Chapter Overview

The Peripheral Nervous System






Learning Points



Know the general vs. special senses
Know the difference between sensation and
perception
Be able to define adaptation, and know which
senses show fast vs. slow adaption
Sensation and perception
Types of sensory receptors
Somatic senses
Structure of nerves
Cranial nerves
Spinal Nerves
Reflexes
General Senses
includes both somatic and visceral
senses

somatic
________________





tactile (touch, pressure, vibration)
thermal (warm and cold)
pain
proprioception (moving, nonmoving, limb
position)
visceral
________________


conditions within internal organs by ANS
Special Senses
smell
taste



vision
________________
hearing
________________

equilibrium or balance

Sensation vs. Perception
sensation
________________


Conscious or subconscious detection of external or
internal stimuli
Sensory impulses travel to CNS



If reach spinal cord – may initiate spinal reflexes
If reach brainstem – may initiate changes in heart rate or
breathing
If reach cerebral cortex – we can locate and identify different
sensations (touch, pain, hearing), and combine with memories
of previous experiences leading to perception
perception
________________

Adaptation
Generator or receptor potential decreases in
amplitude during a maintained constant stimulus

frequency of nerve impulses in first-order neuron
peripheral
decreases (________________
adaptations)
perception of sensation may fade or disappear even
central
though stimulus persists (_____________
adaptation)
receptors vary in how quickly they adapt









rapidly adapting receptors
specialized to signal changes in stimulus
smell
pressure, touch, ________________
slowly adapting receptors
continue to trigger impulses as long as stimulus persists
pain, body position, chemical composition of blood
conscious awareness and interpretation of sensations
Learning Points

Be able to classify sensory receptors based
upon their:



Structure
Origin of the stimulus
Type of stimulus they detect
Types of Sensory Receptors
Types of Sensory Receptors
Structural Classification
Structural
Classification
Separate cells that synapse
with sensory neurons special
3.
Free nerve endings
1.
•
•
senses
Structures of ______________
Receptor potentials trigger
release of neurotransmitter
which then create a
Postsynaptic Potential (PSP)
on a sensory neuron which
may trigger an action potential
and nerve impulse
Examples: hair cells (hearing
and equilibrium), gustatory
receptors (taste),
photoreceptors (vision)
•
bare dendrites
lack structural specialization
examples: pain,
temperature, tickle, itch and
some touch
•
•
Encapsulated nerve endings
2.
dendrites are enclosed in
connective tissue capsule
distinctive microscopic
structure
touch, pressure,
examples: ____________
vibration
__________
•
•
•
•
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Types of Sensory Receptors
Types of Sensory Receptors
Origin of Stimulus
Exterocepters
1.
________________
Origin of Stimulus
Proprioceptors
3.
________________
located at or near external surface of body
sensitive to stimuli from external environment



Interocepters
________________
2.







located inside body

in blood vessels
visceral organs
muscles
nervous system
monitor conditions in internal environment
located in


muscles
tendons
joints
inner ear
provide information about




body position
________________
muscle length and tension
position and movement of joints
Learning Points
Types of Sensory Receptors
Type of stimulus they detect
1.
Mechanoreceptors

Mechanical stimuli (deformation, stretching, bending)

Touch, pressure, vibration, proprioception, hearing, equilibrium
Thermoreceptors
2.
________________
Somatic sensations


Changes in temperature

Nociceptors
________________
3.
4.

5.

6.

Somatic sensory receptors

embedded in





skin or subcutaneous layer
mucous membranes of mouth, vagina, anus
muscle tendons
Joints
________________
inner ear
unevenly
distributed ________________




Photoreceptors
Light on retina
Chemoreceptors
Chemicals in mouth, nose, and body fluids
Osmoreceptors
Osmotic pressure of body fluids
Somatic Sensations
lips, tip of tongue, and fingertips have highest density
four types of somatic sensations: tactile,
thermal, pain, proprioceptive
Where are the receptors located?
How do each of the following somatic sensations
occur?

