Lecture 6- Somatosensory And Motor Systems Flashcards
Where is somatosensation
All over the body
Somatosensory has a closer relationships with what than any other sense
Movement
Receptors are
All over skin, muscles, tendons, joints
More receptors =
More sensitivity to stimulation
What areas have more receptors
Hands, lips
What are the two kinds of skin
- Hairy skin
- Glabrous skin
Glabrous skin
- Skin that does not have skin follicles
- Larger number of sensory receptors than other skin
Hairy skin
Relatively low sensitivity
What are most sensitive
- Fingertips
- Higher density of mechanoreceptors
- Receptors with small receptive fields
Two point-discrimination test reveals
Differences in skin sensitivity across the body
Three main types of somatosensory perception
- Nocioception
- Hapsis
- Proprioception
What’s nocioception
Perception of pain and temperature
Hapsis
Perception of fine touch and pressure
Proprioception
Perception of the location and movement of the body
Nocioceptors
- Free nerve endings
- Sharp/dull pain and heat/cold
- Damage to dendrite or surrounding cells release chemicals that stimulate dendrite and produces an action potential
Haptic receptors
- Dendrite attached to hair, connective tissue or dendrite encased in capsule of tissue
- Distinguish touch, pull, vibration
- Mechanical stimulation provides action potential
- Composition of capsule determines the type of mechanical energy conducted
Proprioceptors
Movements stretch the receptors to mechanically stimulate dendrites and produces an action potential
Somatosensory receptors tell us 2 things about a sensory event
- When it occurs
- Whether it’s still occurring
Rapidly adapting receptor
Body sensory receptor that responds briefly to the beginning and end of a stimulus on the body
Slowly adapting receptor
Body sensory receptor that responds as long as a sensory stimulus is on the body
In the dorsal-root ganglion neuron the dendrite and axon are
Continuous and carry sensory information from the skin to the CNS via the spinal cord
Each spinal cord segment has one
Dorsal-root ganglion on each side that contains many dorsal-root ganglion neurons
In the spinal cord, the axons of these neurons may synapse onto
Other neurons or continue up to the brain
Proprioceptive neurons
- Carry information about locations and movement
- Large
- Well myelinated
Haptic neurons
- Carry information about touch and pressure
- Large
- Well myelinated
Nocioceptive neurons
- Pain and temp info
- Small axons
- Little to no Myelination
What’s deafferentiation
Loss of incoming sensory input usually due to damage to sensory fibres
Dorsal root ganglion neurons consequence of deafferentiation
- Did not lose motor control
- Simple actions for prolonged periods needed visual feedback
- Couldn’t perform many daily tasks
- Afferent feedback is required for fine movement
Dorsal spinothalamic tract carries
Haptic and proprioceptive information
Axons from the dorsal root ganglion neurons enter the spinal cord and ascend
ipsilaterally until they synapse in the dorsal column nuclei (base of the brain)
Axons from the dorsal column cross over to
- opposite side of the brain
- project up through the brain stem as part of the pathway- medial lemniscus
Axon synapses with neurons located in the ventrolateral nucleus of the thalamus project
To the somatosensory cortex and motor cortex
Ventral/ Anterior Spinothalamic Tract carries
Nocioceptive info
Unilateral spinal-cord damage results in
Distinctive sensory losses to both sides of the body below the site of injury
Vestibular system
Comprises a set of receptors in each inner ear that responds to body position and to the movement of the head
Within each ear, there is a vestibular organ that contains
- Three semicircular canals
- Otolith organs
Vestibular organs have which two functions
- Tell is the position of the body in relation to gravity
- Signal changes in the direction and speed of head movements
