Name________________________________Block_____Date______________________ Ch 7 The Nervous System Notes Lisa Peck I. Organization of the Nervous System (pp 222-224) Nervous system- the master controlling and communicating system of the body 3 functions: 1. sensory receptors to monitor changes occurring inside & outside body stimuli- changes sensory input- gathered information 2. processes and interprets the sensory input integration- nervous system makes decisions about what should be done 3. effects a response by activating muscles or glands (effectors) via motor output Regulating and Maintaining Homeostasis nervous system - fast-acting control via electrical impulses endocrine system- slow-acting control via hormones release into the blood Structural Classification (p 223) 2 subdivisions: Central Nervous System Peripheral Nervous System 1. Central Nervous System (CNS) consists of: brain spinal cord functions: integrating center.........interpret incoming sensory information command center..........issue instructions based on past experience & current conditions 2. Peripheral Nervous System (PNS) consists of: nerves 2 types: cranial nerves- carry impulses to and from the brain spinal nerves- carry impulses to and from the spinal cord ganglia- groups of nerve cell bodies function: communication lines, linking all parts of the body Functional Classification (pp 223-224) 2 only deals with peripheral nervous system (PNS) 1. Sensory (Afferent) Division- nerve fibers that carry impulses to the CNS from sensory receptors located throughout body sensory fibers types: 1. somatic sensory fibers- delivering impulses from the skin, skeletal muscles, & joints 2. visceral sensory fibers- transmitting impulses from the visceral organs 2. Motor (Efferent) Division- nerve fibers that carry impulses from the CNS to effector organs ossicles and glands, bringing about a motor response 2 types: 1. somatic nervous system: conscious control of skeletal muscles voluntary control skeletal muscles 2. autonomic nervous system (ANS)- regulates activities that are automatic involuntary cardiac muscle smooth muscle glands 2 nerve types that target same organ but yield opp. effects exception: targeted only by sympathetic: some glands, most blood vessels, most structures of the skin 2 types: 1. sympathetic-” fight or flight” f’ns during extreme situations ex: increase heart rate rapid breathing cold, sweaty skin dilated pupils 2. parasympathetic- “resting & digesting” most active when body at rest causing normal digestion, voiding feces & urine goal: conserving energy Nervous Tissue: Structure and function (pp 224-235) 3 2 types of cells: 1. neuroglia- supporting cells not able to conduct impulses can undergo cell division most brain tumors are gliomas- formed by glial cells 2. neurons nerve cells that transmit impulses functional unit of nervous system neurglia (pp 224-226) not able to conduct impulse glia (glial cells)- f’n: support, insulation, & protection ~90% cells in brain are glial cells CNS: 4 types: astrocytes PNS: 2 types microglia schwann cells ependymal satellite cells oligodendrocytes 1. Astrocytes- star-shaped cells account for over half of neural tissue numerous projections have swollen ends that cling to neurons f’n: 1. brace and anchor neurons to capillaries intermediary cell b/w neuron and capillary (aids in exchange) protects neurons from harmful substances present in blood 2. control chemical environment in brain by picking up excess ions & recapturing released neurotransmitters neurglia 4 2. Microglia- spiderlike phagocytes dispose of debris (dead brain cells & bacteria) smallest of glial cells 3. Ependymal- line cavities of the brain & spinal cord f’n- beating of cilia helps circulate cerebrospinal fluid that fills cavities & forms protective cushion around CNS 4. Oligodendrocytes- (CNS) wrap their flat extensions around axons of many nerves forms myelin sheath- fatty insulating covering protects and cushions nerves speeds up nerve transmission speed gives rise to white matter of brain fewer extensions than astrocytes PNS: 2 types: 1. Schwann cells- cells of PNS that myelinate axons 2. satellite cells- protective & cushioning cells of PNS neurons B. Neurons (pp 226-235) 5 1. Anatomy (of a generalized neuron) cell body- metabolic center contains typical cell organelles (exception: no centrioles .....no mitosis -amitotic) axon- one per cell, process of neuron conduct impulses away from the cell body dendrites- many per cell, extension of neuron (often branched extensively) conduct impulses toward cell body axon hillock- axon arises form this conelike region of cell body axon terminals- 100’s to 1000’s branches at terminal end of axon contain vessicles of neurotransmitters collateral branch- branch off of an axon Nerve Anatomy 