Download Reading Part 5: The Nervous System

Unit 3: Control
Systems of the
Human Body
Dr. Achilly
Part 1: Nervous
Tissue
“Concepts” chapter 14
Nervous System--overview
One of the smallest, but most complex
body systems.
 Made of:

 Brain
 Cranial
nerves—12 pairs emerge from base
of brain.
 Spinal cord—connects to the brain thru
foramen magnum in skull & is encircled by
vertebrae.
Nervous System--overview
 Spinal
nerves—emerge from spinal cord &
serve specific regions of body.
 Ganglia—masses of nerve tissue (mainly
neuron cell bodies) outside brain or spinal
cord.
 Enteric plexuses—networks of neurons that
regulate the digestive system.
 Sensory receptors—ends of sensory neurons
that monitor internal or external environmental
changes.
Nervous System--overview
Nervous System--overview

Nervous system has 3 basic fxns:
 Sensory—detects
internal & external stimuli.
Carries this info to brain & spinal cord.
 Integrative—the analyzing, storing &
responding to sensory info.
 Motor—carry out appropriate response like
myo contraction or gland secretion. Info is
carried from brain or spinal cord to effectors.
Nervous System--overview

The two main divisions of the nervous
system are:
 Central
nervous system (CNS)—consisting of
brain and spinal cord
 Peripheral nervous system (PNS)—all the
nervous tissue outside of CNS
Nervous System--overview

PNS can be further divided:
 Somatic
nervous system—carries sensory
fibers from head, body wall, limbs, special
senses, etc. Also carries motor neurons to
skeletal myos.
Nervous System--overview
 Autonomic
nervous system—carries sensory
neurons from most of the organs and motor
neurons to smooth & cardiac myo and glands.

The ANS can be further divided into the
sympathetic division which handles “flight or fight”
responses and the parasympathetic division for
“rest and digest” responses.
Nervous Tissue
The functional unit of the nervous system
is the neuron.
 It has electrical excitability & can
propagate an electrical signal called an
action potential.
 Various sizes, but all contain similar parts.

Nervous Tissue
Cell body—contains nucleus, cytoplasm,
all other cellular organelles.
 Dendrites—these are the receiving fibers
of the neuron. Usually many of them.
 Axon—propagates action potential away
from cell body toward another neuron.
Usually singular. Place where the axon
joins the cell body is an important area
called axon hillock.

Nervous Tissue
Nervous Tissue
Nervous Tissue



The end of each axon contains many fine
projections called axon terminals.
From here a neuron can communicate with
another thru the synapse (the gap between
neurons).
The axon terminal contains many membraneenclosed sacs called synaptic vesicles. They
store many types of neurotransmitters which are
chemicals that help the electrical impulse cross
the synaptic gap btwn neurons.
Nervous Tissue
Nervous Tissue
Many axons are surrounded by a lipid &
protein covering called a myelin sheath.
 The sheath electrically insulates an axon &
speeds conduction. Also aides in
regeneration of injured neurons.
 In the PNS the myelin is produced by a
support cell called a Schwann cell.
 Gaps in Schwann cells are called nodes of
Ranvier.

Nervous Tissue
Nervous Tissue



In CNS it’s the
oligodendrocytes that
myelinate the axons.
Little re-growth after injury.
Amount of myelin increases
from birth to maturity.
Nervous Tissue
The areas of the nervous system that have
myelinated axons appear white (white
matter).
 Areas of neuronal cell bodies, dendrites &
unmyelinated axons appear gray (gray
matter).

Nervous Tissue
In addition to neurons, about ½ the
nervous system consists of support cells
called neuroglia.
 These cells do not propagate electrical
impulses.
 Can divide & “fill in” areas of injury.

