An Introduction to the Brain and Cranial Nerves

Chapter 14The Brain and Cranial Nerves

An Introduction to the Brain and Cranial Nerves

•Learning Outcomes

•14-1 Name the major brain regions, vesicles, and ventricles, and describe the locations and functions of each.

•14-2 Explain how the brain is protected and supported, and discuss the formation, circulation, and function of cerebrospinal fluid.

•14-3 Describe the anatomical differences between the medulla oblongata and the spinal cord, and identify the main components and functions of the medulla oblongata.

An Introduction to the Brain and Cranial Nerves

•Learning Outcomes

•14-4 List the main components of the pons, and specify the functions of each.

•14-5 List the main components of the cerebellum, and specify the functions of each.

•14-6 List the main components of the midbrain, and specify the functions of each.

•14-7 List the main components of the diencephalon, and specify the functions of each.

An Introduction to the Brain and Cranial Nerves

•Learning Outcomes

•14-8 Identify the main components of the limbic system, and specify the locations and functions of each.

•14-9 Identify the major anatomical subdivisions and functions of the cerebrum, and discuss the origin and significance of the major types brain waves seen in an electroencephalogram.

•14-10 Describe representative examples of cranial reflexes that produce somatic responses or visceral responses to specific stimuli.

An Introduction to the Brain and Cranial Nerves

•The Adult Human Brain

•Ranges from 750 cc to 2100 cc

•Contains almost 97% of the body’s neural tissue

•Average weight about 1.4 kg (3 lb)

14-1 The Brain

•Six Regions of the Brain

1.Cerebrum

2.Cerebellum

3.Diencephalon

4.Mesencephalon

5.Pons

6.Medulla oblongata

14-1 The Brain

•Cerebrum

•Largest part of brain

•Controls higher mental functions

•Divided into left and right cerebral hemispheres

•Surface layer of gray matter (neural cortex)

14-1 The Brain

•Cerebrum

•Neural cortex

•Also called cerebral cortex

•Folded surface increases surface area

•Elevated ridges (gyri)

•Shallow depressions (sulci)

•Deep grooves (fissures)

14-1 The Brain

•Cerebellum

•Second largest part of brain

•Coordinates repetitive body movements

•Two hemispheres

•Covered with cerebellar cortex

14-1 The Brain

•Diencephalon

•Located under cerebrum and cerebellum

•Links cerebrum with brain stem

• Three divisions of the diencephalon

1.Left thalamus

2.Right thalamus

3.Hypothalamus

14-1 The Brain

•Diencephalon

•Thalamus

•Relays and processes sensory information

•Hypothalamus

•Hormone production

•Emotion

•Autonomic function

14-1 The Brain

•Diencephalon

•Pituitary gland

•Major endocrine gland

•Connected to hypothalamus

•Via infundibulum (stalk)

•Interfaces nervous and endocrine systems

14-1 The Brain

•The Brain Stem

•Processes information between:

•Spinal cord and cerebrum or cerebellum

•Includes:

•Midbrain

•Pons

•Medulla oblongata

14-1 The Brain

•Midbrain

•Also called mesencephalon

•Processes sight, sound, and associated reflexes

•Maintains consciousness

•Pons

•Connects cerebellum to brain stem

•Is involved in somatic and visceral motor control

14-1 The Brain

•Medulla Oblongata

•Connects brain to spinal cord

•Relays information

•Regulates autonomic functions

•Heart rate, blood pressure, and digestion

14-1 The Brain

•Embryological Development

•Determines organization of brain structures

•Neural tube

•Origin of brain

•Enlarges into three primary brain vesicles

1.Prosencephalon

2.Mesencephalon

3.Rhombencephalon

14-1 The Brain

•Five Secondary Brain Vesicles

1.Telencephalon

2.Diencephalon

3.Mesencephalon

4.Metencephalon

5.Myelencephalon

14-1 The Brain

•Origins of Brain Structures

•Diencephalon and mesencephalon persist

•Telencephalon

•Becomes cerebrum

•Metencephalon

•Forms cerebellum and pons

•Myelencephalon

•Becomes medulla oblongata

14-1 The Brain

•Ventricles of the Brain

•Origins of ventricles

•Neural tube encloses neurocoel

•Neurocoel expands to form chambers (ventricles) lined with ependyma

•Each cerebral hemisphere contains one large lateral ventricle

•Separated by a thin medial partition (septum pellucidum)