6 synaptic cleft (synapse)- separation b/w axon terminal and next neuron myelin- covering of most long neurons (axon) whitish, fatty substance protects, insulates, speeds up neural transmission CNS: oligodendrocytes- form myelin sheath lacks neurolemma f’n- protects and cushions nerve increases speed of nerve transmission located in CNS PNS: schwann cell’s form myelin sheath covering of most long neurons formed by wrapping of a Schwann cell schwann cell- specialized supportive cells wrap tightly around axon neurolemma- outermost part of schwann cell aids in neuron regeneration nodes of Ranvier- gaps of myelin sheath b/ w Schwann cells loc. @ regular intervals action potential jumps from node to node- faster CNS white matter- dense bundles of myelinated fibers (tracts) brain- inside spinal cord- surface gray matter- unmyelinated fibers and cell bodies brain- surface spinal cord- inside CNS PNS nuclei ganglia groups of cell bodies tracts nerves bundles of nerve fibers Classification of Neurons 7 functional classification- according to direction of impulse is traveling relative to CNS 1. sensory neuron- nerve impulse travels towards CNS afferent cell bodies outside CNS in ganglion receptors- dendrite endings that are specialized activated by specific changes nearby (stimuli) taste, hearing, sight, equilibrium, smell cutaneous sense organs- pacinian & meissner corpuscles proprioceptors- loc. in muscles & tendons detects amt. of stretch or tension determines location, posture, and tone muscle spindle golgi tendon organs pain receptors- bare dendrite endings least specialized cutaneous receptor most numerous cutaneous receptor 2. motor neuron- nerve impulse travels away from CNS efferent neuron cell bodies inside CNS in nuclei 3. association neurons (interneurons)- connect motor and sensory neurons cell bodies in CNS Classification of Neurons 8 structural classification- based on number of processes extending from cell body multipolar- several processes all motor neurons all association neurons most common neuron type bipolar- 2 process on cell body axon & dendrite rare in adults (eg; eye & nose) unipolar- one process on cell body single process is very short process divides into 2 peripheral process- (distal) contains dendrites on end central process- (proximal) contains axon terminals axon- both peripheral & central processes conducts impulses in both directions (toward & away from cell body) sensory neurons located in PNS ganglia are all unipolar 3. Physiology nerve impulse generation (action potential) reflex arcs- neural pathways involve both CNS & PNS reflexes- rapid, predictable and involuntary responses to stimuli once reflex begins...always goes in same direction types: somatic reflexes- stimulate the skeletal muscles eg: pull hand away from hot stove autonomic reflexes- regulate the activity of smooth muscles, heart, & glands eg: secretion of saliva, changes in pupil size, regulates: digestion, elimination, blood pressure, & sweating III. Central Nervous system (pp 235-249) 9 Functional Anatomy of the Brain (pp 235-241) 10 Brain- 3 parts 1. forebrain- cerebrum diencephalon- thalamus hypothalamus 2. midbrain- small superior part of brain stem 3. hindbrain- cerebellum brain stem (part of it)- medulla oblongata pons Forebrain 2 parts: 1. cerebrum (cerebral hemispheres) 2. diencephalon Cerebrum: largest part of brain divided into left and right hemispheres-cerebral hemispheres separated by corpus callosum (internally)- large fiber tract connecting hemispheres longitudinal fissure (surface) the spinal tracts cross over -------> left hemisphere deals w/ right side of body right hemisphere deals w/ left side of body surface is highly convoluted- increasing surface area (increases # of neurons) cortex- (exterior) gray matter thin surface layer (1-4 mm thick) Interior- white matter, nerve tract relaying impulses to & from cerebral cortex gyrus (gyri)- elevated ridges on cerebral cortex sulcus (sulci)- shallow grooves in cortex fissure- deep sulcus in cortex sulci divide hemispheres into 4 lobes separate large areas of brain frontal lobe parietal lobe occipital lobe temporal lobe Functional Anatomy of the Brain (pp 235-241) 11 Forebrain Cerebrum- cerebral cortex: 4 lobes f’n- speech, memory, logical & emotional response, consciousness, interpretation of sensation, voluntary movement, problem solving frontal lobe primary motor area- located anterior to central sulcus initiates voluntary movement of skeletal muscles (motor language too) premotor area- located anterior to primary motor area process input regarding body movement, modify movements prefrontal area- anterior frontal lobe higher level thought, decision making, planning, impulsivity control selective attention, personality, problem solving, behavior, emotions