Anatomy and Physiology Biology 2401 Chapter-15 Neural Integration I

Four Principal Functions of the Nervous System Carry information from receptors to the brain: sensation Integrate the sensory information: association Transmit motor responses to effectors Memory

Perception: conscious awareness and interpretation of sensations Conscious or unconscious awareness of both external and internal stimuli Perception: conscious awareness and interpretation of sensations Process of sensation Stimulation (change in the environment) of sensory receptor Transduction of the stimulus: conversion of stimulus into an electrical potential Generation of a impulse and conduction: if the electrical potential reaches threshold, an action potential is produced and travels to the CNS Integration of the sensory input: the action potential is translated into a sensation

The way one sensation is distinguished from another Sensory Modality The way one sensation is distinguished from another Two major classes of modalities: general and special senses General senses subdivided into Visceral: provide information about conditions of internal organs Somatic: provide information about external stimuli affecting the skin and its accessory structures as well as proprioceptive information from the joints Special senses are smell, taste, vision, hearing and equilibrium

Types of Sensory Receptors A first order neuron acts as the receptor. Primary receptor. Free nerve endings: naked dendrites of the neuron act as the receptor. Pain, heat, cold Encapsulated nerve endings: connective tissue layers surround the dendrites of the first order neuron Sensory receptor cells synapse with a first order neuron. Secondary receptor.

Types of Sensory Receptors

Types of Receptors Based on Location Exteroceptors: used to interpret stimuli that come from the external environment and that are at or near the surface of the body. Touch, pressure, vibration, temperature, pain, hearing, vision, smell, taste. Interoceptors: used to interpret stimuli that are produced internally. Found in organs such as blood vessels and the viscera. Perceived as pain or pressure Proprioceptors: receptors that recognize the position of the body and about body position, muscle tension or activity of joints. Stretch receptors in muscles, tendons, and joints. Equilibrium receptors in inner ear

Types of Receptors Based on Type of Stimulus Detected Mechanoreceptors: touch, pressure, vibration, proprioception, hearing and equilibrium Thermoreceptors: changes in temperature Nocioceptors: respond to physical or chemical damage to tissues. Results in pain perception Photoreceptors: light striking the retina Chemoreceptors: taste, smell, oxygen, carbon dioxide Osmoreceptors: monitor relative concentrations of salt and water in body fluids

Adaptation in Sensory Receptors Tendency for generator or receptor potentials to decrease in amplitude during a maintained, constant stimulus Rapidly adapting (phasic): pressure, touch, smell. Specialized for signaling changes in a particular stimulus. Slow adapting (tonic): Monitor stimuli associated with pain, body position, and chemical composition of the blood

THE SOMATIC SENSATIONS Pain Proprioception Tactile Thermal

Thermal Sensations Free nerve endings in skin and in mucous membranes of mouth, vagina, and anus Separate thermoreceptors respond to hot and cold stimuli Adapt rapidly initially, then more slowly

Pain Sensations Nocioceptors: free nerve endings. Located in every tissue of the body except the brain. Adaptation is slight if at all Provides individual with information about tissue damage. Also, used as a sign during diagnosis of disease or injury.

Types of Pain Fast: recognized rapidly and is described as acute, sharp, or prickly Slow: begins several seconds after the stimulus and increases in intensity. Described as chronic, burning, aching, or throbbing Superficial: arises from the skin Deep: arises from skeletal muscle, joints and tendons Chronic: not a response to immediate, direct tissue injury. Hypothetical causes: cerebrum and thalamus may misinterpret discomfort as pain or brain as a whole may not properly regulate how much pain stimulation is allowed to penetrate the cerebral cortex. Migraine, back pain. Often associated with depression, frustration, helplessness, hopelessness

Types of Pain, cont. Phantom pain: sensations of pain in a limb that has been amputated Brain interprets sensations from the remaining part of the limb as sensations from the amputated part OR neurons in the brain that received input from the missing limb are still firing

THE VISCERAL SENSATIONS Pain and pressure if they are intense enough to reach conscious perception Referred pain: sensation in one region of body that is not the source of the stimulus. Organ pain usually referred to skin Both the organ and that region of the skin input to the same spinal segment and converge on the same ascending neurons

Proprioceptive Sensation Stretch receptors located in muscles (muscle spindles) and tendons and joints (tendon organs or Golgi tendon organs) Receptors for equilibrium (kinesthetic sense) in inner ear Convey information about muscle tone, precise position of a body part, rate of movement of a body part, weight of an object held in the hand, range of movement of a joint, and balance Proprioceptive Sensation

Mapping of Sensory Areas on Postcentral Gyrus Primary Somatosensory Area Specific areas of the cerebral cortex receive somatic sensory input from particular parts of the body. Homunculus maps the destination of somatic sensory signals from different parts of the body. The relative sizes of the regions in the somatosensory area are proportional to the number of specializes sense receptors within the corresponding part of the tissue

INTEGRATIVE FUNCTIONS OF THE CEREBRUM Wakefulness and sleep Learning and memory

Wakefulness and Sleep Reticular activating system (RAS): control and integrate wakefulness and sleep Awakening (arousal) comes about because of increased activity of the RAS. Activation of RAS causes activation of the cerebrum leading to consciousness Sleep: state of altered consciousness or partial unconsciousness from which an individual can be aroused by a number of stimuli. RAS activity is very low Two types of sleep: non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM)

Indirect Motor Pathways All somatic motor tracts other than the corticospinal and corticobulbar tracts Involve the motor cortex, basal ganglia, thalamus, cerebellum, reticular formation and nuclei in the brain stem

Sleep NREM: four stages, each of which gradually merges into the next REM: dreaming Patterns of stages change over the course of 8 hours of sleep, with body temperature changes (warmer means longer periods of REM), and with age (older people exhibit shorter and fewer episodes of REM)

Learning and Memory Learning: ability to acquire new knowledge or skills through instruction or experience Memory: process by which learned knowledge is retained over time Brain exhibits plasticity: capability for change with learning. Memories are represented by persistent functional changes in the brain

Types of Memory Immediate: ability to recall something for a few seconds Short-term memory: ability to recall bits of information for seconds or hours. Electrical and chemical events occur in the brain. Long-term memory: ability to recall information from days to years. Anatomical and biochemical changes at synapses.

Amnesia Loss of memory Anterograde: loss of memory for events that occur after a trauma (inability to form new memories) Retrograde: loss of memory for events that occur before a trauma (inability to recall past events)