Painful stimuli from physical or chemical damage to tissue






Touch
Temperature
Pain
Proprioception
What are dermatomes?
Touch
Crude
________________
touch



ability to perceive that something contacted skin
exact location, shape, size, or texture cannot be
detected
Fine
________________
touch


provides specific information about location,
shape, size, and texture of stimuli
Rapidly Adapting Touch Receptors
Meissner
______________ corpuscles




Slowly Adapting Touch Receptors

AKA Corpuscles of Touch
receptors for fine touch located
in dermal papillae of hairless
skin
abundant in hands, eyelids, tip
of tongue, lips, nipples, soles,
clitoris, and tip of penis








found in hairy skin
free nerve endings - wrapped
around hair follicles
detect movements on skin
surface that disturb them


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Thermal Receptors

Sustained sensation that is felt
over a larger area than is touch



Occurs when deeper tissue are
compressed
pacinian
________________
receptors
(corpuscles)

Dendrite enclosed in a large oval
structures composed of
multilayered connective tissue
capsule

Adapt rapidly

Widely distributed in body

Located in deep dermis, ligaments, and
tendons
Consists of three dendrites enclosed by
elongated capsule of connective tissue
Sense stretching of skin or ligaments and
tendons when you move
Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014".
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Pressure Receptors

Receptors for fine touch
Saucer-shaped, flattened, free nerve
endings
Contact Merkel cells of stratum basale
Abundant in fingertips, hands, lips,
external genitalia
ruffini corpsucles
________________

Hair Root Plexuses
________________

merkle disc
________________
free nerve
________________
endings
two sensations

cold



warmth


Dermis, hypodermis, around
joints, tendons, muscles, in
periosteum, and certain viscera
(urinary bladder)

Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014".
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located in stratum basale
temperatures between 10 and 40oC (50o to 104oF)
dermis
located in ________________
temperatures between 32 and 48oC (90o to 118oF)
extreme temperatures detected by pain receptors
(nociceptors)
Pain Receptors
Dermatomes




Free nerve endings found in every tissue of
body except brain

Dermatome:
Nociceptors
________________

Detect intense thermal, mechanical, or chemical stimuli

Exhibit very little adaptation
The area of skin
innervated by the
cutaneous branches of a
________________
single spinal nerve

Types of pain

Fast
________________
(acute or sharp pain)



Usually occurs within 0.1 second after stimulus is applied
Slow (chronic, burning, throbbing)

One or more seconds after stimulus is applied
Can create a map of which
spinal nerve carries
sensations about touch to
the CNS from each part of
the skin
Spinal injuries: Can
pinpoint which spinal
nerves are damaged by
which area of skin are
affected
Häggström, Mikael. "Medical gallery of Mikael Häggström 2014".
Wikiversity Journal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN
20018762. (File:Gray797.png) [Public domain], via Wikimedia Commons
.
Localization of Pain
fast pain

precisely localized
slow pain

well localized but
more diffuse
referred pain
________________
pain feels like it is
coming from some
part of body other
than part being
stimulated

may occur due to
sensory impulses
from two regions
following a common
nerve pathway to
brain – entering at
same segment of
spinal cord
Proprioceptive Sensations
Text
________________


Allows us to know where head and limbs are, and how they are
moving even when we aren’t looking at them

Proprioceptors

Located in muscles, tendons



By OpenStax College [CC BY 3.0
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Provide feedback on stretch and tension of joint parts
Text
Located in ________________

Monitor orientation of head relative to ground
Allows us to estimate weight of objects and determine muscular
effort necessary to perform a task

Muscle spindles (within skeletal muscles)

Tendon organs (within tendons)

