Lecture 11 - The body senses Flashcards
What are the three main somatosenses?
Cutaneous sense
Organic (internal) sense
Vestibular sense
What are the somatosenses?
All other senses that we have that are not hearing, taste, touch, smell or sight.
What is the cutaneous sense?
Sensitivity to stimuli that involve the skin. e.g. pressure, vibration, heating/cooling, and events that cause tissue damage (i.e. pain).
Multiple receptor types are responsible for detecting specific sensations
What is the organic sense?
A sense modality that arises from receptors located within the inner organs of the body and muscles
Proprioception: ability to sense position of the body and limbs
What is the vestibular sense?
Perception of the body’s position, movement and balance.
Describe the vestibular system
- Part of inner ear
- Made up of 3 semicircular canals and vestibular sacs
- Filled with fluid
- Movement of fluid within the system stimulates hair cells
- Position of fluid in the sacs detect head tilt and linear acceleration
- Movement of fluid in the semicircular canals detect head rotation movements
What are semicircular canals?
A structure in inner ear consisting of three canals (anterior, posterior, and lateral) arranged in different planes to detect angular accelerations during head movements. Contain receptors that respond to rotational head movements.
What are vestibular sacs?
Two fluid-filled sacs in inner ear that sense movement of the head forward and backward or from side to side (horizontally), sensing acceleration, or tilting up and down (vertically), sensing gravity
What are the layers of the skin?
- epidermis
- dermis
- hypodermis
What is the heaviest organ in the body?
skin
What is the epidermis layer?
Thin outer layer that provides a protective barrier against pathogens
What is the dermis layer?
Thickest layer containing connective tissue, capillaries, hair follicles and sensory receptors
What is the hypodermis layer?
Bottom layer of subcutaneous tissue/fat
What are the sensory receptors in the skin?
There are 5
1. Free nerve endings (respond to pain and temperature)
4 different mechanoreceptors:
2. Merkel receptors
3. Meissner corpuscle
4. Ruffini cyliner
5. Pacinain corpuslce
What are free nerve endings?
Found in both hairy and non-hairy skin (e.g., palms and soles of feet)
Located close to the epidermis and in hairy skin surround hair follicles
Also distributed around bones, within muscles and internal organs
Respond to damaging or potentially damaging stimuli
What are merkel receptors?
Fires continuously in response to pressure
Responsible for sensing fine details, shape and texture
What are the meissner corpuscle receptors?
Fires only when a stimulus is first applied and removed
Responsible for controlling hand grip and sensing motion across the skin
What are the ruffini cylinder receptors in the skin?
Located more deeply in the skin
Fires continuously in response to stimulation
Associated with perceiving stretching of the skin
What are the pacinian corpuscle receptors in the skin?
Located more deeply in the skin
Fires only when a stimulus is first applied and removed
Associated with sensing rapid vibrations and fine texture
What is proprioception?
Our sense of body position and movement
How does proprioception occur?
Sensory nerve endings located in our internal organs, bones and joints protect against possible damage from strain.
Specialised receptors in our muscles detect changes in muscle length and mechanoreceptors respond to the movement and the angles of our joints.
These together result in proprioception
What is the spinothalamic tract?
a neural pathway that carries sensory information from the body to the thalamus
What is the dorsal column pathway?
a sensory pathway in the central nervous system that transmits sensory information from the skin and joints to the cerebral cortex
Describe the case of Ian Waterman.
Contracted a viral illness when he was 19
Damaged the dorsal column (medial lemniscal) pathway in his spinal cord
As a result, he could no longer sense touch, pressure or proprioception
Was unable to move and had to relearn to walk and live independently
What is tactile aucity?
The extent to which we can distinguish between two points of tactile stimulation
What are the receptor mechanisms of tactile acuity?
Merkel receptors are densely packed on the fingertips and have small receptive fields.
They fire continuously while a stimulus is present - responsible for sensing fine detail and shape.
Two-point and grating acuity thresholds very low in the fingertips, consistent with the density of Merkel receptors.
Where is tactile acuity greatest in the body?
Areas such as the fingertips and tips (<5mm thresholds)
Where is tactile acuity lowest in the body?
Tactile acuity is poorest in the trunk, back, legs and upper arms
Describe tactile acuity in the cortex.
Neurons in the somatosensory cortex also have distinct receptive fields
Stimulation of two nearby points on the finger causes separated activation in the finger area of the cortex, but stimulation of two nearby points on the arm causes overlapping activation in the arm area of the cortex.
