Download Chapter 12: The Central Nervous System

Chapter 12: The Central Nervous System
Objectives:
1. Describe the process of brain development.
2. Name the major regions of the adult brain.
3. Name and locate the ventricles of the brain.
4. List the major lobes, fissures, and functional areas of the cerebral
cortex.
5. Explain the lateralization of hemisphere function.
6. Differentiate between commissures, association fibers, and
projection fibers.
7. Describe the general function of the basal nuclei (basal ganglia).
8. Describe the location of the diencephalons, and name its
subdivisions.
9. Identify the three major regions of the brain stem, and note the
functions of each area.
10. Describe the structure and function of the cerebellum.
11. Locate the limbic system, and the reticular formation, and explain
the role of each functional system.
12. Define EEG and distinguish between alpha, beta, theta, and delta
brain waves.
13. Compare and contrast the events and importance of slow-wave
and REM sleep, and indicate how their patterns change through life.
14. Describe consciousness clinically.
15. Compare and contrast the stages and categories of memory.
16. Describe the relative roles of the major brain structures believed
to be involved in declarative and procedural memories.
17. Describe how meninges, cerebrospinal fluid, and the blood-brain
barrier protect the CNS.
18. Describe the formation of cerebrospinal fluid, and follow its
circulatory pathway.
19. Describe the cause (if known) and major signs and symptoms of
cerebrovascular accidents, Alzheimer’s disease, Huntington’s
disease, and Parkinson’s disease.
20. Describe the embryonic development of the spinal cord.
21. Describe the gross and microscopic structure of the spinal cord.
22. List the major spinal cord tracts, and classify each as a motor or
sensory tract.
23. Distinguish between flaccid and spastic paralysis and between
paralysis and paesthesia.
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24. List and explain several techniques used to diagnose brain
disorders.
25. Indicate several maternal factors that can impair development of
the nervous system in the embryo.
26. Explain the effects of aging on the brain.
I. The Central Nervous System
A. Composed
1. Brain
2. Spinal cord
B. Cephalization
1. Elaboration of anterior portion of the CNS
2. Increase in number of neurons in the head
3. Highest level is reached in the human brain
II. The Brain
A. Composed of wrinkled, pinkish gray tissue
B. Surface anatomy includes
1. Cerebral hemispheres (paired)
2. Cerebellum (paired)
3. Brain stem
C. Primary Brain Vesicles
1. Anterior end of the neural tube expands and constricts to form
the three primary brain vesicles
a. Prosencephalon – the forebrain
b. Mesencephalon – the midbrain
c. Rhombencephalon – hindbrain
D. Secondary Brain Vesicles
1. Telencephalon and diencephalon arise from the forebrain
2. Mesencephalon remains undivided
3. Metencephalon and myelencephalon arise from the hindbrain
F. Adult Brain Structures
1. Fates of the secondary brain vesicles:
a. Telencephalon
1) Cerebrum
a) Cortex
b) White matter
c) Basal nuclei (nuclei means cluster of soma)
b. Diencephalon
1) Thalamus
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2) Hypothalamus
3) Epithalamus
c. Mesencephalon
1) Brain stem
a) Midbrain
d. Metencephalon
1) Brain stem
a) Pons
e. Myelencephalon
1) Brain stem
a) Medulla oblongata
2. Adult structures derived from the neural canal
a.Telencephalon
1) Lateral ventricles
b. Diencephalon
1) Third ventricle
c. Mesencephalon
1) Cerebral aqueduct
d. Metencephalon and myelencephalon
1) Fourth ventricle
G. Basic Pattern of the Central Nervous System
1. Spinal Cord
a. Central cavity surrounded by a gray matter core
b. External to which is white matter composed of myelinated
fiber tracts
2. Brain
a. Similar to spinal cord but with additional areas of gray matter
b. Cerebellum has gray matter in nuclei
c. Cerebrum has nuclei and additional gray matter in cortex
3. Ventricles of the Brain
a. Arise from expansion of the lumen of the neural tube
b. The ventricles are:
1) Paired C-shaped lateral ventricles
2) Third ventricle found in the diencephalons
3) Fourth ventricle found in the hindbrain dorsal to the pons
III. The Cerebrum
A. Cerebral Hemispheres
1. Form the superior part of the brain and make up 83% of its
mass
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2.
