Chapter 13.pdf.anatomy.and.physiology...

cranial nerves

1. Chapter 13.13
Cranial Nerves

2. Module 13.13: Cranial nerves
Cranial nervesinnervate head, neck, and
some torso regions & the 12 pairs of cranial
nerves can be classified as:
•Sensory
•Special sensory
•Motor
•Mixed

3. Figure 13.13
The branches of the 12 cranial nerves, their functions (motor, sensory, or mixed), and the structures they innervate
Optic nerve (II)
Abducens nerve (VI)
Oculomotor nerve (III)
Trochlear nerve (IV)
Olfactory nerve (I)
Olfactory tract
Olfactory bulb
Pituitary gland
Semilunar
ganglion (V)
Pons
Geniculate
ganglion (VII)
Medulla
oblongata
To tongue
muscles
To sternocleidomastoid
and trapezius muscles
Inferior ganglion (X)
Superior ganglion (X)
Inferior ganglion (IX)
Superior ganglion (IX)
Vestibulocochlear nerve (VIII)
Sensory nerve to
posterior tongue
Motor nerve to
pharyngeal muscles
Sensory nerve to
tongue and soft palate
Motor nerve
to facial muscles
Motor nerve
to muscles of
mastication
Ophthalmic branch
Maxillary branch
Mandibular branch
Trigeminal
nerve (V)
Facial nerve (VII)
Cochlear branch
Vestibular branch
Glossopharyngeal
nerve (IX)
Vagus
nerve (X)
Hypoglossal
nerve (XII)
Accessory
nerve (XI)
KEY
Sensory nerves
Motor nerves

4. Figure 13.13

5. Figure 13.13

6. Figure 13.10 1
The motor and sensory cortexes and the association areas for each
Motor Cortex
Sensory Cortex
Visual Cortex
Auditory Cortex
Central sulcus
Somatic sensory
association area
Primary visual cortex
Visual association area
Lateral sulcus
TEMPORAL LOBE
PARIETAL LOBE
OCCIPITAL
LOBEFRONTAL
LOBE
Somatic motor
association area
Gustatory cortex
of the insula
Olfactory cortex
Primary auditory cortex
Auditory association area
Primary sensory cortex
Primary motor cortex

7. Figure
12.61
Major Peripheral Nerves
Lesser occipital nerve
Great auricular nerve
Transverse cervical nerve
Supraclavicular nerve
Phrenic nerve
Cervical
plexus
Brachial
plexus
Lumbar
plexus
Sacral
plexus
Axillary nerve
Musculocutaneous
nerve
Thoracic nerves
Radial nerve
Ulnar nerve
Median nerve
Iliohypogastric
nerve
Ilioinguinal
nerve
Genitofemoral
nerve
Femoral nerve
Obturator nerve
Superior gluteal nerve
Inferior gluteal nerve
Pudendal nerve
Saphenous nerve
Sciatic nerve

8. Section 2: Sensory and Motor Pathways

9. Basic events occurring along sensoryand motor
pathways:
•Sensory pathway
•Depolarization of receptor
•Stimulus produces graded change in transmembrane
potential of receptor (= transduction)
•Action potential generation
•If depolarized to threshold, initial segment develops action
potentials
•Greater degree of sustained depolarization = higher
frequency of action potentials

10. Basic events occurring along sensoryand motor
pathways (continued):
•Sensory pathway(continued)
•Propagation over labeled line
•= Information about one type of stimulus (touch, pressure,
temperature) carried on axons
•Brain processes sensory information based on what type of
axons are transmitting information
•CNS processing
•Occurs at every synapse along labeled line
•May occur at multiple nuclei and centers in CNS

11. Basic events occurring along sensoryand motor
pathways (continued):
•Motor Pathways (one of two responses)
1.Immediate involuntary response
•Processing centers in spinal cord or brain stem respond
before sensations reach cerebral cortex
2.Voluntary
•Perception(only ~1% of sensations are relayed to the
primary sensory cortex –sensations that may merit a
voluntary response)
•Voluntary response
•Can moderate, enhance, or supplement the relatively
simple reflexive response

