Anatomy and Physiology Nervous System PDF

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Nervous Tissue A&P 2401 Ian Lian...

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Anatomy and Physiology 10/30 Chapter 11 Nervous Tissue Nervous system- 3 divisions 1. Central Nervous System (CNS) ● brain and spinal cord ● information processing: integrates, processes, coordinates sensory and motor commands 2. Peripheral nervous system (PNS) all nervous tissue outside CNS, excluding the ENS 3. Enteric nervous system (ENS) ● neural tissues in wall of gastrointestinal tract; helps control digestive function Subdivisions of the peripheral nervous system ● sensory (afferent) division brings information to CNS rom receptors in peripheral tissues and organs ○ Sensory receptors ■ position, touch, pressure, pain, temperature ○ Special sensory organs ■ smell, taste, sight, balance, hearing ● motor (efferent) division caries motor commands from CNS ○ Somatic nervous system (SNS) ■ voluntary nervous system- conscious control of movement ■ to skeletal muscles; conscious control of movement ○ Autonomic nervous system (ANS) ■ involuntary nervous system: automatically regulates activities ■ to smooth muscle, cardiac muscle, glands adipose tissue General functions of the nervous system 1. Receptors detect changes in internal or external environment 2. Information is sent to the CNS by the sensory division of the PNS 3. Information processing (integration and distribution of information) occurs in the CNS 4. Motor commands are carried by the motor division of the PNS 5. Effectors respond to those commands and change their activities Neurons ● Three general regions 1. Dendrites receive stimuli from environment/other neurons 2. Cell body- contains nucleus, other organelles 3. Axon- carries information toward other cells Synapse- where neuron (presynaptic cell) communicates with another cell (postsynaptic cell) ● most common type: neurotransmitter released from presynaptic membrane and synaptic cleft (narrow space between the cells); binds receptors on postsynaptic membrane ● neurotransmitters are packaged in synaptic vesicles in axon terminals Neuron replacement ● most CNS neurons lack centrioles- cannot divide ○ if lost to injury or disease, seldom replaced

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some neural stem cells exist, but most are inactive ○ exceptions ■ olfactory epithelium (smell) ■ retina of the eye (vision) ■ hippocampus (memory)

Neuron function with the CNS and PNS ● Three major functional classes of neurons 1. Sensory neurons 2. Interneurons 3.

Sensory receptors- detect stimuli; are processes of sensory neurons or cells monitored by sensory neurons ● interoceptors ○ monitor internal organs/systems ○ detect distention (stretch), deep pressure, pain ● proprioceptors ○ monitor position/movement of skeletal muscles/joints ● exteroceptors ○ monitor external environment (touch, temperature, pressure, input for special senses) Afferent fibers carry sensory information to CNS ● Ganglion- collection of neuron cell bodies in PNS Sensory neurons- mostly unipolar neurons with cell bodies in sensory ganglion ● somatic sensory neurons: monitor outside world and body position/awareness ● visceral sensory neurons: monitor internal conditions and organ systems Interneurons- located in CNS ● usually between sensory and motor neurons ● receive information from PNS and CNS ● also responsible for higher functions (e.g., memory, learning) Somatic motor neurons innervate skeletal muscles; provide conscious control ● cell body lies in CNS; axon extends within a peripheral nerve (nerve- a bundle of axons in the PNS) Visceral motor neurons- part of the autonomic nervous system (parasympathetic and sympathetic divisions….)...