3.
4.
5.
Contain ridges (gyri) and shallow grooves (sulci)
Contain deep grooves called fissures
Are separated by the longitudinal fissure
Have three basic regions
a. Cortex
b. White matter
c. Basal nuclei
B. Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere
1. Deep sulci divide the hemispheres into five lobes
a. Frontal
b. Parietal
c. Temporal
d. Occipital
e. Insula
2. Central sulcus
a. Separates the frontal
parietal lobes
3. Parieto-occipital sulcus
a. Separates the parietal and occipital lobes
4. Lateral sulcus
a. Separates the parietal and temporal lobes
5. Precentral and postcentral gyri border the central sulcus
C. Cerebral Cortex
1. Cortex
a. Superficial gray matter
b. Accounts for 40% of the mass of the brain
2. Enables sensation, communication, memory, understanding, and
voluntary movements
3. Each hemisphere acts contralaterally
a. Controls the opposite side of the body
b. Hemispheres are not equal in function
c. No functional area acts alone
1) Conscious behavior involves the entire cortex
4. Functional Areas
a. The three types
1) Motor areas
a) Control voluntary movement
2) Sensory areas
a) Conscious awareness of sensation
3) Association areas
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a) Integrate diverse information
D. Cerebral Cortex: Motor Areas
1. Primary (somatic) motor cortex
2. Premotor cortex
3. Broca’s area
4. Frontal eye field
E. Primary Motor Cortex
1. Located in the precentral gyrus
2. Allows conscious control of precise, skilled, voluntary
movements
Primary Motor Cortex Homunculus
Primary Somatosensory Cortes Homuncul us
F. Premotor Cortex
1. Located anterior to the precentral gyrus
2. Controls learned, repetitious, or patterned motor skills
3. Coordinates simultaneous or sequential actions
4. Involved in the planning of movements
G. Broca’s area
1. Located anterior to the inferior region of the premotor area
2. Present in one hemisphere (usually the left)
3. A motor speech area that directs muscles of the tongue
H. Frontal Eye Field
1. Located anterior to the premotor cortex and superior to Broca’s
area
2. Controls voluntary eye movement
I. Sensory Areas
1. Primary somatosensory cortex
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J.
K.
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2. Somatosensory association cortex
3. Visual and auditory areas
4. Olfactory, gustatory, and vestibular cortices
PrImary Somatosensory Cortex
1. Located in the postcentral gyrus, this area
a. Receives information from the skin and skeletal muscles
b. Exhibits spatial discrimination
Somatosensory Association Cortex
1. Located posterior to the primary somatosensory cortex
2. Integrates sensory information
3. Forms comprehensive understanding of the stimulus
4. Determines size, texture, and relationship of parts
Visual Areas
1. Primary visual (striate) cortex
2. Seen on the extreme posterior tip of the occipital lobe
3. Receives visual information from the retinas
4. Visual association area
a. Surrounds the primary visual cortex
b. Interprets visual stimuli (e.g., color, form, and movement)
Auditory Areas
1. Primary auditory cortex
2. Located at the superior margin of the temporal lobe
3. Receives information related to pitch, rhythm, and loudness
4. Auditory association area
a. Located posterior to the primary auditory cortex
b. Stores memories of sounds and permits perception of sounds
c. Wernicke’s area
Association Areas
1. Prefrontal cortex
2. Language areas
3. General (common) interpretation area
4. Visceral association area
Prefrontal Cortex
1. Located in the anterior portion of the frontal lobe
2. Involved with intellect, cognition, recall, and personality
3. Necessary for judgment, reasoning, persistence, and conscience
4. Closely linked to the limbic system (emotional part of the brain)
Language Areas
1. Located in a large area surrounding the left (or languagedominant) lateral sulcus
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2. Major parts and functions
a. Wernicke’s area
1) Sounding out unfamiliar words
b. Broca’s area
1) Speech preparation and production
c. Lateral prefrontal cortex
1) Language comprehension and word analysis
d. Lateral and ventral temporal lobe
1) Coordinate auditory and visual aspects of language
General (Common) Interpretation Area
1. Found in one hemisphere, usually the left
2. Integrates incoming signals into a single thought
3. Involved in processing spatial relationships
