Unit 2: Nerves, Muscles & the Nervous System

Question 1

Define Depolarization.

Answer 1

Depolarization is the process in which ions move in and out of the cell, and the inside of the cell becomes more positive relative to the RMP.

Question 2

Why can’t an AP be fired during the absolute refractory period (depolarization and repolarization)?

Answer 2

This is due to the inactivation gate of the voltage-gated Na channel.

Question 3

Why is it harder for an Ap to be fired during the relative refractory period (hyperpolarization?

Answer 3

This is because the inside of the cell is more negative relative to its RMP, therefore, a greater stimulus would be required.

Question 4

What triggers the opening in both Na and K voltage-gated channels?

Answer 4

Change in voltage.
Na channels open at -55mV
K channels open at +35mV

Question 5

Why is myelin important for saltatory conduction?

Answer 5

A myelinated neuron conducts an AP 10-15 times faster than an unmyelinated neuron, resulting faster transmission.

Question 6

What are glial cells?

Answer 6

Glial cells make up 90% of the brain, and provide a necessary environment for neurons to function properly

Question 7

What are the 3 types of neurons?

Answer 7

Bipolar: 2 processes extending from the cell body (1 axon and 1 dendrite), found in the retina of the eye.
Unipolar: 1 process (straight connection between axon and dendrites), sensory, transmit signals to the spinal cord.
Multipolar: CNS, connect CNS with effector organs.

Question 8

What are the types of Neuroglia in the CNS?

Answer 8

Ependymal Cells: create CSF and circulate and absorb CSF, line the ventricles of the brain and spinal cord, help distribute hormones and signal molecules associated with the CNS.
Astrocytes: most abundant cell in the brain, provide nutritional support for neuron, clean-up brain debris, hold neurons in place, promote synaptic connections, respond to brain injury and inflammation.
Oligodendrocytes: myelin-forming cells in the CNS.
Microglia: remove foreign materials, cells or organisms, or previously formed synapses.

Question 9

What are the types of Neuroglia in the PNS?

Answer 9

Schwaan Cells: cover the axons of neurons in myelin.
Satellite Cells: provide nutrients and structural support, ensheath the soma of neuron bodies in ganglions.

Question 10

What are the 4 lobes of the brain, and their function?

Answer 10

Frontal Lobe: processes input from skeletal muscles (primary motor cortex), the premotor cortex and prefrontal cortex work together to integrate movement information with other sensory inputs to generate perception of stimuli.
Parietal Lobe: receives input from major senses (primary somatosensory cortex).
Occipital Lobe: responsible for vision, primary visual cortex receives input from the optic nerve, and the visual association areas process visual information and integrate it with other sensory inputs.
Temporal Lobe: consists of the primary auditory cortex and auditory associated areas, which receive and process signals from the auditory nerve and integrate it with other inputs, used for short-term memory and smell (olfaction).

Question 11

Define the role of the cerebellum in the brain.

Answer 11

The cerebellum integrates coordinated movement, and receives sensory information, and coordinates the execution of movement in the body.

Question 12

Define the role of the corpus callosum in the brain.

Answer 12

It is the connection site between both cerebral hemispheres. This connection integrates sensory and motor information, which results in whole-body movement.

Question 13

What are the 3 sections of the brain stem?

Answer 13

Midbrain: controls eye movement, auditory, and visual motor reflexes.
Pons: transfers information between the cerebellum and the cerebral cortex, controls breathing.
Medulla: involuntary functions, fibres from corticospinal tract (motor cortex) cross over to innervate muscles on the opposite side of the body.

Question 14

What are the 3 main components of a chemical synapse?

Answer 14

Pre-synaptic Neuron,
Synaptic Cleft
Post-synaptic Neuron

Question 15

In a chemical synapse neurotransmitters are released from the pre-synaptic neuron into the synaptic cleft. From there, what are the 4 possible fates neurotransmitters have?

Answer 15

Bind to receptors on post-synaptic neuron
Diffuse out of the synapse
Get broken down by enzymes in the synaptic cleft
Re-uptake into pre-synaptic cleft (recycled)

Question 16

Why can’t the dendrites or the soma elict an AP?

Answer 16

The dendrites and the soma do not have voltage-gated channels, which are essential for forming an AP.

Question 17

Define an Excitatory Post-Synaptic Potential (EPSP).

