Nervous System Central and Peripheral

1. Nervous SystemCentral and Peripheral MED 164 William Budd Medical Careers Institute

2. Objectives • Functions of nervous system • Homeostatic mechanisms • Organization of nervous system and components of each branch • Autonomic nervous system effects • Structure of a neuron • Classifications of neurons • Types of neuroglia and functions • Neuronal conduction

3. Objectives • Structure and function of a synapse • Structure and function of organs in nervous system • Common pathologies of nervous system

4. Functions of Nervous System • Control and coordination of all body systems and relates an individual to their environment • Homeostatic regulation • Seat of intellect and reasoning

5. Homeostatic Control • Sensory Input • Receptors monitor changes (stimuli) inside and outside body and information is sent to CNS by an afferent pathway • Integration and interpretation • Sensory information is processed and interpreted and a response decision is made and sent out • Motor Output • Response is sent out by efferent pathway to an effector organ

6. Nervous System Central Nervous System Peripheral Nervous System Sensory (Afferent) Motor (Efferent) • Brain • Spinal Cord Somatic Autonomic Parasympathetic Sympathetic

7. Central Nervous System • Contains the brain and spinal cord • Seat of integration and interpretation

8. Peripheral Nervous System • Consists of nervous system tissue that is outside of CNS • Primarily functions to communicate between organs and CNS • Contains two types of nerves • Spinal • 31 pairs of nerves that connect to spinal cord and transmit signal to and from spinal cord • Cranial • 12 pairs of nerves that connect to the brain and transmit information to and from brain

9. Peripheral Nervous System • Two functional subdivisions • Sensory (Afferent) • Transmits information from receptors in tissues and organs to the CNS • Motor (Efferent) • Transmits information from CNS to effector organs such as muscles and glands • Contains two subdivisions; somatic and autonomic

10. Peripheral Nervous System • Somatic nervous system contains motor fibers that transmit impulses from CNS to skeletal muscles • Commonly called the voluntary nervous system

11. Peripheral Nervous System • Autonomic Nervous System consists of motor fibers that innervate smooth muscle, cardiac muscle, and endocrine glands • Commonly called the involuntary nervous system • Contains two functional subdivisions • Sympathetic (fight or flight) • Innervated by thoracic and lumbar ganglia of spinal nerves • Parasympathetic (Resting and digesting or feed and breed) • Innervated by vagus nerve and nerves of pelvis

12. Autonomic Effects

13. Nervous Tissue • Human body contains 100 billion neurons • Neurons are specialized cells designed to receive information from other neurons or sensory receptors and transmit to other neurons, muscle cells, and/or glands • Neurons are unable to undergo mitosis • Highly active cells that are very sensitive to glucose and oxygen levels

14. Anatomy of a Neuron

15. Anatomy of a Neuron • Soma – cell body of a neuron • Somas are located in gray matter of CNS • Brain • Cerebral cortex is composed of neuronal somas • Nuclei are somas located deep in brain tissue; surrounded by white matter • Spinal cord • Cell somas are located deep to white matter in spinal cord • Groups of cell bodies in PNS are called ganglia

16. Anatomy of a Neuron • Cytoplasm • Contains numerous mitochondria • Neurons utilize large amounts of glucose and oxygem • Contains large amounts of rough ER • Sometimes called Nissi bodies

17. Anatomy of a Neuron • Neurons contain two types of cellular projections • Dendrites are short, branched projections that conduct impulses towards the soma • Neurons often contain many dendrites • Axons are long, singular processes that conduct impulses away from soma

18. Anatomy of an Axon • Axonal hillock – cone shaped region where soma tapers into axon • Telodendria – terminal branches of axon • Axon terminals – button shaped endings of telodendria • Sometimes called synaptic terminals, or synaptic knobs • Axons do not contain ribosomes, Rough ER, or Golgi bodies • Do contain an extensive cytoskeleton involved in bi-directional transport

19. Function of Axon • Axonal terminals are secretory component of axon • Neurotransmitters are stored and released into synapse from axonal terminal

20. Groups of axons • Axons are often found bundled together with other axons that share a common origin and destination • In CNS, bundles of axons are called tracts • In PNS, bundles of axons are called a nerve • Bundles of axons are supported by glial cells and in PNS protected by connective tissue

21. Functional Classification of Neurons • Two systems are used to classify neurons • Based on direction of impulse • Based on structure that is innervated and direction of impulse

22. Classification based on direction • Sensory Neurons (Afferent) • Impulses travel from sensory receptors to CNS • Motor Neurons (Efferent) • Impulses travel from CNS to effector organs (muscles or glands) • Interneurons (Association) • Connect motor and sensory neurons or between interneurons, only in CNS • Accounts for 99% of neurons in CNS

23. Classification based on tissue innervation • Four functional types of neurons found in body • Somatic neurons innervate muscles involved in voluntary activities • General somatic afferent • General somatic efferent • Visceral neurons innervate muscles involved in involuntary activities • General visceral afferent • General visceral efferent

24. Supporting Cells • CNS does not contain any connective tissue • Collectively called neuroglia (nerve glue) • 4 types in CNS • 2 types in PNS • Do not generate or transmit electrical impulses • Possess capability to divide and multiply

25. CNS Neuroglia • Microglia – Macrophages that become phagocytic upon injury to the CNS • Possibly involved in ALS and MDA • Astrocytes – Star shaped cells that are found between soma of neuron and blood vessel capillaries • Provide structural support, repair mechanisms, and metabolic functions that assist neurons

