Chapter 6

Question 0

What are the two roles of sensory systems and what is the difference between these two roles?

Answer 0

The two roles of the sensory systems is detection and understanding. Detection is perceiving the stimuli, whilst understanding is the processing of the input to make a decision, plan or reason. Our detection is always working, however it does not always the conscious perception.

Question 1

What are the common five senses most mammals have? Name some special sensory systems too.

Answer 1

The five common senses are hearing, touch, sight, taste and smell. However animals like the platypus has developed a system called electroreception, and dolphins and bats have developed echolation.
Some animals also have an enhanced or deteriorated version of the common senses such as the mole which has lost almost all of its sight, while the dogs have an incredible sense of smell.

Question 2

What are receptors?

Answer 2

Receptors converts some form of energy such as light or sound into a graded electrical potential. This process is called transduction. This graded potentials are sent to the CNS through the sensory axon.

Question 3

How can receptors show different intensities of a similar stimuli?

Answer 3

Since the actions potentials are identical, the receptors alter the rate of neuronal firing. This is same for increase in duration and intensity.

Question 4

What is different in the receptors found between vertebrates?

Answer 4

The specialisation in a sensory system varies the exact type of the receptor and the numbers. For example, primates are largely visual mammals. Some receptors are even specialised to detect colours.

Question 5

How is the action potential transmitted from the sensory receptors?

Answer 5

The sensory receptors generates the action potential is passed onto the ganglion cell, whose job is to carry the signal to the spinal cord or the brain.

Question 7

How is fine touch sensation, fine pressure, proprioception and vibration transmitted?

Answer 7

The receptors sends their action potentials to the dorsal root ganglion neuron which travels through the spinal cord into the cuneate(C1-T6) and gracile fasiculus. The neurons synapse at the cuneate or gracile nucleus in the hindbrain. The second neuron immediately decussates and carries the signal to the thalamus. The thalamus then sends a third neuron to the cortex.

Question 7

What are the different levels of understanding the sensory information?

Answer 7

The lowest levels of the sensory understanding is the triggering of reflexes based on stimuli. The next level is the use of this information for feedback on our activity and modifying our actions. The third level is the highest level and is using the sensory information for taking decisions, make plans and in order to make the right response.

Question 8

What are sensory maps?

Answer 8

The receptors mapped according to nearby receptors for the comparison of the intensities of stimuli. This is called somatotopy. The mapping of retinal cells is called retinotopy, and tonotopy is the mapping of different tonal regions of the auditory stimuli.

Question 9

Where are the sensory systems in the brains?

Answer 9

The somatosensory cortex(S1) lies in the parietal lobe behind the central sulcus. The primary visual cortex(V1) lies in the posterior part of the cerebrum. Most of it is located medially, between the two hemispheres. The auditory cortex(A1) is located below the the lateral fissure below the somatosensory cortex. The taste information is received by the insula, which is buried deep in the lateral fissure.

Question 10

What are some secondary sensory areas?

Answer 10

V1 has surrounding cortical areas that process certain information like face recognition. Similarly, auditory cortex has separate cortical areas to analyse and decode music.

Question 11

Why is the pathway of the olfactory system totally different?

Answer 11

The fibres do not cross over and the thalamus is not involved. The signals are directly sent to an area near the amygdala called the piriform cortex.

Question 12

What is the spinothalamic tract convey

Answer 12

Temperature and pain

Question 13

What are the 2 major somatosensory pathways

Answer 13

The dorsal column medial lemniscus pathway and the spinothalamic pathway

Question 14

What does the dorsal lemniscus pathway convey

Answer 14

Fine touch and proprioception.
It transmits signals from low threshold mechano receptors in the skin, muscles and joints. This enables tactile discrimination, vibration detection , form recognition and proprioception.

Question 15

What are the receptors, nerve tracts , subcortical relay centers and cortical areas of vision.

Answer 15

receptors - Rods and cones
nerve tracts - Optic nerve and optic tract
subcortical relay centers - Lateral geniculate nuclei, superior colliculus
cortical areas - Visual cortex in the occipital lobe

Question 16

What is the path of the DCLP

Answer 16

Receptors pass on info to pseudounipolar neurons of the dorsal ganglion.
The axons of the pseudounipolar enter the gracile (lower extremities) or cuneate(Upper extremities) fasciculus.
The gracile fasciculus is medial to the cuneate fasciculus.
These axons travels upto the gracile or cuneate nuclei of the hind brain. Here they synapse with the second neuron which immediately crosses the midline to form a compact bundle called medial lemniscus.
The axons travel to the ventro posterior nucleus of the thalamus , here they synapse with the final neuron that carries their axons to the somatosensory gyrus.

Question 17

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for hearing

Answer 17

Receptors - Haircells
Nerve - Vestibulo Cochlear
Sub cortical Relay center - Cochlear nuclei, superior olive, inferior colliculus and medial geniculate nuclei
Cortical area - Auditory cortex in the lower bank of the lateral fissure in the temporal lobe.

Question 18

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for skin senses

Answer 18

Receptors - Pacinian, merkel, ruffini and free nerve endings
Nerve - Spinal and trigeminal nerves
Sub cortical Relay center - Dorsal spinal cord, hindbrain nuclei and thalamic nuclei
Cortical area - Somatosensory cortex or post central gyrus

Question 19

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for smell?

Answer 19

Receptors - Olfactory receptors
Nerve - Olfactory bulb and tract
Sub cortical Relay center - none
Cortical area - Piriform cortex

Question 20

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for proprioception?

