The Spinal Cord and Spinal Nerves

1
Chapter 13

• The Spinal Cord and Spinal Nerves

2
Functions of the nervous system

• Sensory (input)
• Light
• Sound
• Touch
• Temperature
• Taste
• Smell
• Internal Chemical
• Pressure
• Stretch

3
Functions of the nervous system (contd)

• Integration
• Integration means making sense of sensory input.
  Analyzing stimuli based on experience, learning,
  emotion instinct and reacting in a useful way
  (you hope).
• Motor (output)
• The response to the sesnsory input and subsequent
  integration. Sending signals to the muscles and
  other organs of the body instructing them how to
  respond to the stimuli.

4
Nervous System Organization
5
The Spinal Cord Nerves

• The spinal cord is part of the Central Nervous
  System.
• The spinal nerves are part of the Peripheral
  Nervous System.
• The lowest level of integration occurs in the
  spinal cord and peripheral ganglia.

6
Spinal cord anatomythe meninges
Fig. 13.01
7
Spinal cord gross anatomy
Fig. 13.02
8
Cross section of the spinal cord
Fig. 13.03
9
Functional arrangement of the spinal cord tissues
Fig. 13.04
10
White Matter in the Spinal Cord

• Fibers run in three directions ascending,
  descending, and transversely
• Divided into three funiculi (columns)
  posterior, lateral, and anterior
• Each funiculus contains several fiber tracks
• Fiber tract names reveal their origin and
  destination
• Fiber tracts are composed of axons with similar
  functions

11
White Matter Pathway Generalizations

• Pathways decussate (switch sides)
• Most consist of two or three neurons
• Most exhibit somatotopy (precise spatial
  relationships)
• Pathways are paired (one on each side of the
  spinal cord or brain)

12
(No Transcript)
13
Main Ascending Pathways

• Fibers from touch and pressure receptors form
  collateral synapses with interneurons in the
  dorsal horns
• The nonspecific and specific ascending pathways
  send impulses to the sensory cortex
• These pathways are responsible for discriminative
  touch and conscious proprioception
• The spinocerebellar tracts send impulses to the
  cerebellum and do not contribute to sensory
  perception

14
Nonspecific Ascending Pathway

• Nonspecific pathway for pain, temperature, and
  crude touch within the lateral spinothalamic tract

Figure 12.33b
15
Specific and Posterior Spinocerebellar Tracts

• Specific ascending pathways within the fasciculus
  gracilis and fasciculus cuneatus tracts, and
  their continuation in the medial lemniscal tracts
  
• The posterior spinocerebellar tract

16
Specific and Posterior Spinocerebellar Tracts
Figure 12.33a
17
Descending (Motor) Pathways

• Descending tracts deliver efferent impulses from
  the brain to the spinal cord, and are divided
  into two groups
• Direct pathways equivalent to the pyramidal
  tracts
• Indirect pathways, essentially all others
• Motor pathways involve two neurons (upper and
  lower)

18
The Direct (Pyramidal) System

• Direct pathways originate with the pyramidal
  neurons in the precentral gyri
• Impulses are sent through the corticospinal
  tracts and synapse in the anterior horn
• Stimulation of anterior horn neurons activates
  skeletal muscles
• Parts of the direct pathway, called corticobulbar
  tracts, innervate cranial nerve nuclei
• The direct pathway regulates fast and fine
  (skilled) movements

19
The Direct (Pyramidal) System
Figure 12.34a
20
Indirect (Extrapyramidal) System

• Includes the brain stem, motor nuclei, and all
  motor pathways not part of the pyramidal system
• This system includes the rubrospinal,
  vestibulospinal, reticulospinal, and tectospinal
  tracts
• These motor pathways are complex and
  multisynaptic, and regulate
• Axial muscles that maintain balance and posture
• Muscles controlling coarse movements of the
  proximal portions of limbs
• Head, neck, and eye movement

21
Indirect (Extrapyramidal) System
Figure 12.34b
22
Extrapyramidal (Multineuronal) Pathways

• Reticulospinal tracts maintain balance
• Rubrospinal tracts control flexor muscles
• Superior colliculi and tectospinal tracts mediate
  head movements

23
Basic components of a reflex arc
Fig. 13.05
24
A stretch reflexThe patellar reflex
Its monosynaptic!
Fig. 13.06
25
Tendon reflex
Fig. 13.07
Its polysynaptic!
26
Flexor (withdrawal) reflex
Fig. 13.08
27
Crossed extensor reflex
Fig. 13.09
28
Spinal Nerves
Fig. 13.10a
29
Spinal nerves

• Thirty-one pairs of mixed nerves arise from the
  spinal cord and supply all parts of the body
  except the head
• They are named according to their point of issue
• 8 cervical (C1-C8)
• 12 thoracic (T1-T12)
• 5 Lumbar (L1-L5)
• 5 Sacral (S1-S5)
• 1 Coccygeal (C0)

30
Spinal cord gross anatomy
Fig. 13.02
31
Branches of spinal nerves in the thoracic spine
Fig. 13.11
32
Branches of nerve roots
33
Nerve plexuses

• Fibers travel to the periphery via several
  different routes
• Each muscle receives a nerve supply from more
  than one spinal nerve
• Damage to one spinal segment cannot completely
  paralyze a muscle

34
The cervical plexus
Fig. 13.12
35
The brachial plexus
Fig. 13.13a
36
Nerves of the brachial plexus
Fig. 13.13b
37
Some common injuries to the brachial plexus
Fig. 13.14
38
Nerves of the lumbar sacral plexuses
Fig. 13.15b
39
The lumbar plexus
40
The sacral plexus
Fig. 13.16
41
Whats a damn dermatome?
Fig. 13.17
42
Spinal Cord Trauma Paralysis

• Paralysis loss of motor function
• Flaccid paralysis severe damage to the ventral
  root or anterior horn cells
• Lower motor neurons are damaged and impulses do
  not reach muscles
• There is no voluntary or involuntary control of
  muscles

43
Spinal Cord Trauma Paralysis

• Spastic paralysis only upper motor neurons of
  the primary motor cortex are damaged
• Spinal neurons remain intact and muscles are
  stimulated irregularly
• There is no voluntary control of muscles

44
Spinal Cord Trauma Transection

• Cross sectioning of the spinal cord at any level
  results in total motor and sensory loss in
  regions inferior to the cut
• Paraplegia transection between T1 and L1
• Quadriplegia transection in the cervical region

45
Spinal cord transection
46
Poliomyelitis

• Destruction of the anterior horn motor neurons by
  the poliovirus
• Early symptoms fever, headache, muscle pain and
  weakness, and loss of somatic reflexes
• Vaccines are available and can prevent infection

47
Some effects of Polio
48
Amyotrophic Lateral Sclerosis (ALS)

• Lou Gehrigs disease neuromuscular condition
  involving destruction of anterior horn motor
  neurons and fibers of the pyramidal tract
• Symptoms loss of the ability to speak, swallow,
  and breathe
• Death often occurs within five years
• Linked to malfunctioning genes for glutamate
  transporter and/or superoxide dismutase

49
Some Famous Victims of ALS
Lou Gehrig
Steven Hawking, renowned physicist
50
Axonal degeneration of motor neurons evident in
lateral corticospinal (pyramidal) pathways,
especially in the loss of myelinated fibers of
the corticospinal tracts