Outline Nervous System Sensory Systems I. II. III. IV. V. VI. Biol 105 Lecture 11 Chapter 9 Senses Sensory receptors Touch Vision Hearing and balance Smell Senses Sensory receptor cells Sensory receptors are specialized structures that detect stimuli (stimulus) Major senses touch, hearing, smelling, taste, and seeing. Sensory receptor cells change the stimulation into an electrical response that is transmitted through the nerves All the sensory nerves are routed through the thalamus except the nerves for smell. If a sensory receptor is continuously stimulated, it will stop responding = sensory adaptation 12.2 The Central Nervous System 12-18 12-28 1
Touch We can sense different things through touch: Thermal Tactile Pain Vibration Figure 9.2 Sense receptors of the skin Types of receptors in the skin Free nerve endings Merkel disks Meissner s corpuscles Pacinian corpuscles Ruffini corpuscles Thermoreceptors Figure 9.2 Sense receptors of the skin Free Nerve Endings Free nerve endings tips of dendrites of sensory neurons (free nerve endings may be wrapped around hair), detect touch and pain 2
Figure 9.2 Free nerve endings Merkel Disks Figure 9.2 Free nerve endings Merkel disk Merkel disks comprised of free nerve endings and Merkel cells, detect touch Meissner s corpuscles Meissners corpuscle Meissner s corpuscles encapsulated nerve endings - detect light touch, tell us exactly where we were touched 3
Pacinian corpuscles Pacinian corpuscle Pacinian corpuscles layers of tissues surround the nerve ending, detects pressure when first applied, important in sensing vibration Ruffini corpuscles Ruffini corpuscle Ruffini corpuscles encapsulated nerve endings in deep layers that respond to continuous pressure Thermoreceptors Vision Sight is complex: Thermoreceptors specialized nerve endings, detects changes in temperature. Light enters the eye, it is focused, then the light has to be transformed into it into an electrical signal that then has to be processed. 4
Vision Optic nerve Optic disk (blind spot) Light enters through the cornea Fovea Sclera Choroid Retina The lens focuses it to the back of the eye Vitreous humor (fills the posterior chamber) Lens The retina is a layer at the back of the eye where light is transformed into electrical signals Ciliary body Aqueous humor (fills the anterior chamber) Cornea Pupil Iris Sclera Layers of the Eye Outer layer Figure 9.4 Outer Layer of Eye The sclera Protects and shapes the eye Provides attachment for muscles The cornea Allows light to enter Middle Layer of Eye The choroid Contains blood vessels that supply nutrients and oxygen. Contains melanin, absorbs light reflected from the retina Table 9.1 (1 of 4) Middle Layer of Eye The iris The colored portion of the eye Contains smooth muscle that dilates or constrict to regulate the amount of light entering the eye The pupil The ciliary body A ring of muscle that functions to focus the lens on the retina The opening in the center of the iris that lets light into the eye 5
Middle Layer of the Eye Inner Layer of Eye Contains: Retina Photoreceptors - Rods and Cones Fovea Inner Layer of Eye - Retina Table 9.1 (2 of 4) Vision Depends on the Eye The retina contains photoreceptors Rods Cones detect color The fovea is a pit in the retina with a high concentration of cones Structures of the Eye Optic Nerve Fluid Aqueous humor Vitreous humor Table 9.1 (3 of 4) Optic Nerve The optic nerve Carries visual information to the brain Forms a blind spot where it leaves the retina Lens 6
Fluid in the Eye Lens There are two fluid filled chambers in the eye Vitreous humor jelly like fluid in posterior chamber. Holds retina against the wall of the eye Aqueous humor clear fluid in anterior chamber. Supplies nutrients and oxygen to cornea and lens, removes the waste. Creates pressure in eye to maintain shape of eye. The lens can change shape to focus on near and far objects. Focuses the light onto the retina Ciliary muscles are attached to lens by ligaments Vision Depends on the Eye Photoreceptors Cones and Rods have pigments that absorb Cones work best in bright light and provide color vision Rods work in low light situations but can only provide black and white vision Table 9.1 (4 of 4) Photoreceptors The photoreceptors (rods and cones) have pigments that absorb light When there is no light coming in, they are releasing neurotransmitters (opposite of most receptors) When they absorb light they stop releasing neurotransmitters Photoreceptors The neurotransmitters are inhibitory When the neurotransmitters diminish, cells that process the information are stimulated This information from these cells (bipolar and ganglion cells) is transmitted to the optic nerve to the thalamus to the visual cortex 7
Light Vitreous humor Light Ganglion cell layer Electrical signals Choroid Bipolar cell layer Retina Sclera Cone Retina Blind spot Rod Axons Photoreceptor cells Pigment layer Choroid Sclera (a) Light enters the left eye and strikes the retina. Figure 9.8a Figure 9.8b Rods and Cones Light Retina Optic nerve Rod cell Cone cell Visual cortex (c) The axons of the ganglion cells leave the eye at the blind spot, carrying nerve impulses to the brain (viewed from below) by means of the optic nerve. Figure 9.10 A standard test for color blindness Figure 9.8c Figure 9.9 (2 of 2) Vision Vision is much more complicated because these signals have to be processed into a 3-D image 8
