SENSORY!PHYSIOLOGY!faculty.mtsac.edu/mpresch/36_lecture_files_unit_2... · Sensory)Receptors) •...
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SENSORY PHYSIOLOGY
Physiology Unit 2
Sensory System
• Sensory informa4on – Conscious sensa4ons – Unconscious sensa4ons
• Sensory processing – Transferring s4mulus energy into a graded poten4al (receptor poten4al)
– Then to an ac4on poten4al in an afferent neuron • Pa>ern of ac4on poten4als is the code that provides informa4on on the s4mulus
General Classes of Receptors
• Mechanoreceptors • Thermoreceptors • Photoreceptors • Chemoreceptors • Nociceptors
Sensory Receptors • Specialized endings of
sensory neurons • Separate cells that signal
the afferent neurons by releasing chemical messengers
• The energy or chemical that ac4vates a sensory receptor is a s"mulus
• The process by which a s4mulus is transformed into an electrical response is sensory transduc"on
Receptor Poten4al
• Sensory transduc4on involves the opening/closing of ion channels
Graded Poten4al to Ac4on Poten4al
• The ini4al 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
Primary Sensory Coding
• Conver4ng s4mulus energy that conveys relevant sensory informa4on to the CNS is coding – Type of energy it represents (modality)
– Intensity – Loca4on of the body affected
Sensory Unit
Sensory Modality
• Modali4es – Temperature, taste, sound, touch
• Submodali4es of sensa4on – Submodality of temperature: hot/cold – Submodali4es of taste: sweet, bi>er, salty, sour, umame
– Submodality of sound: pitch, volume
S4mulus Intensity
S4mulus Dura4on • Rapid adapta4on
– Phasic receptors – Signal change – Rapid fading of sensa4on – “on” and “off” response
• Slow adapta4on – Tonic receptors – Signal slow changes or
prolonged events – Joint, muscle receptors for
maintaining posture
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 informa4on from a single type of sensa4on (mechanoreceptors, thermoreceptors, etc.)
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
• Excep1on: olfactory neurons branch to the limbic system rather than the thalamus
Soma4c Sensa4on • Sensa4ons from
– Skin – Muscles – Bones – Tendons – Joints
• Sensa4ons of – Touch – Pressure – Body posi4on – Temperature – Pain
Somatosensory System Pathways Spinothalamic Pathway
• 1st neuron travels into the spinal cord
• 2nd neuron decusates in the spinal cord and up to the thalamus
• 3rd neuron travels to the somatosensory cortex
• Processes • Pain • Temperature
DecusaBon in the spinal cord
Somatosensory System Pathways Dorsal Column Pathway
• 1st neuron passes into the spinal cord and up to the brainstem where it decusates
• 2nd neuron travels to the thalamus
• 3rd neuron travels to the somatosensory cortex
• Processes • Fine touch • Vibra4on • Propriocep4on
DecusaBon in the brainstem
Distribu4on of Peripheral S4muli
Special Sense: Vision
• Op4cal component – Focuses visual image on the receptor cells
• Neural component – Transforms the visual image to a pa>ern of graded and ac4on poten4als
Light
• The receptors of the eye are only sensi4ve to a small por4on of the electromagne4c spectrum
• The visible spectrum is between 400-‐750 nm
• Different wavelengths of light are perceived as different colors
Color Vision
The Op4cs of Vision
• Refrac4ng light is how our eyes focus on objects
• The cornea and the lens refract light to focus it in the re4na
• Adjustments for distance is made by changes the shape of the lens. This is accommoda"on
Accommoda4on
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 re"nol • Re4nol is a deriva4ve of
vitamin A
Photoreceptor Cells
• There are 4 unique photopigments in the re4na • Rods have the photopigment rhodopsin
• The others are found in the 3 types cones
Phototransduc4on
Neural Pathway of Vision
• Pathway: – Op4c Nerve (C.N. II) – Op4c chiasm
• SCN
– Op4c tract – Thalamus – Visual cortex
Suprachiasma4c nucleus (SCN) controls circadian rhythms
Special Sense -‐ Hearing
Sound Transmission
Organ of Cor4
Sensory Hair Cells
Neural Pathway for Hearing
• Pathway: – Sensory hair cells – Cochlear branch of ves4bulocochlear nerve (C.N. VII, Auditory Nerve)
– Brainstem – Thalamus – Auditory cortex
Ves4bular System
• Ves4bular apparatus – Semicircular canals
– Utricle – Saccule
Semicircular Canals Rota4onal Movement
Utricle and Sacule • The macula provides info on changes in head posi4on rela4ve to: – Force of gravity – Linear accelera4on
• Ves4bular informa4on is used for: – Control eye movements – Reflexes to maintain posture
– Conscious awareness of ourselves in “space”
Gusta4on
Olfac4on