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a
center for Arlington, MA 02474
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Neurobiology for Yogis
Anatomy of the Nervous System Development and Functioning of the Nervous System The Language of Neurobiology The Mind, the Nervous System and the Self Anatomical Components of the Nervous System Yoga students and teachers should have at least a rudimentary understanding of the human nervous system. We'll begin with a general explanation of the primary anatomical components and then look more deeply at the evolutionary development, the functioning and integration of the various regions. We refer you also to the section on cells, tissues and the living matrix for a description of the more fundamental sub components of all of the body systems. Although the scientific languaging can be confusing, there is really only one "nervous system" in the body. Each subdivision of the system is also called a "nervous system," but all of these smaller systems belong to the single, highly integrated nervous system. Each subdivision does have structural and functional characteristics that distinguish it from the others. Some will be familiar, and others not, so spend some time with those regions that are new to your understanding. To begin, the nervous system as a whole has two subdivisions: the central nervous system (CNS) and the peripheral nervous system (PNS).
Meninges
Cerebrospinal Fluid (CSF) Brain The brain is a network of neurons, the individual cells of the nervous system. It is divided anatomically into 4 regions: the cerebrum, diencephalons, brain stem, and cerebellum, and functionally / developmentally into 3: the reptilian, the limbic and neocortical.
The largest and most obvious portion of the brain is the cerebrum, which is divided by a deep longitudinal fissure into two cerebral hemispheres. The two hemispheres are two separate entities but are connected by an arching band of white fibers, called the corpus callosum that provides a communication pathway between the two halves. Each cerebral hemisphere is divided into five lobes, four of which have the same name as the bone over them: the fontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. A fifth lobe, the insula or Island of Reil, lies deep within the lateral sulcus. The insula will be seen to play a major role in the emotions. Diencephalons
Brain Stem
Cerebellum
Spinal Cord The spinal cord extends from the foramen magnum at the base of the skull to the level of the first lumbar vertebra. The cord is continuous with the medulla oblongata at the foramen magnum. Like the brain, the spinal cord is surrounded by bone, meninges, and cerebrospinal fluid. It is divided into 31 segments with each segment giving rise to a pair of spinal nerves. At the distal end of the cord, many spinal nerves extend beyond the conus medullaris to form a collection that resembles a horse's tail known as the cauda equina. In cross section, the spinal cord appears oval in shape. The spinal cord has two main functions:
• Serving as a reflex center. The reflex arc is the functional unit of the nervous system. Reflexes are responses to stimuli that do not require conscious thought and consequently, they occur more quickly than reactions that require thought processes. For example, with the withdrawal reflex, the reflex action withdraws the affected part before you are aware of the pain. Many reflexes are mediated in the spinal cord without going to the higher brain centers. The Peripheral Nervous System The organs of the peripheral nervous system are the cranial and spinal nerves and ganglia that branch out from the brain and spinal cord and form the communication network between the CNS and the peripheral organs such as muscles and glands. Nerves are bundles of nerve fibers, much like muscles are bundles of muscle fibers. Ganglia are collections, or small knots, of nerve cell bodies outside the CNS. Cranial Nerves
The cranial nerves are designated both by name and by Roman numerals, according to the order in which they appear on the inferior surface of the brain. Most of the nerves have both sensory and motor components. Three of the nerves are associated with the special senses of smell, vision, hearing, and equilibrium and have only sensory fibers. Five other nerves are primarily motor in function but do have some sensory fibers for proprioception. The remaining four nerves consist of significant amounts of both sensory and motor fibers. Spinal Nerves Thirty-one pairs of spinal nerves emerge laterally from the spinal cord. Each pair of nerves corresponds to a segment of the cord and they are named accordingly. This means there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve. Each spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. The cell bodies of the sensory neurons are in the dorsal root ganglion, but the motor neuron cell bodies are in the gray matter. The two roots join to form the spinal nerve just before the nerve leaves the vertebral column. Because all spinal nerves have both sensory and motor components, they are all mixed nerves. Afferent (sensory) and an Efferent (motor) divisions. The peripheral nervous system is further subdivided into an afferent (sensory) division and an efferent (motor) division. The afferent or sensory division transmits impulses from peripheral organs to the CNS. The efferent or motor division transmits impulses from the CNS out to the peripheral organs to cause an effect or action. The efferent (motor) nervous system is further subdivided into the somatic nervous system, also called the somatomotor or somatic efferent nervous system, and the visceral efferent system or the autonomic nervous system. Somatic Nervous System Autonomic Nervous System The autonomic nervous system is a visceral efferent system, which means it sends motor impulses to the visceral organs. