Chapter 17 The Nervous System

1. Chapter 17 The Nervous System

2. Nervous Tissue 2 Major Categories of Nervous System Central Nervous System The brain and spinal cord At midline of body Peripheral Nervous System Nerves carrying messages from CNS to muscles and glands Sensory nerves carrying messages to the CNS

4. 3 Types of Nerves to KnowSensory Nerves , Interneurons & Motor Nerves Sensory Nerves - carry information to the CNS Interneuron � a bridge between a sensory and motor nerve Motor Nerves � carry response from the CNS to an effector � a gland or muscle that creates an action

7. Anatomy of a TypicalNerve CellSensory Neuron shown here

8. Myelin Sheath / Nodes of Ranvier Formed by Schwann cells which secrete a fatty coating over the axon Acts like an insulation around a wire. Electrical signal jumps gap to gap because that is easier than travelling down the high resistance of the axon, itself. Gaps where Schwann cells do not myelinate are called the Nodes of Ranvier

10. More on Myelin Gives nerves white appearance (= WHITE MATTER) MS (mutliple sclerosis) is a disorder where myelin is removed from nerve. Signal passes down axon, weakening. In case of optic nerve, this can cause loss of vision. Ultimately, muscular control is lost. If the breathing and respiration centres in the medulla are affected, the result is fatal. Long Axons � usually myelinated to help signal make it Short Axons � usually non-myelinated, since signal should not degrade over short distance Unmyelinated nerves = GRAY MATTER

11. How does a Nerve Cell Pass an Electrical Signal? Nerve impulse carries information Impulse measured in mV Stages of Nerve Cell firing off a Signal Resting Potential � electric potential before signal Action Potential � potential of nerve when signal goes Refractory Period � potential after signal has passed

12. Action potential Definition: an �all-or-none� change in voltage that propagates itself down the axon Naturally occurring action potentials begin at the axon hillock

13. Resting Potential When not conducting an electrical impulse, the potential difference across the membrane is -65mV Inside of axon is negative compared to outside! Difference between inside/outside charge of membrane is needed to start a signal Similar to a battery, the ends must have a potential difference for current to flow

15. Action potential Definition: an �all-or-none� change in voltage that carries on all the way down the axon, creating electrical impulse. Naturally occurring action potentials begin at the axon hillock = crest of the axon Action potentials do not occur anywhere else in a neuron � not in dendrites, not in cell bodies

16. More K+ Sneaks out than Na+ in!Creates Dipole, enabling an Action Potential

17. Figure 48.11 Saltatory conduction

18. Action Potential Starts ---> -70mV Requires Na / K gates in membrane to open Ends ---> +45mV Lots of repolarizing to do Na moves back outside the membrane K move back inside the membrane Na/K gates must open to allow repolarizing to happen Not ready to fire again until this all happens.

19. How do you get from electrical signals to chemical signals and back again?

20. Axon Bulbs Insert carry Signal

21. Translating signals across Synapses The action potential moves down the axon until it reaches the terminal (synapse) Electric signal converted to chemical ? neurotransmitters Neurotransmitters cross the synaptic cleft  Signal caught on other side gets the electrical signal going again.

22. Translating signals The action potential moves down the axon until it reaches the terminal (synapse) Impulse opens voltage-activated Ca2+ channels to let the neurotransmitters through Transmitter diffuses across synaptic cleft and binds to receptors on post-synaptic cell

23. Signal Blockers Curare � poisonous darts tipped in these in the Amazon Black widow spider venom will cause bursting of synapses. Smoking�s not much good either

24. Translating signals The action potential moves down the axon until it reaches the terminal (synapse) Its wave of depolarization opens voltage-activated Ca2+ channels Influx of Ca2+ causes vesicles to fuse with presynaptic cell membrane

25. Translating signals The action potential moves down the axon until it reaches the terminal (synapse) Its wave of depolarization opens voltage-activated Ca2+ channels Influx of Ca2+ causes vesicles to fuse with presynaptic cell membrane Transmitter diffuses across synaptic cleft and binds to receptors on post-synaptic cell

26. If a transmitter depolarizes (stimulates) the post-synaptic neuron, it is said to be excitatory Excitatory and inhibitory neurotransmitters

27. Some Things You Should Know Acetylcholine involved in learning and memory Reduced levels in Alzheimers patients Excitatory to muscles NH2 Amine-type Neurotransmitters NorEpinepherine Released by Adrenal Glands Excitatory, heightens senses Dopamine Regulates movement, balance, walking Generally inhibatory, evening things out Reduced levels in Schizophrenics/possible Pathological Gamblers Serotonin Regulates mood, emotion, thought Brain cells are bathed in this while you sleep (chemical reset) Derived from amino acid Tryptophan (warm milk, turkey). Causes drowsiness Related to Melatonin � can get this in pill form. May help with sleep disorders

28. The Peripheral Nervous System The Spinal Nerves leading away from the CNS Afferent axons: Name for axons directed toward the central nervous system, conveying sensory information. Efferent axon: An axon directed away from the central nervous system, conveying motor commands to muscles and glands.

