Characteristics of Brain

weighs 1300-1500 g is one of largest organs.

Four principal parts of the Brain

1. Brain stem

2. Diencephalon

3. Cerebrum

4. Cerebellum

Brain stem

continuous with spinal cord composed of medulla,

pons, and mid brain

Diencephalon

thalamus and hypothalamus

Cerebrum

7/8 of total weight of brain, located over diencephalon

Cerebellum

inferior to cerebrum and posterior to brain stem

Function of Meninges

protect brain

(3 separate coverings)

Meninges 3 separate coverings

Dura mater

Arachnoid

Pia mater 

 Dura mater

 "tough mother", separated into 2 layers.

1. Outer periosteal layer adheres to cranium.

2. Inner meningeal layer corresponds to spinal dura mater.

Arachnoid

 delicate net like membrane

Pia mater

"delicate mother", attached to surface of CNS, is

modified areolar connective tissue.

Cerebrospinal fluid

 circulates in subarachnoid space around brain and spinal cord and through ventricles of brain.

4 ventricles

cavities that communicate with each other, subarachnoid space and spinal cord

2 lateral ventricles

 one in each hemisphere under corpus callosum

3rd ventricle

vertical slit inferior and between 2 lobes of thalamus

4th ventricle

between brain stem and cerebellum

Interventricular foramen

opening between lateral ventricle and 3rd ventricle

Aquaduct of Sylvius

connects 3rd and 4th ventricles

Cerebrospinal Fluid

made in choroid plexuses of ventricles. Absorbed

through arachnoid villi into venous sinus, specially superior sagittal sinus.

Brain weight

2% of body weight but uses 20% of oxygen

brain damage

four minutes without oxygen - brain damage -

lysosomes break open and destroy cell

Blood - brain barrier

capillaries differ structurally, they are more

densely packed and surrounded by large number of astrocytes. For substances to cross must be very small or actively transported.

BRAIN PARTS

1. Medulla oblongata

2. Pons "bridge," 
3. Mid brain

superior to spinal cord and inferior to pons.

1 inch in length and contains all ascending and descending tracts that communicate between brain and spinal cord.

Decussation

crossing over - some tracts cross in medulla

Decussation

crossing over - some tracts cross in medulla

Pyramids

enlarged areas on ventral side of medulla containing large motor tracts. Most fibers in left and right pyramids decussate.  Decussation explains why left side of body controlled by right side of brain.

Decussation explains why left side of body controlled by right side of brain.

Nearly all sensory tracts also cross over in medulla.

Nearly all sensory tracts also cross over in medulla.

Important areas in medulla

1. 2 nuclei - gracilis and cuneatus

2. reticular formation

3. Other nuclei for sneezing, coughing, swallowing and vomiting

4. Three vital reflex centers

5. Contains origins for cranial nerves

2 nuclei - gracilis and cuneatus

receive sensory fibers from ascending tracts and relay information to thalamus and sensory areas of cortex.

reticular formation

and arousal areas of dispersed gray matter with white fibers. Concerned with consciousness

Other nuclei for sneezing, coughing, swallowing and vomiting

Other nuclei for sneezing, coughing, swallowing and vomiting

Three vital reflex centers

1. cardiac center - CAC and CIA

2. medulla rhythmicity center

3. vasomotor center

cardiac center - CAC and CIA

regulates heartbeat and force of contraction

medulla rhythmicity center

 regulates rhythm of breathing

vasomotor center

regulates diameter of blood vessels

Contains origins for cranial nerves

VIII - vestibulocochleor

IX - glossopharyngeal 

X - vagus

XI - accessory

XII - hypoglossal

VIII - vestibulocochleor

hearing and equilibrium

IX - glossopharyngeal

 swallowing, salivation, taste

X - vagus

 thoracic and abdominal viscera

XI - accessory

 head and shoulder movement

XII - hypoglossal

tongue movements

Rounded bulge above medulla and anterior to cerebellum.

