Sense of Touch

Sense of touch and the PNS Sensory nerves send message to CNS Message gets processed in CNS Message gets sent out to body via motor nerves

sensory and motor nerves

While other senses are found in specific areas of the body, your sense of touch can be found all over. Types of Mechanoreceptors: pressure light touch pressure and texture free nerve endings: pain, itch, temperature

Receptors convey information to the CNS To do this sensory receptors transduce or convert mechanical, thermal or chemical energy into electrical signals. Signals travel along axons to CNS

All touch signals are sent to the somatosensory cortex.

The representation of each area is related to the number of sensory neuronal connections, not its physical size.

Spinal Reflex Arc A spinal reflex is an automatic, rapid response to a stimulus. The action is involuntary and occurs without any involvement of thought or the brain.

How does the Spinal Reflex Arc Work? A receptor at the point of stimulus relays the message The sensory neuron carries the message from the receptor at the point of the stimulus to the spinal cord. In the spinal cord, a relay neuron, or inter-neuron, carries the message from the sensory neuron to a motor neuron. The motor neuron then carries the message to the appropriate effector, at which point, the reflex occurs. After this spinal reflex occurs, sensory neurons send messages to the brain. The brain then relays this information and the messages are consciously interpreted. It is only at this point that you will begin to feel pain. All this happens within one second.

Pain Pain is detected by specialized free nerve endings called nociceptors. They are "pain receptors" that only respond to tissue damage or other intense chemical (e.g., chilli powder in the eyes), mechanical (e.g., pinching, crushing) or thermal (heat and cold) stimulation.

nociceptors Nociceptors only send message if something could or is causing pain. Activity is initiated only above a certain threshold. threshold = soglia Nociceptors are kind of like alarms.

watch video then take quiz http://ed.ted.com/lessons/how-do-pain-relievers-work#watch 1. What is the difference between regular nerve cells and nociceptors? a Nociceptors only fire when cells are damaged. b Nociceptors only fire when cells are in danger of damage, or are being damaged. c Nociceptors only fire when prostaglandins are present. d Nociceptors only fire when you haven’t taken any painkillers

2. What event triggers the production of chemicals that lower the pain threshold? a Burning your tongue b Stubbing your toe c Listening to Justin Bieber d Anything that damages cells

3. Why might aspirin and ibuprofen reduce fever? a Because COX-1 and COX-2 raise our body temperature b Because prostaglandin H2 raises our body temperature c Because arachidonic acid raises our body temperature d Because prostaglandin H2 is converted into stuff that raises our body temperature

4. How do painkillers “know” where you’re feeling pain? a They don’t know; they just go everywhere b They can sense where COX-1 and COX-2 are being produced c They don’t know; they only go to your brain and block pain from there d They can hear cells screaming

5. What’s the difference between aspirin and ibuprofen? a Aspirin deactivates COX-1 and ibuprofen deactivates COX-2 b Aspirin is a more effective painkiller c Ibuprofen is a more effective painkiller d Aspirin permanently deactivates COX-1 and COX-2; ibuprofen only temporarily deactivates COX-1 and COX-2

answers b d a

think Explain why we feel pain. In your answer, consider what life would be like if we did not feel pain, and give examples of situations in which pain is helpful.