mosby items and derived items © 2007, 2003 by mosby, inc. 1 chapter 13 central nervous system
TRANSCRIPT
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Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Chapter 13Central Nervous System
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Coverings of the Brain and Spinal Cord
Two protective coverings: Outer covering is bone Inner covering is the meninges
continues inside the spinal cavity beyond the end of the spinal cord
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Coverings of the Brain and Spinal Cord
Meninges 3 membranous layers
Dura mater strong, white fibrous tissue outer layer of meninges and
inner periosteum of the cranial bones
Arachnoid mater delicate, cobwebby layer
between the dura mater and pia mater
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Coverings of the Brain and Spinal Cord
Meninges 3 membranous layers (cont.)
Pia mater innermost, transparent layer adheres to the outer surface of the brain and spinal cord
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Cerebrospinal Fluid
Functions Provides a supportive, protective cushion Reservoir of circulating fluid, which is monitored by the brain to
detect changes in the internal environment
Fluid spaces Cerebrospinal fluid— found around the brain and spinal cord
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Cerebrospinal Fluid
Fluid spaces (cont.) Ventricles— fluid-
filled spaces within the brain; four ventricles within the brain
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Spinal Cord
Structure of the spinal cord Oval cylinder that tapers slightly from above
downward Two bulges, one in the cervical region and
one in the lumbar region
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Spinal Cord
Structure of the spinal cord (cont.) Nerve roots
Fibers of dorsal nerve root Carry sensory information into the spinal canal
Fibers of ventral nerve root Carry motor information out of the spinal cord
Interneurons are located in the spinal cord’s gray matter core
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Dorsal (posterior) nerve root
Ventral (anterior) nerve root
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Spinal Cord
Structure of the spinal cord (cont.)
Gray matter
Consists predominantly of cell bodies of interneurons and motor neurons
In transverse section, looks like an H
White matter
Surrounds the gray matter
consists of a large bundle of axons divided into tracts
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Spinal Cord
Functions of the spinal cord Provides conduction routes to and from the brain
Ascending tracts (sensory)— conduct impulses up the cord to the brain
Descending tracts (motor)— conduct impulses down the cord from the brain
Bundles of axons compose all tracts
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Spinal Cord
Functions of the spinal cord (cont.) Important ascending
(sensory) tracts = BLUE crude touch, pain, and
temperature pressure discriminating touch and
conscious kinesthesia (proprioception)
subconscious kinesthesia touch related to visual
reflexes
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Spinal Cord
Functions of the spinal cord (cont.)Important descending (motor) tracts
voluntary movements on opposite side of the body
voluntary movements on same side of body maintain posture during movement transmit impulses that coordinate body movements and
maintenance of posture head and neck movements during visual reflexes coordination of posture and balance
Spinal cord— reflex center for all spinal reflexes reflex centers are located in the gray matter of the
cord
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The Brain
Structures of the brainstem Medulla oblongata
Lowest part of the brainstem Composed of white matter and a network of gray and
white matter called the reticular formation Nuclei— clusters of neuron cell bodies located in the
reticular formation
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The Brain Structures of the brainstem (cont.)
Pons Located above the medulla and below the midbrain Composed of white matter and reticular formation
Midbrain Located above the pons and below the cerebrum; forms the
midsection of the brain Composed of white tracts and reticular formation conduct impulses between the midbrain and cerebrum Red nucleus and substantia nigra (“black matter”)
clusters of cell bodies of neurons involved in muscular control
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The Brain
Functions of the brainstem Performs sensory, motor, and reflex functions Nuclei in medulla— contain reflex centers
Of primary importance— cardiac, vasomotor, and respiratory centers
Nonvital reflexes— vomiting, coughing, sneezing, etc.
Pons— help regulate respiration
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The Brain
Structure of the cerebellum Gray matter makes up the cortex, and white matter
predominates in the interior Cerebellum has numerous sulci (groove) and delicate,
gyri (raised areas)
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The Brain
Functions of the cerebellum coordinates movements to produce the intended action General functions
produce skilled movements by coordinating the activities of muscles
maintains balance Controls posture smooth movements and make movements efficient and
coordinated Processes sensory information
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Stand Up!
