Chapter 14

Brain

• the center for registering sensations,
  correlating them with one another and with stored information, making decisions, and taking action

• It is also the center for intellect, emotions, behavior, and memory, it also directs our behavior towards others

• 2% of body weight

• utilizes about 20% of the body’s oxygen supply

• one of the most metabolically active organs of the body, and the amount of oxygen it uses varies with the degree of mental activity

neural tube

• has three regions called primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)

major parts of the brain

brain stem, diencephalon, cerebrum, and cerebellum

parts of the diencephalon

thalamus, hypothalamus

parts of the brain stem

midbrain, pons, medulla oblongata

A

thalamus (diagram)

B

hypothalamus (diagram)

C

pineal gland (diagram)

D

midbrain (diagram)

E

pons (diagram)

F

medulla oblongata (diagram)

G

cerebellum (diagram)

H

spinal cord (diagram)

I

cerebrum (diagram)

J

pituitary gland (diagram)

Cranial bones, Cranial meninges, cerebrospinal fluid

Protects the brain

Cranial meninges

Pia mater (inner), arachnoidea (middle), and dura mater(outer)

Cranial dura mater

composed of 2 layers: periosteal layer (external) and meningeal layer (internal)

Extensions of the cranial dura mater

• separate parts of the brain:
  1. The falx cerebri: separates the two hemispheres of the cerebrum
  2. The falx cerebelli: separates the two hemispheres of the cerebellum
  3. Tentorium cerebelli: separates the cerebrum from the cerebellum

falx cerebri

separates the two hemispheres of the cerebrum

The falx cerebelli

separates the two hemispheres of the cerebellum

Tentorium cerebelli

separates the cerebrum from the cerebellum

cerebrospinal fluid

• a clear, colorless liquid composed primarily of water that protects the brain and spinal cord against chemical and physical injuries

• Flows over and around the brain and cord in the subarachnoid space (SAS). In essence, the brain "floats" in it

• It carries oxygen, glucose, and other important substances from the blood to nervous tissue cells

• Total volume is 80-150mL, composed of glucose, proteins, lactic acid, ions (Na+, K+, Ca2+, Mg2+, Cl-, HCO3-) some white blood cells

• There are four cavities within the brain
  called ventricles that are filled with this

• contributes to hemostasis by providing
  mechanical protection(shock absorption), chemical protection (pH affects pulmonary ventilation), and circulation
  •The majority comes from ependymal cells
  in the choroid plexuses networks of blood
  capillaries in the walls of the ventricles

• Most is absorbed by the arachnoid villi of the superior sagittal blood sinus. This absorption normally occurs at the same rate at which it is produced in the
  choroid plexuses, thereby maintaining a relatively constant volume and pressure

vertebral (posteriorly) and carotid arteries

blood flows to the brain via

jugular veins

blood flows back to the heart from the brain via

interruption of oxygen to the brain

results in weakening, permanent damage, or death of brain cells

Interruption of the mother’s blood supply to a child during childbirth before it can breathe

may result in paralysis, mental retardation, epilepsy, or death

Glucose deficiency

• produce mental confusion, dizziness, convulsions, and unconsciousness

• because carbohydrate storage in the brain is limited, the supply of this to the brain must be continuous

Blood-Brain Barrier

• consist of tight junctions that seal together the endothelial cells of blood capillaries and a thick basement membrane against which astrocytes press

• protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage
  of many substances from the blood into the brain

• can prevent the entry of therapeutic drugs

• Glucose and lipid soluble substances
  can cross

lateral ventricles

are separated by a thin membrane –septum pellucidum

The 3rd ventricle

lies superior to the hypothalamus and between the right and left halves of the thalamus

The 4th ventricle

lies between the brain stem and cerebellum

bidirectional

The secretory capacity of ependymal
cells is…

ependymal cells

• From blood capillaries substances are filtered and secreted by _______ _______ to produce CSF and metabolites from nervous tissue are transported back to blood through ependymal cells