Nervous Tissue

Neuroglia of CNS
 Astrocytes—give
structural support, wrap
around capillaries of brain to form blood-brain
barrier
 Oligodendrocytes—form myelin
 Microglia—fxn as phagocytes to remove
cellular debris
 Ependymal cells—produce & circulate
cerebral spinal fluid which nourishes the brain
and spinal cord.
Nervous Tissue
Nervous Tissue

Neuroglia of PNS
 Schwann
cells—form myelin
 Satellite cells—surround neuron cell bodies.
Regulate exchange of materials btwn them &
interstitial fluid (the fluid found surrounding all
cells).
Electrical Signals

Production of nerve impulses depends
on two features of the plasma
membrane.
Membrane potential—the separation of ions
across the membrane leading to an
electrical voltage difference.
2. Specific ion channels.
1.
Electrical Signals
When ion channels are open, ions will
move down their concentration gradient
thru the channels & according to charge (+
towards -, and vice versa)
 The opening or closing of ion channels is
due to presence of “gates.”
 Four types of channels:

Electrical Signals

Leakage channels randomly alternate
btwn opened & closed.
 Usually
there are more K+ channels than
Na+. Also K+ ones are “leakier.” Result is
higher membrane permeability to K+.

Voltage gated channels open in response
to change in membrane potential
(voltage).
Electrical Signals

Ligand-gated channels open/close in
response to specific molecules that bind to
the channels.
 E.g.
neurotransmitter binding to it
Electrical Signals

Mechanically gated channel opens/closes
in response to mechanical stimulation:
 Vibration
 Pressure
 Stretch
Electrical Signals

Resting membrane potential
 Exists
b/c of build up of (-) ions just inside the
neuron cell membrane & (+) ions outside.
 Separation of charges is a form of potential
energy. About -70mV in a typical cell.
 Dominant cation inside is K+, many anions
(phosphates, amino acids) also. K+ can leak
out, anions can’t.
Electrical Signals
 Negative
ions inside cell work to attract K+ back in.
 Eventually an equal # of K+ ions enter & leave.
 Na+ leaks inward a little.
 Na+/K+ pump maintains charge difference.
At rest, the inside of a neuron's
membrane has a negative charge.
As the figure shows, a Na+ / K+
pump in the cell membrane pumps
sodium out of the cell and
potassium into it. However,
because the cell membrane is a bit
leakier to potassium than it is to
sodium, more potassium ions leak
out of the cell. As a result, the
inside of the membrane builds up a
net negative charge relative to the
outside.
Electrical Signals

Graded potentials
 Arises
when a stimulus
causes a ligand or
mechanically gated
channel to open or close.
 Depending on the type of
ion channel opened, the
membrane can become
more negative
(hyperpolarized) or more
positive (depolarized).
Electrical Signals
 These
signals are “graded” b/c they vary in
size depending on the strength of the
stimulus.
 Large stimulus  more gates open
 Ion flow is localized, so it’s only useful for
communication over short distances.
 Usually present in dendrites.
Electrical Signals

Action Potentials
 Has
depolarization & repolarization phases
 All or nothing response once threshold is
reached.
Before an AP begins the membrane is at
its resting potential.
 The only movement of ions is thru leakage
gates.

Electrical Signals

At rest both Na+ & K+ gated channels
are closed; membrane is at -70mV
resting potential.
Electrical Signals

A stimulus opens some Na+ channels.
The # of channels opened depends on the
strength of the stimulus. If enough
channels are opened, the inside of the
neuron becomes slightly positively
charged b/c of all the Na+ flowing in.
Electrical Signals

Depolarization—so many Na+ channels
are open that the inside of cell becomes
very positive. Positive feedback is
involved here. In other words, the more
positive the inside becomes, the more Na+
gates that open and so on.
Electrical Signals

Repolarization—finally K+ gates open &
K+ rushes out. At the same time Na+
gates close.
Electrical Signals

Undershoot—so much K+ leaves the cell
that it becomes more negative than the
original resting potential. K+ gates close.
This phase is also called a refractory
period. Another AP cannot occur in this
portion of the membrane until Na/K pumps
can restore the original ion concentration
gradient & resting potential.
Electrical Signals
In order to relay information the AP must
travel all the way down the axon. Called
propagation.
 When one segment of the membrane
depolarizes the flood of Na+ causes gated
channels in the next section to open, etc.
 Called continuous conduction.

