Neuroanatomy The central nervous system (CNS)

Neuroanatomy The central nervous system (CNS)
Human brain Neuroanatomy The central nervous system (CNS) Dr. Haythem Ali Alsayigh MBCHB-FIMBS Surgical Clinical Anatomy University of Babylon-College of Medicine

Objective 1-topography of the nervous system
2-meninges of the brain and spinal cord 3-blood supply and clinical probles pituitary gland 4-basal ganglia 5-limbic system 6-CSF &ventricles 7-Spinal cord 8-Medulla oblengata 8- pone 9-btain stem 10-cerebellum 11-Anatomy of

ORGANIZATION OF THE NERVOUS SYSTEM
BRAIN SPINAL CORD CENTRAL NERVOUS SYSTEM (CNS) AFFERENT NERVES EFFERENT NERVES PERIPHERAL NERVOUS SYSTEM EXTERO- RECEPTORS INTERO- RECEPTORS SOMATIC AUTONOMIC SMOOTH AND CARDIAC MUSCLES AND GLANDS EFFECTOR ORGANS SKELETAL MUSCLES1

Functions of the Nervous System
1-Sensory input: Monitor internal and external stimuli (change) Touch, odor, sound, vision, taste, bp, body temp. 2-Integration. Brain and spinal cord process sensory input and initiate responses 3-Motor output: Controls of muscles and glands 4-Homeostasis. Regulate and coordinate physiology 5-Mental activity. Consciousness, thinking, memory, emotion

MAINTENANCE AND PROTECTION OF THE CNS
1-Glial Cells: physical and metabolic support 2-Skull and Spinal Column 3-Cerebrospinal fluid 4-Blood-brain barrier 5-Blood supply

The Nervous System Components Subdivisions
Brain, spinal cord, nerves, and sensory receptors Subdivisions Central nervous system (CNS): brain and spinal cord Peripheral nervous system (PNS) Nerves: Sensory and Motor

Peripheral Nervous System
Outside the CNS Divided into Sensory (Afferent) Division -incoming information Motor (Efferent Division - outgoing information Sensory Division Use sensory neurons to transmit nerve impulses toward the brain and spinal cord Receptors in various body locations react to stimuli (touch, pressure, heat, stretch, light, etc) and trigger a nerve impulse in the sensory neuron Motor Division Use motor neurons to transmit nerve impulses away from the brain and spinal cord Stimulate effectors (muscle and glands)

Divisions of PNS Sensory (afferent): transmits nerve impulses from receptors to CNS. Motor (efferent): transmits nerve impulses from CNS to effectors (muscles, glands)

Types of Sensory and Motor Information

Sensory Division of the PNS
Transmit nerve impulses over sensory neurons to the CNS from receptors Receptors are classified as: Somatic receptors - those found in skin, joints, skeletal muscles, and special sense organs Respond to touch, pressure, heat, stretch, pain, light Visceral receptors - located in walls of viscera Respond to stretch, pain, temperature, chemical stimuli (CO2)

Motor Division of PNS Transmits impulses away from the CNS to effectors Effector - any muscle or gland Somatic nervous system: Regulates contraction of skeletal muscles. Under our voluntary control - I.e., under conscious control Autonomic nervous system (ANS) Regulates contraction of smooth muscle, cardiac muscle and glands (visceral organs) Subconscious or involuntary control. Divisions of the ANS Sympathetic. Prepares body for physical activity. Parasympathetic. Regulates resting or vegetative functions such as digesting food or emptying of the urinary bladder.

Cells of Nervous System
Neurons The functional unit of the nervous system Transmit electrical signals (action potentials) to other neurons or effectors Neuroglia (Glial cells) Nonexcitable Support and protect neurons

The Neuron Special characteristics of neurons
Longevity – can live and function for a lifetime Do not divide (amitotic) – fetal neurons lose their ability to undergo mitosis; neural stem cells are an exception High metabolic rate – require abundant oxygen and glucose

Parts of the Neuron Cell Body. Aka Soma or Perikaryon
Contains usual organelles plus other structures Nissl bodies = chromatophilic substance = rough E.R: primary site of protein synthesis Cytoskeleton of neurofilaments and neurotubules No centrioles (hence its amitotic nature) Major biosynthetic center Most neuronal cell bodies Located within CNS Ganglia - clusters of cell bodies that lie along nerves in PNS Tapers to form axon hillock

