Nerves and Muscle

Question 1

Define the anatomical components of the central and peripheral nervous systems.

Answer 1

the CNS is the brain and the spinal cord.

the PNS is the nerves that branch out from the brain and spinal cord.

Question 2

Explain the principal functions of neurons and glial cells and know their primary morphological features.

Answer 2

neurons are collectors and integrators of information. they can strengthen or weaken synapses and change connection, which alters their branching. spaces not covered by synapses are covered by glial cells and have a large surface area to volume ratio.

glial cells maintain homeostasis, form myelin, and provide support and protection for neurons.

Question 3

Explain the difference between cells and structures in the peripheral and the central nervous systems.

Answer 3

PNS - peripheral nerves that are covered by ganglia and surrounded my specialized connective tissue cells.

CNS - brain and spinal cord, encased by meninges which contain cerebrospinal fluid

Question 4

Describe the effect of voltage on ion movement.

Answer 4

If there is any change in membrane potential, the voltage gated ion channels will respond. For example, if the Vm nears 0, voltage gated Ca2+ channels will open and Ca2+ will diffuse into the cell.

Question 5

Describe the development of diffusion potential by ion movements - Nernst potential.

Answer 5

This is the voltage at which the electrostatic force on an ion is equal and opposite to the chemical force from the concentration gradient. Nernst potential is when the cell membrane is solely permeable to K+, resting Vm is equal to Ek.

Question 6

Describe the relationship between diffusion potential and membrane potential (Vm).

Answer 6

If there is a concentration difference for an ion across a membrane and the membrane is permeable to that ion, a potential difference (the diffusion potential) is created.

Question 7

Describe the relationship between Vm and ion concentrations.

Answer 7

Differences in the concentrations of ions on opposite sides of a cellular membrane lead to a voltage called the membrane potential

Question 8

Describe the role of Na+/K+-ATPase.

Answer 8

Replenish K+ lost from the cell and remove Na+ accumulated within the cell. Na+/K+-ATPase channel pumps Na+ into the extracellular space and K+ into the intracellular space via ion channels.

Question 9

Describe the characteristics of neuronal action potential.

Answer 9

A threshold potential has to be reached. The rising phase of the action potential is due to depolarization, the charge then goes above the 0 potential. The potential is then repolarized and hyperpolarized.

Question 10

Describe the ionic basis of action potential generation.

Answer 10

• rapid depolarization is due to the opening of Na+ channels once the threshold voltage is reached
• The membrane is repolarized by K+ leaving the cell

Question 11

Describe the refractory period and Na+ channel inactivation.

Answer 11

A given period of time before a stimuli will elicit another response. It can be overcome to some degree with a stronger stimulus. This is up to a certain point known as the absolute refractory period. This is due to Na+ ion channel inactivation.

Question 12

Describe propagation and conduction of action potential.

Answer 12

Nerve conduction velocity is affected by axon diameter, myelination and temperature.

Question 13

Describe synaptic structure and the mechanisms of chemical neurotransmission.

Answer 13

• the presynaptic membrane which is formed by the terminal button of an axon
• the postsynaptic membrane which is composed of a segment of dendrite or cell body
• the space between these two structures which is called the synaptic cleft.

neurotransmitters diffuse across this gap.

Question 14

Describe ionotropic receptors and fast synaptic transmission.

Answer 14

The neurotransmitter is the ligand and binds to and opens ion channels in the postsynaptic membrane. There are then changes in the ionic permeability of the postsynaptic cell membrane. This leads to a rapid and reversible change in the membrane potential of the postsynaptic cell.

Question 15

Describe excitatory and inhibitory synapses and postsynaptic potentials.

Answer 15

excitatory - makes postsynpatic neurone more likely to fire an action potential. brings Vm nearer to the threshold and increases the chance of the AP firing. It also increases excitability and summates to elicit an action potential.

inhibitory - makes postsynpatic neurone less likely to fire an action potential.

Question 16

Describe summation and excitability – target for drugs.

Answer 16

Summation is from both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation).

excitability - the ability to generate a large, rapid change of membrane voltage in response to a very small stimulus

Question 17

Describe metabotropic receptors and slow synaptic transmission.

Answer 17

A metabotropic receptor a type of membrane receptor that initiates a number of metabolic steps to modulate cell activity.

neurotransmitters have to pass the synpase by diffusion, which is relatively slow.

Question 18

Describe pharmacological action of diazepam.

Answer 18

effects are thought to result from a facilitation of the action of gamma aminobutyric acid (GABA), an inhibitory neurotransmitter in the central nervous system

Question 19

List the functions of smooth muscle.

Answer 19

found in walls of hollow organs, work automatically, stomach, arterioles, airways

Question 20

Compare and contrast the properties of smooth muscle and skeletal muscle.

