Unit 9 Nervous System
Dr. Moattar Raza Rizvi
Principles of Physiology
Nervous System
The Nervous system has three major functions:
 Sensory – monitors internal & external
environment through presence of receptors
 Integration – interpretation of sensory information
(information processing); complex (higher order)
functions
 Motor – response to information processed
through stimulation of effectors
 muscle contraction
 glandular secretion
General Organization of the nervous system
•
Two Anatomical Divisions
–
Central nervous system (CNS)
•
•
–
Brain
Spinal cord
Peripheral nervous system (PNS)
•
•
•
All the neural tissue outside CNS
Afferent division (sensory input)
Efferent division (motor output)
–
–
Somatic nervous system
Autonomic nervous system
General Organization of the nervous system
Brain & spinal
cord
This Slide
Summary
Important
Histology of neural tissue
Two types of neural cells in the nervous system:
 Neurons - For processing, transfer, and storage
of information
 Neuroglia – For support, regulation & protection
of neurons
Neuroglia (glial cells)
CNS neuroglia:
• astrocytes
• oligodendrocytes
• microglia
• ependymal cells
PNS neuroglia:
• Schwann cells (neurolemmocytes)
• satellite cells
CNS neuroglia
Astrocytes
• create supportive
framework for neurons
•play a role in the
establishment of a bloodbrain chemical barrier.
•monitor & regulate
interstitial fluid surrounding
neurons
• secrete chemicals for
embryological neuron
formation
• stimulate the formation of
scar tissue secondary to
CNS injury
CNS neuroglia
Oligodendrocytes
• create myelin sheath
around axons of neurons
in the CNS. Myelinated
axons transmit impulses
faster than unmyelinated
axons
Microglia
• “brain macrophages”
• phagocytize cellular wastes
& pathogens
•Increase during infection of
the CNS
CNS neuroglia
Ependymal cells
• line ventricles of brain &
central canal of spinal cord
•Cells found in the choroid
plexus that secrete
cerebrospinal fluid
PNS neuroglia
Schwann cells
• surround all axons of neurons in
the PNS creating a neurilemma
around them. Neurilemma allows
for potential regeneration of
damaged axons
• creates myelin sheath around
most axons of PNS
Satellite cells
• support (structurally &
functionally) groups of cell bodies
of neurons within ganglia of the
PNS
Neuron: Structure
Neuron: Structure
•Most axons of the nervous system are
surrounded by a myelin sheath
(myelinated axons)
of Ranvier
•The presence of myelin speeds up
the transmission of action potentials
along the axon
•Myelin will get laid down in segments
(internodes) along the axon, leaving
unmyelinated gaps known as “nodes
of Ranvier”
•Regions of the nervous system
containing groupings of myelinated
axons make up the “white matter”
•“gray matter” is mainly comprised of
groups of neuron cell bodies, dendrites
& synapses (connections between
neurons)
Anatomical organization of neurons
Neurons of the nervous system tend to group together into
organized bundles
The axons of neurons are bundled together to form nerves in
the PNS & tracts/pathways in the CNS. Since most axons
are myelinated, these regions will look white in appearance
(“white matter”)
The cell bodies of neurons are clustered together into
ganglia in the PNS & nuclei/centers in the CNS. These
parts are not myelinated, therefore will look gray in
appearance (“gray matter”)
Neural Tissue Organization
Figure 8-6
Structural Classification of neurons
Structural classification based on number of processes coming
off of the cell body:
Multipolar neuron
• multiple dendrites & single axon
• most common type
Structural Classification of neurons
Bipolar neuron
• two processes coming off
cell body – one dendrite &
one axon
• only found in eye (retina),
ear & nose (olfactory
mucosa)
Unipolar neuron
• single process coming
off cell body, giving rise
to dendrites (at one end)
& axon (making up rest of
process)
Functional Classification of neurons
Functional classification based on type of information &
direction of information transmission:
• Sensory (afferent) neurons –
• transmit sensory information from receptors of PNS towards the CNS
• most sensory neurons are unipolar, a few are bipolar
• Motor (efferent) neurons –
• transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the body
• all are multipolar
• Association (interneurons) –
• transmit information between neurons within the CNS; analyze inputs,
coordinate outputs
• are the most common type of neuron (20 billion)
• are all multipolar (short dendrites and a long or short axon)
Reflex arc
Reflex – a quick, unconscious response to a stimulus to protect
or maintain homeostasis. e.g. stretch reflex, withdrawal reflex
