Memmler’s The Human Body in Health and Disease 11 th edition

1. Memmler’s The Human Body in Health and Disease11th edition Chapter 9 The Nervous System: The Spinal Cord and Spinal Nerves

2. Role of the Nervous System Nervous system coordinates all body systems • Detects and responds to stimuli • Brain and spinal cord act as switching centers • Nerves carry messages to and from centers

3. Structural Divisions • Central nervous system (CNS) • Brain • Spinal cord • Peripheral nervous system (PNS) • Cranial nerves • Spinal nerves

4. Anatomic divisions of the nervous system.

5. Functional Divisions Somatic nervous system • Controlled voluntarily • Effectors are skeletal muscles • No further subdivisions Autonomic (or visceral) nervous system (ANS) • Controlled involuntarily • Effectors are smooth muscle, cardiac muscle, and glands • Subdivided into • Sympathetic nervous system • Parasympathetic nervous system

6. Neurons and Their Functions Neurons • Functional cells of nervous system • Highly specialized • Unique structure

7. Diagram of a motor neuron. The break in the axon denotes length. The arrows show the direction of the nerve impulse. ZOOMING IN • Is the neuron shown here a sensory or a motor neuron?

8. Structure of a Neuron Cell body • Nucleus • Other organelles Cell fibers • Dendrites • Axons • Some are protected by myelin sheath

9. Formation of a myelin sheath. • Schwann cells wrap around the axon, creating a myelin coating. (B) The outermost layer of the Schwann cell forms the neurilemma. Spaces between the cells are the nodes (of Ranvier).

10. Types of Neurons • Sensory neurons (afferent neurons) • Conduct impulses to spinal cord, brain • Motor neurons (efferent neurons) • Conduct impulses to muscles, glands • Interneurons (central or association neurons) • Conduct information within CNS

11. Nerves and Tracts • Nerve: fiber bundle within PNS • Tract: fiber bundle within CNS • Organized into fascicles • Connective tissue layers • Endoneurium • Perineurium • Epineurium

12. Neuroglia Neuroglia (glial cells) • Protect and nourish nervous tissue • Support nervous tissue • Aid in cell repair • Remove pathogens and impurities • Regulation composition of fluids around and between cells

13. The Nervous System at Work Electrical impulses sent along neuron fibers and transmitted between cells at junctions

14. The Nerve Impulse • Plasma membrane carries electrical charge (potential) • Plasma membrane is polarized (negative charge) • Membrane potential reverses, generates electrical charge (action potential) • Resting state • Depolarization • Repolarization • Sodium/potassium (Na+/K+) pump • Myelin sheath speeds conduction

15. The Synapse Junction point for transmitting nerve impulse • Axon (presynaptic cell) • Dendrite (postsynaptic cell) • Synaptic cleft • Neurotransmitters • Epinephrine (adrenaline) • Norepinephrine (noradrenaline) • Acetylcholine • Receptors

16. Neurotransmitters and Psychoactive Drugs • Psychoactive drugs affect neurotransmitter activity in the brain • Used to treat depression, anxiety, obsessive-compulsive disorder (OCD) • Selective serotonin reuptake inhibitors (Example: Prozac) • Block serotonin uptake • Others block norepinephrine, dopamine.

17. A synapse. • The end-bulb of the presynaptic (transmitting) axon has vesicles containing neurotransmitter, which is released into the synaptic cleft to the membrane of the postsynaptic (receiving) cell. (B) Close-up of a synapse showing receptors for neurotransmitter in the postsynaptic cell membrane.

18. The Spinal Cord • Links PNS and brain • Helps coordinate impulses within CNS • Contained in and protected by vertebrae

19. Spinal cord and spinal nerves. Nerve plexuses (networks) are shown. (A) Lateral view. (B) Posterior view. ZOOMING IN • Is the spinal cord the same length as the spinal column? How does the number of cervical vertebrae compare with the number of cervical spinal nerves?

20. Structure of the Spinal Cord • Unmyelinated tissue (gray matter) • Dorsal horn • Ventral horn • Gray commissure • Central canal • Myelinated axons (white matter) • Posterior median sulcus • Anterior median fissure • Ascending and descending tracts

21. The spinal cord. (A) Cross-section of the spinal cord showing the organization of the gray and white matter. The roots of the spinal nerves are also shown. (B) Microscopic view of the spinal cord in cross-section (x5).

22. The Reflex Arc • Receptor detects stimulus • Sensory neuron transmits impulses to CNS • CNS coordinates impulses and organizes response • Motor neuron carries impulses away from CNS • Effector carries out response

23. Typical reflex arc. Numbers show the sequence of impulses through the spinal cord (solid arrows). Contraction of the biceps brachii results in flexion of the arm at the elbow. ZOOMING IN • Is this a somatic or an autonomic reflex arc? What type of neuron is located between the sensory and motor neuron in the CNS?

24. Reflex Activities • Simple reflex • Rapid • Uncomplicated • Automatic • Spinal reflex • Stretch reflex

25. Medical Procedures Involving theSpinal Cord • Lumbar puncture (spinal tap) • Cerebrospinal fluid (CSF) removed for testing • Drug administration • Anesthetic (an epidural) • Pain medication

26. Diseases and Other Disorders of theSpinal Cord • Multiple sclerosis (MS) • Amyotrophic lateral sclerosis • Poliomyelitis • Tumors • Injuries • Monoplegia • Diplegia • Paraplegia • Hemiplegia • Tetraplegia

27. The Spinal Nerves • 31 pairs • Each nerve attached to spinal cord by two roots • Dorsal root • Dorsal root ganglion • Ventral root • Nerves near end of cord travel together in the cord until each exits from its respective intervertebral foramen • Mixed nerves

28. Branches of the Spinal Nerves • Cervical plexus • Phrenic nerve • Brachial plexus • Radial nerve • Lumbosacral plexus • Sciatic nerve • Dermatomes

29. Dermatomes. A dermatome is a region of the skin supplied by a single spinal nerve. ZOOMING IN • Which spinal nerves carry impulses from the skin of the toes? From the anterior hand and fingers?

30. Disorders of the Spinal Nerves • Peripheral neuritis • Sciatica • Herpes zoster • Guillain-Barré syndrome

31. The Autonomic NervousSystem (ANS) Regulates the action of glands, smooth muscles of hollow organs and vessels, and heart muscle • Preganglionic neuron connects spinal cord to ganglion • Postganglionic neuron connects ganglion to effector

32. Divisions of the Autonomic NervousSystem • Sympathetic nervous system • Parasympathetic nervous system

33. Sympathetic nervous system • Thoracolumbar area • Collateral ganglia • Celiac ganglion • Superior mesenteric ganglion • Inferior mesenteric ganglion • Adrenergic system • Activated in the four E’s: excitement, emergency, embarassment, exercise

34. Parasympathetic nervous system • Arise in craniosacral areas • Terminal ganglia • Cholinergic system

35. Autonomic nervous system. The diagram shows only one side of the body for each division. ZOOMING IN • Which division of the autonomic nervous system has ganglia closer to the effector organ?

36. Cellular Receptors • “Docking sites” on postsynaptic cell membranes Two types: • Cholinergic receptors • Nicotinic (bind nicotine) on skeletal muscle cells • Muscarinic (bind muscarine, a poison) on effector cells of PNS • Adrenergic receptors • Found on receptor cells of sympathetic nervous system • Bind norepinephrine, epinephrine

37. Functions of the Autonomic NervousSystem • Sympathetic nervous system • Fight-or-flight response • Parasympathetic nervous system • Returns body to normal • Systems generally have opposite effects on organ