Ch 16- Sensory, Motor, & Integrative System

How do we structurally and functionally classify sensory receptors:

(1) microscopic structure, (2) location of the receptors and the origin of stimuli that activate them, and (3) type of stimulus detected.

Joint kinesthetic receptors: several types: 3

1) Free nerve endings and type II cutaneous mechanoreceptors in the capsules of joints respond to pressure; 2) small lamellated corpuscles in the connective tissue outside articular capsules respond to acceleration and deceleration of joints during movement. 3) Joint ligaments contain receptors similar to tendon organs that adjust reflex inhibition of the adjacent muscles when excessive strain is placed on the joint.

Only LMNs provide output from the _______. For this reason, they are also called the final common pathway.

CNS to skeletal muscle fibers

What causes tickling?

Free nerve endings are thought to mediate the tickle sensation. This intriguing sensation typically arises only when someone else touches you.

Local motor neurons input comes from where?

Input arrives at lower motor neurons from nearby interneurons called local circuit neurons.

Local circuit neurons receive input from:

Local circuit neurons receive input from somatic sensory receptors, such as nociceptors and muscle spindles, as well as from higher centers in the brain.

Main function of muscle spindle:

Main function is to measure muscle length. Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around 3 to 10 specialized muscle fibers, called intrafusal fibers

Most upper motor neurons synapse with

Most upper motor neurons synapse with local circuit neurons, which in turn synapse with lower motor neurons. (A few upper motor neurons synapse directly with lower motor neurons.)

trigeminothalamic pathway

Nerve impulses for most somatic sensations (tactile, thermal, and pain) from the face, nasal cavity, oral cavity, and teeth ascend to the cerebral cortex along the trigeminothalamic pathway

the anterolateral (spinothalamic) pathway:

Nerve impulses for pain, temperature, itch, and tickle from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex along the anterolateral (spinothalamic) pathway

the posterior column-medial lemniscus pathway:

Nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head ascend to the cerebral cortex along the posterior column-medial lemniscus pathway.

Relay stations:

Regions within the CNS where neurons synapse with other neurons that are a part of a particular sensory or motor pathway

What mediates sensations of touch, pressure, and vibration:

Several types of encapsulated mechanoreceptors attached to large-diameter myelinated A fibers

Encapsulated dendrites have dendrites that are____, and are receptors for ____.

Their dendrites are enclosed in a connective tissue capsule that has a distinctive microscopic structure— for example, lamellated corpuscles. The different types of capsules enhance the sensitivity or specificity of the receptor. Receptors for other somatic and visceral sensations, such as pressure, vibration, and some touch sensations, are encapsulated nerve endings.

Gamma motor neurons terminate near what and function to...:

These motor neurons terminate near both ends of the intrafusal fibers and adjust the tension in a muscle spindle to variations in the length of the muscle. For example, when your biceps muscle shortens in response to lifting a weight, gamma motor neurons stimulate the ends of the intrafusal fibers to contract slightly. This keeps the intrafusal fibers taut even though the contractile muscle fibers surrounding the spindle are reducing spindle tension. This maintains the sensitivity of the muscle spindle to stretching of the muscle.

Local circuit neurons are located where?

These neurons are located close to the lower motor neuron cell bodies in the brainstem and spinal cord.

Two types of slow adapting touch receptors:

Type I cutaneous mechanoreceptor and Type II cutaneous mechanoreceptor

Sensory modality:

When a given sensory neuron carries information for only one sensory modality.

What happens during a generator potential:

When stimulated, the dendrites of free nerve endings, encapsulated nerve endings, and the receptive part of olfactory receptors produce a generator potential. When a generator potential is large enough to reach threshold, it triggers one or more nerve impulses in the axon of a first-order sensory neuron. The resulting nerve impulse propagates along the axon into the CNS. Thus, generator potentials generate action potentials.

The pathways to the cerebral cortex consist of thousands of sets of three neurons:

a first- order neuron, a second-order neuron, and a third-order neuron.