33. 2 Divisions of the Peripheral Nervous System (PNS) Somatic nervous system Part of the peripheral nervous system that controls the movement of skeletal muscles or transmits sensory information (visual, sound, touch, etc.) to the central nervous system Quick to respond to changes in the environment Autonomic nervous system (ANS) The portion of the peripheral nervous system that controls the body�s major systems (on autopilot usually) Controls Cardiac, Smooth muscle and glands Depending what the somatic nervous system picks up, kicks the ANS 1st Gear or ReverseThese systems are complete opposites of each other Sympathetic Nervous System - involuntary Parasympathetic Nervous System - involuntary

34. Fight or Flight Reaction of ANS Is that a cougar on the path in front of you?! When did it eat last? It looks skinny � gulp! If it gets on your back each attack has a 33% chance of killing you. After about 3 attempts, the cougar generally wins with the death bite to the back of the neck. Somatic Nervous System � senses the danger Autonomic Nervous System kicks in Sympathetic division alerts adrenal glands to secrete adrenalin / norepinepherine Senses heighten. Speed increases, pain not so easily felt, strength increases drastically Choice now is ---> FLIGHT OR FIGHT???????

37. The Peripheral Nervous System Autonomic Nervous SystemSympathetic Division of the ANS Adrenal medulla: The inner portion of the adrenal gland, located atop the kidney, controlled by sympathetic nerve fibers; secretes epinephrine and norepinephrine.

38. The Peripheral Nervous System Autonomic Nervous SystemParasympathetic Division of the ANS Parasympathetic division: Portion of the autonomic nervous system that controls functions that occur during a relaxed state; supports activities involved with increases in the body�s supply of stored energy including salivation, gastric and intestinal motility, secretion of digestive juices, and increased blood flow to the gastrointestinal system. Returns body to resting state after a �FIGHT OR FLIGHT� EVENT. So, works opposite to the Sympathetic Nervous System

41. Brain Structures

42. Cerebrum Thinking/Processing Interpretation Initiation of voluntary muscle movement Cortex - External Grey Matter Processing takes place Basal Nuclei - Central Grey Matter may have some voluntary muscle control, when diseased, Parkinson may develop

43. Cerebrum

44. Cerebrum Association areas connected with all lobes. Concerned with intellect, artistic & creative abilities, learning, memory Brain may be more �plastic� than once thought.

45. Cerebrum Left/Right halves communicate via Corpus Callosum Left brain controls right body Left Brain: spoken/written language, number & scientific skills, reasoning Right Brain: music/art awareness, 3D forms, insight, imagination

46. Brain Stem Medulla Oblongata Heart beat, Breathing, BP Cough, Sneeze, Hiccup, Vomit Pons Connects Cerebellum to CNS w/ Medulla regulate breathing/head motion w/ auditory, visual, tactile input

47. Brain Stem Midbrain Relay station Reflexes: Auditory, Visual, Tactile Reticular Formation - Grey Matter Controls wakefulness Inactive: sleep Damage: coma Filters unnecessary stimuli

48. Cerebellum Coordinates movement Oversees skeletal muscle action Maintains muscle tone and posture Interprets info on body position from ear for balance Assists learning of new motor skills

49. Diencephalon Thalamus Relays to/from rest of brain Hypothalamus Regulates homeostasis Link to Pituitary Gland

50. Reticular Activ. Centre The RAC acts like a filter, receiving and sending sensory and motor nerve signals. Controls sleep / alertness � wakes you up. Allows you to study while watching TV

51. Limbic System Parts of Frontal & Temporal Lobes, Thalamus, Hypothalamus, Amygdala, Hippocampus �Emotional Brain�: creates feelings about occurrences which influence how person acts in future. Memory and Learning: not fully understood, but involve Limbic. Emotionally charged = vivid memory

52. The Reflex Arc Sensory stimulation missed stair, sudden load, heat or pain sends signal to spine Interneuron sends signal quickly right back to skeletal muscle Muscle contracts: leg muscles tighen for stair / biceps flex for load / hand pulled away from heat