lecture 13 physiology

Page 1: Introduction

  • Course: BIO 1220 Human Physiology

  • Instructor: Dr. Suzanne Gray, UPEI

  • Topic: Lecture 13 – Sensory Systems

Page 2: Lecture Overview

  • Focus Topics:

    • General Properties of Sensory Systems

    • Skin: Sensory Receptors

    • Muscles and Joints: Proprioceptors

    • Taste and Smell: Chemoreceptors

    • Equilibrium and Hearing: Mechanoreceptors

    • Vision: Photoreceptors

Page 3: General Properties of Sensory Receptors

  • Function: Respond to environmental stimuli

  • Mechanism: Convert various forms of energy into signals interpreted by the brain.

  • Types of receptors:

    • Interoceptors: Respond to internal stimuli

    • Exteroceptors: Respond to external stimuli

Page 4: Information Carried by Sensory Systems

  • General Senses: Detect stimuli relating to touch, temperature, pain, etc.

  • Special Senses: Include vision, hearing, taste, balance, olfaction.

Page 5: Structure of Sensory Neurons

  • Free Nerve Endings:

    • Dendrites that act as receptors.

  • Encapsulated Nerve Endings:

    • Specialized structures with a defined termination.

  • Specialized Receptor Cells:

    • Rods and cones - examples from visual sensors.

Page 6: Classification of Sensory Receptors

  • Categories based on energy conversion:

    • Chemoreceptors: Chemicals

    • Photoreceptors: Photons of light

    • Thermoreceptors: Heat

    • Mechanoreceptors: Physical movement

Page 7: Types of Sensory Receptors

  • Mechanoreceptors: Respond to pressure, vibration, acceleration (e.g. cochlea has ~16,000)

  • Photoreceptors: Detect light; comprise rods and cones (total ~126 million in eyes).

  • Thermoreceptors: Detect temperature changes, mainly located in the skin.

  • Chemoreceptors: Respond to concentration of solutes in fluids, including O2, CO2, and glucose.

Page 8: Sensory Modality and Receptor Types

  • Modalities and their corresponding receptors:

    • Vision: Rods and cones (retina)

    • Hearing: Hair cells (organ of Corti)

    • Taste and Smell: Chemoreceptors

    • Touch: Mechanoreceptors (Pacinian corpuscles, free nerve endings)

Page 9: Sensory Adaptation

  • Phasic Receptors:

    • Fast adaptation; cease response to constant stimuli.

  • Tonic Receptors:

    • Slow adaptation; continuous response to constant stimuli.

Page 10: Skin Sensory Receptors

  • Various types of sensory receptors for:

    • Touch

    • Pressure

    • Heat

    • Cold

    • Pain

Page 11: Skin Structure Overview

  • Key elements:

    • Hair shaft, basement membrane, hair follicles, blood vessels, epidermis, dermis, hypodermis, sudoriferous glands, sebaceous glands.

Page 12: Types of Skin Sensory Receptors

  • Free Nerve Endings

  • Meissner Corpuscles

  • Merkel Disks

  • Krause End Bulbs

  • Ruffini Endings

  • Pacinian Corpuscles

Page 13: Free Nerve Endings in Skin

  • Thermoreceptors that detect temperature:

    • More cold than heat receptors

    • Heat receptors: 32-48ºC

    • Cold receptors: 10-40ºC

Page 14: Nociceptors

  • Purpose: Detect harmful stimuli.

  • Locations: Skin, joints, cornea, deep tissues.

  • Response types:

    • Myelinated: fast response to pain.

    • Nonmyelinated: slower, dull ache response.

Page 15: Special Note

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Page 16: Mechanoreceptors in Skin

  • Free nerve endings around hair follicles.

  • Types of Encapsulated Nerve Endings:

    • Ruffini’s endings: Detect sustained pressure.

    • Meissner’s corpuscles: Detect fine touch and vibrations.

    • Pacinian corpuscles: Respond to deeper pressure.

Page 17: Receptor Density

  • Wide Receptive Fields: Less precision in sensation.

  • Narrow Receptive Fields: Greater density increases sensitivity.

Page 18: Thermoreceptor Pathways

  • Integration of sensory pathways:

    • Thermal input from thermosensory pathways

    • Mechanical inputs from mechanosensory pathways

Page 19: Proprioceptors in Muscles and Joints

  • Receptors located in muscles, joints, tendons, and ligaments.

  • Function: Provide sense of body position and control body positions, detect stretching, contraction.

Page 20: Proprioceptor Types

  • Muscle Spindles:

    • Detect changes in muscle length; trigger action potentials.

  • Golgi Tendon Organs:

    • Located in tendons; provide information on tension.

Page 21: Taste and Smell - Chemoreceptors Overview

  • Both senses involve chemoreceptors.

  • Smell: Detects gaseous molecules.

  • Taste: Detects dissolved food chemicals.

Page 22: Taste Receptor Cells

  • Structure: Clustered in taste buds on the tongue.

  • Microvilli project from surface into saliva.

Page 23: Taste Cell Mechanism

  • Non-neural epithelial cells can depolarize.

  • Bind chemicals via G-protein coupled receptors, leading to neurotransmitter release and sensory neuron activation.

Page 24: Taste Signals

  • Types of Taste:

    • Sweet: Sucrose, fructose.

    • Salty: Sodium ions.

    • Sour: Hydrogen ions.

    • Umami: Glutamate.

    • Bitter: Alkaloids in plants.

Page 25: Olfactory Sensory Neurons

  • Located in nasal cavity; form dendritic connections.

  • Axons contribute to the olfactory nerve; synapse with neurons in the olfactory bulb.

Page 26: Olfactory Receptors

  • Comprise multiple cilia on olfactory neurons.

  • Around 400 different receptors can distinguish approximately 10,000 smells.

Page 27: Emotional Connection to Smell

  • Amygdala’s role: Involved in emotional responses to odors.

  • Olfactory bulb: Part of the limbic system, influencing emotion and memory (linked to the hippocampus).

Page 28: Midterm Information

  • Date: Friday, February 7, 2025 from 8:30 am to 9:20 am.

  • Format: Multiple choice (1 mark each) and short answer.

  • Review materials will be posted on Moodle.

Page 29: Lecture Recap

  • Summary of sensory systems discussed and midterm logistics.

  • Next class: In-class Midterm 1.