Somatic Sensory System (Neurobiology)

What would the patient experience?

-The primary motor area of the cerebral cortex is the precentral gyrus in the frontal lobe -The neurons in the frontal lobe are quite large; they allow conscious control over voluntary movements of skeletal muscle -These neurons have very long axons and they form massive voluntary motor tracts -Most of these neurons are involved with conscious motor control (skeletal muscle) of the face, the tongue, the hands, as well as posture, reflexes and muscle tone -Motor innovations are contralateral (opposite side) -The left frontal lobe controls muscles on the right side of the body and vice versa

What are proprioceptors, where are they located, what types of modalities do they detect and what are their functions?

-They are located in skeletal muscles, tendons, joints, ligaments, in CT coverings of bones and muscles, in and around joints, and in the internal ear and are stimulated by stretching or movement -They provide information about body position, muscle tension, joint position, and equilibrium -They transmit nerve impulses related to muscle tone, movement of body parts, body sensation, and balance

General somatic senses

-Touch, pressure, vibration, itch, tickle, warmth, cold, and pain -Arise from receptors located in the skin as well as proprioception

What is an action potential?

-A brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels -Action potentials sweep like a wave along axons to transfer information from one place to another in the nervous system

Step 5: Integration of the sensory input

-A region of the CNS must receive and integrate the information that is carried by the action potential and converted to a sensation -Final pathway

Step 2: Transduction (Conversion)

-A sensory receptor or sense organ must receive the stimulus and transduce the stimulus into an electrical response (generator potential) -It will eventually lead to a nerve impulse -Each type of sensory receptor can only transduce one type of stimulus

Ruffini corpuscles

-A single encapsulated myelinated nerve ending with multi-branched or sprayed axonal endings -Large receptor fields, slowly adapting -Represent 20% of mechanoreceptors in the hand -Found in skin, ligaments, and tendons -Important in signaling heavy, continuous touch and pressure -Important in regulating the degree of joint rotation

Separate cells

-A synapse with first order neurons located in sense organs -Hair cells in the ears, rods and cones in the retina, and gustatory receptor cells on the taste buds

What is a graded potential?

-A wave of electrical excitation that corresponds to the size of the stimulus -In ligand/mechanically graded ion channels -Localized and the amplitude depends on the stimulus strength -Used by dendrites for returning signals from sensory organs -Get weaker as they travel along nerve fibers -Last for several milliseconds to several minutes

Step 3: Generator Potential

-An electrical response, when this generated potential reaches threshold (if it's large enough) will then generate an action potential in a sensory neuron -It elicits a nerve impulse that will be generated and conducted along a sensory pathway from the CNS to the PNS -It is not propagated like an action potential

Hair cell receptors

-Auditory receptors -Generate receptor potentials because they convert mechanical energy into electrical energy -There are outer and inner hair cell receptors that make up the cranial nerve and contract upon electrical stimulation

Nociceptors

-Detect damage to the tissues whether physical or chemical -They are naked nerve endings located in the skin -Very high concentration of nociceptors in our bones -They are also located in anterior walls and joint surfaces -Most other deep tissues are not extensively supplied with pain receptors -They are stimulated and produce pain at temperature below 10 degrees C and above 48 degrees C -Adapt very little or not at all because it allows the patient to keep being informed of the damaging stimulus and to seek treatment

Meissner's corpusles

-Encapsulated nerve endings that elicit large myelinated sensory nerve fibers -They have small receptive fields and they rapidly adapt -They are found in the thermos of the skin -Mostly non-hairy parts of the skin (lips, fingertips, palms of hands, and soles of feet) -Provide for 40% of the sensory innovation to your hands -Sensitive to weak stimuli -Myelinated axon terminals that are formed by flattened Schwann cells

upper motor neurons

-Extend from the cerebral cortex (frontal lobe) to the anterior horn of the spinal cord as well as the pons and the medulla

Step 4: Impulse Generation and Conduction

-First order neuron - a sensory neuron that conducts impulses from somatic receptors (periphery) to the spinal cord and the brainstem -Second order neuron - synapses with a first order neuron in the brainstem which will conduct impulses from the spinal cord and the brainstem up to the thalamus -Third order neuron - synapses with a second order neuron in the thalamus. They relay impulses from the thalamus up to the somatosensory cortex (post central gyrus) of the cerebrum where the conscious perception of the sensation is elicited