Reflex arc – neural pathway involved in the production of a
reflex. Structures include:
• receptor
• sensory neuron
• integrating center (brain or spinal cord; may or may
not involve association neurons (interneurons))
• motor neuron
• effector
Reflex arc
Stretch reflex
- simplest type of
reflex
- no association
neuron involved
Simplified Withdrawal reflex
Neuron Function
Neurons at rest have an unequal distribution of charged ions inside/outside
the cell, which are kept separate by the plasma membrane
• more Na+ ions outside
• more K+ ions inside
• large negatively charged proteins &
phosphate ions inside
The sum of charges
makes the outside of
the membrane
positive, & the inside
of the membrane
negative
Neuron Function
Because of the difference of ionic charges
inside/outside the cell, the membrane of the resting
neuron is “polarized”
The difference in charges creates a potential
electrical current across the membrane known as
the “membrane potential (transmembrane
potential)”
Neuron Function
At rest, the transmembrane potential can also be referred to as
the “resting membrane potential” (RMP)
The RMP of a neuron = -70mV
Neuron Function
For ions to cross a cell membrane, they must go through
transmembrane channels
“leakage channels” – open all the time, allow for
diffusion
“gated channels” – open & close under specific
circumstances (e.g. voltage changes)
Because Na+ & K+ can move through leakage channels of
nerve cells, the resting membrane potential is maintained
by the sodium-potassium exchange pump
Neuron Function
When a stimulus is applied to a resting neuron, gated
ion channels can open
If a stimulus opens gated K+ channels, positive charges
leave cell  membrane potential becomes more negative
(-70mV  -90mV)
This change in membrane potential is known as
hyperpolarization
Neuron Function
When a stimulus causes Na+ gates open, Na+ diffuses into the
cell
This changes the electrical charge inside the cell membrane,
bringing it away from its RMP of -70mV toward 0mV
When the membrane potential (i.e. -70 mV) becomes less
negative or in other words, approaches zero, the membrane is
said to be depolarized
This change in membrane potential is known as depolarization
Neuron Function
If a stimulus only affects Na+ gates at a specific site of the
axon, the depolarization is small & localized only to that
region of the cell. This is known as a graded potential
But if the stimulus reaches a certain level (threshold level),
voltage controlled Na+ gates will begin to open in sequence
along the length of the axon. The depolarization will
propagate along the entire surface of the cell membrane
This propagated change in the membrane potential is known
as an action potential (nerve impulse)
Action potentials
• APs involve the movement of Na+ ions into the cell (causing
depolarization of the membrane), followed immediately by K+
ions moving out of the cell through voltage controlled K+ gates
(causing repolarization of the membrane), that propagates
down the length of the cell
• APs are due to voltage changes that open & close gated Na+
& K+ channels within excitable cells
• Only nerve cells & muscle cells are excitable, i.e. can generate
APs.
• Once an AP begins, it will propagate down the entire cell at a
constant & maximum rate. This is known as the “all or none”
principle
Action Potential Conduction
Depolarization to threshold
Activation of voltageregulated sodium channels
and rapid depolarization
Sodium ions
Local
current
Potassium ions
Inactivation of sodium
channels and activation of
voltage-regulated
potassium channels
Transmembrane potential (mV)
+30
DEPOLARIZATION
3
REPOLARIZATION
0
2
_ 60
_ 70
The return to normal
permeability and resting state
Threshold
1
4
Resting
potential
REFRACTORY PERIOD
0
1
2
Time (msec)
3
Action Potential Conduction
• Nerve cell at rest (RMP= -70mV)
• Stimulus applied to cell
• Na+ gates at axon hillock cause
localized depolarization (graded
potential)
• If stimulus is strong enough, flow of
Na+ ions into cell reach threshold level
triggering opening of voltage gated Na+
channels & formation of an action
potential (nerve impulse)
Action Potential Conduction
• Once threshold is reached, Na+ will quickly
diffuse into the cell causing a rapid
depolarization of the membrane
•(-70 mV0 mV +30 mV)
• this depolarization will spread to adjacent
parts of the membrane, activating more
voltage controlled Na+ gates in succession
Action Potential Conduction
• When the
transmembrane potential
reaches +30mV, Na+
gates will close & K+
gates will open
• K+ will quickly exit
cell resulting in
repolarization of
membrane & return to
resting state
Action Potential Conduction
A.
Action Potential
B.
Depolarization
C.