14-1 The Brain

•Ventricles of the Brain

•Third ventricle

•Ventricle of the diencephalon

•Lateral ventricles communicate with third ventricle

•Via interventricular foramen (foramen of Monro)

14-1 The Brain

•Ventricles of the Brain

•Fourth ventricle

•Extends into medulla oblongata

•Becomes continuous with central canal of the spinal cord

•Connects with third ventricle

•Via narrow canal in midbrain called the cerebral aqueduct

14-1 The Brain

•The Brain

•The brain is a large, delicate mass of neural tissue

•Containing internal passageways and chambers filled with cerebrospinal fluid

•Each of the six major brain regions has specific functions

•Ascending from the medulla oblongata to the cerebrum, brain functions become more complex and variable

•Conscious thought and intelligence

•Are produced in the neural cortex of the cerebral hemispheres

14-2 Brain Protection and Support

•Physical Protection of the Brain

•Bones of the cranium

•Cranial meninges

•Cerebrospinal fluid

•Biochemical Isolation

•Blood–brain barrier

14-2 Brain Protection and Support

•The Cranial Meninges

•Have three layers

1.Dura mater

2.Arachnoid mater

3.Pia mater

•Are continuous with spinal meninges

•Protect the brain from cranial trauma

14-2 Brain Protection and Support

•The Cranial Meninges

•Dura mater

•Inner fibrous layer (meningeal layer)

•Outer fibrous layer (endosteal layer) fused to periosteum

•Venous sinuses between two layers

14-2 Brain Protection and Support

•The Cranial Meninges

•Arachnoid mater

•Covers brain

•Contacts epithelial layer of dura mater

•Subarachnoid space between arachnoid mater and pia mater

•Pia mater

•Attached to brain surface by astrocytes

14-2 Brain Protection and Support

•Dural Folds

•Folded inner layer of dura mater

•Extend into cranial cavity

•Stabilize and support brain

•Contain collecting veins (dural sinuses)

•Three largest dural folds

1.Falx cerebri

2.Tentorium cerebelli

3.Falx cerebelli

14-2 Brain Protection and Support

•Falx Cerebri

•Projects between the cerebral hemispheres

•Contains superior sagittal sinus and inferior sagittal sinus

•Tentorium Cerebelli

•Separates cerebellum and cerebrum

•Contains transverse sinus

•Falx Cerebelli

•Divides cerebellar hemispheres below the tentorium cerebelli

14-2 Brain Protection and Support

•Cerebrospinal Fluid (CSF)

•Surrounds all exposed surfaces of CNS

•Interchanges with interstitial fluid of brain

•Functions of CSF

•Cushions delicate neural structures

•Supports brain

•Transports nutrients, chemical messengers, and waste products

14-2 Brain Protection and Support

•Cerebrospinal Fluid (CSF)

•Choroid plexus

•Specialized ependymal cells and capillaries

•Secrete CSF into ventricles

•Remove waste products from CSF

•Adjust composition of CSF

•Produces about 500 mL of CSF/day

14-2 Brain Protection and Support

•Cerebrospinal Fluid (CSF)

•CSF circulates:

•From choroid plexus

•Through ventricles

•To central canal of spinal cord

•Into subarachnoid space via two lateral apertures and one median aperture around the brain, spinal cord, and cauda equina

14-2 Brain Protection and Support

•Cerebrospinal Fluid (CSF)

•CSF in subarachnoid space

•Arachnoid villi

•Extensions of subarachnoid space

•Extend through dura mater to superior sagittal sinus

•Arachnoid granulations

•Large clusters of villi

•Absorb CSF into venous circulation

14-2 Brain Protection and Support

•Blood Supply to the Brain

•Supplies nutrients and oxygen to brain

•Delivered by internal carotid arteries and vertebral arteries

•Removed from dural sinuses by internal jugular veins

14-2 Brain Protection and Support

•Cerebrovascular Disease

•Disorders interfere with blood circulation to brain

•Stroke or cerebrovascular accident (CVA)

