THE%20BRAIN%20AND%20FIVE%20SENSES%20

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THE BRAIN AND FIVE SENSES AP Biology

• BRAIN- responsible for overseeing the daily
  operations of the human body and for interpreting
  the vast amount of information received The adult
  human body brain weighs an average of 1.4 kg or
  about 2 of the total body weight.

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• The Brain is the main switching unit of the
  central nervous system it is the place to which
  impulses flow and from which impulses originate.
• The Spinal Cord provides the link between the
  brain and the rest of the body.

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• THE BRAIN HAS THREE MAIN PARTS
• 1) Cerebrum
• 2) Cerebellum
• 3) Brain stem
• -the brain is protected by a bony covering
  called the SKULL.
• Its also wrapped in three layers of connective
  tissue called the MENINGES.

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CEREBROSPINAL FLUID In spinal column, around
brain and in ventricles.

• CSF is a clear liquid that protects the brain
  from mechanical injury by acting as shock
  absorber.
• VENTRICLES Cerebrospinal fluid that separates
  the middle and inner meninges and fills four
  interconnected cavities in the brain.
• In order for the brain to perform its functions
  it must have a constant supply of food and oxygen.

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PARTS OF THE BRAIN

• THE CEREBRUM control center of the brain
• The largest and most prominent part of the human
  brain is the cerebrum (85 of the mass of the
  brain)
• Responsible for all voluntary activities. The
  site of INTELLIGENCE, LEARNING AND JUDGEMENT.
• It functions in language, conscious thought,
  memory, personality development, vision and other
  sensations.

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TWO HEMISPHERES

• -The left and the right cerebral hemispheres.
• -There is a DEEP GROOVE that separates the two
  hemisphere- they are connected in the region
  known as CORPUS CALLOSUM.
• -The right and left cerebral hemispheres are
  linked by a bundle of neurons called a tract.
• -It contains thick layers of unmyelinated neurons
  which look gray(GRAY MATER). Myelin makes neurons
  look white.

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FOUR REGIONS

• LOBES These lobes are named for the skull bones
  that cover them -FRONTAL,PARIETAL,TEMPORAL AND
  OCCIPITAL .
• Scientist have discovered that the left side of
  the body sends sensations to the right hemisphere
  of the cerebrum, and the right side of the body
  send its sensations to the left hemisphere. See
  picture on the next slide.

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• The right hemisphere associated with creativity
  and artistic ability while the left hemisphere
  with analytical and mathematical ability. To test
  yourself, take this online quiz
  http//www.web-us.com/brain/braindominance.htm
• Sometimes blood vessels in the brain are blocked
  by blood clots causing a disorder called stroke.

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CEREBELLUM

• Second largest part of the brain and is located
  at the back of the skull.
• Coordinates muscle movement, balance, posture and
  coordination.
• Receives sensory impulses from muscles, tendons,
  joints, eyes and ears.
• Processes information about position and controls
  posture by keeping skeletal muscles in a constant
  state of partial contraction.

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BRAIN STEM

• Connects the brain to the spinal cord. Maintains
  life support systems!
• Consists of 1) medulla oblongata This section of
  the brain helps transfer messages to the spinal
  cord and the thalamus in the brain from the body
  and controls breathing, heart function, blood
  vessel function, digestion, sneezing, and
  swallowing. Sensory and motor neurons from the
  forebrain and midbrain travel through the
  medulla. 2) Pons The pons is a portion of the
  brain located above the medulla oblongata and
  below the midbrain. Although it is small, at
  roughly 2.5 centimeters long, it serves several
  important functions as it serves as a bridge
  between various parts of the nervous system,
  including the cerebellum and cerebrum.

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SENSORY SYSTEM

• Sensory receptors react directly to stimulation
  from the environment.
• Sense organs receive information from the
  environment and relay the messages to the brain.
• Examples of stimulation are ( LIGHT, SOUND,
  MOTION, CHEMICAL, PRESSURE, PAIN, and CHANGES IN
  TEMPERATURE).