Electrical Signals


In myelinated axons conduction is faster b/c only
the nodes of Ranvier must depolarize.
Impulse “jumps” from node to node. Called
saltatory conduction.
Electrical Signals
Once an AP reaches the terminus of the
axon it must be passed on to the next cell
across the synapse.
 Some cells have direct connections btwn
them (gap junctions—like tunnels btwn
cells). Ions can flow from one cell to
another.
 Called electrical synapse.

 Faster,
synchronized (e.g. heart, viscera)
Electrical Signals
Many cells don’t have direct connections
for ion flow.
 The space btwn them is called synaptic
cleft.
 A chemical transmitter is required to cross
the gap btwn neurons.
 Called chemical synapse.

Electrical Signals
AP arrives at axon terminus of presynaptic
neuron.
 The depolarization here opens voltage
gated Ca++ channels.
 The influx of Ca++ causes exocytosis of
synaptic vesicles that are filled with
neurotransmitters.

Electrical Signals





Neurotransmitter diffuses across cleft & binds to
receptors on postsynaptic neuron.
Often the receptors are ligand-gated ion
channels which open to let ions in.
If the channels are for Na+, a depolarization of
the membrane will occur.
If the channels are for K+ or Cl-,
hyperpolarization will occur.
If threshold is reached, another AP begins.
Electrical Signals

Removal of neurotransmitter from cleft is
essential.
 Diffusion
 Degraded
by enzymes
 Cellular re-uptake
Neurotransmitters
About 100
 Some act quickly, others are slow.
 Many are also hormones.
 Two types:

 Small
molecule
Acetylcholine—excitatory to skeletal myo’s
 GABA—inhibitory in CNS
 Dopamine—active in neurons that govern
emotions, addictive behavior

Neurotransmitters
 Neuropeptides
Endorphins—natural painkiller, euphoria
 Substance P—released by neurons that transmit
pain-related input from peripheral receptors.

Part 2: Spinal Cord
& Spinal Nerves
“Concepts” chapter 15 & 16
Spinal Cord & Spinal Nerves




Spinal cord is vital
part of CNS
Mediates some of our
most rapid, reflex
responses
Integrates signals
Serves as direct path
to the brain for
sensory input & motor
output
Spinal cord anatomy
Vertebral column serves as bony
protection for spinal cord.
 Cord is also surrounded by 3 layers of
tough connective tissue called meninges.

 Dura
matter
 Arachnoid matter
 Pia matter

The spaces btwn these layers contain fluid
(cerebral spinal fluid).
Spinal cord anatomy


Extends from medulla oblongata to L2.
Two obvious enlargements
 Cervical
(C4-T1)—nerves to upper limb arise here.
 Lumbar (T9-T12)—nerves to lower limb



Cord tapers at L2 to form conus medullaris.
An extension of the pia matter anchors the cord
to the coccyx. Called filum terminale.
Nerves that arise from lower end of cord angle
downward before they exit vert. column. Form
cauda equina.
Spinal cord anatomy

Spinal nerves are formed from 2 bundles
of axons called roots.
Spinal cord anatomy

Posterior (dorsal) root = sensory neurons
 Has
an enlarged area where the neuron cell
bodies are. Called ganglion.

Anterior (ventral) root = motor neurons
Spinal cord anatomy

Two grooves divide cord into R & L halves:
 Anterior
median fissure
 Posterior median sulcus
White matter surrounds gray.
 Gray matter is the innermost part. Shaped
like an H.

Spinal cord anatomy


Gray matter is collection of cell bodies.
Form functional groups called nuclei
 Sensory

& motor nuclei
Gray matter is subdivided into regions called
horns.
 Anterior
gray horn = motor nuclei for skeletal myo’s
 Posterior gray horn = somatic & autonomic sensory
nuclei.
 Lateral gray horn = autonomic motor nuclei for
smooth myo, heart & glands (only in part of cord).
Spinal cord anatomy

White matter is organized into regions
also—called columns.
 Anterior
white column
 Posterior white column
 Lateral white column

Each column contains distinct bundles of
axons going to & from the same place.
 Ascending
sensory tracts
 Descending motor tracts
Spinal nerve anatomy
Spinal nerves are part of PNS. Connect
CNS to myo’s, glands, organs & receptors.
 They are mixed nerves b/c they contain
sensory & motor neurons from the roots
that form them.

