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2: The Brain and Nervous System Cognitive Neuroscience David Eagleman Jonathan Downar Chapter Outline An Overview of the Nervous System The Peripheral Nervous System The Spinal Cord The Brainstem The Cerebellum The Diencephalon The Telencephalon Uniting the Inside and Outside Worlds 2 An Overview of the Nervous System Why Put Your Neurons in a Brain At All? The Common Features of Every Central Nervous System Getting Oriented in the Brain 3 Why Put Your Neurons in a Brain At All? The nervous system is made of the brain, spinal cord, and peripheral nerves. Bilateral symmetry provides several survival advantages. For animals with bilateral symmetry, a centrally-located nervous system is more efficient. 4 The Common Features of Every Central Nervous System Precursors of neurons evolved about 600 million years ago. Neuronal circuits first appeared about 500 – 550 million years ago. Similar genes and proteins are used in many animals to guide the development of the nervous system. 5 The Common Features of Every Central Nervous System 6 The Common Features of Every Central Nervous System Central nervous system interacts with the rest of the body via the peripheral nervous system. The brain develops from three bulges Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain) These bulges subdivide to form the adult brain. 7 The Common Features of Every Central Nervous System 8 The Common Features of Every Central Nervous System All neurons connect to and interact with other neurons. The function of the neuron within the nervous system depends on the connections to that neuron. The functions and structure of the brain have been shaped by evolution. 9 Getting Oriented in the Brain There are specialized terms for directions within the nervous system – Caudal: Nose – tail axis Dorsal – Ventral: Back – belly axis Anterior – Posterior: Front – back axis Superior – Inferior: Top – bottom axis Rostral 10 Getting Oriented in the Brain Medial: Towards the middle Lateral: Towards the side Ipsilateral: On the same side Contralateral: On the opposite side Distal: Far end of the limb Proximal: Nearest point of the limb, where it attaches to the body 11 Getting Oriented in the Brain 12 Getting Oriented in the Brain Three common planes are used to describe images of the brain. Axial: A horizontal slice, parallel to the floor when standing up, from the front to the back of the brain. Sagittal: A vertical slice through the brain, separating the left side from the right side. Frontal (Coronal): A vertical slice, separating the front from the back of the brain. 13 Getting Oriented in the Brain 14 The Peripheral Nervous System Separate Systems for the Inner and Outer Environments A Nervous System with Segmental Organization 15 Separate Systems for the Inner and Outer Environments Sensory neurons collect information from outside and inside the body. Motor neurons carry signals to the muscles to enable movement. Neurotransmitters are specialized chemicals released by neurons to communicate with other cells. 16 Separate Systems for the Inner and Outer Environments 17 Separate Systems for the Inner and Outer Environments Peripheral nervous system has two parts Somatic nervous system Deals with external world. Sensory and motor neurons carry information about voluntary movement and conscious awareness. Autonomic nervous system Deals with internal world. Sensory and motor neurons guide automatic processes. 18 Separate Systems for the Inner and Outer Environments Autonomic nervous system is divided into two components. Sympathetic branch Gets the body ready to react to threats. Increases heart and respiration rates and increases blood pressure. Parasympathetic branch Calms the body down. Slows heart and respiration rate and increased digestion. 19 Separate Systems for the Inner and Outer Environments 20 A Nervous System with Segmental Organization The spine is divided into four segments Cervical Thoracic Lumbar Sacral Peripheral nerve roots emerge from between the vertebrae on both sides of the spine and project out to the body. 21 A Nervous System with Segmental Organization 22 A Nervous System with Segmental Organization Sensory input and motor output are separated close to the spinal cord. Each peripheral nerve relates to a particular part of the body, known as a dermatome. 23 A Nervous System with Segmental Organization 24 The Spinal Cord Circuits within a Segment: Spinal Reflexes Complex Circuits across Segments: Central Pattern Generators 25 Spinal Reflexes The spinal cord is divided into gray matter and white matter. The gray matter contains the cell bodies and dendrites of the neurons and is found near the center of the cord. The white matter contains the electricallyinsulated long distance connections between neurons. 26 Spinal Reflexes 27 Spinal Reflexes The spinal cord is divided into laminae, with sensory input occurring on the dorsal side and motor output occurring from the dorsal side. The dorsal root ganglia house the cell bodies for the peripheral sensory neurons. 28 Spinal Reflexes 29 Spinal Reflexes In a reflex arc, a sensory neuron connects with a motor neuron, allowing the sensory stimulation to trigger a movement. The knee-jerk reflex, where you extend your leg after the doctor taps your knee with a hammer, is an example of this. 30 Spinal Reflexes 31 Spinal Reflexes Reflexes can have one or more connections (synapses) between the sensation and the motor response. Interneurons are neurons that are between the sensory input and the motor output. Interneurons can be excitatory or inhibitory. 