This document discusses sensory receptors and the nervous system. It begins by describing different types of sensory receptors, including nociceptors, thermoreceptors, and photoreceptors. It then discusses the structures and locations of sensory receptors in the body. The document concludes by covering topics like sensory adaptation, the cranial nerves, spinal nerves, reflex arcs, and different types of reflexes.

1. Chapter 13

2. Sensory Receptor Types
Nociceptors
Respond to excess heat, pressure,
or chemicals
Tissue damage
All parts of the body but brain
Thermoreceptors
Temperature of skin and blood
Maintains homeostatic control via
the hypothalmus
Photoreceptors
Light absorbing pigments
Light detection

3. Sensory Receptor Types
Mechanoreceptors Chemoreceptors
Touch, pressure, & vibrations
Bend or stretch PM of
receptor cell = changing
permeability
Stretch receptors –
position of body parts
Hair cells - sound waves
and H2O movements
Chemicals in the internal &
external environment
O2 in arterioles
Osmoreceptors - changes in
[blood solute]
Pheromone detection

4. Sensory Receptor Locations
Exteroceptors
Stimuli outside the body
Skin and special sense organs
Interoceptors
Stimuli within the body
Chemical messengers, tissue stretch, and temperature
Proprioceptors
Internal stimuli
Monitor position and stretch of joints, tendons, and
muscles

5. Sensory Receptor Structures
Unencapsulated Encapsulated
Free nerve endings
Most body tissues
Temperature and painful
stimuli
Capsaicin and itch
Merkel discs
Deeper epidermal layers
Light touch
Hair follicle receptors
Shaft of hair follicle
Light touch and hair bending
 Meissner’s corpuscles
 Dermal papillae of sensitive and
hairless skin
 Discriminative touch
 Pacinian corpuscles
 Deep in the dermis
 Deep pressure initially, vibration
 Ruffini endings
 Deep dermis and hypodermis
 Deep continuous pressure
 Muscle spindles
 Perimysium of skeletal muscle
 Detect muscle stretch & initiate a
reflex
 Golgi tendon
 Insertion tendons
 Activation inhibits contracting muscle

6. Sensory Input
All senses trigger the same TYPE of signal
Distinction occurs in activated brain area
Typically graded response, but AP’s possible
Sensory receptors detect sensations and carry to the
brain
Awareness of environmental change
Brain constructs perceptions by integrating
sensations with other information
Neuronal communication involving multiple brain areas

7. The Working Brain

8. Sensory Adaptation
Sensory receptors
become less responsive
Fewer action potentials
Limits reactions to
normal background
stimuli
Shower or hot tub
temperature
Odors over time

9. Decoding Nerves
PNS organ consisting of parallel bundles of
axons enclosed by connective tissue layers
Epineurium
Perineurium
Endoneurium
Direction of transmission
Afferents: only to CNS
 Dorsal root ganglia
Efferents: only from CNS
 Sympathetic & parasympathetic ganglia
Mixed: carry both; most
Classified as cranial or spinal

10. Mature neurons don’t divide*
Cell body damage = death
Cut/compressed axons regenerate
Separated ends seal off and swell
Distal end of injury disintegrates
 Lack of nutrients
 Neurilemma maintained in endoneurium
Schwann cells proliferate & encourage
axon growth
 Guide ‘sprouting’ axons to original contacts
Greater distance decreases chances
Regrowth never exact = retraining
Extremely rare in CNS
Nerve Fiber Regeneration

11. Cranial Nerves
Ventral portion of the
brain
1st
2 pairs attach to
forebrain
Remainders originate on
brainstem

12. Numbers Cranial Nerve Function
I OLFACTORY Smell (sensory)
II OPTIC Vision (sensory)
III OCULOMOTOR Eye movement (motor)
(medial, inferior, superior rectus muscle
& inferior oblique muscle)
IV TROCHLEAR Eye movements (motor)
(superior oblique muscle)
V TRIGEMINAL Temperature, pain, crude touch of face
(sensory) & mastication (motor)
VI ABDUCENS Eye movement (motor)
(lateral rectus muscle)
VII FACIAL Taste (2/3 of anterior tongue) (sensory)
Facial expressions (motor)
VIII VESTIBULOCOCHLEAR Hearing & Equilibrium (sensory)
IX GLOSSOPHRAYNGEAL Taste (1/3 of posterior tongue) (sensory)
Pharynx (swallowing & gag reflex)
(motor)
X VAGUS Senses blood pressure (sensory)
Stimulate heart rate and digestive organs
(motor)
XI ACCESSORY Head and neck movement (motor)
e.g. trapezius, levator scapula
XII HYPOGLOSSAL Tongue movement (motor)