Spinal nerve anatomy




A “nerve” is a bundle of axons with their
protective coverings.
Individual axons are wrapped in endoneurium.
Groups of these are arranged into fascicles,
each wrapped in a perineurium.
The outermost covering on the entire nerve is
called epineurium.
 Contains
many blood vessels to nourish nerve.
Spinal nerve anatomy
Immediately after exiting btwn the
vertebrae, spinal nerves branch into ant. &
post. rami.
 Anterior rami of several spinal nerves can
weave together to form a plexus.

 Cervical
 Brachial
 Lumbar
 Sacral
Spinal nerve anatomy

A dermatome is an area of
skin that provides sensory info
to CNS via posterior roots of
one spinal nerve.
Reflex Arc



Spinal cord helps to maintain homeostasis by
integrating information for reflexes.
Reflex = fast, automatic, unplanned sequence of
actions.
Several types:
 Spinal—knee
jerk
 Cranial—eye tracking
 Somatic—involves contraction of skeletal myo’s
 Autonomic—responses of organs & glands
Reflex Arc

Reflex arc has 5 components
1.
2.
3.
4.
5.
Sensory receptor—AP is generated in
dendrites of this neuron.
Sensory neuron—impulse propagates along
axon to gray matter of spinal cord or brain.
Integrating center—gray matter in CNS
Motor neuron—AP travels down motor
neuron to part of body that will respond.
Effector—part of body that responds.
Reflex Arc
Reflexes are predictable.
 Can provide info about health of nervous
system.

Reflex Arc

Stretch reflex is one example. It causes
contraction of a skeletal myo that’s been
stretched.
 Slight
stretch stimulates receptors in myo
called muscle spindles.
 Spindle generates AP along somatic sensory
neuron thru posterior root of spinal nerve into
spinal cord.
 In cord, sensory neuron synapses with motor
neuron in anterior gray horn.
Reflex Arc
 AP
begins in motor neuron which extends
from spinal cord into anterior root back to the
skeletal myo.
 Neuron synapses on that myo & causes
contraction.
 At same time a small, interneuron is
stimulated so that the opposing myo is
inhibited.
Part 3: The Brain &
Cranial Nerves
“Concepts” chapter 15 & 16
The Brain--overview

Adult brain has 4
main parts:
 Brain

stem
medulla oblongata,
pons, midbrain
 Cerebellum
 Diencephalon

thalamus,
hypothalamus,
epithalamus
 Cerebrum
The Brain -overview
Covered by cranial meninges which are
continuous with spinal ones.
 Internal carotid & vertebral arteries supply
brain. Internal jugular vein drains it.
 Needs constant supply of glucose for
neurons to make ATP.

The Brain -overview
Blood brain barrier protects brain from
harmful substances.
 The capillaries are sealed tightly &
astrocytes surround them as well.

The Brain -overview



Glucose, ions & some
other small molecules
can pass.
Lipid soluble
substances (O2, CO2,
alcohol & anesthetics)
cross easily.
Many drugs do not.
The Brain -overview

Cerebrospinal fluid continuously circulates
thru cavities in brain & spinal cord.
 Contains
glucose, proteins, lactic acid, urea,
ions & WBC’s

Provides shock absorbing protection,
optimal chemical environment & exchange
of nutrients & waste.
The Brain—brain stem

Medulla oblongata
 Most
inferior part of brain stem
 Its white matter contains all sensory & motor
tracts.
 90% of the axons cross here (that’s why right
side of brain controls left side of body).
The Brain—brain stem
 Cardiovascular

Regulates rate & force of heart
rate & diameter of blood
vessels.
 Respiratory

center is here
center
Adjusts basic breathing rhythm
 Monitors
joint & myo position
The Brain—brain stem

Pons
 Just
superior to
medulla
 Has areas that help
control breathing
rhythm also.
 Main “bridge” between
parts of brain.
The Brain—brain stem

Midbrain
 Connects
pons to diencephalon.
 Has superior colliculi —reflex center for eye
tracking
 Also inferior colliculi —relays auditory info to
thalamus.
 Both together allow for the startle reflex.
 Some nuclei here control subconscious myo
movement.
The Brain—brain stem


Also in brain stem is a
less defined area called
reticular formation.
Part of ret. form. is called
reticular activating system
(RAS).

