cerebral cortex · 3/4/2020 · motor areas & their functions • primary motor cortex...

CEREBRAL CORTEX(Guyton, 13th Ed. Pg. 707 – 709 & pg: 737- 744)

Dr. Ayisha Qureshi

Professor

MBBS, MPhil

Learning Objectives

By the end of the lecture, the student should be able to:

• Name the various functional parts of the cerebral cortex.

• Comprehend the concept of left and right brain dominance.

• Explain brain plasticity.

• Describe the functions of motor cortex.

• Explain how language is produced.

• Differentiate between dysarthria and aphasia.

Difference b/w GYRUS & SULCUS?

Identify Longitudinal

Fissure?

Name the Lobes of the

Cerebral Cortex.

Identify the Central Sulcus?

What is it’s significance?

How are the Rt & Lt lobes connected?

Difference b/w Sulci & Gyri:

FACTS ABOUT CEREBRAL CORTEX

Cerebrum forms 80% of the total

brain.

It weighs 1200 g in females & 1400 g in

males.

Larger brains are associated with

larger bodies NOT with greater

intelligence!!!

It looks like a much-folded

walnut & feels like butter!!

Cerebral dominance OR Lt Brain- Rt Brain

Dominance.

What so you understand by Left or Right brain dominance?

LEFT OR RIGHT BRAIN…?

FUNCTIONAL AREAS OF THE CEREBRUM

The cerebral cortex plays an important role in the planning and ongoing control of voluntary motor

movements, and reception and perception of sensory sensations.

REMEMBER:1. Anatomically, the lobes are symmetrical in both

hemispheres, but functionally, they are not symmetrical & the functions do not correspond to the anatomical lobes.

2. Although the brain is divided into lobes anatomically & functionally, with a particular activity performed by discrete

areas, no part of the brain works in isolation. There is complex interplay b/w numerous brain regions.

MOTOR CORTEX

MOTOR AREAS & THEIR FUNCTIONS

• PRIMARY MOTOR CORTEX Brodmann’s Area 4

• PREMOTOR CORTEX Brodmann’s Area 6, 8, 44 & 45.

• SUPPLEMENTARY MOTOR CORTEX

Each of the areas above has its own homunculus (topographical representation of muscle groups and specific motor functions).

MOTOR HOMUNCULUS

(The Motor cortex has 3 areas and each area has its own motor homunculus.)

Excitation of a single motor cortex neuron in the Primary Motor Cortex usually excites a specific

movement rather than one specific muscle!In the Premotor cortex, excitation of a single neuron

causes a “pattern” of movement then a specific muscle.

Note: more than one half of the entire primary motor cortex is concerned with controlling the muscles of the hand and

the muscles of speech.

Cerebral Motor Cortex

PRIMARY MOTOR CORTEX

(M1)

- Executes or carries out the movements of groups of

muscles.

- Premotor and supplementary motor cortex along with Cerebellum tell it

how and when.

- If damaged, person walks with a limp and precision movements are lost but

there is rarely a paralysis or hemiplegia.

PREMOTOR CORTEX

- Causes “patterns” of movements.

- First develops a “motor image” of the movement to be

performed.

- Sets tone & posture at the start of a planned movement, thru basal ganglia and thalamus or

directly.

- Coordination of complex movements.

- Mirror neurons help learn new skills by imitation (Sensory into

motor representation).

- If damaged, patient is unable to initiate the movement.

SUPPLEMENTARY CORTEX

- Stimulation results in bilateral rather than

unilateral movements.

- Conjugate eye and head movements.

- Together with premotor area, provide body-wide attitudinal movements

including diff. segments of the body and head and eyes.

- If damaged, impairment of planned movements (e.g. the patient cannot tie his

shoelaces)

Some specialized areas of motor control found in the human motor cortex

THE FUNCTIONAL LAYERS OF THE CEREBRAL CORTEX!!

