Sensory Nervous System and Special Senses Flashcards
From which peripheral nervous systems do sensory nerves innervate and collect information from?
Somatic (vol) NS - Sensory nerves innervate and collect information from skeletal muscles, skin and joints.
Autonomic (unvol) NS - Sensory nerves innervate and collect information from smooth muscles, cardiac muscle and glands.
What is the common pathway for the detection of senses?
1) Detection from a receptor
2) Amplification
3) Change in membrane potential
4) Firing of action potential to the CNS.
Do ions move readily across the cell membrane, if not, what do they use in order to get across?
No.
Ions will use specifically-gated channels and protein pumps in order to move across the membrane (via facilitated diffusion).
What do ions depend on in order to move across the membrane?
1) Concentration differences (high to low)
2) Voltage differences (positive - negative v/v)
Across an ELECTROCHEMICAL gradient
What is the somatosensory cortex the same as?
The somatosensory cortex is another name for the sensory area (a lobe in the cerebral hemisphere - parietal lobe just past the central sulcus)
Describe the somatosensory pathway:
1) A stimulus is detected by a specific receptor
2) The 1st order neurone transmits sensory information to the 2nd order neurone in the spinal cord.
3) The 2nd order neurone (afferent neurone) will synpase with the 3rd order neurone in the Thalamus
4) The 3rd order neurone transmits the sensory information to the cerebral cortex.
5) The cell bodies in the somatosensory area of the cerebral cortex processes this sensory information (concious perception of the stimulus)
In what nervous systems are the order neurones (in the somatosensory pathway)?
1st order (PNS) 2nd order and 3rd order (CNS)
Which nerves are contained in the dorsal and which nerves are contained in the ventral roots (coming from the spinal cord)?
Dorsal - Sensory afferent nerves
Ventral - Motor efferent nerves
Where do the ventral roots extend out of the spinal cord from?
The anterior of the spinal cord (white matter - nerve fibres)
Where do the dorsal roots enter the of the spinal cord from?
The posterior of the spinal cord (white matter)
After the ventral root nerves leave the spinal cord and before the dorsal root nerves enter the spinal cord, what happens?
The ventral root and dorsal root will clump together in order to form the MIXED NERVE FIBRE.
What are dermatones?
Areas of skin that are innovated by a branch of sensory nerve fibres that come from a single spinal nerve. They are able to detect different stimuli from these areas of the skin.
Does each spinal nerve (31 spinal nerves) have a branch of sensory nerve fibres innervated an area of the skin, in order to create dermatones?
Yes - each spinal cord does!
Why are dermatones useful?
They are a useful diagnostic tools - in order to discover the origin of injury or infection in a spinal nerve or dorsal root nerve.
What is referred pain?
If you have a disturbance in the spinothalamic tract (1st, 2nd or 3rd order neurone) it can feel like the pain is coming from where this path originated from (the 1st order neurone - sensory ending).
The sensory nerve endings of the 1st order neurones can either be:
1) Encapsulated (with connective tissue or GLIAL cells)
or
2) Unencapsulated (without connective tissue)
If a sensory nerve ending is encapsulated then…
it is more sensitive to a stimulus
What are the 4 main receptors that sense touch (2 that sense steady pressure and 2 that sense vibrations):
Steady Pressure: 1) Ruffini endings 2) Merkel endings
Vibrations: 1) Pacinian corpuscles 2) Meissner corpuscles
What is noiciception?
The feeling or perception of pain
What are noiciceptors?
Free nerve endings that signalsTISSUE DAMAGE
How are noiciceptors stimulated?
When a tissue is damaged they will release inflammatory mediators (histamines, cytokines and chemokines) which will stimulate the noiciceptors
What is a noxious stimulus?
Pain
Explain how the pain intensity changes and which noiciceptor is responsible for this perception of different pain intensities?
1st pain = sharp, quick, localised pain (caused by the A-delta noiciceptors)
2nd pain = long, nagging, diffuse pain (caused by the C noiciceptors)
What is the difference between A-delta fibres and C-fibers?
A-delta = myelination (transmission of AP is fast)
C fibres = un-myelinated
What are the 4 different types of pain:
1) Noiceptive pain: Pressure, chemical, hot, cold
2) Inflammation pain: tissue pain
3) Neuropathic pain: Neural lesion
4) Dysfunctional pain: Abnormal processing of information by the nerve
What is important to remember about neuropathic and dysfunctional pain?
The pain is caused by the nerve itself rather than an external stimulus
An example of how neural lesions can occur?
A Herniated disc can cause a neural leision in a spinal nerve - this causes neuropathic pain anywhere along this spinal nerve tract
How is referred pain caused?
1) A visceral organ and area of skin share the same dermatone (i.e. a branch of nerve fibres innovates the skin and visceral organ and this branch leads to the same single nerve).
2) Tissue damage occurs in the visceral organ.
3) Noiciceptors detect the pain and information is sent along the branch of nerve fibres to the single spinal nerve.
4) As the brain doesn’t normally detect pain from this nociceptor - it wrongly assumes that the pain is coming from the skin (as these nociceptors are normally stimulated).
5) In this way the brain perceives pain in the skin
What are the 5 different differences between chronic pain and acute pain?
1) Chronic pain is caused by no specific injury/disease whereas acute pain is caused by a specific injury/disease
2) Chronic pain serves no biology function whereas acute pain does serve a biological function.
3) Chronic pain is associated with psychological functioning whereas acute pain is associated with the F/F responses of the sympathetic NS.
4) Chronic pain can last up to more than 6 months, whereas acute pain is short lasting
5) Chronic pain is hard to treat and acute pain is easier to treat.
What 3 things can cause an absence of pain perception?
1) Diabetes
2) Drugs
3) Genetics
What 2 things control pain?
1) Chemicals (Analgesics or endogenous opiods - e.g. endorphins)
2) The Gate Theory of Pain
What 4 things are involved in the gate theory of pain?
1) Inhibitory neurones
2) Projection neurones
3) C-fibres (nociceptive)
4) alpha-beta fibres (non-nociceptive)
What happens when the alpha-beta fibres are stimulated in the gate theory of pain?
1) The inhibitory neurones are stimulated - which inhbits the projection neurone from projecting the pain.
2) The projection neurones are stimulated - so the inhibited pain is projected.
No pain is percieved.
What happens when the C fibres are stimulated in the gate theory of pain?
1) The inhibitory neurones are inhibited - so the projection of pain isn’t inhibited by the inhibitory neurones, and so pain is projected
2) The projection neurones are stimulated.
Pain is percieved.
What happens when the alpha-beta fibres and the C fibres are both stimulated in the gate theory of pain?
It is more likely that the inhibitory neurones will be stimulated by alpha-beta fibres than inhibited by the C fibres. Therefore, less pain or no pain is perceived.
Does the detection of an itch use the same pathway as pain?
No
Which areas of the brain are stimulated in order to detect an itch?
The areas associated with:
1) Disagreeable feelings
2) Irresistible urges
What are special senses?
Detect information about the external environment and send this information to the CNS.
What are the 4 special senses?
1) Vision
2) Hearing
3) Smell
4) Taste
What stimulus do the eyes detect?
The eyes detects visible light in the form of different colours