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Human Anatomy, Second Edition

McKinley & O'Loughlin

Chapter 15B Lecture Outline: Brain and Cranial Nerves

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Diencephalon Relay and switching

centers for some sensory and motor pathways and for control of visceral activities

Surrounds third ventricle

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Posterior roof of the diencephalon over the third ventricle

Pineal gland (body) Endocrine gland - secretes melatonin

that helps regulate day-night cycles (circadian rhythms)

Epithalamus

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Oval masses of gray matter (nuclei) on either side of the third ventricle connected by the intermediate mass (interthalamic adhesion)

“Gateway” to the cerebral cortex Principal and final relay point for sensory

information that will be processed and projected to the primary sensory cortex

Information filter: edits info and may amplify or tone down

“Tells” the cerebrum where the information came from

Crude interpretation of certain sensory impulses (pain, temp. and pressure)

Thalamus

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About a dozen nuclei of gray matter

Main visceral control center of the body

Pituitary gland hangs from it by the infundibulum

Hypothalamus

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Hypothalamus - 4 major regions Mammillary region

Relay station for smell reflexes Tuberal region

Neurons here synthesize regulating hormones that go to the anterior pituitary

Supraoptic region Nuclei here synthesize posterior pituitary

hormones Preoptic region

Regulates certain autonomic activities

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Master control of the ANS Master control of the endocrine

system Regulation of body temperature Control of emotional behavior (part of

limbic system) Control of food intake Control of water intake Regulation of sleep-wake (circadian)

rhythms (works with pineal gland)

Functions of the Hypothalamus

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Pleasure Center in Hypothalamus Small bundle of neural tissue Norepinephrine and dopamine are the

neurotransmitters (resemble amphetamines)

When the brain is flooded from outside with drugs, then it stops producing the NTs

Cocaine targets this area. It blocks the reabsorption of NTs so they have a prolonged effect, but they eventually diffuse away and the lack leads to depression

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Thumb sized White matter - Bidirectional passageway

for tracts between the cerebrum and the spinal cord

Gray matter Many autonomic centers and reflex centers Has nuclei of most of the cranial nerves Reticular formation - diffuse gray matter

involved in consciousness and sleep/wake cycle

Brainstem

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Cerebral aqueduct passes through Cerebral peduncles (pyramidal tracts) Superior cerebellar peduncles connect

to the cerebellum Substantia nigra relays inhibitory

signals to the cerebral nuclei that regulate their motor output to skeletal muscles. (Parkinson’s disease)

Medial lemniscus just posterior (part of sensory pathway).

Midbrain (Mesencephalon)

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Tegmentum contains the red nuclei and the reticular formation. Red nucleus functions with basal nuclei and cerebellum to coordinate muscle movements. Tegmentum integrates info from the cerebrum and cerebellum and issues involuntary motor commands to the erector spinae to help maintain posture.

Tectum contains the corpora quadrigemina: superior and inferior colliculi, visual and auditory reflex centers

Cranial nerves III and IV

Midbrain (Mesencephalon)

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Sensory and motor projection tracts Middle cerebellar peduncles connect two

halves of cerebellum Autonomic respiratory centers help

control rate and depth of breathing and modify activity of the respiratory center in the medulla oblongata

Cranial nerve nuclei (V-part of VIII) Superior olivary complex receives auditory

input and is involved in the pathway for sound localization

Pons (“Bridge”)

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Decussation of the pyramids Olives have inferior olivary nuclei that relay

ascending sensory impulses (especially proprioceptive info) to cerebellum by inferior cerebellar peduncles. Inferior cerebellar peduncles connect medulla

to cerebellum Cranial nerves part of VIII-XII Nucleus cuneatus and nucleus

gracilis, part of somatic sensory pathway, extend by medial lemniscus to the thalamus.

Medulla Oblongata

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Medulla Oblongata Autonomic nuclei regulate

essential functions (damage or polio can cause problems or even be deadly) Cardiac center (H.R. and strength of

contraction) Vasomotor center (B.P.) Respiratory center (respiratory rate) Other nuclei: coughing, sneezing, salivating,

swallowing, gagging, and vomiting.

