Test 2 Flashcards
Bone (osseous connective tissue)
- hard matrix with mineral salts
- matrix arranged in lamellae around haversian canal
- osteocytes in lacunae
Compact Bone
- shafts of long bones, parallel plates of flat bones
- structural unit – Haversian system
- Haversian canals
- Volkmann’s canals
- matrix arranged in lamellae around Haversian canal
Spongy Bone
- ends of long bones, center of irregular bones
- no Haversian system
Intramembranous Ossification
- bones of the skull, clavicule
- concentration of mesenchyme
- cells producing collagenous fibers and osteoid
- later deposition of salts
Enchondral Ossification
- cartilage model
- formation of primary ossification center
- blood vessels enter the ossification center
- formation of secondary ossification center
- formation of bone marrow cavity
Smooth Muscle
- unstriated
- involuntary (innervated by autonomic nervous system)
- in the walls of visceral organs
- small elongated cells which posess centrally located nucleus
Cardiac Muscle
- striated
- involuntary
- in the heart
- single nucleus, cells connected with special junctions – conducting electrical impulses
Skeletal Muscle
- striated
- voluntary (innervated by somatic nerves)
- attached to the skeleton
- multinucleated
Structure of a Skeletal Muscle
Structure of a Skeletal Muscle Fiber
Sarcomere Structure
Structure of a Thin Filament
Structure of a thick filament
How changes in striation pattern are explained by the sliding-filament model of muscle contraction:
Events in Excitation-Contraction Coupling
Actions of troponin and tropomyosin in excitation-contraction coupling
Skeletal muscle contraction
- basic structure involved in contraction consists of myofilaments
- thick filaments – myosin
- thin filaments – actin and tropomyosin
- filaments slide along each other during contraction / relaxation
- sarcomere – functional unit of the striated muscles
- ATP = ADP+Pi
- ATP from
- aerobic glycolysis
- anaerobic glycolysis
The Crossbridge Cycle
Types of Muscle Contraction
differ in whether the muscle is allowed to shorten as it contracts or not
Isotonic Muscle Contraction
- When a muscle contracts isotonically it generates a tension at least equal to to any forces oposing it (called loads) and so the muscle shortens.
- constant tension
Isometric Muscle Contraction
- When a muscle contracts isometrically it creates tension but does not shorten because the load is greater than the force generated by the muscle.This occurs for example when you try to lift an object that’s too heavy for you to move, or when you stand still and your postural muscles hold your body upright.
- constant length
Neuron (Nervous tissue)
- nerve cell
- is the basic structure of the nervous tissue
- each neuron consists of:
- cell body
- processes
- long (axons)
- short (dendrites)
Structure of a Nerve
Structure of a Typical neuron
Types of Neurons
- unipolar
- bipolar
- multipolar
- Golgi type I (large with long axons)
- Golgi type II (short axon)
Types of Neuroglia
Description and function
Neuroglia – neuron supporting cells
1) Astrocytes (fibrous, protoplasmatic) - star shaped; numerous radiating processes with bulbous ends for attachment. Binds blood vessels to nerves; regulate the composition of fluid around the neurons. Located in CNS. Insulation or barriers
2) Oligodendrocytes – Small cells with few but long processes that wrap around axons. Myelin sheaths formation around axons in central nervous system (CNS)
3) Microglia – small cell with long processes; modified macrophages. Protection; become mobile and phagocytic in response to inflammation. Located in CNS. Residual macrophages
4) Ependyma – columnar cells with cilia. Active role in formation and circulation of cerebrospinal fluid. Located in CNS(lines the ventricles of the brain and central canal of spinal cord) lining of the cavities of the brain
5) Schwann cells – Flat cells with a long flat process that wraps around the axon in the PNS. Form myelin sheaths around axons in the PNS; active role in nerve fiber regeneration. myelin formation in peripheral nervous system (PNS).
6) Satellite cells - flat cells similar to Schwann cells. Support nerve cell bodies within ganglia. Located in PNS.
