Human Anatomy Unit 4 NERVOUS SYSTEM: NEURAL TISSUE In Anatomy Today Nervous System Overview • Includes all neural tissue in the body • 2 divisions 1. Central (CNS) – Brain – Spinal Cord 2. Peripheral (PNS) – Cranial nerves – Spinal nerves – Sensory receptors – Communicates between the CNS and peripheral tissues Nervous System Organization Anatomical Terminology of the Nervous System Central Nervous System Peripheral Nervous System • Control center • Ganglia • Nucleus – Collection of nerve cell bodies – Gray matter – Collection of nerve cell bodies • Spinal nerves • Neural cortex – White matter – Superficial gray matter – Emerge from the spinal cord • Tracts – All mixed nerves – White matter • Cranial nerves • Columns – White matter • Pathways – Emerge from the brain – Sensory – Ascending (sensory) – Motor – Descending (motor) – Mixed Anatomical Terminology of the Nervous System Flow of Information Sensory Motor • Carries sensory information • Carries motor commands from peripheral tissues to from the CNS to peripheral the brain tissues (effectors) • Somatic Sensory • Somatic – All sensory receptors – Controls skeletal muscle throughout the body • Autonomic • Special Sensory – Controls cardiac muscle, – Vision smooth muscle, glands – Hearing – 2 divisions – Equilibrium/balance • Sympathetic – Taste – Fight or flight • Parasympathetic – Smell – Rest and digest Nervous Tissue • 2 distinct types of cells 1. Neurons • Transfer and processing information in the nervous system 2. Neuroglia • Cells that support and protect neurons Neurons Neuroglia CNS Glial Cells • Astrocytes – Regulates the microenvironment of neurons – Blood-brain barrier – Structural support – Repairing damaged nervous tissue – Neuron development • Oligodendrocytes – Myelinate CNS axons – Not all nerves in the CNS are myelinated • Microglia – Macrophage of CNS • Ependymal cells – Cerebral spinal fluid (CSF) CNS Glial Cells PNS Glial Cells • Schwann cells – Myelin • All peripheral nerve axons are myelinated – Nodes of Ranvier • Axolemma – Neuron plasma membrane • Neurilemma – Superficial sheath around the myelin and axon • Satellite cells – macrophage Schwann Cells Neural Development and Growth • Stem cells differentiate into neurons or glia (before birth) • Each neuronal daughter cell differentiates and sends out processes that will be axons and dendrites • Growth cone – Forms a tip at the end of an axon – Directs the route and final target for the axon – Guided along glial cells – Synapses become active before maturation • Determines final function • Apoptosis – Programmed cell death – 50-70% of neurons and synapses in developing CNS Neural Regeneration • Severed neurons can be repaired as long as the damage – Occurs outside of the CNS – Does not damage the soma • Slow process – 1mm/day Types of Synapses Structural Classification of Neurons • Anaxonic neuron • PseuDounipolar neuron – Brain – Continuous axon-dendrite – Retina processes – Soma is off to the side • Bipolar neuron – Visceral sensory neurons – – Single dendrite Axons may be myelinated – Centrally located soma between axon and dendrite • Multipolar neuron – Special senses (vision, – Multiple dendrites smell, hearing) – Single axon – Not myelinated – Most common in CNS • Somatic motor neurons • All axons are myleninated Structural Classification of Neurons Sensory Neurons • Afferent division of PNS • Somatic sensory neurons – Deliver info to CNS • Outside world • Our position in it • Joint position • Tension in muscles • State of homeostasis – Mostly pseudounipolar neurons • Special sensory neurons - Outside world Sensory Receptors • Exteroreceptor – External environment – Touch – Temperature – Pressure – Special senses (vision, hearing, olfaction) • Proprioceptor – Position of joints • Interoreceptor – Monitor internal environment to maintain homeostasis – Sensations of deep pressure – Pain – Taste Motor Neurons • Efferent division of PNS • Mostly multipolar neurons • Stimulates or modifies the activity of effectors – Muscle, glands • Somatic motor • Skeletal muscle • Autonomic nervous system (visceral motor) • Cardiac muscle, smooth muscle, glands Interneurons • Connect neurons within the CNS – Sensory - -> Sensory – Motor - - > Motor – Sensory - - > Motor • Analysis of sensory inputs • Coordination of motor outputs • Receive, process, integrate information coming “down” towards peripheral effectors Somatic Motor Neurons • Innervate skeletal muscles • Soma within CNS (brain or spinal cord) • Axons extend to neuromuscular junction – 1 neuron system • Most activities are consciously controlled Autonomic Motor Neurons • Visceral motor neurons (carDiac muscle, smooth muscles, glanDs) • 2 neuron system – Preganglionic neuron • Soma in the brain or spinal cord • Synapses with neurons in peripheral ganglia – Postganglionic neuron • Soma in a peripheral ganglia • Synapses with peripheral effectors – 2 divisions of the ANS • Sympathetic – Fight or Flight • Parasympathetic – Rest and Repose The Synapse • Communication from a neuron to an effector • A nerve impulse triggers events that transfers information • Chemical synapse – Chemical messenger triggers a cellular response – Neurotransmitter released from presynaptic membrane – Binds to receptors on postsynaptic membrane • Electrical – Gap junctions – Nerve impulse travels from one cell to another The Structure of a Synapse Flow of Information.