Joint kinesthetic receptors (within synovial joint capsules)
Muscle Spindles
Tendon Organs


interspersed among and
aligned parallel to ordinary
muscle fibers

More numerous in muscles
that control fine
movements



primary function is to
measure muscle length
and send signal to


Located at junction of tendon
and muscle
Consists of thin capsule of
connective tissue enclosing a
few tendon fascicles
One or more sensory nerve
endings penetrate the capsule
Dendrites wrap around the
collagen fibers
Applying tension to the tendon
generates a nerve impulse to
the CNS


Text
________________
- for
perception of limb position
and movement
Text
________________
- for
coordination of muscle
contraction


By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human
Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate
938, Public Domain,
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Joint Kinesthetic Receptors



Kinesthesia: perception of body movements
Receptors are located within and around articular capsules of
synovial joints
Several types

Free nerve endings and type II cutaneous mechanoreceptors
Text
(________________
corpuscles)


Text
Small lamellated (________________)
corpuscles


In capsules of joint and respond to pressure
Respond to acceleration and deceleration of joints during movement
Articular ligaments contain receptors similar to tendon organs

Adjust the contraction of adjacent muscles when excessive strain is
placed on joint
Providing information about
Text
changes in ________________
Control muscle tension causing
muscle relaxation before
muscle force damages tendons
Learning Points

Know the structure of nerves
Nerves
Nerves: bundles of axons in the
peripheral nervous system
Cranial nerves




Text
________________


Endoneurium
1.

wraps individual
axons
Text
________________
2.

emerge from brain
Spinal nerves

PNS Connective Tissue Layers
wraps axons bundled
into fascicles
Text
________________
3.


emerge from spinal cord
wraps entire nerve
fuses with dura mater
of CNS
Text
________________
Public Domain,
https://commons.wikimedia.org/w/index.php?curid=1298429
Learning Points

Know the function of each of the cranial
nerves
Cranial Nerves
I.
Olfactory
VII.
Facial
II.
Optic
VIII.
Vestibulocochlear
III.
Oculomotor
IX.
Glossopharyngeal
IV.
Trochlear
X.
Vagus
V.
Trigeminal
XI.
Accessory
VI.
Abducens
XII.
Hypoglossal
Odor Of Orangutan Terrified Tarzan After
Four Voracious Gorillas Viciously Attacked Him
Cranial Nerves
Cranial Nerves
Optic (II)
Olfactory (I)
• ________________
Text
• Fibers transmit impulses
associated with vision
• Two nerves merge
forming the optic
chiasma where some
information crosses to
be processed by
opposite lobe of brain
• Sensory
• Fibers
transmit
impulses
associated
with
__________
Text
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Commons
Cranial Nerves
Cranial Nerves
Text
___________
(IV)
• Primarily motor
• Motor impulses
to muscle
(superior
oblique) that
Text
_____________
Text
_________
(III)
• Primarily motor
• Motor impulses
to muscles that
• raise eyelids
• move the eyes
•
By OpenStax [CC BY 4.0
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Commons
Text
• adjust light
entering eye
• Downward and
away from
midline
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Commons
By OpenStax [CC BY 4.0
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Cranial Nerves
Cranial Nerves
Text
________________
(V)
Text
__________
(VI)
• Mixed
• Sensory: touch, pain,
thermal sensations
• Opthalmic division
• Primarily motor
• Motor impulses
to muscle
(lateral rectus)
that move the
eyes
• sensory from surface of eyes, tear
glands, scalp, forehead, and
upper eyelids
Text
• ________________
division
• sensory from upper teeth, upper
gum, upper lip, palate, and skin of
face
• Moves eyes
laterally
• Mandibular division
• sensory from scalp, skin of jaw,
lower teeth, lower gum, and lower
lip
• motor to muscles of mastication
and muscles in floor of mouth
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Cranial Nerves
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Cranial Nerves
Vestibulocochlear
(VIII)
Facial (VII)
• Mixed
Text
• Sensory from ____
receptors on
anterior 2/3 of
tongue
• Motor to muscles of
Text
______________,
tear glands, and
sublingual and
submandibular
glands salivary
glands
• Primarily sensory
• Sensory from
Text
______________
receptors of ear
(vestibule and
semicircular
canals)
• Sensory from
Text
________
receptors
(cochlea)
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By OpenStax [CC BY 4.0
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Cranial Nerves
Cranial Nerves
Text
________________
(X)

