Senses and Perception Lab 17

Organization of the Vertebrate Nervous System Central nervous system (CNS) – brain & spinal cord. Responsible for more complex reflexes and higher associative functions like learning & memory. Peripheral nervous system (PNS) – motor and sensory neurons.

Organization of the Vertebrate Nervous System Motor neurons carry impulses away from the CNS to effectors (muscles and glands). Sensory neurons carry impulses from sensory receptors to the CNS.

Reflexes A reflex produces a very fast motor response to a stimulus because the sensory neuron bringing information about the threat passes the information directly to the motor neuron.

Sensory Receptors The sensory nervous system carries impulses to the CNS. Sensory receptors are specialized sensory cells that detect changes in blood pressure, strain on ligaments, and smells in the air, among other things. Complex sensory receptors made of many cell & tissue types are called sensory organs. Eyes, ears, taste buds.

Sensory Receptors The brain can tell what kind of impulse is coming (light, sound, pain, etc) because the signal came from a particular type of receptor. Light signals come from light receptors.

The Path of Sensory Information There are many different kinds of sensory receptors. Exteroceptors are receptors that sense stimuli that come from the external environment. Interoceptors sense stimuli that come from inside the body.

Sensing Chemicals: Taste Taste – taste buds embedded in the surface of the tongue contain taste receptor cells. Chemicals from food dissolve in saliva and contact the taste cells. Salty, sour, sweet, & bitter chemicals are detected in different ways.

Sensing Chemicals: Smell Smell – chemically sensitive neurons in the nose detect chemicals and transmit the information to the brain where smell information is processed & analyzed.

Sensing Sounds: Hearing Hearing a sound involves detecting the vibrations of the air. Waves of pressure in the air beat against the ear push the eardrum in & out. Three small bones on the other side of the eardrum increase the force of the vibration.

Sensing Sounds: Hearing The vibration crosses a second membrane to the fluid of the inner ear – the cochlea. The inner ear is connected to the throat by the eustachian tube to equalize pressure.

Sensing Sounds: Hearing The sound receptors occur in the cochlea. When sound vibrations enter the cochlea, they send nerve impulses to the sensory neurons that travel to the brain.

Sensing Sounds: Hearing Sounds of different frequencies cause different parts of the membrane inside the cochlea to vibrate and fire different neurons. Intensity is determined by how often the neurons fire.

Sensing Light: Vision Vision is the perception of light. The eye is a special sensory organ that uses pigments in structures called rods and cones to absorb photons of light.

Structure of the Vertebrate Eye Light passes through the transparent cornea which begins to focus light on the rear of the eye, then through the lens which completes the focusing. The lens is suspended by ciliary muscles.

Structure of the Vertebrate Eye The iris is a shutter that controls the amount of light entering the eye. The pupil is the transparent zone in the center of the iris that gets larger in dim light and smaller in bright light.

Structure of the Vertebrate Eye The light is focused by the lens onto the back of the eye. An array of light sensitive receptor cells called the retina line the back of the eye. Rods & cones – two types of receptor cells generate nerve impulses that pass along the optic nerve.

Structure of the Vertebrate Eye Rods are very sensitive to light and can detect shades of gray in very dim light, but they do not detect color and the images are not sharp. Cones detect colors and produce sharp images.

Color Vision Three kinds of cone cells allow color vision. Each has a different version of the opsin protein and so absorbs different wavelengths of light. The brain compares relative intensities of the signals from the three types of cones.

Binocular Vision Primates and most predators have two eyes facing forward, so the field of view overlaps. This binocular vision allows perception of 3D images and depth. Animals with eyes on the sides can detect motion in a wider field – good for prey animals.