Ascending tracts & Sensory receptors

Question 1

What are sensory receptors

Answer 1

Specialized cells providing CNS with information. Respond to stimuli and convert it into AP’s in the process of transduction to carry it to CNS. CNS interprets info

Question 2

What are sensory mechanisms that collect info form all over the body

Answer 2

Temperature 
Touch 
Pressure 
Vibration 
Proprioception 
Pain

Question 3

What are the special senses that collect info

Answer 3

Vision 
Hearing 
Smell 
Taste 
Equilibrium

Question 4

How can you classify somatic receptors

Answer 4

1- Based on mechanism of activation

2- based on purpose they serve

Question 5

When classifying based on mechanism of action what are the types of somatic receptors

Answer 5

1- Mechanoreceptors : compression/ stretching
2- Thermoreceptors : hot/cold
3- Electromagnetic : light in retina
4- Chemoreceptors : O2, CO2, H+ levels , taste , smell

Question 6

When classifying based on purpose what are the types of somatic receptors

Answer 6

1- Nociceptors : give rise to pain sensation ) mechanisms, thermo and chemoreceptors )

2- Proprioceptors : mechanoreceptors that give info about joint position and body movement

Question 7

Can receptors only respond to 1 type of stimulus

Answer 7

No they can respond to multiple , but will show high sensitivity to one type of stimulus

Ex: pressure on eye can cause whit flash that is interpreted as a visual signal

Question 8

If an area is sensitive it’s receptive field will be …

Answer 8

Small. Receptors will have little overlap to allow fine discrimination between different stimuli

Question 9

Give an example of an area that would have small receptive fields and one that would have larger ones

Answer 9

Small : fingers

big : back / torso

Question 10

What is a pacinian corpuscle and how does it work

Answer 10

A receptor consisting of a bare neurone tip surrounded by concentric tissue layers.

Local pressure will cause deformation of tissue , which will be transmitted to unmyelinated fibre tip. this allows depolarizing Na+ entry and electric signal will be sent if stimulus reaches threshold.

Question 11

When is an AP generated

Answer 11

When receptor potential is above threshold membrane potential

Question 12

The stimulus length is coded for in

Answer 12

1- Size of receptor potential

2- Sensory nerve frequency of AP ( frequency is proportional to stimulus )

Question 13

Explain what a phasic response is and give an example of a receptor

Answer 13

Phasic receptors will adapt rapidly and the receptor potential and AP will diminish.

Brief , phasic response , gives transient info

ex: pacinian corpuscle

Question 14

Explain what a tonic response is and give an example of a receptor

Answer 14

Receptors that respond with prolonged depolarization in presence of stimulus. little deputation. receptor potential and AP is maintained.

Constant sensation

Ex: some proprioceptors

Question 15

Explain what are mechanoreceptors

Answer 15

Receptors that have stretch sensitive membrane channels and respond to distortion of that membrane.

Question 16

List groups of mechanoreceptors and explain each

Answer 16

1- Tactile receptors of skin 
- fine or crude touch receptors 
- different pathways ascending to brain 
2- deep tissue receptors 
- same as skin but in deeper tissue  
3- proprioceptors
- ex:  muscle spindles , Golgi tendon organs, joint receptors  
4- baroreceptors 
- within CVS : carotid sinus , aortic arch ,right atrium. senses stretch caused by  blood pressure 
5- inner ear receptors 
- cochlear ( move hairs ) and vestibular receptors 
( move hairs )

Question 17

What are the types of tactile receptors and explain each ( 6 ) - what they are composed of, where they are found and what do they sense

Answer 17

1- free nerve endings : bare dendrites between skin cells that give rise to tonic discharge when stimulated. small fields. only receptors on cornea of eye

2- root hair plexus : sensory dendrites surrounding hair follicles. rapidly adapting

3- Tactile Merkel’s discs: very sensitive peripheral tonic touch receptor. Closely associated with skin cells. grouped in igoo domes ( bumps on skin ). small field

4- Tactile Meissner’s corpuscles : encapsulated nerve ending in the dermis with dendrite network at the end . fast adapting. senses fine touch and low frequency vibration. In sensitive areas like finger types, eyelids, lips

5- Laminated Pacinian corpuscles: layer of CT with fluid in between surrounding single dendrite. Changes in CT = pressure. Rapid adapting. Senses deep pressure era high frequency vibration. on fingers and viscera ( deep tissue and skin)

6- Ruffini corpuscle : dendrites intertwined with collagen fibres in skin. give distortion sensation and skin pressure

Question 18

What are muscle spindles

Answer 18

Senses muscle length , triggers muscle stretch reflexes.
when muscle shortens it’s detected by sensory receptors around the intramural fibres of the spindle. signals sent to SC via primary afferent nerve.

