Chapter 7. The Nervous System. Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College Pearson Education, Inc.

Transcription

1 Chapter 7 The Nervous System Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College

2 Functions of the Nervous System 1. Sensory input gathering information To monitor Δs occurring inside and outside the body Δs stimuli 2. Integration To process and interpret sensory input and decide whether action is needed

3 Functions of the Nervous System 3. Motor output A response to integrated stimuli The response activates muscles or glands

4 Figure 7.1 The nervous system s functions. Sensory receptor Sensory input Motor output Effector Brain and spinal cord

5 Concept Link

6 Organization of the Nervous System Nervous system is classified based on: Structures (structural classification) Activities (fxnl classification)

7 Structural Classification of the Nervous System Central nervous system (CNS) Organs Fxn Brain Spinal cord Integration; command center Interpret incoming sensory information Issues outgoing instructions

8 Structural Classification of the Nervous System Peripheral nervous system (PNS) Nerves extending from the brain and spinal cord Spinal nerves carry impulses to and from the spinal cord Cranial nerves carry impulses to and from the brain Functions Serve as communication lines among sensory organs, the brain and spinal cord, and glands or muscles

9 Figure 7.2 Organization of the nervous system. Central Nervous System (brain and spinal cord) Peripheral Nervous System (cranial and spinal nerves) Sensory (afferent) Motor (efferent) Sense organs Somatic (voluntary) Skeletal muscles Autonomic (involuntary) Cardiac and smooth muscle, glands Parasympathetic Sympathetic

10 Functional Classification of the Peripheral Nervous System Sensory (afferent) division Nerve fibers that carry information to the central nervous system Somatic sensory fibers carry information from the skin, skeletal muscles, and joints Visceral sensory fibers carry information from visceral organs Motor (efferent) division Nerve fibers that carry impulses away from the central nervous system organs

11 Figure 7.2 Organization of the nervous system. Central Nervous System (brain and spinal cord) Peripheral Nervous System (cranial and spinal nerves) Sensory (afferent) Motor (efferent) Sense organs Somatic (voluntary) Skeletal muscles Autonomic (involuntary) Cardiac and smooth muscle, glands Parasympathetic Sympathetic

12 Functional Classification of the Peripheral Nervous System Motor (efferent) division (continued) Two subdivisions Somatic nervous system voluntary Consciously controls skeletal muscles Autonomic nervous system involuntary Automatically controls smooth and cardiac muscles and glands Further divided into the sympathetic and parasympathetic nervous systems

13 Nervous Tissue: Support Cells Support cells in the CNS are grouped together as neuroglia General functions Support Insulate Protect neurons

14 Nervous Tissue: Support Cells CNS glial cells: astrocytes Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain

15 Figure 7.3a Supporting (glial) cells of nervous tissue. Capillary Neuron Astrocyte (a) Astrocytes are the most abundant and versatile neuroglia.

16 Nervous Tissue: Support Cells CNS glial cells: microglia Spiderlike phagocytes Dispose of debris

17 Figure 7.3b Supporting (glial) cells of nervous tissue. Neuron Microglial cell (b) Microglial cells are phagocytes that defend CNS cells.

18 Nervous Tissue: Support Cells CNS glial cells: ependymal cells Line cavities of the brain and spinal cord Cilia assist with circulation of cerebrospinal fluid

19 Figure 7.3c Supporting (glial) cells of nervous tissue. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinal fluid-filled cavities.

20 Nervous Tissue: Support Cells CNS glial cells: oligodendrocytes Wrap around nerve fibers in the central nervous system Produce myelin sheaths

21 Figure 7.3d Supporting (glial) cells of nervous tissue. Myelin sheath Process of oligodendrocyte Nerve fibers (d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers.

22 Nervous Tissue: Support Cells PNS glial cells Satellite cells Protect neuron cell bodies Schwann cells Form myelin sheath in the peripheral nervous system

23 Figure 7.3e Supporting (glial) cells of nervous tissue. Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS.

24 Nervous Tissue: Neurons Neurons nerve cells Cells specialized to transmit messages Major regions of neurons Cell body nucleus and metabolic center of the cell Processes fibers that extend from the cell body

25 Nervous Tissue: Neurons Cell body Nissl bodies Specialized rough endoplasmic reticulum Neurofibrils Intermediate cytoskeleton Maintains cell shape Nucleus with large nucleolus

26 Figure 7.4a Structure of a typical motor neuron. Mitochondrion Dendrite Cell body Nissl substance Axon hillock Axon Nucleus Neurofibrils Collateral branch One Schwann cell Axon terminal Node of Ranvier Schwann cells, forming the myelin sheath on axon (a)

27 Figure 7.4b Structure of a typical motor neuron. Neuron cell body Dendrite (b)

28 Nervous Tissue: Neurons Processes outside the cell body Dendrites conduct impulses toward the cell body Neurons may have hundreds of dendrites Axons conduct impulses away from the cell body Neurons have only one axon arising from the cell body at the axon hillock

29 Figure 7.4a Structure of a typical motor neuron. Mitochondrion Dendrite Cell body Nissl substance Axon hillock Axon Nucleus Neurofibrils Collateral branch One Schwann cell Axon terminal Node of Ranvier Schwann cells, forming the myelin sheath on axon (a)

30 Nervous Tissue: Neurons Axons End in axon terminals Axon terminals contain vesicles with neurotransmitters Axon terminals are separated from the next neuron by a gap Synaptic cleft gap between adjacent neurons Synapse junction between nerves

