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 No. & Name Type Function I. Olfactory sensory smell
II.Optic
vision
III. Oculomotor
motor
Most eyeball movements
IV. Trochlear
Eyeball movements

6. The Cranial Nerves No. & Name Type Function V. Trigeminal Mixed
Sensory: face
Motor: chewing
VI. Abducens
motor
Lateral eyeball movements
VII. Facial
Sensory: taste Motor: facial expression
VIII. Vestibulocochlear
Sensory: balance & hearing

7. The Cranial Nerves No. & Name Type Function IX. Glosso- pharyngeal
mixed
Sensory: taste
Motor: swallowing
X. Vagus
Sensory: Viscera
Motor: parasymp. to above muscles
XI. Accessory
motor
Muscles of neck
XII. Hypoglossal
Muscles of tongue esp. speech

8. The Cranial Nerves

9. Spinal Nerves 31 pairs of nerves coming off the spinal cord.
They are all mixed nerves – i.e. contain both 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 Nerve Root Plexus Area supplied C1 – C4
(C3-C5 = phrenic)
Cervical
Scalp & neck skin, diaphragm
C5 - T1
Brachial
Arm
T2 - T11
No plexus formed
Intercostal nerves
Serve chest wall
T12 – L4
Lumbar
Abdominal wall, anteromedial thigh
L4 – S4
Sacral
Posterior thigh, lower leg and foot

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 center2
Sensory neuron 3
Integration center 1
Receptor 4
Motor neuron
Skin 5
Effector
Interneuron
Figure 13.1