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What do sensations of the body do? What is this system called?
What are the special senses?
- distinguish different types of stimuli, somatosensory system
- Audition, vision, gustatory, balance
Difference between special senses and somatosensory system (2):
- 1. Somatosensory receptors are distributed throughout the body, special sensory receptors are localized
- 2. Somatosensory system consists of 4 senses, special sensory receptors consist of just 1
What are the 4 somatosensory senses?
- 1. touch (mechanoreceptors)
- 2. temperature (thermoreceptors)
- 3. Pain (nocireceptors)
- 4. Body Position (stretch receptors)
What type of sensory information does a unipolar neuron carry? What about bipolar neuron?
- 1. skin and organs
- 2. special senses
Mechanoreceptors respond to (3):
- 1. Bending
- 2. Stretching or
- 3. Squishing
This is a touch* receptor
The structure of the end of a __________ _____ will determine the neuron's responsivity to stimulus (deep pressure, light pressure, stretching, bending, etc). This is termed as ________. Once the membrane is compressed and the axon has selected for the stimulus (3):
- Mechanoreceptive axon
- 1. Ion channels open
- 2. Depolarization of receptor potential
- 3. Action Potential
______ ______ ___ bring information from receptors to the SC or the brainstem.
There are 4 types of axons that carry different information:
- Primary afferent axons
- 1. Proprioceptors of skeletal muscles (thickest myelin) 80-120 m/sec
- 2. Mechanoreceptors of skin 35-75 m/sec
- 3. Pain, temperature 5-30 m/sec
- 4. Temperature, pain, itch (thinnest myelin) .5-2 m/sec
Where does sensory information from in the head enter CNS?
Where does sensory information from below the head enter CNS?
What is a dermatome?
- Cranial nerves
- Spinal nerves
- Skin area connected to a single sensory spinal nerve
Discuss the path from the sensory receptor to the CNS:
- 1. Afferent axons enter dorsal horn, branch and go to: the brain or: second-order neurons in dorsal horn where the ventral horn will then mediate reflexes.
- 2. Fasciculus Gracilis carries lower body sensation info, Fasciculus Cuneatus carries upper body sensation info: course upwards: decussate at medial lemniscus in the medulla: goes through thalamus: ends at primary somatosensory cortex. Sensory info form the face is carried by the trigeminal nerve: decussates at the cerebellum: goes through the thalamus: ends at primary somatosensory cortex.
What is the purpose of the homonculus?
The Primary Somatosensory Cortex and the Posterior parietal cortex?
- The size of cortex devoted to an area depends on the density and importance of sensory input (articulators, face, hands)
- PSC gathers sensory info then sends it to PPC
The Posterior Parietal Cortex:
Damage of this can result in:
- Simple sensory info converge here to generate complex neural representations.
- Agnosia (tactile agnosia), neglect syndrome
What is the difference between nociception and pain?
What is a nociceptor?
What is an interesting fact?
- Nociception is the process that provides the signals that trigger pain. Pain is a feeling or perception of negative sensations.
- Free nerve endings that signal that body tissue is being damaged.
- The brain does not have nociceptors, but the meninges/blood vessels do (why we feel headaches)
What pathway carries pain/temperature from the body to the brain?
What pathway carries pain/temperature from the face and head to the brain?
What might suppress feelings of pain?
What suppresses nociceptive neuron activity?
- Spinothalamic (anterolateral system)
- Trigeminal pain pathway
- Emotion, stress, determination
- Periaqueductal gray matter (influence raphe nuclei)
What do thermoreceptors do (2)?
- In the hypothalamus and SC thermoreceptors regulate body temperature
- In the skin, thermoreceptors sense temperature in our environment
Thermoreceptors are either sense (2):
- warm or cold (not both)
- warm: 86-113 F
- cold: 50-95 F
- When a stimulus is too hot, nocireceptors will fire, but if a stimulus is too cold, it acts as an anesthetic.
- Temperature and pain pathways are the same