1. Sensory, Motor, and Integrative Systems
CHAPTER 16

2. Introduction
Now that you know the organization of the NS we can explore sensation along with somatic sensory and motor pathways.
Not every stimulation elicits a response – thus many stimuli, along with stored information are integrated.
Two complex integrative functions:
Wakefulness and sleep
Learning and memory

3. Sensation Receptor Nerve Impulses Sensory Info CNS Spinal Cord
Brain Stem
Cerebral Cortex
Reflexes
Complex Autonomic Reflexes
Aware of stimuli (pain, hearing, taste etc)

4. Sensation
Conscious or subconscious awareness of environmental (int or ext) changes.
Perception: conscious interpretation of sensation
If sensory info doesn’t reach the cerebral cortex = no perception (BP)
Sensory Modality = each unique type of sensation (ex. Retina, cochlea)

5. Senses 5 basic In anatomy – perceived senses are: Special
General: Somatic vs visceral
Special

6. Process of Sensation Stimulation Transduction Conduction Translation
Stimulus in receptive field
Transduction
Transduce stimulus to graded potential
Conduction
GP – threshold – nerve impulse - conducted
Translation
CNS translates impulse into sensation

7. Graded Potential vs. Action Potential
Vary in magnitude
All or none principle
Vary in duration
Same duration
Decay with distance
Long distances
Dendrites and cell body (direction can vary)
Axons (hillock – one way direction)
Variety of ion channels open and close to create potential
Voltage-gated ion channels cause potential
No refractory period
Absolute or relative refractory periods possible
Generator potential  Create an action potential
Receptor potentials  neurotransmitter release

8. Graded Potential

9. Types of Sensory Receptors
Microscopic Structure
Free nerve endings
Encapsulated nerve endings
Separate cells
Location
Exteroceptors
Interoceptors
Proprioceptors
Type of Stimulus
Mechanoreceptors
Thermoreceptors
Nociceptors
Photoreceptors
Chemoreceptors
Osmoreceptors

10. Cold stimulus (temp)  Free nerve ending  exteroreceptor  thermoreceptor (generator potential)
Pressure stimulus  encapsulated nerve ending  exteroreceptor  mechanoreceptor (generator potential)
Taste stimulus  Separate cells (gustatory cell)  triggers release of neurotransmitters  synapses with exteroreceptor  chemoreceptor (Receptor potential)

11. Adaptation in Sensory Receptors
Rapidly adapting receptors
Slowly adapting receptors

12. Somatic Sensations Tactile Sensations Thermal Sensations
Proprioceptive Sensations
Pain Sensations

13. Fig. 16.2 Tactile and Thermal Sensations

14. Fig. 16.4 Proprioceptive Sensations: muscle spindle and tendon organ

15. Proprioception Kinesthesia Weight Discrimination Stereognosis
Perception of motion
Weight Discrimination
Ability to assess object weight
Stereognosis
Perception of 3D depth
Usually perception of solid objects by touch

16. Pain Sensations Protective Nociceptors Slowly adapting
Many stimuli (pressure, temp, chem ex. Histamine, bradykinin)
Slowly adapting
2 major Sensory pathways
Fast, slow, referred

17. Fig. 16.3 Distribution of referred pain

19. Somatic Sensory Pathways
Relay sensory info from somatic receptors  primary somatosensory area of cerebral cortex and cerebellum
Key Characteristics:
Decussation
Relay
Sensory pathways  cerebral cortex contain thousands of sets of 3 neurons
First-order neuron
Second-order neuron
Third-order neuron
Symmetry
Somatotopy

20. Spinal Cord Review
Note that the illustration does not demonstrate symmetry: only right-sided sensory pathways and left-sided motor pathways are depicted.

21. Table 16.3: Major Somatic Sensory Tracts and Pathways

22. Posterior column–medial lemniscus pathway
RIGHT SIDE
OF BODY
Posterior column–medial lemniscus pathway
LEFT SIDE
OF BODY
Primary somatosensory
area of cerebral cortex
THIRD-ORDER NEURONS
Thalamus
Medial lemniscus
Midbrain
SECOND-ORDER NEURONS
Gracile nucleus
Cuneate nucleus
FIRST-ORDER NEURONS
POSTERIOR COLUMN:
Medulla
Posterior root ganglion
Gracile fasciculus
Cuneate fasciculus
Receptors for touch and proprioception in the upper limbs, upper trunk, neck, and posterior head
Spinal nerve
Cervical spinal cord
Receptors for touch and proprioception in the lower limbs and lower trunk
Lumbar spinal cord

