The nervous system

1. The nervous system

2. *The Nervous System: Overview • Swift, brief response to stimuli • Monitors internal & external environment • Integrates sensory information • Coordinates voluntary & involuntary responses of other systems

3. Organization • Central Nervous System (CNS) • Processes data and transmits commands • Intelligence, memory, emotion • Consists of: • Brain • Spinal cord • Peripheral Nervous System (PNS) • All neural tissue outside of the CNS • “the highway” of communication

4. Organization, ctd. • PNS • Afferent division • Carries info from receptors to CNS • Efferent division • Carries commands from CNS to muscles, glands, adipose tissue in body • Divided into: • Somatic Nervous System (SNS) – skel musc. contraxns • Autonomic Nervous System (ANS) – automatic stuff like smooth & cardiac muscle, glandular secretion, and adipose tissue…divided into: • Sympathetic Nervous System • Parasympathetic Nervous System

5. Peripheral nervous system (PNS) Central nervous system (CNS) Cranial nerves and spinal nerves Brain and spinal cord Communication lines between the CNS and the rest of the body Integrative and control centers Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory nerve fibers Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Conducts impulses from receptors to the CNS Somatic sensory fiber Autonomic nervous system (ANS) Somatic nervous system Skin Visceral motor (involuntary) Somatic motor (voluntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Conducts impulses from the CNS to skeletal muscles Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Parasympathetic division Mobilizes body systems during activity Conserves energy Promotes house- keeping functions during rest Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) division of PNS Bladder Parasympathetic motor fiber of ANS Motor (efferent) division of PNS Figure 11.2

6. Figure 8.2

8. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Impulse direction Nucleus Node of Ranvier Nissl bodies Axon terminals (secretory region) Axon hillock Schwann cell (one inter- node) Neurilemma (b) Terminal branches Figure 11.4b

9. Figure 8.3

10. *Cellular Organization • Neurons (carry electrical impulses) • Cannot divide (lack centrioles) • Neuroglia (supportive cells) • Regulate environment • Provide framework • Phagocytic • Smaller but more numerous • Can divide

11. *Classification of Neurons Structural Functional Sensory neurons ~10 mil. Motor neurons ~500,000 Interneurons ~20 billion! • Pyrimidal Cell found in brain • Multipolar • Motor neurons • Unipolar • Most sensory neurons • Bipolar • Some special sensory organs – sight, smell, hearing

12. *Sensory Neurons • Form afferent division of PNS • Receive info from sensory receptors • Monitor external and internal envts, then relay to CNS • Somatic sensory receptors • External receptors: touch, temp, pressure, sight, etc. • Proprioceptors: monitor position and movement • Visceral (internal) receptors • Monitor digestion, respiration, CV, etc. and taste, deep pressure, and pain

13. *Motor Neurons • Form efferent division of PNS • Send messages to effectors (which DO something) • Somatic motor neurons (SNS) • Visceral motor neurons (ANS)

14. *Interneurons • Located in CNS only • Connect other neurons • Distribute info and coordinate activity • Also play a role in planning, memory, and learning

15. Figure 8.4

16. Neuroglia -- CNS Cell types: • Astrocytes • lg., numerous, maintain blood-brain barrier, repairs • Oligodendrocytes • Insulate axons (white matter/gray matter) • Microglia • small, rare phagocytes • Ependymal • line CNS cavities

17. Neuroglia • PNS Cell types: • Satellite cells • Surround and support neural cell bodies • Schwann cells • Myelinate axons outside of CNS • Demyelination

18. Schwann cell plasma membrane A Schwann cell envelopes an axon. 1 Schwann cell cytoplasm Axon Schwann cell nucleus 2 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. Neurilemma 3 Myelin sheath (a) Myelination of a nervefiber (axon) Figure 11.5a

19. Anatomical Organization • PNS • Cell bodies (gray matter) located in ganglia • Axons (white matter) bundled together into nerves • CNS • Collection of cell bodies with common function = center • Center with discrete boundary = nucleus • Neural Cortex: thick layer of gray matter • Columns made of tracts (bundles of axons of CNS) • Pathways link centers to rest of body

20. *Membrane Potential • All undisturbed cells are polarized • Outside of cell has + charge, inside has – • This is a potential difference, called membrane potential • Unit = Volt (V) [cell membrane potential usu. measured in millivolts, or mV • “Normal,” or undisturbed cell’s membrane potential = resting potential • In neurons, resting potential is approximately -70mV • Why is there a potential in resting cells?

21. * • https://www.youtube.com/watch?v=_bPFKDdWlCg Sodium Potassium Pump https://www.youtube.com/watch?v=OZG8M_ldA1M Crash Course Action Potential https://www.youtube.com/watch?v=HYLyhXRp298 Action Potential Bozeman

22. Figure 8.7

23. 1 6 2 5 3 4 [Na+] high [K+] low Na+ Na+ Na+ Na+ Na+ ATP [Na+] low [K+] high P Na+ ADP Na+ binding stimulates phosphorylation by ATP. Cytoplasmic Na+ binds to the sodium-potassium pump. CYTOPLASM Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside. Na+ Na+ Na+ K+ P K+ K+ is released and Na+ sites are receptive again; the cycle repeats. K+ K+ K+ K+ Loss of the phosphate restores the protein’s original conformation. Extracellular K+ binds to the protein, triggering release of the Phosphate group. Active Transport EXTRACELLULAR FLUID • The sodium-potassium pump • Is one type of active transport system P P i

