FUNCTIONAL ORGANIZATION OF THE
PNS
 Nervous
structures outside the brain and
spinal cord
- sensory and motor connections to the outside world
- nerves thread throughout the body to allow the CNS
to receive information and take action
 Functional
components of the PNS
- sensory inputs and motor outputs
- categorized as somatic or visceral
- also classified as general or special
FUNCTIONAL COMPONENTS OF THE PNS
 Basic
structural components:
1. Sensory receptors – pick up stimuli from inside
and outside the body, then initiate impulses in
sensory axons
2. Motor endings – the axon terminals of motor
neurons that innervate the effectors
3. Nerves – bundles of peripheral axons and
Ganglia - clusters of peripheral neuronal cell
bodies
- most are mixed nerves, contain both sensory and motor
axons
- some cranial nerves are purely sensory or purely motor in
function
3
MAIN TYPES OF NERVE CELLS
sensory
neurone
relay
neurone/interneuron
motor
neurone
SENSORY
NEURONS
Carries impulses from receptors e.g pain
receptors in skin to the CNS( brain or spinal
cord)
RELAY NEURON/ INTERNEURONS
Carries impulses from sensory nerves to
motor nerves.
MOTOR
NEURON
Carries impulses from CNS to effector e.g.
muscle to bring about movement or gland to
bring about secretion of hormone e.g ADH
SPINAL NERVES
Dorsal roots – sensory fibers arising from cell bodies in dorsal root ganglia
Ventral roots – motor fibers arising from anterior gray column of spinal
cord
12
AUTONOMIC NERVOUS SYSTEM
AUTONOMIC NERVOUS SYSTEM
 The
autonomic nervous system is the subdivision of
the peripheral nervous system that regulates body
activities that are generally not under conscious
control
 General visceral motor part of the PNS
 Has
2 divisions (with opposite effects):
- Parasympathetic: ‘housekeeping’ activities (rest
and digest)
- Sympathetic: extreme situations (fight or flight)
 ANS
is the subdivision of the peripheral
nervous system that regulates body activities
that are generally not under conscious
control
 Visceral motor innervates non-skeletal (nonsomatic) muscles
 Composed of a special group of neurons serving:
Cardiac muscle (the heart)
 Smooth muscle (walls of viscera and blood vessels)
 Internal organs
 Skin

17
Basic anatomical difference between the motor
pathways of the voluntary somatic nervous
system (to skeletal muscles) and those of the
autonomic nervous system
 Somatic division:
 Cell bodies of motor

spinal cord)
Their axons (sheathed in spinal nerves) extend all
the way to their skeletal muscles
 Autonomic
neurons



neurons reside in CNS (brain or
system: chains of two motor
1st = preganglionic neuron (in brain or cord)
2nd = gangionic neuron (cell body in ganglion outside
CNS)
Slower because lightly or unmyelinated
(see next diagram)
18
Axon of 1st (preganglionic) neuron leaves CNS to
synapse with the 2nd (ganglionic) neuron
 Axon of 2nd (ganglionic) neuron extends to the organ it
serves

Diagram contrasts somatic (lower) and autonomic:
this dorsal
root
ganglion is
sensory
autonomic
somatic
Note: the autonomic ganglion is motor
19
DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM (VISCERAL MOTOR PART OF IT)
Parasympathetic division
 Sympathetic division

20
DIVISIONS OF THE AUTONOMIC NERVOUS
SYSTEM
Parasympathetic division
 Sympathetic division

Serve most of the same organs but cause opposing
or antagonistic effects
Parasysmpathetic: routine maintenance
“rest &digest”
Sympathetic: mobilization & increased metabolism
“fight, flight or fright” or “fight, flight or freeze”
21
WHERE THEY COME FROM
Parasympathetic/
Craniosacral:
Cervical
(neck area)
Caudal
(tailbone)
Brain
(cranial nerves)
Sympathetic/
thoracolumbar:
Thoracic
and Lumbar
Vertebrae
22
PARASYMPATHETIC NERVOUS SYSTEM
“REST & DIGEST”

Also called the craniosacral system because all its
preganglionic neurons are in the brain stem or sacral
levels of the spinal cord


Cranial nerves III,VII, IX and X
In lateral horn of gray matter from S2-S4
Only innervate internal organs (not skin)
 Acetylcholine is neurotransmitter at end organ as
well as at preganglionic synapse: “cholinergic”

23
PARASYMPATHETIC CONTINUED
 Cranial




outflow
III - pupils constrict
VII - tears, nasal mucus, saliva
IX – parotid salivary gland
X (Vagus n) – visceral organs of thorax & abdomen:
Stimulates digestive glands
 Increases motility of smooth muscle of digestive tract
 Decreases heart rate
 Causes bronchial constriction

 Sacral
outflow (S2-4): form pelvic splanchnic
nerves


Supply 2nd half of large intestine
Supply all the pelvic (genitourinary) organs
24
PARASYMPATHETIC
(only look at this if it
helps you)
25
SYMPATHETIC NERVOUS SYSTEM
“FIGHT, FLIGHT OR FRIGHT”
 Also
called thoracolumbar system: all its
neurons are in lateral horn of gray matter from
T1-L2
 Lead to every part of the body (unlike parasymp.)


