Chapter 16 - Sensory, Motor and Integrative Systems

sensation

The conscious or unconscious awareness of changes in the external or internal environment.

Perception

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

Sensory modality

each type of sensation - touch, pain, vision, etc.

General senses

refer to both somatic senses and visceral senses.

Somatic senses

includes tactile sensations, thermal sensations, pain sensations, and proprioceptive sensations.

Visceral senses

provide info about conditions within internal organs. Pressure, stretch, chemicals, nausea, hunger and temp.

Special senses

include smell, taste, vision, hearing and equilibrium/balance.

Sensory receptor

can be either a specialized cell of the dendrites of a sensory neuron.

Transduction

the conversion of the energy in the stimulus into a graded potential, by sensory receptors.

Free nerve endings

bare dendrites. ex. receptors for pain, temp, tickle, itch.

encapsulated nerve endings

dendrites are enclosed in a connective tissue capsule. ex. receptors for pressure and vibration.

Separate cells

synapse with sensory neurons for special senses. Includes hair cells for hearing and equilibrium, gustatory receptors in taste buds and photoreceptors for vision.

Exteroceptors

located at or near the external surface and provide info about the external environment. (vision, hearing, small, taste, touch, temp)

Interoceptors

located in blood vessels, organs, muscles and the nervous system and monitor conditions in the internal environment.

Proprioceptors

Located in muscles, tendons, joints and the inner ear. Provide info about body position, muscle length, and tension, and movement of your joints.

Mechanoreceptors

respond to mechanical stimuli such as deformation, stretching, or bending of cells. (touch, pressure, vibration, proprioception, stretching of blood vessels and organs, and hearing and equilibrium.

Thermoreceptors

detect changes in temp

Nociceptors

respond to painful stimuli from physical or chemical damage to tissue,

Photoreceptors

detect light hitting the retina.

Chemoreceptors

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

Osmoreceptors

detect osmotic pressure of body fluids.

Adaptation

when the receptor potential decreases in amplitude during a maintained, constant stimulus.

Rapidly adapting receptors

adapt very quickly and are specialized for signalling changes in a stimulus. (receptors for vibration, touch and smell)

Slowly adapting receptors

adapt slowly and continue to trigger nerve impulses as long as the stimulus persists. (receptors for pain, body position, chemical composition of blood)

Somatic sensations

arise from stimulation of sensory receptors in the skin, mucous membranes, skeletal muscles, tendons and joints.

Cutaneous sensations

somatic sensations that arise from the skin surface

Tactile sensations

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

Corpuscles of touch AKA Meissner corpuscles

touch receptors located in the dermal papillae of hairless skin. Rapidly adapting receptors and egg shaped with a connective tissue capsule.

Hair root plexuses

rapidly adapting touch receptors found in hairy skin. Free nerve endings wrapped around hair follicles.

Type I cutaneous mechanoreceptors AKA Tactile (Merkel) discs

flattened free nerve endings that make contact with tactile epithelial cells (Merkel Cells) of the stratum basale. Respond to continuous touch.

Type II cutaneous mechanoreceptors AKA Ruffini corpuscles

encapsulated receptors located in the dermis, subcutaneous layer and other tissues of the body. Highly sensitive to skin stretching.

The receptors that contribute to sensation of pressure

Type I and II mechanoreceptors.

Lamellated corpuscle

a nerve ending surrounded by a multilayered connective tissue capsule. Adapt rapidly and used to detect vibration.

Receptors used to detect vibration

Lamellated corpuscles for high frequency vibrations and corpuscles of touch for low frequency.

Itch

stimulation of free nerve endings due to chemicals, histamine or mosquito antigens.

Cold Receptors

located in the stratum basale of the epidermis and attached to medium-diameter myelinated A fibers. Detects temps between 10-30 Celsius

Warm receptors

located in the dermis and attached to small-diameter unmyelinated C fibers. Detects temps between 30-45 celsius

Temps out of the 10-45 celsius range stimulate…

pain receptors.

