1. Week 11
The Spinal Cord & PNS

2. What’s ahead Identify structures of the spinal cord
Identify peripheral nerves
Identify components of the reflex arc

3. Activity 1: The Spinal Cord

4. The Spinal Cord Cervical spinal nerves Cervical enlargement Thoracic
Lumbar
enlargement
Lumbar
spinal nerves
Conus
medullaris
Sacral
spinal nerves
Cauda
equina

5. L2
Conus Medullaris L3 L4
Cauda Equina
(horse’s tail) L5

6. Lumbar Tap
T12
Cauda equina
Subarachnoid space L5 L4 L5

7. Spinal Cord Anatomy Spinal meninges Pia mater Arachnoid mater
Subarachnoid
space
Pia mater
Arachnoid mater
Dura mater

8. Spinal Cord Anatomy Posterior median sulcus Central canal
Anterior median fissure

9. Spinal Cord Anatomy Gray matter White matter Dorsal horn
Posterior funiculus
Lateral horn
Ventral horn
Lateral funiculus
Anterior funiculus
Gray commisure
Pia mater
Arachnoid mater
Dura mater
Gray matter = Inside, cell bodies & unmyelinated fiber tracts
White matter = Outside, myelinated fiber tracts

10. Spinal Cord / Spinal Nerve Anatomy
Dorsal Root
Dorsal Root Ganglion
Spinal Nerve
Ventral Root

11. Spinal Cord / Spinal Nerve Anatomy
Dorsal root
Dorsal root
ganglion
Spinal nerve
Dorsal ramus
Ventral ramus
to Plexus
Ventral root

12. Posterior Spinal Cord What do you suppose this is?
median
sulcus
Denticulate
ligament
Dorsal root
Arachnoid
mater
Dorsal root ganglion
Dura mater
What do you suppose this is?
Ventral root

13. How can you tell the Ventral side from the Dorsal side?

14. PMS vs. AMF
Posterior Median Sulcus
AMF
Anterior Median Fissure

15. Cross sectional anatomy of the spinal cord
Gray Matter
Dorsal horns
Sensory/inter neurons
A visual analogy
Dorsal
horn
Ventral
horn
Ventral horns
motor neurons

16. Dorsal horn Lateral horn Vental horn
Posterior median sulcus
1a ?
Dorsal horn
2a ?
Lateral horn
2b ?
Vental horn
2c ?
Anterior median fissure
1b ?

17. Regional Differences Cervical Thoracic Sacral Lumbar Cervical
enlargement
Lateral
horn
Lumbar
enlargement
Sacral
Lumbar

18. Cross sectional anatomy of the spinal cord
White Matter
fiber tracts for transmission of information
ascending (sensory) tracts
descending (motor) tracts
Posterior funiculus
Lateral funiculus
Anterior funiculus

19. Some fiber tracts in the different funiculi
Posterior funiculus:
Faciculus cuneatus and gracilis
Ascending sensory
Lateral funiculus
Spinothalamic tract
Corticospinal tract
Descending motor
Anterior funiculus

20. Spinal cord c.s. microscopic view
Central canal
Dorsal root
Dorsal root ganglion
Gray commissure
Ventral root
Dura mater

21. Dorsal root ganglion Pseudounipolar neuron cell bodies
Identify the structural classification of these neurons

22. Physiology
Posterior
In 
Anterior
 Out

23. Dorsal root: afferent, sensory
Ventral root: efferent, motor
Dorsal ramus: mixed, motor and sensory to trunk
Ventral ramus: mixed motor and sensory form nerve plexi

24. Activity 2: Nerve Plexi & Peripheral Nerves

25. Ventral Rami  Plexus  Peripheral Nerve

26. There are
31 pairs of
spinal nerves &
4 nerve plexi

27. Cervical Plexus The phrenic nerve innervates the respiratory diaphragm
“ C3,4,5 keeps the diaphragm alive!

28. Brachial Plexus

30. Nerves Arising from Thoracic Ventral Rami

31. Lumbar Plexus

32. Sacral Plexus

33. Activity 3: Human Reflex Physiology

34. Reflex Terminologies Reflex: Reflex Arc: Autonomic (Visceral) Reflex:
A rapid, predictable, involuntary motor response to a stimulus that acts to return the body to homeostasis
Mediated by the spinal cord
Reflex Arc:
The neural pathway a nerve impulse follows that mediates a reflex
(from sensory receptor  effector organ)
Autonomic (Visceral) Reflex:
Mediated through the ANS
Not subject to conscious control
Vasoconstriction/dilation, sweating, salivation, digestion, heart rate, pupil dilation/constriction
Somatic Reflex:
Involve stimulation of skeletal muscles by the somatic division of the nervous system
Subject to conscious interference

35. Reflex Arc (1) Receptor - reacts to stimulus
(2) Sensory Neurons - afferent impulses to CNS
(3) Integration centers - synapses in CNS
(4) Motor Neurons - efferent impulses from Integration centers to effector
(5) Effector - muscle or glands

36. Classifications of Sensory Receptors by Location
Exteroceptors* Interoceptors Proprioceptors*
Respond to stimuli arising outside the body:
Touch
Pain
Temperature
Pressure
Detect stretch
Respond to stimuli inside the body (viscera, vessels)

37. Proprioceptors
Stretch Reflexes
Receptor =
Proprioceptor of the muscle

38. Patellar Reflex Receptor = Proprioceptors of (?) muscle
Afferent Neuron =
Afferent fibers of (?) nerve
Integration Center = ?
Efferent Neuron =
Efferent fibers of (?) nerve
Effector=
(?) muscle

39. Patellar Reflex

40. Is the response greater or less than baseline?
Patellar Reflex
3 Tests
Simultaneous muscle activity
Mental distraction
Fatigue
Is the response greater or less than baseline?

41. Pupillary Reflex
Contralateral?
– or -
Ipsilateral?

42. Lab Activity: On the Practical: Study Spinal Cord & Peripheral Nerves
Perform Reflex experiments & analyze
On the Practical:
Identify the structures of the Spinal Cord from models and slides
Identify the Peripheral Nerves and Nerve Plexi from models
Identify the components of the Reflex Arc