Topic 4: Nervous System 2

Question 1

Interpretation of Sensory Stimuli (Afferent)

Answer 1

• Stimuli are detected by receptors (only respond to a specific stimulus e.g. temp)

Question 2

Receptors Can Be: (Afferent)

Answer 2

1) Dendrites on a unipolar neuron

2) An individual cell that synapses to a neutron e.g. hair cell (internal ear)

Question 3

What Happens When A Receptor (R) Is Stimulated? (Afferent)

Answer 3

1) Stimulus causes opening of gated channels (usually Na+) on receptor membrane
2) GP on receptor membrane (stimulus. becomes electrical)

Question 4

GP on receptor membrane (stimulates. becomes electrical) IF:

Answer 4

1) Receptor = dendrite of unipolar neuron and GP (depol) directly generates an AP = a generator potential
2) Receptor = individual cell e.g. hair cell (no axon) = a receptor potential –> nt onto associated neutron –> EPSP on neutron –> generates an AP

Question 5

Phasic Receptors (Type of Receptor)

Answer 5

• Receptor respond to stimulus change

- In the presence of a constant stimulus, show adaptation (usually lower in sensitivity)

Question 6

Examples of Phasic Receptors

Answer 6

#1) put a hat on --> bursts of APs (feel it) --> then get decrease in AP frequency to CNS (can't feel it) even though stimulates. maintained at constant strength 
#2) Take hat off - bursts of APs - feel it again

Question 7

Tonic Receptor (Type of Receptor)

Answer 7

• Frequency of APs remains constant -NO adaptation
• Gives continuous info e.g. posture, condition, pain = Protective
• Monitor presence + intensity of stimulus

Question 8

How Does The Brain Perceive Different TYPES of Stimuli?

Answer 8

• Mainly by type of receptor stimulated
• Axon activated by receptor –> synaptic connections to part of CNS with that sense (hardwired from receptor to brain - always ‘who’ is calling (type of receptor) and from where (location))

Question 9

Examples of How the Brain Perceives Different Types of Stimuli.

Answer 9

#1) Stimulate Messner's corpuscle (touch receptor) in right index finger = impulses to post central gyrus region for right index finger
#2) Mechanical pressure on eyeball --> "seen" as light - ALL signals received from retina perceived as light

Question 10

How Does Brain Perceive Stimuli of Different Strengths?

Answer 10

• e.g. determining if feather or brick on foot
• Mainly by frequency of ap (#/time) going to CNS e.g. higher stimulus = higher AP frequency
• Stronger stimulus also activates more receptors (e.g. pressure + touch)

Question 11

Sensory (ascending) Pathways

Answer 11

• e.g. posterior (Dorsal) Column Pathways for Touch
• 3 neurons in succession - 1st, 2nd and 3rd order
• LOOK AT DIAGRAM

Question 12

Special Senses: Vision

Answer 12

1) Light enters the pupil & image focused on retina (reduced + inverted)
2) Light stimulates chemical reaction on rods and cones - produces a receptor potential (GP)
Rod or cone (receptor potenital, no AP) –nt– Bipolar Neuron (graded potential, no AP) –nt– Ganglion Cell (EPSP, get AP) —- Optic Nerve (formed by axons of ganglion cells) —- Optic Tracts — Visual Cortex of occipital lobe

Question 13

Hearing

Answer 13

• Hair cell in cochlear duct stimulated (receptor potential, no AP)
• nt release onto associated neuron (EPSP, get AP)
• AP on axon in cochlear branch of cranial nerve VIII
• Auditory Cortex (temporal lobe)

Question 14

Equilibrium

Answer 14

• Hair cell in semicircular ducts or saccule & utricle (in vestibule) (receptor potential, no AP)
• nt release onto associated neutron (EPSP, get AP)
• ap on axon in vestibular branch of cranial nerve VIII
• Cerebellum – Brain Stem – Thalamus
• LOOK AT DIAGRAM