2. Organization of Somatic Nervous system Spinal nerve and Reflex arc Dr. Shaheen Haroon Rashid

3. OBJECTIVES 1. Recall various components of somatic nervous system. 2. Explain structure of typical spinal nerve. 3. Describe reflex arc. 4. Identify clinical application.

4. Nervous System Nervous System 1.CNS 2.PNS 1.CNS 2.PNS 1. SOMATIC 2. AUTONOMIC 1. Brain 2. Spinal Cord

7. Somatic nervous system (SNS) All parts of the nervous system outside of the brain and spinal cord 1. Somatic System: Links spinal cord with body and sense organs; controls voluntary behavior 2. Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressure 3. Enteric System

8. Functional Classification BRAIN SPINAL CORD (CNS) PNS AFFERENT NERVES EFFERENT NERVES EXTERO- RECEPTORS INTERO- RECEPTORS SOMATICAUTONOMIC EFFECTOR ORGANS SKELETAL MUSCLES SMOOTH AND CARDIAC MUSCLES AND GLANDS

10. Nerves Spinal nerves 1.Form lateral to intervertebral foramen A.Where dorsal and ventral roots unite B.Then branch and form pathways to destination Motor nerves--- first branch 1. White ramus Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system 2. Gray ramus Unmyelinated nerves, Return from sympathetic ganglion to rejoin spinal nerve Peripheral Distribution of Spinal nerve

12. Spinal Nerves. 1. Based on vertebrae where spinal nerves originate 1. Positions of spinal segment and vertebrae change with age 1. Cervical nervesAre named for inferior vertebra All other nerves Are named for superior vertebra

13. Spinal nerves continued 1. Note: cervical spinal nerves exit from above the respective vertebra 1. Spinal nerve root 1 from above C1 2. Spinal nerve root 2 from between C1 and C2, etc. 2. Clinically, for example when referring to disc impingement, both levels of vertebra mentioned, e.g. C6-7 disc impinging on root 7 3. Symptoms usually indicate which level

14. Peripheral Nerves 1.Epineurium wraps entire nerve 2.Perineurium wraps fascicles of tracts 3.Endoneurium wraps individual axons

15. Nerve structure 1. Nerves are only in the periphery 2. Cable-like organs in PNS = cranial and spinal nerves 3. Consists of 100-100,000 of myelinated + unmyelinated axons (nerve fibers)+ connective tissue + blood vessels 4. Support Cells of the PNS Satellite cells ---Protect neuron cell bodies Schwann cells---Form myelin sheath

16. Morphology of neuron Two parts Cell body (soma) Processes Dendrites Axon 1.membrane 2.nucleus Presynaptic terminals. terminal (bouton / button)

17. AXON 1.Plasmalemma--axolemma 2.Cytoplasm--axoplasm 3. Axon hillock; 3. Axon hillock;Origin No protein synthesis 4. No rough ER--No protein synthesis 5. Axon terminal ( mitochondria,microtubues, Neurofilaments,) 6 6. Chromatophilic----- no Nissl body

18. FUNCTIONAL PARTS OF AXON 1. Processes 1. Processes Integration zone 2.Axon hillock 1 ST portion of the axon plus the region of the cell body fro m which the axon leaves 1 ST portion of the axon plus the region of the cell body fro m which the axon leaves Neuron’s trigger zone 3. Nerve fiber 3. Nerve fiber Single, elongated tubular extension Single, elongated tubular extension that conducts AP away from the cell that conducts AP away from the cell Conducting zone of the neuron Conducting zone of the neuron 4..Collaterals 4..Collaterals Side branches of axon Side branches of axon 5.Axon terminals 5.Axon terminals Release chemical messengers other cells with which they come into close Release chemical messengers other cells with which they come into close Output zone of the neuron Output zone of the neuron

19. REFLEX = reflection is an involuntary, immediate, automatic and stereotyped response to a specific sensory stimulation.

20. Classification 1. Clinical 2. Physiological 3. Number of synapses 4. Site 5. Anatomical 6. Development 7. Functional 8. On purposes 9. Response is confined 10. Depending on the part involved 11. Character of the response 12. Other reflexes

21. SIGNIFICANCE HOMEOSTASIS (autonomic reflexes) 1. TONE DURING RESTING STATE 2. TONE DURING TENSE MOTOR ACTIVITY 3. POSTURE 4. EQUILIBRIM 5. EXECUTION OF MOVEMENTS 6. SMOOTHNESS 7. DAMPNESS during resting, walking, running, states 8. ROLE AS PROPRIOCEPTOR( unconcouscious+ concious kinaesthetic sensations)

22. R-SIM Reflex arc pathway 1. R receptor neuron receives the stimuli 2. S sensory neuron passes the impulse on 3. I interneuron at the spinal cord processes 4. M motor neuron acts

23. Simplified reflex arc stimulus

24. receptor Simplified reflex arc

25. stimulus receptor sensory neurone Simplified reflex arc

26. stimulus receptor sensory neurone spinal cord of central nervous system Simplified reflex arc

27. stimulus receptor sensory neurone spinal cord of central nervous system relay neurone Simplified reflex arc

28. stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone Simplified reflex arc

29. stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone effector Simplified reflex arc

30. stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone effector response Simplified reflex arc

31. Spinal Reflexes 1. Somatic reflexes mediated by the spinal cord are called spinal reflexes 2. These reflexes may occur without the involvement of higher brain centers 3. Additionally, the brain can facilitate or inhibit them

32. R 3 Inputs to Alpha Motor Neurons 31 (3) Spinal interneuron DRG (1) Afferent (sensory) neuron (2) Upper motor neurons

33. Monosynaptic Reflexes

34. Stimulus Biceps (flexor) contracts Hand withdrawn Triceps (extensor) relaxes Ascending pathway to brain Response Integrating center (spinal cord) Thermal pain receptor in finger Efferent pathway Effector organs = Excitatoryinterneuron =Inhibitory interneuron = Synapse = Stimulates =Inhibits Afferent Pathway

35. UMN lesions 1.Weakness, paralysis 2.Spasticity 3. tendon reflexes 4.+ve Babinski sign 5.Little,if muscle atrophy 6.No fasiculation LMN lesions 1.weakness, paralysis 2.flaccidity, hypotonia 3. tendon reflexes 4. -ve Babinski sign 5.Muscle atrophy 6.Fasiculation of muscle

36. UMN v LMN Cortex UMN LMN Muscle Spasticity Flaccidity

37. Reflex testing 0 = ABSENT 1+ = HYPOREFLEXIA 2+ = NORMAL 3+ = HYPERREFLEXIA 4+ = HYPERREFLEXIA & CLONUS

38. SPINAL SHOCK Spinal shock is a state of transient physiological (rather than anatomical) reflex depression of cord function below the level of injury with associated loss of all sensori-motor functions. An initial increase in blood pressure is noted due to the release of catecholamines, followed by hypotension.

39. Shingles ( of the herpes family) In dorsal root ganglia and cranial nerves Initial infection: chicken pox virus Peripheral Neuropathy Regional loss of sensory or motor function Due to trauma or compression R metabolic causes