Mixed

Somatic motor to larynx
muscles of speech,
coughing and swallowing

Autonomic motor to viscera
of thorax and abdomen
Text
______________
(IX)
• Mixed
• Sensory from pharynx,
tonsils, taste buds from
posterior 1/3 of tongue
• Sensory from receptors in
carotid arteries of neck,
and carotid sinuses that
Text
monitor _____________,
and carotid bodies that
Text
monitor __________
levels



• Motor to muscles of
pharynx for swallowing

• Motor to parotid gland for
salivation
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Cranial Nerves
GI tract, heart rate
Sensory from pharynx,
larynx, esophagus, and
viscera of thorax and
abdomen
Aortic bodies to monitor
blood pressure, blood gas
concentrations
Over 90% of
Text
________________
fibers
are derived from this cranial
nerve
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Cranial Nerves
Text
____________
Text
___________
(XII)
(XI)
• Primarily motor
• Motor to muscles
Text
of the _________
• Primarily motor
• Motor to muscles
of pharynx,
larynx, neck, and
back
• Speaking, chewing
and swallowing
• Swallowing and
movement of
head and
shoulders
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Spinal Nerves
Learning Points



Know the branches and roots of a spinal
nerve
Know the major plexuses
Know what structures are innervated by the
major nerves associated with the cervical,
brachial, lumbar, and sacral plexuses


Text
________
pair
Numbered from superior
to inferior associated
with vertebral regions





8 pair of cervical nerves
12 pair of thoracic nerves
Text nerves
5 pair of ______
5 pair of sacral nerves
1 pair of coccygeal
nerves
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Spinal Nerve Structure

Roots:

Text
________________
root


plexus
Motor axons

Branches

Dorsal ramus



Limbs and skin of lateral and
ventral trunk
Meningeal branch



Deep muscles and skin of
dorsal trunk
Ventral ramus


Text
________________

Sensory axons
Text
________________
root


Spinal Nerve Plexuses
Supplies vertebrae, vertebral
ligaments, blood vessels of
spinal cord and meninges

Text
________________
Rami communicans


C1-C5
Along neck
Skin and muscles of
head, neck, superior part
of shoulders and chest
Includes
nerve (stimulates
diaphragm)
Autonomic nervous system
Important in controlling vital
body processes (homeostasis)
By Mysid (original by Tristanb) [GFDL
(http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0
(http://creativecommons.org/licenses/by-sa/3.0/)], via
Wikimedia Commons
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Spinal Nerve Plexuses
Spinal Nerve Plexuses
Text
__________
nerve:
deltoid and teres minor
 Musculocutaneous nerve:
muscles that flex the arm

__________
Text

plexus



C5 – C8, T1
Passes
above 1st rib
Nerve supply
to shoulder
and upper
limbs


axillary
musculocutaneus
Biceps brachii, brachialis,
coracobrachialis
Text
__________
nerve:
posterior aspect of arm
and forearm

Triceps brachii, supinator,
brachioradialis, several muscles
that extend wrist and fingers
By Henry Gray (1918) Anatomy of the Human Body (See "Book" section
below)Bartleby.com: Gray's Anatomy, Plate 811, Public Domain,
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Spinal Nerve Plexuses
Spinal Nerve Plexuses
 __________
Text
nerve:
muscles of anterior
forearm and some of
hand




