Shabba Essays - Peripheral Nervous System, Sensory Systems

Shabba Chapter 12 Neural Tissue An Introduction to the Nervous System The Nervous System Includes all neural tissue in the body Neural tissue contains two kinds of cells 1.Neurons Cells that send and receive signals 2.Neuroglia (glial cells) Cells that support and protect neurons Organs of the Nervous System Brain and spinal cord Sensory receptors of sense organs (eyes, ears, etc.) Nerves connect nervous system with other systems 12-1 Divisions of the Nervous System Anatomical Divisions of the Nervous System Central nervous system (CNS) Peripheral nervous system (PNS) The Central Nervous System (CNS) Consists of the spinal cord and brain Contains neural tissue, connective tissues, and blood vessels Functions of the CNS are to process and coordinate: Sensory data from inside and outside body Motor commands control activities of peripheral organs (e.g., skeletal muscles) Higher functions of brain intelligence, memory, learning, emotion The Peripheral Nervous System (PNS) Includes all neural tissue outside the CNS Functions of the PNS Deliver sensory information to the CNS Carry motor commands to peripheral tissues and systems Nerves (also called peripheral nerves) Bundles of axons with connective tissues and blood vessels Carry sensory information and motor commands in PNS Cranial nerves connect to brain Spinal nerves attach to spinal cord Functional Divisions of the PNS Afferent division Carries sensory information From PNS sensory receptors to CNS Efferent division Carries motor commands From CNS to PNS muscles and glands Receptors and effectors of afferent division Receptors Detect changes or respond to stimuli Neurons and specialized cells Complex sensory organs (e.g., eyes, ears) Effectors Respond to efferent signals Cells and organs The efferent division Somatic nervous system (SNS) Controls voluntary and involuntary (reflexes) muscle skeletal contractions The efferent division Autonomic nervous system (ANS) Controls subconscious actions, contractions of smooth muscle and cardiac muscle, and glandular secretions Sympathetic division has a stimulating effect Parasympathetic division has a relaxing effect 12-2 Neurons Neurons The basic functional units of the nervous system The structure of neurons The multipolar neuron Common in the CNS Cell body (soma) Short, branched dendrites Long, single axon The Cell Body Large nucleus and nucleolus Perikaryon (cytoplasm) Mitochondria (produce energy) RER and ribosomes (produce neurotransmitters) Cytoskeleton Neurofilaments and neurotubules in place of microfilaments and microtubules Neurofibrils: bundles of neurofilaments that provide support for dendrites and axon Nissl bodies Dense areas of RER and ribosomes Make neural tissue appear gray (gray matter) Dendrites Highly branched Dendritic spines Many fine processes Receive information from other neurons 8090% of neuron surface area The axon Is long Carries electrical signal (action potential) to target Axon structure is critical to function Structures of the Axon Axoplasm Cytoplasm of axon Contains neurofibrils, neurotubules, enzymes, organelles Axolemma Specialized cell membrane Covers the axoplasm Axon hillock Thick section of cell body Attaches to initial segment Initial segment Attaches to axon hillock Collaterals Branches of a single axon Telodendria Fine extensions of distal axon Synaptic terminals Tips of telodendria The Structure of Neurons The synapse Area where a neuron communicates with another cell Presynaptic cell Neuron that sends message Postsynaptic cell Cell that receives message The synaptic cleft The small gap that separates the presynaptic membrane and the postsynaptic membrane The synaptic terminal Is expanded area of axon of presynaptic neuron Contains synaptic vesicles of neurotransmitters Neurotransmitters Are chemical messengers Are released at presynaptic membrane Affect receptors of postsynaptic membrane Are broken down by enzymes Are reassembled at synaptic terminal Recycling Neurotransmitters Axoplasmic transport Neurotubules within the axon Transport raw materials Between cell body and synaptic terminal Powered by mitochondria, kinesin, and dynein Types of Synapses Neuromuscular junction Synapse between neuron and muscle Neuroglandular junction Synapse between neuron and gland Structural Classification of Neurons Anaxonic neurons Found in brain and sense organs Bipolar neurons Found in special sensory organs (sight, smell, hearing) Unipolar neurons Found in sensory neurons of PNS Multipolar neurons Common in the CNS Include all skeletal muscle motor neurons Anaxonic Neurons Small All cell processes look alike Bipolar Neurons Are small One dendrite, one axon Unipolar Neurons Also called pseudounipolar neurons Have very long axons Fused dendrites and axon Cell body to one side Multipolar Neurons Have very long axons Multiple dendrites, one axon Three Functional Classifications of Neurons 1.Sensory neurons Afferent neurons of PNS 2.Motor neurons Efferent neurons of PNS 3.Interneurons Association neurons Functions of Sensory Neurons Monitor internal environment (visceral sensory neurons) Monitor effects of external environment (somatic sensory neurons) Structures of Sensory Neurons Unipolar Cell bodies grouped in sensory ganglia Processes (afferent fibers) extend from sensory receptors to CNS Three Types of Sensory Receptors 1.Interoceptors Monitor internal systems (digestive, respiratory, cardiovascular, urinary, reproductive) Internal senses (taste, deep pressure, pain) 2.Exteroceptors External senses (touch, temperature, pressure) Distance senses (sight, smell, hearing) 3.Proprioceptors Monitor position and movement (skeletal muscles and joints) Motor Neurons Carry instructions from CNS to peripheral effectors Via efferent fibers (axons) Two major efferent systems 1.Somatic nervous system (SNS) Includes all somatic motor neurons that innervate skeletal muscles 2.Autonomic (visceral) nervous system (ANS) Visceral motor neurons innervate all other peripheral effectors Smooth muscle, cardiac muscle, glands, adipose tissue Two groups of efferent axons Signals from CNS motor neurons to visceral effectors pass synapses at autonomic ganglia dividing axons into: Preganglionic