Sensory and Motor Functions

Sensory and Motor Functions

Introduction

  • Lecture 23 covers sensory and motor functions, focusing on Chapters 36 and 38.
  • Topics include: different types of receptors, visual senses, taste and smell, sound detection and balance, muscle anatomy, and muscle physiology, including the sliding filament theory.

Action Potential

  • Action potentials facilitate communication between cells.
  • All action potentials are the same; differences arise from which cells send the action potential and how recipient cells interpret it.

Sensory and Motor Functions

  • Sensory Information:
    • A sensory nerve detects a hot flame and transmits this information to the spinal cord.
  • Motor Response:
    • The spinal cord sends a message through a motor nerve to move the hand away from the flame.

Types of Sensory Receptors (Based on Function)

  • Touch
  • Temperature
  • Pressure
  • Pain
  • Sound
  • Chemicals
  • Motion
  • Electromagnetic Radiation

Touch and Pressure

  • Mechanoreceptors: Receptors physically stimulated.
    • Meissner’s corpuscles: Modified dendrites of neurons in the surface skin layers, responsible for light touch.
    • Merkel’s disks: Modified dendrites of neurons in the surface skin layers, responsible for light touch.
    • Pacinian corpuscles: Modified dendrites of neurons deep in skin layers, responsible for deep pressure.

Temperature

  • Thermoreceptors: Detect heat or cold and help regulate body temperature using feedback mechanisms.
    • Ruffini’s end organs: Stimulated by heat.
    • End Bulbs of Kraus: Stimulated by cold.

Pain

  • Nociceptors: Naked dendrites (free nerve endings) that detect excess heat, pressure, or chemicals.

Motion and Sound

  • Stretch receptors: Primarily found within muscles, detect changes in length.
  • Hair cells: Specialized cilia in the ear, important for sound detection and balance.

Chemical

  • Chemoreceptors: Stimulated by chemicals, transmit information about the total solute concentration of a solution (air, liquid).
    • Gustatory receptors: Taste receptors.
    • Olfactory receptors: Smell receptors.

Electromagnetic Radiation

  • Photoreceptors (rods and cones):
    • Detect light, a form of electromagnetic radiation, including visible and non-visible light (infrared).

Special Senses - The Visual System

  • Three distinct layers:
    • Outer fibrous tunic
    • Middle vascular tunic
    • Inner nervous tunic

Layer 1: Outer Tunic

  • Components:
    • Cornea
    • Sclera

Layer 2: Middle Tunic

  • Components:
    • Choroid
    • Ciliary body
    • Iris
    • Lens

Accommodation

  • Accommodation: The changing of the lens shape to view objects at varying distances, facilitated by ciliary muscles and suspensory ligaments.

Refraction

  • Refraction: Bending light to focus it to a point on the retina.
  • Refraction Disorders:
    • Myopia (nearsightedness): Corrected with a concave lens.
    • Hyperopia (farsightedness): Corrected with a convex lens.
  • The cornea and lens are important for focusing (bending) the light onto the retina.

Refraction Disorders 2

  • Presbyopia: Age-related farsightedness.
  • Astigmatism
  • The cornea and lens are important for focusing (bending) the light onto the retina.

Light Regulation

  • Light (bright or dim) regulates the constriction or opening of the iris.
  • Normal light.
  • Dark (dilates).
  • Bright light (constricts).

Layer 3: Inner Tunic

  • Components:
    • Retina
    • Fovea (and macula)

Photoreceptor Cells on Retina

  • Two types of photoreceptor cells on retina - rods and cones - stimulated by light and send impulse to brain.
  • Monochromatic vision.
  • Color vision.

Distribution of Cells Across the Retina

  • The distribution of rods and cones varies across the retina.
  • conescones are concentrated in the fovea, while rodsrods are more prevalent in the periphery.

Aqueous and Vitreous Chambers

  • Aqueous Chamber: The anterior chamber of the eye filled with aqueous (water-like) fluid (humor).
  • Vitreous Chamber: The posterior chamber of the eye filled with vitreous (jelly-like) fluid (humor).

Mammalian Vision

  • Most mammals are primarily nocturnal.
  • Well-developed night vision but lack well-developed color vision.
  • Not colorblind.

Tapetum

  • Tapetum: (reflective choroid under translucent retina).

Primate Vision

  • Primates are diurnal and have color vision.
  • Large amount of cone cells present.

Special Senses - Taste and Smell

  • Taste - Gustation
  • Smell - Olfaction
  • Function of each is similar and related

Sense of Taste

  • Sense of taste comes from taste cells (gustatory cells) located on taste buds
  • Sensitive to five primary tastes: sweet, sour, salty, bitter, and umami.

Taste Reception

  • Microvilli pick up dissolved chemicals in saliva.
  • Gustatory receptor cells are concentrated in groups called taste buds or pores.

Sense of Smell

  • Sense of smell – 400 different olfactory receptors bind odorant
  • Chemicals dissolved in mucus cause dendrites to fire.

Olfaction

  • 400 different olfactory receptors bind odorant
  • Different odors trigger different combinations of receptor cells
  • Unlike taste, not limited to five messages.
  • Olfaction - receptor cells are located in roof of nasal cavity.