[SP 132] Module 1: Overview of Somatosensory System

SENSORY SYSTEM

Responsible for processing sensory information; It helps process physical phenomenon around us into a form we can organize and interpret to make sense of the world (integrates with motor system)

receptors, neural pathways, thalamus, and sensory cortices

Sensory System Contains

Reception -\> Transduction -\> Transmission -\> Perception

SENSORY PROCESSES

sensory cell

RECEPTION takes place in a

RECEPTION

The process by which the body gathers or receives stimuli through sensory receptors

sensory receptors

Reception: It is because of our \____ \___ we receive information and stimuli from our environment

SENSORY RECEPTORS

Specialized cells for detecting particular changes in the environment (How we receive or obtain stimuli)

SENSORY RECEPTORS

Structures that convert stimuli into neuronal activity; Bridge from the outside world to our bodies

Law of Specific Nerve Energy

Sensitive to a specific type of stimulus/modality/physical energy

Mechanoreceptor

sensitive to mechanical energy; Example: vibration, touch, hearing (vibrations of the air)

Photoreceptor

sensitive to electronic magnetic energy or light; For us humans, it is only limited to what's visible for our light spectrum

Thermoreceptor

sensitive to thermal energy; Example: Hot, Cold, Luke Warm

Chemoreceptor

sensitive to chemical energy; Example: Taste or Smell

towards the brain

afferent means?

Type 1

CLASSIFICATIONS - According to Structure or Form: Specialized afferent neuron ending;

Type 1

CLASSIFICATIONS - According to Structure or Form: Cell bodies are attached to the receptors themselves

Free nerve endings, Encapsulated nerve endings

CLASSIFICATIONS - According to Structure or Form: Type 1: Subtypes:

Type 1

CLASSIFICATIONS - According to Structure or Form: Mechanoreceptors, thermoreceptors, nociceptors (pain receptors)

Type II

CLASSIFICATIONS - According to Structure or Form: Separate receptor cell that communicates with an afferent neuron through neurotransmitters and chemical synapses

Type II

CLASSIFICATIONS - According to Structure or Form: Cell body is entirely separate from the receptor cell

Type II

CLASSIFICATIONS - According to Structure or Form: Chemoreceptors, Photoreceptors

Enteroreceptors

CLASSIFICATIONS - According to Stimuli: internal stimuli (inside the body)

Enteroreceptors

CLASSIFICATIONS - According to Stimuli: Chemoreceptors (blood o2 saturation, blood pH), Baroreceptors (blood pressure), Proprioceptors (awareness of body position in space)

Exteroreceptors

CLASSIFICATIONS - According to Stimuli: external stimuli (outside the body)

Exteroreceptors

CLASSIFICATIONS - According to Stimuli: Chemoreceptors (taste, smell, pain), Photoreceptors (light), Thermoreceptors (warm, cold), Mechanoreceptors (hearing, touch), Nociceptors (pain)

chemoreceptors

both in enteroreceptors and exteroreceptors, Because they receive different stimuli depending if there entero or extero

Special Senses

Enteroreceptors and Exteroreceptors leads us to having \___ \___: Senses that have devoted sensory organs (including the vestibular sense)

TRANSDUCTION

Sensory Process: Transforms energy after reception

STIMULUS TRANSDUCTION

Activation of sensory receptors by stimuli -\> change in the electrical potential in the membrane of sensory receptors -\> generates a receptor potential

change in the ion concentration

STIMULUS TRANSDUCTION: Sensory receptors have membrane that surrounds them, so when it is activated by external stimuli, the membrane has a \___ \__ \__ \__ \__ (positive or negative)

Mechanical deformation of the receptor

Ways to induce receptor potentials: Mechanical energy is created, the membrane spreads, ion channels open which is why there is receptor potential to receive and transform energy

Mechanoreceptors

Ways to induce receptor potentials: Mechanical deformation of the receptor

Application of chemical to membrane

Ways to induce receptor potentials: Opening of the ion channels

Chemoreceptors

Ways to induce receptor potentials: Application of chemical to membrane

Change of the temperature of the membrane

Ways to induce receptor potentials: When temp change is detected, it alters the permeability of the membrane

Thermoreceptors

Ways to induce receptor potentials: Change of the temperature of the membrane

Effects of the electromagnetic radiation

Ways to induce receptor potentials: Opens the ion channels, then detects the stimuli

Photoreceptors

Ways to induce receptor potentials: Effects of the electromagnetic radiation

Graded Potential

KINDS OF RECEPTOR POTENTIAL: Results from the passive electrical properties (change in permeability) of cell membranes, which allows ions to diffuse to be able to detect the stimulus

Action Potential

KINDS OF RECEPTOR POTENTIAL: Results from depolarizing stimuli which results to a coordinated activity of voltage-gated ion channels

-70 mV

KINDS OF RECEPTOR POTENTIAL: Resting potential:

-55 mV

KINDS OF RECEPTOR POTENTIAL: Threshold of Excitation:

all or nothing

Action Potential When a stimulus arrives, excitation occurs in the membrane, when you reach that threshold, it becomes an \___ \__ \__ response (it will really reach the peak action potential)

Repolarization -\> Below Resting Potential -\> Hyperpolarization -\> Back to resting potential

Process of Action Potential:

GRADED POTENTIALS

GP or AP: Can be depolarizing or hyperpolarizing depending on the stimulus

ACTION POTENTIALS

GP or AP: Always lead to depolarization and reversal of membrane potential

GRADED POTENTIALS

GP or AP: Amplitude is proportional to the strength of stimulus

ACTION POTENTIALS

GP or AP: Amplitude is all-or-none

GRADED POTENTIALS

GP or AP: No refractory periods

ACTION POTENTIALS

GP or AP: Refractory periods are present

GRADED POTENTIALS

GP or AP: Can be summed over time and across space

ACTION POTENTIALS

GP or AP: Summation is not possible

GRADED POTENTIALS

GP or AP: Brought about by external stimuli or by neurotransmitters released in synapses