•Shuts off blood to portion of brain

•Neurons die

14-2 Brain Protection and Support

•Blood–Brain Barrier (BBB)

•Isolates CNS neural tissue from general circulation

•Formed by network of tight junctions

•Between endothelial cells of CNS capillaries

•Lipid-soluble compounds (O2, CO2), steroids, and prostaglandins

•Diffuse into interstitial fluid of brain and spinal cord

•Astrocytes control blood–brain barrier by:

•Releasing chemicals that control permeability of endothelium

14-2 Brain Protection and Support

•Blood–CSF Barrier

•Formed by special ependymal cells

•Surrounds capillaries of choroid plexus

•Limits movement of compounds transferred

•Allows chemical composition of blood and CSF to differ

14-2 Brain Protection and Support

•Four Breaks in the BBB

1.Portions of hypothalamus

•Secrete hypothalamic hormones

2.Posterior lobe of pituitary gland

•Secretes hormones ADH and oxytocin

3.Pineal gland

•Pineal secretions

4.Choroid plexus

•Where special ependymal cells maintain blood–CSF barrier

14-2 Brain Protection and Support

•Protection and Support

•Meninges stabilize brain in cranial cavity

•Cerebrospinal fluid protects against sudden movement

•CSF provides nutrients and removes wastes

•Blood–brain barrier and blood–CSF barrier

•Selectively isolate brain from chemicals in blood that might disrupt neural function

14-3 The Medulla Oblongata

•The Medulla Oblongata

•Allows brain and spinal cord to communicate

•Coordinates complex autonomic reflexes

•Controls visceral functions

•Nuclei in the Medulla

•Autonomic nuclei control visceral activities

•Sensory and motor nuclei of cranial nerves

•Relay stations along sensory and motor pathways

14-3 The Medulla Oblongata

•The Medulla Oblongata

•Includes three groups of nuclei

1.Autonomic nuclei

2.Sensory and motor nuclei of cranial nerves

3.Relay stations along sensory and motor pathways

14-3 The Medulla Oblongata

•Autonomic Nuclei of the Medulla Oblongata

•Reticular formation

•Gray matter with embedded nuclei

•Regulates autonomic functions

14-3 The Medulla Oblongata

•Autonomic Nuclei of the Medulla Oblongata

•Reflex centers

•Control peripheral systems

•Cardiovascular centers

•Cardiac center

•Control blood flow through peripheral tissues

•Respiratory rhythmicity centers

•Set pace for respiratory movements

14-3 The Medulla Oblongata

•Sensory and Motor Nuclei of the Medulla Oblongata

•Associated with 5 of 12 cranial nerves (VIII, IX, X, XI, XII)

14-3 The Medulla Oblongata

•Relay Stations of the Medulla Oblongata

•Nucleus gracilis and nucleus cuneatus

•Pass somatic sensory information to thalamus

•Solitary nucleus

•Receives visceral sensory information

•Olivary nuclei (olives)

•Relay information about somatic motor commands

14-4 The Pons

•The Pons

1.Sensory and motor nuclei of cranial nerves (V, VI, VII, VIII)

2.Nuclei involved with respiration

•Apneustic center and pneumotaxic center

•Modify respiratory rhythmicity center activity

3.Nucei that process and relay information to and from cerebellum

4.Ascending, descending, and transverse tracts

•Transverse fibers (axons)

