6B - Nervous System Coordination

Question 1

What does the nervous system consist of

Answer 1

• made up of the peripheral and central nervous systems.
  > PNS includes receptors, sensory and motor neurons, while
  > CNS consists of the coordination centers such as the brain and
  spine.
  .
  .
• The electrical impulses that pass along neurons are due to movement of ions across membranes.
• Therefore, topic includesunderstanding transport across a membrane
• and plasma membrane structure is key to understanding this topic.

Question 2

Myleinated neurons

Answer 2

• cell body of neuron contains organelles found in typical animal cell, inc nucleus.
• It is in cell body where proteins and neurotransmitter chemicals are made.
  .
  .
• Dendrites are branched extensions protruding from cell body. These carry action potentials to surrounding cells.
• The axon is conductive, long fiber that carries nervous impulse along the motor neuron.
  .
  .
• Schwann cells wrap around axon to form myelin sheath, wch is a lipid and so
• does not allow charged ions or the impulse to pass through it. There are gaps
  > between these myelin sheaths, called nodes of Ranvier.

Question 3

What is resting potential

Answer 3

• Resting Potential
- When a neuron is not conducting an impulse, theres a difference
- between the electrical charge inside and outside of neuron; the resting potential.
.
- are more positive ions, Na+ and K+, outside compared to inside, so the inside of the neuron
» is comparatively more negative at. -70mV.
- The resting potential is maintained by a Na-K pump, involving AT and therefore ATP.
- The pump moves 2K+ ions in and 3 Na+ ions out.
.
- this creates a conc gradient and results in K+ diffusing out and Na+ diffusing in.
- However, bc membrane is more permeable to K+, more are moved out resulting in - 70mV.

Question 4

What is action potential

Answer 4

• When the potential of the neuron changes, this is an action potential, and it results in nervous impulse.
• Changes in membrane permeability lead to depolarization and generation of action potential.
  .
• Throughout depolarization, the Na+ continues to rush inside until action potential
• reaches its peak and the Na+ gates close. If depolarization is not high enough to exceed a threshold,
• then an action potential and the impulse are not produced.
  .
  »> This is called All-or-None Principle: important as ensures animals only respond to large enough stimuli,
  »> rather than responding to every slight change in environment, wch wd overwhelm them.

Question 5

How does action potential take place

Answer 5

• A stimulus provides energy that cause Na+ voltage-gated channels
• (proteins in membrane only open when certain voltage is reached) in the axon membrane to open.
  > causes Na+ to diffuse in, wch incs positivity inside axon. So causes more voltage-gated channels to open,
  > so even more Na+ diffuses in. When a threshold of +40mV is reached inside axon, voltage-gated Na+ channels close
  .
  .
• and instead voltage-gated K+ ion channels open: results in K+ ions diffusing out,
• and the axon becoming negative again and repolarizes axon.
• Temporarily, axon becomes more negative than -70mV: is hyperpolarized.
• The K+ ion gates will now close, and the Na-K pump restores normal activity to reform resting pot.

Question 6

What happens when an action potential is generated, specifically in myleinated neurons

Answer 6

• Once an AP is generated, it moves along the axon like a Mexican wave.
• will occur along entire axon in a non-myelinated neuron, whereas its much quicker in myelinated axons.
• Action potentials can only occur at the nodes of Ranvier, where there is no myelin insulating.
  .
• Therefore, localized action potentials will jump from node to node and travel much quicker: saltatory conduction.

Question 7

How does temperature and axon diameter impact speed of conduction

Answer 7

• In addition to myelination and saltatory conduction increasing the speed of conduction,
  » temperature and axon diameter also have an impact.
  .
• The higher the temp, faster the ions will diffuse and so increase conduction. The wider
• the diameter of the axon, faster rate of conduction because larger diameter, the less likely
• ions to leak across the membrane and affect the potential.

Question 8

Factors that increase speed of conductionnif neurons

Answer 8

• saltatory conduction, myelination, temp, axon diameter

Question 9

Whats the refractory period and three importances

Answer 9

• Straight after an action potential has been generated, membrane enters a refractory period
• when it can’t be stimulated because Na+ channels are recovering and can’t be opened.
• This means that voltage-gated Na+ channels are closed; important for many reasons
  .
  .
  1. ensures discrete impulses are produced, meaning an action potential cannot be generated
• immediately after another, and this makes sure that each is separate from another.
  .
  2. ensures APs travel in one direction: stops action potential spreading in two directions and prevents a response.
  3. limits number of impulse transmissions to prevent overreaction to stimulus, so overwhelming senses.