Answer 20

Receptors -, spindles, joint capsules
Nerve - spinal nerves, cranial nerves
Sub cortical Relay center - Dorsal spinal cord, hindbrain nuclei and thalamic nuclei
Cortical area -Somatosensory cortex or post central gyrus

Question 21

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for taste?

Answer 21

Receptors - Tastebuds
Nerve - Facial and glossopharyngeal nerves
Sub cortical Relay center - nucleus of the solitary tract and the gustatory thalamus
Cortical area - insular cortex

Question 22

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for pheromone detection(not in humans)?

Answer 22

Receptors - Special olfactory receptors
Nerve - Accesory olfactory bulb and tract
Sub cortical Relay center - None
Cortical area - Bed nucleus of the olfactory tract

Question 23

What are the receptors, nerve tracts , subcortical relay centers and cortical areas for internal senses?

Answer 23

Receptors - Stretch receptors and free endings
Nerve - Visceral afferents
Sub cortical Relay center - Nucleus of the solitary tract
Cortical area - Insular cortex

Question 24

What are the two parts of the spinothalamic tracts?

Answer 24

Lateral(pain and temperature) and ventral(crude touch)

Question 25

What is the pathway of the spinothalamic tract?

Answer 25

The receptors sends their signals to the pseudounipolar cells whose nucleus is found in the dorsal root ganglion. The axons enters the dorsal horn and travels one or two segments up or down the spinal cord, where it synapses with the substantia gelatinosa. the axon of the neuron travels in the ventral direction and crosses over in the anterior white commisure. t then travels upwards to the synapse in the thalamus, which then projects the neuron to the somatosensory cortex.

Question 27

What is the difference between proprioception and pain?

Answer 27

Pain is the negative feelings associated with nociception whilst nociception is the actual sensation of damage to tissue. they both closely related, however can occur independent of each other. Under general anaesthetics, the person has working nociceptors which can trigger reflexes, however pain signalling is blocked. In neuropathic pain, the nervous system can become abnormally sensitised and report pain even when the nociceptors are no longer activated.

Question 28

What are nociceptors?

Answer 28

Nociceptors are free nerve endings in tissue that respond to mechanical, thermal and chemical stimuli that is actual or potential tissue damage.

Question 29

What are the two types of fibres that carry nociception?

Answer 29

There are two types of fibres that carry nociception-fast and slow. The fast pathway is associated with sharp, well localised pricking or stinging pain.This sensation is carried by thin myelinated A delta fibres to superficial dorsal horn or the caudal spinal trigeminal nerve in terms of the head. The transmitter is glutamate. This information is carried to the ventroposterior nucleus of the thalamus and then to the somatosensory cortex. The slow pathway is associated with dull aching pain. It is carried by slow, unmyelinated C fibres to the deep dorsal horn or the caudal spinal trigeminal nerve. This pathway uses Substance P. This information is then sent to the intralamina nucleus of the thalamus via the spinothalamic tract.

Question 30

What is different about nociception as a sensory system?

Answer 30

Sensory systems other than nociception adapts to the stimulus if it persists for too long. however, nociception makes it more sensitive and make previously unresponsive receptors to become responsive. This is called peripheral sensitisation. In CNS sensitisation, chronic stimulation of the pathway can cause other interaction to make the pathway more responsive. THe pathway may be stimulated even by innocuous stimuli such as touch. This is called allodynia.

Question 31

What is spinal cordotomy?

Answer 31

Surgically cutting the lateral spinothalamic tract in cases of intractable pain. It has proven use in cases of mesothelioma, an incurable form of cancer that covers the lungs.

Question 32

What is visceral pain?

Answer 32

Visceral pain is triggered by visceral nociception. The visceral nociception may be triggered by smooth muscle spasm, organ distension, inflammation or ischemia. Since the brain is not constantly aware of visceral pain, it localises it to a region or patch of the skin. This is called referred pain.

Question 33

Give an example of referred pain ?

Answer 33

Gall bladder inflammationion rubs against the coating of the diaphragm which is supplied by C4. This causes the visceral nociception of the diaphragm to be activated. However since the brain cannot localise the pain it is perceived to be a pain the shoulders. This is because both the diaphragm and skin of the shoulder is supplied by the nerve C4.

Question 34

What is proprioception ?

Answer 34

Proprioception is the sense of position of our body parts. Individuals who suffer damage dorsal control system such as tertiary cephalus show loss of deep pressure sensations. If such a person closes their eyes when standing up they risk falling over.

Question 35

What happens if the individual suffer from spinal chord transsection above c4 ?

Answer 35

He dies cannot because he cannot breathe.

Question 36

What is endogenous opiate system ?

Answer 36

Part of the brain which produces chemicals that act like heroine or morphin. These chemicals are enkephalins and endorphins and are therefore called endogenous opiates.They block neurotransmission at synapses to control nociception. They alter mood to change the perception of nociception as pain. It is activated in life threatening situations so the brain does not get distracted from organizing an escape plan.

Question 37

What do local anaesthetics do and give me an example.

Answer 37

They disable nociceptors by preventing them from AP. Example :Lignocaine

Question 38

What are some analgesics and what do they do ?

Answer 38

Analgesics block pain signalling and some of them are aspirin, ibuprofen and morphine.

Question 39

Give some examples of general anaesthetics

Answer 39

Anaesthetics block pain perception by making the person unconscious. Examples Ether and Halothane