Puzzle Piece 12: General and Special Senses

General senses

involve sensing temperature, pain, touch, pressure, and vibration.

Includes somatic and visceral senses (internal organs)

Special senses

unique to the head and include smell (olfaction), taste (gustation), balance (equilibrium), hearing (audition), and vision.

Stimuli

packets of information detected by receptors throughout the body.

Receptor specificity

Each sensory receptor is specialized in detecting one particular type of stimulus

(may also respond to other stimuli)

Sensory receptors

Are the interface between the nervous system and the environment.

- work as transducers, converting stimuli into action potentials.

- Action potentials propagate sensory information to the brain for processing and interpretation.

Sensation

Refers to the detection of stimuli by sensory receptors. Hence, it is the sensory information generated by any stimulus.

Perception

involves the interpretation of sensory information in the brain, resulting in conscious awareness.

- Conscious sensation of different stimuli occurs in the cortical areas of the brain (somatosensory cortex, visual cortex, olfactory cortex,...)

Receptive Field

area of reception a single sensory neuron detects stimuli.

- size affects the precision of where the stimulus happened.

- larger = larger the area you can "touch" for the sensory neuron to detect it, we feel that we were touched but cannot pinpoint where.

- smaller = can pinpoint where we were touched.

Tonic receptors

have a constant response to stimuli and do not adapt, the frequency of action potentials does not decrease over time. ex photoreceptors and pain receptors (nociceptors).

* Pain does not go away until we address the underlying issue causing it

Phasic receptors

adapt to the stimulus over time, become less sensitive, frequency of action potentials decreases over time, leads to ignoring stimuli over time. ex touch receptors, olfactory receptors.
* We become accustomed to the sensation of our clothes (touch) and the smell of the perfume we are wearing (olfactory).

General Senses

include all sensations from inside and outside the body that are not special senses, such as touch, pressure, pain, temperature, and the level of oxygen in the blood.

Classification of Sensory Receptors

Receptors can be classified based on the origin of the stimulus they detect (where the stimulus comes from and based on the type of stimulus they respond to.

Exteroceptors

Detect stimuli from the exterior of the body. ex temperature, touch, pressure in the skin. *Since receptors for the special senses of smell, taste, hearing and vision detect stimuli from the exterior of the body, they are exteroceptors

Interoceptors

Detect stimuli from inside the body (internal organs). ex pressure within internal organs, oxygen levels in the blood.

* we are not aware of what interoceptors are detecting

Proprioceptors

Respond to stimuli related to understanding the position of our body in space. ex they detect stretch within joints and tendons.

Mechanoreceptors

Detect deformations such as pressure within blood vessels as well as pressure of someone holding our hands. type: tactile receptors, baroreceptors, proprioceptors

Thermoreceptors

Detect changes in temperature

- free nerve endings, located in the superficial dermis, phasic receptors

Chemoreceptors

Detect the chemical environment inside the body. ex level of oxygen in the blood, concentration of glucose in the blood

- near respiratory centers of the medulla oblongata and in specific locations in carotid arteries and aortic arch, Provide information on oxygen and carbon dioxide levels, influencing breathing rate.

Nociceptors

Detect tissue damage and harmful stimuli, causing pain

Tactile receptors

detect mechanical deformations associated with touch, pressure, and vibration in the skin. can be unencapsulated or encapsulated.

Unencapsulated tactile receptors

Nerve endings not wrapped in connective tissue. Types include: Free nerve endings, Tactile discs (Merkel's discs), Root hair plexus.

Encapsulated tactile receptors

Nerve endings wrapped in connective tissue or glial cells.

Types include: Tactile corpuscle (Meissner's corpuscle), Bulbous corpuscle, Lamellar corpuscles (Pacini's Corpuscles).

Free Nerve Ending

Unencapsulated tactile receptors found throughout the skin, Located in papillary layer of dermis and extend into the epidermis. Detect light contact, temperature, and pain.

Root Hair Plexus

Unencapsulated tactile receptors, Located in the dermis and associated with hair follicles.

Sense movement of hairs on the body surface, a mosquito lands on the skin.

Tactile Discs (Merkel's discs)

Unencapsulated tactile receptors, Found associated in the stratum basale of the epidermis. Activated by light touch, tactile discs release neurotransmitters activating sensory neuron.

Tactile Corpuscles (Meissner's Corpuscle)

Encapsulated tactile receptors, Located in the papillary layer of the dermis, concentrated in fingertips, lips, nipples, and genitals. Involved in discriminating touch, textures, and sensing low-frequency vibrations.

Bulbous Corpuscles

Encapsulated tactile receptors, Located deep in the dermis and respond to deep and continuous pressure.

Lamellar Corpuscles (Pacini's Corpuscles)

Encapsulated tactile receptors, Located deep in the dermis, sensitive to deep pressure and high-frequency vibrations.

Baroreceptors

detect deformations associated with changing pressure. Found throughout the body, such as the digestive tract, lungs, urinary bladder, carotid sinus, and aortic sinus.

Proprioceptors

detect deformations that enable us to sense the body position in space (limb awareness)

- provide information about body position and movement

- Muscle Spindles, Golgi Tendon Organs, Joint Receptors

Muscle Spindles

Detect changes in muscle length.

Golgi Tendon Organs

Detect tension in the tendon caused by the contraction of the muscle.

Joint Receptors

Detect changes in joints as the body moves.

Nociceptors

Detect tissue damage and cause pain sensation.

- free nerve endings, Located everywhere in the body, tonic receptors, large receptive fields

Pain Sensation

Nociceptors are activated by extreme temperatures, mechanical or chemical damage, or chemicals released from damaged tissue.

Referred Pain

occurs when pain is felt in a different part of the body from its origin, nerve fibers from one body part sharing the same pathway to the brain as another organ.

ex. Pain radiating down the left arm during a heart attack.

Gustation (Sense of Taste)

sweet (sugars), salty(salts), sour(acid), bitter(complex molecules), and umami (glutamate amino acid / "meaty" taste) - Each modality is associated with specific chemoreceptors

gustatory cells

Specialized epithelial cells that have evolved to behave a little like neurons for gustation. Each cell has hairs (microvilli) with chemoreceptors that detect chemicals.

Gustatory cell stimulation

When stimulated, they depolarize opening voltage-gated calcium channels.

Calcium influx triggers vesicles filled with neurotransmitters to fuse with the membrane and release into the synaptic cleft. 

Neurotransmitter then bind the dendrite of the special sensory neuron (cranial nerves VII - facial, IX - glossopharyngeal, X - vagus) that will take the information towards the CNS.

Tongue

papillae: visible bumps on dorsal surface of the tongue.

papilla grooves: tunnels lined with taste buds

taste bud: made up of a taste pore, gustatory cells, supporting cells, and basal cells.

Taste pore: small opening allowing hairs of gustatory cells in taste bud to come into contact with chemicals in saliva.

Supporting cells: support by clearing excess neurotransmitters released by gustatory cells.

Basal cells: act as stem cells to replace gustatory cells and supporting cells.

*Gustatory cells are replaced approximately every 2 weeks.

*As we age, both the replacement activity and the number of taste buds decline, resulting in a decrease in taste sensation.

Taste pore

faces the papilla tunnel, through this opening chemoreceptors in hairs of gustatory cells detect the chemicals dissolved in saliva.