Download Autonomic Nervous System

Nervous System
Spinal Cord
and
Spinal Nerves
Nervous System As a Whole
All body systems work together to maintain
homeostasis
Chief coordinating agency for all body systems
 Nerves
carry messages to & from switching centers
Conditions change inside & outside
Nervous system must detect & respond to
changing conditions (stimuli) so body can adapt
itself to new conditions
Structural (Anatomic) Divisions
Central nervous system (CNS)
 Brain
& spinal cord
Peripheral nervous system
 All
nerves outside the CNS
 Cranial
nerves – carry impulses to & from brain
 Spinal nerves – carry messages to & from spinal
cord
See Figure 8-1, page 138
Central Nervous System
Functional Divisions
Type of control
 Voluntary
– somatic nervous system
 Involuntary – autonomic nervous system or visceral
nervous system
Type of tissue stimulated
 Effector
– muscles or glands that carry out nervous
system commands
See Table 8-1, page 139
Somatic Nervous System
Skeletal muscle control
Voluntary control
 Conscious
will
 All effectors are skeletal muscles
Autonomic Nervous System (ANS)
Involuntary control – automatic activity
Also known as visceral nervous system
 Controls
 Make
smooth muscle, cardiac muscle & glands
up viscera – soft body organs
Subdivisions of ANS
 Sympathetic
nervous system
 Parasympathetic nervous system
Neurons & Their Function
Functional cells of nervous system
 Highly
specialized with a unique structure
Neuron Structures
 Cell
body – main portion
 Contains
 Cell
nucleus & other organelles
fibers (projections out from cell body)
 Dendrites
 Axons
– some protected by myelin sheath
See Figure 8-2, page 139
Dendrites
Function as receptors
Conduct impulses to cell body
Many branches
Receptors in nervous system
 Receive
pathway
stimulus that begins in neural
Neuron
Axons
Conduct impulses away from cell body
Single fiber
 May
be long & branch and branch at end
Impulses may be delivered to another
neuron, to a muscle or to a gland
Myelin Sheath
Fatty material (myelin) covers some axons
 Insulates
& protects the fiber
Speeds conduction
Made by Schwann cells in PNS
 Neurilemma
– outermost layer – aids in axon repair
Made by neuroglia in CNS
See Figure 8-4 page 140
Myelin Sheath
More on Myelin . . .
Myelinated tissue
 White
matter
 Cells
of brain & spinal cord
 Have
no neurilemma
 Permanent damage if injured
Unmyelinated tissue – gray matter
 Not
covered by myelin
Types of Neurons
PNS neurons relay information constantly
to & from the CNS - 2 kinds
 Sensory
(afferent) neurons conduct impulses
to brain & spinal cord (CNS)
 Motor (efferent) carry impulses away from
CNS
Interneurons relay information within CNS
(also called central or association neurons)
Nerves & Tracts
Nerve - bundle of nerve fibers located within
peripheral nervous system (PNS)
Tract - bundle of nerve fibers located in brain &
spinal cord (CNS)
 Conduct
messages to & from brain
Nerves or tracts are bound together with
connective tissue - fascicles
PNS Nerves
Sensory nerve contains only fibers that
carry impulses to CNS (some cranial)
Motor nerve contains only fibers that carry
impulses away from CNS (some cranial
nerves)
Mixed nerve contains both sensory &
motor nerve fibers - may travel to & from
CNS (most cranial & all spinal nerves)
Neuroglia
Non-conducting connective tissue nerve cells
Protect & support nervous tissue
Different types of neuroglia with special
functions
Continue to reproduce (multiply) during lifetime
Most tumors of nervous system are neuroglial
tissue
Neuroglia
More on Neuroglia . . .