31 Nervous Tissue: Neurons Myelin sheath whitish, fatty material covering axons Schwann cells produce myelin sheaths in jelly roll like fashion around axons (PNS) Nodes of Ranvier gaps in myelin sheath along the axon Oligodendrocytes produce myelin sheaths around axons of the CNS Myelin sheaths speed the nerve impulse transmission

32 Figure 7.5 Relationship of Schwann cells to axons in the peripheral nervous system. Schwann cell cytoplasm Axon (a) Schwann cell plasma membrane Schwann cell nucleus (b) Neurilemma Myelin sheath (c)

33 Neuron Cell Body Location Most neuron cell bodies are found in the central nervous system Gray matter cell bodies and unmyelinated fibers Nuclei clusters of cell bodies within the white matter of the central nervous system Ganglia collections of cell bodies outside the central nervous system

34 Neuron Cell Body Location Tracts bundles of nerve fibers in the CNS Nerves bundles of nerve fibers in the PNS White matter collections of myelinated fibers (tracts) Gray matter collections of mostly unmyelinated fibers and cell bodies

35 Functional Classification of Neurons Sensory (afferent) neurons Carry impulses from the sensory receptors to the CNS Cutaneous sense organs Proprioceptors detect stretch or tension

36

37 Figure 7.6 Neurons classified by function. Dendrites Peripheral process (axon) Ganglion Cell body Central process (axon) Sensory neuron Spinal cord (central nervous system) Peripheral nervous system Afferent transmission Interneuron (association neuron) Receptors Efferent transmission Motor neuron To effectors (muscles and glands)

38 Figure 7.7a Types of sensory receptors. Pain receptors nociceptors - are bare nerve endings, least specialized, and most numerous Temperature receptors are thermoreceptors (a) Free nerve endings (pain and temperature receptors)

39 Figure 7.7b Types of sensory receptors. (b) Meissner s corpuscle (touch receptor)

40 Figure 7.7c Types of sensory receptors. Pacinian Corpuscles (c) Lamellar corpuscle (deep pressure receptor)

41 Figure 7.7d Types of sensory receptors. (d) Golgi tendon organ (proprioceptor) Proprioceptors constantly advise brain of own movement

42 Figure 7.7e Types of sensory receptors. (e) Muscle spindle (proprioceptor)

43 Functional Classification of Neurons Motor (efferent) neurons Carry impulses from the central nervous system to viscera, muscles, or glands Interneurons (association neurons) Found in neural pathways in the central nervous system Connect sensory and motor neurons

44 Figure 7.6 Neurons classified by function. Dendrites Peripheral process (axon) Ganglion Cell body Central process (axon) Sensory neuron Spinal cord (central nervous system) Peripheral nervous system Afferent transmission Interneuron (association neuron) Receptors Efferent transmission Motor neuron To effectors (muscles and glands)

45 Structural Classification of Neurons Structural classification is based on number of processes extending from the cell body Multipolar neurons many extensions from the cell body All motor and interneurons are multipolar Most common structure

46 Figure 7.8a Classification of neurons on the basis of structure. Dendrites Cell body (a) Multipolar neuron Axon

47 Structural Classification of Neurons Bipolar neurons one axon and one dendrite Located in special sense organs, such as nose and eye Rare in adults

48 Figure 7.8b Classification of neurons on the basis of structure. Cell body Dendrite (b) Bipolar neuron Axon

49 Structural Classification of Neurons Unipolar neurons have a short single process leaving the cell body Sensory neurons found in PNS ganglia Conduct impulses both toward and away from the cell body

50 Figure 7.8c Classification of neurons on the basis of structure. Dendrites Cell body Short single process Axon Peripheral process (c) Unipolar neuron Central process

51 Functional Properties of Neurons Irritability Ability to respond to a stimulus and convert it to a nerve impulse Conductivity Ability to transmit the impulse to other neurons, muscles, or glands

52 Nerve Impulses Resting neuron The plasma membrane at rest is polarized As long as inside is more negative than outside, the cell stays at rest Fewer positive ions are inside the cell than outside the cell K is the major positive ion inside the cell Na is the major positive ion outside the cell

53 Figure 7.9 The nerve impulse. Slide 2 [Na + ] [K + ] 1 Resting membrane is polarized. In the resting state, the external face of the membrane is slightly positive; its internal face is slightly negative. The chief extracellular ion is sodium (Na + ), whereas the chief intracellular ion is potassium (K + ). The membrane is relatively impermeable to both ions.

54 Nerve Impulses Action potential initiation and generation A stimulus depolarizes the neuron s membrane The membrane is now permeable to sodium as sodium channels open A depolarized membrane allows sodium (Na ) to flow inside the membrane

55 Figure 7.9 The nerve impulse. Slide 3 Na + Na + 2 Stimulus initiates local depolarization. A Stimulus changes the permeability of a local patch of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane (the inside becomes more positive; the outside becomes more negative) at that site.

56 Nerve Impulses Action potential initiation and generation A stimulus leads to the movement of ions, which initiates an action potential in the neuron A graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive If the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)

57 Figure 7.9 The nerve impulse. Slide 4 Na + 3 Depolarization and generation of an action potential. If the stimulus is strong enough, depolarization causes Na + membrane polarity to be completely reversed and an action potential is initiated.

58 Nerve Impulses Propagation of the action potential If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon All-or-none response means the nerve impulse either is propagated or is not Fibers with myelin sheaths conduct nerve impulses more quickly

59 Figure 7.9 The nerve impulse. Slide 5 4 Propagation of the action potential. Depolarization of the first membrane patch causes permeability changes in the adjacent membrane, and the events described in step 2 are repeated. Thus, the action potential propagates rapidly along the entire length of the membrane.

