Neural Tissue-2

Neural Tissue Chapter 12 Functions of the nervous system Monitor the internal and external environment. Integrates sensory information. Coordinates voluntary and involuntary responses of other organ systems. Two anatomical divisions of the nervous system Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Communicates with the rest of the body via Afferent (sensory info. from body to CNS) Efferent (motor info. from CNS to muscles and glands)   Meet the neuron Cell body The cell body contains the nucleus and other organelles important for cell function. Most neurons do not contain centrioles so what can it not do?   Nucleus The nucleus contains DNA and RNA for protein synthesis.   Nucleolus The nucleolus is the site of RNA synthesis.   Nissl bodies Nissl bodies are clusters of rough ER and ribosomes and account for the color of gray matter. What is synthesized here?   Axon hillock Axon hillock is the area where an action potential begins.   Axon Axon is the extension of a neuron that conducts an action potential.   Synaptic terminals The synaptic terminals are where the neuron communicates with other cells.   Dendrite Dendrites receive incoming sensory signals from other cells.   Collateral A collateral is a branch off of the axon that will ultimately end in synaptic terminals. Three Structural Classes of Neurons Multipolar Most common (several dendrites, one axon) Example; motor neurons for skeletal muscle The longest carry motor commands from the spinal cord to the muscles of the toes Unipolar Dendrites and axons not separated by the cell body Example; most sensory neurons of peripheral system The longest carry sensations from the toes to the spinal cord Bipolar One dendrite, one axon separated by cell body Example; special sense organs Three functional classes of neurons. Sensory Neurons (afferent) Motor Neurons (efferent) Interneurons Sensory Neurons Afferent division carrying information from both the internal and external environment to the CNS. They connect a sensory receptor to the CNS (ex: pin prick hits pain receptor in skin and travels via sensory neurons to the spinal cord where signal is received). There are different types of receptors that allow us to be in complete “touch” with our environment, ourselves and our relative position. Somatic sensory neurons monitor external environment and proprioception Visceral sensory neurons monitor internal environment Motor Neurons Efferent division carrying instructions from the CNS to the rest of the body. The peripheral targets (the area of the body that is to react) are called effectors . (The spinal cord forms a reaction to the pain from the pin prick and causes skeletal muscle to move the hand away.) The efferent division of the PNS has two types motor neurons targeting different effectors. Somatic motor neurons (voluntary nervous system) = skeletal muscle Visceral motor neurons (autonomic nervous system) = involuntary actions like cardiac muscle, smooth muscle and glands. Interneurons Located within the brain and spinal cord. Sit between sensory and motor neurons. Function as connections between neurons of the CNS. They are responsible for distributing sensory information and coordinating motor activity. CNS Anatomy Chapter 13 Meninges are specialized membranes surrounding the brain and spinal cord. The meninges provide shock absorption, stability and a nutrient supply to the structures of the CNS. There are three meningeal layers. Dura mater = outermost tough layer Arachnoid = middle layer to reduce friction Pia mater = innermost layer containing blood vessels The spinal cord Main area for the passage of sensory impulses to the brain and motor impulses from the brain. Also controls spinal reflexes which are automatic motor responses. Ends @ cauda equina between L1 & L2 Has two enlargements which provide sensory & motor control of the limbs. Cervical enlargement = shoulders and upper limbs Lumbar enlargement = pelvis and lower limbs Central canal, anterior median fissure and posterior median sulcus Dorsal root ganglia contain the cell bodies of sensory neurons and the dorsal root contains their axons. So what do they do? Ventral roots contain the axons of motor neurons. So what do they do? Distal to each dorsal root ganglion, the dorsal and ventral roots are bound together in a single spinal nerve. Spinal nerves are called mixed nerves because they are both sensory and motor. Gray matter is mainly composed of cell bodies of neurons. Projections of gray matter are called horns. The posterior gray horns contain sensory nuclei. The anterior gray horns deal with the motor control of skeletal muscles. The lateral gray horns contain visceral motor neurons to control smooth muscle, cardiac muscle and glands. White matter is mainly composed of myelinated and unmyelinated axons. The color comes from the myelinated axons. White matter is divided into sections or regions called white columns. The posterior, anterior and lateral white columns contain axons which carry either sensory or motor information.