1. Human Anatomy & Physiology I
Nervous System
Human Anatomy & Physiology I

2. Structures of the Nervous System
The nervous system is a complex, highly organized network of billions of neurons and even more neuroglia.

3. Brain
The skull encloses the brain, which contains about 100 billion (1011) neurons.

4. Cerebral cortex areas & functions
Sensory areas receive information and interpret sensory impulses.
Motor areas initiate movements.
Association areas deal with more complex integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence.

5. Primary motor area
Located in the precentral gyrus of the frontal lobe.
Each region in the primary motor area controls voluntary contractions of specific muscles or groups of muscles (cortical [motor] homunculus).

6. Cortical (sensory) homunculus
Each point within the area receives impulses from a specific part of the body.
The size of the cortical area receiving impulses from a particular depends on the number of receptors there rather than on the size of the body part.
The major function of the primary somatosensory area is to localize exactly the points of the body where sensations originate.

7. Broca’s & Wernicke’s area
Located in the frontal lobe close to the lateral cerebral sulcus.
Speaking and understanding language are complex activities that involve several sensory, association, and motor areas of the cortex.
In 97% of the population, these language areas are localized in the left hemisphere.

8. Broca’s speech area
The planning and production of speech occurs in Broca’s speech area, located in the frontal lobe – the left frontal lobe in most people.
From Broca’s speech area, nerve impulses pass to the premotor regions that control the muscles of the larynx, pharynx, and mouth.

9. Wernicke’s area Broad region in the temporal and parietal lobes.
This area interprets the meaning of speech by recognizing spoken words.
It is active as you translate words into thoughts.

10. Broca’s & Wernicke’s area
The region in the right hemisphere that correspond to Broca’s and Wernicke’s areas in the left hemisphere also contribute to verbal communication by adding emotional content, for instance anger or joy, to spoken words.

11. Cranial Nerves
Twelve pairs (right and left) of cranial nerves, numbered I through XII, emerge from the base of the brain.

12. Nerves
A nerve is a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord.

13. Spinal Cord Anatomy
Protective Structures
Bony vertebrae
Meninges
CSF

14. Vertebral Column
The spinal cord is located within the vertebral canal of the vertebral column.
The vertebral foramina of all the vertebrae, stacked one on top of the other, form the canal.
The vertebral ligaments, meninges, and CFS provide additional support.

15. Meninges
The meninges (meninx: singular) ate the three connective tissue coverings that encircles the spinal cord and brain.
Two subdivision:
Spinal meninges
Cranial meninges
Three layers:
Dura mater
Arachnoid mater
Pia mater

16. Dura mater The most superficial of the three meninges.
Is composed of dense, irregular connective tissue.
Forms a sac form the level of the foramen magnum in the occipital bone, where it is continous with the dura mater in the brain, to the 2nd sacral vertebra.

17. Arachnoid mater
The middle meninx is an avascular covering called the arachnoid mater.
Spider web arrangement of delicate collagen fibers and some elastic fibers.
Between the dura mater and the arachnoid is a thin subdural space, which contains interstitial fluid.

18. Pia mater
The inner most meninx is the pia mater, a thin transparent connective tissue layer that adheres to the surface of the spinal cord and brain.
It consist of interlacing bundles of collagen fibers and some fine elastic fibers.

19. Spinal Cord
The spinal cord connects to the brain through the foramen magnum of the skull and is encircled by the bones of the vertebral column.
It contains about a 100 million neurons.

20. Spinal Cord
The length of the adult spinal cord ranges from 42 to 45 cm (16-18 inches).
It diameter is about 2 cm (0.75 inches) in the midthoracic region, somewhat larger in the lower cervical and midlumbar regions, and the inferior tip.

21. Gray matter
The gray matter of the spinal cord is shaped like the letter H or a butterfly and is surrounded by white matter.
The gray matter consist primarily of the cell bodies of neurons, neuroglia, unmyelinated axons, and the dendrites of interneurons and motor neurons.

22. White matter
The white matter consist of bundles of myelinated and unmyelinated axons of sensory neurons, interneurons, and motor neurons.

23. Conus medullaris
Inferior to the lumbar enlargement, the spinal cord tapers to a conical portion referred to as conus medullaris, which ends at the level of the intervertebral disc between the 1st and 2nd lumbar vertebra.

24. Filum terminale
Arising from the conus medullaris is the filum terminale, an extension of the pia mater that extends inferiorly and anchors the spinal cord to the coccyx.

25. Cauda equina
Nerves that arise from the inferior part of the spinal cord do not leave the vertebral column at the same level as they exit from the cord.
The roots (points of attachment to the spinal cord) of these nerves angle inferiorly in the vertebral canal to from the end of the spinal cord like whips of hair.
The roots of these nerves are collectively named the cauda equina.

26. Spinal Nerves
Thirty-one pairs of spinal nerves emerge from the spinal cord, each serving a specific region on the right or left side of the body.

27. Spinal nerves
Each pair of spinal nerves is said to arise from a spinal segment.
The naming of the spinal nerves and spinal segments is based on their location.

