General Senses

Question 1

General vs Special senses

Answer 1

• general sensory receptors (somatic receptors)
  
  • no structural specializations in free nerve endings that provide us with pain, itch, tickle, temp
  • some structural specializations in receptors for touch, pressure, vibration
• special sensory receptors
  
  • very complex structures: vision, hearing, taste, smell

Question 2

Structural classification of receptors

Answer 2

• free nerve endings
  
  • bare dendrites
  • pain, temp, tickle, itch, light and touch
• encapsulated nerve endings
  
  • dendrites enclosed in connective tissue capsule
  • pressure vibration and deep touch
• separate sensory cells
  
  • specialized cells that respond to stimuli
  • vision, taste, hearing, balance

Question 3

Classification of receptors by location

Answer 3

• exteroceptors
  
  • near surface of body
  • receive external stimuli
  • touch, pressure, pain, vibration and temp
• interoceptors
  
  • monitors internal environment (viscera)
  • not conscious except for pain or pressure
• proprioceptors
  
  • muscle, tendon, joint, internal ear
  • senses body position and movement

Question 4

Classification by stimuli detected

Answer 4

• mechanoreceptors
  
  • touch, pressure, vibration, proprioception, hearing, equilibrium
• thermoreceptors detect temp
• nociceptors detect damage to tissues
• photoreceptors detect light
• chemoreceptors detect molecules
  
  • taste, smell and changes in body fluid chemistry

Question 5

Somatic tactile sensations

Answer 5

• touch
• pain
• pressure
• temp

Question 6

Merkel’s Disc

Answer 6

• epidermis
• flattened dendrites touching cells of stratum basale
• used in discriminative touch

Question 7

Meissner’s corpuscle

Answer 7

• dendrites enclosed in CT in dermal papillae of hairless skin
• discriminative touch and vibration: rapidly adapting
• generate impulses mainly at onset of a touch, and then adapt to sensation

Question 8

Ruffin Corpuscle

Answer 8

• found deep in dermis of skin - reticular layer

- detect heavy touch, continuous touch, and pressure

Question 9

Pacinian Corpuscle

Answer 9

• onion-like connective tissue capsule enclosing a dendrite
• found in subcutaneous tissues and certain viscera
• sensations of pressure or high-frequency vibration

Question 10

Hair root plexus

Answer 10

-free nerve endings found around follicles, detects movement of hair

Question 11

Free nerve endings: pain and temp

Answer 11

• extend between layers of epidermis
• no connective tissue around them
• skin, viscera, muscles
• inadequate blood supply, distinction of stomach, muscle spasms

Question 12

Pain sensations

Answer 12

• nociceptors: pain receptors
• free nerve endings found in every tissue of body except brain
• stimulated by excessive distension, muscle spasms, inadequate blood flow
• tissue injury releases chemicals such as K+, kinins or prostaglandins that stimulate nociceptors
• little adaption occurs

Question 13

Referred Pain

Answer 13

• visceral pain that is felt just deep to the skin overlying the stimulated organ or in a surface area far from the organ
• skin area and organ are served by the same segment of the spinal cord
• heart attack is felt in skin along left arm since both are supplied by spinal cord segment T1-T5

Question 14

Pain relief

Answer 14

• aspiring and ibuprofen block formation of prostaglandins that stimulates nociceptors
• novacaine blocks conduction of nerve impulses along pain fibres
• morphine lessens perception of pain in the brain
• acupuncture

Question 15

Proprioceptive sensations

Answer 15

• awareness of boys position and movement
  
  • walk or type without looking
  • estimate weight of objects
• proprioceptors adapt only slightly
• proprioceptors: muscle spindles, Golgi tendon organs and joint receptors

Question 16

Muscle spindles

Answer 16

• specialized intrafusal muscles fibres enclosed in a CT capsule and inner aged by gamma motor neurons
• stretching of the muscle stretches the muscle spindles sending sensory information back to CNS
• feel stretch until a certain point
• reflexes to avoid tearing

Question 17

Golgi tendon organs

Answer 17

• found at junction of tendon and muscle
• consists of an encapsulated bundle of collagen fibres loaded with sensory fibres
• when the tendon is overly tense, sensory signals head to CNS and result in muscles relaxation
• sometimes not conscious

Question 18

Joint receptors

Answer 18

• ruffini corpuscles
  
  • found in joint capsule
  • respond to pressure
• pacinian corpuscles
  
  • found in connective tissue around the joint
  • respond to acceleration and deceleration of joints

Question 19

Somatic sensory pathways

Answer 19

• first order neuron conduct impulses to brain stem or spinal cord
  
  • either spinal or cranial nerves
• second order neurons conducts impulses from spinal cord or brain stem to thalamus: cross over to opposite side before reaching thalamus
• third order neuron conducts impulses from thalamus to primary somatosensory cortex (postcentral gyrus of parietal lobe)

Question 20

Posterior column-medial lemiscus pathway of CNS

Answer 20

• touch and pressure, proprioception (vibration, discriminative touch, weight discrimination and stereognosis)
• signals travel up spinal cord in posterior column and synapse in nucleus gracious or cuneatus
• fibres cross over in medulla to become the medial lemniscus pathway ending in the thalamus
• thalamic fibres each somatosensory cortex

Question 21

Spinothalamic pathways

Answer 21

• anterior and lateral spinothalamic tracts carries pain and temperature
• first cell body in dorsal (posterior) root ganglion with synapses in spinal cord
• second cell body in gray matter of cord, sends fibres to other side of cord and up through white matter to synapse in thalamus
• third cell body in thalamus projects to cerebral cortex
• second order neurons cross

Question 22

Sensory innervation of head and face

Answer 22

• trigeminal cranial nerve (CN V)
• provides touch and pressure and pain and temp for the face and front of head
• sensory info from face relayed to thalamus then to postcentral gyrus

Question 23

Sensory pathways to cerebellum

Answer 23

• major routes for proprioceptive signals to reach cerebellum
  
  • anterior spinocerebellar tract
  • posterior spinocerebellar tract
• subconscious information used by cerebellum for adjusting posture, balance, and skilled movements
• signal travels up to Same side inferior cerebellar peduncle
• terminates on same side of cerebellum unlike contralateral processing in cerebral cortex