Physiology Unit 2 SENSORY PHYSIOLOGY

Transcription

1 Physiology Unit 2 SENSORY PHYSIOLOGY

2 In Physiology Today

3 Sensory System Sensory information Conscious sensations Unconscious sensations Sensory processing Transferring stimulus energy into a graded potential (receptor potential) Then to an action potential in an afferent neuron Pattern of action potentials is the code that provides information on the stimulus

4 General Classes of Receptors Mechanoreceptors Thermoreceptors Photoreceptors Chemoreceptors Nociceptors

5 Sensory Receptors Specialized endings of sensory neurons Separate cells that signal the afferent neurons by releasing chemical messengers The energy or chemical that activates a sensory receptor is a stimulus The process by which a stimulus is transformed into an electrical response is sensory transduction

6 Receptor Potential Sensory transduction involves the opening/closing of ion channels

7 Graded Potential to Action Potential The initial ion movement generates local current that flows a short distance along the axon to a region where the membrane has voltage-gated ion channels an an AP can be generated Usually the first Node of Ranvier

8 Primary Sensory Coding Sensory Unit Converting stimulus energy that conveys relevant sensory information to the CNS is coding Type of energy it represents (modality) Intensity Location of the body affected

9 Sensory Modality Modalities Temperature, taste, sound, touch Submodalities of sensation Submodality of temperature: hot/cold Submodalities of taste: sweet, bitter, salty, sour, umame Submodality of sound: pitch, volume

10 Stimulus Intensity

11 Stimulus Duration Rapid adaptation Phasic receptors Signal change Rapid fading of sensation on and off response Slow adaptation Tonic receptors Signal slow changes or prolonged events Joint, muscle receptors for maintaining posture

12 Sensory Pathways A Sensory Pathway A bundle of parallel, 3 neuron chains that run together Also called ascending pathways Non-specific Specific Most sensory pathways convey information from a single type of sensation (mechanoreceptors, thermoreceptors, etc.)

13 Specific Ascending Pathways Sensory pathways ascend to 1. Brainstem (RAS) 2. Thalamus 3. Final neurons in the pathway terminate in the specific sensory area of the cortex Exception: olfactory neurons branch to the limbic system rather than the thalamus

14 Somatic Sensation Sensations from Skin Muscles Bones Tendons Joints Sensations of Touch Pressure Body position Temperature Pain

15 Somatosensory System Pathways Anterolateral Pathway Decusation in the spinal cord 1 st neuron travels into the spinal cord 2 nd neuron decusates in the spinal cord and up to the thalamus 3 rd neuron travels to the somatosensory cortex Processes Pain Temperature

16 Somatosensory System Pathways Dorsal Column Pathway Decusation in the brainstem 1 st neuron passes into the spinal cord and up to the brainstem where it decusates 2 nd neuron travels to the thalamus 3 rd neuron travels to the somatosensory cortex Processes Fine touch Vibration Proprioception

17 Distribution of Peripheral Stimuli

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19 Special Sense: Vision Optical component Focuses visual image on the receptor cells Neural component Transforms the visual image to a pattern of graded and action potentials

20 Light The receptors of the eye are only sensitive to a small portion of the electromagnetic spectrum The visible spectrum is between nm Different wavelengths of light are perceived as different colors

21 Color Vision

22 The Optics of Vision Refracting light is how our eyes focus on objects The cornea and the lens refract light to focus it in the retina Adjustments for distance is made by changes the shape of the lens. This is accommodation

23 Accommodation

24 Photoreceptor Cells Outer segment made of stacked layers of membrane (discs). The discs hold the photopigments which absorb light Photopigments are membrane bound proteins called opsins which surround and bind a molecule called retinal Retinol is a derivative of vitamin A

25 Photoreceptor Cells There are 4 unique photopigments in the retina (called photopsins) Rods have the photopigment rhodopsin The others are found in the 3 types cones

26 Phototransduction

27 Neural Pathway of Vision Pathway: Optic Nerve (C.N. II) Optic chiasm SCN Optic tract Thalamus Visual cortex Suprachiasmatic nucleus (SCN) controls circadian rhythms

28 Special Sense - Hearing

29 Sound Transmission

30 Organ of Corti Sensory Hair Cells

31 Neural Pathway for Hearing Pathway: Sensory hair cells Cochlear branch of vestibulocochlear nerve (C.N. VIII, Auditory Nerve) Brainstem Thalamus Auditory cortex

32 Vestibular System Vestibular apparatus Semicircular canals Utricle Saccule

33 Semicircular Canals Rotational Movement

34 Utricle and Sacule The macula provides info on changes in head position relative to: Force of gravity Linear acceleration Vestibular information is used for: Control eye movements Reflexes to maintain posture Conscious awareness of ourselves in space

35 Gustation

36 Olfaction