[ANAPHY LAB] Sensation and Perception

Sensation

- The process in which our sensory receptors and nervous system receive stimuli from the environment that is then converted into neural signals

- RAW DATA of experience

- Any concrete, conscious experience resulting from the stimulation of a specific sense organ, sensory nerve, or sensory area in the brain

Requirements of Sensation

Conscious experience

Stimulation

Sensory system

Can sensation occur without any conscious experience

- Subliminal perception

- Blindsight

- Priming effects

- Automatic sensory perception

- Habituation and sensory adaptation

Sensory processes

Are more about physiological mechanisms (like receptor activation); PASSIVE process

Perception vs Sensation

High cognitive functions and is influenced by experience, context, and expectation; ACTIVE process that builds meaning from the sensory input

Perception

Interpretation of information from the environment so that we can identify its meaning

Pathway of Stimuli

1. Receptors of the skin (Peripheral Nervous System)

2. Primary Sensory Neuron (First-order Neuron)

Mechanoreceptors, Nociceptors, Thermoreceptors, Proprioceptors

Specialized receptors in the skin that detect sensory stimuli

Mechanoreceptors

Touch and Pressure (ex. Meissner's and Pacinian corpuscles)

Nociceptors

Pain

Thermoreceptors

Temperature

Proprioceptors

Muscle and Joint position

Primary Sensory Neuron

- a.k.a First-order Neuron

- The sensory receptor sends signals along afferent fibers through the dorsal root ganglia (DRG) of the spinal nerves

- Synapses in the spinal cord or brainstem, depending on the pathway

Pathway Splits

1. Dorsal Column-Medial Lemniscal (DCML) Pathway

2. Spinothalamic Tract (Anterolateral System)

Dorsal Column-Medial Lemniscal (DCML) Pathway

For fine touch, vibration, and proprioception

Dorsal Column-Medial Lemniscal (DCML) Pathway

1. First-order neurons ascend ipsilaterally in the dorsal column of the spinal cord

2. Synapse occurs in medulla oblongata (gracile or cuneata nuclei)

3. Second-order neurons cross (decussate) and ascend via the medial lemniscus to the thalamus (ventral posterior nucleus)

4. Third-order neurons project to the primary somatosensory cortex (postcentral gyrus) in the parietal lobe

Spinothalamic Tract (Anterolateral System)

For pain, temperature, and crude touch

Spinothalamic Tract (Anterolateral System)

1. First-order neurons synapse immediately in the dorsal horn of the spinal cord

2. Second-order neurons cross to the contralateral side and ascend via the spinothalamic tract to the thalamus (ventral posterior nucleus)

3. Third-order neurons project to the primary somatosensory cortex

Thalamus

A critical relay station for sensory information

Primary Somatosensory Cortex (S1)

Located in the postcentral gyrus; responsible for processing sensory information

Pathway of Auditory Stimuli

Sound wave collection (Outer Ear) -> Vibration Conversion (Middle ear) -> Mechanical to Neural Transduction (Inner Ear) -> Neural Transmission (Auditory Nerve) -> Central Processing (Brainstem to Cortex) -> Perception (Auditory Cortex)

Pinna (Auricle)

Captures sound waves from the environment and directs them into the ear canal

External Auditory Canal

Transmit sound waves toward the tympanic membrane (eardrum)

Tympanic Membrane (Eardrum)

Vibrates in response to sound waves

Ossicles

- Malleus, Incus, Stapes

- Amplify and transmit vibration to the oval window of the cochlea

Stapes

Creates fluid waves in the cochlea by vibrating against the oval window

Cochlea

A spiral-shaped, fluid-filled structure that converts mechanical vibrations into neural signals

Basilar Membrane

Vibrates in response to sound frequencies, causing hair cells in the organ of Corti to deflect

Hair cells (mechanoreceptors)

- The movement of hair cells opens ion channels, leading to depolarization

- This generates action potentials in the auditory nerve fibers

Cochlear Nerve

Part of cranial nerve VIII—vestibulocochlear

- Transmits neural signals from the cochlea to the brainstem

Cochlear Nucleus (Medulla)

Initial processing center for auditory information

Superior Olivary Complex (Pons)

Processes sound localization cues

Lateral Lemniscus

Transmits signals to the midbrain

Inferior Colliculus (Midbrain)

Integrates auditory information

Medial Geniculate Body (Thalamus)

Relays signals to the auditory cortex

Primary Auditory Cortex (Temporal Lobe)

Processes frequency, intensity, and timing of sound signals

Association Areas

Further interpret complex auditory stimuli, such as speech and music

Auditory Cortex

The part of the brain responsible for processing and perceiving sound, and identifying it afterward, involves multiple regions

Primary Auditory Cortex (A1)

- Location: Superior temporal gyrus of the temporal lobe (within the lateral sulcus)

- Processes the basic features of sound such as pitch, volume, and rhythm

- Organized tonotopically, meaning different regions correspond to specific sound frequencies

Secondary Auditory Cortex (A2)

- Location: Adjacent to the A1 in the superior temporal gyrus.

- Processes more complex auditory patterns such as speech and music

- Important for the perception of the temporal structure of sound

Wernicke's Area

Location: Posterior section of the superior temporal gyrus (Left hemisphere in most people)

- Comprehension of spoken language

- Damage can cause Wernicke's Aphasia where language comprehension is impaired

Broca's Area

- Location: Inferior Frontal Gyrus

- Involved in speech production and language processing when identifying or forming responses to auditory stimuli

Amygdala

Processes the emotional content of sounds, such as detecting urgency in tone or scream

Parietal Cortex (Auditory Attention)

Helps in spatial localization and integration of sound within other sensory inputs