23. Anterolateral (spinothalamic) pathways
RIGHT SIDE
OF BODY
Anterolateral (spinothalamic) pathways
LEFT SIDE
OF BODY
Primary somatosensory
area of cerebral cortex
THIRD-ORDER NEURON
Thalamus
Midbrain
SECOND-ORDER NEURON
Posterior gray horn
FIRST-ORDER NEURON
Medulla
LATERAL SPINOTHALAMIC TRACT
Posterior root ganglion
Spinal nerve
Receptors for pain, temp, itch from limbs, trunk, neck and posterior head
Spinal cord
ANTERIOR SPINOTHALAMIC TRACT

24. Posterior Column-Medial Lemniscus Pathway Spinothalamic Pathway
Posterior Column-Medial Lemniscus Pathway
Spinothalamic Pathway
Sensations carried
Pressure, vibration, touch, conscious proprioception
Pain, temperature, itch, tickle 
Beginning of pathway
Sensory receptors in: Limbs, trunk, neck, posterior head
End of pathway
Cerebral cortex
# neurons in pathway 3
Neuron crosses over
Second-order neuron
Crossover location
Medulla oblongata
Spinal cord
First order neuron
Axon
Posterior column of spinal cord
Posterior gray horn SC
Cell body
Posterior root ganglion of spinal nerve
Second order neuron
Gracile fasiculus
Gray commissure  ventral posterior nucleus of thalamus
Gracile nucleus or cuneate nucleus of medulla oblongata
Posterior gray horn of spinal cord
Third order neuron
Primary somatosensory area of cerebral cortex in the parietal lobe
Thalamus 

25. Trigenminothalamic pathways
RIGHT SIDE
OF BODY
Trigenminothalamic pathways
LEFT SIDE
OF BODY
Primary somatosensory
area of cerebral cortex
THIRD-ORDER NEURON
Thalamus
SECOND-ORDER NEURON
TRIGEMINOTHALAMIC TRACT
FIRST-ORDER NEURON
Midbrain
Receptors for touch, pain, and temperature in the face, nasal cavity, oral cavity, and teeth
Pons
Trigeminal ganglion
Trigeminal (V) nerve
SECOND-ORDER NEURON
Medulla

26. Homunculus – Mapping the Primary Somatosensory Area

27. Primary somatosensory area

28. Primary motor area

29. Somatic Motor Pathways
Conduct motor information from cerebral cortex and brain stem to skeletal muscle.
Key Characteristics:
Decussation
Relay. The pathways consist of a chain of 2 neurons
Upper motor neurons.
Direct somatic motor pathways
Indirect somatic motor pathways
Lower motor neurons.
Synapse with skeletal muscles
Symmetry
Somatotopy

30. Somatic motor pathways - coordination and control of mvmt
LMNs receive input directly from:
Local circuit neurons (purple)
UMNs in the cerebral cortex and brain stem (green)
Neural circuits involving basal nuclei and cerebellar neurons (3 & 4) regulate activity of upper motor neurons (red)

31. The lateral corticospinal pathway
RIGHT SIDE
OF BODY
LEFT SIDE
OF BODY
Primary motor area of cerebral cortex
The lateral corticospinal pathway
Internal capsule
Midbrain
Cerebral peduncle
UPPER MOTOR NEURON
Pons
Medulla
Pyramid
Decussation (crossing) in medulla
LATERAL CORTICOSPINAL TRACT
Spinal cord
Spinal nerve
LOWER MOTOR NEURON
To skeletal muscles in the distal parts of the limbs (voluntary mvmt of limbs and trunk)
Spinal cord

32. The anterior corticospinal pathway
RIGHT SIDE
OF BODY
LEFT SIDE
OF BODY
Primary motor area of cerebral cortex
Internal capsule
The anterior corticospinal pathway
Midbrain
Cerebral peduncle
UPPER MOTOR NEURON
Pons
Medulla
Pyramid
Spinal cord
ANTERIOR CORTICOSPINAL TRACT
LOWER MOTOR NEURON
Spinal nerve
Spinal cord
To skeletal muscles in the trunk and proximal parts of the limbs

33. The corticobulbar pathway
RIGHT SIDE
OF BODY
LEFT SIDE
OF BODY
Primary motor area of cerebral cortex
Internal capsule
UPPER MOTOR NEURON
The corticobulbar pathway
CORTICOBULBAR TRACT
Cerebral peduncle
Facial (VII) nerve
Midbrain
LOWER MOTOR NEURON
To skeletal muscles of facial expression
Pons
Hypoglossal (XII) nerve
LOWER MOTOR NEURON
To skeletal muscles of the tongue
Medulla