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis. Sympathetic and Parasympathetic Divisions The autonomic nervous system has two parts, the sympathetic division and the parasympathetic division. Many visceral organs are supplied with fibers from both divisions. In this case, one stimulates and the other inhibits. This antagonistic functional relationship serves as a balance to help maintain homeostasis. Evolutionary Origins of the Nervous System sea squirt, need to move, to predict, to plan, to represent the outside world internally, to create an internal map multicellularity Development and Functioning of the Nervous System neural network "As the child develops, the mind begins to create a sense of continuity across time, linking past experiences with present perceptions and anticipations of the future." DM 5 autobographical narrative; how does the mind create coherence within its own processes? the narrative process " Studies of child development reveal that by the third year of life, a 'narrative function emerges in children that allows them to create stories about the events they encounter during their lives. These narratives are sequential descriptions of people and events that condense numerous experiences into genaralizinf and contrasting stories. NEw experiences are compared to old ones. Simularities are noted in creating generalized rules, and differences are highlighted as memorable exceptions to these rules. The stories are about making sense of the events anf the mental experiences of the characters. Filled with elements of the characters internal experiences in the context of interactios with others in the world, these stories appear to be functioning to create asense of coherent comprehension of the individual in the world across time." DM323 Robbie Rabbit" attachment relationships: feelings and emotions: primary vs secondary emotions "a feeling is a perception of a certain state of the body along with the perception of a certain mode of thinking and of thought with certain themes." LFS 86
Primitive Reflexes and Sensory Systems: The Emergence and Development of The Central Nervous System
Parts of this regular sequence of developmental stages are identified by the movement patterns which occur at each stage. These have been called reflexes. Each reflex is seen to play a part in the necessary growth of the foetus or young child. Each reflex also prepares the way for the next stage of development. Thus in the development of an infant from conception to birth, and on to the toddler stage, there is a sequential occurrence of survival or primitive reflexes. Primitive Reflexes Primitive reflexes are:
Sensory Systems The vestibular system The first sensory system to fully develop by six months after conception is the vestibular system, which controls the sense of movement and balance. This system is the sensory system considered to have the most important influence on the other sensory systems and on the ability to function in everyday life. Directly or indirectly, the vestibular system influences nearly everything we do. It is the unifying system in our brain that modifies and coordinates information received from other systems. The vestibular system functions like a traffic cop, telling each sensation where and when it should go or stop. The sense organs for the vestibular system are located within the inner ear and consist of three semicircular canals, the utricle and saccule (see figure 4). Projections from the vestibular system to other parts of the brain and sensory organs serve as communication channels. One of these projections is the vestibulo-cerebellar projection. Through this connection, the vestibular system influences the autonomic nervous system. This explains why individuals may have problems breathing or may develop nausea or irregular heart rates when the system is overwhelmed. Proprioception Proprioception refers to the brain’s unconscious sense of body-in-space. Essentially we use five systems to determine where our bodies are in relation to their environment and where various parts of our bodies are in relation to one another: 2. The interpretation of messages received by our eyes about both the space and our position and posture 3. The assorted information received by our brain from tactile, kinesthetic and proprioceptive sites located throughout the body 4. The messages received by the brain through smell, a sense on which we unconsciously rely to discern direction and distance from objects and events in our environment 5. The interpretation of the messages we have received through hearing, which also helps us orient to specific objects and events in our environment. If