Question 19

How do muscle spindles maintain their sensitivity

Answer 19

Y gam,a fibres are activated which travel to the contractile ends of muscle spindles and contracts it along with the muscle

Question 20

What are Golgi tendon organs

Answer 20

Located in tendon , in series with muscles. Sense muscle tension. Initiate inhibitory reflex.

Question 21

Explain joint receptors as proprioceptors

Answer 21

Free nerve endings in joint capsules that detect joint pressure & movement & tension

Question 22

Explain Baroreceptors as a form of mechanoreceptors

Answer 22

free nerve endings in elastic tissue of distensible organs , blood vessels and respiratory , digestive and urinary tracts.

Monitor pressure changes in organ walls. Rapidly adapting & produce different afferents according to tissue

Question 23

Explain temperature receptors

Answer 23

Located in : hypothalamus , spine , lover , skeletal muscle, dermis

Free nerve ending phasic receptors , sensitive to hot or cold temperatures. Transduced by TRP channels that open up in specific temperature ranges

Question 24

Explain chemoreceptors

Answer 24

In carotid and aortic bodies : monitor blood pH , CO2 , O2 & elicit respiratory , CVS and behavioural responses

In medulla oblongata : monitor CSF pH and CO2

Hypothalamic receptors : monitor glucose, amino acids , osmolarity

In GI tract : taste buds, trigger gastric secretions

Question 25

Explain Nociceptors

Answer 25

bare nerve endings that respond to mechanical, chemicals and temperature.

Most respond to chemicals released by damaged cells ( K+ , bradykinin )

Don’t adapt but activity can be modified via prostaglandins that sensitize them.

Question 26

Explain the somatosensory system pathway

Answer 26

1- 1st order neurones enter the spinal cord via dorsal roots
2- synapse with 2nd order neurones and travel to brain via 2 primary ascending tracts
3- connect to cerebral cortex via 3rd order neurones

Question 27

Explain primary afferent neurones

Answer 27

Classified based on conduction velocities. larger the diameter of the axon and insulating myelin the faster the conduction velocity. Alpa are fast , C are slower

Question 28

Which fibres synapse first in the dorsal regions

Answer 28

The slower fibres ( C ) will synapse first in dorsal lamina , faster fibres will synapse more ventrally

Question 29

What are dermatomes

Answer 29

area of skin sensation associated with spinal nerve entering spine at particular spinal level .

Question 30

What are the sensory pathways that ascend the spinal cord

Answer 30

1- dorsal column
2- spinothalamic tracts
3- spinocerebelalr tract

Question 31

Explain the spinothalamic tract

Answer 31

1- info from Pain , temp , pressure, tickle and itch ( crude touch )
2- 2nd order neurones CROSS midline of spine and ascend contralateral side to entry in spinothalamic tracts
3- synapse in thalamus and 3rd order neurones travel to sensory cortex

Info being sent has poor spatial discrimination and is sent with slower conduction velocities

Question 32

Explain the Dorsal column

Answer 32

1- info from proprioceptor , touch , vibration
2- ascend ipsilateral dorsal column ( NO synapse in spine )
3- synapse with 2nd order neurones in dorsal column nuclei
4- cross midline in the medulla to thalamus

Fine senses with good spatial discrimination , faster condition

Question 33

Explain the spinocerebellar tract

Answer 33

1- originates in spinal cord
2- 2nd order neurones ascend , some contra laterally some ipsilaterally
3- terminates in the cerebellum

conveys info to cerebellum about limb and joint position

Question 34

Where will the the somatic senses end up

Answer 34

In the primary sensory cortex in the post-central gyrus

Question 35

What are common causes of gradual damage to nerves and what can they result in

Answer 35

1- Diabtes
2- Chemotherapy
3- Multiple Sclerosis
4- Chronic excessive alcohol consumption

can all result in paraesthesia ( pins and needles ) and anaesthesia ( numbness ).

Question 36

Trauma to spine are usually unilateral or bilateral

Answer 36

Usually bilateral. area below lesion is affected