6 Nervous Tissue.pdf

NERVOUS Neurons TISSUE Functional unit of nervous tissue High degree of irritability (the ability to The nervous ti...

NERVOUS Neurons TISSUE Functional unit of nervous tissue High degree of irritability (the ability to The nervous tissue in the body is react to stimulus) and conductivity (ability to organized to comprise the nervous system, transmit stimulus from one cell to another) which is automatically divided into two - Irritability and conductivity are divisions: central nervous system (CNS) chemical reactions that occur within which refers to the brain and the spinal cord, the neurons. and peripheral nervous system (PNS) which Performs all the functions of nervous tissue relates to all other nervous tissues in the body Shapes: Made up of closely packed cells Stellate neurons – ventral gray matter Very little amount of intercellular of the spinal cord and the motor nuclei of Present in all organs the brain stem Arises from embryonic ectoderm Spherical Pyramidal neurons - cerebral cortex Cells of Nervous Tissue Flask-shaped- “Purkinje cells” in the middle layer of the cerebellar cortex Fusiform Ovoid Part of a Neuron Neurons- are the functional cells which perform the basic functions of nervous tissue Neuroglial Cells- are the supporting cells responsible for the distribution of nutrients Perikaryon (soma is where the nucleus and and protection of neurons from physical the processes are) injury and possible infection of Processes (the number and location of these microorganisms. processes, especially the dendrites, largely determine the shape of the neuron). Two types of processes of neurons: - Axon - Dendrite Nervous Tissue-DMXK 1  Neurons are incapable of cell division, so dead neurons can’t be replaced. However, axons and dendrites can regenerate when damaged, provided the cell is intact. Axons and dendrites can regenerate A neuron will only have one axon Dendrites could be absent, solitary, or numerous Basic Functional Classifications: Basic Morphological Types: Sensory (afferent neurons)- when they receive stimuli and transmit impulse toward CNS. Unipolar Motor (efferent neurons)- When they - only one process (axon) is present transmit impulse from CNS to effector cells Pseudounipolar (ex. skeletal muscle). - a single process leaves the cell body but Interneurons (association neurons)- when soon bifurcates into two processes 1 axon they convey impulse from one neuron to and then dendrites. another. Found in between sensory and Bipolar motor neurons. Responsible for the - when one of each process arise at interpretation of the information collected by opposite poles of the cell body the sensory neurons. Multipolar - when numerous dendrites are present/ Dendrite emerge from the neuron perikaryon More than one dendrite is usually present in a neuron Provides most of the receptive surface of the neuron branch more extensively, but are shorter than axons. Contain Nissl bodies, mitochondria, and neurofibrils Does not have Golgi complex relays information to the perikaryon area where dendrites emerge have many Nissl bodies and looking for the Nissl bodies and emerging processes helps in identifying dendrites Nervous Tissue-DMXK 2  Axon Types between neurons: Arises from axon hillock Axodendritic - between the axon and a Devoid of Nissl granules but contains sER dendrite and mitochondria Axosomatic - between the axon and a Slender than dendrite but is typically longer perikaryon – Sciatic nerve – longest nerve; can be Axoaxonic - between axon synapse and longer than 1 meter another axon One axon per neuron, but has collateral Dendrodendritic - between a dendrite and branches another dendrite Capable of axonal transport Somatodendritic - between perikaryon and a - Anterograde: perikaryon to axon dendrite - Retrograde: axon to perikaryon Somatosomatic - between two perikaryon Forms small, rounded swellings called Somatoaxonic - between a perikaryon and terminals or buttons (rounded swellings) an axon - ”bouton terminaux”- at the end of axon Dendroaxonic - between a dendrite and an - “bouton en passant”- along the course of axon it Axoaxodendritic - between an axon, to an axon, then to a dendrite Neurilemmal Sheath- envelopes all axons Neuroglial Cells Coverings of Axons (myelin sheath): Sheath of Schwann cells (PNS) Sheath of Oligodendrocytes (CNS) Synapse Point of contact between a neuron and another cell Supporting cells that intersperse between Site of transmission of a nerve impulse neurons in nervous tissue allows neurons to communicate with each Protect, nourish, and aid neurons in their other or with effector (muscle and gland) functions, and play a role in neural nutrition. cells and accomplish their integration and Outnumber neurons 5-10x control functions Can undergo mitosis unlike neurons Types of synapses (accdg to transmitter): - Electrical – communicate through gap 4 Types of Neuroglia in CNS junctions and through the exchange of – Astrocytes molecules and ions, like sodium and – Oligodendrocytes other electrolytes (electrical synapses