NEURAL INTEGRATION PART I: SENSORY RECEPTORS

Detailed Classification System • Divides the general sensory receptors into 4 types by the nature of the

stimulus that excites them: – nociceptors (pain) – thermoreceptors (temperature) – chemoreceptors (chemical concentration) – mechanoreceptors (physical distortion) – photoreceptos (light)

Nociceptors • Are common in the:

– skin – joint capsules – bones – around blood vessels

• May be sensitive to: – extremes of temperature – mechanical damage – chemicals, such as chemicals released by injured cells

Thermoreceptors • Are free nerve endings located in:

– the dermis – skeletal muscles – liver – hypothalamus

• Sensations sent to: – reticular formation – thalamus – primary sensory cortex

Chemoreceptors • Located in the:

– carotid sinus – aorta – brain – kidney

• Monitors pH, carbon dioxide, and oxygen levels

Mechanoreceptors • Sensitive to stimuli that distort their cell membranes

– Stretching, compression, twisting, or other distortions of the membrane 3 Classes of Mechanoreceptors • Tactile receptors:

– detect touch, pressure, and vibration:

• touch - shape or texture • pressure - degree of

mechanical distortion • vibration - pulsing or

oscillating pressure

• Baroreceptors: – detect pressure changes

• Proprioceptors: – monitor the positions of joints

and muscles

Touch & Pressure Receptors Fine Touch & Pressure • extremely sensitive • narrow receptive field • detailed information about a source of

stimulation: – its exact location – shape – size – texture – movement

Crude Touch & Pressure • large receptive fields • poor localization • give little information about the stimulus Skin Tactile Receptors • Free nerve endings

• touch and pressure • Root hair plexus

• movement of hair • adapt rapidly

• Merkel cells or disks • fine touch and pressure

• Meisner’s corpuscles • fine touch, pressure, and

low-frequency vibration • adapt within 1 second • found in ‘sensitive’ areas

• Pacinian corpuscles • deep pressure and high-

frequency vibration • fast-adapting

• Ruffini corpuscles • pressure and distortion • in the reticular dermis • little if any adaptation

Baroreceptors • Monitor change in pressure • Consist of free nerve endings that branch within elastic tissues in wall of

distensible organ (such as a blood vessel) • Respond immediately to a change in pressure, but adapt rapidly 3 Major Groups of Proprioceptors • Muscle spindles:

– activated by rapid muscle length changes – trigger stretch reflexes

• Golgi tendon organs: – junction between skeletal muscle and its tendon – stimulated by tension in tendon

• Receptors in joint capsules: – free nerve endings detect pressure, tension, and movement at the joint

NEURAL INTEGRATION

PART II: SENSORY PROCESSING

Sensory Processing in the Brain Thalamus • Determines type of sensation:

– fine touch, pressure, vibration, etc. Primary Somatosensory Cortex • Precisely where on the body a specific stimulus originated Somatosensory Association Area • Interpretation of sensations:

– pain from a bee or hammer – touch velvet or rock

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

NEURAL INTEGRATION

PART III: MOTOR CONTROL

Motor Control Originates in the Brain Premotor Cortex • Plans sequence of movements:

– Muscle activation/inactivation sequence, balance, and other sensory input

– Works with cerebellum Primary Motor Cortex • Precisely what muscles are stimulated Medulla Oblongata • Motor neurons cross-over to opposite side:

– Right frontal lobe controls left side of body

Cerebellum Processing • Cerebellum receives proprioceptive

information about position of skeletal muscles, tendons, and joints

• Proprioceptors monitor: – position of joints – tension in tendons and ligaments – state of muscular contraction