Question 10

Whats the synapse

Answer 10

• Synapses are gaps between end of axon of one neuron and dendrite of
  another.
• here, action potential is transmitted as neurotransmitters that diffuse
  across the synapse.
  This is th process:
  .
  .
  1. AP arrives at synaptic knob - depolarisation of knob leads to Ca2+ channels opening
  2. so Ca+ diffuses into synaptic knob. Vesicles containing NT move toward and fuse
  3. W presynaptic membrane . NT released into synaptic cleft
  .
  4. NT diffuses down conc gradient across synaptic cleft, to post synaptic membrane
  5. NT binds by complimentarity of shape to receptors on surface of post synaptic membrane
  6. Na+ channels on postsynaptic open and Na+ diffuse in- if enough NT then enough Na+ diffuses in
  .
  7. Above threshold then post synaptic depolarises , so NT degrades and released from receptor
  8. Na+ channel closes and post synaptic can restablish resting pot
  »
  » NT transported back into presynaptic where it’s recycled

Question 11

Whats a neuromuscular junction and points that define it

Answer 11

• This is a synapse that occurs between a motor neuron and a muscle - very similar to a synaptic junction.
.
- only excitatory
- connects motor neuron to effector: muscles
- end point for action potential
- acetylcholine binds to receptors on muscle fiber membranes - sarcoplasmic reticulum

Question 12

Points of cholinergic synapse

Answer 12

• Could be excitatory or inhibitory.
  > Inhibitory synapses cause Cl- ions to move into postsynaptic and K+ to move out.
  > combined effect of negative ions moving in and positive ions moving out
  > makes membrane potential increase to -80mV, hyperpolarization, and so an AP is highly unlikely.
  .
  .
• connects two neurons (sensory, relay or motor)
• new AP generated in next neuron
• acetylcholine binds to receptors on post synaptic membrane of neuron

Question 13

Why do action pots travel in one direction

Answer 13

Uni directional because of NT receptors only being on post synaptic membrane

Question 14

Whats summation

Answer 14

• Summation is rapid build-up of NTs in synapse to help generate an action potential by two methods:
  » spatial or temporal summation.
  > needed bc some action potentials do not result in sufficient concs of NT
  > being released to generate a new action potential.

Question 15

Whats spatial summation

Answer 15

Spatial summation:
-many different neurons collectively trigger a new action potential
- by combining the neurotransmitter they release to exceed the threshold value.

Question 16

What’s temporal summation

Answer 16

Temporal summation:
- One neuron releases neurotransmitter repeatedly over
- a short period of time to add up to enough to exceed the threshold value.

Question 17

Whats the pacinian corpuscle

Answer 17

> an example of a receptor that detects stimuli

• Each receptor responds only to specific stimuli, and this stimulation of a receptor
• leads to the establishment of a generator potential, wch causes a response.
• The Pacinian corpuscle responds to pressure changes: receptors occur deep in skin, in fingers and feet.
  .
  .
• consists of single sensory neuron wrapped w layers of tissue separated by gel.
• Plasma membranes contain channel proteins that allow ion transportation.
• ## The membranes surrounding sensory neuron have stretch-mediated Na+ channels.
• In resting state, Na+ channels are too narrow for Na+ to diffuse, so resting pot is maintained.
• When pressure is applied, it deforms the membrane, stretches and widens the Na+ channels
• so Na+ diffuses in: leads to the establishment of a generator potential.

Question 18

How does pacinian corpuscle generate a potential

Answer 18

• consists of single sensory neuron wrapped w layers of tissue separated by gel.
• Plasma membranes contain channel proteins that allow ion transportation.
• ## The membranes surrounding sensory neuron have stretch-mediated Na+ channels.
• In resting state, Na+ channels are too narrow for Na+ to diffuse, so resting pot is maintained.
• When pressure is applied, it deforms the membrane, stretches and widens the Na+ channels
• so Na+ diffuses in: leads to the establishment of a generator potential.

Question 19

What are rods ?

