Sensory Physiology Overview

Sensory Physiology Overview

• Sensory Physiology is a study of the nervous system, covering general sensory system properties, somatic senses, vision, hearing, and the spinal cord/motor cortex.

Overview of This Section

• General Properties of Sensory Systems: Includes smell and taste.
• Somatic Senses: Focuses on touch, temperature, and pain.
• Vision
• Hearing
• Spinal Cord and Motor Cortex

Sensation and Motor Control

• Sensory input is transmitted through the nervous system to the brain.
• The brain integrates the sensory information.
• Motor output is created based on the brain's integration.
• The process illustrates how sensory input affects motor control.

Basic Principles of Sensation

• The afferent division of the peripheral nervous system provides information about the internal and external environment.
• Our bodies detect specific types of energies or stimulus modalities.
• Specialized receptors within the afferent division convert stimuli into action potentials, transmitted to the central nervous system (CNS).

General Overview

• A stimulus is converted into a response through receptors, neurons, and the CNS.
• The CNS interprets and responds to the sensory information.

Types of Sensory Receptors

• Photoreceptors respond to wavelengths within the visible spectrum.
• Mechanoreceptors detect mechanical energy like stretch, deformation, or bending.
• Chemoreceptors detect specific chemicals.
• Nociceptors are pain receptors triggered by tissue damage.
• Thermoreceptors detect heat and cold.
• Osmoreceptors monitor solute concentration and osmotic activity.

Two Classes of Sensory Receptors

• Complex Neural Receptors have specialized nerve endings, myelinated axons, and cell bodies (e.g., olfaction and somatic senses).
• Special Senses Receptors include specialized receptors, synapses, myelinated axons, and cell bodies(e.g., vision, hearing, balance, and taste).

Transduction at Complex Neural Receptor

• Stimulus application alters the receptor membrane (e.g., opening sodium channels).
• There's a current flow within the receptor.
• Graded potentials, known as receptor potentials, alter in frequency.
• Action potentials traverse the central nervous system.

Transduction at Special Senses Receptor

• Stimulus application alters receptor membrane (e.g., light causing sodium channels to close).
• Local current flow creates receptor potentials (graded potentials).
• Neurotransmitters are released.
• Postsynaptic membrane potential changes.
• Frequency of action potentials (APs) varies.
• APs travel to the central nervous system.

Action Potentials vs. Receptor Potentials

• Receptor potentials differ from action potentials.
• Action potentials are all-or-none events propagating down the axon.
• Receptor potentials are graded, varying in amplitude and dissipating over time and distance.

Intensity and Duration of Stimulus

• Stronger or longer stimulus leads to higher-frequency action potentials.
• This results in more neurotransmitter release.

Receptive Fields

• A receptive field is the part of the sensory space that can affect a neuron's activity.

Smell

• Olfactory receptor cells (primary sensory neurons) synapse with secondary neurons in the olfactory bulb.
• About 350 different odor receptors.
• Combinations of signals from these neurons allow us to perceive various smells.

Taste

• Taste is a combination of sweet, sour, salty, bitter, and umami sensations.
• About 2000-5000 taste buds.
• Each taste bud has 50-150 taste cells (non-neural epithelial).
• These taste cells are responsible for taste transduction.

Important Structures of the CNS for Sensory Physiology

• Cerebrum (cortex, basal ganglia, limbic system)
• Cerebellum
• Brain stem (medulla oblongata, pons, midbrain)
• Diencephalon (thalamus, hypothalamus, pineal gland, pituitary gland)
• Spinal cord

Cortical Anatomy

• Frontal lobe (movement and cognition)
• Parietal lobe (sensation)
• Temporal lobe (hearing and object perception)
• Occipital lobe (vision)

Smell – Brain Pathways

• Olfactory cortex and olfactory bulb involved.

Taste – Brain Pathways

• Gustatory cortex, thalamus, and brain stem involved.

Touch – Somatic Senses- Brain Pathways

• Somatosensory cortex, thalamus, and brain stem involved.

Vision – Brain Pathways

• Thalamus and visual cortex are part of the pathway.

Hearing – Brain Pathways

• Thalamus and auditory cortex are part of the pathway.

Balance – Brain Pathways

• Thalamus and the vestibular apparatus are part of the pathway.

Explore the intriguing world of sensory physiology, which encompasses the study of the nervous system, sensory systems, and motor control. This overview covers essential topics like vision, hearing, somatic senses, and the role of the spinal cord in sensory integration.