60 Nerve Impulses Repolarization Potassium ions rush out of the neuron after sodium ions rush in, repolarizing the membrane Repolarization involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge Until repolarization is complete, a neuron cannot conduct another nerve impulse

61 Figure 7.9 The nerve impulse. Slide 6 K + 5 Repolarization. Potassium ions diffuse out of the cell as K + the membrane permeability changes again, restoring the negative charge on the inside of the membrane and the positive charge on the outside surface. Repolarization occurs in the same direction as depolarization.

62 Nerve Impulses Repolarization Initial ionic conditions are restored using the sodiumpotassium pump This pump, using ATP, restores the original configuration Three sodium ions are ejected from the cell while two potassium ions are returned to the cell

63 K + Diffusion Na + Diffusion Figure 7.9 The nerve impulse. Slide 7 Cell exterior Cell interior Na + Na Na + K + + Na + pump K + K + K + K + Plasma membrane 6 Initial ionic conditions restored. The ionic conditions of the resting state are restored later by the activity of the sodium-potassium pump. Three sodium ions are ejected for every two potassium ions carried back into the cell.

64 Transmission of a Signal at Synapses When the action potential reaches the axon terminal, the electrical charge opens calcium channels

65 Figure 7.10 How neurons communicate at chemical synapses. Slide 2 Axon of transmitting neuron Receiving neuron Dendrite Axon terminal 1 Action potential arrives. Vesicles Synaptic cleft

66 Transmission of a Signal at Synapses Calcium, in turn, causes the tiny vesicles containing the neurotransmitter chemical to fuse with the axonal membrane

67 Figure 7.10 How neurons communicate at chemical synapses. Slide 3 2 Vesicle Transmitting neuron fuses with plasma membrane. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron

68 Transmission of a Signal at Synapses The entry of calcium into the axon terminal causes porelike openings to form, releasing the transmitter

69 Figure 7.10 How neurons communicate at chemical synapses. Slide 4 Vesicle Transmitting neuron 2 fuses with plasma membrane. 3 Neurotransmitter is released into synaptic cleft. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron

70 Transmission of a Signal at Synapses The neurotransmitter molecules diffuse across the synapse and bind to receptors on the membrane of the next neuron

71 Figure 7.10 How neurons communicate at chemical synapses. Slide 5 Vesicle Transmitting neuron 4 Neurotrans- 3 Neurotransmitter is released into synaptic cleft. 2 fuses with plasma membrane. mitter binds to receptor on receiving neuron s membrane. Synaptic cleft Ion channels Neurotransmitter molecules Receiving neuron

72 Transmission of a Signal at Synapses If enough neurotransmitter is released, graded potential will be generated Eventually an action potential (nerve impulse) will occur in the neuron beyond the synapse

73 Figure 7.10 How neurons communicate at chemical synapses. Slide 6 Neurotransmitter Receptor Na + 5 Ion channel opens.

74 Transmission of a Signal at Synapses The electrical changes prompted by neurotransmitter binding are brief The neurotransmitter is quickly removed from the synapse by either: Reuptake Enzymatic activity Transmission of an impulse is electrochemical Transmission down neuron is electrical Transmission to next neuron is chemical

75 Figure 7.10 How neurons communicate at chemical synapses. Slide 7 Neurotransmitter is broken down and released. Na + 6 Ion channel closes.

76 BioFlix: How Synapses Work

77 The Reflex Arc Reflexes are: Rapid Predictable Involuntary responses to a stimulus Reflexes occur over neural pathways called reflex arcs

78 Figure 7.11a Simple reflex arcs. Stimulus at distal end of neuron 1 Receptor 5 Skin Effector (a) Five basic elements of reflex arc 2 Sensory neuron 4 Motor neuron Spinal cord (in cross section) 3 Integration center Interneuron

79 The Reflex Arc Somatic reflexes Reflexes that stimulate the skeletal muscles Example: pulling your hand away from a hot object Autonomic reflexes Regulate the activity of smooth muscles, the heart, and glands Example: regulation of smooth muscles, heart and blood pressure, glands, digestive system

80 The Reflex Arc Five elements of a reflex: 1. Sensory receptor reacts to a stimulus 2. Sensory neuron carries message to the integration center 3. Integration center (CNS) processes information and directs motor output 4. Motor neuron carries message to an effector 5. Effector organ is the muscle or gland to be stimulated

81 Figure 7.11a Simple reflex arcs. Slide 2 Stimulus at distal end of neuron Skin 1 Receptor (a) Five basic elements of reflex arc

82 Figure 7.11a Simple reflex arcs. Slide 3 Stimulus at distal end of neuron 1 Receptor Skin 2 Sensory neuron Spinal cord (in cross section) Interneuron (a) Five basic elements of reflex arc

83 Figure 7.11a Simple reflex arcs. Slide 4 Stimulus at distal end of neuron 1 Receptor Skin 2 Sensory neuron Spinal cord (in cross section) 3 Integration center Interneuron (a) Five basic elements of reflex arc

84 Figure 7.11a Simple reflex arcs. Slide 5 Stimulus at distal end of neuron 1 Receptor Skin (a) Five basic elements of reflex arc 2 Sensory neuron 4 Motor neuron Spinal cord (in cross section) 3 Integration center Interneuron

85 Figure 7.11a Simple reflex arcs. Slide 6 Stimulus at distal end of neuron 1 Receptor 5 Skin Effector (a) Five basic elements of reflex arc 2 Sensory neuron 4 Motor neuron Spinal cord (in cross section) 3 Integration center Interneuron

