Somatic Senses

Question 1

somatic senses

Answer 1

1) touch
2) proprioception: awareness of body movement and location in space
3) temperature
4) nociception (pain)
- all receptors are neurons
- receptors are located in skin and viscera
- the secondary neurons in spinal cord and medulla synapse onto tertiary neurons in the thalamus
- the information is sent to the somatosensory cortex

Question 2

receptor cells non-neural and neural cell

Answer 2

receptor cell is a non-neural cell -> primary sensory neuron -> secondary neuron -> vision, hearing, balance, taste

receptor cell is a neural cell its a primary sensory neuron as well -> secondary sensory neuron -> olfaction, somatic senses

Question 3

mechanoreceptors

Answer 3

1. pacinian corpuscles - senses vibration
2. meissner’s corpuscles - responds to flutter and stroking movements
3. merkel’s disks - sense stready pressure and texture
4. ruffini’s endings - responds to skin stretch

Question 4

adaption rate

Answer 4

• all sensory receptors quickly respond to the presence of stimulus. then they become used to the presence of the stimulus (they adapt to it)
• some receptors rapidly adapt to the presence of a stimulus (pacinian and meissner’s corpuscles - rapidly adapting)

Question 5

receptive field size

Answer 5

• the area of the skin, when stimulated, influences the firing rate of a given neuron

small receptive fields - merkel (touch) and meissner (touch)

large receptive fields - ruffini (stretch) and pacinian (vibrations)

Question 6

properties of skin receptors

Answer 6

superficial - meissner and merkel

deep - pacinian and ruffini

Question 7

tactile acuity and the body surface

Answer 7

two-point discrimination - the smallest separation between two points on the skin that is perceived as two points rather than one

regions with high tactile acuity have small receptive fields

Question 8

receptive fields

Answer 8

differences in two-point discrimination arise from the size of the receptive fields, and also from different patterns of convergence of primary sensory neurons onto secondary sensory neuron

Question 9

two-point threshold

Answer 9

Question 10

spinal cord

Answer 10

each segment of the spinal cord receives sensory input from a particular region of the body and supplies motor input to a similar region

from sensory receptor -> primary sensory neuron -> dorsal root ganglion -> spinal cord -> ventral root -> motor input

Question 11

dermatome

Answer 11

a dermatome is an area of skin that is mainly supplied by afferent nerve fibers from a single dorsal root of the spinal nerve

Question 12

why arent there dermatomes on the face?

Answer 12

in addition to the 31 pairs of spinal nerves, there are also 12 pairs of cranial nerves that come directly off the brain

Question 13

somatosensory pathways in the CNS

Answer 13

(fine touch, proprioception, vibration) - synapse with secondary sensory neurons cross the midline at the medulla

(nociception, temperature, coarse touch) - synapse with secondary sensory neurons cross the midline at the spinal cord

• goes through spinal cord, medulla, thalamus and processed at somatosensory cortex
• synapse with tertiary sensory neurons at the thalamus to the somatosensory cortex

Question 14

primary somatosensory cortex (S1)

Answer 14

• S1 made up of areas 3, 1 and 2 located on the postcentral gyrus
• primary motor cortex is located on the precentral gyrus

Question 15

body map in somatosensory cortex

Answer 15

• the somatosensory information goes to specific areas in the cortex
• the amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part

Question 16

thermoreceptors

Answer 16

• free nerve endings located at epidermis
• thermoreceptors in the brain - homeostasis
• cold receptors
• warm receptors
• cold and warm receptors are spread across the body
• they present slow adaption between 20-40 C but they dont adapt outside this range

Question 17

pain

Answer 17

• pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
• pain is good and important to protect you from harm

Question 18

congenital insensitivity to pain

Answer 18

autosomal recessive disorder

Question 19

pain fibers

Answer 19

beta fiber - large, myelinated, associated with mechanical stimuli (touch)

delta fiber - small, myelinated, associated with intense mechanical or mechanothermal stimuli, fast pain

C fiber - small, unmyelinated, associated with heat, cold, slow pain

Question 20

thermoreceptors vs nociceptors

Answer 20

• norciceptors have a higher threshold than thermoreceptors (threshold to activate a signal from the neuron)

so when something is too hot nocicepectors (pain) receptors can increase firing rate of action potentials as temperature goes up, but thermoreceptor’s firing rate of action potentials level out at 40 degrees celsius