Nervous System Tissue Notes PDF

The Nervous System Chapter 15 Part 1 Chapter 15 Outline Name the divisions of the nervous system and describe their function Identify the types of neurons (afferent, efferent, interneurons, multipolar, unipolar, bipolar) Identify Glial cells of the PNS and CNS (astrocytes, oligodend...

The Nervous System Chapter 15 Part 1 Chapter 15 Outline Name the divisions of the nervous system and describe their function Identify the types of neurons (afferent, efferent, interneurons, multipolar, unipolar, bipolar) Identify Glial cells of the PNS and CNS (astrocytes, oligodendrocytes, ependymal, microglia, schwann cells, satellite cells) Describe Nervous Tissue (white matter, gray matter, parts of a neuron, myelin, dendrites, axon, axon terminals) Describe the electrical nerve impulse and synapse Nervous Terms Terms Astr/o Blephar/o Cor/o Dacry/o Encephal/o Gli/o Hydro/o Kerat/o Lacrim/o -lemma -lexia Ment/o Ophthalm/o -phobia, phob/o Radicul/o Schiz/o Son/o -taxia, tax/o Reference The neuron is the basic cell type of both systems. Plexus: a specific network of nerves and neurons Afferent – towards Efferent - away Somatic – voluntary Visceral – organs Ganglia- groups of cell bodies in the PNS Neuron – a single cell Nerve – contains thousands of neurons that connect with a specific tissue Glial cells – cells that support the neurons in the CNS and PNS Overview of the Nervous System The nervous system has two major divisions: – The central nervous system (CNS), composed of the brain and spinal cord – The peripheral nervous system (PNS), composed of the nerves that connect the brain or spinal cord with the body’s muscles, glands, and sense organs Overview of the Nervous System Copyright © 2016 by Nelson Education Ltd. Peripheral Nervous System (PNS) 1. Somatic nervous system – voluntary control of movements – Afferent neurons bring signals from peripheral receptors to the CNS. – Efferent neurons bring signals from the CNS to the skeletal muscle fibres. 2. Autonomic nervous system – involuntary control of smooth and cardiac muscle and glands – contains sensory neurons from visceral organs and motor neurons that convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands – This system works with endocrine system to maintain homeostasis. 3. Enteric nervous system (part of ANS) – neurons that regulate gastrointestinal system Nervous System Overview Copyright © 2016 by Nelson Education Ltd. Overview: Functions 1. Sensory Function – Sensory receptors detect internal and external stimuli – Information is carried to brain and spinal cord through cranial and spinal nerves 2. Integrative Function – Integrates sensory information by analyzing and storing some of it and by making decisions for appropriate responses (a.k.a. integration). 3. Motor Function – Elicitation of motor response in response to integrated sensory information – Activates effectors (muscles and/or glands)  Histology: Nervous Tissue Nervous tissue contains two types of cells: neurons and neuroglia 1. Neurons – Possess electrical excitability Three parts i. Cell body ii. Dendrites iii. Axon  Histology: Neurons i. Cell body – Contains nucleus, cytoplasm and typical organelles ii. Dendrites – The receiving or input parts of a neuron – Usually short and highly branched  Histology: Neurons iii. Axon transmit electrical activity, starting from axon hillock and moving toward axon terminals Some have collaterals which increase number of cells influenced by that one neuron (increase thinking = more dendrites and more axon collaterals). Axon terminal – releases neurotransmitters, which connect to other neurons or muscle Synapses two neurons or a neuron and an effector cell communicate. Copyright © 2016 by Nelson Education Ltd.  Classification of Neurons Structural Functional Classification Classification Sensory (afferent) Multipolar neurons Motor (efferent) neurons Bipolar Interneurons (association Unipolar neurons) Classification of Neurons – Functional Sensory (afferent neurons) – Sensory receptors at distal end (dendrites) – Action potential conveyed through cranial or spinal nerves Motor (efferent neurons) – Convey action potential to effectors (muscles and glands). Interneurons (association neurons) – Within CNS between sensory and motor neurons. – Integrate / process incoming sensory information. – Activate appropriate motor neurons to elicit a response. Source: www.wikipedia.com  Histology: 2. Neuroglia – Smaller than neurons and are 5 to 25 times more numerous – They do not