Collin County Community College BIOL Week 5. Nervous System. Nervous System

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1 Collin County Community College BIOL 2401 Week 5 Nervous System 1 Nervous System The process of homeostasis makes sure that the activities that occur in the body are maintained within normal physiological limits. In addition, our body constantly reacts to a multitude of signals, be it external or internal signals. Two body systems are responsible for dealing with these signals and controlling the state of homeostasis Endocrine system : releases hormones into the blood stream, with a slow action response Nervous system : communicates by means of electrical signals, resulting in an immediate response 2 1

2 Nervous System The nervous system has 3 overlapping functions: Sensory : uses sensory receptors to detect internal and external changes (stimuli) Integrative : analyzes the sensory information, stores it and makes decision Motor : responds to stimuli by initiating muscular contractions or glandular secretions The branch of Neurology is the study of the normal and disordered nervous system 3 Organization of the Nervous System The Central Nervous system (CNS) consists out of the Brain and Spinal Cord (integrating and command center ) it is connected to the sensory receptors, muscles and glands in the Peripheral Nervous system The Peripheral Nervous system (PNS) consists out of cranial ( arise from the brain) and spinal ( originate from the spinal cord) nerves they carry impulses in and out of the CNS 4 2

3 The Peripheral Nervous system The Sensory division the input component ( from sensory receptors to the CNS) contain the afferent nerves somatic afferent part : input from skin, skeletal muscle and joints visceral afferent part: input from the organs and glands The Motor division the output component ( from CNS to the muscles, glands) contain the efferent nerves 5 The Motor division The motor division of the PNS has an additional two functional subdivisions The Somatic (motor)nervous system also called the voluntary nervous system composed of somatic motor nerve fibers that conduct impulses from CNS to skeletal muscles The Autonomic Nervous System also called involuntary nervous system consist of visceral motor nerve fibers that regulate the activities of smooth muscles, cardiac muscles and glands 6 3

4 The Autonomic Nervous System The Autonomic Nervous System Sympathetic : usually involves expenditure of body energy, stimulates fight or flight response Parasympathetic : restores and conserves body energy, slows down or inhibits referred to as the rest and digest 7 Nervous system Sensory Division Afferent or Sensory Nerves Central NS Efferent or Motor Nerves Motor Division Somatic Division Visceral Division Somatic Division Autonomic Division Peripheral NS = Sensory and Motor Division and corresponding nerves Sympathetic Parasympathetic 8 4

5 Nervous system 9 Nervous system Organization of the Nervous System Central Nervous System (CNS) (brain and spinal cord) Integrate, process, and coordinate sensory data and motor commands Peripheral Nervous System (PNS) (neural tissue outside the CNS) Sensory information within afferent division Motor commands within efferent division includes Somatic nervous system (SNS) Autonomic nervous system (ANS) Parasympathetic division Sympathetic division Receptors Special sensory receptors monitor smell, taste, vision, balance, and hearing Visceral sensory receptors monitor internal organs Somatic sensory receptors monitor skeletal muscles, joints, and skin surface Effectors Skeletal muscle Smooth muscle Cardiac muscle Glands Adipose tissue 10 5

6 Histology of the Nervous System Nervous tissue is made up of two principle types of cells Neurons : the excitable nerve cells that conduct the electrical signals Supporting cells: support, nurture and protect the neurons (also called Neuroglial cells) 11 Neurons Anatomy s: undergo action potentials to deliver information, typically neurotransmitters, from the axon terminals. Dendrites: receive information (the neurotransmitters) 12 6

7 Figure 12-2a The Anatomy of a Multipolar Neuron. Neuron Anatomy Dendrites Perikaryon Nucleus Cell body or Soma Telodendria This color-coded figure shows the four general regions of a neuron. 13 Neuron Anatomy An understanding of neuron function requires knowing its structural components. Nissl bodies (RER and free ribosomes) Dendritic branches Mitochondrion hillock Initial segment of axon Axolemma Telodendria Nucleolus Golgi apparatus Neurofilament Direction of action potential terminals Nucleus Dendrite Presynaptic cell See Figure 12 3 Postsynaptic cell 14 7

8 Neuronal Synapse Synapse: a special site where two neurons communicate via neurotransmitters (= chemical messengers) 15 NEURONAL COMMUNICATION Presynaptic membranes deliver information in the form of neurotransmitters. Postsynaptic membranes receive information because they have receptors for neurotransmitters. 16 8

