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Topic 14: Spinal Cord & Peripheral Nerves

� Neurons

� What do they look like?

� How do they work?

� Neuronal and spinal organization

� What is the difference between neuron & nerve?

� How does the spine develop?

� How are nerves organized?

� How do nerves work together?

� How is the peripheral nervous system organized?

� Segmentation of the nervous system

� How are the limbs innervated?

� What are the cranial nerves & what do they do?

What do neurons look like?

� Sensory, Interneuron or Motor

� Multipolar, _____ or Pseudounipolar

Liem et al. Fig. 13-1

� ___________

� Cell body

� ___________

� Myelin sheath

Specialized Neurons

� Perkunje Cells� In cerebellum of brain

� Motor coordination

� Multipolar and highly dendritic

Liem et al. Fig. 13-1

How do neurons work? The nervous impulse

� __________________ is

all-or-none response

� ________ Potential

� Negative inside

� ______ potential

� Depolarization

� Influx of Na+

� Fast

� Repolarization

Liem et al. Fig. 13-2

Schwann Cells

� Mesodermal

� Wrap around axon

� ________________

� Small spaces between cells are

_________________

� Force AP to jump from node to node

� Speed up AP

Liem et al. Fig. 13-4

_________________

� Connections between

neurons

� Presynaptic axon

� Postsynaptic dendrite

� _________________� Dump neurotransmitter in

synaptic cleft

� Postsynaptic receptors

� Bind neurotransmitter

� Initiate action potential

� Neurotransmitters can be

Excitatory or Inhibitory

Liem et al. Fig. 13-3

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What is the anatomy of nerves?

� Many neurons

� Blood vessels

� Have a connective tissue sheath

� ______________

Liem et al. Fig. 13-4

How does the spinal cord develop?

� _____________

� Cell proliferation

� Single cell layer

� Non-neuronal

� _____________

� Neuronal cell bodies

� Becomes gray matter

� _____________

� Houses myelinated axons

� Becomes white matter

Liem et al. Fig. 13-9; vetmed.vt.edu

Spinal Morphology

� Lamprey� No well defined zones

� Muller cells are fast due to high-diameter axons

� Gnathostomes� More organized: gray &

White matter

� Many synapses in white matter

� Amniotes� Lots of white matter

� Only axons in white matter

� Pronounced ventral fissure

� Butterfly-shaped gray matter

Liem et al. Fig. 13-12

Lamprey

Frog

Alligator

Spinal Morphology

� Spinal cord runs along long axis of body

� Segmental spinal nerves

� 1 pair per vertebra

� Cauda equina posteriorly

Liem et al. Fig. 13-13

� Protected by 3 layers

� _____________ – Thin & deep

� _____________ – Well vascularized

� _____________ – Tough connective tissue

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How are spinal nerves organized?

� _________________

� Sensory neurons

� _________________

� Motor neurons

� Spinal ganglion

� _________________

� _________________

� Dorsal somatic muscles

� _________________

� Ventral somatic muscles

� Sympathetic ganglion

� Sympathetic trunk

� Visceral muscles

Liem et al. Fig. 13-13

What different types of neurons exist?

Liem et al. Table 13-3

Neuron Type Information From/To

Somatic Sensory - Pain receptors- Touch receptors- Temperature receptors

Visceral Sensory - Gut receptors- e.g. stomach stretch

Somatic Motor - Skeletal muscles

Visceral Motor - Visceral glands- Visceral muscles

Sensory neurons can be special (only in cranial nerves),

or general (in cranial & spinal nerves)

How does each neuron type enter or leave the spinal cord?

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How is the nervous system organized?

Central Nervous

System

Peripheral Nervous System

Sensory

(afferent) System

Motor (efferent)

System

Somatic Nervous

System

Autonomous

Nervous System

Sympathetic

Nervous System

Parasympathetic

Nervous System

Autonomous

Nervous System

Liem et al. Fig. 13-26

� _______________

� Flight or Fight

� Ganglion near spinal cord

� _______________

� Relaxation

� Ganglion near organ

� Organs are innervated by both

Neural Pathways

� _________________

� No brain involvement

1. ____________

2. Sensory neuron

3. ____________

4. Motor neuron

5. ____________

� Stimulation

� Inhibition

� Can you trace the structures that the impulse passes through?

Liem et al. Fig. 13-10

Neural Pathways

Temperature reception pathway

1. Receptor

2. Sensory neuron

3. _________________

4. Ascending interneuron

5. _________________

6. Descending interneuron

7. Motor neuron

8. Muscle

Liem et al. Fig. 13-11

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How are the limbs innervated?

� Pectoral fin

� ~12 anterior spinal nerves

� Pelvic fin

� ~8 more posterior spinal nerves

Liem et al. Fig. 13-15

How are the limbs innervated?

� _________________� 7 Spinal Nerves

� C4 to T2

� Innervate specific portions of front limbs

� Form a tangle near axilla

� _________________� 5 Spinal Nerves

� T12 to L4

� Innervate specific portions of the hind limbs

Liem et al. Fig. 13-17; MMG

What are cranial nerves?

� 12 anterior

segmental nerves

� Exit the brain

Liem et al. Fig. 13-18

� Sensory

� Sensory & Motor

� Motor

The

Cranial Nerves

Liem et al. Table 13-4

# Name G S G S

0 Terminal X X X Pheromone reception

I Olfactory X X X Olfactory bulb

II Optic X X X Eye

III Oculomotor X X X X Eye & iris movements

IV Trochlear X 1 X X Eye movements

V Trigeminal X X 1 X X Upper & lower jaws

VI Abducens X 2 X X Lateral rectus m.

VII Facial X X X X 2 X X Second visceral arch

VIII Statoacoustic X X X Balance & Hearing

IX Glossopharyngeal X X X X 3 X X Third visceral arch

X Vagus X X X X X 4 X X Fourth visceral arch

XI Accessory X X Trapezius mm.

XII Hypoglossal X X Tongue muscles

Lateral Line Nn. X X

Function/innervation

Where do the cranial nerves exit the brain?

� Cranial nerves exit the brain in order, anterior to

posterior

Liem et al. Fig. 13-23

� Telencephalon

� 0, I

� Diencephalon

� II

� Mesencephalon

� III, IV

� Metencephalon

� V, VI, VII, VIII

� Myelencephalon

� IX, X, XI, XII