Transcript Understanding the Nervous System

Cerebral Cortex 1
PL3020
Dr. Deirdre Edge
[email protected]
Cerebrum -The largest division of the brain.
It is
divided into two hemispheres, each of which is
divided into four lobes.
Cerebrum
Cerebrum
Cerebellum
Cerebral Cortex - The outermost layer of gray
matter making up the superficial aspect of the
cerebrum.
Cerebral Cortex
Cerebral
Cortex
Gyri
Sulci
Cerebral Features
• Gyri: elevated ridge/fold
• Sulci – Small depressed
grooves dividing the gyri
•
Central Sulcus – Divides the Frontal
Lobe from the Parietal Lobe
•
Fissures – Deep grooves,
generally dividing large
regions/lobes of the brain
•
Longitudinal Fissure – Divides the
two Cerebral Hemispheres
Transverse Fissure – Separates the
Cerebrum from the Cerebellum
Sylvian/Lateral Fissure – Divides the
Temporal Lobe from the Frontal and
Parietal Lobes
•
•
Gyri
(ridge)
Sulci
(groove)
Fissure
(deep
groove)
Key Functions of the Cerebral
Cortex
• The cerebral cortex is the highest order integration of sensory, motor
and consciousness activities
• It is responsible for the perception and conscious understanding of all
sensations and the integration of different sensory modalities.
• It is involved in higher cognitive and advanced intellectual functions. It
is responsible for features such as emotion, personality and intellect.
• The cerebral cortex is also involved in planning and executing complex,
voluntary motor activities.
Lobes of the Brain (4)
•
•
•
•
Frontal
Parietal
Occipital
Temporal
Lobes are named for
the overlying bones of
the skull
Central
Sulcus
Transverse
Sylvian/Lateral
Fissure
Fissure
* Note: Occasionally, the Insula is considered the fifth lobe. It is located deep
to the Temporal Lobe.
Lobes of the Brain - Frontal
• The Frontal Lobe of the brain is located deep to the Frontal
Bone of the skull. The anterior part of the cerebrum
• It plays an integral role in the following functions/actions:
- Motor Control
(Language)
- Memory Formation
- Emotions
- Planning/Decision
Making/Reasoning
- Personality, humour,
wit
Primary Motor
Cortex/ Precentral
Gyrus
Broca’s Area
Orbitofrontal
Cortex
Olfactory Bulb
Frontal Lobe - Cortical Regions
• Primary Motor Cortex (Precentral Gyrus) Cortical site involved
in planning and executing voluntary motor behaviors
• Motor
• Premotor
• Supplementary motor areas
• Broca’s Area (inferior frontal gyrus)– Motor speech area Controls facial neurons, speech, and language comprehension.
• Prefrontal Cortex – rostral part of the frontal lobe plays a major
role in personality and behaviours.
• Bilateral lesions to this part of the brain, i.e disease/surgery
(lobotomy) produce deficits in attention, difficulty in problem
solving, inappropriate social behaviour.
• Aggressive behaviour can be reduced
• RARELY PREFORMED TODAY!
• Olfactory Bulb - Cranial Nerve I, Responsible for sensation of Smell
Lobes of the Brain - Parietal Lobe
• The Parietal Lobe of the brain is located deep to the
Parietal Bone of the skull.
• It plays a major role in the following functions/actions:
- Senses and integrates sensation(s) – The
Somatosensory Cortex
- Spatial awareness and perception
(Proprioception - Awareness of
body/ body parts in space and in
relation to each other)
Primary Somatosensory
Cortex/ Postcentral
Gyrus
Somatosensory Association
Cortex
Primary Gustatory
Cortex
Parietal Lobe - Cortical Regions
• Primary Somatosensory Cortex (Postcentral Gyrus) – Site
involved with processing of tactile and proprioceptive
information.
• Somatosensory Association Cortex - Assists with the integration
and interpretation of sensations relative to body position and
orientation in space.
• Primary Gustatory Cortex – Primary site involved with the
interpretation of the sensation of Taste.
Lobes of the Brain – Occipital Lobe
• The Occipital Lobe of the Brain
is located deep to the Occipital
Bone of the Skull.
It’s primary function is the
processing, integration,
interpretation, etc. of VISION and
visual stimuli.
•
Modified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg
Primary Visual
Cortex
Visual Association
Area
Occipital Lobe – Cortical Regions
• Primary Visual Cortex
• The primary area of the brain responsible for sight
• recognition of size, color, light, motion, dimensions,
etc.
• Visual Association Area
• Interprets information acquired through the
primary visual cortex.