86 Two-Neuron Reflex Arc Two-neuron reflex arcs Simplest type Example: patellar (knee-jerk) reflex

87 Figure 7.11b Simple reflex arcs. Slide 1 1 Sensory (stretch) receptor 2 Sensory (afferent) neuron 3 4 Motor (efferent) neuron 5 Effector organ (b) Two neuron reflex arc

88 Figure 7.11b Simple reflex arcs. Slide 2 1 Sensory (stretch) receptor (b) Two neuron reflex arc

89 Figure 7.11b Simple reflex arcs. Slide 3 1 Sensory (stretch) receptor 2 Sensory (afferent) neuron (b) Two neuron reflex arc

90 Figure 7.11b Simple reflex arcs. Slide 4 1 Sensory (stretch) receptor 2 Sensory (afferent) neuron 3 (b) Two neuron reflex arc

91 Figure 7.11b Simple reflex arcs. Slide 5 1 Sensory (stretch) receptor 2 Sensory (afferent) neuron 3 4 Motor (efferent) neuron (b) Two neuron reflex arc

92 Figure 7.11b Simple reflex arcs. Slide 6 1 Sensory (stretch) receptor 2 Sensory (afferent) neuron 3 4 Motor (efferent) neuron 5 Effector organ (b) Two neuron reflex arc

93 Three-Neuron Reflex Arc Three-neuron reflex arcs Consists of five elements: receptor, sensory neuron, interneuron, motor neuron, and effector Example: flexor (withdrawal) reflex

94 Figure 7.11c Simple reflex arcs. Slide 1 1 Sensory receptor 2 Sensory (afferent) neuron 3 Interneuron 4 Motor (efferent) neuron 5 Effector organ (c) Three-neuron reflex arc

95 Figure 7.11c Simple reflex arcs. Slide 2 1 Sensory receptor (c) Three-neuron reflex arc

96 Figure 7.11c Simple reflex arcs. Slide 3 1 Sensory receptor 2 Sensory (afferent) neuron (c) Three-neuron reflex arc

97 Figure 7.11c Simple reflex arcs. Slide 4 1 Sensory receptor 2 Sensory (afferent) neuron 3 Interneuron (c) Three-neuron reflex arc

98 Figure 7.11c Simple reflex arcs. Slide 5 1 Sensory receptor 2 Sensory (afferent) neuron 3 Interneuron 4 Motor (efferent) neuron (c) Three-neuron reflex arc

99 Figure 7.11c Simple reflex arcs. Slide 6 1 Sensory receptor 2 Sensory (afferent) neuron 3 Interneuron 4 Motor (efferent) neuron 5 Effector organ (c) Three-neuron reflex arc

100 Central Nervous System (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Four chambers within the brain Filled with cerebrospinal fluid

101 Figure 7.12a Development and regions of the human brain. (a) 13 weeks Cerebral hemisphere Outline of diencephalon Midbrain Cerebellum Brain stem

102 Figure 7.18a Ventricles and location of the cerebrospinal fluid. Lateral ventricle Septum pellucidum Inferior horn Lateral aperture Anterior horn Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view

103 Regions of the Brain Cerebral hemispheres (cerebrum) Diencephalon Brain stem Cerebellum

104 Figure 7.12b Development and regions of the human brain. Cerebral hemisphere Diencephalon Cerebellum (b) Adult brain Brain stem

105 Table 7.1 Functions of Major Brain Regions (1 of 2)

106 Table 7.1 Functions of Major Brain Regions (2 of 2)

107 Regions of the Brain: Cerebrum Cerebral hemispheres are paired (left & right) superior parts of the brain Includes more than half of the brain mass The surface is made of ridges (gyri) and grooves (sulci) Three main regions of cerebral hemisphere 1. Cortex (gray matter) 2. White matter 3. Basal nuclei (deep pockets of gray matter)

108 Figure 7.13a Left lateral view of the brain. Precentral gyrus Frontal lobe Central sulcus Postcentral gyrus Parietal lobe Parieto-occipital sulcus (deep) Lateral sulcus Occipital lobe Cerebral cortex (gray matter) Gyrus Sulcus Temporal lobe Cerebellum Pons Medulla oblongata Spinal cord (a) Fissure (a deep sulcus) Cerebral white matter

109 Regions of the Brain: Cerebrum Lobes of the cerebrum Fissures (deep grooves) divide the cerebrum into lobes Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe

110 Figure 7.13b Left lateral view of the brain. Parietal lobe Left cerebral hemisphere Frontal lobe Temporal lobe Occipital lobe Cephalad (b) Caudal Brain stem Cerebellum

111 Regions of the Brain: Cerebrum Specialized areas of the cerebrum Primary somatic sensory area Receives impulses from the body s sensory receptors Pain, temperature, light touch Located in parietal lobe posterior to central sulcus Sensory homunculus is a spatial map Left side of the primary somatic sensory area receives impulses from right side (and vice versa)

112 Figure 7.13c Left lateral view of the brain. Primary motor area Premotor area Anterior association area Working memory and judgment Problem solving Language comprehension (c) Broca s area (motor speech) Olfactory area Central sulcus Primary somatic sensory area Gustatory area (taste) Speech/language (outlined by dashes) Posterior association area Visual area Auditory area

113 Hip Neck Figure 7.14 Sensory and motor areas of the cerebral cortex. Posterior Motor map in precentral gyrus Motor Anterior Sensory Sensory map in postcentral gyrus Hip Knee Foot Lips Jaw Primary motor cortex (precentral gyrus) Toes Genitals Primary somatic sensory cortex (postcentral gyrus) Tongue Swallowing Intraabdominal

