General Senses Overview

General Senses

• Senses allow perception of the world through sight, hearing, taste, smell, and touch
• Senses provide information from both the external environment and the internal body
• The senses are divided into general and special senses
• General sensory receptors are spread throughout the body
• Special sensory receptors are located in structures on the head like eyes and ears
• Sensory receptors receive information and stimulate sensory nerve fibers to transmit it to relevant areas in the brain
• Sensory information helps maintain vitality
• Sensory receptors are specific to particular stimuli and don't respond or give a very little response to other stimuli
• Sensory receptors are divided into 5 groups according to what stimulates them
• Sensory receptors are stimulated by chemicals like smell and taste receptors.
• Chemoreceptors in internal organs are sensitive to oxygen, hydrogen, and glucose concentrations in the blood.
• Thermoreceptors are sensitive to temperature changes
• Mechanoreceptors are sensitive to physical forces that deform the receptor, baroreceptors in blood vessels are sensitive to blood pressure
• Stretch receptors in lungs are sensitive to tension in the rib cage when breathing
• Proprioceptors are sensitive to tension in muscles and tendons
• Photoreceptors are located in the eye and are sensitive to light energy
• Nociceptors or pain receptors are sensitive to tissue damage caused by excessive mechanical, chemical, thermal or electrical stimulation
• Receptors have limits leading to sensory limits, for instance we can only see part of electromagnetic waves known as the visible light-spectrum
• Ultraviolet, infrared, and x-rays cannot be seen because they do not stimulate photoreceptors in the eyes
• Specific sound frequencies can be heard, allowing for vital environmental information

Stimulus & Sensation

• When a stimulus starts from sensory receptors, it passes to sensory fibers and is transmitted to relevant brain regions
• Events up to this point are the sense stage
• Perception occurs with the processing of sensory information which reaches the cerebral cortex
• It's sensation occurs when a stimulus from sensory fibers reaches the brain, and the region determines the sense
• All stimuli reaching the cerebral cortex related to hearing are interpreted/perceived as "sound"
• Visual cortex stimulation from the outside, can cause a person sees flashes of light without any stimuli

Adaptation

• Adaptation is the mechanism where intensity of smell diminishes overtime.
• Receptors/sensory pathways to the brain provide less response to a stimulus at the same level
• If adaptation occurs, the nerve response decreases, so long as the stimulus intensity doesn't change.
• Adaptation is not the same for all senses, smell and touch adapt quickly, yet adapt very slow if at all to pain

Sensory Receptors

• General sensory receptors are all over the body in the skin, joints, muscles, and internal organs
• Touch, pressure, heat, cold, joint position, pain, and visceral senses are transmitted to the brain by sensory fibers
• Sensory fibers enter the spinal cord from the posterior horn on the same body half
• Sensory information carried to the thalamus by two spinal cord routes
• Sensory information traveling to the spinal cord passes to the opposite side at the medulla oblongata level (brainstem) and some cross at the level of the medulla spinalis before ascending
• Information from both routes ultimately reaches the thalamus
• All sensory pathways except smell pass through the thalamus and are transmitted to the relevant cortex region
• Sensory information crosses in the spinal cord, delivering information to the opposite cerebral hemisphere
• There is a sensory cortex map of the human body (homunculus)
• The face and hands are more broadly represented on the map because of the high sensory receptor density
• Sensations such as burning and stinging are transmitted via fast fibers for protection; pressure, coarse touch, and tickling are transmitted via slow fibers

Touch and Pressure

• Touch, pressure, and vibration are different senses perceived by the same receptors
• These receptors belong to the mechanoreceptor group
• They are stimulated by skin surface touch, deep pressure, and positions that cause deformation of the receptor
• Hairless skin and joint ligaments/tendons/capsules contain free nerve endings, Meissner corpuscles, Merkel discs, Pacinian corpuscles, and Ruffini terminations
• They adapt quickly
• Nerve endings at the hair roots function as receptors
• Hair movement causes stimulation
• These receptors are also sensitive to the sense of vibration

Heat

• Free nerve endings in the skin are the two different receptors for hot and cold
• Hot receptors are most sensitive between 25 °C and 45 °C
• Cold receptors are most sensitive between 10 °C and 20 °C
• Pain receptors are stimulated below 10°C and above 45°C, causing the feeling of burning and freezing pain
• Normal temperature ranges are a combination of two receptor information sent
• It adapts quickly to both heat and cold
• Receptors are mainly sensitive to temperature change.