12. •General senses
•Our sensitivity to temperature, pain, touch, pressure,
vibration, and proprioception
•Receptors that respond to these stimuli are found
throughout the body
•Are relatively simple in structure
•Size of the area each receptor monitors
(= receptive field) varies
•Can be as large as 7 cm (2.5 in.) as on general body
surfaces or as small as 1 mm as on tongue or fingertips
•Size of receptive field is inverselyrelated to ability
to accurately describe location of stimulus

13. Figure 13 Section 2 1
Receptive fields, the areas monitored by a single
receptor cell
Receptive
field 1
Receptive
field 2

14. •General senses (continued)
•Sensory pathways begin at peripheral receptors
and often end at diencephalon and/or cerebral
hemispheres
•Much sensory information does not reach primary
sensory cortex and our awareness
•Sensation:information carried by sensory
pathway
•Perception:conscious awareness of sensation

15. Module 13.14: Receptor classification by function
and sensitivity
•Free nerve endings
•Can be stimulated by many different stimuli
•Examples: chemical, pressure, temperature
changes, trauma
•Sensitivity and specificity may be altered by
location and presences of accessory structures
•Simplest receptors are the dendritesof sensory
neurons
•Have branching tips that are unprotected

16. Figure 13.14 2
A Functional Classification of General Sensory Receptors
Nociceptors Thermoreceptors Chemoreceptors Mechanoreceptors
Pain
receptors
Temperature
receptors
Respond to
water-soluble
and lipid-
soluble
substances
dissolved in body
fluids
Sensitive to
stimuli that
distort their
plasma
membranes
Myelinated Type A fibers
(carry sensations of
fast pain)
Unmyelinated
Type C fibers (carry
sensations of slow
pain)
Proprioceptors
(monitor the
positions of joints
and muscles)
Baroreceptors
(detect pressure
changes)
Tactile receptors (provide the
sensations of touch, pressure,
and vibration)

17. •Receptor classes based on their response to stimulation
•Tonicreceptors
•Always active
•Frequency of action potentials generated reflects
background stimulation level
•As stimulation changes, AP frequency changes accordingly
•Phasicreceptors
•Normally inactive
•Become active transiently in response to changing
conditions

18. •Adaptation: reduction in sensitivity in the
presence of a constant stimulus

19. Figure 13.15
The types of receptors in the skin
Hair
Sensory nerves

20. Module 13.15 Review
a.Identify the six types of tactile receptors
located in the skin, and describe their
sensitivities.
b.Which types of tactile receptors are located
only in the dermis?
c.Which is likely to be more sensitive to
continuous deep pressure: a lamellated
corpuscle or a Ruffini corpuscle?

21. Figure 13.16 4
Posterior column pathway
Spinocerebellar pathway
Spinothalamic pathway
A cross section through the spinal cord showing the
locations of the somatic sensorypathways
Module 13.16: Three major somatic sensory
pathways

22. Figure 13.16
The two tracts within the spinothalamic pathway, which provide conscious sensations of “crude” touch, pressure,
pain, and temperature
Spinothalamic Pathway
The anterior spinothalamic tracts
of the spinothalamic pathway carry
crude touch and pressure sensations.
The lateral spinothalamic tracts of
the spinothalamic pathway carry pain
and temperature sensations.
Sensory homunculus
(functional map of the
primary sensory
cortex)
Synapse of second-
order neurons in
the ventral nuclei
of the thalamus
Midbrain
Medulla
oblongata
Anterior
spinothalamic
tract
Crude touch and pressure sensations
from right side of body
Pain and temperature sensations
from right side of body
Midbrain
Medulla
oblongata
Lateral
spinothalamic
tract
Spinal
cord
KEY
Axon of first-
order neuron
Second-order
neuron
Third-order
neuron
Spinal
cord
Medulla
oblongata
Midbrain
Medial
lemniscus
Ventral nuclei
in thalamus
Nucleus
gracilis and
nucleus
cuneatus
Ascending
sensory
axons
Dorsal root
ganglion
The posterior column pathway, which carries
sensations of “fine” touch, pressure, vibration,
and proprioception
Posterior Column Pathway Spinocerabellar Pathway
The spinocerebellar pathway, which provides the
cerebellum proprioceptive information about the
position of skeletal muscles, tendons, and joints
Medulla
oblongata
Spinal
cord
Posterior column pathway
Spinocerebellar pathway
Spinothalamic pathway
A cross section through the spinal cord showing the
locations of the somatic sensory pathways
Fine-touch, vibration, pressure, and proprioception
sensations from right side of body
Proprioceptive input from Golgi tendon organs,
muscle spindles, and joint capsules
Anterior
spinocerebellar
tract
Posterior
spinocerebellar
tract
Spinocerebellar
pathway
Cerebellum
Pons

