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Human Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Chapter 5

The Central Nervous System

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Chapter 5 The Central Nervous SystemHuman Physiologyby Lauralee Sherwood 2007 Brooks/Cole-Thomson Learning

Nervous System Organization

Central nervous system (CNS)

Consists of brain and spinal cord

Peripheral nervous system (PNS)

Afferent division

Carries information to the CNS Two branches

Sympathetic

Parasympathetic

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Efferent division

Carries information away from CNS to effector organs(muscles and glands)

Divided into

Somatic nervous system

Consists of fibers of motor neurons that supplyskeletal muscles

Autonomic nervous system

Consists of fibers that innervate smooth muscle,

cardiac muscle, and glands

Two divisions:Sympathetic nervous system

Parasympathetic nervous system

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Functional Classes of Neurons

Afferent neurons

Inform CNS about conditions in both the externaland internal environment

Efferent neurons

Carry instructions from CNS to effector organs

muscles and glands Interneurons

Found entirely within CNS

Responsible for Integrating afferent information and formulating an

efferent response

Higher mental functions associated with the mind

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Functional Classes of Neurons

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Neuroglia

Also called glial cells

Physically, metabolically, and functionallysupport interneurons

Four major types of cells

Astrocytes Oligodendrocytes

Microglia

Ependymal cells

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Neuroglia

Astrocytes

Main glue of CNS holds neurons together

Guide neurons during fetal brain development

Aid in establishment of blood-brain barrier

Important in repair of brain injuries and in neuralscar formation

Play role in neurotransmitter activity

Take up excess K+from brain ECF

Along with other glial cellsenhance synapseformation and modify synaptic transmission

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Neuroglia

Oligodendrogytes

Form myelin sheaths around axons in CNS

Microglia

Immune defense cells of the CNS

In resting state release low levels of growthfactors that help neurons and other glial cells

survive and thrive

Ependymal cells

Line internal, fluid-filled cavities of the CNS

In ventricles of brain, help form and circulate

cerebrospinal fluid

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Neuroglia

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Protection of CNS

Enclosed by hard, bony structures

Wrapped by three protective and nourishingmembranesmeninges

Dura mater

Arachnoid mater Pia mater

Floats in cushioning fluidcerebrospinal fluid

(CSF)

Blood-brain barrier limits access of blood-borne

materials into brain tissue

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Cerebrospinal Fluid (CSF)

Surrounds and cushions brain and spinal cord

Formed primarily by choroid plexuses

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Cerebrospinal Fluid

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Blood-Brain Barrier (BBB)

Protects brain from chemical fluctuations in

blood Minimizes possibility that harmful blood-borne

substances might reach central nervous tissue

Prevents certain circulating hormones that couldalso act as neurotransmitters from reaching

brain

Limits use of drugs for treatment of brain and

spinal cord disorders Many drugs cannot penetrate BBB

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Central Nervous System

Enables you to:

Subconsciously regulate your internalenvironment by neural means

Experience emotions

Voluntarily control your movements

Be consciously aware of your own body and your

surroundings

Engage in other higher cognitive processes such

as thought and memory

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Brain Anatomy

Brain components

Brain stem Cerebellum

Forebrain

Diencephalon

Hypothalamus

Thalamus

Cerebrum

Basal nuclei

Cerebral cortex

B i t

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Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus

(medial)

Basal nuclei

(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Bra in com ponent

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,

and medulla)

M j F ti B i t

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Major Functions

1. Sensory perception2. Voluntary control of movement3. Language4. Personality traits5. Sophisticated mental events, such as thinking memory,

decision making, creativity, and self-consciousness

1. Inhibition of muscle tone2. Coordination of slow, sustained movements3. Suppression of useless patterns of movements

1. Relay station for all synaptic input2. Crude awareness of sensation

3. Some degree of consciousness4. Role in motor control

1. Regulation of many homeostatic functions, such as temperaturecontrol, thirst, urine output, and food intake

2. Important link between nervous and endocrine systems3. Extensive involvement with emotion and basic behavioral patterns

1. Maintenance of balance

2. Enhancement of muscle tone3. Coordination and planning of skilled voluntary muscle activity

1. Origin of majority of peripheral cranial nerves

2. Cardiovascular, respiratory, and digestive control centers

3. Regulation of muscle reflexes involved with equilibrium and posture

4. Reception and integration of all synaptic input from spinal cord;

arousal and activation of cerebral cortex5. Role in sleep-wake cycle

Bra in com ponent

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem

(midbrain, pons,

and medulla)

Table 5-2, p. 141

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Brain Stem

Oldest region of the brain

Continuous with spinal cord

Controls many life-sustaining processes, such

as respiration, circulation, and digestion

Consists of Midbrain

Pons

Medulla

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Cerebellum

Attached at top rear portion of brain stem

Maintains proper position of the body in space

Subconscious coordination of motor activity

(movement)

Plays key role in learning skilled motor tasks

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Diencephalon

Houses two brain components

Hypothalamus Controls many homeostatic functions important in

maintaining stability of internal environment

Thalamus

Performs some primitive sensory processing

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Cerebrum

Highly developed

Makes up about 80% of total brain weight(largest portion of brain)