114 Regions of the Brain: Cerebrum Cerebral areas involved in special senses Visual area (occipital lobe) Auditory area (temporal lobe) Olfactory area (temporal lobe)

115 Regions of the Brain: Cerebrum Specialized areas of the cerebrum Primary motor area Sends impulses to skeletal muscles Located in frontal lobe Motor neurons form corticospinal (pyramidal) tract, which descends to spinal cord Motor homunculus is a spatial map

116 Figure 7.13c Left lateral view of the brain. Primary motor area Premotor area Anterior association area Working memory and judgment Problem solving Language comprehension (c) Broca s area (motor speech) Olfactory area Central sulcus Primary somatic sensory area Gustatory area (taste) Speech/language (outlined by dashes) Posterior association area Visual area Auditory area

117 Hip Neck Figure 7.14 Sensory and motor areas of the cerebral cortex. Posterior Motor map in precentral gyrus Motor Anterior Sensory Sensory map in postcentral gyrus Hip Knee Foot Lips Jaw Primary motor cortex (precentral gyrus) Toes Genitals Primary somatic sensory cortex (postcentral gyrus) Tongue Swallowing Intraabdominal

118 Regions of the Brain: Cerebrum Broca s area Involved in our ability to speak Usually in left hemisphere Wernicke s Area Understanding the written and spoken word

119 Figure 7.13c Left lateral view of the brain. Primary motor area Premotor area Anterior association area Working memory and judgment Problem solving Language comprehension (c) Broca s area (motor speech) Olfactory area Central sulcus Primary somatic sensory area Gustatory area (taste) Speech/language (outlined by dashes) Posterior association area Visual area Auditory area

120 Regions of the Brain: Cerebrum Layers of the cerebrum Gray matter outer layer in the cerebral cortex; composed mostly of neuron cell bodies Highly ridged and convoluted White matter fiber tracts deep to the gray matter Corpus callosum connects hemispheres and allows communication between hemispheres Basal nuclei (ganglia) islands of gray matter buried within the white matter

121 Figure 7.13a Left lateral view of the brain. Precentral gyrus Frontal lobe Central sulcus Postcentral gyrus Parietal lobe Parieto-occipital sulcus (deep) Lateral sulcus Occipital lobe Cerebral cortex (gray matter) Gyrus Sulcus Temporal lobe Cerebellum Pons Medulla oblongata Spinal cord (a) Fissure (a deep sulcus) Cerebral white matter

122 Figure 7.15 Frontal section of the brain showing commissural, association, and projection fibers running through the cerebrum and the lower CNS. Longitudinal fissure Lateral ventricle Basal nuclei (basal ganglia) Thalamus Superior Association fibers Commissural fibers (corpus callosum) Corona radiata Fornix Internal capsule Connect areas w/in a hemisphere Allows communication between hemispheres Third ventricle Pons Medulla oblongata Projection fibers Connect cerebrum to lower CNS centers

123 Regions of the Brain: Diencephalon Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts: 1. Thalamus 2. Hypothalamus 3. Epithalamus

124 Figure 7.12b Development and regions of the human brain. Cerebral hemisphere Diencephalon Cerebellum (b) Adult brain Brain stem

125 Figure 7.16a Diencephalon and brain stem structures. Third ventricle Anterior commissure Hypothalamus Optic chiasma Pituitary gland Cerebral hemisphere Corpus callosum Choroid plexus of third ventricle Occipital lobe of cerebral hemisphere Thalamus (encloses third ventricle) Pineal gland (part of epithalamus) Corpora quadrigemina Cerebral aqueduct Cerebral peduncle Midbrain (a) Mammillary body Pons Medulla oblongata Spinal cord Fourth ventricle Choroid plexus Cerebellum

126 Figure 7.16b Diencephalon and brain stem structures. Radiations to cerebral cortex Visual impulses Reticular formation Ascending general sensory tracts (touch, pain, temperature) (b) Auditory impulses Descending motor projections to spinal cord

127 Regions of the Brain: Diencephalon Thalamus Surrounds the third ventricle The relay station for sensory impulses Transfers impulses to the correct part of the cortex for localization and interpretation

128 Regions of the Brain: Diencephalon Hypothalamus Under the thalamus Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism Houses the limbic center for emotions Regulates the nearby pituitary gland Houses mammillary bodies for olfaction (smell)

129 Regions of the Brain: Diencephalon Epithalamus Forms the roof of the third ventricle Houses the pineal body (an endocrine gland) Includes the choroid plexus forms cerebrospinal fluid

130 Regions of the Brain: Brain Stem Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata

131 Figure 7.16a Diencephalon and brain stem structures. Third ventricle Anterior commissure Hypothalamus Optic chiasma Pituitary gland Cerebral hemisphere Corpus callosum Choroid plexus of third ventricle Occipital lobe of cerebral hemisphere Thalamus (encloses third ventricle) Pineal gland (part of epithalamus) Corpora quadrigemina Cerebral aqueduct Cerebral peduncle Midbrain (a) Mammillary body Pons Medulla oblongata Spinal cord Fourth ventricle Choroid plexus Cerebellum

132 Regions of the Brain: Brain Stem Midbrain Composed mostly of tracts of nerve fibers Two bulging fiber tracts, cerebral peduncles, convey ascending and descending impulses Four rounded protrusions, corpora quadrigemina, visual and auditory reflex centers