•Link nuclei of pons with opposite cerebellar hemisphere

14-5 The Cerebellum

•Functions of the Cerebellum

1.Adjusts postural muscles

2.Fine-tunes conscious and subconscious movements

14-5 The Cerebellum

•Structures of the Cerebellum

•Folia

•Surface of cerebellum

•Highly folded neural cortex

•Anterior and posterior lobes

•Separated by primary fissure

•Cerebellar hemispheres

•Separated at midline by vermis

14-5 The Cerebellum

•Structures of the Cerebellum

•Vermis

•Narrow band of cortex

•Flocculonodular lobe

•Below fourth ventricle

14-5 The Cerebellum

•Structures of the Cerebellum

•Purkinje cells

•Large, branched cells

•Found in cerebellar cortex

•Receive input from up to 200,000 synapses

•Arbor vitae (“tree of life”)

•Highly branched, internal white matter of cerebellum

•Cerebellar nuclei embedded in arbor vitae

•Relay information to Purkinje cells

14-5 The Cerebellum

•Structures of the Cerebellum

•The peduncles

•Tracts link cerebellum with brain stem, cerebrum, and spinal cord

•Superior cerebellar peduncles

•Middle cerebellar peduncles

•Inferior cerebellar peduncles

14-5 The Cerebellum

•Disorders of the Cerebellum

•Ataxia

•Damage from trauma or stroke

•Intoxication (temporary impairment)

•Disturbs muscle coordination

14-6 The Midbrain

•Structures of the Midbrain

•Tectum

•Two pairs of sensory nuclei (corpora quadrigemina)

•Superior colliculus (visual)

•Inferior colliculus (auditory)

•Tegmentum

•Red nucleus (many blood vessels)

•Substantia nigra (pigmented gray matter)

14-6 The Midbrain

•Structures of the Midbrain

•Cerebral peduncles

•Nerve fiber bundles on ventrolateral surfaces

•Contain:

1.Descending fibers to cerebellum

2.Motor command fibers

14-7 The Diencephalon

•The Diencephalon

•Integrates sensory information and motor commands

•Thalamus, epithalamus, and hypothalamus

•The pineal gland

•Found in posterior epithalamus

•Secretes hormone melatonin

14-7 The Diencephalon

•The Thalamus

•Filters ascending sensory information for primary sensory cortex

•Relays information between basal nuclei and cerebral cortex

14-7 The Diencephalon

•The Thalamus

•The third ventricle

•Separates left thalamus and right thalamus

•Interthalamic adhesion

•Projection of gray matter

•Extends into ventricle from each side

14-7 The Diencephalon

•The Thalamus

•Thalamic nuclei

•Are rounded masses that form thalamus

•Relay sensory information to basal nuclei and cerebral cortex

14-7 The Diencephalon

•Five Groups of Thalamic Nuclei

1.Anterior group

•Anterior nuclei

•Part of limbic system (emotions)

2.Medial group

•Provides awareness of emotional states

3.Ventral group

•Relays sensory information

14-7 The Diencephalon

•Five Groups of Thalamic Nuclei

4.Posterior group

•Pulvinar nucleus(sensory)

•Lateral geniculate nucleus (visual)

•Medial geniculate nucleus (auditory)

5.Lateral group

•Affects emotional states

•Integrates sensory information

14-7 The Diencephalon

•The Hypothalamus

•Mamillary bodies

•Process olfactory and other sensory information

•Control reflex eating movements

•Infundibulum

•A narrow stalk

•Connects hypothalamus to pituitary gland

•Tuberal area

•Located between the infundibulum and mamillary bodies

•Helps control pituitary gland function

14-7 The Diencephalon

•Eight Functions of the Hypothalamus

1.Provides subconscious control of skeletal muscle

2.Controls autonomic function

3.Coordinates activities of nervous and endocrine systems

4.Secretes hormones

•Antidiuretic hormone (ADH) by supraoptic nucleus

•Oxytocin (OT; OXT) by paraventricular nucleus

14-7 The Diencephalon

•Eight Functions of the Hypothalamus

5.Produces emotions and behavioral drives

•The feeding center (hunger)

•The thirst center (thirst)

6.Coordinates voluntary and autonomic functions

7.Regulates body temperature

•Preoptic area of hypothalamus

8.Controls circadian rhythms (day–night cycles)

•Suprachiasmatic nucleus

14-8 The Limbic System

•The Limbic System

•Is a functional grouping that:

