Sensation Overview 1. Specialized sensory cell (receptor) detects a physical or chemical change. 2. The physical or chemical change causes action potentials in sensory neurons. 3. Sensory neurons carry action potentials through cranial nerves or spinal nerves to the CNS. 4. Typically the sensory information is carried to the thalamus where synapses occur. 5. Neurons transmit sensory information from the thalamus to a specific region of the cerebrum where the sensation is experienced.

Example: vision 1. Rods and Cones (receptors) in the retina of the eye detect light. 2. Sensory neurons in retina begin producing action potentials 3. Action potentials are carried out of the eye through the optic nerve. 4. Optic nerve enters the brain and leads to the thalamus. 5. Neurons are stimulated in the thalamus and transmit action potentials to specific locations in the occipital lobe. 1. Light from the environment enters the eyes and strikes the retina.

Receptors in retina Sensory Neurons Synapse in Thalamus Projection to The Cerebrum

Types of Sensory Receptors (often modified nerve endings) Chemoreceptors (tongue, nasal epithelium) Pain Receptors (respond to chemicals released when tissue is damaged) Thermoreceptors (temperature of skin and at the hypothalamus) Mechanoreceptors (proprioceptors in muscles and joints, hearing, balance) Photoreceptors (detect light - eye)

Visceral Pain - referred pain

Lacrimal gland Lacrimal sac Nasolacrimal duct Eye video

sclera Choroid layer Retina (fovea) Optic disc Posterior chamber (vitreous humor) lens Ciliary body iris Anterior chamber (aqueous humor) cornea conjunctiva

Functions of Key Parts of the Eye Iris: dilates and constricts thereby regulating the amount of light that enters to posterior chamber of the eye. Ciliary body: muscular – pulls on suspensory ligaments and causes the lens to bend and change focus. Fovea centralis: area having the densest amount of photoreceptors Optic Disk (blind spot): area on retina where neurons leave and form optic nerve. No photoreceptors are found here.

Structure of the Retina

Receptors in retina Sensory Neurons Synapse in Thalamus Projection to The Cerebrum

HEARING: System that converts the pressure changes in air into Changes in action potential frequencies. When something vibrates, it causes the air to move back and forth. This generates “sound waves” which are slight increases and decreases Local air pressure.

Auricle (pinna) Auditory canal tympanum malleus incus stapes Semicircular canal cochlea Auditory tube (Eustachian tube)

tympanun Oval window Round window Function of the Ear When air waves strike the tympanum, the malleus, incus and stapes move. The stapes presses up against the oval window causing fluid to move within the cochlea. The movement of the fluids is eventually detected by sensory cells within the cochlea. The cochlea contains sensory cells that provide our perception of hearing Hair cells in the cochlea detect the movement of fluids in the cochlea

The cochlea contains receptor cells that detect sound. At the base of the semicircular canals we find receptor cells that detect dynamic equilibrium (changes in movement in the sagittal, coronal and transverse plains) In each case, “hair cells” are the receptor cells. These cells detect fluid movements in the inner ear and transduce these fluid movements into action potentials. cilia Sensory nerve fiber Current flow Hearing video

To detect motion, sensory cells (hair cells) detect movement of fluids within the semicircular canals

Nasal cavity Cribiform plate of ethmoid bone Olfactory cells Olfactory bulb The Sense of Smell