Answer 17

EPSPs do not produce an AP but they bring the neuron closer to an AP, they are localized which leads to depolarization on one area of the plasma membrane. The magnitude of depolarization is equal to the magnitude of stimulus (higher the stimulus, higher the depolarization). They decay overtime, meaning the stimulus gets weaker overtime and distance. Produced by neurotransmitters that open NA and K channels.

Question 18

Define an Inhibitory Post-Synaptic Potential (IPSP).

Answer 18

IPSPs bring the neuron farther away from an AP. They are localized, meaning it leads to the hyperpolarization of one area of the plasma membrane. The magnitude of the stimulus is equal to the magnitude of hyperpolarization (higher the stimulus, higher the hyperpolarization). They decay, and are produced by neurotransmitters that open K (in), and Cl (out) of the cell.

Question 19

What are the 2 ways in which an EPSPs can be increased?

Answer 19

Temporal Summation: additive effect, one neuron is firing repeatedly on the pre-synaptic neuron.
Spatial Summation: additive effect, many neurons are firing at the same time on the post-synaptic neuron.

Question 20

What is the name of the neurotransmitter at the NMJ?

Answer 20

Acetylcholine.

Question 21

At the NMJ, once acyetlcholine moves into the post-synaptic membrane it can get broken down by acetylcholinesterase. What 2 particles form when ACh gets broken down, and what happens?

Answer 21

Acetate and Choline form once broken down by acetylcholinesterase. Choline is then recycled back into the pre-synaptic cell, and is used to produce more acetylcholine.

Question 22

What may happen if acetylcholinesterase is blocked in the NMJ?

Answer 22

ACh will be present in the synaptic cleft longer, therefore increasing the chance that an AP will develop in the skeletal muscle cell.

Question 23

What is a graded current called in skeletal muscles?

Answer 23

End plate current (EPC), which can generate end plate potentials (EPPs) that can lead to an AP.

Question 24

What happens in your muscle cells if you’re diagnosed with myasthenia gravis?

Answer 24

Myasthenia gravis is an autoimmune disease, that causes weakness in the skeletal muscles. This weakness developed because the body elicits antibodies that restrict the binding of acetylcholine on nicotinic receptors.

Question 25

What is the triad made up of in a muscle fibre?

Answer 25

Transverse Tubules and Terminal Cisternae.

Question 26

What are the 3 associated proteins associated with the thin myofilament?

Answer 26

Actin (globular protein)
Tropomyosin (rod-shaped protein)
Tropinin (troponin A, troponin C, troponin T).

Question 27

What happens to the sarcomere when a muscle contracts?

Answer 27

When a muscle contracts, the sarcomere shortens/constricts.

Question 28

Where is the voltage sensor connected to on the transverse tubules?

Answer 28

It is located on the terminal cisternae of the SR.

Question 29

Describe the role of the voltage sensors during excitation-contraction coupling.

Answer 29

Voltage sensors detect AP. The change in voltage causes the Ca channels to open, releasing Ca ions from the SR into the muscle cell.

Question 30

What is the role of Ca ion in excitation-contraction coupling?

Answer 30

Ca ion binds to troponin C, which removes tropomyosin from the myosin binding sites of actin. Then, troponin changes shape, and moves exposing the myosin binding site.

Question 31

What happens when myosin attaches to actin (cross-bridge formation)?

Answer 31

A power stroke occurs. This causes the thin myofilament to slide past the thick myofilament towards the M-line. This causes the muscle to contract.

Question 32

What is the role of Calcium ATPase in excitation-contraction coupling?

Answer 32

When there is no longer a change in voltage, calcium ATPase pumps Ca ions back into the SR. This causes the concentration of Ca to decrease in the cytoplasm.

Question 33

What is Rigor Mortis?

Answer 33

The stiffening of the muscle after death. Actin and myosin remain fused to each other because no ATP can be produced to remove them from each other.

Question 34

Why is there a short delay in the latent period of a muscle twitch?

Answer 34

This is due to the time Ca ions are being released from the SR, and binding to troponin c. This causes tropomyosin to shift and expose myosin binding sites on actin (forming cross-bridge).

Question 35

Why do our muscles move smoothy without jerky movements?

