Somatic sensory nervous system

Question 1

Type of neuron in the somatic nervous system

Answer 1

Pseudo/ unipolar neuron - one axon

the cell body is laid off to one side and this part is in the dorsal root ganglion

Question 2

somatic and visceral sensations

Answer 2

touch 
pain
warm and cold 
body position 
visceral (autonomic) system sensations

Question 3

special sensations

Answer 3

vision
hearing 
taste 
smell (pheromones) 
vestibular (balance)

Question 4

sensory receptors

Answer 4

sensory endings of an afferent neuron
or
specialised receptor cell (special senses), both are highly sensitive to a particular stimulus

Question 5

Conscious sensations - integration centre

Answer 5

cerebral cortex (outer layer of cerebrum)
conscious sensations and perception
there are multiple sensory inputs not just one

Question 6

Conscious sensations - afferent neurons

Answer 6

peripheral nerve (inputs) 
tract or pathway

Question 7

Conscious sensations - sensory stimulus

Answer 7

sensory stimulus converted into action potentials
transduction
eg. painful stimulus at the fingertip

Question 8

sensory information coding : modality

Answer 8

type of sensory receptor activated - specialisation, which sensory receptor used

Question 9

sensory information coding : intensity

Answer 9

frequency of action potentials firing in afferent neuron - more action potentials

Question 10

sensory information coding : duration

Answer 10

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.

Question 11

sensory information coding : location

Answer 11

location of sensory receptors activated, ‘mapped’ in brain - - particular part of the brain that represents a particular part of the body.

Question 12

proprioception

Answer 12

body posture and position

Question 13

length receptors

Answer 13

muscle spindles 
- stretch reflex
- shortening of muscle
- posture 
the nerve ending is wrapped around the end of the fibre

Question 14

tension receptors

Answer 14

golgi tendon organ 
- tension reflex 
- relaxation 
- protects from tearing 
sensitive to changes in tension

Question 15

touch modality - pain

Answer 15

free nerve endings not in the CNS only the PNS, near the surface

Question 16

touch - textural sensation

Answer 16

krauses’ end - small bulb near the surface

Question 17

touch- deep pressure/ high frequency vibration

Answer 17

pacinis corpuscle - deep and large

can tell how big something is becasue of vibration

Question 18

touch - crude persistent

Answer 18

ruffini ending- good for detecting orientation and direction, deep and large/ wide

Question 19

touch - low frequency vibrations

Answer 19

meissners corpuscle, small near surface

Question 20

touch- light pressure

Answer 20

merkles endings/ disc under the folds of the nerve, near the surface small and thin.

Question 21

stimulus intensity - frequency in afferent neuron

Answer 21

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.

Question 22

stimulus: duration

Answer 22

sensory receptors are most sensitive to change.

often show adaptation: decreasing receptor potential over time in response to a continuous stimulation.

Question 23

stimulus location - receptive field

Answer 23

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

Question 24

Medial Lemniscal pathway (dorsal root column)

Answer 24

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)

Question 25

Somatosensory cortex

Answer 25

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)

Question 26

Somatotopic organisation

Answer 26

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.

Question 27

pain modality

Answer 27

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

Question 28

Lateral Spinothalamic (antero-lateral) pathway

Answer 28

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

Question 29

Arousal

Answer 29

collateral fibers to reticular formation

Question 30

Emotional component

Answer 30

the limbic system