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Lecture 4: Muscle & Nerve Tissue - Coggle Diagram
Lecture 4:
Muscle & Nerve Tissue
Muscle Tissue
Consists of elongated cells (muscle cells; or muscle fibres ormyocytes)
These cells use energy from the hydrolysis of ATP to generate force.
As a result of contraction, muscle tissue produces body movements, maintains posture and generates heat (function).
Cardiac Muscle
Structure --> Striated, Branched, Single central nucleus - Fibres join end-to-end through
intercalated discs
Location --> heart
Control --> Involuntary
Contain actin and myosin
Intercalated discs
contain:
Desmosomes (bind intermediate filaments) Provide adhesion in contraction
Gap junctions (communication) (co ordinated; rapid conduction).
Smooth Muscle
Structure --> Short, Small, spindle shaped (thickest in the middle) - Single central nucleus
Location --> The walls of hollow internal structures (e.g. blood vessels, intestines, skin)
Control --> Involuntary
Muscle fibres
are non-striated
contains bundles of thin (e.g. actin) and thick (e.g myosin) filaments.
Thin filaments (e.g. actin) attach to “dense bodies”, (Dense body: a major protein is Actinin).
Intermediate filaments (non-contractile elements) also connect to dense bodies
Contraction
tension is transmitted to the intermediate filaments (don’t contract), and the cell twists as it contracts about these stable “rods”.
Skeletal Muscle
attached to bones via tendons
Fibres (cells) are cylindrical
Contraction is under conscious control (voluntary; sometimes not always - posture
Long cells; Striated; Multinucleate (many peripheral nuclei pushed to side).
The striations of skeletal muscle fibres (cells) are due to the highly organised arrangement of myofibrils within the cells
Function --> Motion, Posture, Heat, Protection
Myofibrils
fill the cytoplasm (sarcoplasm) of the muscle fibre and extend its entire length within the cell.
Myofibrils are composed of two types of filaments (myofilaments):
Thin filaments: mostly actin
Thick filaments: myosin
Myofilaments
do not extend the length of the muscle fibre, but are arranged in compartments called sarcomeres
Sarcomeres
Is the basic functional unit of a myofibril
Connective Tissue:
Epimysium - surrounds anatomical muscle
Perimysium - around fascicles
Endomysium - around muscle fibers (“cell” layer for capillaries/nerves)
Sarcoplasm - cell cytoplasm
Nervous Tissue
Cells of Nervous Tissue
Neurons
cell body is short & branched
dendrites
convey nerve impulses (action potentials) and from which a longer, single
axon
conducts nerve impulses to another neuron or tissue.
Neurons do not divide, they have a high metabolic rate &die rapidly without oxygen.
Axon
carries the nerve impulse away from the neuron. It is the output portion of the neuron.
Dendrites
The receiving/input part of the neuron.
Bipolar Neurons
Two distinct processes:
1 dendritic process (can branch at tip but not at cell body) & 1 axon
Has cell body between axon and dendrite
Rare and small
Special sense organs (sight, smell, hearing) relay information from receptor to neurons
Unipolar Neurons
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 - like motor nerves CNS-toe tip.
Multipolar Neurons
Have 2 or more dendrites and a single axon.
-mMost common neurons in CNS
All motor neurons (control skeletal muscle) are in this class
Some of longest (spinal cord to toe muscles)
Anaxonic Neurons
Rare and function poorly understood
Anatomy cannot distinguish dendrites from axons
Found in brain and special sense organs
Neuroglia
Found in both CNS and PNS
Smaller than neurons but more of them
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.
CNS Neuroglia
Oligodendrocytes
Form insulating multilayered myelin sheath ( protein lipid layer)around CNS axons.
Can myelinate more than one neuroncell’s axon. Accelerate the action potential
Microglia
Phagocytic (resident macrophages)
protection
Astrocytes
Star-shaped; largest; most numerous of neuroglia. Syncytium network.
Support (have microfilaments) and repair (scar)
Communicate with neurons via ‘gliotransmitters’
Maintain environment around neuron by e.g. regulating ions
Maintain blood-brain barrier via endothelium. Wrap around vessels and influence their permeability
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).
Located in ventricles and in other locations where CSF found.
CSF mechanical buffer; moves nutrients and waste
PNS Neuroglia
Schwann cells
form insulating myelin sheath around axons or can just support and surround several non-myelinated axons.
Satellite cells
surround neuron cell bodies. Support and fluid exchange