133 Regions of the Brain: Brain Stem Pons The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing

134 Regions of the Brain: Brain Stem Medulla oblongata The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts Contains important control centers Heart rate control Blood pressure regulation Breathing Swallowing Vomiting

135 Regions of the Brain: Brain Stem Reticular formation Diffuse mass of gray matter along the brain stem Involved in motor control of visceral organs Reticular activating system (RAS) Plays a role in awake/sleep cycles and consciousness Filter for incoming sensory information

136 Figure 7.16b Diencephalon and brain stem structures. Radiations to cerebral cortex Visual impulses Reticular formation Ascending general sensory tracts (touch, pain, temperature) (b) Auditory impulses Descending motor projections to spinal cord

137 Regions of the Brain: Cerebellum Two hemispheres with convoluted surfaces Controls balance and equilibrium Provides precise timing for skeletal muscle activity and coordination of body movements

138 Figure 7.16a Diencephalon and brain stem structures. Third ventricle Anterior commissure Hypothalamus Optic chiasma Pituitary gland Cerebral hemisphere Corpus callosum Choroid plexus of third ventricle Occipital lobe of cerebral hemisphere Thalamus (encloses third ventricle) Pineal gland (part of epithalamus) Corpora quadrigemina Cerebral aqueduct Cerebral peduncle Midbrain (a) Mammillary body Pons Medulla oblongata Spinal cord Fourth ventricle Choroid plexus Cerebellum

139 Protection of the Central Nervous System Scalp and skin Skull and vertebral column Meninges Cerebrospinal fluid (CSF) Blood-brain barrier

140 Figure 7.17a Meninges of the brain. Skin of scalp Periosteum Bone of skull Superior sagittal sinus Subdural space Subarachnoid space (a) Periosteal Meningeal Dura mater Arachnoid mater Pia mater Arachnoid villus Blood vessel Falx cerebri (in longitudinal fissure only)

141 Meninges Dura mater Tough outermost layer Double-layered external covering Periosteum attached to inner surface of the skull Meningeal layer outer covering of the brain Folds inward in several areas Falx cerebri Tentorium cerebelli

142 Meninges Arachnoid layer Middle layer Weblike extensions span the subarachnoid space Arachnoid villi reabsorb cerebrospinal fluid Pia mater Internal layer Clings to the surface of the brain

143 Figure 7.17b Meninges of the brain. (b) Occipital lobe Tentorium cerebelli Cerebellum Arachnoid mater over medulla oblongata Skull Scalp Superior sagittal sinus Dura mater Transverse sinus Temporal bone

144 Cerebrospinal Fluid (CSF) Similar to blood plasma composition Formed by the choroid plexus Choroid plexuses capillaries in the ventricles of the brain Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord

145 Cerebrospinal Fluid (CSF) Pathway of Flow 1. CSF is produced by the choroid plexus of each ventricle. 2. CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3. CSF flows through the subarachnoid space. 4. CSF is absorbed into the dural venous sinuses via the arachnoid villi.

146 Figure 7.18a Ventricles and location of the cerebrospinal fluid. Lateral ventricle Septum pellucidum Inferior horn Lateral aperture Anterior horn Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Central canal (a) Anterior view

147 Figure 7.18b Ventricles and location of the cerebrospinal fluid. Lateral ventricle Anterior horn Interventricular foramen Third ventricle Cerebral aqueduct Fourth ventricle Central canal Posterior horn Inferior horn Median aperture Lateral aperture (b) Left lateral view

148 Figure 7.18c Ventricles and location of the cerebrospinal fluid. 4 Superior sagittal sinus Choroid plexus Corpus callosum Interventricular foramen Third ventricle (c) CSF circulation 3 Cerebral aqueduct Lateral aperture Fourth ventricle Median aperture Central canal of spinal cord 1 2 Arachnoid villus Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 1 CSF is produced by the choroid plexus of each ventricle. 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. 3 CSF flows through the subarachnoid space. 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi.

149 Hydrocephalus in a Newborn Hydrocephalus CSF accumulates and exerts pressure on the brain if not allowed to drain Possible in an infant because the skull bones have not yet fused In adults, this situation results in brain damage

150 Figure 7.19 Hydrocephalus in a newborn.

151 Blood-Brain Barrier Includes the least permeable capillaries of the body Excludes many potentially harmful substances Useless as a barrier against some substances Fats and fat-soluble molecules Respiratory gases Alcohol Nicotine Anesthesia

152 Blood-Brain Barrier Water-soluble items that can travel through barrier: Water Glucose Essential amino acids Items prevented from passing through: Metabolic wastes Most drugs Nonessential amino acids Potassium ions

153 Traumatic Brain Injuries Concussion Slight brain injury No permanent brain damage Contusion Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue

154 Cerebrovascular Accident (CVA), or Stroke Results from a ruptured blood vessel supplying a region of the brain Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result Hemiplegia one-sided paralysis Aphasia damage to speech center in left hemisphere Transient ischemic attack (TIA) temporary brain ischemia (restriction of blood flow) Warning signs for more serious CVAs

155 Alzheimer s Disease Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Victims experience memory loss, irritability, confusion, and ultimately, hallucinations and death

156 Spinal Cord Extends from the foramen magnum of the skull to the first or second lumbar vertebra Provides a two-way conduction pathway to and from the brain 31 pairs of spinal nerves arise from the spinal cord Ends around vertebra L 1 or L 2 Cauda equina is a collection of spinal nerves at the inferior end

157 Figure 7.20 Anatomy of the spinal cord, posterior view. Cervical enlargement C 8 Cervical spinal nerves Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Cauda equina End of meningeal coverings T 12 L 5 S 1 S 5 End of spinal cord Lumbar spinal nerves Sacral spinal nerves

