Ch. 9 The Nervous System

1. Ch. 9 The Nervous System

2. The Nervous System It is comprised of 3 basic components Brain Spinal cord Nerves

3. General Functions of the Nervous System • Sensation • Monitors changes/events occurring in and outside the body. Such changes are known as stimuli and the cells that monitor them are sensoryreceptors. • Integration • The parallel processing and interpretation of sensory information to determine the appropriate response (Conscious or subconscious) • Reaction • Motor output or the activation of effectors such as muscles or glands (typically via the release of neurotransmitters).

4. Organization of the Nervous System 2 big initial divisions: • Central Nervous System • The brain + the spinal cord • The center of integration and control • Peripheral Nervous System • The nervous system outside of the brain and spinal cord • Consists of: • 31 Spinal nerves • Carry info to and from the spinal cord • 12 Cranial nerves • Carry info to and from the brain

5. What is the basic functional unit of the nervous system? • Neuron! • What does the neuron do? • Carries messages throughoutthe body • How does it carry the messages? • By conducting electrical signals • What are these signals called? • Nerve impulses!

6. Neuron Anatomy • Three parts to a NEURON: • Cell body: Large, central portion of the neuron where all organelles are located. • What is its job? • Interpret incoming signals Cell Body

7. Neuron Anatomy Dendrites 2. Dendrites: Short, highly branched fibers • What is its job? • Carries impulses toward the cell body • Referred to as the afferent process

8. Neuron Anatomy 3. Axon: Long, slightly branched fiber • What is its job? • Carry impulses away from the cell body • Referred to as the efferent process

9. Neuron Anatomy Three parts of the Axon: • Axon hillock: site of initiation of an action potential (point where axon and cell body meet) • B. Axon fiber: the main portion of the axon • C. Axon terminal:branched end of the axon (point of communication with other cells)

10. The Axon Axon Hillock fiber Axon Terminals

11. Structure of a Typical Neuron Dendrite Axon terminal Cell body Nodes of Ranvier Axon Myelin sheath Nucleus Neuron Anatomy Additional Parts of a Neuron

12. 1 6 2 3 5 4 7 Neuron anatomy What do you remember? dendrites Myelinsheath nucleus Direction of impulse Cell body axon Nodes ofRanvier Axonterminals

13. 3 Types of Neurons A. Sensory Neurons: Receive incoming stimuli • Five types of sensory neurons: • Thermo-receptors • Mechano-receptors • Chemo-receptors • Photo-receptors • Pain-receptors

14. Thermo-receptors • Location: • Skin • Hypothalamus • Body Core • Function: • Sensation of hot and cold • Detects change in body core temp.

15. Mechano-receptors • Location: • Skin • Skeletal muscle • Inner ear • Function: • Touch • Pressure • Muscle movement • Motion • Sound

16. Chemo-receptors • Location: • Nose • Tongue (taste buds) • Blood vessels • Function: • Smell • Taste • Detects levels of CO2 in blood

17. Photo-receptors • Location: • Eyes • Function: • Allow vision thru detection of light

18. Pain-receptors • Location: • Everywhere, except the brain • Function: • Sensation of pain • Detects chemicals released by damaged cells

19. Three Types of Neurons B. Motor Neurons: Carry impulses to muscles and glands Cause a response to some stimuli C. Interneurons: Connect sensory and motor neurons Allow for quick response (reflex action)

20. Three types of neurons

21. Structural diversity in neurons • Multipolar- many dendrites, one axon • Most neurons in CNS • Bipolar- one dendrite, one axon • Sensory organs • Unipolar- sensory • Axon termini extend into CNS

22. White matter Gray matter Neurons • What is grey matter? • Collective cell bodies and dendrites of all neurons • What is white matter? • Myelinated nerve fibers • Axons of all neurons • Can be approximatelyone meter in length

23. What is a Nerve? • Bundle of axonsheld together by connective tissue. • What color isa nerve? • White! • Why? • Because axons are white matter and they composenerves

24. How are nerves held together? • Connective tissue • What is this connective tissue called? • Neuroglial cells (nerve glue) • Approximately half of the volume of the brain is composed of neuroglial cells • Most brain tumors develop in mesoglial cells – NOT neurons

25. What do neuroglial cells do? • Support the axons • Insulate the electrical impulses • Like electrical tape insulates electric wires this prevents “leaking”of electric signals

26. Four types of neuroglia in CNS • Oligodendrocytes • Myelinating cells • Astrocytes • Connects neurons and blood vessels together • Microglia • Phagocytes (from bone marrow) • Ependymal cells • Line ventricles of brain; produce cerebrospinal fluid (CSF)

28. Neuroglia of the PNS • Schwann cells • Myelinating cells • Help direct axon regeneration • Satellite cells • Support, protection, regulation of molecular exchange • “Filter out” other stimuli

29. The Nerve Impulse • Resting potential – the charge that exists across a neuron’s membrane while at rest. • -70 mV. • This is the starting point for an action potential.