Neuron Processes Dendrites: short, often highly branched.
Receptive regions of the neuron Axons. Long cytoplasmic process capable of propagating a nerve impulse Neuron has only one Transmits impulse away from soma Axon hillock: Initial segment Few, if any, branches along length Multiple branches at end of axon Terminal branches (telodendria) End in knobs called axon terminals (aka synaptic terminals, end bulbs, boutons, synaptic knobs) Contain vesicles filled with neuro- transmitter (NT)

Axoplasmic Transport Anterograde: Retrograde
Axoplasm moved from cell body toward terminals. Supply materials for growth, repair, renewal. Can move cytoskeletal proteins, organelles away from cell body toward axon terminals. Retrograde Away from axonal terminal toward the cell body Damaged organelles, recycled plasma membrane, and substances taken in by endocytosis can be transported up axon to cell body. Rabies and herpes virus can enter axons in damaged skin and be transported to CNS. Would include toxins such as heavy metals (the chemical, not the noise)

Classification of Neurons
Structural classification Multipolar – possess more than two processes Numerous dendrites and one axon Bipolar – possess two processes Rare neurons – found in some special sensory organs Unipolar (pseudounipolar) – possess one short, single process Start as bipolar neurons during development

Neurons Classified by Structure
Figure 12.10a–c

Structural Classes of Neurons
Table

Functional Classification of Neurons
According to the direction the nerve impulse travels Sensory (afferent) neurons – transmit impulses toward the CNS Virtually all are unipolar neurons Cell bodies in ganglia outside the CNS Short, single process divides into The central process – runs centrally into the CNS The peripheral process – extends peripherally to the receptors

Functional Classification of Neurons
Motor (efferent) neurons Carry impulses away from the CNS to effector organs Most motor neurons are multipolar Cell bodies are within the CNS Form junctions with effector cells Interneurons (association neurons) – most are multipolar Lie between 2 neurons Confined to the CNS

Neurons Classified by Function
Figure 12.11

Supporting Cells (Neuroglial Cells) in the CNS
Neuroglia – usually only refers to supporting cells in the CNS Glial cells have branching processes and a central cell body Outnumber neurons 10 to 1 Make up half the mass of the brain Can divide throughout life May divide abnormally - glioma - brain cancer Do not transmit nerve impulses

Neuroglia of CNS: Astrocytes
Largest and most numerous Functions include: 1. Form the blood-brain barrier Take up and release ions (Na, K) to control the environment around neurons Regulate what substances reach the CNS from the blood 2. Reapture and recycle neurotrans-mitters 3. Involved with synapse formation in developing neural tissue 4. Aid in repair of damaged neural tissue 5. Produce molecules necessary for neural growth (BDTF)

Neuroglia of CNS: Ependymal Cells
Line brain ventricles and spinal cord central canal. Specialized versions of ependymal form choroid plexuses. Choroid plexus Secrete cerebrospinal fluid. Cilia help move fluid thru the cavities of the brain.

Neuroglia of CNS: Microglia and Oligodendrocytes
Microglia: specialized macrophages. Respond to inflammation, phagocytize necrotic tissue, microorganisms, and foreign substances that invade the CNS. Oligodendrocytes: form myelin sheaths if surrounding axon. Single oligodendrocytes can form myelin sheaths around portions of several axons.

Neuroglia of PNS Schwann cells or neurolemmocytes:
Wrap around portion of only one axon to form myelin sheath. Wrap around many times. As cells grow around axon, cytoplasm is squeezed out and multiple layers of cell membrane wrap the axon. Cell membrane primarily phospholipid. Outer surface of Schwann cell called the neurilemma Satellite cells: surround neuron cell bodies in ganglia, provide support and nutrients

Myelin Sheaths Segmented structures composed of the lipoprotein myelin
Surround thicker axons Form an insulating layer Prevent leakage of electrical current Increase the speed of impulse conduction

Myelin Sheaths in the PNS
Formed by Schwann cells Develop during fetal period and in the first year of postnatal life Schwann cells wrap in concentric layers around the axon Cover the axon in a tightly packed coil of membranes Neurilemma – material external to myelin layers Nodes of Ranvier – gaps along axon Degeneration of myelin sheaths occurs in multiple sclerosis and some cases of diabetes mellitus.