Six well-defined layers.• Layer IV: most incoming sensory signals enter• Layer V & VI: Most output signals leave • Layer V: large fibers to the brainstem & cord

arise• Layer I, II & III: intracortical association

functions. These columns extend perpendicularly about 2 mm from the cortical surface down through the thickness of the cortex to the underlying white matter.They consist of horizontal & vertical fibers in large amounts. • 3 main types of cells: 1. Granular or stellate cells- act as

interneurons within the cortex. Release GABA (inhibitory) or Glutamate (excitatory) NT. Are short neurons.

2. Fusiform cells: give rise to output fibres3. Pyramidal cells: larger & more numerous &

give rise to long, large nerve fibres that go all the way to the spinal cord & to different parts of the brain.

Anatomical & functional relations of the Cerebral cortex & the

Thalamus

• The fig. shows the areas of the cerebral cortex that connect in both directions with specific parts of the thalamus.

• When thalamus is damaged along with the cortex, the loss of cerebral function is far greater than when the cortex alone is damaged b/c thalamic excitation of the cortex is necessaryfor almost all cortical activity.

• The thalamus and the cortex together are sometimes called THALAMOCORTICAL SYSTEM.

• Almost all sensory pathways pass through the thalamus on the way to the cortex, EXCEPT some pathways of olfaction.

What do you understand by Brain Plasticity?

Somatotopic maps vary between individuals. They are also dynamic (constantly changing) & not

static.

The Cortical architecture is influenced by use-dependence.

Maps of the motor cortex are not permanent and they change with experience!!

ASSOCIATION AREAS OF THE CEREBRAL CORTEX

(receive & analyse signals simultaneously from both sensory & motor cortex & subcortical regions)

Association Areas and their significance

Association Areas

1. Parieto occipitotemporalAssociation Areas

- It analyses and computes the coordinates of the visual,

auditory & body surroundings.

- Wernicke’s area is important for language comprehension.

- Angular gyrus is needed for initial processing of visual

learning (language).

- Naming objects.

2. Prefrontal Association Area

- Through basal ganglia-thalamic feedback circuit, sends

commands to the motor cortex to plan sequence of motor

movements.

- Receives information from the Parieto occipitotemporal areas.

- Thought processes: elaboration of thought & working memory.

- Word formation.

- Also see slide on Prefrontal Cortex

3. Limbic Association Areas.

- Behaviour, motivation and emotions.

- Area for recognition of faces. Damage results in inability to recognize faces, a condition

called Prosopagnosia.

- Why do you think such a large area is dedicated for recognizing

faces?

Angular Gyrus(the most inferior portion of the posterior parietal lobe, lying

immediately behind the Wernicke’s area & fusing posteriorly into the visual areas of the occipital lobe)

When this area is damaged, although the Wernicke’s area is still intact, the person is able to see words & even know that they are words but not be able to interpret their meanings. This condition is called Dyslexia, or word blindness. It is a neurobiological disorder that is usually seen as a learning disability. It makes it harder for a child to read or write.

Face recognition areas located on the underside of the brain in the medial occipital & temporal lobes

Higher Intellectual Functions of the Prefrontal Association Areas

Prefrontal cortex plays a major role in depth & elaboration of thought and working memory, timed response, plan for future,

solve mathematical and philosophical problems, diagnose diseases and regulate our activities according to moral law.

To understand further we must see what happens when Prefrontal Cortex is damaged or patients undergo Prefrontal Lobotomy:

What happens when Prefrontal Cortex is damaged or patients undergo Prefrontal Lobotomy:

1. The patients lost their ability to solve complex problems. 2. They became unable to string together sequential tasks to reach

complex goals.3. They became unable to learn to do several parallel tasks at the same

time.4. Their level of aggressiveness was decreased, sometimes markedly, and,

in general, they lost ambition.5. Their social responses were often inappropriate for the occasion, often

including loss of morals and little reticence in relation to sexual activity and excretion.

6. The patients could still talk and comprehend language, but they were unable to carry through any long trains of thought, and their moods changed rapidly from sweetness to rage to exhilaration to madness.

7. The patients could also still perform most of the usual patterns of motor function that they had performed throughout life, but often without purpose.

Elaboration of thought, prognostication (what you think will happen in the future), and performance of higher intellectual functions by the prefrontal areas

is called the Concept of a “Working Memory”.