in – Microglia the heart) – Ependymal cells - Chemical – communicate the impulse by 2 Types of Neuroglia in PNS means of neurotransmitters (surface of – Schwann cells skeletal muscle organs – Satellite cells Nervous Tissue-DMXK 3  Oligodendrocytes Types of Neuroglia Located mainly in the white matter Provide neurilemmal covering and myelin sheaths of the axon - have a smaller, fewer, shorter processes than astrocytes - scanty cytoplasm; ovoid/spherical nucleus; smaller but more deeply-staining than astrocytes Astrocytes Microglial Cells Phagocytic cells of the CNS (like Largest and most numerous macrophages) “star-shaped” and has numerous branching smaller than astrocytes and oligodendrocytes processes small and elongated nucleus; scanty From scar tissue damage cytoplasm with many lysosomes Involved in both repair and metabolic probably arise from hematopoietic stem cells functions phagocytes Two types: protoplasmic (gray matter) Remove cellular debris from injury and and fibrous (white matter) normal cell turnover - distributed throughout the CNS a. Protoplasmic - found within gray matter and spinal cord; many branching processes Ependymal Cells b. Fibrous - located chiefly in white matter; longer and more slender processes Cuboidal cells with short cilia and microvilli (involved with the secretion of CSF) Nervous Tissue-DMXK 4  Simple cuboidal epithelium lining the -Myelinitated’s transition of signal is faster cavities (ventricles of brain and central canal than the unmyelinated axons of spinal column) of the CNS Epithelial cells, composition of the colloid The Nervous System plexus which is the source of CSF Secretes and circulates CSF ciliary movement helps circulate CSF. Satellite Cells Nervous System The integration and control functions of the nervous system are performed by: 1. Collection stimuli form the environment by means of receptors (sensory neurons) a.k.a. “mantle cells” or “amphicytes” 2. Transmitting these stimuli, called nerve Small flattened cells that surround cell impulses, to highly organized reception bodies of neurons located in the ganglia of and correlation areas for interpretation PNS (interneurons) Counterpart of the astrocytes 3. Issuing orders to effector organs for provides structural support and involves in appropriate responses to the stimuli (motor numerous neuron metabolic processes as neurons) well as nourishment Anatomic Divisions of the Nervous System Schwann Cells Central Nervous System- has no connective tissue stroma (so brain and spinal cord are only made of nervous tissue), protected by bone (skull, spinal column), lined by meninges made of CT (found on the surface of the organs) - Interprets the information and the brain even has the ability to store information in the form forms the neurilemmal and myelin sheaths of memory. for the axons of peripheral nerves – Brain – Spinal cord Myelinated and Unmyelinated Axons Peripheral Nervous System – Peripheral nerves Central Nervous System Has no connective tissue stroma (brain and spinal cord are only made of nervous tissue) Protected by bone (skull, spinal column) Lined by the meninges (made of CT) - interprets the information and the brain even has the ability to store information in the form of memory. Nervous Tissue-DMXK 5 Meninges Comes primarily from the choroid plexus Dura mater (pachymeninx) – Ependymal cells that act as blood-CSF – dense irregular connective tissue barrier; separates blood from the CSF Arachnoid membrane Drain into the arachnoid villi (which is then – loose CT collected by the Circulatory system.) Pia Mater Only cell that is present in csf is the limited – loose CT number of lymphocytes If there is RBC there is bleeding or Dura mater hemorrhage If WBC there is an infection CSF is an ultra-filtrate of blood where substances and cells that are needed will not be produces by the choroid plexus Meninges are filled with pain receptors not in the brain Plays a role in distributing nutrients and removal of waste products up to 4x everyday Dense irregular connective tissue 6-8 hours CSF is renewed In the brain, the outer surface (periosteal 500 mL is produced everyday, but only 150 dura) of the dura mater adheres to the inner will remain in the CNS at a time aspect of the cranium In the spinal cord, the outer surface of the dura mater is lined by a simple squamous epithelium – Epidural space – a space between periosteum of vertebra and dura mater The inner surface (meningeal dura) is also lined Arachnoid Membrane and Pia Mater Arrangement of Neurons in the CNS Often considered as a single entity, the 2 Areas leptomeninx or pia-arachnoid Gray Matter Arachnoid has cobweb-like connective tissue (arachnoid trabeculae) that connects it to pia mater Arachnoid membrane and pia mater are separated by a space (subarachnoid space) that contains the CSF and arachnoid trabeculae Cerebrospinal fluid – Contains cell bodies, dendrites, proximal - clear, slightly viscous fluid that circulates portions of the axons and glial cells (darker in (CNS) shade due to cell bodies). 80 to 150 mL