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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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

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

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.

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.

Inner ear cont’d: 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.

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.

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

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.

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.

Eye Problems:

SMELL: Located in the upper part of the nasal cavity 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

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.

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.