Department of foreign Languages
Student Individual work
Theme: The brain
Prepared by:Baymetov D
Group no:222 group
Karaganda state medical university
- The brain
- Brain function
- The structure of the brain
- The anatomy brain
- The physiology brain
- his article is about the brains
of all types of animals, including humans. For information specific
to the human brain, see Human brain. For other uses, see Brain (disambiguation).
- A chimpanzee brain
- The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only
a few invertebrates such as sponges, jellyfish, adultsea squirts and starfish do not have one, even if diffuse neural tissue is present. It
is located in the head, usually close to the primary sensory organs
for such senses as vision, hearing, balance, taste, and smell. The brain
of a vertebrate is the most complex organ of its body. In a typical
human thecerebral cortex (the largest part)
is estimated to contain 15–33
The most important is brain disease and the effects of brain damage,
covered in the human brain article because the most common diseases
of the human brain either do not show up in other species, or else manifest
themselves in different ways.
The shape and size of the brains of different species
vary greatly, and identifying common features is often difficult.Nevertheless, there are a number of principles of brain architecture
that apply across a wide range of species. Some aspects of brain structure are common to almost
the entire range of animals species.]
- The simplest way to gain information about brain
anatomy is by visual inspection, but many more sophisticated techniques
have been developed. Brain tissue in its natural state is too soft to
work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior. Visually,
the interior of the brain consists of areas of so-called grey
matter, with a dark color, separated by areas of white
matter, with a lighter color. Further information
can be gained by staining slices of brain tissue with a variety of chemicals
that bring out areas where specific types of molecules are present in
high concentrations. It is also possible to examine the microstructure
of brain tissue using a microscope, and to trace the pattern of connections
from one brain area to another.
The brains of all species are
composed primarily of two broad classes of cells: neurons and glial cells. Glial cells
(also known as glia or neuroglia) come in several types, and perform a number of critical functions,
including structural support, metabolic support, insulation, and guidance
The property that makes neurons unique is their ability
to send signals to specific target cells over long distances. They
send these signals by means of an axon, which is a thin protoplasmic fiber that extends from the cell body
and projects, usually with numerous branches, to other areas, sometimes
nearby, sometimes in distant parts of the brain or body. The length
of an axon can be extraordinary: for example, if a pyramidal
cell of the cerebral
cortex were magnified so that its cell body
became the size of a human body, its axon, equally magnified, would
become a cable a few centimeters in diameter, extending more than a
kilometer. These axons transmit signals
in the form of electrochemical pulses called action
potentials, which last less than a thousandth
of a second and travel along the axon at speeds of 1–100 meters per second. Some
neurons emit action potentials constantly, at rates of 10–100 per second, usually in
irregular patterns; other neurons are quiet most of the time, but occasionally
emit a burst of action potentials.
includes arthropods, molluscs, and numerous types of worms. The diversity of
invertebrate body plans is matched by an equal diversity in brain structures.
of invertebrates have notably complex brains: arthropods (insects, crustaceans, arachnids, and others), and cephalopods (octopuses,squids, and similar molluscs).The brains of arthropods and cephalopods arise from twin parallel
nerve cords that extend through the body of the animal.
The first vertebrates appeared over 500 million years ago (Mya), during the Cambrian period, and may have resembled the modern hagfish in form. Sharks appeared about 450 Mya,
amphibians about 400 Mya,
reptiles about 350 Mya,
and mammals about 200 Mya.
No modern species should be described as more "primitive"
than others, strictly speaking, since each has an equally long evolutionary history—but the brains of modern hagfishes, lampreys, sharks, amphibians, reptiles, and mammals show a gradient of size
and complexity that roughly follows the evolutionary sequence.
- The medulla, along
with the spinal cord, contains many small nuclei involved in a wide
variety of sensory and motor functions.
- The pons lies in the brainstem
directly above the medulla. Among other things, it contains nuclei that
control sleep, respiration, swallowing, bladder function, equilibrium,
eye movement, facial expressions, and posture.
- The hypothalamus is
a small region at the base of the forebrain, whose complexity and importance
belies its size. It is composed of numerous small nuclei, each with
distinct connections and neurochemistry. The hypothalamus regulates
sleep and wake cycles, eating and drinking, hormone release, and many
other critical biological functions.
- The thalamus is
another collection of nuclei with diverse functions. Some are involved
in relaying information to and from the cerebral hemispheres. Others
are involved in motivation.