Repolarization
D.
Threshold
E.
Stimulus
F.
Resting state
G.
Refractory period
Propagation of an Action Potential
Continuous propagation
(continuous conduction)
• Involves entire membrane
surface
• Proceeds in series of small
steps (slower)
• Occurs in unmyelinated
axons (& in muscle cells)
Propagation of an Action Potential
Saltatory propagation
(saltatory conduction)
 Involves patches of
membrane exposed at
nodes of Ranvier
 Proceeds in series of
large steps (faster)
 Occurs in myelinated
axons
“The Big Picture”
• “Information” travels within the nervous
system primarily in the form of propagated
electrical signals known as action potentials.
• An action potential occurs due to a rapid
change in membrane polarity (depolarization
followed by repolarization)
• Depolarization is due to the influx of sodium
ions (Na+); repolarization is due to the efflux
of potassium ions (K+)
Conduction across synapses
In order for neural control to occur, “information” must
not only be conducted along nerve cells, but must
also be transferred from one nerve cell to another
across a synapse
Most synapses within the nervous system are
chemical synapses, & involve the release of a
neurotransmitter
Neurotransmitters are stored in vesicles that are
located primarily in specialized portions of the Axon
The Structure of a Typical Synapse
Synaptic knob is a part of a neuron comes in close proximity to another
neuron at the synapse
Events at a Typical Synapse
Events at a Typical Synapse
• An action potential arrives &
depolarizes the synaptic knob
(end bulb)
• Before repolarization can
occur, Ca+2 gates open & Ca+2
diffuses into end bulb
• Repolarization occurs
Events at a Typical Synapse
• Ca+2 causes the synaptic vessicles to fuse with the end
bulb membrane causing the exocytosis of the
neurotransmitter
Events at a Typical Synapse
• The neurotransmitter diffuses
across the synaptic cleft &
binds to its receptors on the
post synaptic membrane,
causing an effect on the post
synaptic cell
Synapse
The effect on the post synaptic neuron will depend on
whether the neurotransmitter released is
 Excitatory (e.g. Ach, norepinephrine (NE))
 Inhibitory (e.g. seratonin, GABA)
Excitatory neurotransmitters cause Na+ gates to open in the post
synaptic membrane  depolarization (impulse conduction)
Inhibitory neurotransmitters cause K+ or Cl- gates to open in the
post synaptic cell  hyperpolarization (no impulse conduction)
Synapse
 The effects of neurotransmitters on the post
synaptic neurons are usually short lived because
most neurotransmitters are rapidly removed from the
synaptic cleft by enzymes or reuptake
The Central & Peripheral Nervous System
The Central Nervous System
Meninges – Connective tissues that surround and
protect the brain and spinal cord (CNS)
• Dura Mater – tough, fibrous outer layer;
•2 layers thick around brain with creation of dural
sinuses between layers;
•1 layer around spinal cord with epidural space
external
• Arachnoid – “spidery” web-like middle layer
• Pia Mater – delicate, thin inner layer; extension of pia
mater (“filum terminale”) extends from tip of cord to coccyx
to anchor cord in place
Subarachnoid space – between arachnoid & pia mater;
contains cerebral spinal fluid (CSF)
Cranial Meninges
Pia mater: The membrane that supplies most of the blood to the brain
Spinal Meninges
Most of the cerebrospinal fluid is found in the subarachnoid space
The Spinal Cord
• Begins at foramen magnum &
ends at L2 vertebral level by
forming conus medularis
•Has 2 thickened areas- -cervical enlargement supplies nerves to upper
extremity
(conus medularis)
-lumbar enlargement supplies nerves to lower
extremity
• Made up of 31 spinal
cord segments
The Spinal Cord
Dorsal root
ganglion (DRG)
Dorsal
root
Ventral
root
•Each spinal cord segment has a
pair of
• dorsal roots with their
associated dorsal root ganglia
(DRG)
• ventral roots
The Spinal Cord
• Each dorsal root contains the axons of sensory neurons
(unipolar neurons)
• Each dorsal root ganglion contains the cell bodies of these
sensory neurons
• Each ventral root contains the axons of motor neurons
(multipolar neurons whose cell bodies are within the cord)
The Spinal Cord
The dorsal & ventral roots of each segment come
together at the intervertebral foramen (IVF) to form a
mixed spinal nerve
Spinal Nerves
• Part of the PNS
