Chapter 10 Sensory Physiology

About this Chapter What are the senses How sensory systems work Body sensors and homeostatic maintenance Sensing the external environment Mechanisms and pathways to perception

General Properties of Sensory Systems Stimulus Internal External Energy source Receptors Sense organs Transducer Afferent pathway CNS integration

The Human Brain

General Properties of Sensory Systems Figure 10-4: Sensory pathways

Sensory Receptor Types Simple receptors Complex neural Special senses Chemoreceptors Mechanoreceptors Thermoreceptors Photoreceptors

Sensory Receptor Types Figure 10-1: Sensory receptors

The Cerebral Cortex Three kinds of functional areas Motor areas Sensory areas Association areas

Functional and Structural Areas of the Cerebral Cortex

Functional and Structural Areas of the Cerebral Cortex Figure 13.11b

Special Senses – External Stimuli Vision Hearing Taste Smell Equilibrium

Special Senses – External Stimuli Figure 10-4: Sensory pathways

Sensory Areas – Sensory Homunculus Figure 13.10

Motor Homunculus Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 13.10

Homunculus

Somatic Senses – Internal Stimuli Touch Temperature Pain Itch Proprioception Pathway Figure 10-10: The somatosensory cortex

Somatic Pathways Receptor Threshold Action potential Sensory neurons Primary – medulla Secondary – thalamus Tertiary – cortex Integration Receptive field Multiple levels

Somatic Pathways Figure 10-9: Sensory pathways cross the body’s midline

Sensory Modality Location Lateral inhibition Receptive field Intensity Duration Tonic receptors Phasic receptors Adaptation

Touch (pressure) Mechanoreceptors Free nerve endings Pacinian corpuscles Ruffini corpuscles Merkel receptors Meissner's corpuscles Baroreceptors

Touch (pressure) Figure 10-11: Touch-pressure receptors

Temperature Free nerve endings Cold receptors Warm receptors Pain receptors Sensory coding: Intensity Duration

Temperature Figure 10-7: Sensory coding for stimulus intensity and duration

Pain and Itching Nocioceptors Reflexive path Itch Fast pain Slow pain

Pathways of Itch from Skin to Brain. Figure 1. Pathways of Itch from Skin to Brain. Itch originates in the epidermis and dermal–epidermal junction and is transmitted by itch-selective C nerve fibers. Some of these fibers are sensitive to histamine, but the majority are not. A complex interplay among T cells, mast cells, neutrophils, eosinophils, keratinocytes, and nerve cells (along with increased release of cytokines, proteases, and neuropeptides) leads to exacerbation of itch. The C fibers form synapses with second-order projections in the dorsal horn, and the itch signal ascends in the contralateral spinothalamic tract, with projections to the thalamus. From the thalamus, itch is transmitted to several regions of the brain that are involved in sensation, evaluative processes, emotion, reward, and memory. Yosipovitch G, Bernhard JD. N Engl J Med 2013;368:1625-1634.

Gate Control Theory of Pain Figure 10-12: The gate control theory of pain modulation

Pain Ischemia Other visceral pain Modulation Thalamus Gate control Magnification Analgesic drugs Aspirin Opiates

Referred Pain Figure 10-13: Referred pain

Olfactor: Sense of Smell Olfactory cell Chemoreceptor- Humans have about 350 different types of odorant receptors, Mice 1200 Olfactory cilia Olfactory bulb Olfactory nerve CNS integration Amygdala Hippocampus Olfactory

Olfactor: Sense of Smell Figure 10-14a, b: ANATOMY SUMMARY: Olfaction

Olfactor: Sense of Smell Figure 10-14c: ANATOMY SUMMARY: Olfaction

Taste: Chemoreceptors 5 Tastes Taste buds Taste cells Mechanism Transduction Integration Thalamus Gustatory cortex "Specific hunger" Figure 10-16: Summary of taste transduction