generate or conduct nerve impulses – Surround neurons and hold them in place – Supply nutrients and oxygen to neurons – Insulate one neuron from another – Destroy pathogens and remove dead neurons Types i. Neuroglia in the CNS = Astrocytes, oligodendrocytes, microglia, and ependymal cells. ii. Neuroglia in the PNS = Schwann cells and satellite cells Neuroglia Two types of neuroglia produce myelin sheaths: – Oligodendrocytes myelinate axons in the CNS – Schwann cells myelinate axons in the PNS. Astrocytes (CNS) Protect neurons from harmful substances; Maintain proper chemical environment for nerve impulse generation; regulate ion concentration Help form the blood- brain barrier.  Oligodendrocytes and Microglia (CNS) Oligodendrocytes: – Produce / maintain myelin sheath around several adjacent neurons. Microglia: – Protect CNS from disease: engulf invading microbes. – Clear away debris of dead cells in damaged nerve tissue. Ependymal Cells (CNS) Line ventricles of brain and central canal of spinal cord; Form cerebrospinal fluid and assist in circulation.  Neuroglia of PNS Schwann cells (6) – Produce and maintain myelin sheath around a single axon of a PNS neuron. – Participate in regeneration of PNS axons. Satellite cells (5) – Support neurons in PNS ganglia – Regulate exchange of materials between neurons and interstitial fluid.  Myelination Myelin Sheath – many-layered covering composed of lipid and protein. – Protects axon like insulation of an electrical wire. – Increases the speed of nerve impulse conduction. – Up to 100 layers Nodes of Ranvier – Gaps in the myelin sheath Collections of Nervous Tissue Clusters of neuronal cell bodies – Ganglia Clusters of neuronal cell bodies in the PNS Associated with cranial and spinal nerves – Nucleus Cluster of neuronal cell bodies in the CNS Collections of Nervous Tissue Bundles of Axons – Nerve A bundle of axons in the PNS. Cranial nerves connect brain to periphery. Spinal nerves connect spinal cord to periphery. Tract – Bundle of axons in the CNS. – Interconnect neurons in the brain and spinal cord.  Gray and White matter White matter – Primarily myelinated neurons. – White colour imparted by myelin. Gray matter – Neuronal cell bodies, dendrites, unmyelinated axons, axon terminals and neuroglia. – Grayish colour imparted by cellular organelles.  The almighty ACTION POTENTIAL Watch in text 15.3 Action Potentials and Graded Potentials - YouTube Action Potentials and Graded Potentials Recall: Ion concentrations in the cytoplasm and in the interstitial fluid are not the same. There are more sodium ions and chloride ions in the interstitial fluid, and there are more potassium ions in the cytoplasm. The charge inside the membrane of the cell is negative relative to outside the cell. The gradient of sodium and potassium ions is maintained by the Na+/K+ pump. Action Potentials (AP)and Graded Potentials The inside of ALL cells is approximately –70mV. Since the inside of the cell is negative compared to the outside of the cell, it is said to be polarized. If positively charged Na+ ions move into the cell, it will become less negative – this is called depolarization. This is how an action potential and graded potential work. We transmit electrical signals by moving ions across the cell membrane and changing the charge. Action Potentials Action potentials (AP)are generally very rapid (as brief as 1–4 milliseconds) and may repeat at frequencies of several hundred per second. The ability to generate action potentials is known as excitability. This ability is possessed by neurons, muscle cells, and some other types of cells. An action potential is a large change in membrane potential and is an “all or none” response.  Action Potentials Resting membrane potential. ~ –70 mV Threshold level. ~ –55mV, triggered by stimulus Depolarization. Na+ enters the cell, and charge becomes +30mV. Na+ stops entering the cell once the charge reaches +30mV because an inactivation gate is triggered. This +30mV charge also stimulates the K+ channels to open and let K+ move out of the cell. Repolarization. K+ leaves the cell, so charge decreases back toward resting potential. Hyperpolarization. Excess K+ leaves the cells, causing membrane charge to be ~ – 80mV. Copyright © 2016 by Nelson Education **prevents another immediate AP Ltd. Resting membrane potential Synaptic Transmission A synapse includes: – Presynaptic neuron The neuron sending the signal – Synaptic cleft Tiny space between neurons. – Postsynaptic neuron The neuron receiving the signal