Answer 19

• The retina contains two types of photoreceptors: rods and cones.
  .
  • Rods, cannot distinguish diff wavelengths of light and process images in black and white.
• ## Rods detect light of very low intensity bc many rod cells connect to one sensory neuron.
• The threshold to create an action potential can be reached even in low light bc
• so many rod cells are connected to a single bipolar cell: an example of summation.
• ## To create the generator potential, pigment of rod cells (rhodopsin) must be broken down.
• is enough energy from low-intensity light to cause breakdown. However,
• this retinal convergence means brain cant distinguish between separate sources of light
• that stimulated it. Two dots close together cant be seen as separate. Rod cells give low visual acuity.

Question 20

What are cones

Answer 20

• There are three cone cells that contain different types of iodopsin pigment (red, green, and blue),
• which all absorb diff wavelengths of light. Depending on the proportion of each cone cell stimulated,
• ## we perceive color images. lodopsin is only broken down if there is
• a high light intensity, so action potentials can only be generated with enough light.
• Usually, only one cone cell connects to bipolar cell. So, no spatial summation occurs,
• ## and cones can only respond to high light intensity, wch is why we can’t see color when it is dark.
• As each cone is connected to one bipolar cell, brain distinguishes between
• separate sources of light detected. Cone cells give high visual acuity.

Question 21

Distribution of rods and cone cells

Answer 21

• The distribution of rods and cones in the retina is uneven.
• Light is focused by lens on part of the retina opposite pupil, the fovea, which will receive highest intensity of light.
• Therefore, most cone cells are located near the fovea, and rod cells are further away

Question 22

Control of the heart - role of the SAN

Answer 22

Cardiac muscle is myogenic, but rate of contraction is controlled by a wave of electrical activity.
.
- The sinoatrial node (SAN) is in the right atrium and is known as the pacemaker.
- SAN will release a wave of depolarization across atria, causing it to contract.
- The atrioventricular node (AVN) is located near the border of the right and left ventricle within the atria still.

Question 23

Control of the heart - AVNs role

Answer 23

• AVN will release another wave of
  depolarization when first reaches it.
• There is a non-conductive layer between atria and ventricles: prevents wave of depolarization
• ## traveling down to ventricles. Instead, bundle of His, running through septum, can conduct and
• transmit wave of depolarization down septum and Purkinje fibers in the walls of the ventricles.
• As a result, apex and then walls of ventricles contract. Theres a short delay before this happens,
• ## while AVN transmits the second wave of depolarization.
• allows enough time for atria to pump all blood into ventricles. Finally, cells repolarize - cardiac muscle relaxes.

Question 24

Whats the medulla oblongata

Answer 24

• The medulla oblongata in the brain controls the heart rate via the autonomic nervous system.
• There are two parts: a center linked to the sinoatrial node that increases heart rate
• via sympathetic nervous system and another that decreases heart rate via the parasympathetic NS.

Question 25

Heart rate changes in reponse to increased pressure

Answer 25

- The heart rate changes in response to pH and blood pressure: these stimuli - detected by chemoreceptors and pressure receptors in aorta and carotid artery. . . 1. Stimulus: inc pressure 2. Receptor: pressure receptors in wall if aorta/carotid artery are stretched if high bpressure 3. Coordination: more electrical impulses sent to medulla O and then impulses sent via PNS 4. To SAN to decrease frequency of electrical impulses . 5. Effector: cardiac muscle - SAN tissues 6. Response: reduced heart rate

Question 26

Heart rate changes in reponse to increased pressure

Answer 26

1. Stimulus: decreased pressure 2. Receptor: pressure receptors in aorta and carotid artery wall not stretched if low 3. Coordination: more electrical impulses sent to medulla O and then impulses sent via sympathetic NS 4. To SAN to increase frequency of electrical impulses 5. Effector: cardiac muscle - SAN tissues 6. Response: increased heart rate

Question 27

Heart rate changes in response to pH

Answer 27

- The pH of the blood will decrease during times of high respiratory rate - due to the production of carbon dioxide or lactic acid . 1. Stimulus: decrease pH 2. Receptor: chemoreceptor in wall of aorta and carotid artery 3. Coordination: more electrical impulses sent to medulla O then impulses sent via SNS 4. To SAN to inc freq of electrical impulses 5. Effector : cardiac muscle 6. Response: increased heart rate to delivery blood to lungs rapidly to remove CO2