Organization of the NERVOUS System Notes Time! Organization of the NERVOUS System 3-28-12

Nervous System 3 Basic Functions: SENSORY Functions: detect stimuli both within and outside of the body. Nerve cells which carry sensory information are called afferent neurons INTEGRATIVE Functions: analyze info and determine the appropriate response. Nerve cells which carry out this function are called interneurons or association neurons MOTOR Functions: respond to output from interneurons. Nerve cells which carry out this function are called efferent neurons 2

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Nervous System Two main subsystems: CENTRAL NERVOUS SYSTEM (CNS) Brain & spinal cord PERIPHERAL NERVOUS SYSTEM (PNS) All other nervous tissue that is further subdivided: Somatic nervous system (SNS): motor neurons carry info from CNS to skeletal muscles; axons are well myelinated and conduct impulses rapidly Enteric nervous system (ENS): “brain of the gut”: control contraction of smooth muscle in GI tract Autonomic nervous system (ANS): motor neurons carry info from CNS to smooth & cardiac muscle 4

Components of AUTONOMIC NERVOUS SYSTEM: Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons MYELIN: an insulating lipid and protein covering produced by Schwann cells in PNS and Oligodendrocytes (Greek for cells with few branches) in CNS

GANGLION: group of nerve cell bodies located outside of the CNS Tract: bundle of nerve cells inside the CNS

Two divisions of AUTONOMIC NERVOUS SYSTEM: SYMPATHETIC and PARASYMPATHETIC These two divisions typically work in opposition to one another Ex: the sympathetic nervous system would increase heart rate in times of stress, and the parasympathetic nervous system would decrease it 8

fight-or-flight response Pupils dilate Heart rate increases SYMPATHETIC activities include body reactions in time of physical or emotional stress fight-or-flight response Pupils dilate Heart rate increases Airways dilate Blood is routed away from non-essential organs Greater blood flow to skeletal muscle Non-essential processes are inhibited (digestion) 9

PARASYMPATHETIC activities include normal body functioning “rest and digest” functions “SLUDD”: Salivation Lacrimation (tear production) Urination Digestion Defecation 10

Anatomical Differences in Sympathetic and Parasympathetic Divisions Arise from different regions of the CNS Sympathetic – also called the thoracolumbar division Parasympathetic – also called the craniosacral division

Anatomical Differences in Sympathetic and Parasympathetic Divisions Length of postganglionic fibers Sympathetic – long postganglionic fibers Parasympathetic – short postganglionic fibers Branching of axons Sympathetic axons – highly branched Influences many organs Parasympathetic axons – few branches Localized effect

Nervous Tissue Two cells types NEURONS: nerve cells Amitotic- do not divide Responsible for releasing neurotransmitters and conducting nerve impulses 13

Nervous Tissue three parts of a NEURON cell body: contains nucleus surrounded by cytoplasm with cellular organelles dendrites: receiving portion of the neuron. Short and highly branched, arising from the cell body axon: conducts nerve impulses towards another neuron, muscle cell or gland cell. Long and thin 14

Nervous Tissue Neuroglia: 2nd nervous system cell type support and protect neurons Much smaller than neurons, but 5-50 times more numerous Able to divide 15

Neuron Function – Nerve Impulses Some new, some review physiology information in WINGERD questions (#’s 48 – 72) Pages 245 – 251 Wingerd text Pages 222 – 227 your Tortora Text

Spinal Reflexes SPINAL REFLEXES fast, automatic responses to sensory impulses Autonomic reflexes: involving smooth muscle, cardiac muscle, glands ex: swallowing Somatic reflexes: (somatic means body) involve skeletal muscles ex: patellar reflex (knee jerk) 17

Spinal Reflexes The pathway followed by nerve impulses producing reflexes is called the REFLEX ARC: 18

COMPONENTS OF REFLEX ARC: Receptor: the distal end of the sensory neuron that responds to a stimulus and generates nerve impulse(s) Sensory (afferent) neuron: conduct impulse from sensory receptor to the axon terminals Integrating center: within the spinal cord: synapse between sensory & motor neuron; interneuron/association neuron Motor (efferent) neuron: carries impulse triggered by integrating center out of the spinal cord and to body Effector: part of the body responding to the motor nerve impulse; action of the effector is called the reflex 19