Structure of a Nerve A. Note the similarity of a nerve to a muscle
Just as a muscle is a collection of muscle fibers, a nerve is a collection of nerve fibers (axons). Each is broken up in smaller units known as fascicles Each is covered by connective tissue: Epimysium vs. Epineurium Perimysium vs. Perineurium Endomysium vs. Endoneurium Figure 12.16a

Nerve Fiber Types Type A fibers large-diameter nerve
Heavily myelinated; conduct impulses at m/sec Motor neurons supplying skeletal muscles Type B medium-diameter nerves lightly myelinated; conduct at 3-15 m/sec Sensory nerves from sensory receptors Type C: Very small diameter Unmyelinated; conduct at 2 m/sec or less Part of ANS Innervate visceral smooth muscle and glands

The Synapse Site at which neurons communicate
Signals pass across synapse in one direction Types of cells in synapse Presynaptic neuron - conducts impulse toward the synapse Postsynaptic neuron - conducts impulse away from the synapse Average postsynaptic neuron has up to 10,000 synapses Some in cerebellum have up to 100,000 synapses Two major types of synapses Electrical - not common in nervous system Chemical - most common type

Types of Chemical Synapses
Axodendritic Between axon terminals of presynaptic neuron and dendrite of postsynaptic neuron Most common type of synapse Axosomatic Between axon of pre- and soma (cell body) of post-synaptic neuron Axoaxonic Between two axons Not common

Types of Neural Synapses

Chemical Synapse vesicles that contain neurotrans-
Presynaptic bulb has secretory vesicles that contain neurotrans- mitter chemical (NT) NT must pass across the synaptic cleft, space that separates pre- and postsynaptic membranes Postsynaptic membrane contains receptors specific for each type of NT Binding of NT to its receptor causes ion channels to open or close Postsynaptic membrane is thus either stimulated or inhibited

Basic Neuronal Organization of the Nervous System
Reflex arcs – simple chains of neurons Explain reflex behaviors Determine structural plan of the nervous system Responsible for reflexes Rapid, autonomic motor responses Can be visceral or somatic

Five Essential Components to the Reflex Arc
Receptor – site where stimulus acts Sensory neuron – transmits afferent impulses to the CNS Integration center – consists of one or more synapses in the CNS Motor neuron – conducts efferent impulses from integration center to an effector Effector – muscle or gland Responds to efferent impulses Contracting or secreting

Types of Reflexes Monosynaptic reflex – simplest of all reflexes
Just one synapse The fastest of all reflexes Example – knee-jerk reflex Polysynaptic reflex – more common type of reflex Most have a single interneuron between the sensory and motor neuron Example – withdrawal reflexes

Types of Reflexes

Simplified Design of the Nervous System
Three-neuron reflex arcs Basis of the structural plan of the nervous system Similar reflexes are associated with the brain

Sensory neurons – located dorsally Cell bodies outside the CNS in sensory ganglia Central processes enter dorsal aspect of the spinal cord Motor neurons – located ventrally Axons exit the ventral aspect of the spinal cord Interneurons – located centrally Synapse with sensory neurons

Human nervous system is complex Interneurons also include neurons confined to CNS Long chains of interneurons between sensory and motor neurons

Neuronal Pathways and Circuits
Organization of neurons in CNS varies in complexity Convergent pathways: many neurons converge and synapse with smaller number of neurons. E.g., synthesis of data in brain. Divergent pathways: small number of presynaptic neurons synapse with large number of postsynaptic neurons. E.g., important information can be transmitted to many parts of the brain.

Disorders of the Nervous System
Multiple sclerosis – common cause of neural disability Varies widely in intensity among those affected Cause is incompletely understood An autoimmune disease Immune system attacks the myelin around axons in the CNS

Neuronal Regeneration
Neural injuries may cause permanent dysfunction If axons alone are destroyed, cells bodies often survive and the axons may regenerate PNS – macrophages invade and destroy axon distal to the injury Axon filaments grow peripherally from injured site Partial recovery is sometimes possible CNS – neuroglia never form bands to guide regrowing axons and may hinder axon growth with growth-inhibiting chemicals No effective regeneration after injury to the spinal chord and brain

Regeneration of the Peripheral Nerve Fiber

The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals contains the majority of the nervous system and consists of the brain and the spinal cord.

Neuroanatomy The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals contains the majority of the nervous system and consists of the brain and the spinal cord. Some classifications also include the retina and the cranial nerves in the CNS. Together with the peripheral nervous system, it has a fundamental role in the control of behavior. The CNS is contained within the dorsal cavity, with the brain in the cranial cavity and the spinal cord in the spinal cavity. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae, and both are enclosed in the meninges

Developments During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens as ridges on either side of the groove (the neural folds) become elevated, and ultimately meet, transforming the groove into a closed tube, the ectodermal wall of which forms the rudiment of the nervous system. This tube initially differentiates into three vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon.

the rhombencephalon. the prosencephalon at the front,
This tube initially differentiates into three vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon.

