special senses (general)

Question 1

what are general senses

Answer 1

• receptors (dendrites of neurons) scattered throughout the body
• non-localised
• one receptor can respond to different stimuli
• touch, pressure, pain, vibration, temperature, muscle sense

Question 2

what are special senses

Answer 2

• special organ / structure with distinct receptor cells
• localised in head region
• vision, taste, smell, hearing and equilibrium

Question 3

what is the importance of sensory systems

Answer 3

• sensing changes in environment / our body allows for survival
• communication, adjustments, interpretation of surroundings
• sensation: awareness of changes in external / internal
• perception: conscious interpretation of stimuli
• interpretation: development physically / cognitively, memories, interactions

Question 4

what is the purpose of receptors

Answer 4

• specialised receptors throughout eukaryotic organisms

- convert physical / chemical signals to electrical (PNS / CNS)

Question 5

what are sensory receptors

Answer 5

• stimuli in environment activates specialised receptors in PNS, integration in brain and send motor output to effectors
• diff. stimuli is sensed by diff. receptors, classified structurally by cell type, position and function

Question 6

describe classification of receptors by structural differences

Answer 6

• non-encapsulated: free endings, pain and thermo, light touch (can become pain), hair follicle receptors
• encapsulated: endings covered with connective tissue / bubble, pacinian corpuscles (touch / pressure), tacticle / meissners corpuscles (discriminative touch), muscle spindles (proprioceptors / muscle stretch)
• specialised: photoreceptor in eye, tastebuds in mouth, receptors in ears

Question 7

describe classification of receptors by location

Answer 7

• extero: stimuli outside body, receptors in skin (touch, pressure, pain, temp) and sense organs
• intero: stimuli inside body, chemical / temp changes, muscle stretch
• proprio: stretch in skeletal muscles, tendons, joints, ligaments, connective tissue (inform brain of movement)

Question 8

describe classification of receptors by stimulus type

Answer 8

• mechano: physical stimuli, can adapt, stretching of cell membrane opens channels, pressure, touch, vibration, stretch, balance, sound, position / movement
• chemo: chemicals (blood, smell, taste, pH)
• thermo: changes above (heat) or below (cold) normal body temp.
• photo: light energy, free endings,
• osmo: solute conc. of body fluids, chemicals / sugars in blood
• nocic: pain causing / tissue damaging stimuli, don’t adapt, free endings

Question 9

briefly describe the ascending and descending tracts of the spinal cord

Answer 9

• A: afferent signal towards CNS
• D: efferent signal from CNS to elicit appropriate response
• pathways paired symmetrically left / right (parallel)
• lead to different areas of brain to know where stimuli originated

Question 10

describe the arrangement of neurons in ascending tracts

Answer 10

• 1st order: receives stimuli, receptor, connects to 2nd via synapse in medulla oblongata or gray matter
• 2nd order: inter neuron, crosses to other side (decussation) ascends to thalamus, synapse to 3rd
• 3rd order: pass somatosensory cortex, info received, interpreted, perception of peripheral stimuli

Question 11

describe ascending pathways

Answer 11

• arrive at primary sensory cortex (parietal lobe)
• fasciculus gracilis (DC): fine touch, proprioception, vibration of lower limbs, conscious info.
• fasciculus cuneatus (DC): fine touch, proprioception, vibration of upper limbs, conscious info.
• spinothalamic: pain. temp, crude touch, conscious info.
• spinocerebellar: subconscious info., proprioception, awareness, movements / composition of environment

Question 12

describe the descending pathways

Answer 12

• descend from brain to effector region (motor neurons in muscles / glands)
• pyramidal: lateral / anterior corticospinal
• extra-pyramidal: rubrospinal, tectospinal, vestibulospinal and reticulospinal

Question 13

describe sensation, synapse, synaptic cleft and neurons

Answer 13

• sensation: stimulus must excite a receptor, AP must be created
• synapse: transmission of a nerve impulse across a synapse via neurotransmitter
• synaptic cleft: gap between two neurons
• neurons: long-lived (100 years), high metabolic rate, electrical signalling, cell-to-cell interactions during development

Question 14

what is the pathway of a synapse

Answer 14

1. action potential arrives at axon terminal of pre-synaptic cell, depolarising the presynaptic membrane
2. depolarisation opens voltage gated channels, triggering an influx of Ca2+ ions
3. the elevated Ca2+ concentration causes synaptic vessels to migrate towards and fuse with the presynaptic membrane
4. vesicles release neurotransmitter into the synaptic cleft via exocytosis (chemical messenger)
5. neurotransmitter diffuses across synaptic cleft
6. neurotransmitters bind to ligand gated ion channels in the postsynaptic membrane and generate an electric current to depolarise the postsynaptic neuron

Question 15

what is sensory transduction

Answer 15

• physical energy transformed to electrical energy which is produced by receptors (receptor potential)
• stimulus acts by affecting opening / closing of channels or Ca levels
• can be specialised nerve ending (with receptor) or a separate cell (with receptor) that causes the release of neurotransmitters to neuron

Question 16

what are graded potentials

Answer 16

• graded response to stimuli that may be depolarising / hyper-polarising
• must occur to depolarize the neuron to threshold before action potentials can occur
• amplitude of receptor potential is proportional to size of stimulus
• weak stimulus = little neurotransmitter, no threshold reached, no AP
• medium stimulus = more neurotransmitters, threshold reached, AP
• strong stimulus = many neurotransmitters, threshold reached, high frequency AP