BioSci107 Lecture 4 Muscle and Nerve Tissue 2024 PDF

BioSci107 Lecture 4 Muscle and Nerve Tissue 2024 ANTHONY PHILLIPS 1 Objectives Describe general features of muscle tissue – Understand location, structure, function Describe general features of nervous tissue – Understand the function of its component cells. 2 Muscle Tissue Consists of elongated cel...

BioSci107 Lecture 4 Muscle and Nerve Tissue 2024 ANTHONY PHILLIPS 1 Objectives Describe general features of muscle tissue – Understand location, structure, function Describe general features of nervous tissue – Understand the function of its component cells. 2 Muscle Tissue Consists of elongated cells (muscle cells; or muscle fibres or myocytes) that use energy from the hydrolysis of ATP (adenosine triphosphate) to generate force. As a result of contraction, muscle tissue produces body movements, maintains posture and generates heat. 3 Muscle Tissue There are three types of muscle comprising ~50% of the body tissue mass: i. Skeletal Muscle ii. Cardiac Muscle iii.Smooth Muscle 4 i. Skeletal Muscle There are ~650 named skeletal muscles in the body Usually attached to bones via tendons. Appear striated under the microscope. Contraction is under conscious control (voluntary; sometimes not always - posture) Fibres (remember = cells) cylindrical Stapedius Smallest: 1.25 mm stapedius (stabilizes the smallest human bone the stapes in the ear; prevents “hyperacusis*”; tympanic reflex; Bell’s Palsy; facial n) Longest: up to the 60 cm sartorius (“Checking for gum!”; hip: flexor, abductor, lateral rotator; knee: flexor). *Hyperacusis – stapedius n damage - extra loud sound perception. www.dbtechno.com Sartorius 5 NO more detail needed than this slie for the two muscles Skeletal Muscle Tissue Note: cylindrical cells Type Location Structure Control Skeletal Attached to bones by tendons Long cells; Striated; Multinucleate (many peripheral nuclei pushed to side) Voluntary Functions: Motion, Posture, Heat, Protection 6 The striations of skeletal muscle fibres (cells) are due to the highly organised arrangement of myofibrils within the cells Myofibrils (2 µm diam) more or less fill the cytoplasm (sarcoplasm) of the muscle fibre and extend its entire length within the cell 7 Image Source: Boundless. “Skeletal Muscle Fiber Structure.” Boundless Biology. Boundless, 08 Jan. 2016. The striations of skeletal muscle fibres (cells) are due to the highly organised arrangement of myofibrils within the cells Myofibrils are composed of two types of filaments (myofilaments): – Thin filaments: mostly actin; 8 nm diam; 1-2 µm long – Thick filaments: myosin; 16 nm diam; 1-2 µm long Myofilaments do not extend the length of the muscle fibre, but are arranged in compartments called sarcomeres The sarcomere is the basic functional unit of a myofibril Z discs (Z lines) separate sarcomeres 8 Connective tissue of skeletal muscle Epimysium: surrounds anatomical muscle Perimysium: around fascicles Endomysium: around muscle fibers (“cell”) – (layer for capillaries/nerves) Sarcolemma: actual cell plasma membrane Sarcoplasm: cell cytoplasm 9 The thick and thin myofilaments overlap to produce the striations in the myofibril: A band: dark, middle part ; contains all the thick filaments I band: thin filaments, but no thick filaments H zone: thick filaments, but no thin filaments M line: middle of sarcomere (holds thick filaments together) Z disc: passes through centre of I band (between sarcomeres) made up of “actinins” – that link filaments of adjacent sarcomeres Titin: links Z disc to M line; provides resting tension in I band, molecular spring 10 11 ii. Cardiac Muscle Striated. Branched. Single central nucleus. Fibres join end-to-end through intercalated discs. Intercalated discs contain: 1. Desmosomes (bind intermediate filaments) Provide adhesion in contraction 2. Gap junctions (communication) (co ordinated; rapid conduction). Desmosome Gap junction GJ D Wikipedia 12 Intercalated disc TEM Cardiac Muscle Tissue Still have actin and myosin “Purkinje fibres” are specialised muscle cells that conduct electrical activity around the heart. They have less myofibrils and more specialised “connexins” (gap junctions). Type Location Structure Control Cardiac Heart Striated; branched; single Involuntary central nucleus; intercalated 13 discs iii. Smooth Muscle (no striations) Located in the walls of hollow internal structures e.g. intestines (peristalsis); blood vessel walls (constriction); also : Iris of eye, reproductive; digestive; respiratory; urinary; skin erector pili Short, Small, spindle-shaped, about 30-200 µm long; 3-8 µm thickest in the middle Involuntary Non-striated (smooth) Single central nucleus Single smooth muscle cell 14 Generalised blood vessel Smooth muscle fibres are non-striated, but still have bundles of thin (e.g. actin) and thick (e.g myosin) filaments. Thin filaments (e.g. actin) attach to “dense bodies”, functionally similar to Z discs. (Dense body: a major protein is Actinin). Intermediate filaments (non-contractile elements) also connect to dense bodies During contraction tension is transmitted to the intermediate filaments (don’t contract), and the cell twists as it contracts about these stable “rods”. 