Human Physiology BIOL3205 Quiz

Human Physiology BIOL3205

• Course offered by Prof. Chi Bun Chan, School of Biological Sciences, 5N10 Kadoorie Biological Sciences Building, HKU
• Contact information: [email protected], 39173823

Lecture Outline

• General properties of the sensory and motor nervous system
• Sensory receptors
• Sensory coding
• Pain and analgesic systems
• Peripheral nervous system structure
• (Para)Sympathetic nervous system
• Reflex actions

Why We Can Sense the World

• Sensory systems function through specialized receptors detecting specific energy forms (e.g., light, X-ray).
• Perception involves interpreting sensory input, memory, and other neural processes.
• Perception is not absolute; for instance, water temperature in a pool is relative to personal experience.

General Properties of Sensory Systems

• Sensing involves detecting stimuli in the form of physical energy.
• Special senses include vision, hearing, taste, smell, and balance.
• Somatic senses include touch, temperature, pain, itch, and proprioception (awareness of body position).
• Sensory systems can be complex or simple, with single neurons or sense organs (e.g., ear, eye) as components.
• Sensory receptors trigger action potentials, integrated in the CNS leading to conscious or subconscious perception.

Classification of Neurons

• Neurons are classified by function:
• Afferent neurons (sensory): carry signals to the CNS.
  • Somatic afferent neurons detect body sensation.
  • Visceral afferent neurons detect internal organ sensation
• Interneurons (99%): connect sensory and motor neurons within the CNS.
• Efferent neurons (motor): carry signals from the CNS to effectors (muscles or glands).

Sensory Receptors and Units

• Sensory receptors detect specific energy forms from the environment.
• They can be nerve endings or separate cells.
• Sensory units comprise a single afferent neuron and receptor.
• Receptor fields are areas where an adequate stimulus activates the sensory neuron.
• Important receptor types include:
  • Photoreceptors (respond to light)
  • Chemoreceptors (respond to chemical stimuli)
  • Thermoreceptors (respond to temperature changes)
  • Mechanoreceptors (respond to pressure or movement)
  • Proprioceptors (detect body position)
  • Nociceptors (respond to pain or tissue damage)

Sensory Transduction in Neural Pathways

• Sensory transduction converts stimuli into receptor potentials.
• Nerve endings generate action potentials when the stimulus surpasses the threshold.
• Cells transmit signals through neurotransmitters to trigger more action potentials in other neurons.
• Graded receptor potentials decrease over time in the presence of constant stimulation.
• Sensory pathways involve first-, second-, and third-order neurons.

Sensory Coding

• Sensory coding processes information about stimulus type, strength, and location.
• Coding is based on the specific activated receptors and pathways.
• Misinterpretations occur if non-specific pathways are triggered.
• Perception utilizes a combination of pathways to detect stimuli.
• Stimulus intensity is encoded by the frequency of action potentials and the number of receptors activated.
• Stimulus location is based on receptive fields (areas where an adequate stimulus stimulates the afferent neuron) and the time difference in generating action potentials.

Thalamus

• The thalamus acts as a relay station, screening sensory signals before routing important ones to the somatosensory cortex.
• This process filters out insignificant signals.
• E.g., Parents can filter out the general crying of a baby but focus on heightened intensity or location of the crying.

Physiology of Pain

• Pain is classified by its duration (sharp or dull) and location (referred pain, indicating tissue damage).
• Nociceptors (mechanical, thermal, and polymodal) initiate pain signals.
• The pain pathway avoids subsequent encounters with potential damaging stimuli.

Endogenous Analgesic Pathway

• Pain pathways have diverse destinations (cortex, thalamus, reticular formation).
• Substance P transmits pain signals.
• An endogenous pain-suppression system exists (releasing endorphins to inhibit substance P).
• Morphine is a powerful analgesic.

Morphine as an Analgesic

• Opioids act on opioid receptors (morphine is a type of opioid).
• They are pain-relieving drugs.

Why Rubbing the Hurt Site

• Sensory information is modulated at the synapse to alter the final perception.
• Gate-control theory suggests non-painful stimuli inhibit pain signals in the spinal cord.
• Transcutaneous electrical nerve stimulation (TENS) stimulates inhibitory pathways to reduce pain.

Can We Sense the Damage of Internal Organs?

• Referred pain occurs when visceral (organ-related) nociceptors are activated and cause pain sensation in a location other than the affected body surface.
• E.g. Heart attack sensations can cause pain in the left arm because the visceral sensation of the heart is processed with the common sensory neuron in the left arm.

Classification of Neurons (revisited)

• A review of afferent, somatic afferent, visceral afferent, interneurons, and efferent neurons, as well as the 99% interneuron count and all CNS location of interneurons..

Peripheral Nervous System (PNS)

• PNS consists of somatic nervous system (voluntary muscles) and autonomic nervous system (involuntary actions).
• The autonomic system includes sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) divisions.
• Dual innervation - most organs receive input from both divisions, affecting function accordingly.
• Sympathetic and Parasympathetic divisions function within the PNS.

Organization of PNS

• Breakdown of the PNS components, including afferent neurons (receiving stimuli), interneurons, and efferent neurons (triggering responses).
• Specific locations of neuron cell bodies and fiber pathways are included.

Locations of Sympathetic and Parasympathetic Ganglia

• Graphic illustrations demonstrating the locations where ganglia of the sympathetic and parasympathetic nervous systems are located relative to the spinal cord and other internal organs.

Anatomical Comparison of Sympathetic and Parasympathetic Systems

• A comparison of the sympathetic and parasympathetic systems highlighting structural differences (locations of ganglia) and functional ones (neurotransmitters released and type of effects).

Functional Characteristics of Autonomous Nervous System

• Details about sympathetic dominance (fight or flight) and parasympathetic dominance (rest and digest), discussing how the two systems work together.
• Effects (stimulatory or inhibitory) on various organs under different scenarios of nervous system activation.

Comparison of Types of Neurons

• Further classification and overview of neurons, and their characteristics.
• A comparison of afferent, somatic, autonomic, and interneurons.

Control of Autonomous Nervous System

• Overview of the brain regions involved in regulating the autonomic nervous and endocrine systems, with a particular focus on the hypothalamus.
• Discussion of the limbic system's role in emotion and the control of essential functions like body temperature, food intake, and sleep-wake cycle.

Reflexes

• Reflex actions are automatic, subconscious responses.
• Cranial and spinal reflexes are discussed.
• Reflex arcs (the neuronal pathway involved) – including their components (sensory receptors, interneurons, motor neurons).
• Types of reflexes (monosynaptic and polysynaptic) are elucidated.

Basal Nuclei

• Basal nuclei are involved in controlling voluntary movement, supporting smooth and sustained muscle contractions, and inhibiting unwanted movements.
• The role of basal nuclei in posture and their interplay with the cortex, thalamus, and cerebellum are studied.
• Neurological disorders such as Parkinson's disease involve damage to dopamine-producing neurons affecting motor control.

Summary

• Highlights of the major topics covered in the course, including sensory and motor systems, pain and modulation mechanisms, the autonomic system functions and effects on organs, and voluntary movement control mechanisms.