Merkel's discs

-Flattened portions of dendrites of sensory neurons -They contact the stratum basale -Small receptor fields, slowly adapting -Provide for 25% of all mechanoreceptors -Densely populated in the lips, fingertips, genitalia -Found in association to hair follicles -Detect continuous touch of objects against the skin -Important in determining the texture

Pacinian corpuscles

-Lie in the dermis, hypodermis (subcutaneous layer), and in deep fascial tissues -Only stimulated by very movements of the tissues -Adapt at a few hundredths of a second -Rapid adapting -Represent 15% of the mechanoreceptors of the hand -Important in detecting tissue vibrations -Myelinated afferent axon terminal surrounded by layers of lamell -Contain lymph-like fluid inside

lower motor neurons

-Lower motor neurons extend from the brainstem and spinal cord to skeletal muscles -AKA the final common pathway

Location of third order neurons

-Synapses with second order neurons in thalamus -Relay impulses from the thalamus up to the somatosensory cortex (post-central gyrus) of the cerebrum where the conscious perception of the sensation is elicited

Location of first order neurons

A sensory neurons that conducts impulses from somatic receptors (periphery) to the spinal cord and the brainstem

What is receptor potential?

A stimulus-induced change in the membrane potential of a sensory receptor

What is the somatic nervous system?

Carries impulses to skeletal muscles

How are receptors classified?

Classified microscopically, by location, and by the type of stimulus detected

A highly sensitive tactile receptor composed of dendritic processes of a single myelinated fiber that makes contact with specialized cells of the stratum basale is a a) lamellar corpuscle b) tactile (Meissner) corpuscle c) Bulbous corpuscle d) tactile (Merkel) disc e) root hair plexus

D) tactile (Merkel) disc

Free nerve endings

Found everywhere in the skin and they detect pain (nociception), temperature, itch, tickle, touch, pressure, and strethc

Additional sensory pathways that we discussed

Indirect tracts -Rubrospinal (tracts that originate from the red nucleus and are responsible for motor input of gross postural tone) -Tectospinal (a contralateral tract that is responsible for postural muscle tone associated with auditory and visual stimuli -Vestibulospinal (an ipsilateral tract that is responsible for gross postural adjustments in response to head movements)

What is the somatic sensory system, what are its functions and responsibilities?

Input to the nervous system is provided by sensory receptors that detect such stimuli as touch, sound, light, pain, cold, and warmth These receptors change sensory stimuli into nerve signals and the information conveyed of the brain interact to receive sensory input, integrate and store the information, and transmit motor responses

Step 1: Stimulation of the receptive field of a sensory neuron

Receptive field: an area within which a stimulus of appropriate quality and strength will cause a sensory neuron to initiate a nerve impulse

Location of second order neurons

Synapses with a first order neuron in the brainstem which will conduct impulses from the spinal cord and the brainstem up to the thalamus

What parts of the brain make you aware of and able to remember the taste of coffee for example?

Through our sensory memory

Tactile receptors located in the reticular dermis that are tonic and show little if any adaptation are called a) bulbous corpuscles b) lamellar corpuscles c) tactile (Meissner) corpuscles d) tactile discs e) root hair plexuses

a) bulbous corpuscles

Peripheral adaption _______ the number of action potentials that reach the CNS a) decreases b) increases c) stabilizes d) neutralizes e) amplifies

a) decreases

The general senses a) involved receptors that are relatively simple in structure b) are located in specialized structures called sense organs c) are localized to specific areas of the body d) cannot generate action potentials e) include taste and smell

a) involved receptors that are relatively simple in structure

In order for a sensation to become a perception, a) it must be received by the somatosensory cortex b) the individual must vocalize about it c) it must arrive over fast-conducting nerve fibers d) the other senses must be silent e) it must be received by the pulvinar nucleus of the thalamus

a) it must be received by the somatosensory cortex

Endorphins can reduce perception of sensations initiated by a) nociceptors b) mechanoreceptors c) thermoreceptors d) chemoreceptors e) proprioceptors

a) nociceptors

Sensory neurons that adapt quickly are called ___________ receptors a) phasic b) tonic c) intracellular d) chemical-channel e) opioid

a) phasic

Two types of receptors that are least likely to adapt are the a) proprioceptors and nociceptors b) free nerve endings and the root hair plexus c) tactile discs and the free nerve endings d) lamellar corpuscles and barorecptors e) chemoreceptors and baroreceptors

a) proprioceptors and nociceptors

Gustatory receptors are sensitive to dissolved chemicals but insensitive to light. This is due to a) receptor specificity b) accessory cells c) the fact that they are interoceptors d) receptor potentials e) receptor speciation

a) receptor specificity

A receptor that contains many mechanically-gated ion channels would function best as a a) tactile receptor b) chemoreceptor c) photoceptor d) thermoreceptor e) light receptor

a) tactile receptor

Which of the following statements is true about general senses? a) they are distributed all over the body b) they are all mechanoreceptors c) all receptors involved in general sensation consist of free nerve endings d) they are located in sense organs e) the reception of the stimulus occurs slowly with these receptors

a) they are distributed all over the body

Sensory neurons that are always active are called _________ receptors a) tonic b) static c) phasic d) isometric e) isotonic

a) tonic

The conversion of a sensory input to a change in membrane potential in the receptor is known as a) transduction b) reception c) effection d) potential e) stimulation

a) transduction

Events of perception of a sensation (1) Generator potential (2) Stimulation of the Receptive Field of a sensory neuron (3) Transduction (4) Integration of the sensory input (5) Impulse Generation and Conduction a) 1, 2, 3, 4, 5 b) 2, 3, 1, 5, 4 c) 2, 3, 1, 4, 5 d) 2, 1, 3, 5, 4, e) 2, 1, 3, 4, 5

b) 2, 3, 1, 5, 4

A reduction in sensitivity in the presence of a constant stimulus is referred to as a) transduction b) adaptation c) negation d) exhaustion e) transformation

b) adaptation

Mechanoreceptors that respond to changes in blood pressure are called a) nociceptors b) baroreceptors c) chemoreceptors d) proprioceptors e) thermoreceptors

b) baroreceptors

Bladder fullness is to _______ as blood pH is to _______ a) nociceptors; thermoreceptors b) barorecptors; chemoreceptors c) barorecptors; nociceptors d) chemoreceptors; nociceptors e) barorecptors; thermorecptors

b) barorecptors; chemorecptors

General sense receptors are typically the a) dendrites of motor neurons b) dendrites of sensory neurons c) axons of motor neurons d) axons of sensory neurons e) cell bodies of sensory neurons

b) dendrites of sensory neurons

A very large, fast-adapting tactile receptor that is composed of a single dendrite enclosed by concentric layers of collagen is a a) Bulbous corpuscle b) lamellar (Pacinian) corpuscle c) tactile (Meissner) corpuscle d) tactile (Merkel) disc e) root hair plexus

b) lamellar (Pacinian) corpuscle

Action potentials from receptors involved in general sensations are interpreted in the a) premotor cortex b) primary sensory cortex c) general interpretive area d) mesencephalon e) reticular activating system

b) primary sensory cortex

The term general senses refers to sensitivity to all of the following except a) temperature b) taste c) touch d) vibration e) pain

b) taste

Free nerve endings detect which stimulus/stimuli? a) chemical b) temperature, pain, stretch, and touch c) pain only d) stretch e) deep pressure

b) temperature, pain, stretch and touch

The conversion of the stimulus into an action potential to be interpreted by the brain is called a) transformation b) transduction c) translation d) transcription e) transpotential

b) transduction

The sensory receptors, neurons and pathways make up the _______ division of the nervous system a) voluntary b) efferent c) afferent d) involuntary e) somatic

c) afferent

All of the following are true of fast pain sensations except that they a) are carried by type A fibers b) reach the CNS quickly c) are interpreted by the pre-frontal cortex d) receive conscious attention e) often trigger somatic reflexes

c) are interpreted by the pre-frontal cortex

Chemoreceptors of the general senses do not send information to the primary sensory cortex but instead send information to the _______ to control autonomic function a) cerebellum b) cerebrum c) brain stem d) spinal cord e) corpus callosum