Visceral Association Area
1. Involved in conscious perception of visceral sensations
Lateralization of Cortical Function
1. Lateralization
a. Each hemisphere has abilities not shared with its partner
2. Cerebral dominance
a. Designates the hemisphere dominant for language
3. Left hemisphere
a. Controls language, math, and logic
4. Right hemisphere
a. Controls visual-spatial skills, emotion, and artistic skills
Cerebral White Matter
1. Consists of deep myelinated fibers and their tracts
2. It is responsible for communication between
a. Cerebral cortex and lower CNS center, and areas of the
cerebrum
3. Types include
a. Commissures
1) Connect corresponding gray areas of the two hemispheres
b. Association fibers
1) Connect different parts of the same hemisphere
c. Projection fibers
1) Enter the hemispheres from lower brain or cord centers
Basal Nuclei
1. Masses of gray matter found deep within the cortical white
matter
2. Functions
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a. Influence muscular activity
b. Regulate attention and cognition
c. Regulate intensity of slow or stereotyped movements
d. Inhibit antagonistic and unnecessary movement
V. Diencephalon
1. Central core of the forebrain
2. Consists of three paired structures
a. Thalamus
b. Hypothalamus
c. Epithalamus
3. Encloses the third ventricle
W. Thalamus
1. Function
a. Sensual afferent impulses converge and synapse in the
thalamus
b. Impulses of similar function are sorted out, edited, and
relayed as a group
c. All inputs ascending to the cerebral cortex pass through the
thalamus
d. Mediates sensation, motor activities, cortical arousal,
learning, and memory
X. Hypothalamus
1. Mammillary bodies
a. Small, paired nuclei bulging anteriorly from the hypothalamus
b. Relay station for olfactory pathways
2. Infundibulum
a. Stalk of the hypothalamus; connects to the pituitary gland
3. Main visceral control center of the body
4. Function
a. Regulates blood pressure
b. Rate and force of heartbeat
c. Digestive tract motility
d. Rate and depth of breathing
e. Many other visceral activities
f. Perception of pleasure, fear, and rage
g. Maintains normal body temperature
h. Regulates feelings of hunger and satiety
i. Regulates sleep and the sleep cycle
j. Releasing hormones control secretion of hormones by the
anterior pituitary
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Y. Epithalamus
1. Pineal gland
a. Extends from the posterior border and secretes melatonin
2. Melatonin
a. Hormone involved with sleep regulation, sleep-wake cycles,
and mood
3. Choroid plexus
a. Structure that secretes cerebral spinal fluid (CSF)
IV. Brain Stem
A. Consists of three regions
1. Midbrain
2. Pons
3. Medulla oblongata
B. Similar to spinal cord but contains embedded nuclei
C. Controls automatic behaviors necessary for survival
D. Provides the pathway for tracts between higher and lower brain
centers
E. Associated with 10 of the 12 pairs of cranial nerves
F. Midbrain
1. Located between the diencephalon and the pons
2. Midbrain structures include:
3. Cerebral peduncles
a. Two bulging structures that contain descending pyramidal
motor tracts
4. Cerebral aqueduct
a. Hollow tube that connects the third and fourth ventricles
5. Nuclei that control cranial nerves III (oculomotor) and IV
(trochlear)
6. Corpora quadrigemina
a. Four domelike protrusions of the dorsal midbrain
7. Superior colliculi
a. Visual reflex centers
G. Midbrain Nuclei
1. Inferior colliculi
a. Auditory relay centers
2. Red nucleus
a. Relay nuclei for some descending motor pathways
H. Pons
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1. Bulging brainstem region between the midbrain and the medulla
oblongata
2. Forms part of the anterior wall of the fourth ventricle
3. Fibers of the pons
a. Connect higher brain centers and the spinal cord
b. Relay impulses between the motor cortex and the cerebellum
c. Origin of cranial nerves V (trigeminal), VI (abducens), and VII
(facial)
I. Medulla Oblongata
1. Most inferior part of the brain stem
2. Pyramids
a. Two longitudinal ridges formed by corticospinal tracts
b. Crossover points of the corticospinal tracts
J. Medulla Nuclei
1. Cranial nerves X, XI, and XII are associated with the medulla
2. Vestibular nuclear complex
a. Synapses that mediate and maintain equilibrium
3. Ascending sensory tract nuclei
4. Cardiovascular control center
a. Adjusts force and rate of heart contraction
