THE NERVOUS SYSTEM

1. THE NERVOUS SYSTEM

2. About the Powerpoint. • This upcoming test and this powerpoint both have a lot of information throughout them. Here are some studying tips: • The white words are the terminology that will be on the test. The blue wordsare definitions to the terms they follow. • The green notes inform you of the matching sections on the test. • Yellow words are examples of specific terms. • For the test, make sure you understand the difference between the structural and functional classification of the nervous system. • Understand a reflex arc and an action potential. • The orange words identify quiz diagrams.

3. 8-1 Nervous System Anatomical & Functional Divisions • General Functions • Monitors the internal and external environments • Integrates sensory information • Coordinates voluntary and involuntary responses of many organ systems

4. 8-1 Nervous System Anatomical & Functional Divisions Structural Classification • Central Nervous System (CNS)-brain & spinal cord • Peripheral Nervous System (PNS)- outside of CNS, spinal nerves & cranial nerves Functional Classification • Afferent (sensory) division-nerve fibers that send impulses to the CNS from sensory receptors (somatic & visceral) • Efferent (motor) division-nerve fibers that send impulses from the CNS to the effector organs causing a motor response • Somatic Nervous System (SNS)-conscious voluntary control of skeletal muscle • Autonomic Nervous System (ANS)-control over automatic or involuntary responses (smooth & cardiac muscle) • Sympathetic Nervous System-fight or flight • Parasympathetic Nervous System-craniosacral

5. 8-1 Nervous System Anatomical & Functional Divisions

6. BASIC ESSENTIAL TERMS • Stimuli-a change in the environment causing a response by the body • Sensory input-information gathered by the body from the stimuli • Integration-the processing and interpreting of sensory input and deciding what should be done at each moment • Motor output-activation of effectors (muscles or glands) by the nervous system

7. 8-2 NEURONS: STRUCTURE & FUNCTION • Neuroglia – regulate environment around neurons • Neurons-nerve cells Anatomy of a Neuron • Cell body (soma)-metabolic center of cell, no centrioles (no mitosis), contains large round nucleus w/ prominent nucleolus • Lack centrioles (no cell division) • Nissl substance-clusters of rough ER and free ribosomes, function in protein synthesis • Processes (fibers)-vary in length microscopic 3-4 ft • Dendrites- carry impulses to the cell body • Axons-generate impulses and send them away from the cell body

8. 8-2 NEURONS: STRUCTURE & FUNCTION • Neurons- nerve cells • Anatomyof a Neuron (continued) • Axon hillock-cone like region of the cell body that leads to the axon • Synaptic (Axon) terminals-branching end of the axon furthest from the cell body, contain vesicles • Neurotransmitters- chemicals released from the vesicles (send message) • Synaptic cleft/synapse-tiny gap that separates one neuron from another or a neuron from the cell it stimulates • Myelin sheath-fatty whitish material that covers and protects the axon and speeds up impulse transmission (Schwann cells – outside CNS)

9. TYPICAL NEURON

10. Typical Neuron

11. 8-2 NEURONS: STRUCTURE & FUNCTION • Neuron Structural classification- • Multipolar-2+ dendrites and single axon (all motor & association – common in CNS) • Bipolar-1 axon and 1 dendrite, rare in adults, special sense organs (eye, nose), act as receptor cell • Unipolar- have single process, short, but divides into proximal (central) & distal (peripheral) processes, only small branches are dendrites, rest of peripheral & central are axons and serve to both carry away and take in impulses (ie – sensory neurons in PNS ganglia)

13. 8-2 NEURONS: STRUCTURE & FUNCTION • Neuron Functional Classification • groups neurons according to the direction the nerve impulse is traveling relative to the CNS • Sensory (Afferent) neurons-in PNS, carry impulses from sensory receptors to the CNS • Interneurons (association neurons) – connect motor and sensory neurons, cell bodies are in CNS • Motor (Efferent) Neurons – in PNS, carry impulses from CNS to viscera, muscles, or glands • Somatic motor neurons – effect skeletal muscles • Visceral motor neurons – effect cardiac or smooth muscle, Motor Unit – a or glands motor unit & the muscle fibers it stimulates

14. 8-2 NEURONS: STRUCTURE & FUNCTION • Receptors – found in dendrite endings, activated by specific changes nearby • Somatic sensory receptors – detect information about the outside world or our physical position in it • External (cutaneous) receptors: • touch, temperature, pressure, sight, smell, hearing • Proprioceptors: • Monitor position and movement of skeletal muscles and joints • Visceral receptors or internal receptors • Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) • Internal senses (taste, deep pressure, pain)