9 al Transport Communication between cells and along an axon is in the form of electrical signals. However, an axon also transports molecules up and down the long pathway in order to deliver material to and from the axon terminals ( from cell body towards axon terminals = anterograde transport the other way around = retrograde transport) terminal has for example no Nissl bodies ; thus no means to produce proteins! 17 Nervous system al Transport This axonal transport up and down the axon is referred to as axoplasmic transport. Both Anterograde and Retrograde transport is quite fast and uses ATP fueled motor molecules such as Kinesin and Dynein, motor proteins that carry cargo via microtubules that run along the axon. 18 9

10 Structural Classification of Neurons Neurons come in different forms 19 Structural Classification of Neurons Typical Sensory neuron Typical motor neuron Anaxonic neuron Bipolar neuron Unipolar neuron Multipolar neuron Dendrites Dendrites Dendritic branches Initial segment Cell body Dendrite Cell body Cell body terminals Cell body terminals a Anaxonic neurons have more than two processes, and they are all dendrites. b Bipolar neurons have two processes separated by the cell body. c Unipolar neurons have a single elongated process, with the cell body located off to the side. d terminals Multipolar neurons have more than two processes; there is a single axon and multiple dendrites

11 Functional Classification of Neurons Sensory neurons (afferent neurons) deliver information from exteroceptors, interoceptors, or proprioceptors to wards the CNS Somatic sensory neurons bring information in from skin, muscle and joint receptors Visceral sensory neurons are connected to interoceptors (receptors inside organs) Motor neurons (efferent neurons) Form the efferent division of the PNS Somatic motor neurons deliver impulses to skeletal muscles Visceral motor neurons deliver impulses to effectors of the autonomic nervous system Interneurons (association neurons) Located entirely within the CNS, involved in higher functions Distribute sensory input and coordinate motor output 21 Functional Classification of Neurons 22 11

12 23 NeuroGlial Cells in CNS There are Four types of neuroglia in the CNS Ependymal Cells Cross Section of Spinal Cord These are specialized epithelial cells that line the ventricles of the brain and the central canal within the spinal cord. They are instrumental in the production of the cerebrospinal fluid and in circulating this fluid around

13 NeuroGlial Cells in CNS Astrocytes Only found in CNS and perform a variety of functions Stabilize brain capillaries and blood brain barrier Repair / prevent injury Control Interstitial area by mopping up and recycling neurotransmitters, regulate Na+ and K+ ions, release chemicals that enhances communications 25 NeuroGlial Cells in CNS Oligodendrocytes Only found in CNS Are instrumental in forming the insulating coating around axons = myelin sheaths This speeds up electrical transmission Microglia Only found in CNS Very small and migrate through neural tissues Function like macrophages and remove debris, waste products and pathogens 26 13

14 NeuroGlial Cells in CNS Gray matter White matter CENTRAL CANAL Ependymal cells Gray matter Neurons Microglial cell 27 NeuroGlial Cells in CNS Gray matter White matter Myelinated axons Internode White matter Myelin (cut) Axolemma Node Oligodendrocyte Astrocyte Unmyelinated axon Basement membrane Capillary 14

15 NeuroGlial Cells in PNS Schwann cells or Neurilemmocytes Only found in PNS Have similar function as oligodendrocytes and form the myelin sheaths (neurilemma) around axons. Satellite cells or Amphicytes Only found in the ganglia of the PNS Function is similar to that of astrocytes Regulate environment around neuron cell bodies 29 NeuroGlial Cells in PNS node Many Schwann cells are needed to cover one axon. The space between the Schwann cells are called the Nodes (exposed axon membrane is called axolemma)

16 Figure 12-7c Schwann Cells, Peripheral s, and Formation of the Myelin Sheath. NeuroGlial Cells in PNS 1 A Schwann cell first surrounds a 2 The Schwann cell then begins to 3 portion of the axon within a groove of rotate around the axon. its cytoplasm. As the Schwann cell rotates, myelin is wound around the axon in multiple layers, forming a tightly packed membrane Schwann cell Myelin Schwann cell cytoplasm Stages in the formation of a myelin sheath by a single Schwann cell along a portion of a single axon. 31 Important Additional Definitions! White matter refers to the aggregation of myelinated processes in the brain! Gray matter is the combination of nerve cell bodies, dendrites, axonal terminals or bundles of un-myelinated axons and neuroglia in the brain A nerve fiber is the terminology for a single axon. A nerve is a bundle of nerve fibers, surrounded by connective tissue, and running within the PNS. Tracts are bundles of nerve fibers within the CNS. Ganglia are Nerve cell bodies clustered together in the PNS A nucleus (nuclei) is (are) a collection of nerve cell bodies within the CNS 32 16