- The cerebellum modulates
the outputs of other brain systems to make them precise. Removal of
the cerebellum does not prevent an animal from doing anything in particular,
but it makes actions hesitant and clumsy. This precision is not built-in,
but learned by trial and error. Learning how to ride a bicycle is an
example of a type of neural plasticity that may take place largely within
- The optic tectum allows
actions to be directed toward points in space, most commonly in response
to visual input. In mammals it is usually referred to as the superior colliculus, and
its best-studied function is to direct eye movements. It also directs
reaching movements and other object-directed actions. It receives strong
visual inputs, but also inputs from other senses that are useful in
directing actions, such as auditory input in owls and input from the thermosensitive pit organs in snakes. In some fishes, such as lampreys,
this region is the largest part of the brain. The superior colliculus is part of the midbrain.
- The pallium is
a layer of gray matter that lies on the surface of the forebrain. In
reptiles and mammals, it is called the cerebral cortex. Multiple functions involve the pallium, including olfaction and spatial memory. In
mammals, where it becomes so large as to dominate the brain, it takes
over functions from many other brain areas. In many mammals, the cerebral
cortex consists of folded bulges called gyri that create deep furrows or fissures called sulci. The
folds increase the surface area of the cortex and therefore increase
the amount of gray matter and the amount of information that can be
- The hippocampus, strictly
speaking, is found only in mammals. However, the area it derives from,
the medial pallium, has counterparts in all vertebrates. There
is evidence that this part of the brain is involved in spatial memory
and navigation in fishes, birds, reptiles, and mammals.
- The functions of the brain depend on the ability
of neurons to transmit electrochemical signals to other cells, and their
ability to respond appropriately to electrochemical signals received
from other cells. The electrical
properties of neurons are controlled
by a wide variety of biochemical and metabolic processes, most notably
the interactions between neurotransmitters and receptors that take place
- All vertebrates have a blood–brain barrier that allows metabolism
inside the brain to operate differently from metabolism in other parts
of the body. Glial cells play a major role in
brain metabolism, by controlling the chemical composition of the fluid
that surrounds neurons, including levels of ions and nutrients.
- Brain tissue consumes a large
amount of energy in proportion to its volume, so large brains place
severe metabolic demands on animals. The need to limit body weight in
order, for example, to fly, has apparently led to selection for a reduction
of brain size in some species, such as bats. Most of the brain's energy
consumption goes into sustaining the electric charge (membrane
potential) of neurons. Most vertebrate species devote
between 2% and 8% of basal metabolism to the brain
- From an evolutionary-biological perspective, the
function of the brain is to provide coherent control over the actions
of an animal. A centralized brain allows groups of muscles to be co-activated
in complex patterns; it also allows stimuli impinging on one part of
the body to evoke responses in other parts, and it can prevent different
parts of the body from acting at cross-purposes to each other.
- To generate purposeful and unified action, the brain
first brings information from sense organs together at a central location.
It then processes this raw data to extract information about the structure
of the environment. Next it combines the processed sensory information
with information about the current needs of an animal and with memory
of past circumstances. Finally, on the basis of the results, it generates
motor response patterns that are suited to maximize the welfare of the
animal. These signal-processing tasks require intricate interplay between
a variety of functional subsystems.
One of the primary functions of a brain is to extract
biologically relevant information from sensory inputs. The human brain
is provided with information about light, sound, the chemical composition
of the atmosphere, temperature, head orientation, limb position, the
chemical composition of the bloodstream, and more. In other animals
additional senses may be present, such as the infrared heat-sense of
snakes, the magnetic field sense of some birds, or the electric field
sense of some types of fish.
systems are areas of the brain
that are directly or indirectly involved in producing body movements,
that is, in activating muscles. Except for the muscles that control
the eye, which are driven by nuclei in the midbrain, all the voluntary
muscles in the body are directly innervated by motor
neurons in the spinal cord and
hindbrain. Spinal motor neurons are controlled
both by neural circuits intrinsic to the spinal cord, and by inputs
that descend from the brain. The intrinsic spinal circuits implement
many reflex responses, and contain pattern
generators for rhythmic movements
such as walking or swimming. The descending connections from the brain
allow for more sophisticated control.
- The brain contains several motor areas that
project directly to the spinal cord. At the lowest level are motor areas
in the medulla and pons, which control stereotyped
movements such as walking, breathing, or swallowing.