Aid in cell repair
Remove pathogens & impurities
Regulate composition of fluids around &
between cells
Nervous System at Work
Electrical impulses are sent along neuron
fibers
Then transmitted between cells at
junctions
Nerve Impulse
Electrical charge is transmitted along cell
membrane of a neuron
Plasma membrane of non stimulated (resting)
neuron carries an electric charge (potential)
Charge is maintained by sodium (NA) &
potassium (K) charged particles (ions) on each
side of the cell membrane
Nerve Impulse
Nerve Impulse
Plasma (cell) membrane carries the
electrical charge (potential)
Plasma membrane is polarized (negative
charge)
Membrane reverses (changes) charge
Generates electrical charge (action
potential)
Polarization
At rest, cell membrane is polarized
 Inside
of membrane is negative (-) while
outside is positive (+)
See Figure 8-8, page 142
Depolarization
Nerve impulse starts with local reversal of
charge - depolarization
Then spreads along the membrane with a
sudden electrical change in the membrane
(action potential)
Depolarization is rapid
 Followed
by immediate return to normal so
membrane can be stimulated again
Repolarization
Return of membrane to resting state is called
repolarization
Rapid exchange of sodium & potassium ions
across cell membrane bring about
depolarization & repolarization
Stimulus - any force that can start an action
potential & spreads along membrane as a nerve
impulse
Role of Myelin in Conduction
In unmyelinated fiber, action potential spreads
continuously along cell membrane
Myelin fibers conduct faster than unmyelinated
fibers
 Nerve
impulse skips from node to node (space
between cells) along the myelin sheath – called
saltatory conduction
 See
Figure 8-4, page 140
Synapse
Junction point for transmitting nerve impulse
Point of junction for transmission of the nerve
impulse between 2 nerve cells
Synaptic cleft - tiny gap between cells
Neurotransmitters - chemicals that transmit a
nerve impulse across synaptic cleft between
nerve cells
 Contained
 Axon
body
in vesicles of axon ending
- cell fiber carrying impulses away from cell
More on Synapse . . .
Axon - presynaptic cell releases the neurotransmitter
Neurotransmitter acts as chemical signal to
stimulate next cell (post-synaptic cell)
Dendrite - postsynaptic (receiving) cell
membrane has receptors that receive &
respond to specific neurotransmitters
See Figure 8-9, page 143
Synapse
Neurotransmitters
3 main neurotransmitters function in the
autonomic nervous system (ANS)
 Adrenaline (epinephrine)
 Norepinephrine (noradrenaline)
 Acetylcholine (ACh)
 Released
at neuromuscular junction (between
nerve & muscle cell)
More on Neurotransmitters
Various paths of removal of neuro-transmitters
 Diffusion away from synapse
 Enzyme destruction in synaptic cleft
 Return to presynaptic cell to be used again
(reuptake)
Many psychoactive drugs affect the
neurotransmitter’s activity
Spinal Cord
Links peripheral nervous system & brain
Located in & protected by vertebral column
Continuous tube from occipital bone to
coccyx
Ends between 1st & 2nd lumbar vertebrae
See Figure 8-11, page 145
Spinal Cord
Structure of Spinal Cord
Unmyelinated gray matter (nerve cell bodies)
surrounded by larger area of white matter (nerve
cell fibers)
 See
Figure 8-12, page 155
Gray matter is arranged in 2 pairs of columns
called dorsal & ventral horns
H-shaped appearance on cross section
More on Spinal Cord Structure . . .
Central canal of spinal cord contains
cerebrospinal fluid (CSF)
CSF - liquid that circulates around brain & spinal
cord
Myelinated white matter - consists of thousands
of myelinated axons arranged in 3 areas external
to (outside) the gray matter on each side
Functions of Spinal Cord
Links spinal nerves to the brain
 Relays information to & from brain
Center of reflex activities
Helps coordinate impulses within CNS
Spinal Nerves Link to the Brain
White matter divided into tracts that convey
impulses to & from the brain
Sensory impulses enter dorsal horn of cord &
are transmitted up toward brain in ascending
tracts of the white matter
Motor impulses travel from brain in descending
tracts & exit ventral horn of gray matter
See Figure 8-13, page 147
Reflex Arc
Complete pathway through the nervous system
from stimulus to response
Order of impulse conduction
 Receptor
- detects stimulus
 Sensory neuron – transmits impulses to CNS
More on Reflex Arc . . .
