Explain the first order, second order, and third order neurones in the somatosensory system
First order - pass electrical stimulus to spinal cord
Second order - ascends to the brain and synapses with the third order neurone
Third order - Cell body Located in the ventral posterior nucleus in the thalamus of the brain takes the impulse to the necessary part of the brain
Where is the ventral posterior nucleus located? What is it?
It is the somatosensory relay nucleus in the thalamus of the brain
What neuron is used for the sensation of pressure, vibration, and texture?
What type of neuron is used for the sensation of light touch and vibration?
What neuron is used for the sensation of temp?
What neuron is used for the sensation of pressure?
What are proprioceptors and where are they located? What types are there?
Proprioceptors in the muscles tells the body where it is in space and allows it to function properly.
2 main types:
- muscle spindle tells about the length of the muscle
- Golgi tendon organ measures tension in the tendons
How is an intense stimulus transmitted in a neuron?
Frequency coding - Strength determined by rate of APs
Activation of neighbouring cells
What are tonic and phasic receptors? Give example of each
Tonic receptors - slowly adapting and keep firing as long as stimulus lasts e.g. joint and pain receptors
Phasic - rapidly adapting and respond briefly to a stimulus e.g. touch receptors
Precision by which a stimulus can be located
How is acuity improved by lateral inhibition?
Sitimulation of a 1st order neurone will inhibit the adjacent 2nd order neurones so that the stimulus is only felt in the correct 2nd order neurone
Define 2 point discrimination
minimal interstimulus distance required to percieve 2 simultaneously applied skin indentations
What is the link between 2 point discrimination and the size of neuronal receptive fields?
Smaller neuronal receptive field = better 2 point discrimination
Define convergence and divergence of a signal
Convergence - 2+ first order neurones converge onto a single 2nd order neuron
Divergence - 1 first order neurone diverges into 2+ 2nd order neurones
Where is the somatosensory cortex located?
Post central gyrus
How is the white matter of the spinal cord divided?
Funiculi - dorsal, lateral and ventral
How is the grey matter of the spinal cord divided?
Divided into X laminae. Each laminae is equivalent to a neuronal nucleus. Cell bodies of neurones with common functions occur in the same laminae
How many pairs of segmental nerves are there?
Which nerve carries the majority of the cranial sensory system?
Where is priority given in the sensory homonculus?
Face, hands, tongue
What are the 2 categories into which ascending tracts can be divided into?
Conscious and non conscious sensation
What are some examples of non conscious sensation?
muscle length, muscle tension, joint angle
Where is the cell body of spinal sensory neurones located?
Dorsal root ganglion of that spinal segment
What type of neurone is the first order neuron of the somatosensory system?
How would you orientate the spinal cord?
dorsal median sulcus is posterior and is a groove in the spinal cord
Ventral median fissure is an opening at the anterior end o the spinal cord
What runs through the central canal of the spinal cord?
What is the function of the dorsal column - medial lemniscus pathway of the spinal cord?
Fine touch and proprioception
What is the dorsal column - medial lemniscus pathway made up of? To where does it transmit information to?
Cuneate and gracile
Post central gyrus
What does the lateral corticospinal tract carry?
limb motor information
Label the ascending pathways