32 Central Pattern Generators More complex actions, such as walking, are build from more simple spinal reflexes. Central pattern generators are functional units of cells that guide these rhythmic actions. 33 Central Pattern Generators An excitatory neuron fires spontaneously, until becoming fatigued and stopped by an inhibitory interneuron. After a recovery time, the excitatory neuron resumes firing. Inhibitory interneurons cross the midline to inhibit the central pattern generator on the contralateral side, to allow for rhythmic muscle contractions. 34 Central Pattern Generators 35 The Brainstem Medulla Oblongata and Pons Midbrain Most Cranial Nerves Emerge from the Brainstem 36 Medulla Oblongata and Pons The hindbrain is formed by the medulla oblongata and the pons. The medulla controls involuntary functions that are important for life, such as breathing and heart rate. The pons relays information between the cerebrum and the cerebellum. Cells within the pons are important for sleep, arousal, and sensory functions. 37 Medulla Oblongata and Pons 38 Medulla Oblongata and Pons Clusters of cells, called nuclei, process sensory, motor, and visceral information. Circuits in the hindbrain are central pattern generators for swallowing, yawning, coughing, breathing, etc. 39 Midbrain The superior colliculus locates visual stimuli to help coordinate complex movements. The inferior colliculus locates auditory stimuli. Command generators influence activity of central pattern generators in brain stem and spinal cord. 40 Midbrain Periaqueductal gray matter influences complex behaviors such as defense, aggression, or reproduction. Reticular formation regulates consciousness. Locus coeruleus alerts the brain. Substantia nigra influences motor control and cognition. 41 Midbrain 42 Most Cranial Nerves Emerge from the Brainstem Twelve pairs of cranial nerves transmit sensory and motor information between the brain and face. 43 Most Cranial Nerves Emerge from the Brainstem 44 The Cerebellum Circuitry of the “Little Brain” Functions of the Little Brain 45 Circuitry of the “Little Brain” The cerebellum contains more neurons than does the cortex. Neurons are densely packed into folia, which are packed into lobules. Inputs come from brainstem nuclei. 46 Circuitry of the “Little Brain” 47 Functions of the Little Brain Damage to cerebellum interferes with coordinated movement to external targets. Cerebellum may make predictions about expected outcomes of motor actions and use these predictions to refine plans. Cerebellum is also important in language, memory, attention, and emotion. 48 The Diencephalon Hypothalamus: A Keystone Structure in Homeostasis Thalamus 49 Hypothalamus: A Keystone Structure in Homeostasis Homeostasis is the process of maintaining the body within a narrow range of physiological parameters, such as temperature, thirst, hunger, etc. Hypothalamus is important for homeostasis. Nuclei within the hypothalamus regulate homeostasis by comparing the body’s state with set points. 50 Hypothalamus: A Keystone Structure in Homeostasis 51 Hypothalamus: A Keystone Structure in Homeostasis If the body deviates from the set point, compensation can happen via autonomic responses, endocrine responses, or behavioral responses. Hypothalamus releases hormones via the pituitary gland to influence cells throughout the body. 52 Hypothalamus: A Keystone Structure in Homeostasis 53 Thalamus The thalamus relays sensory signals to the brain and motor signals to the body. More than 50 thalamic nuclei serve sensory, motor, motivational, and associational functions through reciprocal connections with the cortex. 54 Thalamus 55 Thalamus 56 The Telencephalon Cerebral Cortex Basal Ganglia 57 Cerebral Cortex The cortex is the thin outer covering of the brain that is necessary for human cognition. The cortex contains six layers of cells, known as gray matter, surrounding the inner white matter. 58 Cerebral Cortex Surface features of the cortex Gyri (singular: gyrus): The rounded convolutions of the cortex. Sulci (singular: sulcus): The grooves between the gyri. There are two hemispheres connected by the corpus callosum. Each hemisphere has four lobes 59 Cerebral Cortex 60 Cerebral Cortex 61 Cerebral Cortex 62 Cerebral Cortex Frontal Lobe Important for motor control and planning. Parietal Lobe Important for processing somatosensory information. Occipital Lobe Processes visual information. Temporal Lobe Processes auditory information. 63 Basal Ganglia Gray matter structures within the white matter of the cortex. Important for initiating and maintaining activity in the cortex, particularly in motor areas. 64 Basal Ganglia Made up of the caudate and putamen, known together as the striatum, and the globus pallidus. Nearby structures, including the subthalamic nucleus and the substantia nigra, are functionally connected to the basal ganglia. 65 Basal Ganglia 66 Uniting the Inside and Outside Worlds The Limbic System The Ventricular System and Brain Function 67 The Limbic System Combines sensory inputs from external and internal environments to help control the internal environment. Hypothalamus and limbic nuclei of thalamus project to the limbic system. Amygdala is important for emotional evaluation and learning. Hippocampus is also important for learning and memory. 68 The Limbic System 69 The Limbic System 70 The Ventricular System and Brain Function Four spaces filled with cerebrospinal fluid can be found at the center of the brain. Known as the lateral ventricles, the third ventricle, and the fourth ventricle. 71 The Ventricular System and Brain Function 72 The Four-Sided Brain 73