Anatomy of the Brain and Brain Stem

Major parts of the Human Brain

1. Cerebral Hemispheres (Cerebrum)

2. Brain Stem

3. Cerebellum

The Cerebrum: Control Center

Performs highest level brain functions

Divided into two hemispheres

left and right

visually identical

subtle functional differences

extremely rich blood supply

Cerebrum Surface

appears wrinkled

Ridges:Gyri

Grooves:Sulci

Together: Increase surface area

Gyri

Singular: Gyrus

Visible outer surface = Grey matter

White matter is deeper

Sulci

Singular: Sulcus

Deep grooves surrounding gyri

Frontal Lobe

Mental / emotional functions & Motor

Temporal Lobe

Hearing and sensory processing

Occipital lobe

Visual processing

Parietal lobe

General Sensory

Insula

Deep to the lateral sulcus

MANY different functions

ntegrate nervous activity

Lobes separated by

major sulci

Central Sulcus

Groove between frontal and parietal lobes

“Dividing line” between sensory and motor regions of brain

Lateral fissure

Separates temporal and frontal lobes 

Two major gyri

Two major gyri

Precentral and Postcentral

Precentral

motor cortex

Postcentral

Sensory cortex

Inside the brain

Each hemisphere composed of Gray & White matter

Grey Matter

Neural Cell Bodies

Also referred to as “cortex”

White matter

Myelinated axons

White due to lipids in myelin sheath

CORPUS COLLOSUM

Large white matter bundle connecting L/R hemispheres

Allows information transfer from one hemisphere to the other

Important for coordination

Brodmann Areas

Numbered regions related to specific brain functions

Brodmann areas 4

Primary motor cortex, Precentral gyrus, Control movement

Brodmann areas 3, 1, 2 Awareness of sensation

Primary somatosensory cortex, Postcentral gyrus,

Brodmann areas 17,18, 19

Visual cortex, Occipital lobe, Visual processing

Brodmann areas 41, 42

Auditory cortex, Temporal lobe, Auditory processing

Brodmann areas 22

Wernicke’s area, Temporal lobe, Speech comprehension

Brodmann areas 44, 45

Broca’s area,Frontal lobe, Speech formation

homunculus

Size of body parts proportionate to amount of innervation to region

Represents degree of:

Fine motor control

Sensory sensitivity

face and upper body

lateral cortex

lower body

medial cortex

Internal carotid arteries

Pass through neck on either side of throat

Vertebral arteries

Pass through foramen magnum

Basilar artery

Formed by vertebral

Posterior cerebral artery

Branch of basilar

Middle cerebral artery

branches from internal carotids

supplies lateral cortex

Posterior communicating arteries

join internal carotids

Anterior cerebral artery

also from internal carotids

supplies medial cortex

Anterior communicating artery

joins anterior cerebral arteries

Circle of Willis

Massively important arterial structure.

Found on inferior surface of brain

Combination of branches from vertebral and internal carotid arteries

Ischemia

Lack of blood flow

Middle Cerebral Artery

Blood to lateral (and superior) surface of cerebrum

Middle Cerebral Artery blocked

Would loose sensation & motor function to upper body down to hips

Anterior Cerebral Artery

Blood to medial surface of cerebrum

Anterior Cerebral Artery Blocked

Would loose sensation & motor function to lower limbs

Basal Ganglia

Movement planning

Initiates movements in an adult.

Controls movements of newborn babies.

Substantia Nigra

Part of Basal Ganglia

Involved in gross motor function

Limbic System

Formed by multiple parts of the brain

(Amygdala & Hippocampus)

Sex drive, Memory, Emotion, Fear

Protecting the CNS

3 layers

Dura Mater

Arachnoid mater

Pia Mater

Outer layer of CNS

Dura Mater

Middle layer of CNS

Arachnoid mater

Inner layer of CNS

Pia mater

Dura mater

Extremely durable outer covering of CNS

Tough like leather

deep to skull

Arachnoid mater

Immediately deep to dura mater

Looks like plastic wrap over brain

Web-like trabeculae connect it to brain

Pia Mater

Attached to external surface of brain like skin of an apple

Just a few cells thick

Impossible to dissect separately

Cerebrospinal fluid

Ultrafiltrate of blood plasma produced in ventricles of the brain

Where is CSF found

Found in subarachnoid space between arachnoid and pia maters

Characteristics of Cerebrospinal fluid

Clear, colorless, odorless

Cushions brain

Provides nourishment to and carries waste away from CNS

CSF Produced by

Choroid plexus

Specialized vascular complex in empty spaces in brain: Ventricles

CSF Produced by Choroid plexus structure

Capillaries of ependymal cells line the cavity

Ependymal cells filter out important substances from blood, creating pure CSF

Order of CSF’s Path through the brain’s ventricular spaces

1. Lateral ventricles

2. Third ventricle

3. Cerebral Aqueduct

4. Fourth ventricle

5. Subarachnoid space surrounding Brain AND spinal cord

Hydrocephalus Buildup of CSF in ventricular system

Blocked CSF pathway 

CSF builds up

Pressure builds

Ventricles expand

Pressure damages brain

Venous Drainage: Venous Dural Sinuses

Venous sinuses (hollow channels) found between layers of Dura mater 

Receive blood from veins of the brain

Receive CSF from subarachnoid space

Empty into the internal jugular vein.

No smooth muscle or valves like normal veins

Arachnoid Granulations

Specialized extensions of arachnoid mater

Pass through dura matter

CSF drains through granulations into venous sinuses

Leaves skull along with blood

Thalamus

Part of region called diencephalon

Immediately superior to brainstem

Direct relay center for all sensations except smell.

Like old-timey telephone operator

Directs sensory to appropriate place in cortex

Diencephalon: Hypothalamus Location

Superior to Midbrain

Inferior to thalamus

Diencephalon: Hypothalamus Multiple Nuclei (colored portions)

Control sleep & wake cycle

Hunger/thirst 

Temperature

Diencephalon: Hypothalamus

Controls Autonomic NS along with pituitary Gland (located inferior to hypothalamus)

Diencephalon: Hypothalamus 

Functional summary

Homeostasis

Reticular formation

Column of neurons located in middle of brain stem

From medulla to thalamus

These neurons maintain a conscious state

When damaged, coma may result

The Brain Stem and Major Nervous Pathways

• Corpus callosum

Thalamus

Hypothalamus

Midbrain

Pons

Medulla

Cerebellum

Midbrain Location

Superior to Pons

Midbrain Contents

Auditory/ocular reflex center

Auditory stimulation Turn eyes towards loud sound

Pons

Superior to Medulla

Attachment for cerebellum

Contains major respiratory centers

Cranial nerve nuclei

Cerebellum

Coordinates movements

Does NOT initiate them

Medulla Oblongata Location

Inferiormost portion of brainstem

At level of Foramen Magnum

Medulla Oblongata Major features

Cardiovascular &Respiratory Centers

Motor &Sensory Decussation (cross over)

Some cranial nerve nuclei

Decussate

Cross to opposite side

Crisscrossing neurons in the medulla

Right side motor cortex controls left side actions (and vice versa)

Right side sensory cortex receives left side sensation (and vice versa)