Bio 201 Chapter 16 Lecture

Chapter 16: Sensory, Motor, and Integrative Systems

Sensation  Conscious

and subconscious awareness of changes in the external or internal environment.  Components of sensation: Stimulation of the sensory receptor → transduction of the stimulus → generation of nerve impulses → integration of sensory input.

Classification of Sensory Receptors  General

senses: somatic and

visceral. Somatic- tactile, thermal, pain and proprioceptive sensations. Visceral- provide information about conditions within internal organs.  Special senses- smell, taste, vision, hearing and equilibrium or balance.

Types of Sensory Receptors  Free

nerve endings: pain and thermoreceptors.  Encapsulated nerve endings: pacinian corpuscles.  Separate cells: hair cells, photoreceptors and gustatory receptor cells.

Generator Potential and Receptor Potential  Generator

potential is produced by free nerve endings, encapsulated nerve endings, and olfactory receptors. When it reaches a threshold, it triggers one or more nerve impulses in the axon of a firstorder sensory neuron.  Receptor potential triggers the release of neurotransmitter → postsynaptic potential → action

Sensory Receptors and their Relationship to First-Order Sensory Neurons

Classification of Sensory Receptors Based on the Location  Exteroceptors  Interoceptors  Proprioceptors

Classification of Sensory Receptors based on the type of Stimulus  Mechanoreceptors  Thermoreceptors  Nociceptors  Photoreceptors  Chemoreceptors  Osmoreceptors

Adaptation of Sensory Receptors  Rapidly

adapting receptors: receptors that detect pressure, touch and smell.  Slowly adapting receptors: receptors that detect pain, body position, and chemical composition of the blood.

Somatic Sensations  Sensory

receptors in the skin (cutaneous sensations), muscles, tendons and joints and in the inner ear.  Uneven distribution of receptors.  Four modalities: tactile, thermal, pain and proprioceptive.

Sensory Receptors in the Skin

Tactile Sensations  Include

touch, pressure, vibration, itch and tickle.  Tactile receptors in the skin are Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings.

Meissner Corpuscles or Corpuscles of Touch  Egg-shaped

mass of dendrites enclosed by a capsule of connective tissue.  Rapidly adapting receptors.  Found in the dermal papillae of hairless skin such as in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis.

Hair Root Plexuses  Rapidly

adapting touch receptors found in the hairy skin.  Free nerve endings wrapped around hair follicles.  Detect movements on the skin surface that disturb hairs.

Merkel Discs or Tactile Discs  Also

known as type I cutaneous mechanoreceptors.  Slowly adapting touch receptors.  Saucer-shaped, flattened free nerve endings.  Found in the fingertips, hands, lips, and external genitalia.

Ruffini Corpuscles  Also

called as type II cutaneous mechanoreceptors.  Elongated, encapsulated receptors.  Located deep in the dermis and in ligaments and tendons.  Found in the hands, and soles.

Pacinian or Lamellated Corpuscles  Large

oval structure composed of a multilayered connective tissue capsule that encloses a dendrite.  Fast adapting receptors.  Found around joints, tendons, and muscles; in the periosteum, mammary glands, external genitalia, pancreas and urinary bladder.

Thermal Sensations  Thermoreceptors

are free nerve

endings.  Two distinct thermal sensations: cold receptorswarm receptors-

Pain Sensations  Protective.  Sensory receptors are nociceptors.  Free nerve endings.  Two types of pain: fast and slow.  Fast pain: acute, sharp or pricking

pain.  Slow pain: chronic, burning, aching or throbbing pain.

Referred Pain  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.

Distribution of Referred Pain

Proprioceptive Sensations  Receptors are called proprioceptors.  Slow adaptation.  Weight discrimination.  Three types: muscle spindles, tendon

organs and joint kinesthetic receptors.

Muscle Spindles  Interspersed

among most skeletal muscle fibers and aligned parallel to them.  Measure muscle stretching.  Consists of intrafusal muscle fibersspecialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons.  Extrafusal muscle fibers- surrounding

A Muscle Spindle and a Tendon Organ

Tendon Organs  Located

at the junction of a tendon and a muscle.  Protect tendons and their associated muscles from damage due to excessive tension.  Consists of a thin capsule of connective tissue that encloses a few tendon fascicles.

Joint Kinesthetic Receptors  Found

within or around the articular capsules of synovial joints.  Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure.  Pacinian corpuscles respond to acceleration and deceleration of joints during movement.

End of Chapter 16