24. *What happens when it changes? • Any substance that alters permeability of membrane or alters the activity of pumps in the membrane • Exposure to chemicals • Mechanical changes • Temperature changes • Change in extracellular fluid • Change in resting potential can have an immediate effect

25. Vocab • Depolarization • Polarization • Graded potential • Ex: goblet/gland cell • Action potential • Skeletal muscles • Axons of neurons • Threshold • Trigger analogy • All – or – none principle

26. *Neural Communication • Info travels thru action potentials (=electrical or nerve impulses) • At end of axon, info (neurotransmitters) is passed to another neuron or to an effector

27. https://www.youtube.com/watch?v=VitFvNvRIIY The Synapse Bozeman

28. *Neurotransmitters • A single neurotransmitter may bind specifically to more than a dozen different receptors • Receptor activation and postsynaptic response cease when neurotransmitters are cleared from the synaptic cleft • Neurotransmitters are removed by simple diffusion, inactivation by enzymes, or recapture (reabsorption) into the presynaptic neuron

29. PRESYNAPTIC NEURON Figure 48.18 Neurotransmitter Neurotransmitter receptor Inactivating enzyme POSTSYNAPTIC NEURON Enzymatic breakdown of neurotransmitter in the synaptic cleft (a) Neurotransmitter Neuro- transmitter transport channel Neurotransmitter receptor (b) Reuptake of neurotransmitter by presynaptic neuron

30. *The Synapse • Presynaptic neuron—conducts impulses toward the synapse • Postsynaptic neuron—transmits impulses away from the synapse

31. Figure 48.18a PRESYNAPTIC NEURON Neurotransmitter Neurotransmitter receptor Inactivating enzyme POSTSYNAPTIC NEURON Enzymatic breakdown of neurotransmitter in the synaptic cleft (a)

32. Figure 48.18b Neurotransmitter Neuro- transmitter transport channel Neurotransmitter receptor Reuptake of neurotransmitter by presynaptic neuron (b)

33. Acetylcholine • Acetylcholine is a common neurotransmitter in vertebrates and invertebrates • It is involved in muscle stimulation, memory formation, and learning • Vertebrates have two major classes of acetylcholine receptor, one that is ligand gated and one that is metabotropic

34. A number of toxins disrupt acetylcholine neurotransmission • These include the nerve gas, sarin, and the botulism toxin produced by certain bacteria • Acetylcholine is just one of more than 100 known neurotransmitters • The remainder fall into four classes: amino acids, biogenic amines, neuropeptides, and gases

35. Table 48.2

36. Table 48.2a

37. Table 48.2b

38. Table 48.2c

39. Amino Acids • Amino acid neurotransmitters are active in the CNS and PNS • Known to function in the CNS are • Glutamate • Gamma-aminobutyric acid (GABA) • Glycine

40. Biogenic Amines • Biogenic amines include • Epinephrine • Norepinephrine • Dopamine • Serotonin • They are active in the CNS and PNS

41. Neuropeptides • Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters • Neuropeptides include substance P and endorphins, which both affect our perception of pain • Opiates bind to the same receptors as endorphins and can be used as painkillers

42. Gases • Gases such as nitric oxide (NO) and carbon monoxide (CO) are local regulators in the PNS • Unlike most neurotransmitters, NO is not stored in cytoplasmic vesicles, but is synthesized on demand • It is broken down within a few seconds of production • Although inhaling CO can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter

43. Neurotransmitter overview • https://www.youtube.com/watch?v=ThsT8HOeOtQ

44. Figure 8.15

45. PNS: Anatomy • Peripheral Nerves, ctd • Spinal Nerves • Connect to the spinal cord • 31 pairs, ea monitors a dermatome

46. *Reflexes • Reflex arc • Wiring of a single reflex • Is this an example of positive or negative feedback? • Types of reflexes • Monosynaptic – sensory neuron synapses directly on motor neuron • Ex: stretch reflex used by docs to test general condition of spinal cord, peripheral nerves, and muscles. • Polysynaptic reflexes – contain interneurons, so longer delay between stimulus and response • Withdrawal reflex • Flexor reflex

47. *Reflex Arc* • Components of a reflex arc (neural path) • Receptor—site of stimulus action • Sensory neuron—transmits afferent impulses to the CNS • Integration center—either monosynaptic or polysynaptic region within the CNS • Motor neuron—conducts efferent impulses from the integration center to an effector organ • Effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

48. Figure 8.28

49. Stimulus Skin Interneuron 1 Receptor 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (in cross section) Figure 13.14

50. The patellar (knee-jerk) reflex—a specific example of a stretch reflex 2 Quadriceps(extensors) 3a 3b 3b 1 Patella Musclespindle Spinal cord(L2–L4) Tapping the patellar ligament excitesmuscle spindles in the quadriceps. 1 Hamstrings(flexors) Patellarligament 2 Afferent impulses (blue) travel to thespinal cord, where synapses occur withmotor neurons and interneurons. 3a The motor neurons (red) sendactivating impulses to the quadricepscausing it to contract, extending theknee. +– Excitatory synapseInhibitory synapse 3b The interneurons (green) makeinhibitory synapses with ventral horn neurons (purple) that prevent theantagonist muscles (hamstrings) fromresisting the contraction of thequadriceps. Figure 13.17 (2 of 2)