As the vertebrate grows, these vesicles differentiate further still.
The telencephalon differentiates into, among other things, the striatum, the hippocampus and the neocortex, and its cavity becomes the first and second ventricles. Diencephalon elaborations include the subthalamus, hypothalamus, thalamus and epithalamus, and its cavity forms the third ventricle.

The tectum, pretectum, cerebral peduncle and other structures develop out of the mesencephalon, and its cavity grows into the mesencephalic duct (cerebral aqueduct). The metencephalon becomes, among other things, the pons and the cerebellum, the myelencephalon forms the medulla oblongata, and their cavities develop into the fourth ventricle.

The human brain The human brain has the same general structure as the brains of other mammals, but is larger than expected on the basis of body size among other primates Estimates for the number of neurons (nerve cells) in the human brain range from 80 to 120 billion.Most of the expansion comes from the cerebral cortex, especially the frontal lobes, which are associated with executive functions such as self-control, planning, reasoning, and abstract thought. The portion of the cerebral cortex devoted to vision is also greatly enlarged in human beings, and several cortical areas play specific roles in language, a skill that is unique to humans.

The human brain Despite being protected by the thick bones of the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier, the human brain is susceptible to many types of damage and disease. The most common forms of physical damage are closed head injuries such as a blow to the head, a stroke, or poisoning by a variety of chemicals that can act as neurotoxins. Infection of the brain, though serious, is rare due to the biological barriers which protect it. The human brain is also susceptible to degenerative disorders, such as Parkinson's disease, multiple sclerosis, and Alzheimer's disease. A number of psychiatric conditions, such as schizophrenia and depression, are thought to be associated with brain dysfunctions, although the nature of such brain anomalies is not well understood

Contents 1 Structure 1.1 General features 1.2 Cortical divisions
1.2.1 Four lobes 1.2.2 Major folds 1.3 Functional divisions 1.3.1 Cytoarchitecture 1.3.2 Topography

2 Cognition 3 Lateralization 4 Development 5 Evolution 6 Sources of information 6.1 EEG 6.2 MEG 6.3 Structural and functional imaging 6.4 Effects of brain damage 7 Language 8 Pathology 9 Metabolism

Brain size The adult human brain weighs on average about 3 lb (1.5 kg)] with a size (volume) of around 1130 cubic centimetres (cm3) in women and 1260 cm3 in men, although there is substantial individual variation. Neanderthals, an extinct subspecies of modern humans, had larger brains at adulthood than present-day humans. Men with the same body height and body surface area as women have on average 100g heavier brains, although these differences do not correlate in any simple way with gray matter neuron counts or with overall measures of cognitive performance

The brain is very soft, having a consistency similar to soft gelatin or soft tofu.
Despite being referred to as "grey matter", the live cortex is pinkish-beige in color and slightly off-white in the interior. At the age of 20, a man has around 176,000 km and a woman about 149,000 km of myelinated axons in their brains

General features The cerebral hemispheres form the largest part of the human brain and are situated above most other brain structures. They are covered with a cortical layer with a convoluted topography. Underneath the cerebrum lies the brainstem, resembling a stalk on which the cerebrum is attached. At the rear of the brain, beneath the cerebrum and behind the brainstem, is the cerebellum, a structure with a horizontally furrowed surface that makes it look different from any other brain area. The same structures are present in other mammals, although the cerebellum is not so large relative to the rest of the brain. As a rule, the smaller the cerebrum, the less convoluted the cortex. The cortex of a rat or mouse is almost completely smooth. The cortex of a dolphin or whale, on the other hand, is more convoluted than the cortex of a human.

General features The dominant feature of the human brain is corticalization. The cerebral cortex in humans is so large that it overshadows every other part of the brain. A few subcortical structures show alterations reflecting this trend. The cerebellum, for example, has a medial zone connected mainly to subcortical motor areas, and a lateral zone connected primarily to the cortex. In humans the lateral zone takes up a much larger fraction of the cerebellum than in most other mammalian species. Corticalization is reflected in function as well as structure. The cerebral cortex is essentially a sheet of neural tissue, folded in a way that allows a large surface area to fit within the confines of the skull. Each cerebral hemisphere, in fact, has a total surface area of about 1.3 square feet.[16] Anatomists call each cortical fold a sulcus, and the smooth area between folds a gyrus

