Chapter 16: Sensory, Motor, and Integrative Systems
Sensation n Conscious and subconscious awareness of changes in the external or internal environment. n Components of sensation: Stimulation of the sensory receptor transduction of the stimulus generation of nerve impulses integration of sensory input.
Classification of Sensory Receptors n General senses: somatic and visceral. Somatic- tactile, thermal, pain and proprioceptive sensations. Visceral- provide information about conditions within internal organs. n Special senses- smell, taste, vision, hearing and equilibrium or balance.
Types of Sensory Receptors n Free nerve endings: pain and thermoreceptors. n Encapsulated nerve endings: pacinian corpuscles. n Separate cells: hair cells, photoreceptors and gustatory receptor cells.
Generator Potential and Receptor Potential n 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 first-order sensory neuron. n Receptor potential triggers the release of neurotransmitter postsynaptic potential action potential.
Sensory Receptors and their Relation-ship to First-Order Sensory Neurons
Classification of Sensory Receptors Based on the Location n Exteroceptors n Interoceptors n Proprioceptors
Classification of Sensory Receptors based on the type of Stimulus n Mechanoreceptors n Thermoreceptors n Nociceptors n Photoreceptors n Chemoreceptors n Osmoreceptors
Adaptation of Sensory Receptors n Rapidly adapting receptors: receptors that detect pressure, touch and smell. n Slowly adapting receptors: receptors that detect pain, body position, and chemical composition of the blood.
Somatic Sensations n Sensory receptors in the skin (cutaneous sensations), muscles, tendons and joints and in the inner ear. n Uneven distribution of receptors. n Four modalities: tactile, thermal, pain and proprioceptive.
Sensory Receptors in the Skin
Tactile Sensations n Include touch, pressure, vibration, itch and tickle. n 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 n Egg-shaped mass of dendrites enclosed by a capsule of connective tissue. n Rapidly adapting receptors. n 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 n Rapidly adapting touch receptors found in the hairy skin. n Free nerve endings wrapped around hair follicles. n Detect movements on the skin surface that disturb hairs.
Merkel Discs or Tactile Discs n Also known as type I cutaneous mechanoreceptors. n Slowly adapting touch receptors. n Saucer-shaped, flattened free nerve endings. n Found in the fingertips, hands, lips, and external genitalia.
Ruffini Corpuscles n Also called as type II cutaneous mechanoreceptors. n Elongated, encapsulated receptors. n Located deep in the dermis and in ligaments and tendons. n Found in the hands, and soles.
Pacinian or Lamellated Corpuscles n Large oval structure composed of a multilayered connective tissue capsule that encloses a dendrite. n Fast adapting receptors. n Found around joints, tendons, and muscles; in the periosteum, mammary glands, external genitalia, pancreas and urinary bladder.
Thermal Sensations n Thermoreceptors are free nerve endings. n Two distinct thermal sensations: cold receptorswarm receptors-
Pain Sensations n Protective. n Sensory receptors are nociceptors. n Free nerve endings. n Two types of pain: fast and slow. n Fast pain: acute, sharp or pricking pain. n Slow pain: chronic, burning, aching or throbbing pain.
Referred Pain n 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 n Receptors are called proprioceptors. n Slow adaptation. n Weight discrimination. n Three types: muscle spindles, tendon organs and joint kinesthetic receptors.
Muscle Spindles n Interspersed among most skeletal muscle fibers and aligned parallel to them. n Measure muscle stretching. n Consists of intrafusal muscle fibersspecialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons. n Extrafusal muscle fibers- surrounding muscle fibers supplied by alpha motor neurons.
A Muscle Spindle and a Tendon Organ
Tendon Organs n Located at the junction of a tendon and a muscle. n Protect tendons and their associated muscles from damage due to excessive tension. n Consists of a thin capsule of connective tissue that encloses a few tendon fascicles.
Joint Kinesthetic Receptors n Found within or around the articular capsules of synovial joints. n Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure. n Pacinian corpuscles respond to acceleration and deceleration of joints during movement.
Somatic Sensory Pathways n First-order neuron(somatic receptor to the brain stem/spinal cord) second order neuron(brain stem/spinal cord too the thalamus; decussate) third-order neuron(thalamus to the primary somatosensory area of the cortex).
Major Somatic Sensory Pathways n The posterior column-medial lemniscus pathway. n The anterolateral (spinothalamic) pathway. n The trigeminothalamic pathway. n The anterior and posterior spinocerebellar pathway.
The Posterior Column-Medial Lemniscus Pathway n Conveys nerve impulses for touch, pressure, vibration and conscious proprioception from the limbs, trunk, neck, and posterior head to the cerebral cortex.
The Anterolateral (spinothalamic) pathway n Conveys nerve impulses for pain, cold, warmth, itch, and tickle from the limbs, trunk, neck, and posterior head to the cerebral cortex.
Trigeminothalamic Pathway n Conveys nerve impulses for most somatic sensations from the face, nasal cavity, oral cavity and teeth to the cerebral cortex.
Mapping of the Primary Somatosensory Area n Mapping of the postcentral gyrus. n Size of the cortical region representing a body part depends on the sensory impulses received from that part.
Somatic Motor Pathways n Upper motor neurons lower motor neurons skeletal muscles. n Neural circuits involving basal ganglia and cerebellum regulate activity of the upper motor neurons.
Organization of the Upper Motor Neuron Pathways n Direct motor pathway- originates in the cerebral cortex. Corticospinal pathway: to the limbs and trunk. Corticobulbar pathway: to the head. n Indirect motor pathway- originates in the brain stem.
Mapping of the Motor Areas n Located in the precentral gyrus of the frontal lobe. n More cortical area is devoted to those muscles involved in skilled, complex or delicate movements.
The Corticospinal Pathways
The Corticobulbar Pathway
Indirect or Extrapyramidal Pathways n Originate in the brain stem. Include: q Rubrospinal tract q Tectospinal tract q Vestibulospinal tract q Reticulospinal tract
Modulation of Movement from the Cerebellum n The cerebellum coordinates and smoothes contractions of skeletal muscles during skilled movements and helps maintain posture and balance.
Sagittal plane Motor areas of cerebral cortex Corrective feedback Thalamus Cortex of cerebellum Motor centers in brainstem 4 1 Pons 3 2 Pontine nuclei Direct pathways Sensory signals from proprioceptors in muscles and joints, vestibular apparatus, and eyes Indirect pathways Signals to lower motor neurons Sagittal section through brain and spinal cord
Integrative Functions of the Cerebrum n Wakefulness and sleepn Learning and memory-
The role of Reticular Activating System (RAS) in Awakening n Consists of neurons whose axons project from the reticular formation through the thalamus to the cerebral cortex. n Increased activity of the RAS causes awakening from sleep (arousal).
Sleep n A state of altered consciousness. n Two components: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. n NREM sleep consists of four stages: q Stage 1- q Stage 2- q Stage 3- q Stage 4-
Learning and Memory n Learning is the ability to acquire new information or skills through instruction or experience. n Memory is the process by which information acquired through learning is stored and retrieved.
Memory Types n Immediate memory- recall for a few seconds. n Short-term memory- temporary ability to recall. n Long-term memory- more permanent. n Memory consolidation.