• Because of tight junctions between __________ _______ material cannot leak from choroid capillaries, they must pass through the ________ ________

blood-cerebrospinal fluid barrier(BCFB)

formed by tight junctions of ependymal cells 

Flow of cerebrospinal fluid

Lateral ventricles → interventricular foramina → 3rd ventricle → cerebral aqueduct (aqueduct of Sylvius)→ 4th ventricle → median aperture (of Majendie) and the lateral apertures (of Luschka) → subarachnoid space (SAS) and central canal

arachnoid villi (glandulae Pacchioni)

fingerlike extensions of the arachnoid mater that project into the dural venous sinuses especially the superior sagittal sinus

How the CSF maintains volume and pressure

Absorption normally occurs at the same rate at which CSF is produced in the choroid plexuses

The medulla oblongata

• continuous with the superior aspect of the spinal cord

• It forms the inferior part of the brain stem

• It is part of the hindbrain (rhombencephalon)

• Contains portions of both motor and sensory tracts

• has two pyramids formed by large corticospinal (motor) tracts controlling voluntary movements in the body

• contain nuclei which control vital body functions

pyramids

Some white matter forms bulges or _______ on the
anterior aspect of the medulla

decussation of pyramids

Axons from the left pyramid cross over to the right and axons on the right cross over to the left so that the left hemisphere of the brain controls the right side muscles, while the right hemisphere controls the left side

nuclei

collections of neuronal cell bodies

Nuclei of the medulla oblongata

cardiovascular center, respiratory center, vomiting center, deglutition center (swallowing), gustatory, cochlear (auditory), vestibular(equilibrium)

Olive

• lateral to each pyramid

• oval-shaped swelling

• in the medulla oblongata

inferior olivary nucleus

• within the olive

• receives input from the cerebral cortex and regulate the activity of cerebellar neurons

gracile nucleus

Nuclei associated with sensation of touch, pressure,
vibration and conscious proprioception

cuneate nucleus

are continuations of the ascending sensory (start out as) gracile fasciculus and cuneate fasciculus

Posterior column-medial pathway

• Nuclei associated with sensation of touch, pressure, vibration and conscious proprioception are the gracile nucleus and cuneate nucleus are continuations of the ascending sensory(start out as) gracile fasciculus and cuneate fasciculus
  •They continue(white matter-axons) to thalamus as medial lemniscus and the entire pathway is known as

nuclei in the medulla associated with cranial nerves

1. Vestibulocochlear (VIII) nerve: sensory and motor impulses related to hearing

2. Glossopharyngeal (IX) nerve: motor impulses related to swallowing and salivation

3. Vagus (X) nerve: motor impulses related to thoracic, abdominal viscera

4. Accessory (XI) nerves: impulses related to swallowing

5. Hypoglossal (XII) nerves: impulses controlling tongue movement and swallowing
   

Pons

• known as the bridge or ______ Varolii

• located superior to the medulla oblongata and anterior to the cerebellum

• part of the hindbrain

• links parts of the brain with one another by way of tracts

• It consist of both nuclei and tracts

• It relays nerve impulses related to voluntary skeletal movements from the cerebral cortex to the cerebellum

major structural components of the pons

ventral and dorsal regions

ventral region of the pons

forms a large synaptic relay station with pontine nuclei

dorsal region

contains ascending and descending tracts

pontine respiratory group

• within the pons

• helps control breathing, the pneumotaxic and apneustic areas

nuclei of cranial nerves associated with the pons

1. Trigeminal (V) nerve: sensory impulses from head and face, motor impulses governing chewing

2. Abducens (VI) nerve: motor impulses for eyeball movement

3. Facial (VII) nerve: sensory impulses for taste, secretion of saliva, tears and facial muscles

4. Vestibulocochlear (VIII) nerve: sensory and motor impulses for balance and equilibrium

midbrain

• also called the mesencephalon

• the superior portion of the brain stem and extends from the pons to the diencephalon

