chapter 12 part 2 (2)

PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

12

The Central Nervous System:


Brain Stem

• Three regions

• Midbrain

• Pons

• Medulla oblongata

Copyright © 2010 Pearson Education, Inc. Figure 12.12

Corporaquadrigemina

PonsMedulla oblongata

Mid-brain


Brain Stem

• Similar structure to spinal cord but contains embedded nuclei

• Controls automatic behaviors necessary for survival

• Contains fiber tracts connecting higher and lower neural centers

• Associated with 10 of the 12 pairs of cranial nerves


Frontal lobeOlfactory bulb(synapse point ofcranial nerve I)Optic chiasmaOptic nerve (II)Optic tractMammillary body

Pons

MedullaoblongataCerebellum

Temporal lobe

Spinal cord

Midbrain

Copyright © 2010 Pearson Education, Inc. Figure 12.15a

Optic chiasmaView (a)

Optic nerve (II)

Mammillary body

Oculomotor nerve (III)

Crus cerebri ofcerebral peduncles (midbrain)

Trigeminal nerve (V)

Abducens nerve (VI)Facial nerve (VII)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Ventral root of firstcervical nerve

Trochlear nerve (IV)

PonsMiddle cerebellarpeduncle

Pyramid

Decussation of pyramids

(a) Ventral view

Spinal cord

Vestibulocochlearnerve (VIII)

Glossopharyngeal nerve (IX)

Diencephalon• Thalamus• Hypothalamus

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Copyright © 2010 Pearson Education, Inc. Figure 12.15b

View (b)


InfundibulumPituitary gland


Abducens nerve (VI)

Facial nerve (VII)

Vagus nerve (X)



Pons

(b) Left lateral view


Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Thalamus

Superior colliculusInferior colliculusTrochlear nerve (IV)

Superior cerebellar peduncle

Middle cerebellar peduncle

Inferior cerebellar peduncle

Vestibulocochlear nerve (VIII)Olive

Copyright © 2010 Pearson Education, Inc. Figure 12.15c

View (c)

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata

Pineal gland

Diencephalon

Anterior wall offourth ventricle

(c) Dorsal view

Thalamus

Dorsal root offirst cervical nerve

Midbrain• Superior

colliculus• Inferior

colliculus• Trochlear nerve (IV)• Superior cerebellar peduncle

Corporaquadrigeminaof tectum

Medulla oblongata• Inferior cerebellar peduncle• Facial nerve (VII)• Vestibulocochlear nerve (VIII)• Glossopharyngeal nerve (IX)• Vagus nerve (X)• Accessory nerve (XI)

Pons• Middle cerebellar peduncle

Dorsal median sulcus

Choroid plexus(fourth ventricle)


Midbrain

• Located between the diencephalon and the pons

• Cerebral peduncles

• Contain pyramidal motor tracts

• Cerebral aqueduct

• Channel between third and fourth ventricles


Midbrain Nuclei

• Nuclei that control cranial nerves III (oculomotor) and IV (trochlear)

• Corpora quadrigemina—domelike dorsal protrusions

• Superior colliculi—visual reflex centers

• Inferior colliculi—auditory relay centers

• Substantia nigra—functionally linked to basal nuclei

• Red nucleus—relay nuclei for some descending motor pathways and part of reticular formation


Dorsal

Cerebral aqueduct

Superiorcolliculus

Reticular formation

Crus cerebri ofcerebral peduncle

Ventral

Fibers ofpyramidal tract

Substantianigra

(a) Midbrain

Rednucleus

Mediallemniscus

Oculomotornucleus (III)

Periaqueductal graymatter

Tectum


Pons

• Forms part of the anterior wall of the fourth ventricle

• Fibers of the pons

• Connect higher brain centers and the spinal cord

• Relay impulses between the motor cortex and the cerebellum

• Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial)

• Some nuclei of the reticular formation

• Nuclei that help maintain normal rhythm of breathing


Reticularformation

Trigeminalnerve (V)

Pontinenuclei

Fibers ofpyramidaltract

Middlecerebellarpeduncle

Trigeminal mainsensory nucleus Trigeminalmotor nucleus

Superior cerebellarpeduncle

Medial lemniscus

Fourthventricle

(b) Pons


Medulla Oblongata

• Joins spinal cord at foramen magnum

• Forms part of the ventral wall of the fourth ventricle

• Contains a choroid plexus of the fourth ventricle

• Pyramids—two ventral longitudinal ridges formed by pyramidal tracts

• Decussation of the pyramids—crossover of the corticospinal tracts


Optic chiasmaView (a)

Optic nerve (II)

Mammillary body

Oculomotor nerve (III)



Abducens nerve (VI)Facial nerve (VII)

Vagus nerve (X)



Ventral root of firstcervical nerve

Trochlear nerve (IV)

PonsMiddle cerebellarpeduncle

Pyramid

Decussation of pyramids

(a) Ventral view

Spinal cord

Vestibulocochlearnerve (VIII)


