Chapter 15: The Cutaneous Senses Flashcards
functions of touch
- Signals pain, reducing the chance of injury
- Makes it easier to interact with the environment (less force is needed)
- Motivating sexual activity
- Social function
somatosensory system
the system that includes the cutaneous senses, proprioception, and kinesthesis
cutaneous senses
responsible for perception such as touch and pain
proprioception
the ability to sense the position of the body and limbs
Kinesthesis
the ability to sense the movement of the body and limbs
Comel, 1953 on the skin
the skin is the monumental facade of the human body
epidermis
the outer layers of the skin, including a layer of dead skin cells
dermis
the layer of skin below the epidermis
mechanoreceptors
Receptors that respond to mechanical stimulation such as pressure, stretching, and vibration
4 types of mechanoreceptors
- merkel receptors
- meissner corpuscles
- rufficini cylinders
- pacinian corpuscles
merkel receptor
a disk-shaped receptor in the skin associated with slowly adapting fibres and the perception of fine details
location of the merkel receptor
Located near the epidermis
receptive fields of merkel receptors
small receptive field
alternative name for merkel receptors
Also called a slowly adapting (SA1) fibre because it fires continuously as long as the stimulus is on
meissner corpuscles
a receptor in the skin, associated with RA1 mechanoreceptors. It has been proposed that the Meissner corpuscle is important for perceiving tactile slip and for controlling the force needed to grip object
location of meissner corpuscles
Located near the epidermis
receptive field size of Meissner corpuscles
small receptive field
alternative name for meissner corpuscles
Also called a rapidly adapting fibre (RA1) because it fires when the stimulus is first applied and when it is removed
cutaneous receptive field
the area of skin which, when stimulated influences the firing rate of the neuron
ruffini cylinder
associated with perceiving stretching of the skin
location of ruffini cylinders
Located deep in the skin
size of receptive field of ruffini cylinders
Has a large receptive field
alternative name of ruffini cylinders
Also called a slowly adapting (SA2) fibre because it fires continuously as long as the stimulus is on
pacinian corpuscle
associated with sensing rapid vibrations and fine texture
where are pacinian corpuscles located?
deep in the skin
size of receptive field of pacinian corpuscles?
Has a large receptive field
alternative name of pacinian corpuscles
Also called a rapidly adapting fibre (RA2 or PC) because it fires when the stimulus is first applied and when it is removed
where are cutaneous receptors located
Cutaneous receptors are distributed all over the body
dorsal root
a bundle of fibres
how many segments does the spinal cord have?
31
where does the spinal cord receive signals from?
the dorsal root
2 major cutaneous pathways
- medial lemniscal pathway
- spinothalamic pathways
The medial lemniscal pathway
consists of large fibres that carry signals related to proprioception and perceiving touch
speed of signals in the medial lemniscal pathways
Transmits signals at a high speed
the spinothalamic pathway
consists of smaller fibres that transmit signals related to temperature and pain
where do cutaneous fibres cross over & synapse?
Fibres from both pathways cross over to the other side of the body and synapse in the ventrolateral nucleus of the thalamus
what brain areas are associated with cutaneous functions?
Many brain areas are associated with cutaneous functions
Primary somatosensory cortex (S1)
the area of the cortex in the parietal lobe that receives signals that originate from the body and stimulation of the skin
Secondary somatosensory cortex (S2)
the area in the parietal lobe next to S1 that processes neural signals related to touch, temperature, and pain
insula
important for sensing light touch
Anterior cingulate cortex (ACC)
involved in pain
The Jacksonian march
Jackson, 1870 noticed that seizures in epilepsy patients progressed around the body in an orderly way
stimulating S1
stimulating the ventral part of S1 (lower on the parietal lobe) caused sensations on the lips and face, stimulating higher on S1 caused sensations in the hands and fingers, and stimulating the dorsal S1 caused sensations in the legs and feet
Homunculus
a body map that shows that adjacent areas of the skin project to adjacent areas in the brain. Areas with more tactile receptors are disproportionately larger.
what does recent research show about the homunculus?
Recent research shows that S1 is divided into four interconnected areas, each with its body map
braille
the system of raised dots that enables blind people to read with their fingertips
speed of braille reading
Experienced Braille readers can read at a rate of about 100 words/ minute, slower than the average visual reader who averages 250-300 words/ minute
tactile acuity
the capacity to detect details of stimuli presented to the skin
two-point threshold
the minimum separation between two points on the skin that when stimulated is perceived as two points
how is two-point threshold measured?
Measured by gently touching the skin with two points and having the person indicate whether they feel one or two points
grating acuity
the narrowest spacing of a grooved surface on the skin for which the orientation can be accurately judged
how is grading acuity measured?
Measured by pressing a grooved stimulus onto the skin and asking the person to indicate the orientation of the grating