5. Respiratory centers
a. Control rate and depth of breathing
6. Additional centers regulate
a. Vomiting
b. Hiccuping
c. Swallowing
d. Coughing
e. Sneezing
V. Cerebellum
A. Located dorsal to the pons and medulla
B. Protrudes under the occipital lobes of the cerebrum
C. Makes up 11% of the brain’s mass
D. Provides precise timing and appropriate patterns of skeletal muscle
contraction
E. Cerebellar activity occurs subconsciously
F. Anatomy of the Cerebellum
1. Two bilaterally symmetrical hemispheres connected medially by
the vermis
2. Arbor vitae
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a. Distinctive treelike pattern of the cerebellar white matter
G. Cerebellar Peduncles
1. Three paired fiber tracts that connect the cerebellum to the
brain stem
2. All fibers in the cerebellum are ipsilateral
3. Superior peduncles connect the cerebellum to the midbrain
4. Middle peduncles connect the pons to the cerebellum
5. Inferior peduncles connect the medulla to the cerebellum
H. Cerebellar Processing
1. Cerebellum receives impulses of the intent to initiate voluntary
muscle contraction
2. Proprioceptors and visual signals “inform” the cerebellum of the
body’s condition
3. Cerebellar cortex calculates the best way to perform a
movement
4. A “blueprint” of coordinated movement is sent to the cerebral
motor cortex
I. Cerebellar Cognitive Function
1. Plays a role in language and problem solving
2. Recognizes and predicts sequences of events
VI. Functional Brain System
A. Networks of neurons working together and spanning wide areas of
the brain
B. The two systems are
1. Limbic system
2. Reticular formation
C. Limbic System
1. Structures located on the medial aspects of cerebral
hemispheres and diencephalon
2. Includes
a. Rhinencephalon
b. Amygdala
c. Hypothalamus
d. Anterior nucleus of the thalamus
3. Parts especially important in emotions:
a. Amygdala
1. deals with anger, danger, and fear responses
b. Cingulate gyrus
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1) plays a role in expressing emotions via gestures, and
resolves mental conflict
2) Puts emotional responses to odors
a) e.g., skunks smell bad
4. Emotion and Cognition
a. Limbic system interacts with the prefrontal lobes, therefore
1) One can react emotionally to conscious understandings
2) One is consciously aware of emotion in one’s life
3) Hippocampal structures
a) Convert new information into long-term memories
D. Reticular Formation
1. Composed of three broad columns along the length of the brain
stem
a. Has axonal connections with hypothalamus, thalamus,
cerebellum, and spinal cord
E. RAS and Motor Function
1. RAS – Reticular Activating System
a. Sends impulses to the cerebral cortex to keep it conscious
and alert
b. Filters out repetitive and weak stimuli
2. Motor function
a. Helps control coarse motor movements
b. Autonomic centers regulate visceral motor
c. functions – e.g., vasomotor, cardiac, and respiratory centers
F. Brain Waves
1. Normal brain function involves continuous electrical activity
2. An electroencephalogram (EEG) records this activity
3. Patterns of neuronal electrical activity
4. Each person’s brain waves are unique
5. Continuous train of peaks and troughs
6. Wave frequency is expressed in Hertz (Hz)
7. Types of Brain Waves
a. Alpha waves
1) regular and rhythmic, low-amplitude, slow, synchronous
waves indicating an “idling” brain
b. Beta waves
1) rhythmic, more irregular waves occurring during the awake
and mentally alert state
c. Theta waves
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1) more irregular than alpha waves; common in children but
abnormal in adults
d. Delta waves
1) high-amplitude waves seen in deep sleep and when
reticular activating system is damped
G. Types of Sleep
1. There are two major types of sleep:
a. Non-rapid eye movement (NREM)
b. Rapid eye movement (REM)
2. One passes through four stages of NREM during the first 30-45
minutes of sleep
3. REM sleep occurs after the fourth NREM stage has been achieved
4. Types and Stages of Sleep: NREM
a. NREM stages include
1) Stage 1
a) eyes are closed and relaxation begins
b) EEG shows alpha waves
c) one can be easily awakened
2) Stage 2
a) EEG pattern is irregular with sleep spindles (highvoltage wave bursts)
b) waking is more difficult
3) Stage 3
a) sleep deepens
b) theta and delta waves appear
c) vital signs decline
d) dreaming is common
4) Stage 4