30. The Nerve Impulse • A nerve signal or action potential is an electrochemical message of neurons. • An all-or-none phenomenon – either the fiber is conducting an action potential or it is not. • Across its plasma membrane, every cell has a voltage called a membrane potential. • The inside of a cell is negative relative to the outside.

31. The Nerve Impulse • Neuron at rest – active transport channels in the neuron’s plasma membrane pump: • Sodium ions (Na+) out of the cell. • Potassium ions (K+) into the cell. • More sodium is moved out; less potassium is moved in. • Result is a negative charge inside the cell. • Cell membrane is now polarized.

32. Sodium-Potassium Exchange Pump • Na+ flows into the cell during an action potential, it must be pumped out using sodium pumps so that the action potential will continue.

33. The Nerve Impulse • A nerve impulsestarts when pressure or other sensory inputs disturb a neuron’s plasma membrane, causing sodium channels on a dendrite to open. • Sodium ions flood into the neuron and the membrane is depolarized – more positive inside than outside.

34. The Nerve Impulse • This moving local reversal of voltage is called an action potential. • A very rapid and brief depolarization of the cell membrane. • Membrane potential changes from -70 mV to +35 mV. • After the action potential has passed, the voltage gated channels snap closed and the resting potential is restored. • The membrane potential quickly returns to -70 mV during the repolarization phase. • An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane. • Carries information along axons. • An action potential is self-propagating – once started it continues to the end.

36. Synapses: Junctions Between Nerves • Eventually, the impulse reaches the end of the axon. • Neurons do not make direct contact with each other. • The junction between the axon of one neuron and the dendrite of the next is called a synapse .

37. Synaptic Pathways • Presynaptic neurons bring action potentials toward the synapse. • Postsynaptic neurons carry action potentials away from the synapse. • A synaptic cleft is the small gap between the two neurons.

38. Neurotransmitters • Chemical messengers called neurotransmitters carry the message of the nerve impulse across the synapse.

39. Neurotransmitters • Neurotransmitters are released into the synapse and bind with receptors on the postsynaptic cell membrane, which cause ion channels to open in the new cell.

40. Acetylcholine – Example Neurotransmitter

41. Reflex Arc • A simple reflex produces a very fast motor response to a stimulus because the sensory neuron bringing information about the stimulus passes the information directly to the motor neuron.

42. Reflex Arc • Usually, there are interneurons between sensory and motor neurons. • An interneuron may connect two neurons on the same side of the spinal cord, or on opposite sides.

43. The Central Nervous System • Meninges – are membranes that protect the brain and spinal cord • Dura mater (outermost layer) • Arachnoid membrane ( middle layer) • Pia mater (innermost layer)

44. The Central Nervous System • Cerebrospinal Fluid (CSF) • Located between the arachnoid mater and pia mater is an area called the subarachnoid space • Continuously secreted from specialized cells (ependymal cells) in the choroid plexus in ventricles • Functions: Physical and chemical protection of the CNS

45. Spinal Cord • Slender structure that is continuous with the brain • Descends into the vertebral canal and ends around the level of the first or second lumbar vertebra. • Function of the spinal cord is to carry sensory information to and from the brain • 31 spinal segments: • 8 cervical segments • 12 thoracic segments • 5 lumbar segments • 5 sacral segments • 1 coccygeal segment

46. Spinal Cord - Ascending and Descending Tracts • Ascending tracts - carry sensory information up to the brain • Descending tracts - carry motor information down from the brain to muscles and glands

47. The Brain Four Parts: Cerebrum Diencephalons Brain stem Cerebellum

48. The Brain - Cerebrum • Largest part of the brain • Two halves cerebral hemispheres • Thick bundle of nerve fibers called the corpus callosum connect the two hemispheres • Lobes • Frontal • Parietal • Temporal • Occipital • Cortex • Ventricles

49. The Brain - Diencephalons Located between the cerebral hemispheres and is superior to the brain stem • Thalamus - relay station for sensory information that heads to the cerebral cortex for interpretation • Hypothalamus - maintains balance by regulating many vital activities such as heart rate, blood pressure, and breathing rate.

50. The Brain - Brain stem • Midbrain - controls both visual and auditory reflexes • Pons - regulates breathing Connects the cerebrum to the spinal cord • Medulla oblongata - controls many vital activities such as heart rate, blood pressure, and breathing