Pressure:

a sustained sensation that is felt over a larger area than touch, occurs with deformation of deeper tissues.

Generator potentials generate...

action potentials

A characteristic of most sensory receptors is ______, in which the generator potential or receptor potential decreases in amplitude during a maintained, constant stimulus.

adaptation

Proprioceptive sensations:

allow perception of both the static (nonmoving) positions of limbs and body parts (joint and muscle position sense) and movements of the limbs and head.

Proprioceptive sensations allow us to

allow us to recognize that parts of our body belong to us (self).

Type I cutaneous mechanoreceptor are:

also called tactile discs, are saucer-shaped, flattened free nerve endings that make contact with tactile epithelial cells (Merkel cells) of the stratum basale. These touch receptors are plentiful in the fingertips, hands, lips, and external genitalia.

Free nerve endings are ____, and receptors for ___:

are bare dendrites; they lack any structural specializations that can be seen under a light microscope. Receptors for pain, temperature, tickle, itch, and some touch sensations are free nerve endings.

Nociceptors are

are free nerve endings found in every tissue of the body except the brain. Intense thermal, mechanical, or chemical stimuli can activate nociceptors

Exteroceptors location and detect what:

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. The sensations of hearing, vision, smell, taste, touch, pressure, vibration, temperature, and pain are conveyed by exteroceptors.

Interoceptors location and detect

are located in blood vessels, visceral organs, muscles, and the nervous system and monitor conditions in the internal environment. The nerve impulses produced by interoceptors usually are not consciously perceived; occasionally, however, activation of interoceptors by strong stimuli may be felt as pain or pressure.

Proreceptors location and detect:

are located in muscles, tendons, joints, and the inner ear. They provide information about body position, muscle length and tension, and the position and movement of your joints.

Cold receptors are located where and detect what temperature?

are located in the stratum basale of the epidermis and are attached to medium-diameter, myelinated A fibers, although a few connect to small-diameter, unmyelinated C fibers. Temperatures between 10 and 40C (50 -105F) activate cold receptors.

Hair root plexus location, and detect what?

are rapidly adapting touch receptors found in hairy skin; they consist of free nerve endings wrapped around hair follicles. Hair root plexuses detect movements on the skin surface that disturb hairs. For example, an insect landing on a hair causes movement of the hair shaft that stimulates the free nerve endings.

Corpuscles of touch location, and generate nerve impulses mainly at ____. Most abundant where?

are touch receptors that are located in the dermal papillae of hairless skin. Because corpuscles of touch 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, clitoris, and tip of the penis.

Slow pain:

begins a second or more after a stimulus is applied. It then gradually increases in intensity over a period of several seconds or minutes. Impulses for slow pain conduct along small- diameter, unmyelinated C fibers. This type of pain, which may be excruciating, is also referred to as chronic, burning, aching, or throbbing pain. Slow pain can occur both in the skin and in deeper tissues or internal organs.

Second-order neurons: conduct impulses from the ____ to the _____.

brainstem and spinal cord to the thalamus. Axons of second-order neurons decussate (cross over to the opposite side) in the brainstem or spinal cord before ascending to the ventral posterior nucleus of the thalamus. Thus, all somatic sensory information from one side of the body reaches the thalamus on the opposite side.

Thermal sensations are detected by two different sensory receptors. They are:

cold receptors and warm receptors

What are the two distinct thermal sensations:

coldness and warmth

Two types of rapidly adapting touch receptors:

corpuscles of touch and hair root plexus

Stimulation of receptors in skeletal muscles, joints, tendons, and fascia causes

deep somatic pain.

Thermoreceptors:

detect change in temperature

Chemoreceptors:

detect chemicals in the mouth (taste), nose (smell), and body fluids

Photoreceptors:

detect the light that strikes the retina of the eye

Osmoreceptors:

detect the osmotic pressure of fluids

What detects sensation for itches and tickles:

detected by free nerve endings attached to small-diameter, unmyelinated C fibers.

