The Nervous System

1. The Nervous System Chapter 9

2. Functions • sensory input – uses sensory receptors to monitor changes inside and outside body • integration – interprets sensory input and decides what should be done about it • motor output– causes a response by activating muscles or glands • all 3 overlap

3. Histology of Nervous Tissue • Made mostly of 2 types of cells – • neurons • supporting cells= neurogliaand glialcells

4. neurons = nerve cells • conduct messages in the form of nerve impulses from one part of the body to another • amiotic* • high metabolic rate

5. Anatomy of a Neuron • Thecell bodycontains the nucleus and other organelles • Dendrites receive stimuli and conduct impulses towards the cell body • Theaxon carries impulses away from the cell body Cell Body Dendrite Axon

6. Axon Terminals Direction of impulse • Themyelin sheathis composed of glial cells called Schwann cells and insulate the axon • Nodes of Ranvierare the gaps between neighboring Schwann cells • Axon terminals(terminal buttons) are the ends of the axon Nodes of Ranvier Myelin Sheath

7. A synapse is the space between a neuron and another cell • presynaptic cell= cell that carries electrical impulses to a synapse • postsynaptic cell= cell that receives the impulse

8. Neurotransmittersare chemical messengers stored in the axon terminals of presynaptic cells - released into synapse when triggered by an impulse - bind with specific receptor proteins on postsynaptic cell’s dendrite

9. Classification of Neurons • Sensory neurons/afferent - environment  CNS • Motor neurons/efferent- CNS  effectors (muscle or gland) • Interneurons/association neurons - most abundant and confined entirely within CNS

10. Sending a Message • controlled by electrical activity within and between neurons • nerve impulse = series of electrical and chemical changes that travel like a wave over the length of a neuron in response to a stimulus

11. potential – difference in electrical charge between the inside of neurons and the fluid surrounding them Terms to know: • resting potential (resting state) – inside of the cell is more negatively charged than outside the cell • depolarization – inside becomes less neg.

12. Action Potentials • do not decrease in strength with distance • Na+ ions move across the nerve membrane and into the cell – this signals more Na+ ions to move as well (depolarization) • A fraction of a second later, K+ ions move out to restore the charge (repolarizataion) • the reversal of charge followed by the return to the resting state is called an action potential (nerve impulse)

14. refractory period - resting membrane potential is restored before next action potential can occur • action potentials follow the all-or-none principle

15. Divisions of the Nervous System 2 Major Divisions: • Central Nervous System(CNS) = the brain and spinal cord • Peripheral Nervous System(PNS) = cranial and spinal nerves

16. The Central Nervous System • function = serves as integrating and command center • average adult brain ~3-3.5 lb. • complexity of neural wiring more important than size when it comes to intelligence

17. Regions & Organization of Brain • cerebral hemispheres • diencephalon • brain stem • cerebellum

18. Cerebral Hemispheres • account for 83% of brain mass • covered by elevated ridges (gyri) separated by shallow grooves (sulci) • 2 hemispheres connected by corpus callosum • fissures = deeper grooves that separate large regions of the brain • longitudinal fissure– separates • hemispheres • transverse fissure– separates cerebral hemispheres from • cerebellum

19. cerebral cortex– 2-4 mm thick gray-matter (neuron cell bodies) that accounts for 40% of brain mass; contains motor, sensory and association areas • cerebral white matter– (myelinated axons) provides communication between cerebral areas

20. lobes = large regions of the brain • frontal – reasoning, planning, speech, movement & emotions • parietal – movement, orientation, recognition & perception of stimuli • occipital – visual processing • temporal – perception and recognition of auditory stimuli, memory and speech

21. 3 Functional Regions • motor areas: • govern muscular movements (R-L, L-R) • motor speech area = Broca’s area • sensory areas: • interpret impulses from sensory receptors, producing feelings or sensations • cutaneous senses, vision, hearing, taste, smell (also R-L, L-R)

22. association areas: • concerned with integrative functions -concentration -planning -complex problem solving -judging consequences of behavior -personality traits -intelligence -understanding speech (Wernicke’s area) -choosing words to express thoughts & feelings -reading -memory of visual scenes & music -visual recognition

24. Other Important Parts of Hemispheres • ventricles – cavities continuous with one another and the spinal cord that contain cerebrospinal fluid