Diencephalon• Thalamus• Hypothalamus

Diencephalon

Brainstem

Thalamus

Hypothalamus

Midbrain

Pons

Medullaoblongata


Medulla Oblongata

• Inferior olivary nuclei—relay sensory information from muscles and joints to cerebellum

• Cranial nerves VIII, X, and XII are associated with the medulla

• Vestibular nuclear complex—mediates responses that maintain equilibrium

• Several nuclei (e.g., nucleus cuneatus and nucleus gracilis) relay sensory information


Medulla Oblongata

• Autonomic reflex centers

• Cardiovascular center

• Cardiac center adjusts force and rate of heart contraction

• Vasomotor center adjusts blood vessel diameter for blood pressure regulation


Medulla Oblongata

• Respiratory centers

• Generate respiratory rhythm

• Control rate and depth of breathing, with pontine centers


Medulla Oblongata

• Additional centers regulate

• Vomiting

• Hiccuping

• Swallowing

• Coughing

• Sneezing

Copyright © 2010 Pearson Education, Inc. Figure 12.16c

Choroidplexus

Fourth ventricle

PyramidMedial lemniscus

Inferior olivarynucleus

Nucleusambiguus

Inferior cerebellarpeduncle

Cochlearnuclei (VIII)

Vestibular nuclearcomplex (VIII)

Solitarynucleus

Dorsal motor nucleusof vagus (X)

Hypoglossal nucleus (XII)

(c) Medulla oblongata

LateralnucleargroupMedialnucleargroupRaphenucleusRet

icu

lar

form

atio

n


The Cerebellum

• 11% of brain mass

• Dorsal to the pons and medulla

• Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction


Anatomy of the Cerebellum

• Two hemispheres connected by vermis

• Each hemisphere has three lobes

• Anterior, posterior, and flocculonodular

• Folia—transversely oriented gyri

• Arbor vitae—distinctive treelike pattern of the cerebellar white matter

Copyright © 2010 Pearson Education, Inc.Figure 12.17

arbor vitae


(b)

Medullaoblongata

Flocculonodularlobe

Choroidplexus offourth ventricle

Posteriorlobe

Arborvitae

Cerebellar cortex

Anterior lobe

Cerebellarpeduncles• Superior• Middle• Inferior

Copyright © 2010 Pearson Education, Inc. Figure 12.17d

(d)

Anteriorlobe

Posteriorlobe

Vermis(d)


Cerebellar Peduncles

• All fibers in the cerebellum are ipsilateral

• Three paired fiber tracts connect the cerebellum to the brain stem

• Superior peduncles connect the cerebellum to the midbrain

• Middle peduncles connect the pons to the cerebellum

• Inferior peduncles connect the medulla to the cerebellum


Cerebellar Processing for Motor Activity

• Cerebellum receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction (MCP)

• Signals from proprioceptors and visual and equilibrium pathways continuously “inform” the cerebellum of the body’s position and momentum (ICP)

• Cerebellar cortex calculates the best way to smoothly coordinate a muscle contraction

• A “blueprint” of coordinated movement is sent to the cerebral motor cortex and to brain stem nuclei (SCP)


Cerebellar Injuryg

• Injury to cerebellum = loss of muscle tone, and clumsy unsure movement


Cognitive Function of the Cerebellum

• Recognizes and predicts sequences of events during complex movements

• Plays a role in nonmotor functions such as word association and puzzle solving


Functional Brain Systems

• Networks of neurons that work together and span wide areas of the brain

• Limbic system

• Reticular formation


Limbic System

• Structures on the medial aspects of cerebral hemispheres and diencephalon

• Includes parts of the diencephalon and some cerebral structures that encircle the brain stem


Corpus callosum

Septum pellucidum

Olfactory bulb

Diencephalic structuresof the limbic system

•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body

Fiber tractsconnecting limbic system structures

•Fornix•Anterior commissure

Cerebral struc-tures of the limbic system

•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus


Limbic System

• Emotional or affective brain

• Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response

• Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict

• Puts emotional responses to odors

• Example: skunks smell bad


Limbic System: Emotion and Cognition

• The limbic system interacts with the prefrontal lobes, therefore:

• We can react emotionally to things we consciously understand to be happening

• We are consciously aware of emotional richness in our lives

• Hippocampus and amygdala—play a role in memory


Reticular Formation

• Three broad columns along the length of the brain stem

• Raphe nuclei

• Medial (large cell) group of nuclei

• Lateral (small cell) group of nuclei

• Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord


Visualimpulses

Reticular formation

Ascending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex


Reticular Formation: RAS and Motor Function

• RAS (reticular activating system)

• Sends impulses to the cerebral cortex to keep it conscious and alert

• Filters out repetitive and weak stimuli (~99% of all stimuli!)

