The Eight Senses: Touch, Pain, Balance and Kinesthesis

The Eight Senses: Touch, Pain, Balance and Kinesthesis

 

 

Types

Physical stimulus

Equipment

Sub-Structures

Roles of the Brain

Theories

Touch Cutaneous receptors for stimuli:

pressure, vibration, heat, cold, etc.

Hair follicle ending (in the skin): for hair displacement

Ruffini endings (under epidermis): for pressure

 

Krause corpuscle (lips, tongue, genitals): for pressure

 

Pacinian corpuscle (deep skin layers): for vibration (150-300 Hz)

 

Meissner corpuscle (deep hairless skin layers): for vibration (20-40 Hz)

 

Merkel discs (hairless skin top layer): for pressure

 

Thermoreceptors (under epidermis): for temperature (30-43o)

 

Cold receptors (under epidermis): for temperature (20-35 o)

Receptors -> action potential -> afferent nerve tracts -> spinal column -> thalamus -> parietal lobes (cerebral cortex) Primary somatosensory cortex, motor cortex:

frontal lobe (elaboration of thought, mastication, motor elaboration, swallowing, tongue);

occipital lobe (bilateral vision, contralateral vision), cerebellum;

parietal lobe (sensory elaboration, salivation);

temporal lobe (perceptual judgment, visual and auditory recollection, hearing);

motor (arm, leg, hand, lips, articulation);

sensory (arm, leg, hand, lips, tongue, mouth);

The sensory homunculus

Phantom limb phenomenon:

the brain has specific space for the limb, stimulation in neighboring areas

-> cause physical sensation

Pain Nociception:

an unpleasant response caused by tissue damage and emotional responses as warning messages to avoid self-injury

Nociceptor: free nerve endings for sending pain messages (action potentials -> afferent nerve tracts -> spinal cord)   Pain + touch messages  -> primary somatosensory cortex Gate control theory:

pain messages have to get through a neuronal gateway -> proceed/block

Substance P: elevate pain signals Pain -> brain -> emotional response (with memory in the limbic system) -> avoid future stimuli
Endorphins: decrease substance P’s effects Hypnosis, placebo effect -> pain relief
Balance Vestibular sense:

head position, head/body moving speed

Semicircular canals: in different directions, with fluid, hair cells   Posture, movements, self-protection Motion sickness:

conflicts of information between the balance system (e.g., no motion) and the visual system (e.g., motion)

Otolith organs: otoliths (calcium carbonate particles) -> hair cells -> cranial nerve 8 -> the brain
Kinesthesis Limb and joint motions, weights;

procedural memory

Proprioceptors/mechanoreceptors:

Muscle spindle in skeletal muscles for muscle stretching;

Golgi tendon organs for tension in tendons;

Joint receptors around joints for joint motions

  Muscle, tendons, joint information -> brain regions  

 

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