25. Diencephalon • includes thalamus, hypothalamus and epithalamus • thalamus “inner room” – major relay station for impulses

26. hypothalamus – caps top of brain stem and pituitary gland attached to bottom • center of emotional response and behavior • regulates body temp, food intake, water balance/thirst, sleep-wake cycle and controls endocrine system functioning

27. epithalamus • most dorsal portion of diencephalon • connects limbic system (helps control emotions) to other parts of the brain

28. Brain Stem • composed of midbrain, pons, and medulla • midbrain – contains visual and auditory reflex centers • pons – conduction area; helps regulate respiration and cranial nerves

29. medulla oblongata– site of fibers crossing over so messages are sent to/from one side of brain to/from opposite side of body • controls blood pressure, HR, rate and depth of breathing • regulates vomiting, hiccupping, swallowing, coughing and sneezing

30. Cerebellum • Controls coordination and balance by receiving and processing info from visual and equilibrium pathways

31. Protection of the brain • 3 protective layers (meninges) surround the brain & spinal cord: • dura mater – outer • arachnoid– middle • pia mater – inner

32. The spinal cord • starts at medulla oblongata  through vertebral column ends in sacrum • composed of inner gray matter shaped like a butterfly surrounded by white matter

33. The Peripheral Nervous System • 2 types of nerves – cranial & spinal • function = serve as communication lines that connect all body parts to CNS • 2 divisions – sensory & motor

34. cranial nerves – 12 pairs • most are mixed, but some are purely sensory & others are primarily motor • some are somatic, some are autonomic

35. CRANIAL NERVES • I = olfactory nerves (smell) • II = optic nerves (sight) • III = oculomotor (moves eyeballs) • IV = trochlear (moves the eye) • V = trigeminal (ophthalmic, maxillary, mandibular) • VI = abducens (abducts the eye) • VII = facial (move the face, taste) • VIII = vestibulocochlear (balance, hearing) • IX = glossopharyngeal (tongue & pharynx / swallowing) • X = vagus (“wanderer”: speech, swallowing, heartbeat) • XI = spinal accessory (move neck & back) • XII = hypoglossal (moves the tongue) “On Occasion Our Trusty Truck Acts Funny – Very Good Vehicle AnyHow”

36. spinal nerves – 31 pairs • named (numbered) for the level from which they arise • 8 cervical nerves • 12 thoracic nerves • 5 lumbar nerves • 5 sacral nerves • 1 coccygeal

37. each spinal nerve emerges from the spinal cord in 2 roots • dorsal root has an enlargement called the dorsal root ganglion - contains sensory / afferent neurons • ventral root contains motor / efferent neurons • interneuronslocated within the spinal cord connect sensory & motor neurons together

39. the main portion of spinal nerves combine to form complex networks called plexuses – allows fibers associated with the same part to reach it together • cervical plexus • brachial plexus • lumbosacral plexus

40. MAJOR NERVES OF THE LEG

41. MAJOR NERVES OF THE LEG • Common fibular • Inferior gluteal • Plantar nerve • Sciatic nerve • Superior gluteal • Sural nerve • Tibial nerve

42. MAJOR NERVES OF THE ARM

43. MAJOR NERVES OF THE ARM • Axillary nerve • Musculocutaneous • Median nerve • Radial nerve • Ulnar nerve

44. a spinal reflex involves nerves and the spinal cord – not the brain • example = the patellar reflex (a stretch reflex) • reflexes are involuntary and typically self-protective

45. 2 Divisions of Motor Division 1) Somatic Nervous System • connect CNS to the skeletal muscles • oversees conscious/voluntary activities

46. 2) Autonomic Nervous System • connects the CNS to viscera(heart, stomach, intestines) and glands • controls unconsciousactivities such as respiration & heartbeat

47. 2 divisions of autonomic NS: 1) sympathetic– “fight or flight” • activated by physical or emotional stress, i.e. emergency situations or being frightened • one major function is shunting blood from one part of the body to another • redirects blood flow from the digestive organs towards the heart & skeletal muscles

48. 2) parasympathetic– maintains homeostasis • brings the body back to normal after “fight or flight” • induces the body to conserve energy

49. under normal conditions, both the sympathetic and the parasympathetic are activated to some degree