structure and functions of brain

STRUCTURE AND FUNCTION OF BRAIN

PRESENTED BY:VISHAL.V.14O00291ST YEAR

SANKARA COLLEGE OF OPTOMETRY

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THE BRAIN• The adult human brain weighs an average of 1.4

kg, or about 2 percent of the total body weight.

• Despite this relatively small mass, the brain contains approximately 100 billion neurons.

• Functioning as a unit, these neurons make up the most complex and highly organized structure on Earth.

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THE BRAIN• The brain is responsible for many of the qualities

that make each individual unique-thoughts, feelings, emotions, talents, memories, and the ability to process information.

• Much of the brain is dedicated to running the body, the brain is responsible for maintaining Homeostasis by controlling and integrating the various systems that make up the body.

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• Brain– Occupies 80% of cranium– Comprised of 3 major structures

• Cerebrum• Cerebellum• Brainstem

– High metabolic rate• Receives 15% of cardiac output• Consumes 20% of body’s oxygen• Requires constant circulation

– IF blood supply stops:• Unconscious within 10 seconds• Death in 4–6 minutes

Covering of brain

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Meninges• membranes surrounding CNS• protect CNS• three layers

• dura mater – outer, tough• arachnoid mater – thin, weblike• pia mater – inner, very thin

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• Meninges– Pia Mater

• Closest to brain and spinal cord• Delicate tissue• Covers all areas of brain and spinal cord• Very vascular

– Supply superficial areas of brain– Arachnoid Membrane

• “Spider-web like”• Covers inner dura• Suspends brain in cranial cavity

– Collagen and elastin fibers• It is seperated from pia matter through sub-arachnoid space

– CSF– Cushions brain

– Dura matter– The outermost– Thick,double layered membrane– Lines the inner surface of cranial cavity

Meninges of the Spinal Cord

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Blood-Brain Barrier

• Tight junctions prevent materials from diffusing across the capillary wall.

• Astrocytes act as “gatekeepers” that permit materials to pass to the neurons after leaving the capillaries.

• Is markedly reduced or missing in three distinct locations in the CNS: the choroid plexus, hypothalamus, and pineal gland.

Ventricles

• interconnected cavities within cerebral hemispheres and brain stem• continuous with central canal of spinal cord• filled with cerebrospinal fluid (CSF)

• lateral ventricles(1 & 2)• third ventricle• fourth ventricle• cerebral aqueduct

Cerebrospinal Fluid

• secreted by choroid plexus• circulates in ventricles, central canal of spinal cord, and subarachnoid space• completely surrounds brain and spinal cord• clear liquid• nutritive and protective• helps maintain stable ion concentrations in CNS

Cerebrospinal FluidCSF

• Made in choroid plexuses (roofs of ventricles)– Filtration of plasma from capillaries through

ependymal cells (electrolytes, glucose)

• total volume 100-160 ml • Cushions and nourishes brain• Hydrocephalus: excessive accumulation

CSF circulation: through ventricles, median and lateral apertures, subarachnoid space, arachnoid villi, and into the blood of the superior sagittal sinus

CSF:-Made in choroid plexus-Drained through arachnoid villus

Hydrocephalus

Brain Development

Three Major Vesicles1. Forebrain2. Midbrain3. Hindbrain

Brain Development

Brain

GROSS ANATOMY

• CEREBRUM

• CEREBELLUM

• DIENCEPHALON

• BRAIN STEM

Brain

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Structure of Cerebrum

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• corpus callosum• connects cerebral hemispheres

• convolutions • bumps or gyri

• sulci• grooves

• longitudinal fissure• separates hemispheres

• transverse fissure• separates cerebrum from cerebellum

Organization of Brain Tissue • Gray matter:

– motor neuron and interneuron cell bodies, dendrites, axon terminals– unmyelinated axons.

• White matter:– composed primarily of myelinated axons.

• External sheets of gray matter, called the cortex, cover the surface of most of the adult brain (the cerebrum and the cerebellum).

