1. The Nervous System
The Spinal Cord-part of the CNS found within the spinal column
The spinal cord communicates with the sense organs and muscles below the level of the head
Bell-Magendie Law-the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information to the muscles and glands
Dorsal Root Ganglia-clusters of neurons outside the spinal cord

2. Spinal Cord Extends from foramen magnum to second lumbar vertebra
Segmented
Cervical
Thoracic
Lumbar
Sacral
Gives rise to 31 pairs of spinal nerves
Not uniform in diameter throughout length

3. The spinal cord and spinal nerves

4. Gross anatomical structures of the spinal cord
A. Two enlargements of the spinal cord occur in
regions where the amount of gray matter is greater than others; regions of sensory/motor control of the limbs.
1. Cervical enlargement - nerves supply the shoulder and upper limbs;
2. Lumbar enlargement - nerves supply the pelvis and the lower limb.
B. Conus medullaris: region at the end of the spinal cord where the tissue tapers into a cone shape; approximately in region of L2.
C. Filum terminale: connective tissue, continuous with the pia mater of the spinal cord.
D. Cauda equina: extension of nerves exiting from the base of the spinal cord; appears like a horse's tail.

5. Cross Section of Spinal Cord

6. Cross Section of Spinal Cord
Gray matter:
Neuron cell cell bodies, dendrites, axons
‘Horns’:
Posterior (dorsal)
Anterior (ventral)
Lateral
Commissures:
Gray: Central canal
White
White matter:
Myelinated axons forming nerve tracts
Fissure and sulcus
Three columns:
Ventral
Dorsal
Lateral
(see later for white matter
pathways)

7. Spinal Cord
In the spinal cord, the grey matter is found in the centre (the butterfly shape) and the white matter surrounds it. The opposite arrangement is found in the cortex of the brain. Notice the surrounding dura mater .

8. See ANS
lecture 4

9. intermingling / merging of nerves and subsequent re-organisation
‘Plexus’:
intermingling / merging of nerves and subsequent re-organisation
--> distribution of peripheral nerves is different from that of spinal nerves 6

11. Dermatomal Map
Skin area supplied with sensory innervation by spinal nerves
Equivalent for motor output to muscle groups:
Myotome

12. spinal cord brain CNS PNS The Organisation of the Nervous System
spinal nerves (31p) cranial nerves (12p)
PNS
sensory motor
motor sensory
Sensory information has to be passed on from the spinal cord to the brain
ascending pathways (red)
Commands from the brain have to be sent out to the PNS
descending pathways (green)

13. Ascending (afferent) spinal tracts:
Pathways that carry sensory information to a conscious level
Basic principle of information flow:
receptor
(e.g. pain receptor in skin)
primary sensory neurone
(cell body in dorsal root ganglia)
second order neurone
(in the spinal cord or brainstem)
third order neurone
(in thalamus)
target area: cortex
somatosensory (somatic sensory) area
(postcentral gyrus) of the cortex

14. Example
Conscious
perception
Light touch

15. Sensory information travels to the brain via 3 main pathways: To somatosensory cortex (see lecture 3!): 1) Spinothalamic system (lateral and anterior tract): somatosensory information to brain:pain and temperature, light touch, pressure, tickle, itch 2) Dorsal column / medial lemniscus: Two-point discrimination, proprioception, pressure, vibration To cerebellum: 3) Spinocerebellar system (posterior and anterior): proprioception, for comparator function (see lecture 2!)

16. Sensory Nerve Tracts
Transmit action potentials from periphery to brain
Each pathway involved with specific modalities
First half of word indicates origin, second half indicates termination

17. Pain
Types
Referred: Sensation in one region of body that is not source of stimulus
Phantom: Occurs in people who have appendage amputated or structure removed as tooth
Chronic: Not a response to immediate direct tissue injury

18. Descending (efferent) spinal tracts:
Pathways that carry motor commands from the brain to the muscle
2 Systems: direct (pyramidal) and indirect (extrapyramidal)
Basic principle of information flow:
1) Pyramidal System
initiation in (pre-) motor cortex
upper motor neurone
(from motor cortex to brain stem
or spinal cord via pyramids)
lower motor neurone
(target: muscle)
2) Extrapyramidal System
originate in motor cortex and cerebellum(4 different pathways)
involve projections via brainstem nuclei
lower motor neurones
(target: muscle)
Unconscious movements
(posture, balance, reflexes)
Functions:
Muscle tone,
voluntary movement

19. Pyramidal system

20. * * SUMMARY: PATHWAYS IN THE SPINAL CORD
Ascending (afferent) pathways (sensation)
Descending (efferent) pathways (motor commands) * *

21. Spinal Cord Anatomy Central canal filled with cerebrospinal fluid
Figure 7.19
Slide 7.53c
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

22. Spinal Cord Anatomy Meninges cover the spinal cord
Nerves leave at the level of each vertebrae
Dorsal root
Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system
Ventral root
Slide 7.54
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

23. Peripheral Nervous System
Nerves and ganglia outside the central nervous system
Nerve = bundle of neuron fibers
Neuron fibers are bundled by connective tissue
Slide 7.55
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

24. Structure of a Nerve Endoneurium surrounds each fiber
Groups of fibers are bound into fascicles by perineurium
Fascicles are bound together by epineurium
Figure 7.20
Slide 7.56
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

25. Classification of Nerves
Mixed nerves – both sensory and motor fibers
Afferent (sensory) nerves – carry impulses toward the CNS
Efferent (motor) nerves – carry impulses away from the CNS
Slide 7.57
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

26. Spinal Nerves
There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs
Slide 7.63
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

27. Spinal Nerves Slide 7.64 Figure 7.22a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

28. Autonomic Nervous System
The involuntary branch of the nervous system
Consists of only motor nerves
Divided into two divisions
Sympathetic division
Parasympathetic division
Slide 7.67
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

29. Comparison of Somatic and Autonomic Nervous Systems
Figure 7.24
Slide 7.69
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

30. Anatomy of the Autonomic Nervous System
Figure 7.25
Slide 7.73
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

31. Autonomic Functioning
Sympathetic – “fight-or-flight”
Response to unusual stimulus
Takes over to increase activities
Remember as the “E” division = exercise, excitement, emergency, and embarrassment
Slide 7.74a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

32. Autonomic Functioning
Parasympathetic – housekeeping activites
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division - digestion, defecation, and diuresis
Slide 7.74b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

33. Development Aspects of the Nervous System
The nervous system is formed during the first month of embryonic development
Any maternal infection can have extremely harmful effects
The hypothalamus is one of the last areas of the brain to develop
Slide 7.75a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

34. Development Aspects of the Nervous System
No more neurons are formed after birth, but growth and maturation continues for several years (new evidence!)
The brain reaches maximum weight as a young adult
However, we can always grow dendrites!
Slide 7.75b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings