CH16: Sensory, Motor, and Integrative Systems Flashcards
What is the difference between perception and sensation?
Sensation is the conscious or subconscious awareness to changes in the external or internal environment. Perception is the conscious interpretation of these sensations. Perception generally arises when information reaches the cerebral cortex
What is a sensory modality and what types are there?
A sensory modality is any unique type of sensation, and they are divided into two classes
General senses refer to somatic and visceral senses. The first includes tactile sensations, while the latter provide information about conditions within internal organs, for example, pressure, stretch, chemicals, nausea, hunger, and temperature.
Special senses involve the sensory modalities of taste, hearing, smell, vision and equilibrium
Describe the process of sensation
Stimulation of the sensory receptor: An appropriate stimulus must occur within the sensory receptor’s receptive field, the body region where stimulation activates the receptor and produces a response
Transduction of the stimulus: A sensory receptor converts the energy in the stimulus into a graded potential in a process called transduction. Recall a graded potential is a small deviation from the membrane potential that varies in amplitude and makes the membrane either more polarized (inside more negative) or less polarized (inside less negative). When the response makes the membrane more polarized, it is a hyperpolarizing graded potential, and when the response makes the membrane less polarized, it is termed a depolarizing graded potential. Each type of sensory receptor exhibits selectivity, meaning it can only transduce (convert) one kind of stimulus.
For example, odorant molecules in the air stimulate olfactory (smell) sensory neurons in the nose, which transduce the molecules’ chemical energy into electrical energy in the form of a graded potential.
Generation of nerve impulses: When a graded potential in a sensory neuron reaches threshold, it triggers one or more nerve impulses, which then propagate toward the CNS. Sensory neurons that conduct nerve impulses from the PNS into the CNS are called first-order neurons.
Integration of sensory input: A particular region of the of the CNS receives and integrates (processes) the sensory nerve impulses. Conscious sensations or perceptions are integrated in the cerebral cortex. You seem to see with your eyes, what with your ears, and feel pain in an injured part of your body because sensory impulses from each part of the body arrive in a specific region of the cerebral cortex, which interprets the sensation as coming from the stimulated sensory receptors
Upon which characteristics can sensory receptor be classified?
(1) microscopic structure, (2) location of the receptors and the origin of stimuli that activate them, and (3) type of stimulus detected
What are the different groups of neurons when classified under a microscopic level:
On a microscopic level, sensory receptors may be one of the following; free nerve endings of first-order neurons, encapsulated nerve endings of first order neurons, or separate cells that synapse with first-order sensory neurons.
Free nerve endings are bare, dendrites (not encapsulated), the lack any structural specializations that can be seen under a light microscope
They receptors for pain, temperature, tickle, itch, and some touch sensations
Encapsulated nerve endings are receptors for other somatic and visceral sensations. Their dendrites are enclosed in a connective tissue capsule that has a distinctive microscopic structure, like lamella corpuscles. The different types of capsules enhance the sensitivity or specificity of the receptor
Separate cells are specialized cells that synapse with sensory neurons. These include hair cells for hearing and equilibrium in the inner ear, gustatory receptors in tase buds and photoreceptors in the retina of the eye for vision.
What are the classifications of receptors based on their locations and origin of stimuli?
Another way to group sensory receptors is based on the location of the receptors and the origin of the stimuli that activate them
Exteroceptors are located at or near the external surface of the body. They are sensitive to stimuli originating outside the body and provide information about the external environment, such as vision, smell, tase, touch, pressure, vibration, temperature and pain
Interoceptors or visceroceptors are located in blood vessels, visceral organs, muscles and the nervous system. They monitor conditions in the internal environment, and their impulses are not normally consciously perceived, though activation of interoceptors by strong stimuli may be felt as pain or pressure. ANS receives input from primarily interoceptors!
Proprioceptors are located in muscles, tendons and joints, and provide information about equilibrium, body position, muscle length and tension, and the position and movement of your joints
What are the different modalities of somatic sensation. Now that I mention it, wtf is somatic sensation?
Somatic sensations are general sensations that arise form stimulation of sensory receptors embedded in the skin or subcutaneous tissue; mucous membranes of the mouth, vagina and anus; and in skeletal muscles, tendons and joints
There are four modalities of somatic sensation: tactile, pain, thermal, and proprioceptive
What types of touch receptors do we have, and where are they located and describe the nerve build
There are two types of rapidly adapting touch receptors.
Tactile corpuscles, or Meissner corpuscles are touch receptors located primarily in hairless skin.
Each corpuscle is an egg-shaped mass of modified Schwann cells and nerve endings enclosed by a capsule of connective tissue. Because tactile corpuscles are rapidly adapting receptors, they generate nerve impulses mainly at the onset of a touch. They are abundant in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles
Hair root plexuses are rapidly adapting touch receptors in hair skin, which consist of free nerve endings wrapped round hair follicles. They detect movements on the skin surface that disturb chairs
There are also two types of slow adapting touch receptors.
Non Encapsulated sensory corpuscles (Merkel discs) are saucer-shaped, flattened free nerve endings that make contact with tactile epithelial cells (Merkcel cells) of the stratum basale.
They are plentiful in the fingertips, hands, lips, and external genitals.
These receptors respond to continuous touch, such as holding an object in your hand for an extended period of time
Bulbous corpuscles are elongated, encapsulated receptors located in the dermis, subcutaneous tissue and other tissues of the body. They are highly sensitive to stretching, such as when a massage therapist stretches your skin during a massage
What types of pressure receptors do we have and briefly describe how they detect
Pressure, a sustained sensation that is felt over a longer area than touch, occurs with deeper deformation of the skin and subcutaneous tissue. The receptors that contribute to sensations of pressure are lamellar and bulbous corpuscles. These receptors are able to respond to a steady pressure stimulus because they are slow adapting
What types of pressure receptors do we have and briefly describe how they detect vibration
Sensations of vibration result from rapidly repetitive sensory signals from tactile receptors. More specifically, lamellar corpuscles and tactical corpuscles
A lamellar corpuscle, or Pacinian corpuscle, consists of a nerve endings surrounded by a multilayered connective tissue capsule that resembles a sliced onion. Like tactile corpuscles, lamellar corpuscles adapt rapidly. They are found in the dermis, subcutaneous tissue, and other body tissues.
How do we detect itch and tickle
Itch
The itch sensation results form stimulation of free nerve endings by certain chemicals, such as bradykinin (a kinin, a potent vasodilator), histamine, or antigens in mosquito saliva injected from a bite, often because of a local inflammatory response
Scratching usually alleviates itching by activating a pathway that blocks transmission of the itch signal through the spinal cord.
Tickle
Free nerve endings are thought to mediate the tickle sensation. This intriguing sensation typically arises only when someone else touches you, not when you touch yourself. The solution to this puzzle seems to lie in the nerve impulses that conduct to and from the cerebellum when you are moving your fingers and touching yourself that don’t occur when someone else is tickling you.
What receptors exist for pain and how to they detect?
Nociceptors, the receptors for pain, are free nerve endings found in every tissue of the body except the brain. Intense thermal, mechanical or chemical stimuli can activate nociceptors.
Tissue irritation or injury releases chemicals such as prostaglandins, kinins, and potassium ions (K+) that stimulate nociceptors
Pain may persist even after a pain-producing stimulus is removed because pain-mediating chemicals linger, and because nociceptors exhibit very little adaptation
What are the types of neurons involved in a somatosensory pathway?
A somatic sensory pathway consists of thousands of three sets of three neurons: A first order neuron, a second-order neuron and a third-order neuron. Integration of information occurs at each synapse along the pathway
First order (primary) neurons are sensory neurons that conduct nerve impulses from somatic sensory receptors into the brain stem or spinal cord. All other neurons in a somatic sensory pathway are interneurons, which are located completely within the central nervous system (CNS)
Second order (secondary) neurons conduct nerve impulses from the brainstem or spinal cord to the thalamus. Axons of secondary neurons decussate (cross over to the opposite side) as they course through the brainstem before ascending to the thalamus
Third-order (tertiary) neurons conduct impulses from the thalamus to the primary somatosensory cortex on the same side. As the impulses reach the primary somatosensory cortex, perception of the sensation occurs. Because the axons of second-order neurons decussate as they pass through the brainstem or spinal cord, somatic sensory information on one side of the body is perceived by the primary somatosensory cortex on the opposite side of the brain
What are the three somatic sensory pathways
Somatic sensory impulses ascend to the cerebral cortex via three general pathways: the posterior column-medial lemniscus pathway, the anterolateral (spinothalamic) pathway and the trigeminothalamic pathway
Describe the posterior column- medial lemniscus pathway
The posterior column medial-lemniscus pathway conveys nerve impulses for touch, pressure, vibration and proprioception to the cerebral cortex.
This pathway begins with first order neurons that extend from peripheral sensory receptors receptors into the spinal cord.
After entering the spinal cord, the axons of these first order ascend to the medulla via tracts known as the posterior columns. Once the axons of the first-order neurons are in the medulla, they synapse with second-order neurons
Axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus (lem-NIS-kus = ribbon), a thin ribbonlike projection tract that extends from the medulla to the thalamus
In the thalamus, the axon terminals of second-order neurons synapse with third-order neurons. Axons of the third-order neurons in turn project to the primary somatosensory cortex of the cerebrum.
