Chapter 2

1. Chapter 2 Biological Basis of Behaavior

2. The Nervous System • Nervous System: transmits messages throughout the body • Neuron: specialized cell • basic (smallest) unit of the nervous system • it transmits messages • Glial cells: provide “support” for neurons • form the myelin sheath, remove waste products

3. Parts of the Neuron dendrites soma (cell body) axon terminal axon myelin sheath nodes of Ranvier

4. Parts of the Neuron • Soma (cell body): cell metabolism • Dendrites: short fibers on cell body, receive “incoming” chemical messages • Axon: single fiber extending from cell body, carries “outgoing” chemical message • Axon Terminal: the end of the axon • Nerve (tract): group or bundle of axons

5. Parts of the Neuron • Myelin Sheath: white fatty covering on longer axons • composed of Glial cells • “insulates”the axon • helps messages travel further and faster • Nodes of Ranvier: points where myelin sheath is “pinched” together

6. 3 Types of Neurons • sensory (afferent) neurons:carry messages from sense organs to spinal cord and brain • interneurons (association neurons):carry messages from one neuron to another • motor (efferent) neurons:carry messages from spinal cord or brain to muscles

7. Communication Within a NeuronThe Action Potential

8. The Action Potential • Action Potential: an “electrical” message that travels down the axon causing release of chemicals from axon terminal (neuron “fires”) • Ions: charged particles that move in and out of the axon • sodium “NA” + is most important • also Potassium “K” + and Chloride “CL” --

9. Action Potential threshold of excitation absolute refractory period relative refractory period resting potential Membrane Potential Time (msec)

10. 1. Resting State • neuron is at rest:more “NA” + isoutside than inside axon • neuron is “polarized”:difference in electrical potential between inside and outside of axon is -- 70 millivolts + + + + + + + + + + soma + + + terminal + + + + + + + + + +

11. 2. Depolarization • depolarization: dendrites are chemically stimulated • channels open, positive NA + ions enter axon • difference in potential reaches, then exceeds 0 mv • message travels down the axon + + + + + soma + + + + + + + + + terminal + + + + +

12. 3. Neuron fires • Neuron fires: only if “threshold of excitation” (firing threshold) is reached • now more “NA” + inside than outside the axon • charge inside is (+ 40 mv) relative to outside • signal reaches axon terminal + + + soma + + + + + + + + + + terminal + + +

13. Neuron May Fail to Fire • threshold of excitation: (firing threshold) level of “depolarization” that must be reached for neuron to fire • graded potential: stimulation of dendrites was too weak to reach threshold and neuron fails to fire (depolarization just “fades away”) + + + + soma + + + terminal + + + +

14. 4. Neuron resets • return to resting state: • positive ions now flow back out of axon • as before, more “NA” + is outside than inside axon • difference in electrical potential between inside and outside of axon is again - 70 millivolts + + + + + + + + + + soma + + + terminal + + + + + + + + + +

15. 4. Neuron resets (cont.) • absolute refractory period: right after firing, neuron will not fire again no matter how strong the incoming message • relative refractory period: after partially “resetting,”neuron will fire again but only if the incoming message is unusually strong

16. Other facts about the Action Potential • The entire process has taken only a few milliseconds! • All or None Law: strength of the action potential does not vary. The neuron either fires or it doesn’t. • The “Rate of firing” is really what changes. The neuron is never really “at rest”

17. Communication Between Two Neurons Synaptic Transmission

18. A “Chemical” Process synapse axon terminal synaptic vesicle neurotransmitter receptor site on dendrite

19. The Synapse • Synapse has three parts: • 1. axon terminal of first neuron • 2. synaptic “cleft” or “space” • 3. receptor site on dendrite of second neuron • Neurotransmitters: chemicals released from the axon terminal • Synaptic Vescicles: sacs in the axon terminal that contain neurotransmitter

20. 1. Release • Action potential reaches axon terminal of neuron #1 • Vescicles open and release neurotransmitter in to synaptic space • neurotransmitter crosses synaptic space

21. 2. Communication • Neurotransmitter attaches to receptor site and “stimulates” neuron #2 • Each specific neurotransmitter and its receptor site fit like a “Lock and Key” Serotonin molecule -- Will fit > Dopamine molecule -- Won’t fit > Serotonin Receptor site

22. 3. Inactivation • Neurotransmitter releases from receptor site, moves back into synaptic space, and is either: • 1. taken back up into axon #1 terminal for re-use OR • 2. “broken down” into basic components and carried away for disposal

23. Neurotransmitters can speed OR slow rate of firing Excitatory Neurotransmitters: “increase”firing rate in the neuron they attach to Inhibitory Neurotransmitters: “decrease” firing rate in the neuron they attach to (see Summary Table in book)