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The Brain
Diencephalon Located between the cerebrum and the midbrain Consists of several structures: thalamus, hypothalamus, pineal
gland, and several others Thalamus
Dumbbell-shaped mass of gray matter made up of many nuclei plays role in processing auditory and visual input
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The Brain
Thalamus (cont.)Serves as a major relay station for sensory impulses
on their way to the cerebral cortexPerforms the following primary functions:
Two parts for sensations: conscious recognition of the crude, less critical
sensations of pain, temperature, and touch Neurons relay all kinds of sensory impulses, except
possibly olfactory, to the cerebrum emotions by associating sensory impulses with feeling of
pleasantness and unpleasantness arousal mechanism
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The Brain
Diencephalon (cont.) Hypothalamus
lies beneath (hypo) the thalamus Small but functionally important area of the brain,
performs many functions of greatest importance for survival and enjoyment
Links mind and body Links nervous system to endocrine system
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The Brain
Hypothalamus (cont.) Summary of hypothalamic functions
Regulator and coordinator of autonomic activities Major relay station between the cerebral cortex and lower
autonomic centers crucial part of the route by which emotions can express
themselves in changed bodily functions maintaining water balance arousal mechanism regulating appetite maintaining normal body temperature
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The Brain
Diencephalon (cont.) Pineal gland
Involved in regulating the body’s biological clock Produces melatonin as a “timekeeping hormone”
Melatonin is made from the neurotransmitter serotonin Melatonin levels increase when sunlight is absent and
decreases when sunlight is present, thus regulating the circadian (daily) biological clock (Figure 13-15)
Melatonin is the “sleep hormone”
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The Brain
Structure of the cerebrum Cerebral cortex
Largest and uppermost division of the brain consists of right and left cerebral hemispheres each hemisphere is divided into four lobes:
Frontal lobe Parietal lobe Temporal lobe Occipital lobe
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The Brain
Cerebral cortex (cont.)Cerebral cortex— outer surface made up of six
layers of gray matter Gyri— raised areas Sulci— shallow grooves
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The Brain
Cerebral cortex (cont.) Fissures— deeper grooves, divide each cerebral
hemisphere into lobes Central sulcus— groove between frontal and parietal
lobes Lateral fissure— groove between temporal lobe below
and parietal lobes above
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Structure of the cerebrum
Basal nuclei (or cerebral nuclei) Basal nuclei— islands of gray matter located deep
inside the white matter of each hemisphere Unsure of exact function but important in regulating
voluntary motor functions, especially repetitive actions Example: maintaining posture, walking
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The Brain
Functions of the cerebral cortex Certain areas of
cortex have certain functions
Transverse gyrus— auditory area
Occipital lobe— visual areas
Precentral gyrus- somatic motor
Postcentral gyrus- somatic sensory
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The Brain
Functions of the cerebral cortex (cont.) Sensory functions of the cortex
Cortex contains a “somatic sensory map” of the body
Senses send information to primary sensory areas, as well as to other parts of the brain
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The Brain
Motor functions of the cortex For normal movements to occur,
many parts of the nervous system must function
Precentral gyrus primary somatic motor area controls individual muscles
Secondary motor area (premotor) in the gyrus immediately anterior
to the precentral gyrus activates groups of muscles
simultaneously
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The Brain Integrative functions of the cortex
Consciousness State of awareness of one’s self,
one’s environment, and other beings
Depends on excitation of neurons from the reticular formation
Two about reticular activating system:
Functions as the alert system for the cerebral cortex
Its functioning is crucial for maintaining consciousness
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The Brain
Integrative functions of the cortex (cont) Language
Ability to speak and write words AND ability to understand spoken and written words
Left cerebral hemisphere contains speech centers in approximately 90% of the population
FYI: Explains Broca’s and Wernicke’s area
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The Brain Integrative functions of the cortex (cont.)
Emotions Limbic system— also known as the “emotional brain”
hippocampus Have primary connections with other parts of the
brain, such as thalamus, amygdaloid nucleus, and hypothalamus
FYI: removal of hippocampus causes inability to recall new info
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The Brain
Integrative functions of the cortex (cont) Memory
One of the major human mental activities Cortex is capable of storing and retrieving both
short- and long-term memory Temporal, parietal, and occipital lobes are among
the areas responsible for short- and long-term memory
Cerebrum’s limbic system plays a key role in memory
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The Brain
Right and left hemispheres of the cerebrum specialize in different functions
Both sides communicate with each other to accomplish complex functions
Left hemisphere is responsible for: Language functions Dominating control of certain hand movements
Right hemisphere is responsible for: Auditory Tactual perception Perceiving and visualizing spatial relationships
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Cycle of Life: Central Nervous System
The development and degeneration of the CNS is the most obvious functional change over the life span
Development of the brain and spinal cord begins in the womb
Lack of development in the newborn is evidenced by lack of: Language- both speech and reading Comprehension of spatial relationships Complex motor skills- walking
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Cycle of Life: Central Nervous System
Complex functions develop by adulthood Late adulthood— tissues degenerate
Profound degeneration— unable to perform complex functions
Milder degeneration— temporary memory lapse or difficulty with complex motor tasks
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The Big Picture: The Central Nervous System and the Whole Body
Central nervous system ultimate regulator of the body essential to survival
Able to integrate bits of information from all over the body, make sense of them, and make decisions