•Establishes emotional states

•Links conscious functions of cerebral cortex with autonomic functions of brain stem

•Facilitates memory storage and retrieval

14-8 The Limbic System

•Components of the Limbic System

•Amygdaloid body

•Acts as interface between the limbic system, the cerebrum, and various sensory systems

•Limbic lobe of cerebral hemisphere

•Cingulate gyrus

•Dentate gyrus

•Parahippocampal gyrus

•Hippocampus

14-8 The Limbic System

•Components of the Limbic System

•Fornix

•Tract of white matter

•Connects hippocampus with hypothalamus

•Anterior nucleusof the thalamus

•Relays information from mamillary body to cingulate gyrus

•Reticular formation

•Stimulation or inhibition affects emotions (rage, fear, pain, sexual arousal, pleasure)

14-9 The Cerebrum

•The Cerebrum

•Is the largest part of the brain

•Controls all conscious thoughts and intellectual functions

•Processes somatic sensory and motor information

14-9 The Cerebrum

•Gray Matter

•In cerebral cortex and basal nuclei

•White Matter

•Deep to basal cortex

•Around basal nuclei

14-9 The Cerebrum

•Structures of the Cerebrum

•Gyri of neural cortex

•Increase surface area (number of cortical neurons)

•Insula (“island” of cortex)

•Lies medial to lateral sulcus

•Longitudinal fissure

•Separates cerebral hemispheres

•Lobes

•Divisions of hemispheres

14-9 The Cerebrum

•Structures of the Cerebrum

•Central sulcus divides:

•Anterior frontal lobe from posterior parietal lobe

•Lateral sulcus divides:

•Frontal lobe from temporal lobe

•Parieto-occipital sulcus divides:

•Parietal lobe from occipital lobe

14-9 The Cerebrum

•Three Functional Principles of the Cerebrum

1.Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body

2.The two hemispheres have different functions, although their structures are alike

3.Correspondence between a specific function and a specific region of cerebral cortex is not precise

14-9 The Cerebrum

•White Matter of the Cerebrum

•Association fibers

•Connections within one hemisphere

•Commissural fibers

•Bands of fibers connecting two hemispheres

•Projection fibers

•Connect cerebrum with lower areas

14-9 The Cerebrum

•Association Fibers

•Arcuate fibers

•Are short fibers

•Connect one gyrus to another

•Longitudinal fasciculi

•Are longer bundles

•Connect frontal lobe to other lobes in same hemisphere

14-9 The Cerebrum

•Commissural Fibers

•Corpus callosum

•Anterior commissure

14-9 The Cerebrum

•Projection Fibers

•Pass through diencephalon

•Link cerebral cortex with:

•Diencephalon, brain stem, cerebellum, and spinal cord

•Internal capsule

•All ascending and descending projection fibers

14-9 The Cerebrum

•The Basal Nuclei

•Are masses of gray matter

•Are embedded in white matter of cerebrum

•Direct subconscious activities

14-9 The Cerebrum

•Anatomy of Basal Nuclei

•Caudate nucleus

•Curving, slender tail

•Lentiform nucleus

•Globus pallidus

•Putamen

14-9 The Cerebrum

•Functions of Basal Nuclei

•Involved with:

•The subconscious control of skeletal muscle tone

•The coordination of learned movement patterns (walking, lifting)

14-9 The Cerebrum

•Motor and Sensory Areas of the Cortex

•Central sulcus separates motor and sensory areas

•Motor areas

•Precentral gyrus of frontal lobe

•Directs voluntary movements

•Primary motor cortex

•Is the surface of precentral gyrus

• Pyramidal cells

•Are neurons of primary motor cortex

14-9 The Cerebrum

•Motor and Sensory Areas of the Cortex

•Sensory areas

•Postcentral gyrus of parietal lobe

•Receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)

•Primary sensory cortex

•Surface of postcentral gyrus

14-9 The Cerebrum

•Special Sensory Cortexes

•Visual cortex

•Information from sight receptors

•Auditory cortex

•Information from sound receptors

•Olfactory cortex