TOPIC IV: Nervous System II – SENSORY “INPUT” Flashcards
What is the main function of the sensory (afferent) nervous system?
Detecting and relaying information from the body and external environment to the central nervous system. This is essential for perception, homeostasis, and reflexes.
What do specialized sensory receptors detect?
Stimuli such as temperature, pain, pressure, stretch, light, sound, and chemical changes.
What are the two types of receptors, based on their response to a constant stimulus?
Phasic receptors and tonic receptors
How do phasic receptors respond to a constant stimulus?
They show adaptation (usually a decrease in sensitivity) in the presence of a constant stimulus. Examples: touch (mechanoreceptors in skin) and smell (olfactory receptors).
How do tonic receptors respond to a constant stimulus?
he frequency of action potentials remains constant; there is no adaptation. They provide continuous monitoring of sensory information and have a protective function. Examples: proprioceptors (posture) and some nociceptors (pain).
How does the brain perceive different types of stimuli?
Mainly by the type of receptor stimulated. The axon activated by the receptor has synaptic connections to the part of the CNS concerned with that sense. It is “hardwired” from receptor to brain
How does the brain perceive stimuli of different strengths?
Mainly by the frequency of action potentials (number per time) going to the CNS. A stronger stimulus results in a higher action potential frequency and activates more receptors.
What are the two types of graded potentials that occur on receptors?
Generator potential and receptor potential.
What is a generator potential?
A type of graded potential that occurs on the dendrites of a first-order sensory neuron and directly generates an action potential on the axon of that same neuron.
What is a receptor potential?
It occurs when the receptor cell is separate from the sensory neuron. The receptor potential occurs on the specialized receptor cell, causing the release of neurotransmitter onto the dendrites of the sensory neuron.
Describe the sequence of events in the inner ear’s hair cells.
- A stimulus creates a receptor potential on the hair cell. 2. The receptor potential causes the hair cell to release neurotransmitter onto the associated sensory neuron. 3. An EPSP occurs on the dendrites of the sensory neuron. 4. The EPSP generates an action potential on the axon of the sensory neuron.
Outline the vision pathway from light entering the eye to the visual cortex.
- Light enters the pupil and the image is focused on the retina (image is reduced and inverted). 2. Light stimulates a chemical reaction on rods and/or cones that produces a receptor potential (graded potential). 3. rods or cones → neurotransmitter → bipolar neuron (graded potential, no AP) → neurotransmitter → ganglion cell (EPSP, get AP) → optic nerve (formed by axons of ganglion cells) → optic tracts → visual cortex of occipital lobe
Outline the hearing pathway from hair cells to the auditory cortex.
- Hair cells in the cochlear duct are stimulated (receptor potential, no AP). 2. Neurotransmitter release onto associated neuron (EPSP, get AP). 3. AP on axon of cochlear branch of cranial nerve VIII. 4. Auditory cortex (temporal lobe).
Outline the equilibrium pathway from hair cells to other areas of the brain.
- Hair cells in semicircular ducts & saccule or utricle (in vestibule) (receptor potential, no AP). 2. Neurotransmitter release onto associated neuron (EPSP, get AP). 3. AP on axon of vestibular branch of cranial nerve VIII. 4. Cerebellum (coordinates muscle contraction), brain stem, and thalamus which leads to eye muscles and other muscles of neck and trunk for balance.
Give an example of a sensory pathway.
Posterior (Dorsal) Column Pathways for touch, which involves 3 neurons in succession: 1st, 2nd, and 3rd order.
