The Nervous System

1. The Nervous System Ch 9

2. Aids to Understanding Words

4. Introduction Section 9.1

5. Intro • The nervous system – controls many things! • Made of nervous tissue: • Has masses of nerve cells – neurons. • Specialized to react to physical and chemicalchanges in their surroundings. • Nerve impulses: electrochemical changes that transmit information.

6. Parts of a neuron • Cell body: rounded area; sometimes in middle, sometimes at end. • Dendrites: extensions that receive information. • Axons: extensions that send information.

8. Two Divisions of the Nervous System Central Nervous System Peripheral Nervous System Brain Spinal Cord All the nerves to the rest of the body.

9. General Functions of the Nervous System Section 9.2

10. Different Functions • Sensory Function • Based on sensory receptors – detect changes inside and outside of the body • Integrative Function • Translates sensory receptions into sensations, adding to memory, or helping to produce thoughts that translate sensations into perceptions • Motor Functions • Movements caused by the nervous system.

11. Motor Functions • Use peripheral neurons to carry impulses from the central nervous systemto effectors. • Effectors: structures outside of the nervous system. • Muscles • Glands • Two divisions: • Somatic – consciously controlled • Autonomic - involuntary

12. Practice! • Dendrites • Axons • Motor Functions • Autonomic Nervous System • Peripheral Nervous System • Sensory Function • Cell Body • Rounded area of a neuron • Use effectors to act • Receive electrochemical messages • Involunary effectors • Does not include the brain and spinal cord. • Send electrochemical messges • Monitors changes in temperature, light, sound Answers: 1-c, 2-f, 3-b, 4-d, 5-e, 6-g, 7-a

13. Neuroglial Cells Section 9.3

14. Neuroglia • Cells other than neurons that are important to nervous tissue. • Microglial Cells – support neurons and phagocytize (kill) bacterial cells and debris. • Oligodendrocytes – provide insulating layers of myelin (myelin sheaths) around axons in the CNS

15. 3. Astrocytes – Found between nerves and blood vessels, structural support, regulates concentrations of ions and nutrients. Form scar tissue in CNS. 4. Ependymal cells – Covers brain parts, forms inner linings within brain and spinal cord. 5. Schwann cells – form the myelin sheath around axons.

16. Neurons Section 9.4

17. Neuron Structure • Basic parts of a neuron: • Axon: Information leaving • Dendrite: Information receiving • Cell body • Relative sizes: • If the cell body was the size of a tennis ball the axon would be a mile long and ½ inch thick. The dendrites would fill a large bedroom! • Neurons do not divide.

18. Myelin Sheath • Schwann cells surround the axons of many peripheral neurons. • Wrap around in many layers. • Made of myelin – a lipoprotein (lipids and proteins) • Called a myelin sheath. • Gaps in the myelin sheath are called: nodes of Ranvier • Myelinated: Has a myelin sheath • Unmyelinated: has no myelin sheath • In CNS: myelinated are called white matter, unmyelinated are called grey matter.

19. Classifications of neurons STRUCTURAL: • Bipolar – has two processes, one from each end. • Usually in specialized parts (eyes, nose, ears) • Unipolar – has on process that splits once it leaves the cell body. • Multipolar – many processes. • One process is an axon, the rest are dendrites.

20. Classifications of neurons PHYSICAL • Sensory (afferent) – carry from body parts to the CNS. • Interneurons (association or internuncial) – are entirely in the brain or spinal cord. • Motor (efferent) – carry from CNS to effectors.

21. Cell Membrane Potential and Nerve Impulse Section 9.5 and 9.6

22. 1. Neuron membrane maintains resting potential • A resting neuron is polarized. • An unequal distribution of positive and negative charges. • There are more sodium ions (Na+) outside of the membrane and more potassium ions (K+) inside the membrane. • Resting potential: the difference in electrical charge in a nerve cell when left undisturbed.

23. 2. Threshold stimulus is received. • Must have a threshold stimulus for the message to be passed down the nerve. • Caused by many little stimuli that add up (summation). • Each stimuli causes a depolarization.

24. 3. Sodium channels in a local region of the membrane open. 4. Sodium ions diffuse inward, depolarizing the membrane. 5. Potassium channels in the membrane open. 6. Potassium ions diffuse outward, repolarizing the membrane.

25. 7. The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane. 8. Wave of action potentials travels the length of the axon as a nerve impulse.

26. Impulse Conduction • Impulses travel by conduction down the surface of the axon. • On unmyelinated axons, the impulse must travel across the entire surface. • On myelinated axons, the impulse jumps between nodes of Ranvier. • This is much faster! • In multiple sclerosis, the myelination is destroyed and removed from the axons of nerves. This accounts for much of the slowed movement and lost of control.

27. All-or-none Response • If a neuron responds at all, it responds completely. • A stronger “feeling” doesn’t mean a stronger impulse, but more impulses per second.

28. The Synapse Section 9.7

29. Terms • Synapse: the junction between two communicating neurons. • Nerve pathways: the path that nerve impulses travel on from neuron to neuron. • Presynaptic neuron: the neuron that is sending a message from it’s cell body through its axon. • Postsynaptic neuron: the neuron that is receiving the message in its dendrites.

30. Synaptic Transmission • The impulse from the presynaptic neuron travels to the postsynaptic neuron through synaptic transmission. • The synapse is not a surface/surface meeting, there is a break called the synaptic cleft. • The information crosses that gap by using neurotransmitters – chemicals that transmit information. • They are carried in synaptic vessicles.

31. Excitatory vs inhibitory • Excitatory neurotransmitters – increase the ability for the nerve to send an impulse/trigger impulses • Inhibitory neurotransmitters – decrease the chance that the nerve will send an impulse.

32. Peripheral Nervous System Section 9.14

33. Spinal Nerves • Originate from the spinal cord. • Named according to groupings: • 8 pairs of cervical nerves • 12 pairs of thoracic nerves • 5 pairs of lumbar nerves • 5 pairs of sacral nerves • 1 pair of coccygeal nerves • 3 plesuxes • Cervical – form from the branches of the first 4 cervical nerves • Brachial – branches of the lower 4 cervical nerves and 1st thoracic nerve • Lumbosacral – last thoracic nerve and lumbar, sacral and coccygeal nerves

34. Autonomic Nervous System Section 9.15

35. Autonomic Nervous system • Portion of the PNS that functions independently • Has two parts: • Sympathetic • Parasympathetic • The two parts work as antagonists