Organization of Brain Tissue

• White matter lies deep to the gray matter of the cortex. • Within the masses of white matter:

– discrete innermost clusters of gray matter called cerebral nuclei (or basal nuclei).

– are oval, spherical, or sometimes irregularly shaped clusters of neuron cell bodies.

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Functional Regions of Cerebral Cortex

Cerebral Cortex – thin layer of gray matter that constitutes the outermost portion of cerebrum; contains 75% of all neurons in nervous system

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Lobes of Cerebral Hemispheres

• Frontal• Parietal• Temporal• Occipital• Insula

Frontal Lobe

The frontal lobe is the area of the brain responsible for higher cognitive functions.

These include:

• Problem solving• Spontaneity• Memory• Language• Motivation• Judgment• Impulse control• Social and sexual behavior.

Temporal Lobe• The temporal lobe

plays a role in emotions, and is also responsible for smelling, tasting, perception, memory, understanding music, aggressiveness, and sexual behavior.

• The temporal lobe also contains the language area of the brain.

Parietal Lobe• The parietal lobe

plays a role in our sensations of touch, smell, and taste. It also processes sensory and spatial awareness, and is a key component in eye-hand co-ordination and arm movement.

Occipital Lobe

The occipital lobe is at the rear of the brain and controls vision and recognition.

Limbic Lobe (or) insula

The limbic lobe is located deep in the brain, and makes up the. limbic system

The Limbic System

A. Cingulate gyrusB. FornixC. Anterior thalamic

nucleiD. HypothalamusE. Amygdaloid

nucleusF. Hippocampus

The limbic system is the area of the brain that regulates emotion and memory. It directly connects the lower and higher brain functions.

Functions of the Cerebrum

• interpreting impulses• initiating voluntary movements• storing information as memory• retrieving stored information • reasoning• seat of intelligence and personality

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Funcional area of cerebrum

Homunculus – “little man”• Body map: human body spatially represented

– Where on cortex; upside down

Cerebral White Matter

• Types of tracts– Commissures – composed of commissural fibers

• Allows communication between cerebral hemispheres• Corpus callosum – the largest commissure

– Association fibers • Connect different parts of the same hemisphere

Basal Nuclei

• masses of gray matter• deep within cerebral hemispheres• caudate nucleus,• putamen• globuspallidus produce dopamine

Basal nuclei functions

• Cooperate with the cerebral cortex in controlling movements

• Receive input from many cortical areas• Evidence shows that they:

– Start, stop, and regulate intensity of voluntary movements

– In some way estimate the passage of time

Cerebellum

The cerebellum is connected to the brainstem, and is the center for body movement and balance.

The Brainstem

• The brainstem is the most primitive part of the brain and controls the basic functions of life: breathing, heart rate, swallowing, reflexes to sight or sound, sweating, blood pressure, sleep, and balance.

• The brainstem can be divided into three major sections:

• Mid brain

• Pons

• Medulla oblongata

Brainstem Divisions

Midbrain

Pons

Medulla Oblongata

10 of the 12 pairs of Cranial Nerves attached to it

The Cranial Nerves

I. Olfactory nerveII. Optic nerveIII. Oculomotor nerveIV. Trochlear nerveV. Trigeminal nerveVI. Abducens nerveVII. Facial nerveVIII. Vestibulocochlear

nerveIX. Glossopharyngeal

nerveX. Vagus nerveXI. Accessory nerveXII. Hypoglossal nerve

Anatomy and Physiology of the Head

• Midbrain–Upper portion of brainstem

• Structures:

THALAMUS

HYPOTHALAMUS

ThalamusThalamus means “inner room” in Greek, as it sits deep in the brain at the top of the brainstem.