Nociceptors

free nerve endings, found in every tissue of the body except the brain.

Fast pain

felt in less than 0.1 seconds and propagates along medium-diameter myelinated A fibers. Superficial pain.

Slow pain

slower and gradually increases. Propagates along small-diameter unmyelinated C fibers. Can be superficial or deep tissue pain.

Referred pain

the perception of pain in a location different from the source. Pained organ and referred pain area are usually served by the same segment of the spinal cord.

Analgesic drugs

Aspirin and ibuprofen - block formation of prostaglandins, which stimulate nociceptors.

Local anesthetics

Novocaine - provide short term pain relief by blocking nerve impulse conduction.

Opiate drugs

Morphine - Alters pain perception. Pain is sensed but it is not felt as noxious.

Kinesthesia

the perception of body movements.

Proprioceptors

present in muscles and tendons.

Weight discrimination

the ability to assess the weight of an object via proprioceptors.

Muscle spindles

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

Muscle spindle structure

several slowly adapting sensory nerve endings that wrap around intrafusal fibers. A connective tissue capsule encloses and anchors the spindle to the endomysium and perimysium.

Gamma motor neurons

motor neurons in muscle spindles. Terminate at each end of the intrafusal fibers and adjust the tension in a muscle spindle to variations in the length of the muscle.

Extrafusal muscle fibers

surround muscle spindles and are supplied by large-diameter A fibers called alpha motor neurons.

The cell bodies of both gamma and alpha motor neurons are located in…

the anterior gray horn of the spinal cord or the brainstem.

Tendon organs

slowly adapting receptors located at the junction of a tendon and a muscle. Protect the tendon and muscles from excessive tension.

Consists of a thin capsule of connective tissue that encloses a few tendon fascicles.

Joint kinesthetic receptors

present within and around the synovial joints. Consists of many types of receptors

Free nerve endings and type II cutaneous mechanoreceptors

in the capsules of joints and respond to pressure.

Small lamellated corpuscles

in the connective tissue outside articular capsules and respond to acceleration and deceleration of joints during movement.

Joint ligaments

contain receptors similar to tendon organs that adjust reflex inhibition of the adjacent muscles when excessive stain is placed on the joint.

Somatic sensory (somatosensory) pathways

relay info from somatic sensory receptors to the primary somatosensory area in the parietal lobe and to the cerebellum.

First-order neurons

conduct impulses from somatic sensory receptors into the brainstem via cranial nerves or into the spinal cord via the spinal nerves.

Second-order neurons

Conduct impulses from the brainstem or spinal cord to the thalamus and decussate (cross over) before they reach there.

Third-order neurons

conduct impulses from the thalamus to the primary somatosensory area on the same side.

Relay stations

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

Posterior Column-Medial Lemniscus Pathway

Takes nerve impulses for touch, pressure, vibration and proprioception from the limbs, trunk, neck and posterior head to the cerebral cortex.

Cuneate fasciculus to cuneate nucleus

(Posterior column-medial lemniscus pathway) takes info from upper limbs, upper trunk, neck and posterior head.

Gracile fasciculus to gracile nucleus

(Posterior column-medial lemniscus pathway) takes info from lowewr limbs and lower trunk.

Medial lemniscus

thin ribbon like projection tract that extends from the medulla to the ventral posterior nucleus of the thalamus.

Anterolateral (Spinothalamic) Pathway

nerve impulses for pain, temp, itch and tickle from the limbs, trunk and posterior head to the cerebral cortex.

Trigeminothalamic Pathway

most somatic sensations from the face, nasal cavity, oral cavity and teeth to the cerebral cortex.

Primary somatosensory area

located at the postcentral gyri of the parietal lobes.

Somatic Sensory Pathways to the Cerebellum

the anterior spinocerebellar tract and the posterior spinocerebellar tract - important for posture, balance, and coordination of skilled movements.

Lower motor neurons

located in the lower parts of the CNS - brainstem and spinal cord. Provide output from the CNS to skeletal muscles.