Deep and Position Sense

• Proprioception is another name for position sense
• Superficial skin receptors and deep receptors in joints/tendons are used together
• The proprioception-related receptors are mechanoreceptors that transmit information to the brain about body position, muscle length, and tension
• This is important in perceiving the body parts' position such as hands, arms, legs, fingers relative to each other and how fast they move

Other information

• Knowing the angles and joint movement changes in each plane are necessary
• The most important information is the joint position information coming from muscle spindles, but this is not consciously perceived
• Information goes to the spinal cord and enables reflex mechanisms
• Reflex mechanisms are activated when there is excessive muscle and tendon tension to prevent damage and relax the necessary muscles

Visceral Sense

• "Visceral" means pertaining to the internal organs
• Receptors in internal organs carry information from our body to the brain
• Tension in the intestinal wall, stomach wall, and lungs is transmitted via the visceral sense
• Some of this information is transmitted before perception and the body's homeostasis/internal balance is provided
• Information such as pressure, tension, and abdominal pain in the occluded intestinal wall, reaches the cortex and is perceived

Pain

• Pain receptors are free nerve endings common throughout the body
• The brain tissue lacks pain receptors
• Headache pain comes from stretching brain membranes/vessels or damage the tentorium because these tissues have receptors
• The sense of pain functions to protect the organism, determine the pain source, and get away from it
• Pain receptors can be stimulated by mechanical force, chemicals, extreme heat/cold, decreased blood circulation (ischemia) or hypoxia
• Adaptation to pain usually does not occur
• Once stimulated a pain receptor can continue to send signals to the brain.
• Internal organs also have pain receptors that can trigger from extensive tissue damage called visceral pain
• Sensations from internal organs and the body surface have common nerve pathways
• Visceral pain is sometimes interpreted by the brain as originating from the superficial region using the same pathway causing what is called referred pain

Heart Attacks and Referred Pain

• Heart attacks cause pain in the left shoulder and arm, because the brain thinks the arm is where the pain is starting
• This is because the main source of pain from a heart attack is heart tissue

Types of Pain

• Acute pain is a sudden, sharp, stabbing pain transmitted by fast fibers, stopping in a short time when the source disappears
• Chronic pain is deeper, blunt, prolonged pain, transmitted by slow fibers, and persists even after the source is gone, potentially worsening
• Pain-transmitting fibers follow the same path as sensory fibers to the thalamus
• Pain can be perceived at the thalamus level, but exact location and severity can only be determined at the cortex level
• The pain receptor is the nociceptor
• Pain sensation is nociception

Pain & Nociception

• Pain is an unpleasant sensory and emotional state resulting from tissue damage
• Pain informs the nervous system that there is not compliance with physiological conditions
• Pain protects the organism by avoiding the unsuitable situation
• Nociception is the neural mechanisms of the nervous system's recognition of pain-causing conditions
• Pain perception is a subjective situation arising from the evaluation and elaboration of the process initiated by receptors
• Pain perception is affected in soldiers wounded in war, athletes injured in sports match and emotional states
• The subjective structure of pain combines the sense of pain with experiences and emotional state, which is processed in neuronal circuits
• People have differing pain reactions

Conduction Rate in Neurons

• Speed of nerve transmission varies by axon
• The table provided shows the rate of transmission of multiple neuron types from A-C