23. Module 13.16: Three major somatic sensory
pathways
1.Spinothalamic pathway
•Neural path
•First-order neuron
•From receptor to synapse in spinal cord posterior gray horn
•Second-order neuron
•From posterior gray horn, crosses spinal cord and reaches
thalamus
•Third-order neuron
•From thalamus to primary sensory cortex
•Sensory homunculus (“little man”) maps somatic
sensations to discrete areas in cortex

24. 1.Spinothalamic pathway (continued)
•Anteriorspinothalamic tracts
•Carry crudetouchand pressuresensations
from body
•Lateralspinothalamic tracts
•Carry painand temperaturesensations from
body

25. Figure 13.161
The two tracts within the spinothalamic pathway, which provide conscious sensations of “crude” touch, pressure,
pain, and temperature
Spinothalamic Pathway
The anterior spinothalamic tracts
of the spinothalamic pathway carry
crude touch and pressure sensations.
The lateral spinothalamic tracts of
the spinothalamic pathway carry pain
and temperature sensations.
Sensory homunculus
(functional map of the
primary sensory
cortex)
Synapse of second-
order neurons in
the ventral nuclei
of the thalamus
Midbrain
Medulla
oblongata
Anterior
spinothalamic
tract
Crude touch and pressure sensations
from right side of body
Pain and temperature sensations
from right side of body
Midbrain
Medulla
oblongata
Lateral
spinothalamic
tract
Spinal
cord
KEY
Axon of first-
order neuron
Second-order
neuron
Third-order
neuron

26. 2.Posterior column pathway
•Carries sensations of highly localized “fine”
touch, pressure, vibration, and
proprioception
•Begins at peripheral receptor and ends in
primary sensory cortex
•Sensory axons ascend in fasciculus gracilis
and cuneatus
•Medial lemniscus (tract) leads to thalamus

27. Figure 13.16 2
Spinal
cord
Medulla
oblongata
Midbrain
Medial
lemniscus
Ventral nuclei
in thalamus
Nucleus
gracilis and
nucleus
cuneatus
Ascending
sensory
axons
Dorsal root
ganglion
The posterior column pathway, which carries
sensations of “fine” touch, pressure, vibration,
and proprioception
Posterior Column Pathway
Fine-touch, vibration, pressure, and proprioception
sensations from right side of body
KEY
Axon of first-
order neuron
Second-order
neuron
Third-order
neuron

28. 3.Spinocerebellar pathway
•Carries proprioceptiveinformation about
position of skeletal muscles, joints, and
tendons to cerebellum
•Posterior axons do not cross sides of spinal
cord
•Anterior axons do crossover to opposite
side of spinal cord

29. Figure 13.16
3
Spinocerabellar Pathway
The spinocerebellar pathway, which provides the
cerebellum proprioceptive information about the
position of skeletal muscles, tendons, and joints
Medulla
oblongata
Spinal
cord
Proprioceptive input from Golgi tendon organs,
muscle spindles, and joint capsules
Anterior
spinocerebellar
tract
Posterior
spinocerebellar
tract
Spinocerebellar
pathway
Cerebellum
Pons
KEY
Axon of first-
order neuron
Second-order
neuron
Third-order
neuron

30. Homework: answer the questions from the
Module13.16 Review:
a.Define sensory homunculus.
b.Which spinal tracts carry action potentials
generated by nociceptors?
c.Which cerebral hemisphere receives impulses
conducted by the right fasciculus gracilis of
the spinal cord?

