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Chapter Three THE PHYSIOLOGICAL BASIS OF BEHAVIOR THE THREE MECHANISMS OF BEHAVIOR
- THE RECEIVING MECHANISM – consists of the sense organs
- THE CONNECTING MECHANISM – consists of the nervous system
- THE REACTING MECHANISM – consists of the muscles and the endocrine system THE RECEIVING MECHANISM THE SENSE ORGANS (de Guzman, 2008; Freberg, 2010) Sense Organs are sensitive nerve endings located in certain body parts. Characteristics:
- Sensitivity and Irritability – power to react to stimuli
- Conductivity – power to conduct and transport nerve impulses
- Specificity – attribute of reacting to particular stimuli
- Adaptability – power to become used to a particular stimulus Stimulus Receptor(s) Neural Processing Vision (Sense of Sight) Light rays Retina: Rods – function in low light conditions and are not sensitive to colors (to optic nerve) Cones – function in bright light and are sensitive to colors (to optic nerve) Occipital Lobe Audition (Sense of Hearing) Sound Waves Cochlea: Organ of Corti – hair cells which act as specific receptors for the sense of hearing (to auditory nerve) Vestibular Portion / Semicircular Canals – sense of balance or equilibrium (to auditory nerve) Temporal Lobe of both hemispheres
Olfaction (Sense of Smell) Chemical substances in a gaseous state Olfactory Cells – found in the nasal cavity; excitation leads to neural impulses (to olfactory nerve) Temporal lobes and Frontal Lobes Gustation (Sense of Taste) Chemical substances in liquid state Papillae – contain taste buds with taste receptor cells (to facial nerve and glossopharyngeal nerve) Frontal lobe and Insular lobe Somatosensation (Sense of Touch) Pressure, Pain, Temperature Meissner’s Corpuscles – pressure Merkel’s Disks - pressure Pacinian Corpuscles – vibration Ruffini endings – stretch/warmth Krause’s corpuscle – cold C-fibers/Free nerve endings – pain, itch, temperature Parietal lobe
THE CONNECTING MECHANISM
Neuron – is the basic structural unit of the nervous system. PARTS OF THE NEURON (Freberg, 2010) :
- Dendrite – the branch of a neuron that generally receives information from other neurons.
- Cell body/Soma – main mass of a neuron, containing the nucleus and many organelles.
- Nucleus – the substructure within a cell body that contains the cell’s DNA.
- Axon – The branch of a neuron usually responsible for carrying signals to other neurons.
- Axon Hillock – the cone-shaped segment of axon located at the junctions of the axon and cell body that is specialized for the generation of action potentials.
- Axon Terminal – the swelling at the top of an axon collateral specialized for the release of neurotransmitter substance.
- Myelin (sheath) – the fatty insulating material covering some axons that boosts the speed and efficiency of electrical signaling.
- Synaptic Vesicle – a small structure in the axon terminal that contains neurotransmitters.
- Node of Ranvier ( RAHN-vee-ay) – the uncovered section of axon membrane between two adjacent segments of myelin.
FUNCTIONAL VARIATIONS IN NEURONS
- Sensory Neurons – specialized neurons that receive information from the outside such as vision, hearing, touch, taste, and smell and all depend on specialized receptor neurons.
- Motor Neurons – transmit commands from the central nervous system (brain and spinal cords) directly to muscles and glands.
