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

• No specific content on this page.

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.