Hearing Three regions of the ear Sound enters the ear canal and hits the tympanic membrane (ear drum). Outer ear the receiver The tympanic membrane vibrates. The middle ear the amplifier The inner ear the transmitter This causes small bones in the ear to vibrate. These bones focus and amplifies the vibrations onto a small place (oval window) on the cochlea. The cochlea is a fluid filled coiled membrane. The vibrations shakes the fluid in the cochlea Three Regions of the Ear The Outer Ear Outer Middle Inner ear ear ear (receiver) (amplifier) (transmitter) Consists of the: Pinna gathers the sound, acts like a funnel External auditory canal brings the sound from pinna to the tympanic membrane Figure 9.12 (1 of 2) 9
Middle Ear Consists of the: The tympanic membrane separates the outer ear from the middle ear, vibrates when sound waves hit it. Three auditory bones amplify the vibration Malleus Incus Stapes Middle Ear The tympanic membrane vibrates when sound waves hit it and transmits the vibration to the malleus The vibrations are amplified by the three bones and transmitted to the oval window Auditory tube (eustachian tube) equalizes pressure between outer and middle ear Parts of the Inner Ear Hearing Depends on the Ear Outer ear (receiver) Oval window transmits sound from the stapes to the fluid in the cochlea Middle ear (amplifier) Eardrum Malleus Incus Stapes (tympanic membrane) (hammer) (anvil) (stirrup) Vestibular apparatus: Semicircular canals Vestibule Round window relieves pressure Auditory nerve Cochlea contains the receptor cells that transform the signal from vibration to an electrochemical signal to the neurons. Oval window Cochlea Round window External auditory canal Auditory tube (Eustachian tube) Vestibular apparatus monitors position of the head The pinna gathers sound and funnels it into the external auditory canal to the tympanic membrane (eardrum). Cochlea Inner ear (transmitter) The eardrum vibrates synchronously with sound waves, causing the bones of the middle ear to move. The three bones of the middle ear amplify the pressure waves and convey the vibrations of the eardrum to the inner ear. The cochlea converts pressure waves to neural messages that are sent to the brain for interpretation as sound. Figure 9.12 (2 of 2) Hearing Depends on the Ear It is in the cochlea where vibrations are transformed into electrical signals that can be sent by neurons When the fluid in the cochlea moves, it moves small hair cells against a membrane. This allows ion channels to open This leads to the release of neurotransmitters, which trigger the neuron to send the message Figure 9.13 (1 of 2) 10
Hearing Depends on the Ear The Vestibular Apparatus Balance depends on the vestibular apparatus of the inner ear Tectorial membrane Hair cell Figure 9.13 (2 of 2) The Vestibular Apparatus - Dynamic equilibrium Fluid filled cupulas at base of the semicircular canals have hair cells that are stimulated when head moves. Hair cells send message to the brain. The Vestibular Apparatus - Static equilibrium Otoliths are small chalk like granules When head is tilted the otoliths move and stimulate hair cells that send message to the brain Balance Depends on the Vestibular Apparatus The vestibular apparatus is a fluid-filled maze of chambers and canals within the inner ear Balance Depends on the Vestibular Apparatus Figure 9.16a (1 of 2) Figure 9.16a (2 of 2) 11
The Vestibular Apparatus The Vestibular Apparatus Figure 9.16b (1 of 2) Smell - olfaction Sensory nerves for smell go directly to the cerebral cortex and to the amygdala and the hypothalamus. They do not pass through the thalamus Figure 9.17 Sense of Smell Figure 9.16b (2 of 2) Smell - olfaction Odor molecules bind to the receptors in the cilia of olfactory receptor cells The receptor cells send the message to the neurons in the olfactory bulb which carry the message to the brain. Figure 9.17 Sense of Smell 12
Taste Taste Food molecules bind to taste cells and stimulate them. The taste cells send the messages to the sensory neurons which send the message to the brain. Taste and smell is very connected. The tongue has taste buds on them The taste buds have taste cells (receptor cells) in them Smell and Taste Important Concepts Read Chapter 6 What is the function of sensory receptor cells? What is an example of sensory adaptation? What are the types of senses of touch? What are the types of sensory receptors in skin, what type of touch do they detect, be able to describe them? Figure 9.18 Important Concepts Important Concepts What are all of the layers and structures (including the fluids) of the eye and what are their functions? What are all the parts of the ear, are they part of the inner, middle or outer ear, and what is their functions? What is the path of sound waves and vibrations through the ear What is the blind spot? How does the ear detect head movement and position? How does the signal travel from the photoreceptors to the brain, what part of the brain receives the signal? Be able to describe in detail this process, including the cells that transmit the messages. How do we detect odor? What part of the brain receives the signal? Where are olfactory receptors found? How do we detect tastes? What structures are responsible for taste? 13
Definitions stimuli (stimulus), sensory adaptation, dilates, constrict, bipolar cells, ganglion cells, photoreceptors, transmits, amplifies, otoliths, cupula, taste buds, 14