Nociceptors

• Thermal nociceptors
  • Respond to extreme cold (<5°C) or extreme heat (>45°C)
  • Use small diameter A type myelinated fibers (5-30 m/sec)
• Mechanical nociceptors
  • Activated by intense pressure
  • Use small diameter A type myelinated fibers (5-30 m/sec)
• Polymodal nociceptors
  • Respond to high-intensity mechanical, chemical, or thermal stimuli
  • Use unmyelinated type C fibers (0.5-2 m/sec)
• Viscera have silent receptors
  • Remain quiet under normal conditions but activate when there is a stimulus

Subjective Pain Conditions

• Pain naming
  • By Speed
    • Fast (A)
    • slow (C)
  • allodynia
    • Pain sensation occurs against innocuous stimuli
    • Ex: Pain due to sitting, sunburn pain
  • hyperalgesia
    • Increased sensitivity to stimuli
    • Primary hyperalgesia: increased pain receptor sensitivity
    • Secondary hyperalgesia: facilitation of pain transmission
      • Visceral hypersensitivity
  • Nociceptive Pain
    • Activation of pain receptors in skin and soft tissue
    • Substances produced as a result of tissue damage
  • Neuropathic Pain
    • Acceleration at dorsal horn synapses of pain pathways
    • Pain persists despite cutting of pain fibers
    • Resistant to analgesics

Pain Types

• Superficial pain originates
  • on the skin surface
  • well localized
• Deep pain is
  • Caused by lesions in bones, joints, and tendons
  • difficult to localize
  • May be accompanied by nausea, sweating and increased blood pressure
  • Muscle spasm can be seen as a reflex
• Muscle Pain
  • Insufficient blood circulation during muscle Activity
  • Cause of pain in myocardial infarction
• Visceral pain
  • Spasm, stretching, etc. of organs in the abdomen and thorax. cause pain
  • Very difficult to localize and uncomfortable
  • Can be accompanied by autonomic symptoms and is often reflected in other areas.
  • Causes muscle spasm as a reflex
  • Spasm increases, especially if the inflammation includes the peritoneum.
    • In cases of acute abdomen (such as appendicitis), the abdomen is severely hardened on abdominal examination.
• Parietal pain
  • A sharp pain that differs from visceral pain
  • A result of the damage to the internal organs spreading to the parietal peritoneum, pleura and pericardium.
  • Pain sensation of the visceral parts of the membranes is carried by autonomic fibers
  • The pain sensation of the parietal parts is carried by spinal fibers is how pain in the the skin (sharp pain).

Causes for Reflected Pain

• Reflected pain
  • Pain fibers from the visceral meet with from the somatic regions in the V. Lamina
  • For example, pain in the left arm along with the chest in patients with myocardial infarction
  • Chest pain in reflux patients -Dermatome rule: The area of skin affected is that the source of the is usually is related to the same source

Headache

• Headache -Usually felt as reflected pain, headache stems from areas such as the brain
  • Stretching of the venous sinuses around the brain or the dura at the base of the brain
  • Any damage to the meningeal vessels, inflammation or inflammation of the meninges
  • CSF pressure drop
  • migraine headache
  • Extracranial headache
    • Due to muscle spasm (especially neck region muscles)
    • As a result of irritation of nasal structures - Pain due to excessive contractions of the ciliary muscle

Pain related items:

• Endogenous substances that activates or sensitizes pain
  • Potasiun -Source: Damaged cells
  • Effect: Activation
  • Serotonine - Source: Trombocytes
    • Effect: Activation -Bradikinine -Source: Plasma kininojens
    • Effect: Activation -histamine
• Source: Mast Cell Effect Activation
  • Prostaglandins
• Damaged cells Effect: Sensitization -Lökotriens -Damaged Cells Sensitization -P Substances -Primary afferents -Sensitization

Pain Perception

• primary sensory cortex
• Cingulate gyrus and
• Insula