15 Smooth Muscle Tissue Lots of gap junctions: e.g. gut; or no gap junctions: e.g Iris Type Location Structure Control Smooth In the walls of hollow internal structures e.g. blood vessels, intestines, skin Non-striated (smooth); single, central nucleus Involuntary 16 17 Martini and Ober 2015 Edition Nervous Tissue 18 4. Nervous Tissue Nervous tissue is the essential component of the nervous system. The nervous system has two main subdivisions: – Central nervous system (CNS): brain and spinal cord (and optic nerve) – Peripheral nervous system (PNS): all nervous tissue outside CNS i) Sensory/afferent division: Information to the CNS. ii) Motor/efferent division: Information from CNS to the organs (muscles and glands). The nervous system helps to: Maintain homeostasis (along with the endocrine system), Initiates voluntary movements Responsible for perception, behaviour and memory. Activities grouped under three major functions: i. Sensory: Detection of internal and external stimuli and transfer to CNS ii. Integrative: analysis and storing of information iii. Motor: stimulation of effectors (e.g. muscle and glands) through PNS i.e. motor here means “effector” 19 Nervous tissue consists of two types of cells: neurons (nerve cells that can be very large) neuroglia (supportive cells – usually small). Neurons are longest cells in body (up to 1m – spinal cord to toe) Conscious and unconscious control 20 21 Neurons Have a cell body into which short, branched dendrites convey nerve impulses (action potentials) and from which a longer, single axon conducts nerve impulses to another neuron or tissue. (Soma) Dendrites: The receiving/input part of the neuron. Axon: carries the nerve impulse away from the neuron. It is the output portion of the neuron. For our purposes neurons: Do not divide. High metabolic rate. (die rapidly without O2) 22 Multipolar Neurons Have 2 or more dendrites and a single axon. Most common neurons in CNS All motor neurons (control skeletal muscle) are in this class Some of longest (spinal cord to toe muscles) 23 Bipolar Neurons Two distinct processes – 1 dendritic process (can branch at tip but not at cell body) – And 1 axon Has cell body between axon and dendrite Rare and small (30µm) Special sense organs (sight, smell, hearing) relay information from receptor to neurons 24 Unipolar Neuron The dendrites and axon are continuous Cell body off to one side Whole thing from where dendrites converge called axon Most sensory nerves are unipolar Very long (1m) like motor nerves CNS-toe tip. 25 Anaxonic neuron Rare and function poorly understood Anatomy cannot distinguish dendrites from axons Found in brain and special sense organs 26 Neuroglia Found in both CNS and PNS. Make up ~50% the volume of the CNS (“glue”). Smaller than neurons but more numerous (5-50x) Do not propagate action potentials, but can communicate. Can divide within the mature nervous system Functions Physical structure of nervous tissue Repair framework of nervous tissue Undertake phagocytosis Nutrient supply to Neurons Regulate interstitial fluid in neural tissue. 27 Classification of Neuroglia 1. CNS Neuroglia i. Astrocytes: a. Star-shaped; largest; most numerous of neuroglia. Syncytium network. b. Support (have microfilaments) and repair (scar). c. Communicate with neurons via ‘gliotransmitters’ e.g. glutamate d. Maintain environment around neuron by e.g. regulating ions. e. Maintain blood-brain barrier via endothelium. Wrap around vessels and influence their permeability Front. Pharmacol. 4:140. doi: 10.3389/fphar.2013.00140 (Pericyte is CT cell around vessel) 28 ii. Oligodendrocytes: – Form insulating multilayered myelin sheath ( protein lipid layer) around CNS axons. – Can myelinate more than one neuron cell’s axon. Accelerate the action potential. iii. Microglia: Phagocytic (resident macrophages) - protection Oligodendrocyte Inactive microglia Active microglia 29 IV. Ependymal cells: Produce cerebrospinal fluid (CSF). Line the Cerebrospinal Fluid (CSF)-filled ventricles in the brain and the central canal of the spinal cord. These single layer of predominantly cuboidal cells have cilia (flow) and microvilli (sampling). Blausen.com staff Martin Hasselblatt Located in ventricles and in other locations where CSF found. CSF mechanical buffer; moves nutrients and waste Ependymal cells 30 31 2. Peripheral Nervous System Neuroglia i. ii. Schwann cells (“PNS version of CNS oligodendrocyte”): form insulating myelin sheath around axons or can just support and surround several nonmyelinated axons. (Note: One Schwann cell per axon for myelination but more axons/cell if just support). Satellite cells: surround neuron cell bodies. Support and fluid exchange (equiv. to astrocytes in CNS). Martini and Ober 2015 Edition 32 Myelinating Schwann Non-Myelinating Schwann 33 Martini and Ober 2015 Edition NOTE: Text Book Resources Tortora and Derrickson 3rd Asia Pacific Edition: Pg:176-179, 383-386, 388-390, 517-525 2nd Asia Pacific Edition: Pg: 206-209, 440-443, 446-448, 588-597 “14th Edition”: Pg:134-136, 293-294,298-299, 402-404, 406-408 “13th Edition”: Pg:143-145, 329-330, 334-335, 450-452, 454-456, Image Acknowledgements: Various editions of the course Tortora text books and also from Martini and Ober 2015 Edition or Wikipedia (free creative commons) were the sources for the images used in BioSci 107 Lectures 1-5 in 2023; unless otherwise stated. 34