The thalamus is called the gateway to the cerebral cortex, as nearly all sensory inputs pass through it to the higher levels of the brain(cerebral cortex)

HypothalamusThe hypothalamus sits under the thalamus at the top of the brainstem. Although the hypothalamus is small, it controls many critical bodily functions:

• Controls autonomic nervous system

• Center for emotional response and behavior

• Regulates body temperature

• Regulates food intake

• Regulates water balance and thirst

• Controls sleep-wake cycles

• Controls endocrine system

The hypothalamus is shaded blue. The pituitary gland extends from the hypothalamus.

The Pons• The pons is the rounded

brainstem region between the midbrain and the medulla oblongata. In fact, pons means “bridge” in Latin

• Communication interchange b/w cerebellum,cerebrum,midbrain & spinal cord.

• The pons is the origin of several cranial nerves.

The Medulla Oblongata Most caudal level of the brain stem

• Choroid plexus lies in the roof of the fourth ventricle

• Continuous with the spinal cord• Cranial nerves VIII–XII attach to the medulla• The medulla is primarily a control center

for vital involuntary reflexes such as swallowing, vomiting, sneezing, coughing, and regulation of cardiovascular and respiratory activity.

Blood supply & venous drainage

• CNS Circulation– Arterial

• Four Major Arteries– 2 Internal carotid arteries

» From the common carotid– 2 vertebral arteries

• Circle of Willis– Internal carotids and vertebral arteries– Encircle the base of the brain

– Venous• Venous drainage occurs through bridging veins• Bridge dural sinuses• Drain into internal jugular veins

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Brain Functions

• Vision• Taste• Cognition• Emotion• Speech• Language• Hearing• Motor Cortex• Sensory Cortex• Autonomic Functions

Vision• The visual cortex

resides in the occipital lobe of the brain.

• Sensory impulses travel from the eyes via the optic nerve to the visual cortex.

• Damage to the visual cortex can result in blindness.

Taste• The gustatory

complex (green circle) is the part of the sensory cortex (purple area) that is responsible for taste.

Cognition

• The prefrontal cortex is involved with intellect, complex learning, and personality.

• Injuries to the front lobe can cause mental and personality changes.

Emotion

• Emotions are an extremely complex brain function. The emotional core of the brain is the limbic system . This is where senses and awareness are first processed in the brain.

• Mood and personality are mediated through the prefrontal cortex. This part of the brain is the center of higher cognitive and emotional functions.

Prefrontal cortex

Limbic system

Speech

• Broca’s area is where we formulate speech and the area of the brain that sends motor instructions to the motor cortex

• Injury to Broca’s area can cause difficulty in speaking. The individual may know what words he or she wishes to speak, but will be unable to do so.

Broca’s Area

Language

Wernicke’s area is a specialized portion of the parietal lobe that recognizes and understands written and spoken language.

Wernicke’s area surrounds the auditory association area.

Damage to this part of the brain can result in someone hearing speech, but not understanding it.

Wernicke’s Area

Auditory Association Area

HearingThere are two auditory areas of the brain:

• The primary auditory area (brown circle) is what detects sounds that are transmitted from the ear. It is located in the sensory cortex.

• The auditory association area (purple circle) is the part of the brain that is used to recognize the sounds as speech, music, or noise.

Motor Cortex

• The motor portion of the cerebrum is illustrated here. The light red area is the premotor cortex, which is responsible for repetitive motions of learned motor skills. The dark red area is the primary motor area, and is responsible for control of skeletal muscles.

• Different areas of the brain are associated with different parts of the body.

• Injury to the motor cortex can result in motor disturbance in the associated body part.

Sensory Cortex• The sensory portion of the

cerebrum is illustrated here.

• Different areas of the brain are associated with different parts of the body, as can be seen below.

• Injury to the sensory cortex can result in sensory disturbance in the associated body part.

Autonomic Functions

• The brainstem controls the basic functions of life. Damage to these areas of the brain are usually fatal:

• The pons plays a critical role in respiration.

• The medulla oblongata is responsible for respiration and cardiovascular functions.

Pons

Medulla Oblongata

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