Somatic slow pain also is well localized but more...

diffuse (involves large areas); it usually appears to come from a larger area of the skin.

3 classifications of sensory neurons based on location and activating stimuli:

exteroceptors, interoceptors, propriceptors

Two types of pain:

fast and slow pain

What are the 3 microscopic structural characteristics of a sensory neuron:

free nerve endings, encapsulated nerve endings, and separate cells

First-order neuron: conduct impulses from and into what?

from somatic receptors into the brainstem or spinal cord. From the face, mouth, teeth, and eyes, somatic sensory impulses propagate along cranial nerves into the brain stem. From the neck, trunk, limbs, and posterior aspect of the head, somatic sensory impulses propagate along spinal nerves into the spinal cord.

The different sensory modalities can be grouped into two classes:

general senses and special senses

Sensory receptors produce two different kinds of graded potentials—____ and _____—in response to a stimulus:

generator potentials and receptor potentials

Somatic senses: 4

include tactile sensations (touch, pressure, vibration, itch, and tickle), thermal sensations (warm and cold), pain sensations, and proprioceptive sensations.

Special senses include...

include the sensory modalities of smell, taste, vision, hearing, and equilibrium or balance.

Tactile sensations include:

include touch, pressure, vibration, itch, and tickle.

Perception:

is the conscious interpretation of sensations and is primarily a function of the cerebral cortex.

Tendon organs: located at and function to do....

junction of tendon and muscle. By initiating tendon reflexes, tendon organs protect tendons and their associated muscles from damage due to excessive tension

What detects pressure?

lamellated corpuscle

Direct motor pathways provide input to

lower motor neurons via axons that extend directly from the cerebral cortex.

Nerve impulses for voluntary movements propagate from the cerebral cortex to

lower motor neurons via the direct motor pathways.

Types of stimulus detected classification (6):

mechanoreceptor, thermoreceptor, nociceptors, photoreceptors, chemoreceptors, osmoreceptors

Lower motor neurons are motor neurons that:

motor neurons that extend out of the brainstem and spinal cord to innervate skeletal muscles in the body. Have their cell bodies in the brainstem and spinal cord.

UMNs from the brain stem regulate

muscle tone, control postural muscles, and help maintain balance and orientation of the head and body.

Slowly adapting receptors, by contrast, adapt slowly and continue to trigger _______ as long as the stimulus persists. Slowly adapting receptors monitor stimuli associated with ____

nerve impulses; pain, body position, and chemical composition of the blood.

Fast pain:

occurs very rapidly, usually within 0.1 second after a stimulus is applied, because the nerve impulses propagate along medium-diameter, myelinated A fibers. This type of pain is also known as acute, sharp, or pricking pain. The pain felt from a needle puncture or knife cut to the skin is fast pain. Fast pain is not felt in deeper tissues of the body.

Type II cutaneous mechanoreceptor:

or Ruffini corpuscles, are elongated, encapsulated receptors located deep in the dermis, and in ligaments and tendons. Present in the hands and abundant on the soles, they are most sensitive to stretching that occurs as digits or limbs are moved.

Extrafusal muscle fibers are ordinary _____ supplied by ____ fibers called alpha motor neurons. What do they do?

ordinary skeletal muscle fibers supplied by A fibers called alpha motor neurons. During the stretch reflex, impulses in muscle spindle sensory axons propagate into the spinal cord and brain stem and activate alpha motor neurons that connect to extrafusal muscle fibers in the same muscle. In this way, activation of its muscle spindles causes contraction of a skeletal muscle, which relieves the stretching.

Temperatures below 10C and above 48C primarily stimulate:

pain receptors

Primary motor area: located in the

precentral gyrus of the frontal lobe.

Muscle spindles are the

proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in stretch reflexes. .

Visceral sensations:

provide information about conditions within internal organs, for example, pressure, stretch, chemicals, nausea, hunger, and temperature.

However, in many instances of visceral pain, the pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area far from the stimulated organ. This phenomenon is called

referred pain.

Somatic sensory pathways:

relay information from the somatic sensory receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum.