158 Spinal Cord Anatomy Internal gray matter is mostly cell bodies Dorsal (posterior) horns house interneurons Receive information from sensory neurons in the dorsal root Anterior (ventral) horns house motor neurons of the somatic (voluntary) nervous system Send information out ventral root Gray matter surrounds the central canal, which is filled with cerebrospinal fluid

159 Spinal Cord Anatomy Exterior white mater conduction tracts Dorsal, lateral, ventral columns Sensory (afferent) tracts conduct impulses toward brain Motor (efferent) tracts carry impulses from brain to skeletal muscles

160 Figure 7.21 Spinal cord with meninges (three-dimensional view). Dorsal root ganglion White matter Central canal Dorsal (posterior) horn of gray matter Lateral horn of gray matter Spinal nerve Dorsal root of spinal nerve Ventral (anterior) horn of gray matter Ventral root of spinal nerve Pia mater Arachnoid mater Dura mater

161 Figure 7.22 Schematic of ascending (sensory) and descending (motor) pathways between the brain and the spinal cord. Interneuron carrying sensory information to cerebral cortex Cerebral cortex (gray matter) White matter Thalamus Integration (processing and interpretation of sensory input) occurs Interneuron carrying response to motor neurons Cerebrum Interneuron carrying response to motor neuron Cell body of sensory neuron in sensory ganglion Nerve Skin Sensory receptors Brain stem Interneuron carrying sensory information to cerebral cortex Cervical spinal cord Muscle White matter Gray matter Motor output Interneuron Motor neuron cell body

162 Spinal Cord Anatomy Meninges cover the spinal cord Spinal nerves leave at the level of each vertebra Dorsal root Associated with the dorsal root ganglia collections of cell bodies outside the central nervous system Ventral root Contains axons

163 Peripheral Nervous System (PNS) PNS consists of nerves and ganglia outside the central nervous system Nerve bundle of neuron fibers Neuron fibers are bundled by connective tissue

164 PNS: Structure of a Nerve Endoneurium surrounds each fiber Groups of fibers are bound into fascicles by perineurium Fascicles are bound together by epineurium

165 Figure 7.23 Structure of a nerve. Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels

166 Concept Link

167 PNS: Classification of Nerves Mixed nerves Both sensory and motor fibers Sensory (afferent) nerves Carry impulses toward the CNS Motor (efferent) nerves Carry impulses away from the CNS

168 PNS: Cranial Nerves 12 pairs of nerves that mostly serve the head and neck Only the pair of vagus nerves extends to thoracic and abdominal cavities Most are mixed nerves, but three are sensory only: 1. Optic 2. Olfactory 3. Vestibulocochlear

169 PNS: Cranial Nerves Mnemonic Device Oh Olfactory Oh Optic Oh Oculomotor To Trochlear Touch Trigeminal And Abducens Feel Facial Very Vestibulocochlear Green Glossopharyngeal Vegetables Vagus A Accessory H Hypoglossal On Old Olympus Towering Top A Finn And (Acousitic) German Viewed A Hop

170

171 Table 7.2 The Cranial Nerves (1 of 6)

172 Table 7.2 The Cranial Nerves (2 of 6)

173 Table 7.2 The Cranial Nerves (3 of 6)

174 Table 7.2 The Cranial Nerves (4 of 6)

175 Table 7.2 The Cranial Nerves (5 of 6)

176 Table 7.2 The Cranial Nerves (6 of 6) Cervical nerves

177 Figure 7.24 Distribution of cranial nerves. I Olfactory II Optic III Oculomotor IV Trochlear VI Abducens V Trigeminal V Trigeminal VII Facial Vestibular branch Cochlear branch VIII Vestibulocochlear XII Hypoglossal XI Accessory X Vagus IX Glossopharyngeal

178

179 PNS: Spinal Nerves There is a pair of spinal nerves at the level of each vertebra, for a total of 31 pairs Formed by the combination of the ventral and dorsal roots of the spinal cord Named for the region from which they arise

180 Figure 7.25a Spinal nerves. Cervical nerves Thoracic nerves Lumbar nerves Sacral nerves (a) C T L S Ventral rami form cervical plexus (C 1 C 5 ) Ventral rami form brachial plexus (C 5 C 8 ; T 1 ) No plexus formed (intercostal nerves) (T 1 T 12 ) Ventral rami form lumbar plexus (L 1 L 4 ) Ventral rami form sacral plexus (L 4 L 5 ; S 1 S 4 )

181 PNS: Anatomy of Spinal Nerves Spinal nerves divide soon after leaving the spinal cord Ramus branch of a spinal nerve; contains both motor and sensory fibers Dorsal rami serve the skin and muscles of the posterior trunk Ventral rami form a complex of networks (plexus) for the anterior

182 Figure 7.25b Spinal nerves. Dorsal root Dorsal root ganglion Spinal cord Ventral root Spinal nerve Ventral ramus Dorsal ramus (b)

183 PNS: Spinal Nerve Plexuses Plexus networks of nerves serving motor and sensory needs of the limbs Form from ventral rami of spinal nerves in the cervical, lumbar, and sacral regions Four plexuses: 1. Cervical 2. Brachial 3. Lumbar 4. Sacral

184 Table 7.3 Spinal Nerves Plexuses (1 of 3)

185 Figure 7.26a Distribution of the major peripheral nerves of the upper and lower limbs. Axillary nerve Humerus Radial nerve Musculocutaneous nerve Ulna Radius Ulnar nerve Radial nerve (superficial branch) Median nerve (a) The major nerves of the upper limb