Helps maintain
consciousness especially
when waking up.
The Brain--cerebellum
The Brain--cerebellum




Second largest part of brain
(cerebrum is 1st).
Located posterior to medulla &
pons & inferior to the post.
portion of cerebrum.
Has 2 cerebellar hemispheres
separated by the vermis.
Cortex is gray matter, interior
“tree like” area is white matter.
The Brain--cerebellum
Inferior view of the
Brain Stem and
Cerebellum.
1. Pons
2. Medulla oblongata
3. Tonsilla cerebelli
4. Uvula
5. Pyramis
6. Tuber vermis
7. Biventer lobule
8. Inferior semilunar
lobule
9. Vermis
10. Cerebellar
hemisphere
The Brain--cerebellum
Receives sensory info from the vestibular
apparatus (balance sensors) of inner ear &
from proprioceptors (position sensors) thru
out the body.
 Cerebrum initiates movements,
cerebellum evaluates how well they are
being carried out.

The Brain--cerebellum

Function:
 Can
correct movements & smooth them out.
 Regulates posture & balance.
 Helps coordinate myo’s for speech.
 Also has nonmotor fxns.

Cognition & language processing
The Brain--diencephalon


Extends from brain stem to cerebrum.
Includes thalamus, hypothalamus &
epithalamus.
The Brain--diencephalon

Thalamus



Relays all sensory info to cerebral cortex
Crude perception of pain, touch, pressure, temp.
Epithalamus



Contains pineal gland which secretes melatonin.
Involved in sleep-wake cycle.
Involved in emotional response to odors
The Brain--diencephalon

Hypothalamus
 Controls
& integrates autonomic nervous system
(contraction of smooth & cardiac myo & gland
secretions).
 Produces many hormones.
 Regulates behavior patterns (anger, pleasure, etc).
 Regulates eating & thirst.
 Monitors body temp.
 Regulates sleep-wake cycle.
The Brain--diencephalon
The Brain--cerebrum


Called the “seat of intelligence.”
Allows us to:
 Read
 Write
 Speak
 Calculate
 Compose
 Remember
 Plan
 Imagine
The Brain--cerebrum
Has right & left hemispheres separated by
longitudinal fissure.
 Outer rim of gray matter.
 Inner cortex of white matter.
 Some gray matter nuclei deep within white
matter.
 Has many folds called gyri (sing.--gyrus)
with valleys called sulci (sing.--sulcus).

The Brain--cerebrum

Corpus callosum connects the
hemispheres.
The Brain--cerebrum

Each hemisphere is divided into 4 lobes
 Frontal
 Parietal
 Temporal
 Occipital
The Brain--cerebrum





Central sulcus—separates frontal & parietal
lobes.
Precentral gyrus—ant. to central sulcus, primary
motor area
Postcentral gyrus—post. to central sulcus,
somatosensory area
Lateral cerebral sulcus—separates frontal lobe
from temporal.
Parieto-occipital sulcus—separates parietal lobe
from occipital.
The Brain--cerebrum

1.
2.
3.
White matter consists of axons that form
3 types of tracts:
Association—connect gyri in same
hemisphere
Commissural—connects gyri of different
hemispheres
Projection—to & from lower part of CNS
The Brain--cerebrum
Basal ganglia are the masses of gray
matter within each cerebral hemisphere.
 Coordinates gross, automatic myo
movements (swinging arms while walking,
etc.), & myo tone.

