PSY247 Lecture Notes - Lecture 3: Vestibular Nuclei, Saccule, Otolith
4 Jun 2018
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Body senses
The somatosensory system
- Touch is used to sense physical properties.
- Proprioception is used to sense the position of body parts
in space.
- Kinesthesis is used to sense the movement of body parts
through space.
- Both proprioception and kinesthesis use the same organ
and therefore are generally studied as one. Somatosensory
transduction Tactile receptors
- These are sometimes called mechanoreceptors.
- Meissner’s corpuscles, which are located in the
epidermis.
- Merkel’s discs, which are located in the epidermis.
- Ruffini’s corpuscles, which are located in the dermis.
- Pacinian corpuscles, which are located in the subcutis.
Selectivity in the tactile receptors
- Meissner’s corpuscles and Merkel’s discs respond to light
touch.
- Ruffini corpuscles and Pacinian corpuscles respond best to
deep pressure and stretch.
- These receptors transduce environmental energy into
electrical impulses that can be processed in the brain.
Thermoceptors
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- These are free nerve endings.
- Warmth fibres signal an increase in skin temperature.
- Cold fibres signal a decrease in skin temperature.
Proprioception/kinaesthesia
- There are three sets of proprioceptive/kinaesthetic cells;
muscle spindles, Golgi tendon organs, and joint receptors.
- Muscle spindles, which respond to the length of muscle
length as well as the rate of stretch. o Muscle spindles wrap
around intrafusal muscle fibres.
- Golgi tendon organs, which respond to muscle tension.
- Joint receptors, which respond to joint position. The
somatosensory hierarchy
- When triggered, neurons follow one of two routes to the
brain; the spinothalamic or lemniscal tracts.
- The spinothalamic tract carries slow temperature signals
from free nerve endings, whilst the lemniscal tract carries fast
signals from mechanoreceptors.
- These varying speeds can lead to paradoxical sensations,
where you know you’ve experienced something before you
actually feel it. o This is a result of the mechanoreceptors feel
pressure before temperature, such as when you feel oil hit you
before you realise that it is hit.
- Both pathways have branching circuits in the spinal cord,
which mediate reflex responses. 20
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Somatosensory cortical organisation
- The primary somatosensory cortex is a thin strip that runs
across the top of the head, from ear to ear.
- Each neuron is selective to different areas of the skin, such
as the leg or hand. Somatotopic organisation
- The spatial layout of the body is preserved in the layout of
the brain. This means that the neurons for the fingers are next to
the neurons for the hand, etc.
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Document Summary
Touch is used to sense physical properties. Proprioception is used to sense the position of body parts in space. Kinesthesis is used to sense the movement of body parts through space. Both proprioception and kinesthesis use the same organ and therefore are generally studied as one. Meissner"s corpuscles, which are located in the epidermis. Merkel"s discs, which are located in the epidermis. Ruffini"s corpuscles, which are located in the dermis. Pacinian corpuscles, which are located in the subcutis. Meissner"s corpuscles and merkel"s discs respond to light touch. Ruffini corpuscles and pacinian corpuscles respond best to deep pressure and stretch. These receptors transduce environmental energy into electrical impulses that can be processed in the brain. Warmth fibres signal an increase in skin temperature. Cold fibres signal a decrease in skin temperature. There are three sets of proprioceptive/kinaesthetic cells; muscle spindles, golgi tendon organs, and joint receptors.