Local circuit neurons

Help coordinate rhythmic activity on specific muscle groups, like walking.

Upper motor neurons

Help regulate posture, balance, muscle tone, and reflexive movements of the head and trunk.

Basal nuclei neurons

Circuits help initiate and terminate movements, suppress unwanted movements and establish a normal level of muscle tone.

Cerebellar neurons

Issues commands to upper motor neurons to reduce errors in movement. Coordinating movement and maintaining posture and balance.

Premotor area

Develops a motor plan, stores info about learned motor activities and causes specific groups of muscles to contract in a specific sequence

Primary Motor Area

major control region for the execution of voluntary movements

Direct motor pathways

provide input directly from cerebral cortex to LMNs.

Indirect motor pathways

Provide input to LMNs from motor centers in the brainstem. Control involuntary movements.

Pyramidal pathways

a direct motor pathway that consists of axons that descend from pyramidal cells of the primary motor area and premotor area.

Pyramidal cells

upper motor neurons with pyramid-shaped cellbodies. Main output cells of the cerebral cortex.

Corticospinal pathways

conduct impulses for the control of muscles of the limbs and trunk.

Corticospinal Tract

consists of the axons of the upper motor neurons in the cerebral cortex. Pass through the medulla oblongata (where they cross over) and synapse with a local circuit or LMN in the spinal cord.

Lateral corticospinal tract

corticospinal axons that decussate in the medulla form this tract in the lateral white column of the spinal cord.

Synapse in the anterior gray horn of the spinal cord.

Control movements of the distal parts of the limbs.

Anterior corticospinal tract

axons do not decussate in the medulla and form the tract in the anterior white column of the spinal cord.

Synapse in the anterior gray horn

control movements of the trunk and proximal parts of the limbs.

Corticobulbar Pathway

conducts impulses for the control of skeletal muscles in the head. ex. voluntary facial movements, chewing, speech and swallowing.

Corticobulbar tract

formed by the axons of upper motor neurons from the cerebrum which descend along with corticospinal tracts. Some axons decussate, some dont. Axons terminate in the motor nuclei of nine pairs of cranial nerves.

Vestibular nuclei

(brainstem) receive info from vestibulocochlear (VIII) nerve regarding the state of equilibrium.

Generate action potentials that move along the vestibulospinal tract and convey info to skeletal muscles of the trunk and proximal parts of the limbs.

Maintains posture in response to changes in equilibrium.

Reticular formation

(Brainstem) receive input for eyes, ear, cerebellum and basal nuclei.

generate action potentials along the medial reticulospinal tract and lateral reticulospinal tract which convey info to skeletal muscles of the trunk and proximal limbs.

Medial reticulospinal tract

excites the skeletal muscles of the trunk and extensor muscles of the proximal limbs

Lateral reticulospinal tract

inhibits the skeletal muscles of the trunk and extensor muscles of the proximal limbs.

Superior Colliculus

(brainstem) receives input from the eyes and ears.

in response to sudden, unexpected input, it generates action potentials along the tectospinal tract that go to the skeletal muscles in the head and trunk.

Allows for sudden movement in response to something in the visual field or a sudden loud noise.

Saccades

small, rapid, jerking movements of the eyes that occur as a person looks at different points in the visual field.

The integrating center for saccades is the…

superior colliculus in the brainstem.

Red Nucleus

(brainstem) Receives input from the cerebral cortex and the cerebellum

generates action potentials along the rubrospinal tract

activates the skeletal muscles that cause fine, precise, voluntary movements of the distal parts of the upper limbs.

Function of the cerebrum

Integration

Circadian rhythm

24-hour sleep/awaken cycle established by the suprachiasmatic nucleus of the hypothalamus

Reticular activating system

part of the reticular formation. Stimulation causes generalized increase in cortical activity in the cerebrum. Causes wakefulness and arousal.

NREM sleep is induced by…

NREM sleep centers in the hypothalamus and basal forebrain.