24. Neurotransmitters

25. How Drugs Work • Acetylcholine (Ach) is an excitatory neurotransmitter at muscle synapses • Botulism: prevents Ach release, result is paralysis • Black Widow Venom: causes excess Ach release, result is shaking/tremors • Curare: blocks (occupies) Ach receptros, result is paralysis • LSD visual hallucinations may be due to blocking of serotonin receptors

26. Experience and Plasticity

27. Mark Rosenzweig’s Experiment • Two groups of rats • one raised in a boring unstimulating environment • one raised in a complex stimulating environment • The second group had larger neurons with more synapses • Plasticity: extent to which the brain will change in response to experience

28. The Nervous System

29. Nervous System Central Nervous System Peripheral Nervous System Spinal Cord Brain Somatic Nervous System Autonomic Nervous System Sympathetic Nervous System Sensory Neurons Motor Neurons Parasympathetic Nervous System

30. Central Nervous System (2 parts) • 1. Brain: has 3 divisions. . . . later • 2. Spinal Cord: large bundle of “nerves” which connects the rest of the body to the brain Cross-section of spinal cord, with numerous nerves (tracts)

31. Peripheral Nervous System • Autonomic Division:carries messages between the internal organs and CNS • Sympathetic: arouses, prepares body for “fight or flight” • Parasympathetic: relaxes body • Somatic Division:carries messages between sense organs/muscles and CNS • messages from CNS to muscles • “reflex arc” - example of a complete circuit

32. The Reflexe Arc

33. The Reflex Arc • involves 3 neurons • 1. Afferent (sensory) neuron: carries sensory information from body to spinal cord (hit with hammer) • 2. Efferent (motor) neuron: carries motor information from spinal cord to muscles (move leg) • 3. Association (inter) neuron: connects the two other neurons

34. Cross-section of the Brain Forebrain Cerebral cortex Thalamus Hypothalamus Midbrain Hindbrain Cerebellum Pons Medulla

35. 1. Hindbrain (Brainstem) • The “oldest” part of the brain (3 parts) • 1. medulla: controls “automatic” functions such as breathing, heart rate, blood pressure, ALSOplace where many axons “cross over” from right to left • 2. pons:links cerebellum to motor areas of brain and to muscles of body • 3. cerebellum:balance and movement

36. Reticular Formation • Also located in the brainstem, the reticular formation plays an important role in controlling alertness and the “sleep-wake cycle”

37. 2. Midbrain • A large “relay station” • Many synapses are located here • Visual and Auditory information is relayed here Limbic System Group (ring) of structures surrounding the midbrain 1. Amygdala - Self preservation (fear and aggression) 2. Hippocampus - Formation of new memories

38. 3. Forebrain (3 basic parts) • 1. thalamus: “arelay station” for visual and auditory sensory information • 2. hypothalamus: controls“motivated behaviors”:thirst, hunger, and sexual behavior • 3. cerebral cortex: see next slide

39. Forebrain (cont.) • 3. Cerebral Cortex: “newest” part of the brain, consists of TWO hemispheres, right and left • Corpus Callossum: bundle of axons connecting right and left hemispheres • Convolutions: folds and creases that allow the cortex to fit in the skull

40. Lobes of the Brain • Each hemisphere is divided into four “lobes” • 1. Occipital Lobes: interprets visual information • 2. Parietal Lobes: sense of touch (primary somatosensory cortex)

41. Lobes of the Brain (cont.) • 3. Temporal Lobes: process auditory information • 4. Frontal Lobes: higher mental processes • language, personality, problem solving, etc. • motor projection areas control muscles

42. Hemispheric Specialization Right and left hemispheres are involved in specific functions

43. Left Hemisphere • right hand touch • right visual field • language • logic / math

44. Right Hemisphere • left hand touch • left visual field • spatial ability • art • fantasy

45. Path to Occipital Lobe

46. Split Brain Patients • In 1950s, cutting the Corpus Callosum reduced siezures in cases of severe epilepsy • This severs the connection between right and left hemispheres • Sperry and Gazzaniga discovered some unusual consequences

47. Split Brain Research • Right visual field: what is to the right of the person • is directed to left hemisphere • Left visual field: what is to the left of the person • is directed to right hemisphere • This “crossing over” from right to left takes place at the “optic chiasm”

48. Split Brain Research • Right hand touch: what is felt with the right hand • is directed to left hemisphere • Left hand touch: what is felt with the left hand • is directed to right hemisphere • Remember, language is on the left so the image stored in the right brain cannot be verbally identified (if corpus calossum is cut)

49. Split Brain Research can pick out hammer with left hand can’t pick out hammer with right hand

50. Split Brain Research can pick out ball with right hand can’t pick out ball with left hand