chapter 15 a&p

Tactile corpuscles

Also called Meissner's corpuscles Perceive sensations of fine touch, pressure, and low-frequency vibration Adapt to stimulation within 1 second after contact Fairly large structures Most abundant in the eyelids, lips, fingertips, nipples, and external genitalia

Tactile discs

Also called Merkel discs Fine touch and pressure receptors Extremely sensitive to tonic receptors Have very small receptive fields

Lamellated corpuscles

Also called Pacinian corpuscles Sensitive to deep pressure Fast-adapting receptors Most sensitive to pulsing or high-frequency vibrating stimuli

The Somatic Nervous System (SNS)

Also called the somatic motor system Controls contractions of skeletal muscles (discussed next)

The Autonomic Nervous System (ANS)

Also called the visceral motor system Controls visceral effectors, such as smooth muscle, cardiac muscle, and glands

Ruffini corpuscles

Also sensitive to pressure and distortion of the skin Located in the reticular (deep) dermis Tonic receptors that show little if any adaptation

Tonic receptors

Are always active Show little peripheral adaptation Are slow-adapting receptors Remind you of an injury long after the initial damage has occurred

General Sensory Receptors

Are divided into four types by the nature of the stimulus that excites them

Fine touch and pressure receptors are..

Are extremely sensitive Have a relatively narrow receptive field Provide detailed information about a source of stimulation

Special Sensory Receptors

Are located in sense organs such as the eye or ear Are protected by surrounding tissues

The Special Senses

Are provided by special sensory receptors

Receptive field

Area is monitored by a single receptor cell The larger the receptive field, the more difficult it is to localize a stimulus

Posterior Column Pathway

Carries sensations of highly localized ("fine") touch, pressure, vibration, and proprioception

Nociceptors (type C fibers)

Carry sensations of slow pain, or burning and aching pain Cause a generalized activation of the reticular formation and thalamus You become aware of the pain but only have a general idea of the area affected

Somatic Sensory Pathways

Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs

Perception

Conscious awareness of a sensation

Control skeletal muscles by traveling over three integrated motor pathways

Corticospinal pathway Medial pathway Lateral pathway

Baroreceptors

Detect pressure changes in the walls of blood vessels and in portions of the digestive, reproductive, and urinary tracts

Receptor specificity

Each receptor has a characteristic sensitivity

Six Types of Tactile Receptors in the Skin

Free nerve endings, Root hair plexus nerve endings, Tactile discs, Tactile corpuscles, Lamellated corpuscles, Ruffini corpuscles

Crude touch and pressure receptors are...

Have relatively large receptive fields Provide poor localization Give little information about the stimulus

A small fraction of the arriving sensory information is

Is projected to the cerebral cortex and reaches our awareness

Spinal tracts involved with posterior column pathway

Left and right fasciculus gracilis Left and right fasciculus cuneatus

Root hair plexus

Monitor distortions and movements across the body surface wherever hairs are located Adapt rapidly, so are best at detecting initial contact and subsequent movements

Proprioceptors

Monitor the positions of joints and muscles The most structurally and functionally complex of general sensory receptors

Nociceptors (Myelinated Type A fibers)

Myelinated Type A fibers Carry sensations of fast pain, or prickling pain, such as that caused by an injection or a deep cut Sensations reach the CNS quickly and often trigger somatic reflexes Relayed to the primary sensory cortex and receive conscious attention

the four types of general sensory receptors are..

Nociceptors (pain) Thermoreceptors (temperature) Mechanoreceptors (physical distortion) Chemoreceptors (chemical concentration)

Special Senses

Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing

what sensations indicate degree of mechanical distortion?

Pressure

The Medial Pathway

Primarily concerned with control of muscle tone and gross movements of neck, trunk, and proximal limb muscles

The Lateral Pathway

Primarily concerned with control of muscle tone and more precise movements of distal parts of limbs Axons of upper motor neurons in red nuclei cross to opposite side of brain and descend into spinal cord in rubrospinal tracts

The Cerebellum monitors

Proprioceptive (position) sensations Visual information from the eyes Vestibular (balance) sensations from inner ear as movements are under way

Corticobulbar Tracts

Provide conscious control over skeletal muscles that move the eye, jaw, face, and some muscles of neck and pharynx Innervate motor centers of medial and lateral pathways

Tactile receptors

Provide the sensations of touch, pressure, and vibration

The Spinothalamic Pathway

Provides conscious sensations of poorly localized ("crude") touch, pressure, pain, and temperature

Free nerve endings

Sensitive to touch and pressure Situated between epidermal cells Free nerve endings providing touch sensations are tonic receptors with small receptive fields

Cerebellum receives proprioceptive information about position of:

Skeletal muscles, Tendons, Joints

Three Classes of Mechanoreceptors

Tactile receptors, Baroreceptors, Proprioceptors

General Senses

Temperature, Pain, Touch, Pressure, Vibration, and Proprioception

Sensation

The arriving information from these senses

Referred pain

The pain of a heart attack is frequently felt in the left arm The pain of appendicitis is generally felt first in the area around the navel and then in the right, lower quadrant

Three major somatic sensory pathways

The spinothalamic pathway The posterior column pathway The spinocerebellar pathway

what sensations provide information about shape or texture?

Touch

Upper motor neurons of medial pathway are located in:

Vestibular nuclei Superior and inferior colliculi Reticular formation

what sensations indicate pulsing or oscillating pressure?

Vibration

The Basal Nuclei and Cerebellum are responsible for?

coordination and feedback control over muscle contractions Whether contractions are consciously or subconsciously directed

Interoceptors

monitor visceral organs and functions

Exteroceptors

provide information about the external environment

Proprioceptors

report the positions of skeletal muscles and joints

Most somatic sensory information is relayed where?

to the thalamus for processing