Text
 __________

Text
__________
plexus

Muscles that flex that wrist and
fingers
nerve:
anteromedial muscles of
forearm and most of hand
median
radial
ulnar
L1-L4
Posterior to psoas
major muscle
Supplies
anterolateral
abdominal wall,
external genitals,
part of lower limb
Intrinsic muscles of the hand
By Donthatemebro - Edited an image from wikipedia, CC BYSA 3.0,
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Leg nerves
Spinal Nerve Plexuses

__________
Text


plexus



Femoral nerve: from lumbar
plexus

L4-L5 and S1-S4
Anterior to the
sacrum
Supplies buttocks,
perineum, lower
limbs
Anterior thigh and medial leg
Obturator nerve: from lumbar
plexus




Longest and thickest nerve in
body
All of lower limb except
anteromedial thigh
Text
__________
nerve: from sciatic


By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body
(See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 828, Public
Domain, https://commons.wikimedia.org/w/index.php?curid=541685
nerves



Anterior rami of
T2 to T12
Intercostal
muscles between
ribs
Muscles and skin
of chest wall and
back
Abdominal
muscles
Tibial
Common
fibular
Gastrocnemius, soleus, flexors of
toes
Fibularis muscles (brevis, longus),
tibialis anterior, extensors of toes.
http://digikalla.info/nerves-of-the-lower-leg/nerves-of-the-lowerleg-lower-extremity-innervation-prephockey/
Learning Points
Text
__________

obturator
Common fibular: from sciatic


sciatic
Adductor muscles of thigh
Text
__________
nerve: from sacral
plexus

Spinal Nerve Plexuses
femoral


Intercostal
nerves
By BruceBlaus - Own work, CC BY 3.0,
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
Know the parts of a reflex arc
Be able to compare monosynaptic and
polysynaptic reflexes
Be able to give an example of a stretch and
flexor reflex
Reflex Arc Components
Reflexes






Not consciously perceived
Responses of smooth muscle, cardiac muscle, and glands

Text
__________

Somatic reflexes that are mediated by the spinal cord without
involvement of higher brain function



Pathway followed by nerve impulses that produce reflex


May be monosynaptic or polysynaptic
Function: help maintain homeostasis by controlling involuntary
processes
Rapid, predictable motor response to a stimulus
Reflex arcs – pathways that nerve impulses follow to carry
out reflexes

Text
__________

Reflexes – automatic, subconscious responses to stimuli

Involve contraction of skeletal muscles
Autonomic reflexes



Somatic reflexes
Receptor: at end of sensory neuron, sensitive to a specific type
of internal or external change
Sensory neuron: transmits nerve impulse from receptor into
brain or spinal cord
__________
: in CNS, processing center
Text
Motor neuron: transmits nerve impulse out to effectors
Text
__________


Stretch Reflexes


Helps prevent overstretching of
muscles
Text
Also called simple __________
reflexes


Sensory neuron communicates
directly with motor neuron
Example – knee-jerk reflex

Strike patellar ligament below
the patella

Muscle spindle (receptor)
detects stretch

Sends signal to spinal cord
(along sensory neuron)

sensory neuron synapses with
motor neuron in gray matter of
spinal cord - NO
INTERNEURON

Motor neuron carries signal to
quadriceps femoris muscle
(effector)

Quadriceps femoris contracts Leg extends
skeletal muscle if somatic reflex
Cardiac muscle, smooth muscle or gland if autonomic reflex
Flexor Reflexes

Quadriceps
femoris
Sensory
neuron

Effector muscle
Motor neuron
Synapse
By Юкатан - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=27605165
Text (AKA
Triggered by _______
withdrawal reflex)
Polysynaptic or intersegmental reflex
arc
1.
Pain-sensitive sensory neuron
stimulated
Text
2.
Sensory neuron to __________
3.
Activates interneuron and may
send signal to several segments
4.
Several motor neurons activated
5.
Causes flexor muscles to contract
withdrawing body part from painful
stimulus
http://ib.bioninja.com.au/options/option-a-neurobiology-and/a4innate-and-learned-behav/reflex-arcs.html