Answer 35

This is due to the motor unit ordering and firing.
Ordering - interspread arrangement of muscle cells ensures the muscle contracts smoothy, even if not all motor units are contracting at the same time.
Firing - motor units fore asynchronously

Question 36

Why might more motor units need to be recruited during a muscle contraction?

Answer 36

This is due to an increased load or demand on the muscle to generate force

Question 37

What is the difference between unfused tetanus and complete tetanus?

Answer 37

Unfused Tetanus - when the frequency of the AP still allows for partial relaxation between twitches. this causes tension in the muscle to plateau.
Complete Tetanus - when AP frequency is so high, there is no relaxation between muscle twitches. All twitches summate to provide smooth, sustained movements.

Question 38

Is the somatic motor system control voluntary or involuntary movement to the skeletal muscles?

Answer 38

Voluntary movement.

Question 39

Explain the function of the premotor cortex.

Answer 39

Located in the frontal lobe of the brain, and it is responsible for developing the appropriate strategy for movements that are necessary to perform a task (origin of the sequence of events).

Question 40

Explain the function of the supplementary cortex.

Answer 40

Information from the premotor cortex travels here, (frontal lobe of the brain) and it programs the motor sequences needed to perform and action.

Question 40

Explain the function of the primary motor cortex.

Answer 40

Responsible for activating the neurons needed for the appropriate muscles to perform an action/task. Includes the motor homunculus as well.

Question 41

Explain the function of the motor homunculus.

Answer 41

Illustrates/projection of the brain areas that are responsible for motor function in different parts of the body. Medial to lateral.

Question 42

Explain the function of the primary somatosensory cortex.

Answer 42

Receives information from the thalamus, and detect sensory information from the body (temperature, proprioception, touch, texture, and pain).

Question 43

What is the main function of the corticospinal tract?

Answer 43

Major pathway from the primary motor cortex to the motor neurons that innervate the muscle cells.

Question 44

In the corticospinal tract, where does the splitting of the nerve fibres occur?

Answer 44

At the decussation of the pyramids.

Question 44

If a nerve cell is activated in the left pre central gyrus near the midline (top and central region) of the brain what will occur?

Answer 44

Muscle contraction will occur in the right leg.

Question 45

What is the main function of the muscle spindles?

Answer 45

Detect muscle stretch, length, and the rate of change in the skeletal muscle. The muscle spindle can sense when the muscle is over stretch, and send signals to our brain to increase force production (increasing frequency of the AP) to reduce injury/damage to our muscles. The more stretched the muscle, the more stretched the region, resulting in a higher. frequency of the AP.

Question 46

What is the main function of the Golgi tendon organ?

Answer 46

Detect muscle tension and signals information about the load or force applied to a muscle. When force is applied to the muscle, the collagen fibres squeeze and distort the plasma membranes, causing a depolarization of the afferent neuron, firing an AP.

Question 47

What is the difference between a primary afferent and a secondary afferent stretch receptor?

Answer 47

Primary afferents provide information about length and velocity of a muscle, and they fire at high rates during stretching of the muscle (firing rate depends on the rate of change of the muscle length). Secondary Afferents provide information about length of a muscle only. The firing rate depends only on the immediate length of the muscle, not the rate of change of the muscle length. However, they both send sensory information from the spindle to the CNS.

Question 48

Define alpha-gamma coactivation.

Answer 48

Needed for the muscle to function properly, and for the brain to always know where the muscle is in space and how much power it needs to perform an action. In order for this to occur, commands are sent simultaneously through the gamma motor neurons to the intrafusal fibres, causing a contraction within the infrafusal fibres. This contraction maintains stretch on the central region where central receptors are located, therefore the muscle spindles can send information to the brain about muscle and limb position.

Question 49

What is the difference between an alpha motor nueron and a gamma motor neuron?

Answer 49

Alpha motor neurons innervate extrafusal fibers, which are the fibres that contract to generate power. It can also innervate many muscle fibres at the same time. Gamma motor neurons innervate intrafusal fibres, which are the fibres that keep the muscle sensitive to stretch. They allow the intrafusal fibres to stretch along the extrafusal fibres, allowing for continuous communication with the CNS.

Question 50

True or False.
In the reflex arc, information is carried to your brain, and afferent neurons synapse with efferent neurons.

Answer 50

False. Information is carried to your spinal cord via afferent pathways, and the afferent neuron synapses with an interneuron within the spinal cord. From there, the interneuron will synapse with and efferent neuron, and travel to affector organ via efferent pathways.