a) EEG pattern is dominated by delta waves
b) skeletal muscles are relaxed
c) waking is difficult
5. Types and Stages of Sleep: REM
a. Characteristics of REM sleep
1) EEG pattern reverts through the NREM stages to the stage
1 pattern
2) Vital signs increase
3) Skeletal muscles (except ocular muscles) are inhibited
4) Most dreaming takes place
6. Sleep Patterns
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a. Alternating cycles of sleep and wakefulness reflect a natural
circadian rhythm
b. Although RAS activity declines in sleep, sleep is more than
turning off RAS
c. Brain is actively guided into sleep
d. Typical sleep pattern alternates between REM and NREM sleep
7. Importance of Sleep
a. Slow-wave sleep is presumed to be the restorative stage
b. Those deprived of REM sleep become moody and depressed
c. REM sleep may be a reverse learning process where
superfluous information is purged from the brain
d. Daily sleep requirements decline with age
8. Sleep Disorders
a. Narcolepsy
1) lapsing abruptly into sleep from the awake state
b. Insomnia
1) chronic inability to obtain the amount or quality of sleep
needed
c. Sleep apnea
1) temporary cessation of breathing during sleep
H. Memory
1. Memory is the storage and retrieval of information
2. The three principles of memory are:
3. Storage
a. occurs in stages and is continually changing
4. Processing
a. accomplished by the hippocampus and surrounding structures
5. Memory traces
a. chemical or structural changes that encode memory
6. Stages of Memory
a. Two stages of memory are short-term memory and long-term
memory
7. Short-term memory (STM, or working memory)
a. fleeting memory of the events that continually happen
b. STM lasts seconds to hours and is limited to 7 or 8 pieces of
information
8. Long-term memory (LTM) has limitless capacity
9. Transfer from STM to LTM
a. Factors that effect transfer of memory from STM to LTM
1) Emotional state
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a) we learn best when we are alert, motivated
2) Rehearsal
a) repeating or rehearsing material enhances memory
3) Association
a) associating new information with old memories in LTM
enhances memory
9. Automatic memory
a. subconscious information stored in LTM
10. Categories of Memory
a. Two categories of memory are fact memory and skill memory
b. Fact (declarative) memory:
1) Entails learning explicit information
2) Related to our conscious thoughts and our language
ability
3) Stored with the context in which it was learned
c. Skill Memory
1) Skill memory is less conscious than fact memory and
involves motor activity
2) It is acquired through practice
3) Skill memories do not retain the context in which they
were learned
VII. Protection of the Brain
A. Brain is protected by bone, meninges, and cerebrospinal fluid
B. Harmful substances are shielded from the brain by the blood-brain
barrier
C. Meninges
1. Three connective tissue membranes lie external to the CNS
a. dura mater
b. arachnoid mater
c. pia mater
2. Functions of the meninges
a. Cover and protect the CNS
b. Protect blood vessels and enclose venous sinuses
c. Contain cerebrospinal fluid (CSF)
d. Form partitions within the skull
3. Dura Mater
a. Outermost membrane that is attached to the inner
periosteum of the skull
b. Tough, white fibrous CT
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c. Contains many blood vessels & nerves
4. Subdural space
a. Space between dura mater & arachnoid mater
5. Arachnoid Mater
a. Middle layer
b. Thin net-like membrane
c. Highly vascularized
6. Subarachnoid Space
a. Space between the arachnoid mater and pia mater
b. Filled with cerebrospinal fluid (CSF)
c. Serves as a cushion for the brain
7. Pia Mater
a. Inner layer that clings to brain surface
b. Very thin delicate CT
c. Many nerves & blood vessels = nourishment
d. Dips into grooves & contours
D. Cerebrospinal Fluid (CSF)
1. Watery solution similar in composition to blood plasma
2. Contains less protein and different ion concentrations than
plasma
3. Forms a liquid cushion that gives buoyancy to the CNS organs
4. Prevents the brain from crushing under its own weight
5. Protects the CNS from blows and other trauma
6. Nourishes the brain and carries chemical signals throughout it
E. Choroid Plexuses
1. Clusters of capillaries that form tissue fluid filters
2. Hang from the roof of each ventricle
3. Help cleanse CSF by removing wastes
