The Somatosensory System Flashcards
What is generator potential? (a.k.a. receptor potential)
A stationary depolarization of a receptor that occurs in response to a stimulus and is graded according to stimulus intensity. It results in an action potential when the appropriate threshold is reached
Which structure in the muscle is responsible for sensation?
Muscle Spindle (responsive to stretch)
Which kind of receptor mediates touch vibration and pressure?
Low threshold mechanoreceptor
Which kind of receptor mediates cold, indifferent, warm and hot sensation?
Low threshold thermoreceptors
Which kind of receptors respond to high intensity mechanical stimuli? e.g. hammer to the thumb
High threshold mechanoreceptors (a.k.a. mechanical nociceptors)
Which kind of receptors respond to extremes of temperature?
High threshold thermoreceptors (a.k.a. thermal nociceptors)
Which kind of receptors respond to inflammatory substances in tissues? e.g. prostaglandins, histamine etc.
Chemical nociceptors
If a receptor responds to more than one type of noxious stimuli, it is called ______?
A polymodal nociceptor
If a neurone fires constantly throughout a constant stimulus, it could be described as ______?
Slowly-adapting
If a neurone becomes less sensitive over time, or alters its firing in response to a change in stimulus strength, it could be described as ______?
Rapidly-adapting
Classifications of axons from the skin, in decreasing order of diameter, degree of myelination and conduction velocity.
Aα, Aβ, Aδ, C
Which axon classification is responsible for proprioception of skeletal muscle?
Aα
Which axon classification is responsible for mechanoreception in the skin?
Aβ
Which axon classification is responsible for temperature and pain?
Aδ
Which axon classification is responsible for temperature, pain and itch?
C
What is the receptive field of a neurone?
The region that when stimulated with an adequate stimulus causes a response in that neurone. The size of each RF differs greatly across the body.
How is the grey matter in the spinal cord divided?
Dorsal (posterior) and Ventral (anterior) horns + 10 laminae of Rexed
What does the Dorsal Column Medial Leminscal Pathway (DCML) convey?
Touch, pressure, vibration and proprioception (Aα + Aβ)
What does the Spinothalamic Tract (STT) convey?
Pain, temperature, crude touch, itch (Aδ + C)
Where do fibres decussate (cross over) in the DCLM?
All fibres travel ipsilaterally and cross together in the brainstem
Where do fibres decussate (cross over) in the STT?
These fibres each cross independently, synapsing shortly after entering the spinal cord, then travel contralaterally.
What are the 2 subsections of the dorsal column?
Fasciulus Gracilis (medial) and Fasiculus Cuneatus (lateral)
What travels in the Fasiculus Gracilis?
Sensory input from below T6
What travels in the Fasiculus Cuneatus?
Sensory input from above T6
What is lateral inhibition?
The capacity of an excited neuron to reduce the activity of its neighbours. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception.
How does somatic information from the anterior head reach the brain?
The Trigeminal Nerve (CN V)
Where is the soma of the trigeminal nerve located?
Trigeminal Sensory Ganglion
Where is the somatosensory cortex located?
The post-central gyrus of the parietal cortex, immediately posterior to the central sulcus.
The somatosensory cortex can be divided functional areas known as _______?
Brodmann Areas (BA)
What is the input to BA 3a?
Muscle spindles (proprioception) - body position
What is the input to BA 3b?
Cutaneous mechanoreceptors + BA 3a (touch)
What is the input to BA 1?
Cutaneous mechanoreceptors + BA 3b (texture discrimination)
What is the input to BA 2?
Joint afferents, Golgi tendon organs, BA 3a, BA 3b
What happens to the area responsible for sensory interpretation if a corresponding body part is lost?
The area int he cortex becomes responsive to the input from the area around the site of loss. This can cause phantom limbs.
What happens to the area responsible for sensory interpretation if input from the corresponding body part is increased?
The cortical representation of that area, over months, increases, relative that of inputs generating less activity
What is the function of the posterior cortex?
It receives information from cortical areas (Brodmann areas, visual, auditory) and sub-cortical areas. it deciphers the deeper meaning.
