CELLS OF THE NERVOUS SYSTEM

1. CELLS OF THE NERVOUS SYSTEM CHAPTER 12

2. Nervous system • 3 main parts: brain, spinal cord, nerves • Function: To detect changes in the internal and external environment, evaluate the information and possibly respond by initiating changes in muscles or glands. • Endocrine system works very closely with nervous system. • Nervous system: immediate responses • Endocrine: slower uses hormones.

3. Divisions • Central Nervous System (CNS)= Brain and spinal cord • Peripheral Nervous System (PNS)= nerves outside of SC • Afferent division- incoming sensory information. Toward the SC • Efferent division- outgoing pathways. Motor neurons.

4. Divisions cont… • Somatic Nervous System: • 12 pairs of cranial nerves • 31 pairs of spinal nerves • Bundles of neuron axons bound together by connective tissue. Cell bodies are in the spinal column. • Relay to skeletal muscle • Reflexes

5. Autonomic Nervous System • Carries impulses from the CNS to internal organs. Involuntary responses • -Sympathetic Nervous System: Stress fight or flight. • -Parasympathetic Nervous System: Rest and repair functions (digestion)

6. Cells in the nervous system • 30 billion cells in the NS with over 100 trillion connections that are electrical in nature and generate a great deal of heat. Heat loss is primarily through head. • Neuron-basic unit of the nervous system • Many support cells as well.

7. Glial- satellite cells of the nervous system 4 types • 1. Microglial • 2. fibrous astroglial • 3. protoplasmic astroglial • 4. oligodendroglial • Also known as ASTROCYTES

8. Support Cells • Microglial- small. Immune function. Act like white blood cells in the CNS. Fight bacteria, breakdown worn out organelles. • Epedemal Cells – surround spinal cord and make cerebrospinal fluid. This bathes the brain and spinal cord. • Fibrous Astroglia- white matter. • Protoplasmic Astroglia-white matter. • Both work to form the blood brain barrier.

9. Blood Brain Barrier • You do not get the same free exchange of nutrients and gases through the capillaries into nervous tissue of the brain. Astroglia form a protoplasmic foot that guards the capillary to prevent material from coming through. • Astroglia- forms scar tissue in the brain

10. 4. Oligodendroglia • Creates the myelin that surrounds the axon by wrapping several times around the axon. • Myelin insulates the nerve and speeds nerve transmission.

11. Schwann Cells • Found in the peripheral nervous system (PNS) and have the same function as oligodenrdriocytes. • Gaps between these cells create NODES OF RANVIER. These gaps are important for proper nerve conduction as an impulse jumps from node to node. • Schwann Cells form the NEURILEMMA • Forms WHITE MATTER or myelinated fibers

12. Neuron. • Cell body = soma • Dendrites= several ways into cell body • Axon = 3-4 inches in length. Dendrite Myelin sheath Axon Axon endings Cell body Nucleus

13. Structural classification of neurons • Classified by their number of extensions from the cell body. • Multipolar- most neurons of brain and spinal cord. Have one axon but several dendrites • Bipolar-One axon and one highly branched dendrite. Only found in the retina of the eye inner ear, and in the olfactory pathway (nose). • Unipolar-single extending process from the cell body. Branches to form one way into the CNS, the second toward the PNS. Always sensory conducting information to the CNS.

15. 3 types of neurons: • Sensory- impulses from spine to brain (AFFERENT NERVES) • Motor- carry response brain to organ or muscle that was stimulated to respond. (EFFERENT NERVES) • Interneurons- within the spinal cord

16. Nerves and Tracts • Nerves are bundles of peripheral nerves that are held together by several layers of connective tissues. Surrounding each nerve fiver is an delicate layer of fibrous connective tissue: Endoneurium, perineurium, epineurium (sound familiar?)

17. Repair of Nerve Fibers • 1. Injury or cut nerve • 2. Distal portion of axon degenerates • 3. Remaining neurolemma forms a tunnel from effector to nerve body. • 4. Axons sprout on form within the tunnel. • 5. Neruon’s connection is re-established • Can grow from 3-5mm per day. • Page 352 Figure 12-10

19. Electrical Function of a Neuron • Volt= difference in electrical potential. • Energy flows from the point of higher voltage to an area of low voltage.

21. Depolarization occurs when a stimulus hits the nerve and Na++ flows into the axon in a wave pattern. As the stimulus travels it is called an ACTION POTENTIAL. • Na++ is High outside the cell (4:1) • K++ is High inside the cell (30:1) • Na++ flows into the area of lower potential and is pumped out by Active transport (requiring ATP) after the impulse passes. This is called REPOLARIZATION • The difference between the inside and outside of the cell is called the RESTING POTENTIAL.

22. High K+ concentration in tissue increases the resting potential making it harder to stimulate. If K+ concentration gets too high you can go into cardiac arrest. • Neurons are high energy users.

23. Threshold • Threshold is the minimum amount of stimulus required to produce a response. (elicit an action potential) • All or none law- If you stimulate a nerve below the threshold you will get NO response. • At threshold you get a maximum response. • The strength of a stimulus or action potential remains constant from the time it is generated until it is complete. The impulse does not weaken in transit.

24. Refractory period. • For a few milliseconds after a threshold potential has been reached the nerve will not respond to a stimuli no matter how strong. This is called the refractory period.

25. Neurotransmitters- how nerves communicate • More than 30 kinds of transmitters • Classified by function and structure • Acetylcholine • Various locations. Excitatory in muscles, inhibitory in the heart. • Amines • From amino acids. In brain, learning, emotions, motor control

26. Amino Acid • Most common NTs in the Central Nervous System • In PNS- stored in synaptic vesicles • Neuropeptides • Co- transmitter used to regulate the effects of other NTs when they are released. • Neurotransmitters released through the blood stream are called HORMONES.

27. SYNAPSE

28. CNS Cerebrum Skull Medulla oblongata Cerebellum • Brain Anatomy: • Brain: control system of entire nervous system. 3 main parts.

29. Section 36.1 Summary – pages 943 - 950 Anatomy of the brain Cerebrum Motor area Sensory area Speech area Language area Vision area Taste area General interpretation area Intellect, learning, and personality Balance area Hearing area Brain stem Cerebellum

30. Cerebrum • 2 hemispheres connected by bundles of nerves • Conscious activity

31. Lobes of the brain • Parietal lobe • Sensory association areas- impulses from skin such as pain and temp. Estimates distances • Frontal lobe • Motor cortex, controls skeletal muscles • Broca’s speech area- forming words • Personality • Temporal lobe • Auditory, memory and speech • Occipital lobe • vision

32. Cerebellum • Back of your brain • Balance • Posture • Coordination

33. Brain stem: 3 main parts Midbrain Cerebellum Pons Medulla oblongata Medulla oblongata- Involuntary activity- breathing and heart rate Pons-Connect various parts of the brain together Midbrain- similar function to the Pons