Essentials of Biology Sylvia S. Mader Chapter 28 Lecture Outline Prepared by: Dr. Stephen Ebbs Southern Illinois University Carbondale Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

28.1 The Senses All living organisms respond to environmental signals (stimuli). The stimuli are received by sense organs which transmit a signal to the central nervous system. The central nervous system sends signals to generate a motor response to the stimuli.

28.1 The Senses (cont.)

Chemical Senses Chemicals in the environment are detected with chemoreceptors. Chemoreceptors are found in different places on different organisms.

Taste and Smell An example of human chemoreceptors are the taste buds on the tongue. There are four primary tastes. –Sweet –Sour –Bitter –Salty A particular food or chemical can stimulate more than one type of taste bud.

Taste and Smell (cont.)

Hearing and Balance The ears provide two sensory functions. – Hearing – Balance and equilibrium The sensory receptors for these functions are mechanoreceptors, dependent upon mechanical stimulation.

Hearing The sound receptors in many animals involves a tympanic membrane, which transmits sound vibrations to the sensory receptors. In humans, the outer ear collects sounds, transmit them through the tympanic membrane and to the three bones of the inner ear. The hearing portion of the inner ear is the cochlea, which contains sensory receptors called the spiral organ.

Hearing (cont.)

The spiral organ can distinguish between the volume and pitch of sounds. Damage to ear structures can lead to deafness. –Damage to the middle ear produces conduction deafness. –Damage to the spiral organ produces nerve deafness.

Balance There are two senses of balance. – Rotational equilibrium, mediated by the semicircular canals, provides balance in three-dimensional space. – Gravitational equilibrium, mediated by two membranous sacs (the utricle and auricle), provides balance with respect to gravity.

Similar Receptors in Other Animals Gravitational equilibrium in invertebrates is provided by statocysts, which provides information about the position of the head relative to the body. The lateral line of fish senses changes in water pressure and currents.

Similar Receptors in Other Animals (cont.)

Vision Light is perceived by photoreceptors, typically in the eyes of an organism. – Compound eyes consist of several independent visual units that each focus light towards the photoreceptors. –The camera-type eye has a single lens that focuses light and images on photoreceptors. The photoreceptors of some organisms can also perceive colors.

Vision (cont.)

The Human Eye The human eye is structured so that external stimuli is prepared for the photoreceptors in the retina. –The cornea and lens focus light rays on the photoreceptors. –The iris uses the pupil to regulate the amount of light that enters the eye.

The Human Eye (cont.)

Photoreceptors of the Eye There are two photoreceptors in the human eye. –The cones, which provide color vision, are located in the fovea of the retina. –The rods, which are sensitive to light and provide night vision, are scattered across the retina. The retina is composed of several cell layers containing the photoreceptors and the sensory neurons. The blind spot is the point where the optic nerve is attached to the retina.

Photoreceptors of the Eye (cont.)

Cutaneous Receptors and Proprioreceptors Cutaneous receptors are located in the two layers of the skin. –The epidermis of the skin contains receptors for temperature and pain. –The dermis of the skin has receptors for pressure (Pacinian corpuscle) and touch. Proprioreceptors help maintain equilibrium and posture.

Cutaneous Receptors and Proprioceptors (cont.)

Cutaneous Receptors and Proprioreceptors (cont.)

28.2 The Motor Systems The musculoskeletal system work together to provide specific functions. –Support and movement –Protection of internal organs –Support to other organ systems, such as the respiratory and digestive systems The muscles and skeletal systems also have individual functions. –Skeletal muscles assist movement of the blood and help maintain body temperature. –Bones store fat and calcium.

28.2 The Motor Systems (cont.)

Other organisms in the animal kingdom use a hydrostatic skeleton to provide support and movement.

Axial and Appendicular Skeletons The axial skeleton has several bones. –The skull, which is composed of the cranium and facial bones. –The vertebral column and the sacrum –The rib cage and sternum The appendicular skeleton has several bones. –The shoulder girdle has the clavicle and scapula. –The pectoral girdle has coxal bones of the pelvis. –Arms consist of the humerus, ulna, and radius. –Legs consist of the femur, tibia, and fibula.

Structure of a Bone Bones are often comprised of more than one type of bone tissue. – Compact bone, which surrounds the central cavity of long bones – Spongy bone at each end of the bone has red bone marrow Two cell types function in bones. – Osteoblasts deposit bone. – Osteoclasts liberate calcium from bone for release into the bloodstream.

Structure of a Bone (cont.)

Skeletal Muscle and Physiology There are three types of muscle in the human body, each with a different structure. – Cardiac muscle, found in the heart, consists of striated, branched cells forming a lattice. – Smooth muscle are long, spindle-shaped cells that are formed in sheets. – Skeletal muscle cells are elongated fibers running the length of the muscle.

Skeletal Muscle and Physiology (cont.)

Skeletal Muscle Contraction The contractile portion of a muscle fiber has many parallel myofibrils. The striations of muscle fibers are caused by the placement of protein filaments with contractile units called sarcomeres comprised of actin and myosin. The contraction of muscles is described by the sliding filament model.

Skeletal Muscle Contraction (cont.)

In the presence of calcium, myosin binds to the actin filaments. The myosin head flexes inward and backward, causing the actin filament to shorten. In the presence of ATP, the myosin head detaches and then reattaches at a new position on the actin filament. This cycle repeats to continue the shortening of the muscle (contraction).

Muscles Move Bones at Joints Muscles generally work in antagonistic pairs to provide movement. Muscles articulate movement at joints. – Synovial joints have a fluid filled cavity that ease friction as the bones move. – Hinged joints move only in one direction. – Ball-and-socket joints allow for rotational movement.

Muscles Move Bones at Joints (cont.)

There are several joint disorders. – Sprains occur when tendons or ligaments are over-stretched at a joint. – Bursitis is inflammation of a synovial joint. –The cartilage that supports some joints can be torn. – Arthritis can occur when joints deteriorate.