c) brain steam

Sensations of burning or aching pain a) are carried by type A fibers b) reach the CNS quickly c) cause a generalized activation of the reticular formation and the thalamus d) are well localized e) are fast adapting

c) cause a generalized activation of the reticular formation and the thalamus

Central adaptation refers to a) the decline in activity of peripheral receptors when stimulated b) a characteristic of phasic receptors c) inhibition of nuclei located along a sensory pathway d) increases in conscious perception of a sensory stimulus e) a change in motor receptivity of a neuron

c) inhibition of nuclei located along a sensory pathway

You cannot tell when your small intestines shift position as food enters because you do not have any __________ there a) chemorecptors b) nociceptors c) proprioceptors d) thermoreceptors e) photoreceptors

c) propioceptors

A tactile receptor composed of highly coiled dendrites that are surrounded by modified Schwann cells and a fibrous capsule is a a) lamellar corpuscle b) Bulbous corpuscle c) tactile (Meissner) corpuscle d) tactile (Merkel) disc e) root hair plexus

c) tactile (Meissner) corpuscle

Sensory encoding of the perceived location of a stimulus depends on a) the frequency of action potentials b) which labeled line is active c) the specific location of the cortical neuron that is stimulated d) the specific sensitivity of the peripheral receptor e) the number of receptors stimulated

c) the specific location of the cortical neuron that is stimulated

The heart muscle is a _______ effector a) somatic b) sympathetic c) visceral d) afferent e) higher-order

c) visceral

Which of the following is/are sometimes called "prickling pain"? a) mechanical damage b) proprioception c) extremes of temperature d) fast pain e) fast and slow pain

d) fast pain

A ________ potential is a depolarization of a sensory dendrite that can lead to an afferent nerve impulse if strong enough a) resting b) refractory c) postsynaptic d) generator e) presynaptic

d) generator

A sensory receptor characterized peripherally as a free nerve ending which centrally uses glutamate and/or substance P as neurotransmitters would most likely be a a) chemoreceptor b) mechanoreceptor c) thermoreceptor d) nociceptor e) free receptor

d) nociceptor

Your brain is not constantly bombarded with signals telling it that you are wearing socks. This is because the touch receptors are around your ankle are a) tonic receptors b) tonic receptors and slow-adapting c) phasic receptors and slow-adapting d) phasic receptors and fast-adapting e) nociceptors

d) phasic receptors and fast-adapting

Receptors that monitor the position of joints belong to the category called a) nociceptors b) chemoreceptors c) baroreceptors d) proprioceptors e) thermoreceptors

d) proprioceptors

Using the two-point discrimination test you can fairly accurately determine whether you have been touched with one point or two because of the density of the a) effectors b) perception c) labeled line d) receptor fields e) action potential

d) receptor fields

Sensory information from all parts of the body is routed to a) the prefrontal cortex b) the cerebellum c) the primary motor cortex d) the somatosensory cortex e) Broca's area

d) the somatosensory cortex

Receptors in your stomach that determine when food enters because the pH changes would be classified as a) mechanoreceptors b) nociceptors c) proprioceptors d) baroreceptors e) chemoreceptors

e) chemoreceptors

The link between peripheral receptor and cortical neuron is called a(n) a) efferent pathway b) spinocortical line c) sympathetic chain d) adaptation pathway e) labeled line

e) labeled line

Which is an example of a slow-adapting receptor? a) phasic b) touch c) smell d) temperature e) pain

e) pain

A mechanoreceptor in the papillary layer of the dermis that responds to fine touch is a a) tactile (Merkel) disc b) root hair plexus c) free nerve ending d) Bulbous corpuscle e) tactile (Meissner) corpuscle

e) tactile (Meissner) corpuscle

All of the following can contribute to receptor specificity except a) the structure of the receptor cell b) characteristics of the receptor cell membrane c) accessory cells that function with the receptor d) accessory structures and tissues that shield the receptors from other stimuli e) the metabolism of the receptor cell

e) the metabolism of the receptor cell

A receptor potential may cause all of the following responses except a) increase neurotransmitter release b) decrease neurotransmitter release c) cause hyper polarization d) cause depolarization e) turning off the original stimulus

e) turning off the original stimulus