Somatic sensory system

Question 1

What are sensory receptors?

Answer 1

• Specialised cells that monitor specific conditions, e.g. temperature, pain, touch, pressure, vibration.
• When stimulated, receptor passes info to CNS in form of action potential along axon.
• Sensation = arriving info from senses.
• Perception = conscious awareness of sensation.

Question 2

Name some special senses?

Answer 2

• Olfaction (smell).
• Vision
• Gustation (taste).
• Hearing
• Equilibrium

Question 3

Describe the detection of stimuli?

Answer 3

• Each receptor has a characteristic sensitivity.

- An area is monitored by a single receptor cell, the larger the field the more difficult it is to localize stimuli.

Question 4

How to classify sensory receptors?

Answer 4

• Exteroceptors = provide info to the body about external environment.
• Proprioceptors = report positions of skeletal muscle and joint.
• Interoceptors = monitor visceral organs.

Question 5

Name the 4 types of sensory receptors?

Answer 5

• Nociceptors (pain)
• Thermoreceptors (temp)
• Mechanoreceptors (physical distortion)
• Chemoreceptors (chemical conc)

Question 6

Describe the nociceptors?

Answer 6

• In skin, joint capsules, bones, walls of BV.
• Sensitive to temp, damage, dissolved chemicals.
• Type A and C fibres.
• Type A (myelinated) = carry sensation of pain, caused by injection or deep cut. Sensations reach CNS quick, relayed to sensory cortex.
• Type C = carry sensations of slow pain, burning, aches.Cause generalized activation of thalamus, become aware of pain, only have general idea of area.

Question 7

Describe thermoreceptors?

Answer 7

• Temp receptors; in skin, skeletal muscle, liver, hypothalamus.
• Carry temp sensation, along same pathway as pain.
• Sent to reticular formation, thalamus, primary sensory cortex.

Question 8

Name and describe 3 types of mechanoreceptors?

Answer 8

• Tactile = sensation of touch, pressure, vibration. Fine touch, narrow field, provide detailed info about source of stimulation. Crude touch; large field, poor localization.
• Baroreceptors = detect pressure changes in walls of BV and digestive, reproductive.
• Proprioceptors = position of joints, tendons, ligaments. State of muscle contraction. (muscle spindles, golgi tendon organs, receptors in joint capsules).

Question 9

Describe the chemoreceptors?

Answer 9

-Monitor pH, carbon dioxide and oxygen levels in blood.

Question 10

Where does somatic sensory info go?

Answer 10

• Relayed to the thalamus.

- Some arrives at the cerebral cortex and reaches awareness.

Question 11

Describe the posterior column pathway?

Answer 11

• Carries sensation of highly localized touch, pressure..
• Include fasciculus gracilis (lower limbs, trunk) and cuneatus(upper trunk, arms).
• 1st order = from dorsal root of spinal cord, same side to medulla, synapse.
• 2nd order = from muscle cross over to travel through brain stem, synapse at thalamus.
• 3rd order = from thalamus to primary sensory cortex.

Question 12

Describe the spino - thalamic tract pathways?

Answer 12

• Anterior = carrying crude sensations of touch and pressure.
• Lateral = carry sensations of pain and temperature.
• 1st order = from dorsal root of cord and synapses in posterior grey horn of cord.
• 2nd order ANTERIOR = crosses over, ascends in anterior column of white matter.
• 2nd order LATERAL = ascends cord in lateral column of WM.
• 2nd order both = through brain stem and synapses at thalamus.
• 3rd order = from thalamus to sensory cortex.

Question 13

Describe neurotransmitters?

Answer 13

• Stimulation of nocicpetor and impulse into CNS, lead to substance P and glutamate releasing. Facilitate pain.
• Endorphines inhibit pain and release P.

Question 14

Describe the posterior spinocerebellar pathways?

Answer 14

• Receives proprioceptive info from muscles, tendons, joints.
• 1st order = from proprioceptors to posterior grey horn.
• 2nd order = from grey to lateral columns of WM, passes through inferior cerebellar peduncle to cerebellum.
• NO cross over.

Question 15

Describe the anterior spinocerebellar pathway?

Answer 15

• Receives proprioceptive info from muscles, tendons, joints.
• 1st order = from p to posterior grey horns.
• 2nd order = from grey horn, crosses over to other side of cord to lateral white matter, crosses back over at pons, passes through superior cerebellar peduncle to cerebellum.
• Most re cross in cerebellum.