F. Blood-Brain Barrier
1. Protective mechanism that helps maintain a stable environment
for the brain
2. Functions
a. Selective barrier that allows nutrients to pass freely
b. Ineffective against substances that can diffuse through
plasma membranes
c. Absent in some areas (vomiting center and the
hypothalamus), allowing these areas to monitor the
chemical composition of the blood
d. Stress increases the ability of chemicals to pass through the
blood-brain barrier
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VIII. Cerebrovascular Accidents (Strokes)
A. Caused when blood circulation to the brain is blocked and brain
tissue dies
B. Most commonly caused by blockage of a cerebral artery
C. Other causes include compression of the brain by hemorrhage or
edema, and atherosclerosis
IX. Degenerative Brain Disorders
A. Alzheimer’s disease
1. Progressive degenerative disease of the brain that results in
dementia
B. Parkinson’s disease
1. Degeneration of the dopamine-releasing neurons of the
substantia nigra
C. Huntington’s disease
1. Fatal hereditary disorder caused by accumulation of the protein
huntingtin that leads to degeneration of the basal nuclei
X. Spinal Cord
A. CNS tissue is enclosed within the vertebral column from the
foramen magnum to L1
B. Provides two-way communication to and from the brain
C. Protected by bone, meninges, and CSF
D. Epidural space
1. Space between the vertebrae and the dural mater filled with fat
and a network of veins
2. Filum terminale
a. Fibrous extension of the pia mater
b. Anchors the spinal cord to the coccyx
E. Spinal nerves
1. 31 pairs attach to the cord by paired roots
F. Cauda equina
1. Collection of nerve roots at the inferior end of the vertebral
canal
XI. Cross-Sectional Anatomy of the Spinal Cord
A. Anterior median fissure
B. Posterior median sulcus
C. Gray Matter and Spinal Roots
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1. Gray matter consists of soma, unmyelinated processes, and
neuroglia
2. Gray commissure
a. connects masses of gray matter; encloses central canal
3. Posterior (dorsal) horns
4. Anterior (ventral) horns
5. Lateral horns
6. Dorsal half
a. Sensory roots and ganglia
7. Ventral half
a. Motor roots
8. Dorsal and ventral roots fuse laterally to form spinal nerves
D. White Matter in the Spinal Cord
1. Fibers run in three directions
a. Ascending
b. Descending
c. Transversely
E. Main Ascending Pathways
1. Central processes of fist-order neurons branch diffusely as they
enter the spinal cord and medulla
2. Some branches take part in spinal cord reflexes
F. Descending (Motor) Pathways
1. Descending tracts deliver efferent impulses from the brain to the
spinal cord, and are divided into two groups
XII. Spinal Cord Trauma
A. Paralysis
1. Loss of motor function
2. Lower motor neurons are damaged and impulses do not reach
muscles
3. There is no voluntary or involuntary control of muscles
B. Transection
1. Cross sectioning of the spinal cord at any level results in total
motor and sensory loss in regions inferior to the cut
2. Paraplegia
a. Transection between T1 and L1
3. Quadriplegia
a. Transection in the cervical region
C. Amyotrophic Lateral Sclerosis (ALS)
1. Lou Gehrig’s disease
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a. Neuromuscular condition involving destruction of anterior
horn motor neurons and fibers of the pyramidal tract
b. Symptoms
1) Loss of the ability to speak, swallow, and breathe
c. Death occurs within five years
d. Linked to malfunctioning genes for glutamate transporter
and/or superoxide dismutase
XIII. Developmental Aspects of the CNS
A. CNS is established during the first month of development
B. Gender-specific areas appear in response to testosterone (or lack
thereof)
C. Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or
infection can harm the fetus’ developing CNS
E. Smoking decreases oxygen in the blood, which can lead to neuron
death and fetal brain damage
F. The hypothalamus is one of the last areas of the CNS to develop
G. Visual cortex develops slowly over the first 11 weeks
H. Growth and maturation of the nervous system occurs throughout
childhood and reflects progressive myelination
I. Age brings some cognitive declines, but these are not significant in
healthy individuals until they reach their 80s
J. Excessive use of alcohol causes signs of senility unrelated to the
aging process
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