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Brain and Cranial Nerves

Chapter 13

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Formation of the Neural Tube• Brain and spinal cord

develop from the neural plate under the influence of the notochord.

• Neural folds elevate to form the neural crest and a neural groove.

• Neural crest cells become the peripheral nerves.

• Ventricles and central canal develop from the lumen of the neural tube

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Development of Brain Segments and Ventricles

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Brain and Cranial Nerves

• Brain– Part of CNS contained in cranial cavity– Control center for many of body’s functions

• Structures of the Brain– Brainstem

• Includes the Medulla Oblongata, Pons and Midbrain

– Cerebellum– Diencephalon

• Includes the Thalamus, Subthalamus, Epithalamus and Hypothalamus

– Cerebrum and basal nuclei

• Cranial nerves– Part of PNS arise directly from brain

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Brainstem

• Connects spinal cord to brain• Parts

– Medulla oblongata– Pons– Midbrain

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Brainstem • Medulla oblongata– Functions:

• Regulates: Heart rate, blood vessel diameter, respiration, swallowing, vomiting, hiccupping, coughing, and sneezing

• Contains ascending and descending fiber tracts.

– Pyramids: • Function: Controls voluntary muscle

movement• Fiber tracts Decussate at the lower

pyramid

– Olives• Function: equilbrium, coordination

and modulation of sound in inner ear.• Contains Nuclei for many cranial

nerves

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Brainstem• Pons

– Function• Contains Ascending and

Descending nerve tracks and Pontine nuclei

• Contains Sleep and respiratory center

– Pontine Nuclei• Anterior nuclei: relay

information from cerebrum to cerebellum

• Posterior Nuclei: Cranial nerves V – IX.

• Respiratory and Sleep Nuclei

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Brainstem• Midbrain

– Contains: • Cranial nerve nuclei III, IV, V

• Tectum– Corpora Quadrigemina

» Superior Colliculus – visual reflexes

» Inferior Colliculus – auditory reflexes.

• Tegmentum– Ascending tracts and Red nucleus

• Cerebral Peduncles– Major descending motor pathways

• Substantia Nigra– Muscle tone and movement

• Reticular Formation– Sleep wake cycle and arousal.

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Brainstem and Diencephalon

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Cerebellum

• Involved in control of: balance, posture, locomotion, and fine motor coordination producing smooth flowing movements

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Diencephalon

• Components– Thalamus, Subthalamus, Epithalamus, Hypothalamus

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Diencephalon• Thalamus

– Largest part of diencephalon

– Most sensory input projects to here

– Influences mood and actions as fear or rage

• Subthalamus– Involved in controlling

motor functions

• Epithalamus– Pineal gland may influence

sleep-wake cycle

• Hypothalamus– Functions

• ANS control

• Endocrine control

• Muscle control

• Temperature regulation

• Regulation of food and water intake

• Emotions

• Urine production

• Regulation of sleep-wake cycle

• Regulation of reproductive behavior

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Cerebrum• Functions: sensation,

perception, voluntary movement, learning, speech and cognition.

• Divisions– Right

– Left

• Lobes: Frontal, parietal, occipital, temporal, insula

• Cortex: Outer surface

• Medulla: Center

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Basal Nuclei• Structure:

– Corpus Striatum• Lentiform Nucleus

(Putamen)• Caudate Nucleus

– Subthalamic nucleus– Substantia Nigra– Motor function control

• Function: Facilitate the initiation of willed movements

• Basal Ganglian Disorders lead to Diskinesias.– Hypokinesia -paucity of

movement caused by over inhibition.

– Hyperkinesia -excess movement.

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•Hypokinesia – Parkinson’s Disease•Affects 1% of people over 50•Difficult to initiate willed movements•Leads to Akinesea, rigidity and tremors of hands and jaw•Due to degeneration of substantia nigra and dopamine circuits.

•Hyperkinesia- Huntington’s Disease•Hereditary, progressive and lethal syndrome•Characterized by: demetia, chorea (uncontrolled movements) and ballistic movements•Due to Damage in the basal nuclei

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Limbic System

•Basic survival functions such as:

• Memory• Reproduction• Nutrition• Emotions

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Meninges

• Connective tissue membranes– Dura mater: Superficial

– Arachnoid mater

– Pia mater: Bound tightly to brain

– Spaces • Subdural: Serous fluid

• Subarachnoid: CSF

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Ventricles

• Ventricles: Lateral ventricles (2), third ventricle, fourth ventricle

• Choroid plexuses produce CSF which fills ventricles and other parts of brain and spinal cord– Blood-cerebrospinal fluid barrier: Substances do not pass between

cells but through due to tight junctions of blood endothelial cells

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Cerebrospinal Fluid (CSF)

• Similar to serum with most of proteins removed

• Bathes brain and spinal cord

• Provides a protective cushion around CNS

• Provides some nutrients to CNS tissues

• Produced by ependymal cells

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Flow of CSF

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Brain Blood Supply

• Brain – Requires tremendous amount of blood– Receives 15-20% of blood pumped by heart– Interruption can cause unconsciousness and irreversible

brain damage– High metabolic rate and dependence on constant supply

of oxygen and glucose– Receives blood through arteries

• Blood-Brain barrier– Capillary endothelial cells along with astrocytes and

basement membrane– To be considered when developing drugs

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Cranial Nerves

• Indicated by Roman numerals I-XII from anterior to posterior

• May have one or more of 3 functions– Sensory (special or general)

– Somatic motor (skeletal muscles)

– Parasympathetic (regulation of glands, smooth muscles, cardiac muscle)

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Cranial Nerves

• Olfactory (I)• Optic (II)• Oculomotor (III)• Trochlear (IV)• Trigeminal (V)• Abducens (VI)

• Facial (VII)• Vestibulocochlear (VIII)• Glossopharyngeal (IX)• Vagus (X)• Accessory (XI)• Hypoglossal (XII)

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