Inner core houses basal nuclei

Outer surface is highly convoluted cerebralcortex

Highest, most complex integrating area of the

brain

Plays key role in most sophisticated neuralfunctions

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Cerebral Cortex

Organized into six well-defined layers

Layers are organized into functional verticalcolumns

Each half of cortex divided into four major lobes

Occipital Temporal

Parietal

Frontal

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Cerebral cortex

Occipital lobe

Carries out initial processing of visual input

Temporal lobe

Initial reception of sound sensation

Parietal lobe Somatosensory processing

Frontal lobe

Responsible for

Voluntary motor activity

Speaking ability

Elaboration of thought

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Cerebral Cortex

Primary motor cortex

Located in frontal lobe Confers voluntary control over movement

produced by skeletal muscles

Primarily controls muscles on the opposite side of

the body

Motor homunculus

Depicts location and relative amount of motor cortex

devoted to output to muscles of each body part

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Cerebral Cortex

Supplementary motor area

Plays preparatory role I n programming complexsequences of movement

Premotor cortex

Important in orienting the body and arms toward a

specific target

Posterior parietal cortex

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Cerebral Cortex

Primary areas of cortical specialization for

language Brocas area

Governs speaking ability

Wernickes area

Concerned with language comprehension Responsible for formulating coherent patterns of

speech

Language disorders

Aphasias Speech impediments

Dyslexia

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Chapter 5 The Central Nervous System


Cerebral Hemispheres

Left cerebral hemisphere

Excels in logical, analytic, sequential, and verbaltasks

Math, language forms, philosophy

Right cerebral hemisphere

Excels in nonlanguage skills

Spatial perception and artistic and musical talents

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Cerebral Cortex

Schematic Linking

of Various Regions

of the Cortex

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Electroencephalogram (EEG)

Record of postsynaptic activity in cortical

neurons Brain waves

Three major uses

Clinical tool in diagnosis of cerebral dysfunction Used in legal determination of brain death

Used to distinguish various stages of sleep

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Electroencephalogram (EEG)

B l N l i

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Basal Nuclei

Act by modifying ongoing activity in motor

pathways Primary functions

Inhibiting muscle tone throughout the body

Selecting and maintaining purposeful motoractivity while suppressing useless or unwanted

patterns of movement

Helping monitor and coordinate slow, sustained

contractions, especially those related to postureand support

Th l

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Thalamus

Part of diencephalon

Serves as relay station and synaptic integratingcenter for processing sensory input on its way to

cerebral cortex

Along with brain stem and cortical association

areas, important in ability to direct attention to

stimuli of interest

Capable of crude awareness of various types of

sensation but cannot distinguish their location orintensity

H th l

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Hypothalamus

Brain area most involved in directly regulating internal

environment Functions

Controls body temperature

Controls thirst and urine output

Controls food intake Controls anterior pituitary hormone secretion

Produces posterior pituitary hormones

Controls uterine contractions and milk ejection

Serves as a major ANS coordinating center Plays role in emotional and behavioral patterns

Participates in sleep-wake cycle

Li bi S t

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Limbic System

Includes portions of the hypothalamus and other

forebrain structures that encircle brain stem Responsible for

Emotion

Basic, inborn behavioral patterns related to

survival and perpetuation of the species

Plays important role in motivation and learning

M

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Memory

Storage of acquired knowledge for later recall

Memory trace Neural change responsible for retention or storage ofknowledge

Short-term memory

Lasts for seconds to hours

Long-term memory Retained for days to years

Consolidation

Process of transferring and fixing short-term memory

traces into long-term memory stores Working memory

Temporarily holds and interrelates various pieces ofinformation relevant to a current mental task

Comparison of Long Term and Short Term Memory

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Comparison of Long-Term and Short-Term Memory

C b ll

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Cerebellum

Important in balance and in planning and

executing voluntary movement Three different parts

Vestibulocerebellum Important in maintaining balance and controls eye

movements Spinocerebellum

Enhances muscle tone and coordinates skilled,voluntary movements

Cerebrocerebellum Plays role in planning and initiating voluntary activity by

providing input to cortical motor areas

Stores procedural memories

B i St

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Brain Stem

Critical connecting link between rest of brain and

spinal cord Consists of

Medulla

Pons

Midbrain

B i St

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Brain Stem

Functions

Most of cranial nerves arise from brain stem Neuronal clusters within brain stem control heart

and blood vessel function, respiration, and manydigestive functions

Plays role in regulating muscle reflexes involvedin equilibrium and posture

Reticular formation within brain stem receivesand integrates all incoming sensory synaptic input

Centers that govern sleep are in brain stem(evidence suggests center promoting slow-wavesleep lies in hypothalamus)

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Cranial

Nerves

Sl

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Sleep

Function of sleep is unclear

Sleep-wake cycle Normal cyclic variation in awareness of

surroundings

Active process consisting of two types of sleep

characterized by different EEG patterns and

different behaviors

Slow-wave sleep

Paradoxical, or REM sleep

Comparison of Slow Wave and Paradoxical Sleep

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Comparison of Slow-Wave and Paradoxical Sleep

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EEG

Patterns

During

DifferentTypes of

Sleep

Spinal Cord

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Spinal Cord

Extends from brain stem through vertebral canal

31 pairs of spinal nerves emerge from spinalcord through spaces formed between arches of

adjacent vertebrae

Named for region of vertebral column from which

they emerge

8 pairs cervical (neck) nerves

12 pairs thoracic (chest) nerves

5 pairs lumbar (abdominal) nerves

5 pairs sacral (pelvic) nerves

1 pair coccygeal (tailbone) nerves

Spinal Nerves

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Spinal Nerves

Spinal Cord

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Spinal Cord

Two vital functions

Neuronal link between brain and PNS Integrating center for spinal reflexes

Reflex

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Reflex

Reflex

Any response that occurs automatically withoutconscious effort

Two types of reflexes

Simple, or basic, reflexes

Built-in, unlearned responses

Acquired, or conditioned, reflexes

Result of practice and learning

Reflex Arc

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Reflex Arc

Neural pathway involved in accomplishing reflex

activity Five basic components

Receptor

Afferent pathway

Integrating center

Efferent pathway

effector

Crossed Extensor Reflex Coupled with the

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Crossed Extensor Reflex Coupled with the

Withdrawal Reflex

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