Physiology: The central nervous system

Permission required for reproduction or display Prosen- / Telen- /“Ñ-ZàCerebral Lateral f Ẩ\ aphalon — KA @/ hemisphere ventricles idbrai HN \ 77-Hypothalamus ventricle : imidbra

¢ Groove appears in ectoderm to fuse to form neurol tube bụ 2oth

day after conception Neural tube eventually forms the CNS

¢ During 5** week, modified:

¢ Forebrain: telencephalon and diencephalon

¢ Midbrain: unchanged

¢ Hindbrain: metencephalon and myelencephalon

¢ Part of ectoderm where fusion occurs becomes neural crest

¢ Neural crest forms ganglia of PNS

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Embrvwonic Deuelopment

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Prosen- / Telen- /“Ñ-ZàCerebral Lateral

f Ẩ\ aphalon — KA @/ hemisphere ventricles

( ( idbrai ) HN \ 77-Hypothalamus ventricle

: imidbrain) cephalon—{ 7 Midbrain Aqueduct

Embrvwonic Deuelopment

¢ Telencephalon grows disproportionately forming 2 the hemispheres of the cerebrum

¢ Ventricles and central canal become filled with

cerebral spinal fluid (CSF)

¢ CNS composed of gray and white matter

¢ Gray matter consists of neuron cell bodies and dendrites

¢ White matter (myelin) consists of axon tracts

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Cerebrum

¢ Only structure of the telencephalon

¢ Largest portion of brain (80% mass)

¢ Responsible for higher mental functions

¢ Corpus callosum:

¢ Major tract of axons that functionally interconnects right and left cerebral hemispheres

Ce | e lor er mm (continued)

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Motor areas involved Central sulcus

Frontah “<2 ™® other senses

Cerebral Cortex

e Characterized by numerous convolutions

© Elevated folds: gyri

© Depressed groves: sulci

@ Frontal lobe:

© Anterior portion of each cerebral hemisphere

© Precentral gyri:

¢ Contains upper motor neurons

¢ Involved in motor control

® Body regions with the greatest number of motor

innervation are represented by largest areas of motor

cortex

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€Cerebral Certex

¢ Parietal lobe:

¢ Primary area responsible for perception of somatesthetic sensation

¢ Body regions with highest densities of receptors are

represented by largest areas of sensory cortex

¢ Implicated in memory encoding

¢ Integration of sensory information with visceral

responses

¢ Coordinated cardiovascular response to stress

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Visualizing the Brain

¢ X-ray computed tomography (CT):

¢ Complex computer manipulations of data obtained from x-ray absorption by tissues of different densities

° Soft tissue

¢ Positron-emission tomography (PET):

¢ Radioisotopes that emit positrons are injected into blood stream

¢ Collision of positron and electron result in emission of gamma rays

¢ Pinpoint brain cells that are most active

¢ Brain metabolism, drug distribution

¢ Magnetic resonance imaging (MRI):

¢ Protons (H*) respond to magnetic field, which align the protons

¢ Emit a radio-wave signal when stimulated

¢ Brain function

EEG Patterns

Alpha:

c Recorded from parietal and occipital regions

Person is awake, relaxed, with eyes closed

10-12 cycles/sec

Beta:

c S$trongest from frontal lobes near precentral gyrus

Produced by visual stimuli and mental activity

« Emitted in a general pattern

Common during sleep and awake infant

In awake adult indicate brain damage

1-5 cycles/sec

EEG Sleep Patterns

¢ 2 types of EEG patterns during sleep:

¢ REM (rapid eye movement):

¢ Dreams occur

¢ Low-amplitude, high-frequency oscillations

¢ Similar to wakefulness (beta waves)

¢ Non-Rem (resting):

¢ High-amplitude, low-frequency waves (delta waves)

¢ Superimposed on these are sleep spindles:

¢ Waxing and waning bursts of 7-14 cycles/sec

¢ Last for 1-3 sec

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Basal Nuclei (basal ganglia)

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composed of neuronal cell

bodies located deep within

¢ Corpus striatum: ¢ Caudate nucleus P nuclel InucleuslGlobus .` Corpus _ |Lentiform pallidu ˆ 4

¢ Lentiform nucleus: striatum [ƒ8bÔ

e Putman and globus Caudate pallidus nucleus

¢ Functions in the control of

voluntary movements

¢ Severe speech problems ; WF Ith g

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Language

Broca’s area:

¢ Involves articulation of speech

¢ In damage, comprehension of speech in unimpaired

Wernicke’s area:

¢ Involves language comprehension

¢ In damage, language comprehension is destroyed, but speech is rapid without any meaning

¢ To speak intelligibly, words originating in Wernicke’s area must be

sent to Broca’s area

-_ lmportơnt in the neurdl bosis of

emotional states are

hypothalamus and limbic

system

e Limbic system:

c Group of forebrain nuclei and

fiber tracts that form a ring

around the brain stem

* Center for basic emotional drives

© Closed circuit (Papez circuit):

© Fornix connects hippocampus

to hypothalamus, which projects

to the thalamus which sends

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Emotien Til: Mettiuetieon (continued)

¢ Areas or the hypothalamus and limbic system are

involved in feelings and behaviors

¢ Hypothalamus (feeding and satiety centers)

¢ Sexual drive and behavior:

¢ Hypothalamus and limbic system

¢ Goal directed behavior (reward and punishment):

¢ Hypothalamus and frontal cortex

¢ Short-term:

¢ Memory of recent events

¢ Medial temporal lobe:

¢ Consolidates short term into long term memory

¢ Hippocampus is critical component of memory

¢ Acquisition of new information, facts and events requires both the medial temporal lobe and

hippocampus

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¢ Altered postsynaptic growth of dendritic spines in area of contact