any of these functions are irregular, we either have a diminished sense of body-in-space or place greater reliance on another system (such as vision) to compensate which in turn causes us to use our eyes inefficiently for broader or higher level visual functions. Proprioception differs from kinesthesia in that kinesthesia is the sense of relative muscle, joint and tendon position in specific situations. Kinesthetic memory involves learning these positions and the sequence of shifts in these positions for rote, repeated movements (such as gymnastics). Proprioception is a dynamic sense, allowing continuous accommodations and adaptations to a shifting environment (such as in dance, or moving through a crowded room). . Differentiation Differentiation of response is the inhibition of primitive reflexes and more. It is the ability to direct one part of the body to move according to plan while all other parts remain still. It is the precursor to the development of lateralisation, and helps the brain establish specialised centres. Children with immature differentiation may demonstrate overflow movements. This means that when one part of the body (e.g. a hand) moves, other parts move as well. Immature differentiation also accompanies an apparent weakness in kinesthetic memory (the memory that the muscles have for movement), since overflow movement defocuses the brain’s processing of the intended movement. Such children may not realise that they are kicking, knocking over, or in other ways disturbing people and objects in their environment. They disclaim responsibility for these actions and may be viewed as liars. It is usually evident that there was no malice in their actions. However, after prolonged periods of receiving blame and punishment for these problems, an individual may begin to exhibit the behaviours that his/her peers seem to expect. It becomes easy to see how irregularities in differentiation can cause poor academic learning and also serious social problems. Lateralisation The visual sense The Language of Neurobiology Representation: a pattern of neuronal activation or cluster of neuronal activations, arising in a variety of possible modalities and levels of complexity, that 'represent' specific information about an experience. For example, we have visual representations for shapes and colors, for familiar faces, for abstract symbols such as words. Each sense provides differing representations as can abstract thought. Memory: " The way past events affect future function" DS, DM pg 24 also: the way the mind encodes elements of experience into various forms of representation The Mind, the Nervous System and the Self mindness: " In my view, from its evolutionary inception, mindness is the internalization of movement." RL pg 5 mind: the patterns in the flow of energy and information...emanating from the activity of the neurons of the brain. DS the mind emerges from the substance of the brain as it is shaped by interpersonal relationships...DM 1 My view is that having a mind means that an organism forms neural representations which can become images, be manipulated in a process called thought, and eventually influence behavior by helping predict the future, plan accordingly, and and choos trhe next action." DE 90 (The) self is the centralization of prediction" The self is not born out of the realm of consciousness, only the noticing of it is (i.e., self-awareness). ... Understanding that the brain performs prediction on the basis of an assumed self "entity" will lead us to how the brain generates the mindness state." RL pg 23 "Our notions of selfhood start from the way the brain represents our body image, our physical self-as its implicit main physical axis. This body image represent our soma. Infants soon begin to develop their representations of a implicit psychic self (their psyche) at many covert levels along the framework of thsi physical core. Only from this overconditioned psyche do we look out later into the world, and behave accordingly, for better and for worse." ZBR 24 The pejorative self vs the transformed self: Problem Self: Transformed Self an arrogant I An Actualized i A beseiged ME A buoyant me a clutching Mine A Compassionate mine " the self-other interface"' ZBR 18
olfactory center as beginning of emotional center grows to encompass top of brainstem attunement: orienting response “ The behavior of an animal when it experiences and responds to novelty in its environment” (PL ‘tiger’ pg 93) “ instinctive, coordinated patterns of muscle movement and perceptual awareness”, reacting plus enquiring, what is going on here?, “orienting responses are the primary means through which an animal tunes into its environment. PL, tiger, pg 94 top of brain stem is thalamus: gateway of sensory information with connections to neo-cortex limbic system - limbic region - two powerful tools: learning and memory (DG) no longer just reactive also contains medial temporal lobes including hippocampus which may paly role in comnsious access to memory Neo cortex - thinking, reasoning, more complex information processing hypo-thalamic-pituitary-adrenocortical axis (HPA) “psychotherapy: “ systematic emotional relearning” DG emotional intelligence pg 225
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