• Contain both motor & sensory fibers (“mixed
nerve”)
• 31 pair of nerves – each nerve forms from union of
dorsal/ventral root of spinal cord segment & exits
between vertebra at IVF (intervertebral foramen)
•8 pair cervical spinal nerves – 1st cervical nerve exits between
occipital bone & C1, 8th cervical nerve exits the IVF between C7-T1
• 12 pair thoracic spinal nerves
• 5 pair lumbar nerves
• 5 pair sacral nerves
• 1 pair coccygeal nerves
Spinal Nerves
Below the conus medularis,
spinal nerves must angle
downward (in the
subarachnoid space) before
exiting their IVF. These spinal
nerves make up the cauda
equina
Spinal Nerves
• Once formed, spinal nerves
will branch
•The branches of most spinal
nerves (comprised of axons)
interweave to form nerve
plexuses
• peripheral nerves then
branch from the plexuses to
provide motor & sensory
innervation to specific areas of
the body
Nerve Plexus
 4 major plexuses
 cervical
 brachial
 lumbar
 sacral
Spinal Nerve plexuses
 Cervical plexus (C1-C5)
 gives off phrenic nerve
 Brachial plexus (C5-T1)
 gives off median, ulnar & radial nerve
 Lumbar plexus (T12-L4)
 gives off femoral nerve
 Sacral plexus (L4-S4)
 gives off sciatic nerve
 No plexus forms between T2-T11 – intercostal nerves
Sectional Anatomy of the Spinal cord
Posterior median sulcus
Posterior column
Posterior gray horn sensory
Central canal
Lateral column
Gray commissure
Anterior column
Lateral gray horn (T1-L2, S2S4) - autonomic
Anterior gray horn motor
Anterior median fissure
“The Big Picture”
The spinal cord has a narrow central canal
surrounded by “horns” of gray matter connected by a
commissure. Gray matter horns contain sensory &
motor nuclei (groups of cell bodies).
Gray matter is surrounded by white matter “columns”
which are made up of groups of myelinated axons
creating organized ascending & descending tracts.
Tracts (Sensory & Motor Pathways)
• Groups of axons found in the white matter columns
of the spinal cord that carry specific information
• Ascending tracts - carry sensory information up the
spinal cord to areas of the brain
• Descending tracts – carry motor information from
the brain down to specific levels of the spinal cord
• Ascending & descending tracts within the spinal
cord are part of the sensory & motor pathways of the
nervous system
Tracts (Sensory & Motor Pathways)
Ascending Tracts (sensory pathways)
 Spinothalamic tracts
 carries poorly localized touch, pressure, pain &
temperature from cutaneous receptors to the thalamus
 from thalamus, some of this sensory info reaches primary
sensory cortex of the cerebrum for “interpretation” &
conscious awareness
Ascending Tracts (sensory pathways)
 Posterior Columns
 carries highly localized discriminative (fine) touch,
vibration, conscious proprioception (position sense) to
nucleus in medulla oblongata (M.O.)
 from M.O., info travels along rest of pathway to thalamus
& then to primary sensory cortex of cerebrum
 Spinocerebellar
 carries proprioceptive (positional) information to the
cerebellum (unconscious awareness)
Posterior Column Pathway
Descending Tracts (motor pathways)
 Corticospinal (pyramidal)
 carries commands from primary motor cortex of
cerebrum for conscious (voluntary) control of skeletal
muscles.
 most fibers cross in “pyramidal decussation” of medulla
oblongata so that left cerebral cortex controls muscles on
right side of body, & vice-versa.
 Medial & lateral pathways
 originate from a variety of brain nuclei & send signals to
motor neurons in the spinal cord for (subconscious)
coordination of skeletal muscle activity, maintenance of
posture & muscle tone.
Corticospinal (pyramidal) Pathway
“The Big Picture”
 Ascending & descending tracts are part of
larger sensory & motor pathways
These sensory & motor pathways
include the afferent & efferent neurons of
the PNS
 Sensory & motor information gets in/out
of spinal cord via spinal nerves
The Brain
 Brain stem
 medulla oblongata (M.O.)
Cerebrum
 pons
 midbrain
 Diencephalon
T
H
M
 thalamus
PP
 hypothalamus
midbrain
Cerebellum
 epithalamus (pineal gland)
 mamillary body
pons
m.o.
 Cerebrum
 Cerebellum
Cerebrospinal Fluid (CSF)
 clear, colorless fluid formed by filtration of blood
plasma by choroid plexuses within ventricles of the
brain.
 circulates through ventricles, into central canal of
spinal cord & around brain & SC in subarachnoid space.