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Cerebellar cortex in folds, folia Vermis separates the two hemispheres Arbor vitae (“tree of life”), white matter

Cerebellar nuclei are deep Coordinates, a comparator function Stores memories of learned movement

patterns Equilibrium and posture Receives proprioceptive info and other info

Cerebellum

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Connect to brainstem Allow cerebellum to “fine-tune”

skeletal muscle movements and interpret all body proprioceptive movement.

Cerebellar Peduncles

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Impaired skeletal muscle function such as ataxia or loss of equilibrium that may lead to uncoordinated walking movements

Sobriety tests Disturbance of gait Loss of balance and posture Inability to detect proprioceptive

information

Effects of Alcohol and Drugs on the Cerebellum

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Limbic System “Emotional brain” (emotions related

to survival) Behavior is a function of the entire brain, but the

limbic system controls most of the involuntary aspects. Interacts with the prefrontal lobes a lot, i.e., thinking and feelings interact.

Structures border the diencephalon Cingulate gyrus receives input from other components

of limbic system Hippocampus connects to diencephalon via the

fornix. It and parahippocampal gyrus important in storing memories and forming long-term memory.

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Limbic System Amygdala connects to hippocampus. Involved in

several aspects of emotion, esp. fear. It can help store and code memories based on how a person emotionally perceives them.

Olfactory bulbs, tracts, and cortex - odors can provoke certain emotions or be associated with certain memories

Fornix is white matter connecting the hippocampus with other limbic system structures.

Various nuclei in the diencephalon also interconnect other parts of the limbic system and contribute to its overall function.

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Lesions in Limbic System Memory impairment Voracious appetite Increased sexual activity (often

perverse in nature) Docility

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Later, Chapter 17

Reticular Formation

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May be sensory or motor malfunctions or both

Headache Cerebral palsy Encephalitis Epilepsy Huntington disease Parkinson disease

Brain Disorders

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12 pairs on underside of brain numbered anterior to posterior for emergence: 1st 2 pairs from forebrain. Rest from the brainstem.

All go through foramina Names reflect structure and/or function Mainly to head and neck except vagus Most mixed: sensory and motor Three sensory: I, II, and VIII Motor also proprioceptive in scheme we will

use Some parasympathetic: III, VII, IX, and X (!).

Cranial Nerves

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Cranial Nerve Mnemonic Devices Oh, oh, oh, to touch and feel

very good velvet, ah (use the a and the h)

Some (Sister) say marry money, but my brother says “Bad business marry money.”

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Cranial Nerves in Forebrain CN I (olfactory): smell CN II (optic): vision

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Cranial Nerves in Midbrain CN III (oculomotor, “eye mover”): controls 3

of 4 rectus and inferior oblique muscles, constricts pupil and makes lens bulge for near vision (ANS)

CN IV (trochlear): controls superior oblique muscle

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Cranial Nerves in Pons CN V (trigeminal): sensory to face, motor for

mastication, largest CN CN VI (abducens): controls lateral rectus

muscle CN VII (facial): motor to face, anterior 2/3 of

taste (ANS) CN VIII, part (vestibulocochlear): balance

and hearing

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Cranial Nerves in Medulla CN VIII, part (vestibulocochlear): balance

and hearing CN IX (glossopharyngeal): posterior 1/3 of

taste, monitors B.P. and [gas] in major blood vessels, controls swallowing muscles (ANS)

CN X (vagus, the “wanderer”): motor to soft palate, pharynx, and esophagus and viscera in thorax and abdominopelvic regions, unconscious sensations from viscera, etc.- important for ANS function (major ANS)

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CN XI (accessory): some motor fibers from lateral gray horns of C1-C5. Motor to voluntary swallowing muscles, laryngeal muscles to vocal cords. Motor to trapezius and sternocleidomastoid. Accessory to vagus.

CN XII (hypoglossal): motor to tongue

Cranial Nerves in Medulla