- Interneurons – act as bridges between sensory and motor systems. NERVE IMPULSE TRANSMISSION Source: Boundless. “Nerve Impulse Transmission within a Neuron: Action Potential.” Boundless Biology. Boundless, 21 Jul. 2015. Retrieved 03 Aug. 2015 from https://www.boundless.com/ biology/textbooks/boundless-biology- textbook/the-nervous-system-35/how-neurons-communicate-200/nerve-impulse- transmission-within-a-neuron-action-potential- 762 - 11995/ Action Potential A neuron can receive input from other neurons via a chemical called a neurotransmitter. If this input is strong enough, the neuron will pass the signal to downstream neurons. Transmission of a signal within a neuron (in one direction only, from dendrite to axon terminal) is carried out by the opening and closing of voltage-gated ion channels, which cause a
A node of Ranvier is a natural gap in the myelin sheath along the axon. These unmyelinated spaces are about one micrometer long and contain voltage gated Na+^ and K+^ channels. The flow of ions through these channels, particularly the Na
channels, regenerates the action potential over and over again along the axon. Action potential "jumps" from one node to the next through saltatory conduction. If nodes of Ranvier were not present along an axon, the action potential would propagate very slowly; Na+^ and K+^ channels would have to continuously regenerate action potentials at every point along the axon. Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon.
THE NERVOUS SYSTEM
CENTRAL NERVOUS SYSTEM – consists of the brain and spinal cord STRUCTURES IN THE BRAIN (de Guzman, 2008) Brainstem
- Where motor signals from the brain pass through before reaching the spinal cord
- Where sensory signals from the spinal cord pass through before reaching the brain
Cerebellum – concerned with the coordination of somatic motor activities, or voluntary movements, the regulation of muscle tone, and mechanisms that influence and maintain equilibrium. Cerebrum - Outer layer consists of gray matter (unmyelinated fibers) called the cerebral cortex, and the inner layer consists of white matter (myelinated fibers) Corpus callosum – large band of commissural fibers (nerve fibers) that go to the opposite side of the brain and spinal cord and join the two cerebral hemispheres Gyri (gyrus) – numerous folds in the cerebral hemispheres Sulci (sulcus) or fissures – canals or grooves in between the gyri Fissure of Rolando – separates frontal lobe from parietal lobe Sylvian fissure – separates temporal lobe from lateral cerebral fissure Lobes of the brain, the cortical areas, and their functions: Frontal lobe – location of the primary motor area which controls voluntary movement in a contralateral manner (left side controls the right side of the body, and vice versa). Temporal lobe – location of the primary auditory area in charge of hearing and processing of auditory stimuli.
Parietal lobe – contains the primary somatosensory area which processes sensory signals such as touch, pressure, pain, thermal sense, and sense of body movements (kinesthesia). Occipital lobe – contains the primary visual area which receives visual signals from the thalamus and processes visual sensations. Association area – areas of cerebral hemispheres not concerned with primary sensory and motor processes and occupy a larger part of the brain; in charge of meaningful interpretation of sensory experiences. PERIPHERAL NERVOUS SYSTEM – consists of the autonomic nervous system and the somatic nervous system. Autonomic Nervous System – is concerned with the involuntary activities of the organism and consists of the sympathetic and parasympathetic divisions, which function antagonistically (de Guzman, 2008).
- The sympathetic division is considered as the “fight-or-flight” system and activates under stressful situations.
- The parasympathetic division is considered as the “rest-and-digest” system and takes over when the stressful situation has passed. The next figure shows the influence of the antagonistic nature of the sympathetic and parasympathetic nervous system to the different parts of the body (see next page).
Somatic Nervous System – consists of the cranial nerves and spinal nerves and innervate peripheral structures such as the skin and muscles and the visceral organs (de Guzman, 2008).
THE REACTING MECHANISM
MUSCLES (http://www.innerbody.com/image/musfov.html#full-description)
- The muscular system is responsible for the movement of the human body.
- Attached to the bones of the skeletal system are about 700 named muscles that make up roughly half of a person’s body weight.
- Muscle tissue is also found inside of the heart, digestive organs, and blood vessels where muscles serve to move substances throughout the body.
ENDOCRINE SYSTEM
The endocrine system controls the way the body functions. It is composed of glands and organs which produce different hormones that travel to all parts of the body to maintain tissues and organs. Some areas governed by the endocrine system:
- Reproduction
- Responses to stress and injury
- Growth and sexual development
- Body energy levels
- Internal balance of body systems
- Bone and muscle strength
The Glands of the Endocrine System
- Hypothalamus - part of the brain that controls hormone production by releasing different chemicals to the pituitary gland.