31. Module 13.17: Somatic motorpathways
•Somatic motorpathways
•Always involve at least two motor neurons
1.Uppermotor neuron
•Cell body in a CNS processing center
2.Lowermotor neuron
•Cell body in a nucleus of brain stem or spinal cord
•Uppermotor neuron synapses on lower, which then
innervates a single motor unit of skeletal muscle

32. Module 13.17: Somatic motorpathways
•Corticospinal pathway
•Provides voluntary controlover skeletal muscles
•Sometimes called the pyramidal system
•Begins at pyramidal cells in primary motor cortex
•Upper axons descend into brain stem and spinal
cord
•Synapse with lower motor neuronsthat control
muscles

33. •Corticospinal pathway (continued)
•Upper motor neurons begin along specific areas of
the primary motor cortex that map to muscles in
specific areas of the body (=motor homunculus)
•Motor homunculus pattern varies with number of motor
units innervated and degree of motor control available
•Synapses with lower motor neurons occur in two
tracts:
1.Corticobulbar (bulbar, brain stem) tracts
•Synapses occur in motor nuclei of cranial nerves
•Provide conscious control over skeletal muscles that
move eye, jaw, face, and some muscles of neck and
pharynx

34. •Corticospinal pathway (continued)
Synapses with lower motor neurons occur in two tracts
(continued)
2.Corticospinal tracts
•Visible along ventral surface of medulla oblongata as pair
of thick bands (pyramids)
•~85% of corticospinal axons cross midline to enter
lateral corticospinal tracts
•~15% descend uncrossed as anterior corticospinal
tracts (crossing over occurs through anterior white
commissure at specific spinal segment)
•Provide conscious control over skeletal muscles that
move various body areas

35. Figure 13.17 3
A cross section of the spinal cord showing the
locations of the Corticospinal Pathway
Anterior
corticospinal
tract
Tectospinal tract
Vestibulospinal tract
Reticulospinal tract
Medial Pathway
Involved primarily with the control of
muscle tone and gross movements of
the neck, trunk, and proximal limb
muscles
Lateral
corticospinal
tract
Lateral Pathway
Involved primarily with the
control of muscle tone and
the more precise movements
of the distal parts of the
limbs
Rubrospinal tract

36. Figure 13.17 1
The corticospinal pathway, which provides
voluntary control over skeletal muscles
To skeletal
muscles
Motor nuclei
of cranial
nerves
Motor nuclei
of cranial
nerves
To skeletal
muscles
To skeletal
musclesKEY
Lateralcorticospinal tract
Anteriorcorticospinal tract
Corticobulbar tract
Medulla oblongata
Spinal cord
Upper motor
neuron
Lower motor
neuron
Pyramid
Midbrain
Cerebral
peduncle
Motor
homunculus

37. •Two main pathways for subconsciousmotor
commands
1.Lateral pathway
•Primarily concerned with muscle tone and precise
movements of distal limb parts
•Red nucleus(primary nucleus of lateral pathway)
•Receives information from cerebrum and cerebellum
•Adjusts upper limb position and background muscle tone
•Axons cross to opposite side of brain and descend
through rubrospinal (ruber, red) tracts

38. •Two main pathways for subconsciousmotor
commands (continued)
2.Medial pathway
•Primarily concerned with muscle tone and gross motor
control of neck, trunk, and proximal limb muscles
•Upper motor neurons located in three areas
1.Superior and inferior colliculi
•Tectospinal tracts pass axons down to direct reflexive
movements of head, neck, and upper limbs to visual/auditory
stimuli
2.Reticular formation
•Reticulospinal tracts conduct impulses down spinal cord
3.Vestibular nucleus (of CN VIII)
•Receive information from inner ear about position and
movement of head
•Issue motor commands through vestibulospinal tractsto
adjust muscle tone in neck, eyes, head, and limbs

39. Figure 13.17 3
A cross section of the spinal cord showing the
locations of the medialand lateral pathways
Anterior
corticospinal
tract
Tectospinal tract
Vestibulospinal tract
Reticulospinal tract
Medial Pathway
Involved primarily with the control of
muscle tone and gross movements of
the neck, trunk, and proximal limb
muscles
Lateral
corticospinal
tract
Lateral Pathway
Involved primarily with the
control of muscle tone and
the more precise movements
of the distal parts of the
limbs
Rubrospinal tract

40. Figure 13.17 2
The locations of centers in the cerebrum, diencephalon, and brain stem
that may issue somatic motor commands as a result of processing
performed at a subconscious level
Nuclei of the Medial Pathway
Superior and inferior colliculi
Reticular formation
Vestibular nucleus
Motor
cortex
Basal
nuclei
Red nucleus
Medulla oblongata
Thalamus
Cerebellar
nuclei

41. Module 13.17 Review
a.Define corticospinal tracts.
b.Describe the role of the corticobulbar tracts.
c.What effect would increased stimulation of the
motor neurons of the red nucleus have on
muscle tone?