• conveys motor impulses from the cerebrum to the cerebellum and spinal cord, sends sensory impulses from the spinal cord to the thalamus, and regulates auditory and visual reflexes

• Structures within the midbrain include the cerebral aqueduct, the cerebral peduncles (pedunculus =little feet)

cerebral aqueduct

connects the 3rd ventricle above and 4th ventricle below

cerebral peduncles (pedunculus =little feet)

• consist of the corticospinal, corticobulbar, and corticopontine tracts

• anterior part of the midbrain

corticopontine tracts

• part of the cerebral peduncles

• convey nerve impulses from motor areas in the cortex to spinal cord, medulla and pons

Tectum

• posterior part of the midbrain

• contains 4 rounded elevations

Superior colliculi (little hills)

serves as reflex centers for visual activities: scanning, tracking images

Inferior colliculi

part of the auditory pathway

Substantia nigra

• left and right;

• pathway to basal ganglia have neurons with
  dopaminergic tracts - control subconscious muscle movements

Red nuclei

control voluntary muscular movement

nuclei of cranial nerves in the midbrain

1. Oculomotor (III) nerve: motor impulses for eyeball

2. Trochlear(IV) nerve: motor impulses for eyeball

Reticular formation

• is a netlike arrangement consisting of small areas of gray matter interspersed among fibers of white matter and has both sensory and motor functions

• extends from the superior part of the spinal
  cord throughout the brain stem and into the
  inferior part of the diencephalon

• helps regulate muscle tone, alerts the cortex to incoming sensory signals (reticular activating system, or RAS), and is responsible for maintaining consciousness and awakening from sleep

cerebellum

• “little brain”

• attached to the brain stem by three pairs of
  cerebellar peduncles

• the second largest part of the brain, has a highly folded surface for neuron accommodation and their connections

• part of the hindbrain

• Nearly half of all the neurons are located in here

• functions in the coordination of skeletal muscle contractions and in the maintenance of normal muscle tone, posture, and balance

• occupies the inferior and posterior aspects of the cranial cavity and consists of two
  hemispheres and a central vermis

• separated from the cerebrum by the transverse fissure and tentorium cerebelli

• has a butterfly shape with central vermis and cerebellar hemispheres or wings or lobes

• anterior and posterior lobe govern the subconscious aspects of muscle movements

The flocculonodular lobe

• part of the cerebellum

• contributes to equilibrium and balance

cerebellar cortex

• The superficial layer of the cerebellum

• consist of the gray matter in a series of folds
  slender and parallel called folia

arbor vitae

• in the cerebellum

• Deep are the tracts of white matter

cerebellar nuclei

Deeper in arbor vitae of the cerebellum

cerebellar peduncles

The superior cerebellar peduncle, the middle cerebellar peduncle, the inferior cerebellar peduncle

The superior cerebellar peduncle

axons from cerebellum to red nuclei and thalamus

The middle cerebellar peduncle

axons carrying impulses for voluntary movements from pontine nuclei into the cerebellum

The inferior cerebellar peduncle

• Spinocerebellar sensory tracts from trunk and limbs into cerebellum

• Axons from vestibular apparatus and vestibular nuclei of medulla and pons into cerebellum

• Axons from inferior olivary nucleus of the medulla into cerebellum

• Axons from cerebellum to vestibular nuclei of medulla and pons

• Axons from cerebellum to reticular formation

The diencephalon

• inner brain

• forms the central core of the brain just superior to the midbrain

• extends from the brain stem to the cerebrum and surrounds the 3rd ventricle

• composed of the:
   Thalamus
   Hypothalamus
   Epithalamus

The thalamus

• inner chamber

• 3cm in length and makes up 80% the diencephalon

• is located superior to the midbrain and contains nuclei that serve as relay stations for all sensory impulses (except smell) to the cerebral cortex

the interthalamic adhesion

• A bridge of gray matter

• connects the two halves of thalamus

internal medullary lamina

The Y shaped white matter in the thalamus

internal capsule

• Axons that connect the thalamus and cerebral cortex pass through this

• a thick white band lateral to the thalamus

seven major groups of thalamic nuclei

The anterior nucleus, the medial nucleus, nuclei in the lateral group, five ventral nuclei, intralaminar nuclei, the midline nucleus, the reticular nucleus