186 Table 7.3 Spinal Nerves Plexuses (2 of 3)

187 Figure 7.26b Distribution of the major peripheral nerves of the upper and lower limbs. Femoral Lateral femoral cutaneous Obturator Anterior femoral cutaneous Saphenous (b) Lumbar plexus, anterior view

188 Table 7.3 Spinal Nerves Plexuses (3 of 3)

189 Figure 7.26c Distribution of the major peripheral nerves of the upper and lower limbs. Superior gluteal Inferior gluteal Sciatic Posterior femoral cutaneous Common fibular Tibial Sural (cut) Deep fibular Superficial fibular Plantar branches (c) Sacral plexus, posterior view

190 PNS: Autonomic Nervous System Motor subdivision of the PNS Consists only of motor nerves Also known as the involuntary nervous system Regulates activities of cardiac and smooth muscles and glands Two subdivisions: 1. Sympathetic division 2. Parasympathetic division

191 PNS: Differences Between Somatic and Autonomic Nervous Systems Somatic Nervous System Autonomic Nervous System Nerves One-neuron system; it originates in the CNS, and axons extend to the skeletal muscles served Two-neuron system consisting of preganglionic and postganglionic neurons Effector organ Skeletal muscle Smooth muscle, cardiac muscle, glands Subdivisions None Sympathetic and parasympathetic Neurotransmitter Acetylcholine Acetylcholine, epinephrine, norepinephrine

192 Figure 7.27 Comparison of the somatic and autonomic nervous systems. Central nervous system Peripheral nervous system Effector organs Somatic nervous system Acetylcholine Skeletal muscle Acetylcholine Norepinephrine Smooth muscle (e.g., in stomach) Autonomic nervous system Sympathetic division Acetylcholine Ganglion Epinephrine and norepinephrine Blood vessel Glands Parasympathetic division Acetylcholine Ganglion Cardiac muscle KEY: Preganglionic axons (sympathetic) Postganglionic axons (sympathetic) Myelination Preganglionic axons (parasympathetic) Postganglionic axons (parasympathetic)

193 PNS: Anatomy of the Parasympathetic Division Preganglionic neurons originate from the craniosacral regions: The cranial nerves III, VII, IX, and X S 2 through S 4 regions of the spinal cord Because it is the site of preganglionic neuron origination, the parasympathetic division is also known as the craniosacral division Terminal ganglia are at the effector organs Neurotransmitter: acetylcholine

194 Figure 7.28 Anatomy of the autonomic nervous system. Parasympathetic Eye Salivary glands Heart Cervical Brain stem Cranial Sympathetic ganglia Sympathetic Eye Skin Salivary glands Lungs T 1 Lungs Heart Stomach Pancreas Liver and gallbladder Thoracic L 1 Lumbar Stomach Pancreas Liver and gallbladder Adrenal gland Bladder Genitals Sacral nerves (S 2 S 4 ) Bladder Genitals

195 PNS: Anatomy of the Sympathetic Division Preganglionic neurons originate from T 1 through L 2 Ganglia are at the sympathetic trunk (near the spinal cord) Short preganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector Neurotransmitters: norepinephrine and epinephrine (effector organs)

196 Figure 7.28 Anatomy of the autonomic nervous system. Parasympathetic Eye Salivary glands Heart Cervical Brain stem Cranial Sympathetic ganglia Sympathetic Eye Skin Salivary glands Lungs T 1 Lungs Heart Stomach Pancreas Liver and gallbladder Thoracic L 1 Lumbar Stomach Pancreas Liver and gallbladder Adrenal gland Bladder Genitals Sacral nerves (S 2 S 4 ) Bladder Genitals

197 Figure 7.29 Sympathetic pathways. Lateral horn of gray matter Dorsal root Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Sympathetic trunk Spinal nerve (c) (a) (b) To effector: blood vessels, arrector pili muscles, and sweat glands of the skin Sympathetic trunk ganglion Ventral root Splanchnic nerve Gray ramus communicans Collateral ganglion (such as the celiac) White ramus communicans Visceral effector organ (such as small intestine)

198 PNS: Autonomic Functioning Sympathetic fight or flight division Response to unusual stimulus Takes over to increase activities Remember as the E division: Exercise Excitement Emergency Embarrassment

199 PNS: Autonomic Functioning Parasympathetic housekeeping activites Conserves energy Maintains daily necessary body functions Remember as the D division Digestion Defecation Diuresis

200 Table 7.4 Effects of the Sympathetic Divisions of the Autonomic Nervous System (1 of 2)

201 Table 7.4 Effects of the Sympathetic Divisions of the Autonomic Nervous System (2 of 2)

202 Developmental Aspects of the Nervous System The nervous system is formed during the first month of embryonic development Any maternal infection can have extremely harmful effects Oxygen deprivation destroys brain cells The hypothalamus is one of the last areas of the brain to develop

203 Developmental Aspects of the Nervous System Severe congenital brain diseases include: Cerebral palsy Anencephaly Hydrocephalus Spina bifida

204 Developmental Aspects of the Nervous System Premature babies have trouble regulating body temperature because the hypothalamus is one of the last brain areas to mature prenatally. Development of motor control indicates the progressive myelination and maturation of a child s nervous system.

205 Developmental Aspects of the Nervous System Brain growth ends in young adulthood. Neurons die throughout life and are not replaced; thus, brain mass declines with age. Healthy aged people maintain nearly optimal intellectual function. Disease particularly cardiovascular disease is the major cause of declining mental function with age.