Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
Learning Outcomes
 Upon completing this chapter, you will be able to:
 15-1 Specify the components of the afferent and efferent divisions of the nervous system, and
explain what is meant by the somatic nervous system.
 15-2 Explain why receptors respond to specific stimuli, and how the organization of a receptor
affects its sensitivity. Identify sensory information relayed by general and special
senses. Describe how stimuli are detected and interpreted.
 15-3 Identify the receptors for the general senses, and describe their location and how they
function. Given a scenario describe what receptors would be used to monitor stimuli and how
the body would respond. Describe location of receptors and classify as tonic or phasic.
 Be able to answer questions similar to clinical scenario application questions.
Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
I.
Nervous System Organization
Nervous
System
Peripheral
Nervous
System (PNS)
Central Nervous
System (CNS)
Brain + Spinal Cord
Afferent
division
Efferent
division
(to bring to)
(to bring out)
Somatic
Nervous
System (SNS)
Sympathetic
Division
II.
Autonomic
Nervous System
(ANS)
Parasympathetic
Division
Sensory Receptors
A. Detect info about external/internal environment
B. 3 classifications of sensory receptors:
1. Interoceptors: monitor internal environment
2. Exteroceptors: monitor external environment
3. Proprioceptors: monitor position of muscles/joints
C. Stimulus translated to AP  CNS = transduction
D. If no transduction = no awareness of stimuli
E. Receptors, sensory neurons and sensory pathways make up afferent division of PNS
Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
III.
15-1 Sensory Information
A. General Senses
1. receptors found throughout body
2. simple structure
3. information relayed to primary sensory cortex
4. receptors are sensitive to:
a. Temperature
b. Pain
c. Touch
d. Pressure
e. Vibration
f. Proprioception
B. Special Senses
1. Receptors are more complex
2. Information distributed to specific areas of cerebral cortex
3. Provide information about
a. Olfaction (smell)
b. Vision (sight)
c. Gustation (taste)
d. Equilibrium (balance)
e. Hearing
IV.
The Detection of Stimuli
A. Receptor specificity:
1. receptors sensitive to specific stimuli
2. Examples:
a. Touch receptors sensitive to pressure, not chemical stimuli
b. Taste receptors sensitive to chemicals, not pressure stimuli
B. Sensation: arriving information from receptors via AP
C. Perception: conscious awareness of sensation
D. Receptive field:
1. area monitored by single receptor
2. the larger the field the harder to localize stimulus
3. body = larger fields
4. tongue/fingertips = very small receptive fields
E. Simple receptors
1. dendrites of sensory neurons
2. Branching tips of dendrites = free nerve endings
3. Not protected by accessory structures
4. Little specificity (i.e.: free nerve endings respond to stimulus caused by
chemicals, pressure, temperature or trauma)
F. Complex receptors
1. Found in sense organs
2. Example: eye’s visual receptors
3. Protected by accessory cells and CT
4. Specific (i.e.: receptors cells in eye are protected by accessory structures and CT,
usually only stimulus reaches these cells is light)
Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
V.
Interpretation of Sensory Information
A. Sensory neurons relay info from receptor to specific cortex areas (i.e. primary sensory
cortex receives information about touch, pressure, pain and temperature)
B. Link between receptor and cortical neuron = labeled line
C. Axons of labeled line carry info about one type of stimulus (modality)
D. CNS interprets modality based on labeled line
1. Cannot tell difference between true/false sensation
2. i.e.: rub eyes = mechanical stimulus causes visual of flashes of lights; any activity
along optic nerve travels to visual cortex = visual perception
E. Frequency/pattern of AP determines strength, duration and variation of stimulus
F. Sensory coding = translation of complex sensory info into meaningful patterns of AP
VI.
Receptor Type
A. Tonic
1.
2.
3.
B. Phasic
1.
2.
3.
Always active
A.k.a slow-adapting receptors: little change in receptor activity over time
Indicates background level of stimulation
Normally inactive
Provide info about intensity and rate of change of stimulus
A.k.a. fast-adapting receptors: respond strongly at first, activity declines
Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
VII.
General Sensory Receptors
A. Classified into four types based on stimulus that excites them
Receptor
General Information Location(s)
Function(s)
Mechanoreceptors Stimulus caused by
Tactile Receptors
Tactile Receptors
distortion of plasma
 Free nerve endings:
 Free nerve endings: tonic, small
membranes; three
between epidermal cells
receptive fields; sensitive to
classes: tactile
touch/pressure
receptors,
baroreceptors,
 Root hair plexus: w/ hair
 Root hair plexus: phasic,
proprioceptors
follicles
respond rapidly; detect initial
contact and subsequent
movement

Merkel cells and tactile
discs: stratum basale

Merkel cells and tactile discs:
tonic, small receptive field,
extremely sensitive; sense fine
touch and pressure

Tactile corpuscle: eyelids,
lips, fingertips, nipples,
external genitalia

Tactile corpuscle: phasic, fine
touch/pressure

Lamellated corpuscle:
dermis

Lamellated corpuscle: phasic;
deep pressure


Ruffini corpuscle: deep
dermis
Baroreceptors: free nerve
endings in elastic tissue; respond
immediately, adapt rapidly
Ruffini corpuscle: tonic;
pressure
Baroreceptors: monitor pressure
changes in organs (i.e. monitor BP in
walls of major vessels or degree of lung
expansion)
Proprioceptors: 3 major groups
 Muscle spindles: found in
skeletal muscles
Proprioceptors:
 Muscle spindles: monitor length
of skeletal muscle and trigger
stretch reflexes

Golgi tendon organs:
located at junction
between skeletal muscle
and its tendon

Golgi tendon organs: monitor
external tension developed
during muscle contraction

Receptors in joint
capsules

Receptors in joint capsules:
detect pressure, tension and
movement at the joint
Chapter 15: Neural Integration I – Sensory Pathways and the Somatic Nervous System
Receptor
Nociceptors
General Information Location(s)
Tonic
 Superficial portions of
skin
 Joint capsules
 Periosteum
 Walls of BVs
Thermoreceptors
Phasic; more cold
receptors than
warm receptors;
carried along same
pathway as pain
sensations
Chemoreceptors
Only respond to
water or lipid
soluble substances
dissolved in body
fluids (i.e. interstitial
fluid, CSF, plasma);
information sent to
brain stem, not
cortex

Free nerve endings in
dermis, skeletal muscles,
liver and hypothalamus
 Information sent to
thalamus, reticular
formation of midbrain,
primary sensory cortex
Carotid and aortic bodies
Function(s)
 Detects pain
 Myelinated Type A fibers detect
fast or prickling pain (i.e.
injection or deep cut)
 Type C fibers detect slow or
burning/aching pain
 Detect information about
temperature
Monitor pH, CO2 and O2 levels