28. Roots
Spinal nerves are the path of communication between the spinal cord and the nerves innervating specific regions of the body.
Two bundles of axons, called roots, connect each spinal nerve to a segment in the cord.

29. Posterior or Dorsal root
The posterior or dorsal root contains only sensory axons, which conduct nerve impulses form sensory receptors in the skin, muscles, and internal organs into the CNS.
Each dorsal root contains also has a swelling, the posterior or dorsal root ganglion, which contains the cell bodies of sensory neurons.

30. Ganglia
Ganglia (swelling or knot) are small masses of nervous tissue, containing primarily cell bodies of neurons, that are located outside the brain and spinal cord.
Ganglia are closely associated with cranial and spinal nerves.

31. Anterior or Ventral root
The anterior or ventral root contains axons of motor neurons, which conduct nerve impulses from the CNS to effector organs and cells.

32. Anterior (ventral) horns
The gray matter on each side of the spinal cord is subdivided into regions called horns.
The ventral horns contain cell bodies of somatic motor neurons and motor nuclei, which provide nerve impulses for contraction of skeletal muscles.

33. Posterior (dorsal) horns
The dorsal horns contain somatic and autonomic sensory nuclei.

34. Lateral horns Located between the anterior or posterior horns.
Present only in the thoracic, upper lumbar, and sacral segments of the spinal cord.
The lateral horns contain the cell bodies of autonomic motor neurons that regulate activity of smooth muscle, cardiac muscle, and glands.

35. Enteric Plexuses
In the walls of organs of the gastrointestinal tract are extensive networks of neurons, called enteric plexuses.
They help regulate the digestive system.

36. Sensory Receptors
Sensory receptors are either the dendrites of sensory neurons or separate, specialized cells that monitor changes in the internal or external environment, such as photoreceptors in the retina of the eye.

38. Functions of the Nervous System
Sensory
Integrative
Motor

39. Sensory Function
Sensory receptors detect internal stimuli, such as an increase in blood acidity, and external stimuli such as a raindrop landing in your arm.
The neurons that carry sensory information from cranial and spinal nerves into the brain and spinal cord or from lower to a higher level in the spinal cord and brain are sensory or afferent neurons (af – toward; ferrent – carried).

40. Integrative Function
The nervous system integrates or processes sensory information by analyzing and storing some of it and by making decision for appropriate responses.

41. Integrative Functions
Many of the neurons that participate in integration are interneurons, whose axons extend only for a short distance and contact nearby neurons in the brain, spinal cord, or a ganglion.
Interneurons comprise the vast majority of neurons in the body.

42. Motor Functions
The nervous system’s motor function involves responding to integration decisions.
The neurons that serve this function are motor or efferent neurons (ef: away from).

43. Motor Functions
Motor neurons carry information from the brain toward the spinal cord or out of the brain and spinal cord into cranial nerves or spinal nerves.
The cells and organs contacted by motor neurons in cranial and spinal nerves are termed effectors.
Muscle fibers and glandular cells are examples of effectors.

44. Organization of the Nervous System
The CNS (brain and spinal cord) integrates and correlates many different kind of incoming sensory information.
The CNS is also the source of thoughts, emotions, and memories.

45. Central Nervous System
Most nerves impulses that stimulate muscles to contract and glands to secrete originate in the CNS.

46. Peripheral Nervous System
Components of the PNS are cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory receptors.

47. Peripheral Nervous System
The PNS may be subdivided further into a somatic nervous system (SNS), and autonomic nervous system (ANS), and an enteric nervous system (ENS).

48. Somatic Nervous System
The SNS consists of (1) sensory neurons that convey information from somatic receptors in the head, body walls, and limbs and from receptors for the special senses of vision, taste, and smell to the CNS.

49. Somatic Nervous System
The SNS consists of (2) motor neurons that conduct impulses from the CNS to skeletal muscles only.
Because these motor responses can be consciously controlled, the action of this part of the PNS is voluntary.

50. Autonomic Nervous System
The ANS consists of (1) sensory neurons that convey information from autonomic sensory receptors, located primarily in visceral organs such as the stomach and lungs, to the CNS.

51. Autonomic Nervous System
The ANS consists of (2) motor neurons that conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands.
Because its motor responses are not normally under conscious control, the actions of the ANS is involuntary.

52. Autonomic Nervous System
The motor part of the ANS consists of two branches: the sympathetic division and the parasympathetic division.
With a few exceptions, effectors are innervated by both divisions, and usually the two divisions have opposing actions.
For example, sympathetic neurons increase heart rate, whereas parasympathetic neurons slow it down.

53. Enteric Nervous System
The ENS is the “brain of the guts”, and its operation is involuntary.
Once considered part of the ANS, the ENS consists of approximately 100 million neurons in enteric plexuses that extend the entire length of the GI tract.

54. Histology of Nervous Tissue
Nervous tissue consists of two types of cells: neurons and neuroglia.
Neurons provide most of the unique functions of the nervous system (i.e. sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions.

55. Histology of Nervous Tissue
Neuroglia supports, nourish, and protect the neurons and maintain homeostasis in the interstitial fluid that bathes neurons.