Reabsorbed through arachnoid granulations into dural
sinuses & then into bloodstream
 functions in protection of CNS, support, nutrient
supply, waste removal
 sample of CSF can be taken at subarachnoid space
inferior to the conus medularis by “lumbar puncture”
(spinal tap)
CSF Circulation
The Brainstem
 Medulla oblongata
 continuation of the SC above the foramen
magnum
 contains the pyramidal decussation
 cranial nerve nuclei (XII-VIII (cochlear)
 cardiac, vasomotor, & respiratory reflex
centers
 Pons
The region of the brain stem located
between the midbrain and medulla oblongata
cranial nerve nuclei (VIII (vestibular) – V)
 respiratory center
The Brainstem
 Midbrain
 cerebral peduncles – location of
descending (motor) tracts
 Corpora quadrigemina
 superior colliculi – visual
reflex centers
 inferior colliculi – auditory
reflex centers
 cranial nerve nuclei (IV-III)
 reticular formation – network of
interconnected nuclei throughout
brainstem responsible for
maintaining states of
consciousness (awake & aroused)
Visual and auditory reflexes are centered in Midbrain
The Diencephalon
 Thalamus
 surrounds 3rd
ventricle
 2 halves
connected by
intermediate mass
 comprised of
sensory nuclei
The thalamus is
a primary site of
sensory
integration
The Diencephalon
Hypothalamus

 mamillary bodies – reflex centers
associated with eating, & processing of
olfactory sensations
 connects to pituitary gland via the
infundibulum
has many important functions
relating to maintaining homeostasis
including:
 integrating nervous &
endocrine systems through
control over pituitary gland
 integration of ANS from
visceral stimuli
 hunger/satiety, thirst, body
temp. regulation
hormone production (ADH,
oxytocin)
 subconscious coordination of
motor responses associated with
rage, pleasure, pain, sexual
arousal
The Diencephalon
 Pineal gland
 secretes
Melatonin which
helps regulate
day-night cycles
(circadian rhythm)
Limbic system
 functionally related areas in cerebrum,
thalamus & hypothalamus involved in
 emotional states & behaviors
 linking conscious areas of cerebrum
with unconscious areas of brainstem
 long term memory
Cerebrum
Higher thought processes for learning and memory are primarily in the
cerebrum
gyrus
sulcus
Lobes of Cerebral Hemispheres
The central sulcus in the cerebrum,
separates the frontal from the
parietal lobe.
Central sulcus
Parietal lobe
Parieto-occipital
sulcus
Frontal lobe
Occipital
lobe
Lateral sulcus
(Insula is deep to
lateral sulcus)
Temporal lobe
Lobes of Cerebral Hemispheres
insula
Gray & White matter of cerebrum
 Gray matter – outer
cortex & inner nuclei
(centers)
 White matter – deep to
cortex; comprised of
fibers (pathways for
communication):
 association
 commissural
 projection
White matter of cerebrum
 association fibers –
connect gyri in same
hemisphere
 commissural fibers –
connect gyri in opposite
hemispheres (e.g.
corpus callosum)
 projection fibers –
connect cerebrum with
other parts of brain &
spinal cord
Functional areas of Cerebrum
 Motor and Sensory areas
 Association areas
 Cerebral processing centers
Motor & Sensory
primary motor cortex
(precentral gyrus)
primary sensory cortex
(postcentral gyrus)
Motor & Sensory
Motor & Sensory
primary motor cortex
(precentral gyrus)
primary sensory cortex
(postcentral gyrus)
gustatory
cortex
visual
cortex
auditory cortex
olfactory cortex
Association areas
• interpret incoming
somatic motor association
area (premotor cortex)
sensations; coordinate motor
responses
visual
association
area
Cerebral Processing Centers
• higher-order integrative
centers
• may be unilateral
general interpretive
area (Wernike’s) –Lt
hemisphere usually
motor speech
center (Broca’s) Lt hemisphere
usually
Prefrontal
cortex (bilat.)
