4 Photoreceptor CellsPhotoreceptor cells are neurons that are found in the eye’s retina.They are used for phototransduction, in which light is converted into electrical signals.When they absorb photons, their membrane potential change which allows them to send signals to other neurons.All this is used by the visual system as information to help form images.A photoreceptor, or photoreceptor cell, is a specialized type of neuron found in the eye's retina that is capable of phototransduction. More specifically, the photoreceptor sends signals to other neurons by a change in its membrane potential when it absorbs photons. Eventually, this information will be used by the visual system to form a complete representation of the visual world.
5 Rod Cells They are in the retina. They function in less intense light Because they are more light sensitive, they assist in night vision.They can be found on the outer edges of the retina and are used in peripheral vision.There are more then 100 million rod cells located in a human’s retina.Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of photoreceptor, cone cells. Since they are more light-sensitive, rods are responsible for night vision. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. There are about 100 million rod cells in the human retina.
6 Cone Cells Cone Cells are found in the Retina. They function in high intensive light.They are concentrated in the foeva.In a human’s retina, there are about 6 million cone cells.Cone cells are less sensitive to light in comparison to Rod Cells.They allow the perception of color and also give finer detail and the rapid changes in images, since their response time to stimuli is faster then rod cells.Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods
7 Rods Cones Used for night vision Used for day vision Very light sensitive; sensitive to scattered lightDensitive only to direct lightLoss causes night blindnessLoss constitue legal blindnessLow visual acuityHigh visual acuityFound on the outer edge of the RetinaFound in the foevaSow response to light, stimuli added over timeFast response to light, can perceive more rapid changes in stimuliOne type of photosensitive pigment (monochrome vision)Three types of photosensitive pigment in humans (color vision)Confer achromatic visionConfer color vision
8 Nerve Cells Nerve Cells can be found in the eyes. They transmit information to the brain through electrical signalsThey have excitable membranes that propagate electrical impulses.
9 Ciliary MusclesThere are two sets of ciliary muscles in the eye; near the front of the eye, and above and below the lens.Zinn, which is a connective tissue, connects the lens to the ciliary muscles.They are in charge of shaping the lens to focus light on the retina.
10 Ciliary Muscles (cont.) When the muscles contract or relax, it changes the lens:Contract: lens become more convex, which improves the focus for closer objectsRelax: flattens the lens, for focusing on further objects
12 The Evolution of EyesEyes evolved from a “proto-eye” about 540 million years agoThe earliest eyes were called “eyespots”They were simple patches of photoreceptor cellsThey first only sensed the brightness of things, and could not determine the direction the light was coming fromThe “eyespot” then evolved into a “cup” shape, which then allowed us to see where the light is coming from
13 The Evolution of Eyes (cont.) The “cup” deepened over time and the number of photoreceptor cells increased.Transparent Protective Cells developed to protect the eyes.Soon we were able to see color and block harmful radiation.The Transparent Protective Cells then evolved into two layers to help improve imagesTransparent layers eventually evolved into the cornea and iris
14 The Eye Eyes are an organ of vision. They allow the detection of light.Eyes can be as simple as detecting light and dark to as complex as distinguishing shapes, colors, and filtering radiation.
16 The Function of the Brain The brain controls all involuntary activities, such as: Heartbeat, respiration, and digestion.The brain also controls reasoning, thought, and abstraction.The human brain is thought to be the source of the conscious, or “cognitive mind.”This means the brain is the source of perception, imagination, interpretation, and memories.
18 The Brain (Cont.)Frontal Lobe: Reasoning, planning, parts of speech, movement, emotions, and problem solving.Parietal Lobe: Movement, Recognition, Orientation.Temporal Lobe: Auditory, memory, and speech.Occipital Lobe: Visual processing.Cerebellum: Movement, posture, and balance.
20 The Neuron (Cont.)Neurons are nerve cells that transmit nerve signals to and from the brain.The axon: Takes infromation away from the cell body. Bundles of axons are known as nerves or nerve tracts or pathways.Myelin: Coats and insulates the axon. Myelin is manufactured by Schwann's cells, and consists of 70-80% lipids (fat) and 20-30% protein.The cell body (soma): Contains the neuron's nucleus.A typical neuron has about 1,000 to 10,000 synapses (that means it communicates with 1,000-10,000 other neurons, muscle cells, glands.)Over 100 Billion in the brain!!!
23 Bones Rigid connective tissues consisted of cells packed in a matrix Make up the body’s frameworkBones Hierarchy: Bone cells -> bone tissues -> bones -> skeletal system
24 Bone Tissues Outer Bone (Cortical Bone): Contains structures called osteons where Haversian canals allow blood vessels and nerves to pass throughMade up of compact tissuesInner Bone (Trabecular Bone):Contains cavities where red marrow tissue is locatedMade up of spongy (cancellous) tissuesHollow Core:Contains yellow bone marrow and blood vessels
26 Bone Cells In the bone matrix: In red bone marrow: Bone-lining cellsOsteoblastsOsteocytesOsteoclastsIn red bone marrow:Stem cells (hematopoietic and mesenchymal)Red blood cellsIn yellow bone marrow:Mainly fat cells
28 Bone-Lining Cells Old osteoblasts Coat the surface of the bone Shape: flat and longRegulate calcium level in bone
29 Osteoblasts Located where the bone marrow meets the matrix Created when mesenchymal cells in bone marrow differentiateSecrete osteoid, which later crystallizes and becomes new bone, and hormones to make bones flexible and durable
30 Osteoclasts Comes from haemopoietic cells in bone marrow Formed from two or more cells and thus have two or more nucleiHave ruffled edges and big surface areas to maximize their efficiency in dissolving and absorbing old boneFound on surface of bone in between osteoblasts and next to dissolving bone
32 Osteocytes Formed when osteoblasts are trapped in the bone matrix Star-shaped, connect to one another using their branches called canaliculi, which are also used for the transportation of nutrients and wasteMaintain living bone by secreting enzymes and controlling minerals in boneSenses pressure and cracks in the bone to direct the osteoclasts
34 Hematopoietic CellsProduce white blood cells, red blood cells, and plateletsGive rise to osteoclasts
35 Mesenchymal Cells Lie between the bone marrow and the bone matrix Differentiate into osteoblasts, chondrocytes (in cartilage), myocytes (in muscles) and many other types of cell.Regulate substances in and out of bone marrow
36 Skeletal SystemConsisted of 206 bones connected together by tendons and ligamentsFunctions:Works with the muscular system to control movementSupport and balanceProtects organs