56. Structures of a Neuron

57. Parts of a Neuron
Cell body
Dendrites
Axon

58. Cell Body
The cell body contains a nucleus surrounded by cytoplasm that includes typical organelles such as lysosomes, mitochondria, and a Golgi complex.

59. Dendrites & Axon
Two kinds of processes or extensions emerge from the cell body of a neuron: multiple dendrites and a single axon.
Nerve fiber is the general term for any neuronal process (dendrite or axon).

60. Dendrites
Dendrites (little trees) are the receiving or input portions of a neuron.
They are usually short, tapering, and highly branched.

61. Axon
The single axon (axis) of a neuron propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell.
An axon is a long, thin, cylindrical projection that often joints the body at a cone shaped elevation called the axon hillock (small hill).

62. Synapse
The site of communication between two neurons or between a neuron and an effector cell is called a synapse.
The tips of axon terminals swell into bulb-shaped structures called synaptic end bulbs.

63. Synaptic Vesicles
Synaptic end bulbs contain many membrane-enclosed sacs called synaptic vesicles that store a chemical neurotransmitter.
Many neurons contain two or three types of neurotransmitters.
When neurotransmitters are released from synaptic vesicles, they excite or inhibit other neurons, muscle fibers, or gland cells.

64. Structural Diversity in Neurons
Multipolar neurons
Bipolar neurons
Unipolar neurons

65. Multipolar Neuron Usually have several dendrites and one axon.
Most neurons in the brain and spinal cord are of this type.

66. Bipolar Neurons They have one main dendrite and one axon.
They are found in the retina of the eye, in the inner ear, and in the olfactory area of the brain.

67. Unipolar Neurons
These are sensory neurons that begin in the embryo as bipolar neurons.
During development, the axon and dendrite fuse into a single process that divides into two branches a short distance from the body.

68. Neuroglia
Neuroglia or glia (glue) constitute about half the volume of the CNS.
Neuroglia are smaller than neurons, and they are 5 to 50 times more numerous.
In contrast to neurons, glia do not generate of propagate action potentials, and they can multiply and divide in the mature nervous system.
In the case of injury or disease, neuroglia multiply and to fill the in the spaces formerly occupied by neurons.

69. Neuroglial Cells of CNS
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Capillary
Neurons
Astrocyte
Oligodendrocyte
Perivascular feet
Myelinated axon
Ependymal cell
Myelin (cut)
Cerebrospinal fluid
Microglia
Figure 12.6
12-69

70. Myelination
The axons of most mammalian neurons are surrounded by a multilayer lipid and protein covering, called the myelin sheath, that is produced by neuroglia.
The sheath electrically insulates the axon of a neuron and increases the speed of nerve impulse conduction.

71. Myelination
Axons without such a covering are said to be unmyelinated, whereas those with it are myelinated.
Two types of neuroglia produce myelin sheaths: Schawnn cells (PNS) and oligodendrocytes (CNS).
Gaps in the myelin sheath, called Nodes of Ranvier, appear at intervals along the axon.

72. Myelination in PNS Figure 12.7a 12-72 Schwann cell Axon Basal lamina
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Schwann cell
Axon
Basal lamina
Endoneurium
Nucleus
(a)
Neurilemma
Myelin sheath
Figure 12.7a
12-72

73. Myelination in CNS Figure 12.7b 12-73 Oligodendrocyte Myelin
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Oligodendrocyte
Myelin
Nerve fiber
Figure 12.7b
12-73
(b)

74. Electrical Signal in Neurons
Like muscle fibers, neurons are electrically excitable.
They communicate with one another using two types of electrical signals:
Action potentials
Graded potentials

75. Electrical Signal in Neurons
Action potentials allow the communication over both short and long distances within the body.
Graded potentials are used for short-distance only.

76. Action Potentials
An action potential (AP) or nerve impulse is a sequence of rapidly occurring events that take place in two phases: depolarizing phase and repolarizing phase.

77. Action Potentials
During the depolarizing phase, the negative membrane potential decreases toward zero and eventually becomes positive.
Then, the repolarizing phase restores the membrane potential to the resting state of -70 mV.

78. Action Potentials
During an AP, two types of voltage-gated channels open and then close.
These channels are present mainly in the plasma membrane of the axon and axon terminals.
The first channels that open, the Na+ channels, allow Na+ to rush into the cell, which causes depolarization.

79. Action Potentials
Then K+ channels open, allowing K+ to flow out, which produces the repolarizing phase.
Together, the depolarization and repolarization phases last about 1 msec (0.001 sec) in a typical neuron.

80. All-or-none principle
Action potentials arise according to the all-or-none principle.
When depolarization reaches a certain level termed the threshold (about -55 mV in most neurons), the voltage-gated channels open, and an AP that is always the same amplitude (size) occurs.

81. Saltatory Conduction
Nerve impulses propagate more rapidly along myelinated axons than along unmyelinated axons.
Saltatory conduction (saltat: leaping) is the special mode of impulse propagation that occurs along myelinated axons.