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SENSORY RECEPTORS

• Are neurons that are specialized to detect the
  stimuli they respond to
• Mechanoreceptors- respond to movement, pressure
  and tension (sound, touch)
• Photoreceptors (RODS AND CONES)- respond to
  light energy
• Chemoreceptors - respond to chemical substances
  like oxygen levels in blood, smells and food
• Thermoreceptors - respond to changes in
  temperature, skin
• Pain receptors - respond to tissue damage-PAIN

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FIVE SENSES

• SIGHT-HEARING-SMELL-TASTE-TOUCH
• Organs eyes, ears, nose, taste buds and hands
  (skin)
• These receptors convert the energy of a stimulus
  into an electrical energy impulse that can travel
  in the NERVOUS SYSTEMS

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Hearing and Balance

• The ear is really two sense organs in one -not
  only detecting sound waves but also sensing the
  position of the head (whether it is moving in a
  straight line or rotating).
• Consists of the visible fleshly part which helps
  to collect sound and funnel it into the auditory
  canal, to the tympanic membrane (also called
  eardrum).
• The AUDITORY CANAL- contains small hair and wax
  producing glands that prevent foreign objects
  from entering the ear.

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Inner Ear

• Sound variations strike the eardrum and are
  transmitted into three tiny bones the
  malleus(HAMMER), incus (ANVIL) and
  STAPES(stirrup).
• THE STIRRUP TRANSFERS THE VIBRATIONS TO A THIN
  MEMBRANE CALLED OVAL WINDOW.
• This membrane transmits the vibrations to the
  cochlea which begins the inner ear.

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Inner ear contd

• The COCHLEA is snail shaped and consists of fluid
  filled chambers that are separated by membranes.
• Organ of Corti contains hair cells that synapse
  with nerve fibers of the cohlear nerve.
• These nerve impulses are carried to the brain by
  the AUDITORY OR ACOUSTIC NERVE
• The ears also contain structures for detecting
  stimuli that make us aware of our movement and
  allow us to maintain our BALANCE.

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EYE- VISION

• The organ we use to sense light is the eye.
• Composed of three layers 1)outer layer-consists
  of the sclera and cornea 2)middle layer is thin,
  dark brown choroid, iris (colored portion) and
  lens 3)inner layer is the retina which contains
  rods and cones.

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• IRIS - portion of the eye that gives your eye its
  color and controls the amount of light entering
  the eye by altering the diameter of the pupil
• PUPIL middle of the iris ,a small opening
  through which light enters the eye

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LENS How a human eye focuses

• Light rays from each point on an object are bent
  by the cornea and the lens in such a ways that an
  inverted and reversed image of the object forms
  on the retina.

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PHOTORECEPTORS

• CONVERT light energy into impulses that are
  carried to the CNS.
• CONTAIN pigment called rhodopsin-which responds
  to wavelengths of light (a derivative of vitamin
  A)
• There are 2 types
• a)RODS sensitive to all colors of light and
  suitable for night vision.
• b) CONES activated by bright light, allow us
  to detect the fine detail and color on an object.
  3 kinds 1) B (blue), 2) G (green) and 3) R
  (red) pigments.

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Eye Problems
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SMELL

• The sense of smell is a chemical sense
  responsible of smell called the olfactory
  receptors.
• Located in the upper part of the nasal cavity
• Chemoreceptors contain cilia that extend into the
  air passages of the nose and react to chemicals
  in the air. Chemicals that come into contact
  with the chemoreceptors stimulate them causing
  impulses to be sent to the brain by the OLFACTORY
  NERVE

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TASTE

• The sense of taste is a chemical sense
• Stimulated by the chemicals called chemoreceptors
• The sense organ detects tastes. Taste are the
  taste buds not the tongue.
• Most 10,000 taste buds are embedded between bumps
  called PAPILLAE on the tongue but can also found
  on the roof of the mouth, on the lips and in the
  throat.

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TOUCH

• All regions of the body are sensitive to touch
• SKIN - largest sense organ
• Mechanoreceptors located throughout the skin
  make it possible to sense touch, pressure and
  tension.