Question 51

Does the autonomic nervous system control voluntary or involuntary movement?

Answer 51

Involuntary movement.

Question 52

What is the main functions of the hypothalamus?

Answer 52

The control centre. It makes decisions on the course of action and information sent from the CNS out to effector organs via efferent pathways. It performs important functions through negative feedback control.

Question 52

What is the difference between sympathetic and parasympathetic nervous systems?

Answer 52

The sympathetic nervous system responds to fight or flight situations, and parasympathetic responds to rest and digest/relaxation situations.

Question 53

How does the cerebellum correct movement?

Answer 53

The cerebellum integrates information, by comparing It to the information it gets from the proprioceptors. Feedback received from sensory input gives the cerebellum additional information for making adjustments initially sent by the motor cortex.

Question 54

Define the autonomic ganglion.

Answer 54

In both the sympathetic and parasympathetic nervous systems, and it is a group of cell bodies that the preganglionic neuron synapses onto to relay information to target organ(s).

Question 55

True or false.
The post ganglionic neuron in the sympathetic nervous system is long, myelinated, and releases epinephrine and noradrenaline onto the target organ.

Answer 55

True.

Question 56

What is the main neurotransmitter released at the target organ of the postganglionic neuron of the parasympathetic nervous system?

Answer 56

Acetylcholine.

Question 57

True or false.
The preganglionic neuron of the parasympathetic nervous system is short and closer to the CNS.

Answer 57

False. The perganglionic neuron of the parasympathetic nervous system is long, and closer to the target organ.

Question 58

What are the 4 types of environmental stimuli?

Answer 58

Mechanical (touch, pressure, vibration, sound), chemical (taste, odours, pains), electromagnetic (light), other stimuli (gravity, motion, acceleration, heat).

Question 59

Define an adequate stimulus.

Answer 59

It is a particular form of environmental stimulus to which the sensory receptor is most sensitive.

Question 60

Define the somatosensory system.

Answer 60

Detects and processes sensations of touch, vibration, temperature and pain. Majority of these sensations originate in the skin.

Question 61

True or false.
Free nerve endings detect deep pressure and high frequency vibrations.

Answer 61

False. Free nerve endings detect pain, temperature, and light touch.

Question 62

What type of sensations do the Ruffini corpuscles detect?

Answer 62

Sustained pressure and skin stretch. Slow/continuous response.

Question 63

How do these sensory nerves respond to a stimulus?

Answer 63

They release neurotransmitters, which stimulate the dendrites of a sensory neuron, then gets translated into an AP.

Question 64

True or false.
Receptor generated potentials proportional to the stimulus; they themselves are not AP.

Answer 64

True.

Question 65

What is neural coding?

Answer 65

It is a response to stimulus. It elicts fewer or more AP, and the Brin interprets the frequency of the AP.

Question 66

True or false.
The spinothalamic tract brings fine detail, proprioception and vibration to the brain.

Answer 66

False. The spinothalamic tract brings pain, crude touch, and temperature information to the brain. The dorsal column-medial lemniscal system takes fine detail, proprioception and vibration to the brain.

Question 67

What are the 3 photopigments that the cones contain?

Answer 67

S-cones (short wavelengths, blue). M-cones (medium wavelengths, green). L-cones (long wavelengths, red).

Question 68

What is the difference between rod cells and cone cells?

Answer 68

Rod cells function best under low-light, and do not detect colour or fine detail. Cone cells function best under bright light, and detect colours and fine details.

Question 69

What happens to both rod and cone cells in complete darkness?

Answer 69

In complete darkness, both cells will depolarize and release neurotransmitters that inhibits bipolar cells. Na/K pumps are open, and Na enters the cell and K exits the cell.

Question 70

What happens to both rod and cone cells in bright light?

Answer 70

In bright light, both cells will hyperpolarize, and stop releasing neurotransmitters. This causes bipolar cells to release neurotransmitters to ganglion cells, and have a graded potential. Na channel is closed, no Na movement, K channel is open, K is leaving the cell.

Question 71

What are the 4 types of eye movement?

Answer 71

Saccades (rapid, jerky movements), smooth pursuit (smooth movement), Vestibular Ocular Reflex (eye is focus when head is moving), Vergences (movement when an object is approaching or moving away)