV - Trochlear nerve
Tries
 V - Trigeminal nerve/dentist nerve
Trigonometry
 VI - Abducens nerve
And
 VII - Facial nerve
Feels
 VIII - Vestibulocochlear nerve/Auditory nerve
Very
 IX - Glossopharyngeal nerve
Gloomy
 X - Vagus nerve
Vague
 XI - Accessory nerve/Spinal accessory nerve
And
 XII - Hypoglossal nerve
hypoactive
KNOW THE FIRST FOUR AND ONE OF THE SENTENCES. (You pick whichever one
you like best.)
 Odor Of Orangutan Terrified Tarzan After
Forty Voracious Gorillas Viciously Attacked
Him
 Old Opie Occasionally Tries Trigonometry
And Feels Very Gloomy, Vague And
Hypoactive
Frontal lobe
Temporal lobe
Infundibulum
Facial
nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve
(II)
Optic chiasma
Optic tract
Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Abducens
nerve (VI)
Cerebellum
Medulla
oblongata
(a)
Figure 13.5 (a)
A PERSON ATTEMPTING
TO SHOW HIS TEETH AND
RAISE HIS EYEBROWS
WITH BELL'S PALSY ON HIS
RIGHT SIDE
BELL'S PALSY IS THE MOST
COMMON ACUTE
MONONEUROPATHY
CRANIAL NERVE VII
CAUSED BY A HERPES
VIRUS
Cranial nerves
I – VI
I
II
III
IV
V
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
VI Abducens
Cranial nerves
VII – XII
VII Facial
VIII Vestibulocochlear
IX
X
XI
XII
(b)
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Sensory
function
Motor
function
PS*
fibers
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
Yes
Yes
Yes
No
No
Yes
No
No
No
Yes
No
Sensory
function
Motor
function
PS*
fibers
Yes (taste)
Yes (hearing
and balance)
Yes
Some
Yes
No
Yes (taste)
Yes (taste)
No
No
Yes
Yes
Yes
Yes
Yes
Yes
No
No
*PS = parasympathetic
Figure 13.5 (b)
*SPINAL NERVES
 31 pairs of mixed nerves named according to
their point of issue from the spinal cord
 8 cervical (C1–C8)
 12 thoracic (T1–T12)
 5 Lumbar (L1–L5)
 5 Sacral (S1–S5)
 1 Coccygeal (C0)
Cervical plexus
Brachial plexus
Cervical
enlargement
Intercostal
nerves
Cervical
nerves
C1 – C8
Thoracic
nerves
T1 – T12
Lumbar
enlargement
Lumbar plexus
Sacral plexus
Cauda equina
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Figure 13.6
*SPINAL NERVES: ROOTS
 Each spinal nerve connects to the spinal
cord via two roots
 Ventral roots
 Contain motor (efferent) fibers from the
ventral horn motor neurons
 Fibers innervate skeletal muscles)
*SPINAL NERVES: ROOTS
 Dorsal roots
 Contain sensory (afferent) fibers from sensory neurons in
the dorsal root ganglia
 Conduct impulses from peripheral receptors
 Dorsal and ventral roots unite to form spinal
nerves, which then emerge from the vertebral
column via the intervertebral foramina
Gray matter
White matter
Ventral root
Dorsal root
Dorsal root
ganglion
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Spinal nerve
Dorsal and
ventral rootlets
of spinal nerve
Rami communicantes
Sympathetic trunk
ganglion
Anterior view showing spinal cord, associated nerves, and vertebrae.
The dorsal and ventral roots arise medially as rootlets and join
laterally to form the spinal nerve.
Figure 13.7 (a)
*INNERVATION OF SKIN
 Dermatome: the area of skin innervated by
the cutaneous branches of a single spinal
nerve
 All spinal nerves except C1 participate in
dermatomes
 Most dermatomes overlap, so destruction of
a single spinal nerve will not cause complete
numbness
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
C2
C3
C4
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T2
C5
C6
C6
C7
L1
C8
L2
T12
S2
S3
T2
C5
C6
L1
C8
L2
S1
L4
S2
S3
S4
S5
C6
C7
C6
C7
C8
C8
L2
S2
S1
L1
L3
L5
L4
T11
T12
L1
L3
L5
C7
C6
S1 S2
L3
C5
L2
L5
L4
L3
L5
L5
L4
S1
Anterior
view
S1
(b) Posterior
view
L4
L5
L4
L5
S1
Figure 13.12
THE AUTONOMIC NERVOUS SYSTEM
“In practical terms, conscious activities have
little to do with our immediate or long term
survival…”
 Sympathetic
 Fight or flight
 Parasympathetic
 Rest and digest
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Motor (efferent) division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.1
FIGURE 8.33
*AUTONOMIC NERVOUS SYSTEM (SUMMARY)
 The Sympathetic Nervous System
 Stimulates tissue metabolism
 Increases alertness
 Prepares for emergency (sudden, intense activity)
 Stimulates sweat glands and arrector pili muscles
 Reduces circ. to skin and body wall
 Accelerates blood flow to muscles
 Releases stored lipids from fat tissue
 Dilates pupils
 Increases heart rate
 Reduces blood flow by visceral organs not
important to short term survival (digestion)
AUTONOMIC NERVOUS SYSTEM
 The Parasympathetic Nervous System
 Constricts pupils
 Increases secretions by digestive glands
 Increases smooth muscle activity of digestive
tract
 Constricts respiratory pathways
 Reduces heart rate
 Relaxation, food processing, and energy
absorption
FIGURE 8.34
*AGING AND THE NERVOUS SYSTEM
 Reduction in brain size/weight
 Reduction in number of neurons
 Decreased blood flow to brain
 Fewer dendritic branchings and interconnections,
neurotransmitter production goes down
 Intracellular and extracellular changes in neurons
*
 Memory consolidation more difficult
 Senses less acute
 Reaction times and reflexes slower
 Precision of motor control decreases
*
Sciatica -- A common condition arising from
compression of, or damage to, a nerve or
nerve root.
Restless legs syndrome (RLS) is a disorder of
the part of the nervous system that affects
the legs and causes an urge to move them.
Because it usually interferes with sleep, it also
is considered a sleep disorder
*
 Guillain-Barré syndrome -- causes muscle
weakness, loss of reflexes, and numbness or
tingling in your arms, legs, face, and other
parts of your body. In GBS, the immune
system attacks the myelin sheath of certain
nerves. This causes nerve damage. May be
triggered by a viral or bacterial infection
*MULTIPLE SCLEROSIS (MS)
 An autoimmune disease that mainly affects young adults
 Symptoms: visual disturbances, weakness, loss of
muscular control, speech disturbances, and urinary
incontinence
 Myelin sheaths in the CNS become nonfunctional
scleroses
 Shunting and short-circuiting of nerve impulses occurs
 Impulse conduction slows and eventually ceases
*MULTIPLE SCLEROSIS: TREATMENT
 Some immune system–modifying drugs,
including interferons and Copazone:
 Hold symptoms at bay
 Reduce complications
 Reduce disability