- Pituitary gland – likely the most important gland in the body, it is crucial to growth, mental development and reproduction; influences or controls the rest of the endocrine system.
- Pineal gland - connects the endocrine system with the nervous system; produces several important hormones, including melatonin, important to sleep/wake cycles and sexual development.
- Thyroid gland – located in the front of the neck, it releases hormones that control metabolism and govern the way the body uses energy.
- Parathyroid gland - located behind the thyroid gland; essential for proper bone development.
- Thymus - crucial to normal immune function in childhood; once a child reaches puberty, its tissue is replaced by fat
- Adrenal glands - influence the way the body uses energy, they also release a hormone called adrenaline when the individual is under stress.
- Pancreas - releases insulin to metabolize sugar; problems with the pancreas can lead to diabetes.
- Ovaries - produce estrogen and progesterone in women, and also release egg cells.
- Testes - produce the hormone testosterone; in men, testosterone maintains sperm production and bone mass.
The Process of Perception For stimulation, to become meaningful perception, it must undergo several transformations. First, physical stimulation (light waves from the butterfly) is transduced by the eye, where information about the wavelength and intensity of the light is coded into neural signals. Second, the neural messages travel to the sensory cortex of the brain, where they become sensations of color, brightness, form and movement. Finally, the process of perception interprets these sensations by making connections with memories, emotions, and motives in other parts of the brain. Similar processes operate on the information taken in by the other senses. FUNCTIONS OF PERCEPTION
1. Guessing what is out there. Because our brain relies so much on what we know and have experienced, we can usually get away with economizing in our sensory processing ad making educated guesses about what sensory information is telling us. 2. Helping us focus on particular inputs. It is the process of selecting one sensory channel and ignoring or minimizing others. It allows us to select one channel and turn off the others or at least turn down their volume. An attention related phenomenon called the cocktail party effect refers to our ability to pick out an important message, like our name, in a conversation that does not involve us. 3. Putting the pieces together. It refers to how our brain takes multiple pieces of information and combines them to represent something concrete like an apple. An apple looks red and round, feels smooth, tastes sweet and tart and smells, well, like an apple.. Any one of its characteristics in isolation is not an apple or even a part of an apple (that would be an apple slice). How does our brain pull off biding? We do not know for sure, but one suggestion is that coordinated activity in fast-frequency oscillations across multiple cortical
areas provides the timing signal that does the trick. Other part of the brain can recognize signals from disparate specialized processing regions as belonging together as part of a single perceptual object or scene, because the signals from these regions are oscillating in synchrony. When that synchrony is lost the percept dissolves (Engel & Singer, 2001). ATTRIBUTES OF PERCEPTION Two individuals would have different interpretations of one and the same stimulus. This may be explained by the following attributes of perceptions. a) Perception is limited to sensory discrimination. An individual must be able to discriminate among stimuli in his environment considering the following: a. Condition of the organism. There are certain biological and psychological conditions that critically affect behavioral responses and stimulus discrimination. Illness, fatigue, intoxication, trauma, acute sleep deprivation, severe food or water deprivation decease and increase work performance. Drugs like morphine, heroin and caffeine affect stimulation, discrimination and behavior. Congenital disorders or traumatic brain injury may also affect ability to learn. b. Properties of stimulus. The visual stimuli which affect its discrimination are size, proximity and illumination, whereas the properties of the auditory stimuli affecting one’s behavior are pitch, loudness, and timbre. b) Perception is selective and subjective. A person is bombarded with multiple sensory stimuli and because it is impossible to attend to them all, a person responds to meaningful stimuli and minimizes or ignores others. External and internal factors affect the individual’s process of responding to the world.