Nociceptors:

respond to painful stimuli resulting from physical or chemical damage to tissue.

What are vibrations and what detects it?

result from rapidly repetitive sensory signals from tactile receptors. The receptors for vibration sensations are corpuscles of touch and lamellated corpuscles. Corpuscles of touch can detect lower-frequency vibrations, and lamellated corpuscles detect higher-frequency vibrations.

Sensory receptors are _____, meaning a sensory receptor responds only weakly or not at all to other stimuli.

selective

The process of sensation begins in a _____, which can be either a specialized cell or the dendrites of a sensory neuron.

sensory receptor

Receptor potentials are...

sensory receptors that are separate cells produce graded potentials termed receptor potentials. Receptor potentials trigger release of neurotransmitter through exocytosis of synaptic vesicles. The neurotransmitter molecules liberated from synaptic vesicles diffuse across the synaptic cleft and produce a postsynaptic potential (PSP) in the first-order neuron. In turn, the PSPs may trigger one or more nerve impulses, which propagate along the axon into the CNS.

Rapidly adapting receptors adapt very quickly. They are specialized for ____, and have receptors specialized for __-

signaling changes in a stimulus. Receptors associated with pressure, touch, and smell are rapidly adapting.

General senses include what type of senses:

somatic and visceral

Cutaneous sensations:

somatic sensations that arise from stimulating the skin surface

itch sensation results from

stimulation of free nerve endings by certain chemicals, such as bradykinin or antigens in mosquito saliva injected from a bite, often because of a local inflammatory response

Visceral pain results from

stimulation of nociceptors in visceral organs. If stimulation is diffuse (involves large areas), visceral pain can be severe. Diffuse stimulation of visceral nociceptors might result from distension or ischemia of an internal organ. For example, a kidney stone or a gallstone might cause severe pain by obstructing and distending a ureter or bile duct.

The amplitude of both generator potentials and receptor potentials varies with the intensity of the _____

stimulus

Pain that arises from stimulation of receptors in the skin is called

superficial somatic pain

Separate cells synapse with ____, and are found ____.

synapse with sensory neurons. These include hair cells for hearing and equilibrium in the inner ear, gustatory receptor cells in taste buds, and photoreceptors in the retina of the eye for vision.

There are four modalities of somatic sensation:

tactile, thermal, pain, and proprioceptive.

Sensation:

the conscious or subconscious awareness of changes in the external or internal environment.

Kinesthesia:

the perception of body movements

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

Somatic sensory pathways to the cerebellum: Two tracts in the spinal cord—_____ and the ____-- are the major routes proprioceptive impulses take to reach the cerebellum.

the posterior spinocerebellar tract and the anterior spinocerebellar tract—

Fast pain is localized in

the stimulated area

Third-order neurons: conduct impulses from

the thalamus to the primary somatosensory area of the cortex on the same side.

Local circuit neuron function:

they help coordinate rhythmic activity in specific muscle groups, such as alternating flexion and extension of the lower limbs during walking.

The areas with the highest density of somatic sensory receptors are the:

tip of the tongue, the lips, and the fingertips.

Mechanoreceptors: are sensitive to...

to mechanical stimuli such as the deformation, stretching, or bending of cells. Mechano- receptors provide sensations of touch, pressure, vibration, proprioception, and hearing and equilibrium. They also monitor the stretching of blood vessels and internal organs

Both local circuit neurons and lower motor neurons receive input from

upper motor neurons (UMNs).

UMNs from the cerebral cortex are essential for the execution of

voluntary movements of the body.

Proprioceptor:

where proprioceptive sensations arise. Those proprioceptors embedded in muscles (especially postural muscles) and tendons inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints. Hair cells of the inner ear monitor the orientation of the head relative to the ground and head position during movements.

Warm receptors are located where and detect what temperature?

which are not as abundant as cold receptors, are located in the dermis and are attached to small-diameter, unmyelinated C fibers; they are activated by temperatures between 32 and 48C (90-118F).