15. 8-2 NEURONS: STRUCTURE & FUNCTION • Neuroglial Cell Classification • Astrocytes- in CNS, star-shaped, function in exchanges between capillaries & neurons, protect from harmful substances in the blood, control chemical environment of brain (maintain blood-brain barrier) • Microglia- in CNS, spider-like phagocytes, get rid of dead brain cells & bacteria, rare • Ependymal cells-in CNS, line cavities of brain & spinal cord, cilia help circulate cerebrospinal fluid (CSF) • Oligodendrocytes- in CNS, wrap flat extensions around nerve fibers creating insulating myelin sheaths (see next slide for more) • Schwann cells-in PNS, form myelin sheaths around axons, outer surface of cells called the neurilemma • Satellite cells-in PNS, protective cushioning cells

16. 8-2 NEURONS: STRUCTURE & FUNCTION • Myelinated axon – contains sections of myelin around axon • Nodes of Ranvier – gaps between sections of myelinated axon • Internodes – areas of axon covered in myelin • Unmyelinated axon – axons w/o myelin • White matter – white areas of CNS containing myelinated axons • Gray matter – darker areas of CNS consisting mostly of neuron cell bodies (little myelination)

17. 8-2 NEURONS: STRUCTURE & FUNCTION Organization of Neurons

18. 8-3 NERVE IMPULSE • What is an Ion? • An atom or molecule in which the total number of electrons is not equal to the total number of protons • Has a net positive (+) or negative (-) charge • Common human body ions: • Na+ (sodium) • K+ (potassium) • Ca2+ (calcium) • Cl- (chloride) • OH- (hydroxide) • Important to neurons because all plasma (cell) membranes produce electrical signals by ion movements

19. 8-3 NERVE IMPULSE + • Membrane Potential (transmembrane potential or membrane voltage) – difference in electrical charge between the inside and outside of a cell • Factors Responsible for Membrane Potential • Concentration gradient of ions (Na+ outside, K+ inside) • Channel Proteins selectively allow ions to cross cell membrane (sodium channels, potassium channels) • Passive or leak channels – always allow ions thru • Active or gated channels – only open when stimulated - - + - - - + - + - - +

20. 8-3 NERVE IMPULSE Extracellular fluid • Membrane Potential • Resting Potential – membrane potential of a resting cell • Outside of cell (+) charge, inside of cell (-) charge • Cell in state of polarization with fewer K+ inside than Na+ outside • Graded Potential – temporary, localized change in resting potential caused by a stimulus – if it reaches a specific threshold, an action potential occurs • Action Potential – shortlasting event in which electrical membrane potential of a cell rapidly rises and falls • An electrical impulse produced by graded potential that travels along an axon to the synapse (all or none response) + + + + + + + + + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Cytosol - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + +

21. 8-3 NERVE IMPULSE • Nerve Impulses - neurons have 2 major functional properties: irritability and conductivity • Conductivity-ability to transmit an electrical impulse • Irritability (generation and propagation of an action potential) -the ability to respond to a stimulus & convert it into a nerve impulse • STEP1: Depolarization - when cell membrane allows Na+ to rush into the cell (diffusion) which changes the polarity of the neuron’s membrane at that site (inside is more +) creating a graded potential to the threshold. (-70mV to -60mV)

22. 8-3 NERVE IMPULSE • STEP 2: Activation of voltage-gated sodium channels and rapid depolarization. Sodium rushes into the cell. Inside of cell becomes more positive. Outside of cell becomes more negative. • inside of the cell, excess of positive ions are attracted to the negative charges. • causes a local current. • local current depolarizes adjacent portions of the membrane like a chain reaction. This is called continuous propagation. • action potential can move forward, but not backward.

23. 8-3 NERVE IMPULSE • STEP 3: Inactivation of sodium channels and activation of voltage-gated potassium channels. This starts repolarization - potassium ions diffuse out of the cell as membrane permeability changes again, restoring the negative charge on the inside of the membrane and the positive charge on the outside surface.