• Severe injury results in permanent unconsciousness (coma)


Reticular Formation: RAS and Motor Function

• Motor function

• Helps control coarse limb movements

• Reticular autonomic centers regulate visceral motor functions

• Vasomotor

• Cardiac

• Respiratory centers


Electroencephalogram (EEG)

• Records electrical activity that accompanies brain function

• Measures electrical potential differences between various cortical areas


Brain Waves

• Patterns of neuronal electrical activity

• Generated by synaptic activity in the cortex

• Each person’s brain waves are unique

• Can be grouped into four classes based on frequency


Types of Brain Waves

• Alpha waves—regular and rhythmic, synchronous waves indicating an “idling” brain

• Beta waves —rhythmic, less regular waves occurring when mentally alert

• Theta waves —more irregular; common in children and uncommon in adults

• Delta waves —seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage


Alpha waves—awake but relaxed

Beta waves—awake, alert

Theta waves—common in children

Delta waves—deep sleep

(b) Brain waves shown in EEGs fall intofour general classes.

1-second interval


Brain Waves: State of the Brain

• Change with age, sensory stimuli, brain disease, and the chemical state of the body

• EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions

• A flat EEG (no electrical activity) is clinical evidence of death


Epilepsy

• A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking

• Epilepsy is not associated with intellectual impairments

• Epilepsy occurs in 1% of the population


Epileptic Seizures

• Absence seizures, or petit mal

• Mild seizures seen in young children where the expression goes blank

• Tonic-clonic (grand mal) seizures

• Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue


Control of Epilepsy

• Anticonvulsive drugs

• Vagus nerve stimulators implanted under the skin of the chest can keep electrical activity of the brain from becoming chaotic


Consciousness

• Conscious perception of sensation

• Voluntary initiation and control of movement

• Capabilities associated with higher mental processing (memory, logic, judgment, etc.)

• Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired


Consciousness

• Clinically defined on a continuum that grades behavior in response to stimuli

• Alertness

• Drowsiness (lethargy)

• Stupor

• Coma


Sleep

• State of partial unconsciousness from which a person can be aroused by stimulation

• Two major types of sleep (defined by EEG patterns)

• Nonrapid eye movement (NREM)

• Rapid eye movement (REM)


(b) Typical progression of an adult through onenight’s sleep stages

Awake

REM

Stage 1

Stage 2NonREM Stage 3

Stage 4

Time (hrs)


Importance of Sleep

• Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage

• People deprived of REM sleep become moody and depressed

• REM sleep may be a reverse learning process where superfluous information is purged from the brain

• Daily sleep requirements decline with age

• Stage 4 sleep declines steadily and may disappear after age 60


Sleep Disorders

• Narcolepsy

• Lapsing abruptly into sleep from the awake state

• Insomnia

• Chronic inability to obtain the amount or quality of sleep needed

• Sleep apnea

• Temporary cessation of breathing during sleep


Language

• Language implementation system

• Basal nuclei

• Broca’s area (lesions - understand but can’t speak) and Wernicke’s area (lesions - speak nonsense and but can’t understand )

(in the association cortex on the left side)

• Analyzes incoming word sounds

• Produces outgoing word sounds and grammatical structures

• Corresponding areas on the right side are involved with nonverbal language components


Memory

• Storage and retrieval of information

• Two stages of storage

• Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information

• Long-term memory (LTM) has limitless capacity


Outside stimuli

General and special sensory receptors

Data transferinfluenced by:

ExcitementRehearsalAssociation ofold and new data

Long-termmemory(LTM)

Data permanentlylost

Afferent inputs

Retrieval

Forget

Forget

Data selectedfor transfer

Automaticmemory

Data unretrievable

Temporary storage(buffer) in cerebral cortex

Short-termmemory (STM)


Transfer from STM to LTM

• Factors that affect transfer from STM to LTM

• Emotional state—best if alert, motivated, surprised, and aroused

• Rehearsal—repetition and practice

• Association—tying new information with old memories

• Automatic memory—subconscious information stored in LTM


Categories of Memory

1. Declarative memory (factual knowledge)

• Explicit information

• Related to our conscious thoughts and our language ability

• Stored in LTM with context in which it was learned


Categories of Memory

2. Nondeclarative memory

• Less conscious or unconscious

• Acquired through experience and repetition

• Best remembered by doing; hard to unlearn

• Includes procedural (skills) memory, motor memory, and emotional memory


Homeostatic Imbalances of the Brain

• Traumatic brain injuries

• Concussion—temporary alteration in function

• Contusion—permanent damage

• Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death

• Cerebral edema—swelling of the brain associated with traumatic head injury



• Cerebrovascular accidents (CVAs)(strokes) 3rd leading cause of death

• Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot

• Typically leads to hemiplegia, or sensory and speed deficits

• Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia (deprivation of blood supply to any tissue)

• Tissue plasminogen activator (TPA) is the only approved treatment for stroke


Stroke Symptoms

The symptoms of stroke are distinct because they happen quickly:

• Sudden numbness or weakness of the face, arm, or leg (especially on one side of the body)

• Sudden confusion, trouble speaking or understanding speech

• Sudden trouble seeing in one or both eyes

• Sudden trouble walking, dizziness, loss of balance or coordination

• Sudden severe headache with no known cause



• Degenerative brain disorders

• Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia

• Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra

• Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex

chapter 12 part 2 (2)

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