Composed of white fibers and nuclei.

Functions to connect spinal cord with brain and parts of brain with each other.

Important structures in Pons

1. transverse fibers

2. longitudinal fibers

3. Contains nuclei for cranial nerves

4. Pneumotaxic and Apneustic areas

transverse fibers

 connects to cerebellum through cerebral peduncles

longitudinal fibers

connects spinal cord with upper parts of brain stem.

Contains nuclei for cranial nerves

V - trigeminal

VI - abducens

VII - facial

VIII - vestibularcochlear

V - trigeminal

chewing, sensations for head and face

VI - abducens

regulates eyeball movement

VII - facial

taste, salivation and facial expression

VIII - vestibularcochlear

vestibular branch (equilibrium)

Pneumotaxic and Apneustic areas

 regulate the depth of inspiration and expiration

Mid brain

connects pons to lower diencephalon. Aquaduct of

Sylvias passes through midbrain.

The midbrain is the main connection for tracts between upper brain and lower brain parts and cord

Important structures located in midbrain

Cerebral peduncles

Tectum

Red nucleus

Nuclei for cranial nerves

Cerebral peduncles

contains white fibers for both motor and sensory impulses.

Tectum

contains 4 rounded projections on dorsal portion of midbrain called corpora quadrigemina

corpora quadrigemina

 2 superior colliculi - visual reflexes

2 inferior colliculi - auditory reflexes

Red nucleus

 gray matter that connects cerebral hemispheres and cerebellum and functions in reflexes concerned with motor coordination and maintaining posture.

Nuclei for cranial nerves

III - oculomotor

IV - trochlea

III - oculomotor

movement of eyeball and change pupil in size

and lens shapes.

IV - trochlea

conducts impulses for eye movement

Thalamus

2 oval masses of mostly gray matter organized into nuclei and making 4/5 of diencephalon.

Located below lateral ventricles of respective cerebral hemispheres.

The 2 mass are connected by the intermediate mass.

1. serves as relay station for all sensory impulses except smell to an exact part of cerebrum

2. centers for synapse in somatic motor system

3. interpretation center for sensory impulses such as pain,

temperature, crude touch, and pressure

4. reticular nucleus - consciousness and arousal

5. anterior nucleus - concerned with emotions and memory

6. partially responsible for physiological shock following serious trama.

Hypothalamus

located below thalamus and forms floor and part of lateral walls of 3rd ventricle

What is hypothalamus responsible for?

Responsible for vital functions due to its role in accelerating and decreasing body functions.

1. regulates heart rate

2. regulates body temperature

3. regulates water and electrolyte balance

4. regulation of hunger and gastrointestinal activity

5. regulates sleeping and wakefulness

6. regulates sexual response

7. contains nuclei associated with emotional responses

8. controls endocrine functions - is principle intermediary between nervous system and endocrine system

Cerebellum

second largest portion of brain. Located inferior to cerebrum and posterior to brain stem and is separated from cerebrum by transverse fissure.

Anatomy of cerebellum

2 hemispheres each divided into 3 lobes

2 hemispheres each divided into 3 lobes

a. anterior lobe subconscious movement of

b. posterior lobe skeletal muscles

c. flocculonodular lobe - sense of equilibrium

Vermis

central constricted area between hemispheres

tentorium cerebelli

dura mater separating cerebellum from cerebrum

falx cerebelli

dura mater between hemispheres

foli

ridges (like gyri) of gray matter

arbor vitae

 white matter tracts

Cerebellar peduncles

 3 paired bundles connecting with brain stem.

Functions of cerebellum

motor area concerned with subconscious movements in skeletal muscles (movements concerned with coordination, posture, and balance.

Proprioception

sense of position of one body part relative to another.

The cortex relays information to cerebellum and cerebellum sends impulses from inferior peduncle to muscles to coordinate movement.

Cerebrum