24. 8-3 NERVE IMPULSE • STEP 4: The return of normal permeability and resting state. • Transmission of an impulse is an electrochemical event • Sodium-Potassium Pump

25. Refractory Period - From the moment the voltage-gated sodium channels open at threshold until repolarization (Steps 2-3) is complete, the membrane cannot respond normally to further stimulation

26. 8-3 NERVE IMPULSE • Continuous Propagation vs. Saltatory Propagation • Continuous Propagation –occurs along unmyelinated axons – travels along entire axon • Saltatory Propagation -faster type of impulse conduction that occurs in myelinated fibers where the impulse jumps from node of ranvier to node of ranvier

27. 8-4 SYNAPSES • Synaptic Activity • Action potentials transmitted from presynaptic neuron to postsynaptic neuron (neuron to neuron communication) or postsynaptic cell (neuron to other tissue/organ) • Presynaptic – neurotransmitters released • Postsynaptic – binds neurotransmitters, either excites or inhibits the neuron/cell

28. 8-4 SYNAPSES • Effects of neurotransmitters on a postsynaptic membrane depends on the receptor NOT the neurotransmitter • Ex. Acetylcholine (Ach) usually promotes action potentials, but in cardiac neuromuscular junctions it inhibits (slows) heart rate • Types of Neurotransmitters • Norepinephrenine (NE) – increases heart rate, fight or flight response • Dopamine– movement, emotional response, ability to experience pleasure and pain, high levels linked to schizophrenia, low levels linked to Parkinson’s • Gamma aminobutyric acid (GABA) – inhibitory, low levels linked to extreme anxiety • Serotonin – mood control, regulation of sleep, pain perception, body temperature, blood pressure and hormonal activity, low levels linked to depression

29. 8-4 SYNAPSES Events at a Cholinergic Synapse

30. 8-5 MENINGES QUIZ#2 DIAGRAM

31. 8-7 THE BRAIN QUIZ#2 DIAGRAM

32. 8-5 MENINGES • Protection of the Central Nervous System • Meninges –3 protective tissue coverings (membranes) that cover & protect the CNS from physical impacts and blood-borne pathogens/compounds • Dura mater (“tough mother”) –outermost layer; tough, double-layered membrane; surrounds entire brain • Periosteal layer/periosteum –attached to inner surface of skull • Meningeal layer –forms outermost covering of brain & continues as dura mater of spinal cord • Dural folds help hold brain in place • Arachnoid mater (“spidery stuff”)–middle meningeal layer separated from dura mater by subdural space • Subarachnoid space –deep to arachnoid mater; filled with cerebrospinal fluid (CSF) (circulates) • Arachnoid villi –projections of arachnoid membrane; place where CSF is absorbed into venous blood

33. 8-5 MENINGES • Protection of the Central Nervous System • Meninges (cont.) • Pia mater(“delicate mother”)– innermost membrane, extremely vascularized to provide oxygen for very high rate of metabolism (3 lb. brain at rest = 61 lbs. skeletal muscle in O2 usage)

34. blood-brain barrier CENTRAL NERVOUS SYSTEM: PROTECTION • Cerebrospinal fluid (a.k.a. CSF) –fluid containing less protein & more vitamin C; formed from blood by choroid plexuses (capillaries) • Protects and cushions brain and spinal cord from trauma (circulates) • Forms and drains at a constant rate • Presence of blood cells or change in composition  meningitis, brain tumor, multiple sclerosis • Blood-Brain Barrier –keeps neurons separate from bloodborne substances; least permeable capillaries in entire body - only glucose, water, & essential amino acids through, while metabolic wastes (urea, toxins, proteins, & most drugs) are prevented from entering brain tissue; forms after 2 years

35. The central nervous system (brain and spinal cord) during embryonic development. CENTRAL NERVOUS SYSTEM During embryonic development, the CNS first appears as a neural tube, which extends down the dorsal median plane. By the fourth week, the anterior end begins to expand, forming the brain, while posterior to the forming brain, becomes the spinal cord. The central canal, which is continuous between the brain and spinal cord, becomes enlarged in four regions of the brain to form ventricles.

36. Intro to the Brain • The Adult Human Brain • Ranges from 750 cc to 2100 cc • Contains almost 97% of the body’s neural tissue • Average weight about 1.4 kg (3 lb) • Six Regions of the Brain • Cerebrum • Diencephalon • Midbrain • Pons • Medulla oblongata • Cerebellum

37. Anatomy of the Brain

38. 8-7 THE BRAIN • Functional Anatomy of the Brain • Cerebrum – largest part of the brain • Gyri (gyrus):ridges • Sulci (sulcus):grooves • Central sulcus:separates frontal and parietal lobes • Fissures: deep grooves • Longitudinal fissure:separates the two hemispheres • Hemispheres • Left Hemisphere:dominant for speech and motor activity • Right Hemisphere:dominant for spatial (recognition of shape and form) and temporal (timing, music) activities

