Integrative Functions of the Nervous System

• Sensation


  Brain receiving information about environment and body.
• Perception


  Conscious awareness of sensations.
• General senses


  Information about body and environment like touch, pressure, temperature.
• Special senses


  Smell, taste, sight, hearing, balance.
• Proprioception


  Sense of body position and movement.
• Visceral senses


  Information about internal organs like pain and pressure.
• Mechanoreceptors


  Detect compression, bending, stretching; e.g., touch, pressure, hearing.
• Chemoreceptors


  Detect chemicals attached to receptors; e.g., smell, taste.
• Thermoreceptors


  Respond to changes in temperature.
• Photoreceptors


  Respond to light for vision.
• Nociceptors


  Detect extreme mechanical, chemical, or thermal stimuli causing pain.
• Cutaneous receptors


  Associated with skin.
• Visceroreceptors


  Associated with organs.
• Proprioceptors


  Associated with joints, tendons, detect stretch, provide info about precise position and rate of movement of body parts, types: tonic, phasic
• Free nerve endings


  Simplest sensory receptor for temperature sensation, scattered thru body mostly on epithelia and CT, types: cold, warm, pain receptors
• Merkel (Tactile) Disks


  Associated with light touch and superficial pressure, basal layer of epidermis, axonal branches end as flattened expansions associated w epithelial cells, associated with thickened epidermis of hairy skin
• Hair Follicle Receptors


  Respond to slight bending of hair for light touch, hair end organs, receptor fields overlap, sensation not localized but very sensitive
• Pacinian (Lamellated) Corpuscles


  Respond to deep cutaneous pressure and vibration, single dendrite w layers of corpuscles arranged like onion, hypodermis, when associated with joints, proprioception
• Meissner (Tactile) Corpuscles


  Detect two-point discrimination (simultaneous stimulation) and texture, on dermal papillae, tongue ands fingertips
• Ruffini End Organ


  Respond to continuous touch or pressure, dermis of fingers
• Muscle Spindles


  Provide information about muscle length and involved in stretch reflex, 3 to 10 specialzied skeletal muscle cells
• Golgi Tendon Organs


  Respond to increased tension on tendons, proprioceptors associated with tendons
• Receptor potential


  Graded potential from sensory receptor interaction with stimulus.
• Primary receptors


  Axons conducting action potentials in response to receptor potential.
• Secondary receptors


  Release neurotransmitters binding to receptors on neurons, smell taste hearing balance
• Adaptation


  Decreased sensitivity to continued stimulus.
• Tonic receptors


  Accommodate slowly; e.g., Merkel disks and Ruffini end organs.
• Phasic receptors


  Accommodate rapidly; e.g., Pacinian and Meissner corpuscles.
• Ascending pathways


  Transmit action potentials from periphery to brain.
• Anterolateral System


  Conveys pain, temperature, touch, pressure, tickle, and itch sensations.
• Dorsal-Column/Medial-Lemniscal System


  Carries two-point discrimination, proprioception, pressure, vibration sensations to cerebrum and cerebellum, primary neurons have axons enter spinal cord--> medulla oblongota-->secondary neurons, secondary neurons: axons decussate and ascend to thalamus, tertiary neurons: project to somatic sensory cortex
• fasciculus gracialis


  sensations from inferior and midthoracic level
• fasciculus cuneatus


  impulses from above midthorax
• Axons


  Nerve fibers that enter the spinal cord and ascend to the medulla oblongata without crossing over.
• Decussate


  Cross over to the opposite side of the body.
• Thalamus


  Brain region where sensory information is relayed and processed before reaching the cortex.
• Trigeminothalamic Tract


  Pathway carrying sensory information from the face, nasal cavity, and oral cavity to the brainstem.
• Proprioceptive


  Sensory information about body position and movement.
• Spinocerebellar Tracts


  Pathways that transmit unconscious proprioceptive information to the cerebellum for coordination of movements.
• Descending Pathways


  Nerve tracts from the brain to the spinal cord that modulate sensory perception.