The anterior nucleus

• Input from hypothalamus, output to limbic system

• Function in emotions and memory

The medial nucleus

• input from limbic system and basal ganglia(nuclei), output to cerebral cortex

• function in emotions, learning, memory, cognition

Nuclei in the lateral group

• Input from limbic system, superior colliculi and cerebral cortex, output to cerebral cortex.

• types: the lateral dorsal nucleus(emotions), the lateral posterior nucleus and pulvinar nucleus

Five ventral nuclei

• Ventral anterior nucleus: input from basal ganglia output to cerebral cortex

• Ventral lateral nucleus: input from cerebellum and basal ganglia, output to cerebral cortex

• Ventral posterior nucleus relays impulses from touch, pressure, vibration, itch, tickle, temperature, pain, proprioception to cerebral cortex

• Lateral geniculate nucleus relays visual impulses to the primary visual area of the cerebral cortex

• Medial geniculate nucleus relays auditory impulses from ear to primary auditory area of the cerebral cortex

Ventral anterior nucleus

input from basal ganglia output to cerebral cortex

Ventral lateral nucleus

input from cerebellum and basal ganglia, output to cerebral cortex

Ventral posterior nucleus

relays impulses from touch, pressure, vibration, itch, tickle, temperature, pain, proprioception to cerebral cortex

Lateral geniculate nucleus

relays visual impulses to the primary visual area of the cerebral cortex

Medial geniculate nucleus

relays auditory impulses from ear to primary auditory area of the cerebral cortex

Hypothalamus

• is found inferior to the thalamus, composed of ~ dozen nuclei in four major regions (mammillary, tuberal, supraoptic, and preoptic)

• controls many body activities, and is one of the major regulators of homeostasis

functions of the hypothalamus

• Control of the ANS

• Production of hormones

• It functions in regulation of emotional and behavioral patterns

• It regulates eating and drinking through the feeding center, satiety center, and thirst center

• It aids in controlling body temperature

• It regulates circadian rhythms and states of consciousness

The mammillary region of hypothalamus

• the most posterior part of the hypothalamus

• Includes the mammillary bodies and posterior hypothalamic nuclei

• The mammillary bodies are two rounded projections: relay station for sense of smell

The tuberal region of the hypothalamus

• widest part of the hypothalamus

• Includes the dorsomedial nucleus, ventromedial nucleus and arcuate nucleus and the infundibulum which connects the pituitary gland to the hypothalamus

The supraoptic region of the hypothalamus

• lies superior to the optic chiasm

• Includses the paraventricular nucleus, supraoptic nucleus, anterior hypothalamic nucleus and suprachiasmatic nucleus

• The paraventricular and supraoptic nuclei are part of the hypothalamohypophyseal tract

The pre-optic region of the hypothalamus

contains the medial and lateral pre-optic nuclei

The epithalamus

lies superior and posterior to the thalamus and contains the pineal gland which secretes melatonin and habenular nuclei which are involved in olfaction

pineal gland

secretes melatonin

habenular nuclei

involved in olfaction

Circumventricular Organs (CVOs) of the Diencephalon

• They lie in the wall of the 3rd ventricle

• Parts of the diencephalon

• monitor chemical changes in the blood
  because they lack a blood-brain barrier

• include the hypothalamus (a portion of
  it), pineal gland, and the pituitary gland

• coordinate homeostatic activities of the endocrine and nervous systems