Easy to remember that when nervous, you sweat; when
afraid, hair stands on end; when excited blood pressure
rises (vasoconstriction): these sympathetic only
Also causes: dry mouth, pupils to dilate, increased
heart & respiratory rates to increase O2 to skeletal
muscles, and liver to release glucose
 Norepinephrine
(aka noradrenaline) is
neurotransmitter released by most postganglionic
fibers (acetylcholine in preganglionic):
“adrenergic”
26
SYMPATHETIC NERVOUS SYSTEM
CONTINUED
 Regardless
of target, all
begin same
 Preganglionic axons exit
spinal cord through
ventral root and enter
spinal nerve
 Exit spinal nerve via
communicating ramus
 Enter sympathetic
trunk/chain where
postganglionic neurons
are
 Has three options…
27
OPTIONS OF PREGANGLIONIC AXONS IN SYMPATHETIC
TRUNK
(see next slides for drawing examples)
Synapse on postganglionic neuron in chain
ganglion then return to spinal nerve and
follow its branch to the skin
Ascend or descend within sympathetic trunk,
synapse with a posganglionic neuron within a
chain ganglion, and return to spinal nerve at
that level and follow branches to skin
Enter sympathetic chain, pass through without
synapsing, form a splanchnic nerve that
passes toward thoracic or abdominal organs
1.
2.
3.


These synapse in prevertebral ganglion in front of aorta
Postganglionic axons follow arteries to organs
28
SYNAPSE IN CHAIN GANGLIA
AT SAME LEVEL OR DIFFERENT LEVEL
29
PASS THROUGH GANGLIA AND SYNAPSE
IN PREVERTEBRAL GANGLION
30
SYMPATHETIC
31
SENSORY RECEPTORS OF THE PNS
SENSORY RECEPTORS OF THE PNS
 Also
classified according to:
a) Location – based on body location or
location of stimuli to which they respond
b) Type of stimulus detected – kinds of
stimuli that most readily activate them
c) Structure – divided into 2 broad
categories free or encapsulated nerve
endings
CLASSIFICATION BY LOCATION
 Exteroceptors
– sensitive to stimuli arising from
outside the body
- located at or near body surfaces
- include receptors for touch, pressure, pain, temperature, and
most receptors of the special sense organs
 Interoceptors
(visceroceptors) – receive stimuli from
internal viscera (digestive tube, bladder, lungs)
- monitor a variety of stimuli such as changes in chemical
concentration, taste stimuli, stretching of tissues, and
temperature
- activation causes visceral pain, nausea, hunger, or satiety
CLASSIFICATION BY LOCATION
 Proprioceptors
– monitors degree of stretch and
sends input on body movements to the CNS
- located in musculoskeletal organs such as skeletal
muscles, tendons, joints, and ligaments
CLASSIFICATION BY STIMULUS
DETECTED
 Mechanoreceptors
– respond to mechanical forces
- such as touch, pressure, stretch, vibrations, and itch
 Thermoreceptors
changes
– respond to temperature
 Chemoreceptors
– respond to chemicals in solution
(molecules tasted or smelled) and to change in
blood chemistry
 Photoreceptors
 Nociceptors
in the eye – respond to light
– respond to harmful stimuli that
result in pain (noci = harm)
CLASSIFICATION BY STRUCTURE
 General
 Nerve
sensory receptors – widely distributed
endings of sensory neurons moniter:
- Touch
- Pressure
- Vibration
- Stretch
- Pain
- Temperture
- Proprioception
CLASSIFICATION BY STRUCTURE
 General
sensory receptors are divided into
2 groups
- Free nerve endings
- Encapsulated nerve endings
Note: there is no perfect ‘one receptor – one
function’
- one receptor can respond to several kinds of
stimuli and different receptor types can respond
to similar stimuli
FREE NERVE ENDINGS
 Abundant
 Respond
 Monitor
in epithelia and underlying CT
to pain and temperature
affective senses – those to which people
have an emotional response (pain)
 2 specialized types of free nerve endings:
- Merkel discs: lie in the epidermis
- Hair follicle receptors: wrap around hair
follicles
FREE NERVE ENDINGS
 Merkel
discs – a disc-shaped epithelial cell
innervated by a sensory nerve ending
- slowly adapting receptors for light touch (respond and
send out action potentials even after continual
stimulation)
 Hair
follicle receptors – receptors for light touch
- monitor the bending of hairs
- rapidly adapting (sensation disappears quickly even if
the stimulus is maintained)
 Itch
receptor – in the dermis (newly discovered)