Which senses is the somatosensory system concerned with?
Touch (inc. fine, firm, pressure, vibration)
Which structures are classed as the
a) Brain and spinal cord
b) Nerves outside the brain and spinal cord
In which nervous system are the bodies of first-order neurons of the somatosensory system found?
Where in the PNS are most first-order neurons found?
Dorsal root ganglion
Most first-order neurons are found at the dorsal root ganglion. Where are they found in the head and neck?
Which cranial nerve supplies sensory fibres to the anterior head?
Where do pre-ganglionic sensory fibres from the trigeminal nerve synapse?
Second-order neurons of the somatosensory system can be found in either the dorsal horn or the medulla.
Which sensory pathways have second order neurons in the
a) dorsal horn
a) Dorsal column - medial lemniscus system
b) Spinothalamic tract
What sensations are picked up by the
a) DC/ML system
b) spinothalamic tract?
a) Fine touch, proprioception, vibration
b) Firm touch, pressure, temperature, pain
Where are third-order neurons of the somatosensory system found?
No matter which pathway
a) DC/ML pathway
b) spinothalamic tract
which structures are connected by the first-order neurons?
a) Dorsal root ganglia TO medulla
b) Dorsal root ganglia TO spinal cord
As the intensity of a sensory stimulus increases, what happens to the amplitude of the receptor's potential?
As intensity increases, receptor potential amplitude increases
A somatic receptor will generate an action potential once a ___ potential has been reached.
To generate a sensory signal, a stimulus must have enough ___ to overcome the threshold potential of the receptor.
In relation to sensory receptors, what is meant by the term adequate stimulus?
Receptors are only activated by the stimulus they are programmed for
e.g a mechanoreceptor won't generate an action potential in response to heat
Which type of receptors sense touch, pressure and vibration?
Where are they found?
Which type of receptors are responsible for proprioception?
Where are they found?
Joints and muscles
Which type of receptors are responsible for detecting temperature?
Which type of receptors are responsible for the sensation of pain?
What is an adequate stimulus?
A stimulus matching the type of receptor which senses it
Different receptors respond to increasing ___ of stimulus.
What happens to the frequency of action potentials generated by a receptor as the intensity of a stimulus increases?
APs become more frequent
Which receptors respond to
a) low intensity stimuli
b) high intensity, damaging stimuli?
a) Thermoreceptors, mechanoreceptors, etc.
What is the difference between low intensity receptors and high intensity nociceptors?
Different threshold potentials
i.e each is activated by different intensities of stimulus
In slowly adapting receptors, what is the relationship between stimulus intensity and firing rate?
The greater the stimulus intensity, the greater the firing rate
In fast adapting receptors, what increases the firing rate?
Greater RATE of change in stimulus
i.e a sharp increase will increase the firing rate more than a slow one
Which two factors affect the conduction velocity of an axon?
1. Diameter of axon (which is difficult to change in real time)
2. Degree of myelination
Which type of receptors tend to have the
b) slowest conduction velocities?
a) Proprioceptors (body needs constant feedback on where its bits are)
b) Pain fibres (why there's a delayed response between burning your hand on something and feeling it)
Sensory axons are arranged in groups from A to C.
What happens to the axon diameter and degree of myelination as you go from A to C?
Axon diameter decreases
Degree of myelination decreases
So conduction velocity decreases
What is the term for a sensory nerve's territory on the skin?