ACTION POTENTIALS

GP or AP: Triggered by membrane depolarization to threshold

Depolarization

Change in action potential is caused by

Depolarization or Hyperpolarization

Change in graded potential is caused by \___ \__ \___depending on type of sensory receptors

Graded Potential -\> Depolarization -\> Action Potential

What happens usually in Receptor Potentials:

Graded potential

responsible for the initial membrane depolarization

Deformed area from depolarization -\> Graded Receptor Potential -\> reach threshold of excitement -\> action potential

Process of Receptor Potentials

SENSORY UNIT

Primary afferent neuron and all receptors associated with it, has receptor endings which helps receive the stimuli from external environment

receptive field

All of the sensory receptors, create a \___ \___ (area that can detect stimuli)

RECEPTIVE FIELD

Area of the body surface in which a stimulus leads to activation of the sensory unit

density

RECEPTIVE FIELD Inversely proportional to \___ of receptors

dense

Smaller the area, receptors are more \___ (Ex: fingertips and lips are more sensitive compared to back): Two-point discrimination test

SENSORY CODING

A type of information processing at the receptor level by which sensations are encoded according to 4 properties

MODALITY

PROPERTIES OF SENSORY CODING: All receptors of a sensory unit respond to same stimulus,

Law of specific nerve energies

MODALITY: PROPERTIES OF SENSORY CODING: All receptors of a sensory unit respond to same stimulus,

overlap

MODALITY: PROPERTIES OF SENSORY CODING: Receptive fields of sensory units responding to different modalities often \___

INTENSITY

PROPERTIES OF SENSORY CODING: sensory threshold, frequency doing and population coding

Sensory threshold

INTENSITY: PROPERTIES OF SENSORY CODING: lowest strength of stimulus that can be detected, Absolute Threshold

Frequency Coding

INTENSITY: PROPERTIES OF SENSORY CODING: How often does the action potential happen?

higher frequency

Frequency Coding: After reaching the threshold, the stronger stimuli will produce a \___ \___ of action potentials

Population Coding

INTENSITY: PROPERTIES OF SENSORY CODING: Recruitment/activation of more receptors

recruits/activates

Population Coding: Stronger stimulus \____ more receptors

simultaneously

Frequency Coding and Population Coding happen \___, one part doesn't go first

LOCATION

PROPERTIES OF SENSORY CODING: Localization Acuity, Lateral Inhibition

Localization Acuity

LOCATION: PROPERTIES OF SENSORY CODING: Precision of stimulus localization

receptive field, density

Localization Acuity Depends on size of \___ \___ and the \___ of sensory units

Lateral Inhibition

LOCATION: PROPERTIES OF SENSORY CODING: Stimulus that activates the receptors in a specific location inhibits (deactivates) the activity in nearby areas to enhance localization

DURATION

PROPERTIES OF SENSORY CODING: Dependent on the time you were exposed to the stimuli; Adaptation

Adaptation

DURATION: PROPERTIES OF SENSORY CODING: decreased amplitude of receptor potential over time in presence of constant stimulus (habituation)

Habituation

diminishing of a physiological or emotional response to a frequently repeated stimulus, kung paulit ulit you tend to ignore a while

phasic receptors

rapidly adapting also called

Rapidly adapting or phasic receptors

DURATION: PROPERTIES OF SENSORY CODING: Respond to the onset of the stimulus, Kapag kakarating lang ng stimulus that's when you notice it

tonic receptors

slowly adapting also called

Slowly adapting or tonic receptors

DURATION: PROPERTIES OF SENSORY CODING: Signal the continued presence of the stimulus, You know the stimulus is still there but you are learning to ignore , It doesn't seem as intense as the first stimulus kahit wala naman nagbago

rapidly adapting

when the slowly adapting receptors begin to work yung \___ \___ receptors stop

TRANSMISSION

Sensory Process: Takes place at the synapse, pathway where the signal goes through; Energy goes to different pathways, depending on the different system, but generally follow the general sensory pathway

Stimulus -\> Receptor -\> First-order Neuron -\> Spina Cord/Brainstem -\> Second-order Neuron -\> Thalamus -\> Third-order Neuron -\> Cortex

General Sensory Pathway

Olfactory Pathway

Exception of General Sensory Pathway

PNS, CNS

General Sensory Pathway: from the receptor to the first order neuron \= \___, from the spinal cord to the cortex \= __

Divergence

TRANSMISSION: One first-order neuron may synapse into several higher-order neurons

Convergence

TRANSMISSION: High-order neurons may receive input from more than one first-order neurons

Specific

TRANSMISSION: Pathways that carry only one stimulus modality, Only a specific type of input will be accepted

Nonspecific

TRANSMISSION: Pathways that carry more than one stimulus modality (polymodal), Any kind of input will be accepted, A lot of different input na natanggap

Descending pathways

TRANSMISSION: INFLUENCE OF DESCENDING PATHWAYS: \___ \___ may inhibit transmission of sensory information

Afferent, Descending

Excitatory \= \___; Inhibitory \= \___ (trying to inhibit)

THALAMUS

Located in the middle of the brain, large mass of gray matter that forms major part of diencephalon; Relay structure in processing sensory (and motor) information

olfactory system

THALAMUS: All sensory pathways except \___ \___ relay sensory information to the thalamus before it reaches the cortex

Thalamic Nuclei

\___ \___ can process information from cerebellum, limbic system, basal ganglia, and structures that process information