Hearing: Mechanoreceptors Sound waves Conduction Air Bone Fluid Membranes To hair cell

Hearing: Mechanoreceptors Figure 10-19: Sound transmission through the ear

Hearing: Hair Cell Transduction Fluid wave moves Tectoral membrane Steriocilia move Ion channels open Depolarization NT release Sensory nerve AP

Hearing: Hair Cell Transduction Figure 10-20: The cochlea

Hearing: Hair Cell Transduction Figure 10-21: Signal transduction in hair cells

Hearing: Integration and Problems Pitch Intensity Localization Integration Medulla Thalamus Auditory cortex Deafness Conductive Sensorineural Figure 10-5: Localization of sound

Hearing: Integration and Problems Figure 10-22: Sensory coding for pitch

Equilibrium: Mechanoreceptor Body balance Body position Body movement Propioceptors Vision Vestibular apparatus

Equilibrium: Mechanoreceptor Integration Medulla Cerebellum Thalamus Cortex Figure 10-26: Central nervous system pathways for equilibrium

Equilibrium: Vestibular Apparatus Otolith organs Gravity Calcite crystals Hair cells Semicircular canals Endolymph Fluid moves which stimulates Each Crista which consists of: Cupula Embedded Hair cells: activate CN VIII

Semicircular Canals of the Vestibular Apparatus Have Posterior, Horizontal and Superior Semicircular Canals They sense Rotational Acceleration in various directions The Cristae within the Ampula (enlarged chamber at the end of each canal) are the sensory receptors Endolymph moves the gelatinous cupula with the hair cells embedded in it and stimulates vestibulocochlear nerve (CN VIII)

Equilibrium: Vestibular Apparatus Figure 10-23a, b: ANATOMY SUMMARY: Vestibular Apparatus

Otolith Organs of the Vestibular Apparatus Otolith Organs of the Utricle and Saccule Sense Linear Acceleration and Head Position They are arranged horizontally (Utricle-if head tips back gravity causes othliths to slide) and vertically (Saccule-senses vertical forces such as an elevator dropping) Macula are the sensory receptors of the utricle and saccule Otoliths are crystals that move in response to gravitational forces

Equilibrium: Vestibular Apparatus Figure 10-23c, d: ANATOMY SUMMARY: Vestibular Apparatus

Vision: Photoreceptors Reflected light translated into mental image Pupil limits light, lens focuses light Retinal rods and cones are photoreceptors Figure 10-36: Photoreceptors in the fovea

Cataract

Retina (Right Eye)

Retina (Left Eye)

Hypercholesterolemia Accumulations of lipids leak from surrounding capillaries and microaneuryisms, they may form a circinate pattern.

Hypertension

Proliferative diabetic retinopathy

Panretinal laser photocoagulation

Photoreception and Local Integration Rods – night vision Cones – color & details Bipolar & ganglion cells converge, integrate APs

Photoreception and Local Integration Figure 10-35: ANATOMY SUMMARY: The Retina

Retina: More Detail Rod cells: monochromatic Cone cells: red, green, & blue Discs: visual pigments Pigmented epithelium Melanin granules Prevents reflection

Retina: More Detail Figure 10-38: Photoreceptors: rods and cones

Phototransduction Photons "bleach" opsin, retinal released, cascade, Na+ channel closes, K+ opens , hyperpolarization Reduces NT release

Phototransduction Figure 10-40: Phototransduction in rods

Vision: Integration of Signals to Perception Bipolar Ganglion Movement Color Optic nerve Optic chiasm Optic tract Thalamus Visual cortex Figure 10-29b, c: Neural pathways for vision and the papillary reflex

Summary Sensory pathway: receptor, sensory neuron(s) & CNS Somatic senses: touch, temperature, pain & proprioception communicate body information to CNS Special senses: taste, smell, hearing, equilibrium, & vision Outside conditions for CNS integration into perception Receptors transduce mechanical, chemical or photon energy into GPs then to APs