System Neurophysiology Flashcards
somatosensory system
the body’s sensory system
Three types of sensory receptors
1) exteroceptive: external skin contact, temperature
2) proprioceptive: body, limb, joint position
3) enteroceptive: internal organ status (e.g. bladder fullness, blood gases)
What does the somatosensory system do?
this system provides information about the state of the body
- this information is then used to guide behaviour and maintain homeostatic function
What are the 4 main features of a stimulus?
1) modality
2) intensity
3) Location
4) duration
Modality
receptor specificity
e.g. touch and temperature are reported by different receptors and signaled separately (the labelled line)
Intensity
the frequency of action potential firing in a sensory axon, and the number of activated axons encodes the intensity (strength) of stimulus
Location
the somatotopic mapping of receptors in specific areas allows the location (site) of the stimulus to be known
Duration
the beginning/end of a stimulus are encoded by the start and end of action potential firing
Does noxious stimuli detect pain?
noxious stimuli does not detect pain, pain is the brain interpretation of a signal
Skin mechanoreceptors features
- sensitive to mechanical deformation
- all associated with fast-conducting myelinated axons
- all have mechanosensitive ion channels (some mechanical stimuli)
Meissner’s Corpuscles
- glabrous skin (mostly;non hairy)
- pressure
- dynamic
- rapidly adapting
- low threshold
Pacinian corpuscle
-subcutaneous (all skin)
- interosseous
- viscera
- deep pressure
- vibration
- dynamic
- rapidly adapting
- low threshold
Merkel’s discs
- all skin
- static pressure
- convey information about shape and texture of object
- slowly adapting
- low threshold
Ruffini endings
- all skin
- deeper pressure & stretch
- slow adapting
- low threshold
Hair units (goosebumps)
- hairy skin
- hair displacement
- low threshold
- rapidly adapting
Difference between rapidly adapting and slowly adapting?
Rapidly adapting stimuli is even though the stimuli remains in the cell, It does not continue to fire AP but it only triggers spikes on the set of the stimulus
whereas
Slowly adapting stimuli we have the same stimuli and a burst of AP. The AP does not stop and it is slowly adapting to firing more AP over time
Information given by Rapidly adapting
This is dynamic because it is only detecting the change in the sensory stimulus (only telling brain the onset of when the stimulus happen)
Information given by slowly adapting
These slowly adapting neurons gives information about the duration of the stimulus
Free nerve endings
These are found in all types of the skin. Classified by type of axon
- myelinated axons: temperature
- unmyelinated or thinly myelinated axons: Nociceptors
- they don’t have specialised sensory ending
- nociceptors have a high threshold for activation
Proprioceptors function
Tells the brain about limb and body position through CNS
- provides information about the change in muscle length (stretch reflex) and force
Enteroceptors function
- important for homesatatic control
Unipolar
It is structured in a way that one axon goes to the dendrites which are receiving input and the nerve endings that are releasing neurotransmitters are in the central nervous system
Receptive field
this is the area where neurons are sensitive to stimulation
Where is the receptive field features dependent at?
the location and shape of the receptive field is determined but the location of the neurons sensory ending
Receptive fields association with 2 point discrimination
When receptive fields are larger in the body means that there is a low number of neurons innovating that area
- the larger the receptive field, the poorer the 2 point discrimination
Where is the somatosensory cortex located?
In the post central gyrus (in front) and behind the central sulcus (fold in the brain)
What are the area taken up by the head and arms in the somatosensory cortex much larger than of the legs?
This is because there are more receptive fields and sensory neurons in the head and arms than of the legs, therefore greater representation
What are the main pathways for transmission of somatosensory information?
1) Dorsal coloumns: fine touch and vibration
2) Spinothalamic (anterolateral) tract: pain, temperature, and crude touch
3) Spinocerebellar tracts: proprioception
What is pain?
an unpleasant sensory and emotional experience associate with, or resembling that associated with actual or potential tissue damage
What are nociceptors activated by?
these are activated by noxious stimuli
CIPA
a condition where individual cannot feel pain or temperature. They are also unable to sweat
Wat causes CIPA?
CIPA is caused by a mutation in a gene which encodes for a particular growth factor
- in this case the mutation causes the sensory nerves and autonomic nerves to not grow properly
What are a-delta fibres?
thinly myelinated axons
Signal produce of a-delta results to?
generally signals the acute onset of nociceptors of stimuli which is associated with thermo and mechanoreceptors
What are C fibres?
unmyelinated axons
Signal produce of C fibres results to?
they signal ongoing slow and dull pain which are associated with polymodal receptors
Transient Receptor Potential (TRP)
- common ion channels associated with nociceptors
- could be sensitive to different stimuli and is often associated with nociceptors in detecting noxious stimuli
Hyperalgesia
persistent or enhanced sensation which is often due to inflammation and the release of chemicals from damaged site (often happening due to another injury)
- increased pain from a stimulus that usually provokes pain
Allodynia
pain in response to innocuous (harmless) sensory stimuli
- something that was not painful before is now reported as painful
- pain is due to a stimulus that does not usually provoke pain
NSAIDs (non-steroid anti-inflammatory drugs)
They act to reduce pain by targeting some of the signalling molecules
What do NSAIDs reduce?
this helps reduce the production of prostaglandins, reducing the production of these molecules means that we reduce the activation of the nerve fibers
prostaglandins function
can activate a number of different ion channels to stimulate the nociceptors of axons
Importance of targeting prostaglandins synthesis
important for pain modulation
What is referred pain?
this is when the brain cannot distinguish whether the pain stimulus arose from the skin or the viscera
- the origin of pain is wrongly identified
Does the brain have pain receptors?
The brain has no pain receptors but intracranial and head tissues (meninges, blood vessels, head & neck muscles, eyes, ears, teeth, mouth) do.
Common causes of headaches
- dehydration
- fatigue
- sleep deprivation
- tension
- medication and drug use
- infections (meningitis)
Why do phantom limb sensation occurs?
This is because an amputation can cut sensory nerves but the cell body can stay alive in the dorsal root ganglion and so can lots of projector neurons
- although the axon is cut, it can still transmit AP through the neuron into a pathway up to the brain (this results in the brain interpreting this signal sent as if the amputated area is still present)
Central pattern generators
Networks of neurons in spinal cord capable of drving rhythmic, stereotyped behaviours without input from higher centres
(e.g. walking and breathing)
- simple reflexes
What are some activities that could occur in CPG?
Brusting activity and reciprocal inhibition
Bursting activity
this refers to “burst of action potential”
- when we have a neurons that fires action potential at a short amount of time
- neurons involve involved in CPG are often firing AP in bursting pattern
Reciprocal Inhibition
when two neurons are both inhibiting one another
- when one neuron is excited, it inhibits the other neuron
Function of the primary motor cortex
these areas are devoted to muscles in each region that are related to the level of fine control and movement complexity
Lateral corticospinal tract
Also known as the “lateral pathway”
- in the medulla of this area is where 90% of axons cross the midline into the other side and descends into the lateral corticospinal tract
Ventral corticospinal tract
Also known as the “medial pathway”
- instead of axons crossing the medulla across the midline, about 10% of the axons stay on the same side which then descends into the ventral corticospinal tract
- controls postural functions
Cerebullum
a highly folded brain structure which is important for when learning motor task