Order of impulse conduction, continued
 Interneuron
– in CNS
 Coordinates
 Motor
impulses & organizes response
neuron - CNS to effector
 Carries
 Effector
impulse away from CNS
- responding muscle or gland
 Carries
out response
Reflex Arc
Reflex Activities
Reflex - simple, rapid, automatic response
using few neurons (uncomplicated)
Specific - given stimulus always produces same
response
Spinal reflex - simple reflex arc that passes
through spinal cord & does not involve the brain
 Stretch reflex, eye blink, withdrawal reflex
Spinal Nerves
31 pairs of spinal nerves
Each nerves is attached to spinal cord by 2 roots
-dorsal & ventral roots
Connect spinal cord with peripheral tissues
All spinal nerves are mixed nerves
 Motor
and sensory
 Messages
go to and from CNS
See Figure 8-11, page 145
Spinal Nerve Root
Spinal Nerve Roots
Dorsal root has a marked swelling of gray matter
(ganglion)
 Contains
the cell bodies of sensory neurons
Ganglion - collection of nerve cell bodies located
outside the CNS
Sensory receptor fibers throughout body lead to
dorsal root ganglia
More on Spinal Nerve Roots . . .
Ventral roots of spinal nerves
 Combination
of motor (efferent) fibers
 Supply effectors (muscles & glands)
 Cell bodies located in ventral horn gray matter of
spinal cord
Dorsal (sensory) & ventral (motor) roots are
combined to form spinal nerves - mixed nerves
Spinal Nerve Root
Branches of Spinal Nerves
Spinal nerves branch into divisions short
distance from spinal cord
 Small
posterior division
 Larger anterior branches with plexus
Plexus - network of nerve branches that
distribute branches to body parts
See Figure 8-11, page 145
Brachial Plexus
More on Spinal Nerve Branches . . .
3 main plexuses
 Cervical
plexus - neck & back of head
 Phrenic
nerve that activates the diaphragm
 Brachial
plexus - radial nerve – shoulders, arms ,
forearms, wrists & hands
 Lumbosacral plexus - sciatic nerve – pelvis, legs
& feet
Spinal nerves affect skin sensations

Dermatones – see Fig. 8-15, page 149
Dermatomes
Autonomic Nervous System (ANS)
Motor (efferent) divisions of the visceral
(involuntary) nervous system
Regulates action of glands, smooth muscles
of hollow organs & vessels & cardiac (heart)
muscles
Actions occur automatically
No conscious awareness of regulatory
adjustments & actions
Characteristics of ANS
ANS sensory (afferent) neurons are grouped
with skin & voluntary muscle
Motor (efferent) neurons - arranged in a distinct
pattern - supply glands & involuntary muscles
Autonomic pathway has 2 motor neurons that
connect spinal cord with effector organ
 Synapse
in ganglia - relay stations
More on ANS Pathways . . .
Pre ganglionic neuron - extends from spinal
cord to ganglion
Post ganlionic neuron - travels from ganglion to
effector
Autonomic fibers
 Some
are within spinal nerves
 Some are within cranial nerves
See Figure 8-16, page 151
Divisions of ANS
Sympathetic nervous system
 Thoracolumbar
- thoracic & lumbar regions of spinal
cord
Parasympathetic nervous system
 Craniosacral
- brain stem & sacral regions of spinal
cord
See Table 8-3, page 150
Sympathetic Nervous System
Motor neurons originate in spinal cord
 Cell
bodies in thoracic & lumbar area
 Level of 1st thoracic nerve down to level of 2nd
lumbar spinal nerve
Nerve fibers extend to ganglia where they
synapse with second neurons
 Fibers
extend to glands & involuntary muscle
tissues
More on Sympathetic NS . . .
Sympathetic ganglia form sympathetic chains
along spinal column from lower neck to upper
abdominal area
Nerves that supply organs of pelvic &
abdominal cavities synapse in 3 single
collateral ganglia
Release epinephrine & norepinephrine
(adrenaline/noradrenaline)
Adrenergic - activated by adrenaline
Parasympathetic Nervous System
Motor pathways begin in fibers from cell bodies
in the brainstem (midbrain & medulla) & the
lower part (sacral) of the spinal cord
 Extend
to terminal ganglia in or near the effector
organs, then stimulate the involuntary tissues
Neurons release acetylcholine
 Cholinergic
Functions of ANS
Most organs are supplied by both sympathetic &
parasympathetic fibers (the two have somewhat opposite
effects on organs)
 Sympathetic
- stimulates fight or flight (stress) response
4
E’s = emergency, excitement, embarrassment, exercise
 Also brake for systems not involved in stress response
 Parasympathetic
- acts as balance once crisis has passed
 “rest
and digest”
 SLUDD –salivation, lacrimation, urination, digestion, defecation
See Table 8-4, page 152