Answer 20

skeletal muscle is striated, smooth muscle does not act on structures, both need calcium for contraction, smooth muscle is single unit and multi unit.

Question 21

Describe the functional significance of single-unit behaviour of smooth muscle and explain how co-ordination of this activity is achieved.

Answer 21

cells are close together with few innervations of varicosities. electrically coupled to eachother via gap junctions. myogenic

Question 22

Identify two sources of calcium ions that can promote contraction of smooth muscle.

Answer 22

calcium in the sarcoplasmic reticulum, extracellular calcium

Question 23

Provide one example of how the autonomic nerves can increase and decrease smooth muscle activity and link your answer to a physiological response.

Answer 23

the autonomic nerve fires an action potential which leads to the release of neurotransmitters from the varicosities to the muscle cell.

Question 24

Understand the function of the actomyosin system and recognise its importance for movement in the human body.

Answer 24

the actin-myosin complex that forms in the cytoskeleton and allows for muscle contraction. the myosin head binds to actin using ATP

Question 25

Know how the main structural differences between skeletal, heart and smooth muscle.

Answer 25

skeletal: cross striations, peripheral nuclei, unbranched, no intercalated disks
cardiac: cross striations, central nucleus, branched, intercalated disks
smooth: no striations, central nucleus, unbranched, no intercalated disks.

Question 26

Comprehend how contraction in the three muscle types is controlled.

Answer 26

skeletal - actin-myosin system
cardiac - depolarization leads to calcium release. travels down t-tubules and sarcolemma
smooth - actin-myosin bridges created, calcium binds to calmodulin and activates MLCK. MLC phosphorylated so actin can bind

Question 27

Appreciate proprioception and know the main sensory cells involved (muscle spindles, golgi tendon organs).

Answer 27

proprioception is a neural feedback loop. Muscle spindles, are innervated by gamma motor neurons and provide information about the length changes of a muscle. Golgi tendon organs provide information about the strength of a muscle’s contraction.

Question 28

Describe the structure of cardiac muscle.

Answer 28

homologous myosin isoforms, branched for simultaneous contraction, branched fibres joined with intercalated disks

Question 29

List the factors which affect cardiac muscle force generation.

Answer 29

the more calcium released, more contractility, ATP present, strength of action potential

Question 30

Describe the metabolic requirements for cardiac muscle.

Answer 30

cardiac muscle is constantly contracting so has high energy demands to avoid ischaemia

Question 31

Describe the basic structure of the spinal cord.

Answer 31

cervical enlargement, lumbar enlargement, thoracic and sacral region, white and grey matter, dorsal (posterior), lateral and ventral (anterior)

Question 32

List some basic somatic and autonomic reflexes.

Answer 32

somatic - patella, moving hand after touching something hot

autonomic reflexes - breathing, swallowing, pupillary, micturition, heart rate

Question 33

Draw the circuitry underlying monosynaptic reflexes and reciprocal inhibition.

Answer 33

monosynaptic: receptor - sensory neuron - spinal cord - motor neuron - muscle
reciprocal inhibition: motor neuron sends signal to extensor rather than flexor

Question 34

Describe the structure of a motor endplate (neuromuscular junction).

Answer 34

The motor endplate contains the presynaptic bouton, which contains synaptic vesicles. This is a very active region. the presynaptic membrane, the synaptic cleft (0.1 to 0.3pm wide), junctional folds and the postsynaptic membrane.

Question 35

State the events that occur during chemical transmission at a neuromuscular junction.

Answer 35

1. voltage gated Ca channels open
2. calcium mediated excoytosis of ACh into extracellular space
3. Na influx, K efflux via nAChRs results in RGPs
4. if RGP is sufficient, action potential is generated.

Question 36

Relate the symptoms of myasthenia gravis to dysfunction in the neuromuscular junction.

Answer 36

muscle weakness, can’t prolong muscle contraction, an autoimmune disorder of neuromuscular transmission. The production of autoantibodies directed against the nicotinic AChR.

Question 37

Explain how pharmacological agents acting in the neuromuscular junction can reduce the symptoms of myasthenia gravis.

Answer 37

increase ACh levels at neuromuscular junctions

Question 38

Structure of the heart wall

Answer 38

spiral, fibre-like arrangment of heart muscle cells, single or mono or dinucleated cells with limb-like extensions.

Question 39

Heart muscle cells (cardiomyocytes) as mononucleated cells with myofibrils that attach to each other via extensions

Answer 39

perform wringing motion of the heart, arranged in complicated manner.

Question 40

arrangement of actins and myosins into myofibrils and the bundling of myofibrils into skeletal muscle fibres.

Answer 40

hundreds of myofibrils packed into muscle fibres. myosin and actin are arranged into sarcomeres. sarcomeres lined up at z disk to form myofibrils.