13. Testing Cranial Nerves for Disorders
 Olfactory
 Smell substances
 Anosima
 Optic
 Eye chart
 Anopsias
 Oculomotor
 Follow object; pupil reflex
 Strabismus, double vision, ptosis
 Trochlear
 See oculomotor
 Trigeminal
 Close/move jaws; touch face with
objects
 Abducens
 See oculomotor
 Facial
 Make various faces; tasting substances
 Bell’s palsy, loss of taste, can’t close eye
 Vestibulocochlear
 Tuning fork; distance of sound
 Deafness, vertigo, tinnitus
 Glossopharyngeal
 Swallowing & gag reflex; say ‘ah’
 Vagus
 See glossopharyngeal
 Horseness, swallowing problems, death
 (Spinal) accessory
 Move head/shoulders against resistance
 Hypoglossal
 Stick out, retract, & move tongue to sides

14. Roots: medial & afferent OR
efferent
Dorsal root: peripheral receptors to
spinal cord
Ventral root: ventral horn to
skeletal muscles
Branches: laterally pass through
intervertebral foramen
Dorsal ramus: dorsal trunk
Ventral ramus: limbs & rest of
trunk
Meningeal branch: meninges and
blood vessels
Plexus
Criss cross joining of ventral rami
Excludes T2 – T12
Spinal Nerve Anatomy

15. 31 Pairs of Spinal Nerves
8 cervical
Cervical plexus
Brachial plexus
12 thoracic
Intercostal nerves & enlargements
5 lumbar
Lumbar plexus
5 sacral
Sacral plexus
1 coccygeal
Tailbone & perineum

16. Cervical Nerves
Cervical plexus
Phrenic nerve: diaphragm
 Irritation causes hiccups
Brachial plexus C5 – C8
Median nerve: flexor muscles of the anterior forearm
and small hand muscles
 Carpal tunnel syndrome and suicide attempts
Radial nerve: extensor muscle of posterior forearm and
triceps brachii
 ‘Saturday night paralysis’
Ulnar nerve: similar to median nerve


17. Lumbosacral Plexus
Innervates lower limbs, buttocks, and pelvic muscles
Lumbar plexus L1 – L4
Femoral nerve: quadriceps and sartorius
 Branches to saphenous
Obturator nerve: adductor muscles
Sacral plexus L4 – S4
Sciatic nerve: entire lower leg (except anteriomedial
thigh)
 Tibial: hamstrings
 Common fibular nerve: anterior tibialis

18. Reflex Arc
Receptor
Senses stimulus
Sensory neuron (afferents)
Message to the CNS
Integration center
Synapses in CNS
 Monosynaptic (single motor or sensory neuron)
 Polysynaptic (multiple interneurons)
Motor neuron (efferents)
Message to effectors
Effector
Muscle fibers or glands
Reflexes are rapid, predictable motor responses to a
stimulus
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s/common/dorlands/dorland/images/arc_reflex%20a.(1).jpg

19. Classifying Reflexes
Somatic: activate skeletal muscle
Spinal: integration center is spinal cord
 Stretch: ensures muscle length maintained (knee-jerk reflex)
 Crossed extensor: withdrawl from painful stimuli (pin prick)
 Superficial: cutaneous stimulation (plantar reflex)
Cranial nerve: integration center is brain stem
 Corneal: stimulation causes blinking
Autonomic (visceral): activate smooth or cardiac
muscle
Pupillary light: controls diameter of pupil
(inside/outside)
Ciliospinal: ipsilateral pupil dilation from pain