¢ Cerebral cortex stores factual information:

¢ Visual memories lateralized to left hemisphere

¢ Visuospatial information lateralized to right hemisphere

¢ Prefrontal lobes:

¢ Involved in performing exact mathematical calculations

¢ Complex, problem-solving and planning activities

Long-Term Potentiation

° Type of synaptic learning

« Synapses that are 1* stimulated at high frequency will

subsequently exhibit increased excitability

° In hippocampus, glutamate is NT

a Requires activation of the NMDA receptors for glutamate

¢ Glutamate and glycine or D-serine binding and partial

depolarization are required for opening of channels for Ca2* and Nat’

° May also involve presynaptic changes:

© Binding of glutamate to NMDA receptors and simultaneous

depolarization, open receptor channels for Ca"

- Ca’ causes long-term potentiation in postsynaptic neuron, release of

NO from postsynaptic neuron

- NO acts as a retrograde messenger, causing release of NT

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Neuronel $tem Cells in Learning

œnd Memor

¢ Neural stem cells:

¢ Cells that both renew themselves through mitosis and produce differentiated neurons and neuroglia

¢ Hippocampus has been shown to contain stem cells (required for long-term memory)

¢ Neurogenesis:

¢ Production of new neurons

¢ Indirect evidence that links neuogenesis in

hippocampus with learning and memory

Thalœmu‡ and Epithaleamu$

-_ Tholqamu:s:

2 Composes 4/5 of the diencephalon

- Forms most of the walls of the 3" ventricle

« Acts as relay center through which all sensory information (except olfactory) passes to the cerebrum

¢ Lateral geniculate nuclei:

¢ Relay visual information

¢ Medial geniculate nuclei:

* Relay auditory information

¢ Intralaminar nuclei:

- Activated by many sensory modalities

¢ Projects to many areas

= Promotes alertness and arousal from sleep

° Epithalamus contains:

« Choroid plexus where CSF is formed

« Pineal gland which secretes melatonin

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Hypothalamus

¢ Contains neural centers for hunger, thirst, and

body temperature

¢ Contributes to the regulation of sleep,

wakefulness, emotions, sexual arousal, anger, fear,

pain, and pleasure

¢ Stimulates hormonal release from anterior

pituitary

¢ Produces ADH and oxytocin

¢ Coordinates sympathetic and parasympathetic

reflexes

¢ Posterior pituitary:

¢ Stores and releases ADH (vasopressin) and oxytocin

¢ Hypothalamus produces releasing and inhibiting hormones that are transported to anterior

¢ Maintains connections with cerebrum and cerebellum

¢ Involved in motor coordination

¢ Metencephalon:

¢ Pons:

¢ Surface fibers connect to cerebellum, and deeper fibers are part of motor and sensory tracts

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¢ Contains several nuclei associated with

cranial nerves V, VI, VII

¢ Contains the apneustic and

pneumotaxic respiratory centerss

¢ Cerebellum:

¢ Receives input from proprioceptors

¢ Necessary for motor learning, Brain stem Pneumotaxic area

coordinating different joints during respiratory Apneustic area movement, and limb movements centers Rhythmicity area

Reticular formation—\ _ Medulla oblongata~

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n in fa yy a@ i Sy (continued)

Myelencephalon (medulla oblongata):

All descending and ascending fiber tracts between

spinal cord and brain must pass through the medulla

¢ Nuclei contained within the medulla include VIII, IX, X, XI, XIl

¢- Pyramids:

- Fiber tracts cross to contralateral side

Vasomotor center:

- Controls autonomic innervation of blood vessels

Cardiac control center:

- Regulates autonomic nerve control of heart

Regulates respiration with the pons

¢ Reticular Formation:

¢ Complex network of nuclei and nerve fibers within

medulla, pons, midbrain, thalamus and

hypothalamus

¢ Functions as the reticular activating system (RAS)

¢ Non specific arousal of cerebral cortex to incoming sensory information

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Ascending Spinal Tracts

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cutaneous receptors, Thư |

decussation may occur (Z_ oblongata —Fascicul tus 4p Va © second-order

Joint stretch receptor receptor

(proprioceptor) Spinal cord (not part of

cons of first-order | ⁄ j tract) nsory neurons) ey tm _ Touch receptor Temperature receptor

De¿cending $pinal Treaet$

¢ Pyramidal (corticospinal)

tracts descend directly

without synaptic

interruption from cerebral

cortex to spinal cord

¢ Function in control of fine

movements that require

¢ Gross motor movement

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Primary motor area of cerebral ~—

cortex

Internal capsule

Medulla oblongata, : j

Cranial and Spinal Nerves

° Cranial nerves:

© 2 pairs arise from neuron cell bodies in forebrain

© 10 pairs arise from the midbrain and hindbrain

Roman numerals refer to the order in which the nerves are positioned from front of the brain to the back

« Most are mixed nerves containing both sensory and motor fibers

Produces 2 roots to each nerve

- Dorsal root composed of sensory fibers

¢ Ventral root composed of motor fibers

Reflex Are

response to a sensory Copyright © The MoGraw-Hill Companies, Inc Permission required for reproduction or displa

stimulus

Stimulation of sensory Dorsal root body of Dorsal

receptors evoRes APs that ganglion neuron root

¢ Synapses with association neuron _ |

neuron, which synapses (interneuron) —

with somatic motor White —_

Conducts impulses to Tay youre

muscle and stimulates a Spinal ⁄ Ventra “Effector (muscle)

reflex contraction cord

¢ Brain is not directly

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