The basal ganglia consists of the
striatum, the globus pallidus and
the subthalamic nucleus.
The Brain--cerebrum

Encircling upper brain stem & corpus
callosum are a ring of structures that form
the limbic system.
The Brain--cerebrum

Limbic system is
called “emotional
brain.”
 Pain
 Pleasure
 Docility
 Affection
 Anger
 Smell
& memory
The Brain--cerebrum

Cerebrum can be divided into functional
areas:
 Sensory
 Motor
 Association
The Brain--cerebrum

Sensory
 This
info arrives
mostly in the post. half
of both hemispheres.
 Primary
somatosensory area—
receives nerve
impulses for touch,
joint/myo position,
pain, temp, itch, tickle
The Brain--cerebrum
The Brain--cerebrum
 Primary
visual area—
receives visual info.
 Primary auditory area—
receives info for sound &
its perception.
 Primary gustatory area—
taste info & perception.
 Primary olfactory area—
smell & its perception.
The Brain--cerebrum

Motor
 Info
from here flows mostly from anterior part
of each hemisphere.
 Primary motor area—controls voluntary myo
contraction on opposite side of body.
Motor homunculus
The Brain--cerebrum
 Broca’s
speech area—involved in articulation
of speech. Located in left hemisphere in most
people.

Activates myo of larynx, pharynx, mouth &
breathing.
The Brain--cerebrum

Association
 Consists
of motor & sensory areas.
Somatosensory—permits you to determine
size/shape of object w/out looking, compare
current & previous experiences.
 Frontal—connections w/ many areas, deals with
make up of your personality, intelligence…
 Visual—recognize & evaluate what is seen
 Auditory—recognize sound/speech patterns

The Brain--cerebrum
Wernicke’s—in left hemisphere, involved in
interpreting & recognizing speech.
 Common integrative—receives info from many
sensory areas, integrates them & formulates
thoughts on them.
 Premotor—deals with motor movements of
complicated sequential nature
 Frontal eye field—voluntary scanning

The Brain--cerebrum


Brain structure on
each side is nearly
symmetrical.
There are functional
differences. Some
regions are lateralized
more to one side.
The Brain--cerebrum
The Brain—cranial nerves
Twelve pairs
 Given their name b/c they exit the cranium
thru various foramen.
 Part of PNS.
 Given a roman numeral which indicates
their order from ant.  post.
 Also given a name that indicates their
distribution or fxn.

The Brain—cranial nerves

Olfactory (I) nerve
 Sensory
 From
nasal mucosa to
olfactory area in
cerebral cortex.
 Fxn: smell
The Brain—cranial nerves

Optic (II) nerve
 Sensory
 From
retina to
thalamus & primary
visual area.
 Fxn: vision
The Brain—cranial nerves

Oculomotor (III) nerve
 Mixed


Sensory portion:
proprioceptors in eye
myo’s to midbrain
Motor portion: from
midbrain to eye myo’s
 Fxn:
proprioception,
movement, lens &
pupil
The Brain—cranial nerves

Trochlear (IV) nerve
 Mixed


Sensory portion: proprioceptors in eye myo’s to midbrain
Motor portion: midbrain to eye myo
 Fxn:
proprioception & eye movement
The Brain—cranial nerves

Trigeminal (V) nerve
 Mixed


Sensory portion: has 3
branches that receive
info from many areas of
face to pons
Motor portion: pons to
myo’s of mastication.
 Fxn:
pain, touch, temp.
& proprioception,
chewing
The Brain—cranial nerves

Abducens (VI) nerve
 Mixed


Sensory portion: proprioceptors in eye myo’s to pons
Motor portion: pons to eye myo’s
 Fxn:
proprioception, eyeball movement
The Brain—cranial nerves

Facial (VII) nerve
 Mixed


Sensory portion: tongue
to cerebral cortex
Motor portion: pons to
facial myo’s, facial
glands
 Fxn:
proprioception,
taste, facial
expression, secretion
of saliva & tears.
The Brain—cranial nerves

