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Anatomy of Spinal Nerves

Anatomy of Spinal Nerves. The Peripheral Nervous System. Introduction: PNS – all neural structures outside the brain and spinal cord. Provides links to and from the external environment . Peripheral Nervous System. Structural division = cranial nerves & spinal nerves.

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Anatomy of Spinal Nerves

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  1. Anatomy of Spinal Nerves

  2. The Peripheral Nervous System Introduction: • PNS – all neural structures outside the brain and spinal cord. • Provides links to and from the external environment.

  3. Peripheral Nervous System Structural division = cranial nerves & spinal nerves. Functional divisions = Afferent (sensory) & Efferent (motor).

  4. The Cranial Nerves • 12 pairs of nerves – first two arise from forebrain and remaining 10 arise from the brain stem • Numbered 1 to 12 from anterior to posterior • Names indicate primary functions or areas served • Some are mixed nerves; some are purely sensory; some are purely motor (although motor nerves may carry some afferent fibres from proprioceptors)

  5. The Cranial Nerves

  6. The Cranial Nerves

  7. The Cranial Nerves

  8. The Cranial Nerves

  9. Spinal Nerves • 31 pairs of nerves coming off the spinal cord. • They are all mixed nerves – i.e. containboth afferent (sensory) and efferent (motor) fibres. • Supply all parts of the body except for the head and some areas of the neck. • Named according to their point of emergence from the spinal cord.

  10. Spinal Nerves

  11. Mixed Spinal Nerves Structurally, a spinal nerve attaches to the spinal cord via: • A Ventral Root – which attaches to the anterior horns of grey matter & • A Dorsal Root – which attaches to the posterior horns of grey matter. Note: The dorsal root is characterised a swelling (the Dorsal Root Ganglion)

  12. Mixed nerves

  13. Mixed Spinal Nerves Functionally: Ventral root – carries sensory input (messages in) Dorsal Root – carries motor output (messages out)

  14. Distribution of Spinal Nerves Spinal nerves branch into several rami. • Dorsal Ramus – supplies the skin and deep muscles of the back • Ventral Ramus – supplies superficial back muscles, lateral & anterior trunk, limbs • Rami Communicantes – serve visceral organs (part of Autonomic system)

  15. Spinal Nerves

  16. Spinal Nerve Plexuses All ventral rami except T2-T12 form interlacing nerve networks called plexuses. (There are 4 nerve Plexuses). This is achieved by small branches joining with those of adjacent nerves Each resulting nerve of a plexus contains fibers from several spinal nerves. Damage to one spinal segment cannot completely paralyze a muscle.

  17. Nerve Plexuses

  18. Eg: Lumbar Plexus

  19. Reflexes • Reflex – a rapid, unconscious response to a stimulus. examples - stretch reflex; flexor (withdrawal) reflex • A Reflex Arc is a simple neural pathway by which sensory impulses from receptors cause a response in effectors without necessarily travelling to the brain

  20. Components of a Reflex Arc • Receptor – responds to stimulus • Sensory Neuron – transmits message to CNS • Integration Centre (within CNS) – link between sensory and motor neurons • Motor Neuron – impulse transmitted from CNS to effector • Effector – muscle or gland which responds to the nerve impulse

  21. Characteristics of reflexes • Somatic reflex – activates skeletal muscle • Autonomic reflex – activates visceral muscle • Note: Although inborn; most reflexes are subject to modification through learning & conscious effort • Primary Function = protection

  22. Reflex Arc Spinal cord (in cross-section) Stimulus Integration center 3 Sensory neuron 2 Receptor 1 Motor neuron 4 Interneuron Effector 5 Skin Figure 13.1

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