Chapter 47

Sensory Receptors

• Nociceptors detect damage (pain receptors) and the term 'Noci' in 'Nociceptors' derives from the Greek word for pain.
• Photoreceptors detect light.

Chemoreceptors

• Chemoreceptors detect changes in oxygen and carbon dioxide levels, as well as pH levels.

Receptor Function

• The principle of specific nerve energies states that each receptor responds to a limited range of stimuli and has a direct line to the brain.
• Mechanical deformation generates receptor potentials through mechanoreceptors.

Receptor Potentials

• The electrotonic potential generated by a receptor potential is called the receptor potential.
• Receptor potentials are graded potentials, and their amplitude depends on the strength of the stimulus.

Action Potential

• Action potentials (AP) only occur in the axon, not in the dendrites or cell body.
• Factors that can lead to changes in membrane permeability to ions, causing hyperpolarization or depolarization, include changes in ion concentrations, neurotransmitters, and mechanical distortion.

Mechanoreceptors

• Mechanical distortion causes the membrane of a sensory receptor to stretch or deform, leading to changes in membrane permeability.

Axon Activity

• Abnormal ion concentration in the axon can lead to changes in axon activity.
• Underactivity in the axon leads to decreased muscle tone, while overactivity leads to increased muscle tone.
• Underactivity in the axon can lead to muscle weakness, while overactivity can lead to muscle spasms.

Reverberatory Circuits

• The function of reverberatory circuits is to maintain a steady output signal for a prolonged period of time.
• Reverberatory circuits are used in the autonomic nervous system to control vascular tone, gut tone, and heart rate.
• The autonomic nervous system uses continuous output from reverberating circuits to control these functions.
• The effect of reverberatory circuits on synaptic sensitivity is to increase it.

Receptor Types

• Phasic receptors respond only when a change is taking place.
• The mechanism of adaptation for mechanoreceptors in the Pacinian corpuscle is through the deactivation of the receptor.
• Tonic receptors continue to transmit impulses to the brain for long periods of time while the stimulus is present.
• The importance of signal intensity in the interpretation of signals by the brain is that it allows the brain to distinguish between strong and weak stimuli.

Inhibitory Circuits

• The function of inhibitory circuits in the brain is to decrease the activity of neurons.

Slowly Adapting Receptors

• The main characteristic of slowly adapting receptors is that they continue to transmit impulses to the brain over a long period of time.

Converging Neuronal Circuits

• The purpose of converging neuronal circuits is to allow for the integration of information from multiple sources.

Reverberatory Circuit Termination

• The mechanism that stops the reverberatory circuit from continuing to produce output signals is through the depletion of neurotransmitters.

Receptor Properties

• The Weber-Fechner law states that a receptor allows for the detection of only large changes in stimulus strength when the stimulus strength is high.
• The role of tonic receptors in the body is to provide continuous feedback about the environment.