LECTURE NINETEEN

HUMANS HAVE 13 PAIRS OF CRANIAL NERVES




THE LEFT SIDE OF THE CENTRAL NERVOUS
SYSTEM CONTROLS THE RIGHT SIDE OF THE
BODY; THE RIGHT SIDE OF THE CNS CONTROLS
THE LEFT SIDE OF THE BODY



IN EVOLUTION, THE BRAIN DEVELOPED FROM
THE BASE UPWARD




THE BRAINS OF MODERN HIGHER ANIMALS
DIFFER IN THE RELATIVE SIZES OF
THEIR PARTS BUT NOT IN ABSOLUTE STRUCTURE



THE PARTS OF THE BRAIN WILL BE BEST
DEVELOPED THAT CONTROL FUNCTIONS THAT
ARE USED EXTENSIVELY BY THE ANIMAL OR
THAT RECEIVE INFORMATION FROM SENSE
ORGANS THAT ARE VERY VALUABLE TO THE
SURVIVAL OF THE ANIMAL




GENERAL SENSES: TOUCH-PRESSURE, TEMPERATURE,
POSITION (KINESTHESIS), PAIN
SIMPLE RECEPTOR ORGANS THAT ARE WIDELY
DISTRIBUTED OVER THE ENTIRE BODY



SPECIAL SENSES: VISION, HEARING,
SMELL AND TASTE
STRUCTURALLY SOPHISTICATED RECEPTORS THAT
ARE LOCALIZED IN THE BODY




A GIVEN RECEPTOR IS STRUCTURED TO DETECT
CHANGES IN ENERGY OF A PARTICULAR TYPE
CHEMORECEPTORS DETECT CHEMICAL ENERGY
MECHANORECEPTORS DETECT MECHANICAL ENERGY PHOTORECEPTORS DETECT LIGHT
THERMORECEPTORS DETECT HEAT




A STIMULUS IS A CHANGE IN THE PARTICULAR
TYPE OF ENERGY THAT A RECEPTOR DETECTS



A STIMULUS PRODUCES A GENERATOR POTENTIAL
IN THE RECEPTOR; THE GENERATOR POTENTIAL
IS LOCALIZED IN THE RECEPTOR AND DOES NOT
LEAVE IT

THE GENERATOR POTENTIAL INDUCES THE ACTION
POTENTIAL IN THE AFFERENT NEURON LEADING
FROM THE RECEPTOR




RODS AND CONES CONTAIN PIGMENTS WHICH
ABSORB LIGHT AND CHANGE THEIR SHAPE AFTER
DOING SO; THIS LEADS TO THE PRODUCTION
OF THE GENERATOR POTENTIAL IN THE EYE




RHODOPSIN = RETINAL AND OPSIN

A DEFICIENCY OF VITAMIN A LEADS TO
NIGHT BLINDNESS




ACTION POTENTIALS INDUCED BY THE RODS
AND CONES PASS THROUGH BIPOLAR CELLS
AND GANGLION CELLS BEFORE LEAVING THE EYE

THE GANGLION CELLS FUSE TO FORM THE
OPTIC NERVE




RODS ARE MOST PLENTIFUL ON THE PERIPHERY
OF THE RETINA, CONES ARE CONCENTRATED
IN THE CENTER

THE FOVEA HAS CONES BUT NO RODS




THE ANTERIOR AND POSTERIOR CHAMBERS ARE
FILLED WITH AQUEOUS HUMOR
THE PRINCIPAL CHAMBER IS FILLED WITH
VITREOUS HUMOR

GLAUCOMA RESULTS FROM TOO MUCH PRESSURE
INSIDE THE EYE




NEAR-SIGHTEDNESS OR MYOPIA OCCURS WHEN
THE IMAGE IS FOCUSED IN FRONT OF THE
RETINA
FAR-SIGHTEDNESS OR HYPEROPIA OCCURS WHEN
THE IMAGE IS FOCUSED BEHIND THE RETINA




THE CONJUNCTIVA COVERS THE OUTER SURFACE
OF THE EYE AND IS CONTINUOUS WITH THE
EYELIDS




6 MUSCLES CONTROL THE MOVEMENT OF THE
ENTIRE EYEBALL




TEAR GLANDS PRODUCE TEARS THAT ARE
DRAINED BY THE LACRIMAL DUCT




THE EAR IS MADE OF THREE REGIONS:
EXTERNAL, MIDDLE AND INNER




THE PINNA IS PART OF THE EXTERNAL EAR
WHICH DIRECTS THE SOUND WAVES DOWN THE
EAR CANAL




THE TYMPANIC MEMBRANE OR EARDRUM IS
LOCATED A SHORT DISTANCE DOWN THE
EAR CANAL



THE MIDDLE EAR IS A CAVITY IN THE SKULL
WHICH CONTAINS THE MALLEUS, INCUS AND
STAPES




THE STAPES IS IN CONTACT WITH THE COCHLEA,
A SNAIL-SHAPED STRUCTURE MADE OF MEMBRANES




THE COCHLEA HAS 3 INTERNAL REGIONS:
SCALA VESTIBULI, COCHLEAR DUCT, AND
SCALA TYMPANI




THE ACTUAL SOUND RECEPTOR IS THE ORGAN
OF CORTI INSIDE THE COCHLEAR DUCT

THE ORGAN OF CORTI IS MADE UP OF THE
BASILAR MEMBRANE, TECTORIAL MEMBRANE
AND MANY TINY HAIRS




THE SCALA VESTIBULI AND SCALA TYMPANI
ARE FILLED WITH PERILYMPH; THE COCHLEAR
DUCT IS FILLED WITH ENDOLYMPH