The Cerebellum
 2 hemispheres connected by vermis
 separated from cerebrum by transverse fissure
 outer folia with inner arbor vitae
 functions include control
of skeletal muscles
(unconscious) for balance,
coordination & posture
 Stores patterns of
movement
 links to brainstem by
cerebellar peduncles
transverse fissure
arbor vitae (white matter)
folia (gray matter)
Cranial Nerves
 12 pairs of nerves (part of PNS) that connect to
the brain; provide motor, sensory &/or autonomic
(parasympathetic) function
Cranial Nerves (know #, name & basic function)
I Olfactory – smell
II Optic – sight
III Oculomotor – motor to eye muscles; ANS for accommodation of lens &
pupil constriction
IV Trochlear – motor to one eye muscle
V Trigeminal – motor to muscles of mastication, sensation to face & mouth
VI Abducens – motor to one eye muscle
VII Facial – motor to muscles of facial expression; taste; ANS to lacrimal &
salivary glands
VIII Vestibulocochlear – equilibrium & hearing
IX Glossopharyngeal – swallowing, taste, ANS to salivary glands, sensory
reception from monitoring of blood pressure in large arteries
X Vagus – sensation from viscera; ANS visceral muscle movement
(respiratory, digestive, cardiovascular systems)
XI Accessory – motor to muscle of pharynx, SCM & Trapezius
XII Hypoglossal – motor to tongue muscles
Autonomic Nervous System (ANS)
Motor regulation of smooth muscle, cardiac muscle,
glands & adipose tissue (“visceral effectors”) through
stimulation of “visceral efferent fibers”
 Sympathetic (Σ) division – “fight or flight” response
 Parasympathetic (PΣ) division – rest & repose
(“conserve & restore”) response
“dual innervation” – if organ receives both Σ & PΣ,
one division excites, the other inhibits activity
Overview of ANS anatomy
Somatic efferent:
CNS
Somatic motor neuron
Skeletal
muscle
Visceral (autonomic) efferent:
CNS
Preganglionic neuron
Autonomic
ganglion
(myelinated, cholinergic)
Postganglionic neuron
Visceral
effector
unmyelinated, cholinergic or
adrenergic)
(excitatory
synapse)
Effect may be
excitatory or
inhibitory
depending on
receptors
Sympathetic
 cell bodies of preganglionic neurons
in lateral gray horns of spinal cord T1-L2
(“thoracolumbar division”)
 axons of pregg Σ neurons travel to:
 sympathetic chain ganglion, or
 prevertebral (collateral) ganglion,&
 adrenal medulla
 pregg Σ fibers release Ach
 postgg Σ neurons usually release
norepinephrine (NE)
 effects on visceral effectors usually
excitatory but depend upon specific
receptor present - alpha (α) or beta (β)
Sympathetic
Lateral gray
horns T1-L2
Preganglionic neuron
(myelinated, cholinergic)
Σ Chain
ganglion
Prevertebral
ganglion
(excitatory
synapse)
Postganglionic neuron
Visceral
effector
unmyelinated
NE released
(adrenergic)
Effect may be
excitatory or
inhibitory
depending on
receptors
Alpha(α) or beta
(β)
Parasympathetic
 cell bodies of preganglionic neurons
found in cranial nerve nuclei (III, VII, IX,
X) & lateral gray horns S2-S4
(“craniosacral division”)
 pregg PΣ neurons travel to terminal
ganglion (close to) or intramural ganglion
(within wall) of effector
 both pre & postganglionic PΣ fibers
release Ach
 effects on organ depend on specific
receptor present (nicotinic or muscarinic)
Parasympathetic
CNs (III, VII, IX,
X) & Lateral
gray horns S2S4
Preganglionic neuron
(myelinated, cholinergic)
Terminal
ganglion
Intramural
ganglion
(excitatory
synapse)
Postganglionic neuron
Visceral
effector
unmyelinated
Ach released
(cholinergic)
Effect may be
excitatory or
inhibitory
depending on
receptors
Nicotinic or
Muscarinic
Activities of the ANS
Effects of Sympathetic Activation -“fight or flight”
response (energy expenditure):
 increased cardiovascular & respiratory activity
 increased blood flow to brain (increased alertness),
skeletal muscles, heart muscle, lungs
 increased visual acuity (pupil dilation)
 release of energy reserves from adipose, liver, &
skeletal muscles
 decrease in “non-essential” functions (ie. digestion)
 release of Epi & NE from adrenal medullae to
continue effects
Activities of the ANS
Effects of Parasympathetic Activation -“rest &
repose” response (conserve & restore energy):
 decreased cardiovascular & respiratory activity
increased GI motility & enzyme secretion
pupil constriction
 nutrient uptake & energy storage into adipose,
liver, & skeletal muscles (glycogen)