Hair follicle receptors
touch
merkel endings
pressure and low frequency vibrations
meissners corpuscles
light touch
Pacinian Corpuscles
Vibration and JPS
Ruffini Endings
skin stretch, pressure and JPS
Nociceptors
Pain
Muscle spindles
determine muscle length and proprioception
Golgi tendon organs
JPS
Meissner’s corpuscles receptive fields
these have limited receptive fields when they are in the tips of the fingers than when they are on the palms of the hands
Pacinian receptive fields
however have generally large receptive fields each of which has a smaller more sensitive area within it
What is the contents of a receptive field
in the centre of a receptive field dendrites are dense and then diffuse as they reach the periphery (this results in faster firing at the centre as they activate more dendrites)
the concept of lateral inhibition
relies on reciprocal inhibition between two adjacent neurons where the extent of inhibition from each one is linked to the stimulus point on the neuronal receptive field overlap
different axon types effect what
the speed of transmission of the information to the CNS
• Some modalities therefore are slower at being transmitted to the brain than others
Fasciculus gracilis carries information from
the lower body extremities
Fasciculus cuneatus carries information from
the upper body extremities
Dorsal and ventral spinocerebellar tracts carry
proprioceptive information from muscle spindles (Dorsal) & Golgi organs (ventral)
Spinothalamic tracts
pain and temperature transmission etc.
where does en route sensory information pass through on its way to the cortex
thought the thalamus
EXCEPT OLFACTORY
what is the thalamus
this acts as a relay station between the periphery and the cortex
- it has reciprocal connection to all the cortical regions and can read information, receive feedback and modulate cortical activity
thalamic peduncles
they are thalamic connection that form between the thalamus and the cortex
What are the three principle ascending tract systems of the spinal cord
- Dorsal column-medial lemniscus pathways
- Spinothalamic pathways
- Spinocerebellar pathways
Dorsal column - medial lemniscal pathway
mechanical stimuli
- Conscious proprioception,
- Discriminative touch,
- Vibration and
- Pressure
Dorsal column - medial lemniscal pathway cortical functions
1.
To determine the shape of an object (without sight)
Proprioception from the finger joints and fine discriminating touch provides a very accurate model of any object that is handled
Dorsal column - medial lemniscal pathway cortical functions
2.
- To determine the texture of an object (without sight)
Texture is determined by vibration and slip receptors as well as fine discriminating touch. Note pleasure can be associated with this pathway
Lesions of one of the somatosensory association cortex leads to
amorphosynthesis’
what is amorphosynthesis’
Patient unable to recognise complex object by feel on the opposite side to the lesion Patients often only explore one half of an object during testing of object recognition
Patients can also neglect the whole of the opposite side of their body such that they overlook motor output on that side.
what is one thing to note about patients with ‘amorphosynthesis’
these patients still have an appreciation of pain and temperature, they are unable to locate with any certainty the location of the source of the stimulus
Lesions of the gracile fasciculus can cause
ait ataxia, as the brain (cortex and cerebellum) is deprived of information about the position of the feet.
• Lesions in the cervical cord also cause
upper extremity ataxia.
• Often patient is able to compensate with Vision and thus
minimize sensory ataxia.
Classic sign of gait (or sensory) ataxia is the
stamp and stick gait.
• Patient stamps down feet to enhance sensory input and
maintains a broad based stance.
Spinothalamic Pathways are composed of what kind of fibres
Composed of smaller diameter (slow either Aδ or C fibres) with no specialized sensory
endings
Lightly or unmyelinated fibers which are ‘Quick to cross’
Aδ fibres detect
non-discriminative touch (strong stimuli that does not damage the skin) heat or cold and sharp pain
C fibres detect
ull aching pain and itch (histamine sensitive) plus thermal and mechanical
1st order neurons synapse with 2nd order neurons in the
dorsal horn, which then decussate and ascend in either the lateral or anterior spinothalamic tract depending on the sensory modality
when 2nd order neurones reach the thalamus
they synapse with 3rd order neurons which then projects to the sensory cortex in the same way as the dorsal lemniscal pathway
Spinothalamic lateral route of the anterolateral spinothalamic pathway
Mixture of Aδ and C fibres
carrying information about pain and temperature via Aδ heat or cold activated fibres and C fibres (dull pain and itch)
Spinothalamic anterior or ventral route of the anterolateral spinothalamic pathway
Only C fibres carrying
information about coarse, non discriminating touch via mechanosensitive fibres
lesions in the lateral spinothalamic tract cause
decreased perception of pain and temperature on the contralateral side of the body, always one or two dermatomes below the level of the lesion.
Spinothalamic tract lesions can cause
paraesthesia which is experienced as shooting pain or ‘electrical’ pain.
Patients can also become aware of their pain and temperature deficit when they experience painless cuts or burns.
The Neospinothalamic tract (lateral pathway)
which terminates in the ventral posterior lateral nucleus (VPL) is mainly composed of Aδ fibres.
The Palaeospinothalamic tract (anterior pathway)
which terminates in the dorsomedial (DM) and intra laminar areas is composed of C fibres.
Anterolateral tract lesions
Lesions in the neo part of the anterolateral tract cause decreased perception of pain and temperature on the contralateral side of the body, always one or two dermatomes below the level of the lesion (Lissauers tract).
Used as a surgical procedure (cordotomy) for terminal disease pain, pain returns after about 1 year.
Spinocerebellar pathway
Takes information about the body’s position and movements to the cerebellum for integration with motor intention and other sensory inputs
2 principal routes for information,
they are the
anterior route and the posterior route (each of which only contains two neurones)
where does motor information come from in the spinocerebellar pathway
from muscle spindles (muscle length), Golgi organs (proprioception) and touch receptors
• used by cerebellum for the control of posture and co-ordination of movement
where are the cell bodies of the 2nd order neurones located in the spinocerebellar pathway
in the dorsal horn of the spinal cord, and terminate in the vermis of the cerebellum
lesions in the cerebellum always produce
ipsilateral effects. It is thought that some parts of the anterior pathway are double-crossed and others not, however the posterior pathway is entirely ipsilateral