Four lobes Cortical divisions

Four lobes The four lobes of the cerebral cortex
The cerebral cortex is nearly symmetrical, with left and right hemispheres that are approximate mirror images of each other. Anatomists conventionally divide each hemisphere into four "lobes", the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. This division into lobes does not actually arise from the structure of the cortex itself, though: the lobes are named after the bones of the skull that overlie them, the frontal bone, parietal bone, temporal bone, and occipital bone. The borders between lobes are placed beneath the sutures that link the skull bones together. There is one exception: the border between the frontal and parietal lobes is shifted backward from the corresponding suture, to the central sulcus, a deep fold that marks the line where the primary somatosensory cortex and primary motor cortex come together.

Because of the arbitrary way most of the borders between lobes are demarcated, they have little functional significance. With the exception of the occipital lobe, a small area that is entirely dedicated to vision, each of the lobes contains a variety of brain areas that have minimal functional relationship. The parietal lobe, for example, contains areas involved in somatosensation, hearing, language, attention, and spatial cognition. In spite of this heterogeneity, the division into lobes is convenient for reference, and is universally used.

The frontal lobe The frontal lobe is located at the front of the brain and is associated with reasoning, motor skills, higher level cognition, and expressive language. At the back of the frontal lobe, near the central sulcus, lies the motor cortex. This area of the brain receives information from various lobes of the brain and utilizes this information to carry out body movements. Damage to the frontal lobe can lead to changes in sexual habits, socialization, attention as well as increased risk-taking

Frontal Lobe Behavior ,Abstract thought processes ,Problem solving ,Attention , Creative thought ,Some emotion ,Intellect ,Reflection ,Judgment ,Initiative , Inhibition ,Coordination of movements ,Generalized and mass movements , Some eye movements ,Sense of smell ,Muscle movements ,Skilled movements ,Some motor skills ,Physical reaction, Libido (sexual urges)

The parietal lobe The parietal lobe is located in the middle section of the brain and is associated with processing tactile sensory information such as pressure, touch, and pain. A portion of the brain known as the somatosensory cortex is located in this lobe and is essential to the processing of the body's senses. Damage to the parietal lobe can result in problems with verbal memory, an impaired ability to control eye gaze and problems with language among other ailments.

Parietal Lobe Sense of touch (tactile senstation)
Appreciation of form through touch (stereognosis) Response to internal stimuli (proprioception) Sensory combination and comprehension Some language and reading functions Some visual functions

The temporal lobe The temporal lobe is located on the bottom section of the brain. This lobe is also the location of the primary auditory cortex, which is important for interpreting sounds and the language we hear. The hippocampus is also located in the temporal lobe, which is why this portion of the brain is also heavily associated with the formation of memories. Damage to the temporal lobe can lead to problems with memory, speech perception and language skills.

Temporal Lobe Auditory memories Some hearing Visual memories
Some vision pathways Other memory Music Fear Some language Some speech Some behavior amd emotions Sense of identity

The occipital lobe The occipital lobe is located at the back portion of the brain and is associated with interpreting visual stimuli and information. The primary visual cortex, which receives and interprets information from the retinas of the eyes, is located in the occipital lobe. Damage to this lobe can cause visual problems such as difficulty recognizing objects, an inability to identify colors and trouble recognizing words.

Occipital Lobe Vision Reading

Corpus Callosum Right Hemisphere (the representational hemisphere)
The right hemisphere controls the left side of the body Temporal and spatial relationships Analyzing nonverbal information Communicating emotion Left Hemisphere (the categorical hemisphere) The left hemisphere controls the right side of the body Produce and understand language Corpus Callosum Communication between the left and right side of the brain

THE CEREBELLUM Balance Posture Cardiac, respiratory, and vasomotor centers THE BRAIN STEM Motor and sensory pathway to body and face Vital centers: cardiac, respiratory, vasomotor

Hypothalamus Moods and motivation Sexual maturation Temperature regulation Hormonal body processes Optic Chiasm Vision and the optic nerve

Pituitary Gland Hormonal body processes Physical maturation Growth (height and form) Sexual maturation Sexual functioning Spinal Cord Conduit and source of sensation and movement Pineal Body Unknown Ventricles and Cerebral Aqueduct Contains the cerebrospinal fluid that bathes the brain and spinal cord

