2: Physiology - Primary sensory neurons and their modalities Flashcards
Which senses is the somatosensory system concerned with?
Touch (inc. fine, firm, pressure, vibration)
Pain
Temperature
Itch
Proprioception
Which structures are classed as the
a) CNS
b) PNS?
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?
PNS
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?
Cervical ganglia
Which cranial nerve supplies sensory fibres to the anterior head?
CN V
Trigeminal nerve
Where do pre-ganglionic sensory fibres from the trigeminal nerve synapse?
Cervical ganglia
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
b) medulla?
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?
Thalamus
No matter which pathway
In the
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.
threshold
To generate a sensory signal, a stimulus must have enough ___ to overcome the threshold potential of the receptor.
intensity
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?
Mechanoreceptors
Skin
Which type of receptors are responsible for proprioception?
Where are they found?
Mechanoreceptors
Joints and muscles
Which type of receptors are responsible for detecting temperature?
Thermoreceptors
Which type of receptors are responsible for the sensation of pain?
Nociceptors
What is an adequate stimulus?
A stimulus matching the type of receptor which senses it
Different receptors respond to increasing ___ of stimulus.
intensities
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.
b) Nociceptors
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?
Directly proportional
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
a) fastest
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?
Receptive field
What is a receptive field?
Area on the skin corresponding to the territory of ONE sensory neuron
How are sensory nerves arranged in areas of
a) low acuity
b) high acuity?
a) Few neurons, big receptive fields
b) Loads of neurons each with their own small receptive fields
Sensory nerves have numbered types depending on whether they have small receptive fields or large receptive fields.
What are these types?
Type 1 - small sensory fields (high acuity)
Type 2 - large sensory fields (lower acuity)
From Dermatology, which skin cells/structures are notable for being prone to a high mortality cancer?
Merkel cells
Which sensory receptors are found as complexes with Merkel cells?
What a) adaptation and b) receptive field properties do they have?
What do they sense?
Merkel cell-neurite complexes
Slow adapting, small receptive fields (so SA1 for short)
Pressure, texture and object edges
What do Meissner corpuscles sense?
Light touch
What do Pacinian corpuscles sense?
Pressure
What do Ruffini endings detect?
Shearing forces
What is detected by
a) Merkel cell-neurite complexes
b) Ruffini endings
c) Pacinian corpuscles
d) Meissner corpuscles?
a) Fine touch
b) Shearing forces (skin stretching))
c) Pressure, high frequency vibration
d) Low frequency vibration
What is a dermatome?
Area of skin supplied with sensory fibres from a root of a spinal nerve
So anterior root does the anterior dermatome, posterior root does the posterior dermatome
The skin of most of the body is supplied with sensory fibres by spinal nerves.
Which part of the body is supplied with sensory fibres by CN V?
Face
Which ganglion becomes infected by varicella zoster to cause shingles in a dermatomal pattern?
Dorsal root ganglion