Lobes of the Brain – Temporal Lobe
• The Temporal Lobes are located on the sides of the
brain, deep to the Temporal Bones of the skull.
They play an integral role
in the following functions:
•
- Hearing
- Organization/Comprehension
of language
- Information Retrieval
(Memory and Memory
Formation)
Primary Auditory
Cortex
Wernike’s Area
Primary Olfactory
Cortex (Deep)
Conducted from Olfactory Bulb
Temporal Lobe – Cortical Regions
• Primary Auditory Cortex – Responsible for hearing
– Receives info related to pitch, rhythm and loudness
• Primary Olfactory Cortex – Interprets the sense of
smell once it reaches the cortex via the olfactory
bulbs.
• Wernicke’s Area – Language comprehension.
• Medial portion of Temporal lobe belongs to the
limbic system – which participates in emotional
behavior and motivation
Association Areas
Large areas of the CC
That do not rigidly into
Primary and secondary
Motor/sensory areas
These association areas
Receive and analyse
Signals simultaneously
From multiple regions of
Both motor and sensory
As well as subcortical
Structures
Structural Organisation of Cerebral
Cortex
• Different subdivisions of the CC can be identified on
the basis of their layering pattern
• There are 3 phylogenetic categories of the CC
– Neocortex (90%)
– Archicortex
– Paleocortex
• Cell Types
– Pyramidal
– Stellate/Granule cells
6 Layers (Horizontal)
3 Layers
4-5 Layers
The Neocortex – Only found in mammals, organized horizontally
into 6 layers – with varied thickness along different regions of the
hemispheres
Subcortical
White Matter
Cerebral cortex is inhomogeneous
Primary Somatosensory Cortex
Primary Motor Cortex
• Different regions of
neocortex
throughout the
cerebral cortex vary
in overall thickness.
• Differences arise
from: the thickness
of the individual
layers, differences in
cell size and differences in cell
density.
Broadmann’s
Classiffication
• In a paper published in
1909, Brodmann identified
more than 40 cortical areas
(47) based on cellular and
laminar histology of
cerebral cortex.
• This is the most widely
reproduced figure in the
fields of neurology and
neuroanatomy.
• Each area is linked to
functional specialization.
Brodmann’s nomenclature
is still used today, e.g., area
17 is primary visual cortex
e.g. area 4 = 1° motor
cortex.
Connections of the Neocortex
• Much of the cerebral
hemispheres is occupied by
subcortical white matter –
which is anatomically
organized
• Within the white matter
myelinated axons (fibres)
connect the cerebral cortex
with other brain regions - one
region of gray matter with
another
• Three main categories of
white matter fibres are
recognised:
Connections of the Neocortex
1. Intracortical: Association fibres.
• i.e. fibres that connect regions of the cerebral cortex within
one hemisphere
• 2 types of association fibres
– short: connecting adjacent gyri
– Long: connecting distant gyri (i.e. in different lobes)
2. Extracortical: Projection Fibres
• Efferent (outgoing): descending motor pathways (e.g. spinal
cord/cerebellum)
• Afferent (incoming): specific sensory systems (visual),
monoamine inputs (motivation, learning), RAS (arousal)
Connections of the Neocortex
• Intercortical: Commissural fibres.
• i.e. fibres that connect right and left cerebral hemispheres
– Anterior and posterior commissures
– Corpus collosum (largest Bundle)
commissural fibers
corpus callosum
Connections of the Neocortex
Cerebral Dominance
• Although the brain is symmetrical in structure with
two hemispheres.
• One Hemisphere, the LEFT H is dominant for motor
control. Language and general interpretative
functions (logic) – (95%) of people
• Right H is dominant for visuospatial skills, musical
ability.
Cerebral Dominance
• Hemispheric dominance is associated with the size of
the planum temporale (in the floor of the lateral
ventricle) i.e. the left PT is larger than the right,
hence this correlates with language dominance
• The Corpus collosum co-ordinates the activity of the
two hemispheres
• Normal Functioning requires communication
between the hemispheres
Split Brain Experiments
• Spyer (Nobel Prize 1981) and Gazzaniga
studied people who had the corpus collasum
surgically cut. These studies are called SplitBrain Experiments
• Much of the understanding of the individual
functions of each hemisphere has come from
these patients
Learning Objectives:
After studying this topic, you should be able to:
–
–
–
–
name the lobes of the cerebral cortex
list the main functions of each of those lobes
describe the structural organization of the cerebral cortex
explain the concept of Brodmann’s classification and it’s
functional relevance
– classify the connections of the cortex, and list the principle
connections
– explain the concept of cerebral dominance
– describe split brain experiments and explain their significance