39. Anatomy of the Brain

40. 8-7 THE BRAIN • Functional Anatomy of the Brain • Cerebrum • Lobes:named for the bones that lie over them • Parietal lobe-The somatic sensory area is located in the parietal lobe posterior to the central sulcus- impulses traveling from body’s sense receptors (pain, cold, touch), except special senses, are localized and interpreted here • Occipital lobe-visual area • Temporal lobe-auditory area • Frontal lobe-The primary motor area (allows us to consciously move our skeletal muscles) is anterior to the central sulcus in the frontal lobe

41. 8-7 THE BRAIN PRACTICAL DIAGRAM

42. 8-7 THE BRAIN

43. 8-7 THE BRAIN • Diencephalon/Interbrain- sits atop brain stem, linking it to the cerebrum, and is enclosed by cerebral hemispheres • Thalamus-encloses 3rd ventricle • a complex relay station for sensory impulses passing upward to the sensory cortex (except smell) • get crude recognition of whether sensation we’re about to experience is pleasant or unpleasant; actual interpret. is done in sensory cortex • regulates states of sleep and wakefulness • plays a major role in regulating arousal, levels of awareness and activity • damage to area can cause permanent coma • Hypothalamus-makes up floor of diencephalon • important autonomic nervous system center b/c it plays a role in regulation of body temp., water balance and metabolism • Hormone production • Pituitary Gland, center for many drives (hunger, thirst, sex- pain and pleasure) and emotions (therefore an important part of limbic system) • deals with sleep/wake cycle

44. 8-7 THE BRAIN • Hypothalamus (continued) • Limbic system- “emotional-visceral” brain made up of many different brain areas • deals with emotion, motivation, and emotions associated with memory • influences formation of memory by integrating emotional states with stored memories of physical sensations • Amygdala- aggression, jealousy, and fear • Hippocampus- formation of long-term memories • Pituitary gland- hangs from anterior floor of hypothalamus by a slender stalk • Mammillary bodies- reflex centers involved in olfaction; bulge from floor of hypothalamus, may be important for memory

45. 8-7 THE BRAIN • Diencephalon (cont.) • Epithalamus – forms roof of third ventricle • Pineal Gland – secretes melatonin, which induces sleep • Choroid Plexus – forms CFS, knots of capillaries within each ventricle

46. 8-7 THE BRAIN • Brain stem-provides pathways for ascending and descending tracts, has many small gray matter areas, which are part of cranial nerves and control vital activities (breathing, blood pressure…) • Midbrain (mesencephalon)-extends from mammilary bodies to pons inferiorly; divided into three parts: • Cerebral aqueduct • Cerebral peduncles • Corpora quadrigemina • Process visual & auditory info • Generate involuntary motor responses • Maintains consciousness • Pons-rounded structure; protrudes just below midbrain – connects cerebellum to brain stem • Somatic & visceral motor control, especially important in the control of breathing

47. 8-7 THE BRAIN • Brain stem (cont.) • Medulla Oblongata-most inferior part of brain stem; merges into spinal cord inferiorly • regulate vital visceral activities (heart rate, blood pressure, breathing, swallowing, vomiting, etc.) • Fourth ventricle-lies posterior to pons and medulla and anterior to cerebellum

48. 8-7 THE BRAIN Cerebellum- projects dorsally from under the occipital lobe; like cerebrum, it has two hemispheres, convoluted surface, outer cortex made of gray matter and inner region of white matter • precise timing for skeletal muscle activity and coordination • controls our balance and equilibrium • monitors body position and amount of tension in various body parts and adjusts voluntary & involuntary motor activities accordingly • Repetition and rote memorization

49. 8-7 THE BRAIN • Ventricles of the Brain • 4 internal cavities of the brain that contain cerebrospinal fluid • 1. Lateral ventricles (2) • 2. Third ventricle • 3. Fourth ventricle

50. 8-7 THE BRAIN • Broca’s area-involved with ability to speak; found at base of precentralgyrus; located in only one hemisphere, usually left; damage to this area causes inability to say words properly- you know what you want to say, but you can’t vocalize the words • Speech area- located at junction of temporal, parietal, and occipital lobes; allows one to sound out words • Cerebral Cortex: gray matter in outermost areas • Corpus callosum-large tract; connects cerebral hemispheres • Basal nuclei-(formerly called the basal ganglia)- islands of gray matter buried deep within white matter; help regulate voluntary motor activities by modifying instructions sent to skeletal muscles by primary motor cortex; problem with basal nuclei  people cannot carry out voluntary movement normally; ex. Parkinson’s disease