. The Hindbrain The hindbrain is the structure that connects the spinal cord to the brain. The medulla is located directly above the spinal cord and controls many vital autonomic functions such as heart rate, breathing and blood pressure. The pons connects the medulla to the cerebellum and helps coordinate movement on each side of the body. The reticular formation is a neural network located in the medulla that helps control functions such as sleep and attention. The Brain Stem The brain stem is comprised of the hindbrain and midbrain. The hindbrain contains structures including medulla, the pons and the reticular formation

The midbrain is the smallest region of the brain that acts as a sort of relay station for auditory and visual information. The midbrain controls many important functions such as the visual and auditory systems as well as eye movement. Portions of the midbrain called the red nucleus and the substantia nigra are involved in the control of body movement. The darkly pigmented substantia nigra contains a large number of dopamine-producing neurons are located. The degeneration of neurons in the substantia nigra is associated with Parkinson’s disease. The Midbrain

The Cerebellum Sometimes referred to as the "little brain," the cerebellum lies on top of the pons, behind the brain stem. The cerebellum is comprised of small lobes and receives information from the balance system of the inner ear, sensory nerves, and the auditory and visual systems. It is involved in the coordination of motor movements as well as basic facets of memory and learning.

The Thalamus Located above the brainstem, the thalamus processes and relays movement and sensory information. It is essentially a relay station, taking in sensory information and then passing it on to the cerebral cortex. The cerebral cortex also sends information to the thalamus, which then sends this information to other systems.

The Hypothalamus The hypothalamus is a grouping of nuclei that lie along the base of the brain near the pituitary gland. The hypothalamus connects with many other regions of the brain and is responsible for controlling hunger, thirst, emotions, body temperature regulation, and circadian rhythms. The hypothalamus also controls the pituitary gland by secreting hormones, which gives the hypothalamus a great deal of control over many body functions

The Limbic System The amygdala is one of the major structures found in the limbic system. The limbic system is comprised of four main structures: the amygdala, the hippocampus, regions of the limbic cortex and the septal area. These structures form connections between the limbic system and the hypothalamus, thalamus and cerebral cortex. The hippocampus is important in memory and learning, while the limbic system itself is central in the control of emotional responses.

The Basal Ganglia The basal ganglia are a group of large nuclei that partially surround the thalamus. These nuclei are important in the control of movement. The red nucleus and substantia nigra of the midbrain have connections with the basal ganglia.

Major folds: Major gyri and sulci on the lateral surface of the cortex Although there are enough variations in the shape and placement of gyri and sulci (cortical folds) to make every brain unique, most human brains show sufficiently consistent patterns of folding that allow them to be named. Many of the gyri and sulci are named according to the location on the lobes or other major folds on the cortex. These include: Superior, Middle, Inferior frontal gyrus: in reference to the frontal lobe Precentral and Postcentral sulcus: in reference to the central sulcus Trans-occipital sulcus: in reference to the occipital lobe Deep folding features in the brain, such as the inter-hemispheric and lateral fissure, which divides the left and right brain, and the lateral sulcus, which "splits-off" the temporal lobe, are present in almost all normal subjects

Functional divisions Researchers who study the functions of the cortex divide it into three functional categories of regions, or areas. One consists of the primary sensory areas, which receive signals from the sensory nerves and tracts by way of relay nuclei in the thalamus. Primary sensory areas include the visual area of the occipital lobe, the auditory area in parts of the temporal lobe and insular cortex, and the somatosensory area in the parietal lobe. A second category is the primary motor area, which sends axons down to motor neurons in the brainstem and spinal cord. This area occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The third category consists of the remaining parts of the cortex, which are called the association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex process that we call perception, thought, and decision making.

The end

Cytoarchitecture

Cytoarchitecture Different parts of the cerebral cortex are involved in different cognitive and behavioral functions. The differences show up in a number of ways: the effects of localized brain damage, regional activity patterns exposed when the brain is examined using functional imaging techniques, connectivity with subcortical areas, and regional differences in the cellular architecture of the cortex. Anatomists describe most of the cortex—the part they call isocortex—as having six layers, but not all layers are apparent in all areas, and even when a layer is present, its thickness and cellular organization may vary. Several anatomists have constructed maps of cortical areas on the basis of variations in the appearance of the layers as seen with a microscope. One of the most widely used schemes came from Brodmann, who split the cortex into 51 different areas and assigned each a number (anatomists have since subdivided many of the Brodmann areas). For example, Brodmann area 1 is the primary somatosensory cortex, Brodmann area 17 is the primary visual cortex, and Brodmann area 25 is the anterior cingulate cortex

Topography Topography of the primary motor cortex, showing which body part is controlled by each zone

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