42. Module 13.18: Levels of somatic motor control
•Levels of somatic motor control
•Many brain areas are involved in controlling body
movements
•Generally, the closer the motor center to the
cerebral cortex, the more complex the motor
activity
•Cerebellum is the exception as it is involved at
multiple levels

43. •Brain areas involved in increasing levels of
motor complexity (as indicated by increasing
numbers)
1.Brain stem and spinal cord
2.Pons and medulla oblongata
3.Hypothalamus
4.Thalamus and midbrain
5.Basal nuclei
6.Cerebral cortex
7.Cerebellum: coordinates complex motor
patterns through feedback loops involving
cerebral cortex, basal nuclei, and nuclei of
medial and lateral pathways

44. Figure 13.18 1
The brain structures involved in increasing levels of motor complexity;
the cerebellum is involved in coordinating motor activities at multiple levels
Basal Nuclei
Cerebral Cortex
Thalamus and
Midbrain
Hypothalamus
Pons and Medulla
Oblongata
Brain Stem and Spinal Cord
Cerebellum
Controls reflex motor
patterns related to
eating, drinking, and
sexual activity;
modifies respiratory
reflexes
Control balance
reflexes and more
complex respiratory
reflexes
Control simple cranial and
spinal reflexes
Control reflexes in
response to visual
and auditory stimuli
Modify voluntary and
reflexive motor
patterns at the
subconscious level
Plans and
initiates voluntary
motor activity
Coordinates complex
motor patterns
through feedback
loops involving the
cerebral cortex and
basal nuclei as well as
nuclei of the medial
and lateral pathways

45. Figure 13.18 2
The path of information flow when an individual makes a conscious
decision to perform a specific movement:
Decision in
frontal lobes
Basal
nuclei
Motor
association
areas
Cerebellum
Cerebral
cortex

46. •Performing a movement
•As movement begins, responses are relayed from
motor association areas
•Motor association areas →primary motor cortex →
medial and lateral pathways
•Basal nuclei adjust movement patterns in two
ways
1.Alter pyramidal cell sensitivity, adjusting
corticospinal output
2.Change excitatory or inhibitory output of medial and
lateral pathways
•Cerebellum monitors somatic sensory input and
adjusts motor output as necessary

47. Figure 13.18 3
The flow of information as an individual begins a movement:
Basal
nuclei
Motor
association
areas
Primary
motor
cortex
Other nuclei of
the medial and
lateral pathways
Cerebellum
Cerebral
cortex
Lower
motor
neurons
Corticospinal
pathway
Motor activity
The basal nuclei adjust patterns
of movement in two ways:
1. They alter the sensitivity of the
pyramidal cells to adjust the
output along the corticospinal
tract.
2. They change the excitatory or
inhibitory output of the medial
and lateral pathways.
As the movement proceeds,
the cerebellum monitors
proprioceptive and vestibular
information and compares
the arriving sensations with
those experienced during
previous movements. It then
adjusts the activities of the
upper motor neurons
involved.

48. •Effects of primary motor cortex damage
•Individual loses ability to exert fine control of
skeletal muscles
•Some voluntary movements can still be controlled
by basal nuclei
•Cerebellum cannot fine-tune movements because
corticospinal pathwayis inoperative
•An individual can stand, balance, and walk
•All movements are hesitant, awkward, and poorly
controlled

49. Homework: answer the questions from the
Module13.18 Review:
a.The basic motor patterns related to eating and
drinking are controlled by what region of the brain?
b.Which brain regions control reflexes in response to
visual and auditory stimuli that are experienced while
viewing a movie?
c.During a tennis match, you decide how and where to
hit the ball. Explain how the motor association areas
are involved.