Vestibularcochlear (VIII) nerve
 Mixed


Sensory portion: from receptors in inner ear to pons,
cerebellum & cerebrum
Motor portion: pons to hair cells in balance organ of inner ear.
 Fxn:
equilibrium & hearing
The Brain—cranial nerves

Glossopharyngeal (IX)
nerve

Mixed



Sensory portion: from
tongue & carotid arteries
to medulla
Motor portion: medulla to
myo’s of tongue & larynx
Fxn: taste, touch/pain,
proprioception for
swallowing, monitor O2 &
CO2 & regulates breathing
rate
The Brain—cranial nerves

Vagus (X) nerve

Mixed



Sensory portion: taste buds,
myo of throat, receptors in
aorta, receptors in organs to
medulla & pons.
Motor portion: medulla to myo
of throat & organs
Fxn: taste, touch of throat,
monitor blood pressure &
breathing, organ sensation,
swallowing, coughing, organ
myo contraction.
The Brain—cranial nerves

Accessory (XI) nerve
 Mixed


Sensory portion:
proprioceptors in throat
to medulla
Motor portion: medulla
& SC to throat & neck
myo’s
 Fxn:
proprioception,
swallowing, head &
shoulder movement
The Brain—cranial nerves

Hypoglossal (XII)
nerve
 Mixed


Sensory portion:
proprioceptors in
tongue to medulla
Motor portion: medulla
to tongue
 Fxn:
proprioception,
movement of tongue
Part 4: Autonomic
Nervous System
“Concepts” chapter 17
Autonomic Nervous System



Recall that the cranial & spinal nerves discussed
earlier are part of the somatic division of the
PNS.
Somatic sensory neurons convey info about
things like proprioception, pain, special sense…
Somatic motor neurons stimulate skeletal myo’s
to contract. They are under voluntary control
(most).
Autonomic Nervous System


The main input into the ANS comes from
autonomic sensory neurons.
Sensory receptors in blood vessels, organs &
myo’s called interoceptors monitor internal
conditions.
 E.g.

CO2 in blood, amount of stretch in an organ
This info gets conveyed to integrating centers in
the CNS.
Autonomic Nervous System

Autonomic motor neurons regulate visceral
activity by either increasing or decreasing
activity in the effector tissue.
 E.g.
dilate blood vessels, increase heart rate, dilate
pupils


Remember that most somatic motor neurons
went from CNS directly to skeletal myo.
Autonomic motor pathways usually have 2
neurons.
Autonomic Nervous System

Myelinated axon from CNS  autonomic
ganglion (collection of nerve cell bodies)
unmyelinated axon to the effector
Autonomic Nervous System

The (output) motor part of ANS has 2 types of
functions.
 Sympathetic
division
 Parasympathetic division

The nerve impulse from a division will either
increase or decrease activity in an effector.
 E.g.
impulses from sympathetic nerves to heart will
speed it up, while impulses from parasympathetic
nerves will slow it down.
Autonomic Nervous System

By the way…


These autonomic fibers run
right along with somatic
fibers in the cranial & spinal
nerves.
A “nerve” is made of a
collection of neurons, some
of which may be somatic &
some may be autonomic
types. Some neurons may
be sensory & some motor.
Autonomic Nervous System
The preganglionic neurons of the
sympathetic division have their cell
bodies in the gray matter of the spinal cord
in the thoracic & lumbar region.
 So the sympathetic division is a.k.a
thoracolumbar division.

Autonomic Nervous System
Preganglionic cell bodies of
parasympathetic division originate in 4
cranial nerves, brain stem & sacral
segments.
 So it’s called craniosacral division.

Parasympathetic vs. sympathetic
ANS neurotransmitters & receptors

Cholinergic neurons use acetylcholine
(ACh) as a neurotransmitter.
 All
sympathetic & parasympathetic pre-gang
neurons
 Sympathetic post-gang neurons to sweat
glands
 All parasympathetic post-gang neurons

Short lived effects
ANS neurotransmitters & receptors
ACh will be released as a neurotransmitter
via exocytosis from the neuron. It will bind
to the post-ganglionic cell or effector cell
membrane if there is a receptor for it.
 Two main types of receptors & each
triggers a different effect.

