Somatic sensory nervous system Flashcards
Type of neuron in the somatic nervous system
Pseudo/ unipolar neuron - one axon
the cell body is laid off to one side and this part is in the dorsal root ganglion
somatic and visceral sensations
touch pain warm and cold body position visceral (autonomic) system sensations
special sensations
vision hearing taste smell (pheromones) vestibular (balance)
sensory receptors
sensory endings of an afferent neuron
or
specialised receptor cell (special senses), both are highly sensitive to a particular stimulus
Conscious sensations - integration centre
cerebral cortex (outer layer of cerebrum)
conscious sensations and perception
there are multiple sensory inputs not just one
Conscious sensations - afferent neurons
peripheral nerve (inputs) tract or pathway
Conscious sensations - sensory stimulus
sensory stimulus converted into action potentials
transduction
eg. painful stimulus at the fingertip
sensory information coding : modality
type of sensory receptor activated - specialisation, which sensory receptor used
sensory information coding : intensity
frequency of action potentials firing in afferent neuron - more action potentials
sensory information coding : duration
duration of action potentials firing in afferent neuron.
- if we touch something for ages our body gets used to it and once it happens again they will stop firing and the body gets used to it.
sensory information coding : location
location of sensory receptors activated, ‘mapped’ in brain - - particular part of the brain that represents a particular part of the body.
proprioception
body posture and position
length receptors
muscle spindles - stretch reflex - shortening of muscle - posture the nerve ending is wrapped around the end of the fibre
tension receptors
golgi tendon organ - tension reflex - relaxation - protects from tearing sensitive to changes in tension
touch modality - pain
free nerve endings not in the CNS only the PNS, near the surface
touch - textural sensation
krauses’ end - small bulb near the surface
touch- deep pressure/ high frequency vibration
pacinis corpuscle - deep and large
can tell how big something is becasue of vibration
touch - crude persistent
ruffini ending- good for detecting orientation and direction, deep and large/ wide
touch - low frequency vibrations
meissners corpuscle, small near surface
touch- light pressure
merkles endings/ disc under the folds of the nerve, near the surface small and thin.
stimulus intensity - frequency in afferent neuron
the action potential is initiated in the first node of ranvier closest to the receptor membrane end
below threshold : no response in afferent neuron, increasing the stimulus increases the action potential frequency.
push it harder we get a bigger response and the threshold will be met. in the refractory period we can have the threshold met again and another action potential can be met.
stimulus: duration
sensory receptors are most sensitive to change.
often show adaptation: decreasing receptor potential over time in response to a continuous stimulation.
stimulus location - receptive field
region of space in which a stimulus can lead to activity in a particular afferent neuron
small fields and dense innervation can give good discrimination
fields can overlap
eg- 2 point discrimination test in lab
when the field is large it is hard to recognise a point where a sensation is coming from. the fingertip has very small and accurate receptive fields
Medial Lemniscal pathway (dorsal root column)
afferent pathway for touch and pressure
3 neurons in relay
neurons from muscle spindles - very fast
UP AND ACROSS
1- primary sensory neuron goes from the stimulus to the dorsal root in the spine and then travels up the spine to the medulla oblongata.
2- secondary sensory neuron, synapse at the medulla oblongata where the second neuron crosses sides and goes up to the thalamus.
3- tertiary sensory neuron goes synapses at the thalamus and travels up to the somatic sensory area of the cerebral cortex (post central gyrus)
Somatosensory cortex
sensation
- conscious identification of ‘what and where’
- primary region of the cortex - post central gryus
perception
- meaningful interpretation
- association (secondary) region of the cortex (other region of the cortex)
Somatotopic organisation
areas of the cortex respond to areas of the body
densely innervated area of the body occupy large regions of the cortex
left cortex represents the right side of the body and visa versa
no pain fibres in the brain so we can expose this region and look at it.
pain modality
sensed by free nerve endings (nociceptors)
- located in organs of the body but not brain
- specialises sensitivity to local chemical signals in damaged tissue
fast (acute) pain
- small receptive field
- largish myelinated afferent axons (A fibres)
- somatic pain
slow (chronic) pain
- large receptive field
- small unmyelinated axons (B fibres)
- visceral pain throbbing sensation
Lateral Spinothalamic (antero-lateral) pathway
afferent pathway for pain and temperature
minimum of 3 neurons in relay (can have interneurons)
ACROSS AND UP
1- sensory receptor to the dorsal root ganglion in the spine
2- synapses with the 1st neuron and travels to the other side of the spinal cord then up the spinal cord to the thalamus
3- synapses with the 2nd neuron at the thalamus and then travels to the somatosensory cortex
Arousal
collateral fibers to reticular formation
Emotional component
the limbic system