Types of Nerve fibers
1) myelinated – surrounded by a myelin sheath which is
formed by a supporting cell:
- central (oligodendrocytes)
- peripheral (Schwann cells)
2) nonmyelinated (smaller axons)
Neuron reaction to injury
- injury to nervous tissue elicits response by neurons and neuroglia
- severe injury causes cell death
- once a neuron is lost it can not be replaced because neurons are ’postmitotic cells’ - that is neurons are fully differentiated and no longer undergo cells division
1) chromatolysis (cell body and axon proximal to the site ofinjury) - disorganisation of rybosomes and cellular swelling
2) Wallerian degeneration (distal axon) - disintegration of axon and all the synaptic endings
3) Schwann cells exhibit mitotic activity and produce trophic substances
4) regeneration - many neurons can regenerate a new axon if the axon is lost through injury
Signal conductivity in neurons
- most animal cells have an electrical potential differenceacross their plasma membranes
- the cytoplasm is usually electrically negative relative to extracellular fluid
- the electrical potential difference across the plasma membrane in a resting cell is called the resting membrane potential
- the resting membrane potential (50-100mV) plays a centralrole in the excitability of nerve and muscle cells
- the resting potential is due to uneven distribution of ions between the inside and the outside of the cell membrane
Resting membrane
Depolarizing membrane
Reverse Polarization
Repolarization
Graph
Action potential(AP)
- maintenance of the membrane potential is a property of all living cells, excitability however is shown only by specialized cells - nerves and muscles
- nerves and muscles respond to a stimulus by production oftransient changes in the ion conductance and potential of their membranes
- if the stimulus is sufficiently strong an action pottential is generated which in the case of the nerve is the signal that is transmitted along the nerve cell and in muscle leads tocontraction
Action Potential events
An AP consists of the following events:
- the stimulus reduces the resting membrane potential to a less negative value (depolarization)
- when it reaches a critical voltage to a so called threshold potential, a Na+ channel becomes activated leading to fast Na+ influx into the cell
- the Na + conductivity decreases, coupled with a slow rise in K + conductance (repolarization faze)
- once the threshold potential is attained, the cells responds with all-or-none depolarization
- for a brief period following the depolarization faze the nerve can not be excited even by the strongest stimulus – this is the absolute refractory period and is followed bya relative refractory period (at the end of the repolarization faze)
Propagation of the action potential in nerve fibers
- 2 types of potential propagation: serial and salutatory
- serial - slow, in nerves devoid of myelin sheath, the conductance rate - about 1 m/s
- salutatory - much faster - in myelinated nerves the conductance rate up to 120 m/s
- since the myelinated fibers are insulated like a cable, the depolarizing electrotonic discharge along the fiber can span a greater distance, in this case the AP is transmitted “in jumps” (salutatory propagation)
Synaptic potentials
- the AP transmitted along the axon releases a transmitter substance from the terminal button
- depending upon the type, this substance can bring about depolarization (excitation) or hyperpolarization (inhibition)of the postsynaptic membrane
- excitatory transmitters: acetylocholin, substance P, glutamate - they evoke excitatory post synaptic potentials (EPSP)
- single EPSP is usually insufficient to generate AP, but several simultaneous EPSPs are able to depolarize cells tothe threshold potentials (spatial and temporal summation)
- inhibitory transmitters (e.g. GABA, glycin) - cause hyperpolarization and lower the excitability of the cells, this is an inhibitory postsynaptic potential (IPSP)
- EPSP and IPSP can occur at the same time in the same cells
- the sum of all of the EPSPs and IPSPs determines whether or not the AP is transmitted postsynaptically
Common Neurotransmitters
- Acetylcholine: Located in CNS and PNS. Found in the skeletal neuromuscular junctions and in many ANS synapses. Generally excitatory but is inhibitory to some visceral effectors
- Norepinephrine: Located in CNS and PNS. Found in the visceral and cardiac muscle neuromuscular junctions; cocaine and amphetamines exaggerate the effects. May be excitatory or inhibitory depending on the receptors
- Epinephrine: Located in CNS and PNS. Found in pathways concerned with mood and behaviour. May be excitatory or inhibitory depending on the receptors.
- Dopamine: Located in CNS and PNS. Found in pathways that regulate emotional responses; decreased levels in parkinson’s diseases. Generally excitatory
- Serotonin: Located in CNS. Found in pathways that regulate temperature, sensory perception, mood, onset of sleep. Generally inhibitory.
- gamma-Aminobutyric acid(GABA): Located in CNS. Inhibits excessive discharge of neurons. Generally inhibitory.
- Endorphins and Enkephalins: Located in CNS. Inhibit release of sensory pain neurotransmitters; opiates mimic the effects of these peptides. Generally inhibitory.