 E.g. ACh
can inhibit GI myo’s but excite myo’s
that cause pupil contraction.
ANS neurotransmitters & receptors

Adrenergic neurons release norepinephrine (NE)
 Most

sympathetic post-gang neurons
Adrenergic receptors bind both NE &
epinephrine.
 NE
is a neurotransmitter & it can be released into
blood by adrenal gland as a hormone.
 Epinephrine is released as a hormone.

Longer effects
ANS
Most organs receive sympathetic &
parasympathetic stimulation.
 They usually work in opposition to each
other.
 The balance of each is called autonomic
tone & is regulated by hypothalamus.

Sympathetic response
During physical or emotional stress,
sympathetic division dominates.
 Favors functions that support activity &
production of ATP.
 “E” situations:

 Exercise,
emergency,
excitement, embarrassment.

Fight or flight responses.
Parasympathetic response



Supports fxns that conserve & restore energy
Rest & digest
SLUDD






Salivation
Lacrimation
Urination
Digestion
Defecation
Decreases

Heart rate, diameter of airway, diameter of pupil
Part 5: Endocrine
System
“Concepts” chapter 19
Comparison of control
Nervous & endocrine systems act together
to coordinate body functions and maintain
homeostasis.
 There are similarities and differences in
how they do it.

Comparison of control
Nervous
Endocrine
Mediator
Neurotransmitter
Hormone
Distance to target
cell
Short
Usually far
Receptor on target Yes
cell?
Yes
Response
Fast
Usually slow
Duration of
response
Short
long
Endocrine system glands

Some glands can be “exocrine” type
 Secrete
their product into a duct that opens
into a body cavity

Sweat, mucous, & digestive glands
Endocrine system glands

Some glands are “endocrine” type
 Secrete
their products into a blood vessel so
that it can be carried to the target
Glands &
organs of the
endocrine
system
Mechanism of hormone action


Even though a hormone
may travel in the blood
stream and contact
thousands of cells, not all
of those cells will
respond.
Cell must have a specific
receptor for the hormone.
Mechanism of hormone action

Also, two cells may have a receptor for a
hormone, but respond differently
depending on the “machinery” inside.
Mechanism of hormone action

The binding of a
hormone to a receptor
will start a chain
reaction response
inside of a cell.
Mechanism of hormone action

Synergistic effect—when the effect of 2
hormones acting together is greater than
each acting alone.
 Epinephrine
& glucagon both raise blood
glucose levels

Antagonistic effect—when one hormone
opposes the action of another.
 E.g.
calcitonin & PTH
Hypothalamus





Called “master gland”
Receives input from many areas of brain &
internal organs
Controls ANS, regulates body temp., thirst,
hunger, sexual drive, fear, rage
Crucial endocrine gland that secretes many
hormones
Works along with the pituitary gland
Hypothalamus




There are specialized neurons in the
hypothalamus called neurosecretory cells.
They synthesize “stimulating” and “inhibiting”
hormones in their cell bodies & package them in
vesicles.
Nerve impulses cause exocytosis of the contents
of these vesicles into the blood vessels that
connect the hypothalamus & pituitary.
Pituitary then secretes the appropriate hormone
to travel throughout the body.
Homeostasis


There are
hundreds of body
functions that need
to be kept in
balance.
Focus on the
selected ones that
follow
Homeostasis

Thyroid hormone
balance is important
for body metabolism
Homeostasis
Homeostasis
Homeostasis
Homeostasis—epinephrine &
norepinephrine





Secretion regulated by the nervous system in
response to stress.
Raises blood glucose level and blood fatty acid
level.
Increase metabolic activities.
Increases heart rate and stroke volume and
dilates bronchioles.
Shunts blood away from skin, digestive organs,
and kidneys, and increases blood flow to heart,
brain, and skeletal muscle.
Homeostasis—glucocorticoids &
mineralcorticoids
Raises blood glucose level
 Causes kidney to excrete less water

The End