Review of the map of specific functional areas of the cerebral cortex:

LANGUAGE & SPEECH

Unlike the sensory and motor regions of the cortex, which are present in both hemispheres, the areas of the brain responsible for language ability are found in only one

hemisphere—the dominant hemisphere- which in most cases is the Left hemisphere.

Language involves the integration of 2 distinct capabilities:

- Comprehension (ability to understand what you have heard or read)

- Expression (ability to speak)

Language Input

(thru eyes & ears)

COMPREHENSION

(Wernicke’s Area)

Language Output

(involving vocalization)

Vocalization

(Broca’s Area)

Auditory Association Area damage: Auditory Receptive Aphasia (word

Deafness)

Visual Association Area Damage: Visual Receptive Aphasia (Word Blindness)

Broca’s Area damage: Dysarthria (inability to articulate words)

WERNICKE’S AREA & SPEECH

Wernicke’s Area, which is concerned with language comprehension, is located in the left temporal lobe, at the juncture of the parietal, temporal, and occipital lobes.

Wernicke’s Area plays a critical role in understanding both spoken and written words. It is considered to be the language comprehension center (also called the General Interpretative Area, the Gnostic Area and the Knowing Area).

When part of the Wernicke’s area in the dominant hemisphere is damaged, the person understands the word (written or spoken) but is unable to interpret the thought that is expressed. This is called Wenicke’s Aphasia.

If the damage is widespread to the Wernicke’s area, then person is totally demented for language understanding & communication. This is called Global Aphasia.

BROCA’S AREA & SPEECH

Broca’s area, which governs speaking ability and articulation, is located in the Left Frontal Lobe, close to the motor cortex, near the areas responsible for muscles of the face, tongue, jaw and throat.

Broca's area is responsible for producing words. It controls motor functions involved with speech production.

Damage to Broca’s area makes a person incapable of speaking or emiting the words, although he or she knows what they want to say. This is called Motor Aphasia.

WHAT IS APHASIA?

Aphasia is a communication disorder that results from damage or injury to language parts of the brain. It's more

common in older adults, particularly those who have had a stroke. Aphasia does not impair the person's intelligence.

The affected person may have: • Difficulty reading (Visual Receptive Aphasia)

• Difficulty understanding (Wernicke’s or Global Aphasia)• Difficulty speaking (Motor Aphasia)

Let’s Review Cerebral Cortex:

Give 2 functions for each of the lobes that you see.

A large portion of the cerebral cortex does not fit intothe conventional definition of motor or sensory cortex.Which of the terms below is used to refer to the typeof cortex that receives input primarily from severalother regions of the cerebral cortex?A) Cortex that is agranularB) Secondary somatosensory cortexC) Association cortexD) Supplementary motor cortexE) Secondary visual cortex

Lesions of which of the following areas of the brain

would have the most devastating effect on verbal and

symbolic intelligence?

A) Hippocampus

B) Broca’s area on the non-dominant side of the brain

C) Wernicke’s area on the non-dominant side of the brain

D) Broca’s area on the dominant side of the brain

E) Wernicke’s area on the dominant side of the brain

The two hemispheres of the brain are connected by which nerve fibers or pathways?

A) Lateral lemniscus

B) Corticofugal fibers

C) Corpus callosum

D) Arcuate fasciculus

E) Medial longitudinal fasciculus

Broca’s area is a specialized portion of motor cortex.

Which of the following conditions best describes the

deficit resulting from damage to Broca’s area?

A) Spastic paralysis of the contralateral hand

B) Paralysis of the muscles of the larynx and pharynx

C) Inability to use the two hands to grasp an object

D) Inability to direct the two eyes to the contralateral side

E) Inability to speak whole words correctly

Which of the following structures serve to connect Wernicke’s area to Broca’s area in the cerebral cortex?

A) Arcuate fasciculus

B) Lateral lemniscus

C) Medial longitudinal fasciculus

D) Anterior commissure

E) Internal capsule

cerebral cortex · 3/4/2020 · motor areas & their functions • primary motor cortex...

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