26. CNS Neuroglia • Oligodendrocyte forms myelin around CNS axons • Ependymal Cells – Cells that line cavities in brain and spinal cord • Responsible for secretion and movement of cerebrospinal fluid

27. PNS Neuroglia • Schwann cells – Responsible for formation of myelin on peripheral nervous system neurons • Satelite cells – Surround and support neuron cell bodies within ganglia

28. Myelinated Neurons • Myelinated axons have a multilayered wrapping of the plasma membrane of oligodendrocytes or schwann cells • White matter is a collection of myelinated axons in brain and spinal cord • Functions of myelination is to insulate axon and speed impulse of nerve conduction • Nodes of Ranvier are gaps in myelin sheath

29. Pathologies Caused by demyleination • Guillein-Barre Syndrome • Multiple Sclerosis • Devic’s Disease (Causes blindness) • Progressive MulitfocalLeukoencephalopathy • Transverse Myelitis

30. Cellular Conduction • Differences in electrical potentials across cell membrane creates a polarization • At rest, neurons and muscles contain large amounts of potassium inside of cell and sodium outside of cell • When stimulated, a sodium channel opens and sodium travels down its concentration gradient and electrical difference decreases (voltage moves closer to zero) • When voltage reaches a certain point, potassium channels open and potassium leaves the cell

31. Cellular Conduction • The signal continues down through the neuron • Re-polarization begins when potassium starts to leave the cell and concludes with the activation of a sodium/potassium pump that is utilized to return the cell to its starting position • Process is accomplished within a few milliseconds and occurs millions of times per minute

32. Types of stimulus • Stimuli can result in one of two types of potentials to occur • Excitatory potentials occur when the stimulus causes the inside of the cell to become less negative (depolarized • Inhibitory potentials occur when the stimulus causes the inside of the cell to become more negative (hyperpolarized)

33. How do they occur? • Depolarization occurs when sodium channels open and sodium comes into cell • Hyperpolarization occurs when potassium channels open and potassium leaves the cell or chloride channels open and chloride enters the cell

34. Polarization Muscle Cell - 70mV 30 mV Na+ Na+ Na+ Na+ Na+ 130 mV Na+ Na+ Na+ Na+ K+ K+ K+ K+ K+ K+

35. Synapses • Neuron does not touch muscles and in only very rare circumstances does it connect directly to other neurons • Two types of synapses • Electrical • Rare; occurs when two neurons connect directly together and allows current to flow directly from one neuron to another • Chemical • Most common; neuron does not connect to anything but is seperated by a synaptic cleft that must be crossed with a chemical neurotransmitter

36. Anatomy of a chemical synapse

37. Synaptic Physiology • Action potential travels down axon and causes calcium channels in pre-synaptic terminal to open and calcium rushes into neuron • Calcium causes vesicles containing neurotransmitter to fuse with cell membrane and neurotransmitter is exocytized into synaptic cleft • Neurotransmitter binds reversibly to specific receptors on post-synaptic membrane

38. 4. Neurotransmitter binding causes an ion channel in post-synaptic membrane to open • As long as neurotransmitter is bound to receptor, channel remains open. • Neurotransmitter must be removed from synapse • Degraded by specific enzymes (acetylcholine) • Removed by astrocytes (Norepinephrine) • Re-uptook back to presynaptic neuron (Serotonin)

39. Chemicals that affect synapse • Botulinum toxin • Black widow venom • Nicotine • Sarin gas • Organophosphate insecticides • Medications

40. Conditions affected by synaptic physiology • Depression • Parkinson’s disease • Myasthenia gravis • Drug addiction and alcohol

41. Meninges • Protective connective tissue covering of the brain and spinal cord • Contains three layers • Dura mater (Tough mother) – Outermost layer of meninges • Composed of two layers of tough dense connective tissue • Archanoid mater (Spider mother) – Loose middle covering that contains weblike extensions that connect to the pia mater

42. Meninges • Pia mater (Tender mother) – Delicate inner layer of meninges that contains many small blood vessels

43. Meningeal Spaces • Epidural space – Located between the dura mater and the skull/ vertebral column • In skull contains arteries • In spinal cord contains fat and veins • Subdural space – Potential space between dura mater and arachanoid mater • Subarchanoid space – Space between arachanoid mater and pia mater • Filled with cerebrospinal fluid

44. Ventricles • Fluid filled cavities within the brain • Lateral ventricles – Two ventricles; one on each side of the brain in the cerebrum • Ventricular foramen – Channel that connects the lateral ventricles to third ventricle • Third ventricle – Inferior to lateral ventricles and enclosed by diencephalon

45. Ventricles • Fourth ventricle – Dorsal to pons, ventral to cerebellum, communicates with subarchanoid space and continuous with central canal of spinal cord

48. Cerebrospinal Fluid • Fluid surrounds brain and spinal cord • Cushions brain and gives buoyancy to CNS • Effectively reduces weight of brain • Protects CNS from trauma • Aids in nourishment of nerual tissue • Produced by choroid plexus in ventricles • Choroid plexus is network of capillaries in pia mater • Blood brain barrier seperates substances in blood from brain tissue

49. Flow of CSF in CNS • CSF is made in lateral ventricles and flows to the third ventricle through the ventricular foramen • Flows through the cerebral aquaduct to the fourth ventricle • Flows to the central canal of spinal cord and down the spine • Fluid moves into the subarchanoid space of the meninges • Reabsorbed in the sagital sinus of the brain by arachanoidvilli

50. CSF and Diagnosis • CSF can be used to diagnose pathologies of the meninges and brain or used to treat some conditions • Drawn out through a procedure called a lumbar puncture