6A: Nervous Coordination

Question 1

What are the 2 major parts of the nervous system?

Answer 1

● Central nervous system
○ Brain and spinal cord
○ The spinal cord is a column of nervous tissue that runs along back and lies inside the vertebral column for protection
● Peripheral nervous system
○ Pairs of nerves that originate from either brain or spinal cord

Question 2

Parts of the peripheral nervous system

Answer 2

Peripheral nervous system:
● Sensory neurones - carry nerve impulses from receptors towards the CNS
● Motor neurones - carry nerve impulses away from CNS to effectors
● Intermediate neurones (coordinator) - connect spinal motor and sensory neurons
● Relay neurones - between sensory and motor neurons in the brain and spinal cord

Question 3

Motor neurones further subdivided

Answer 3

● Voluntary nervous system - carries nerve impulses to body muscles and is under voluntary (conscious) control
● Autonomic nervous system - carries nerve impulses to glands, smooth muscle and cardiac muscle and is not under
voluntary control, that is, it is involuntary (subconscious)

Question 4

What is a reflex?

Answer 4

Involuntary response to a sensory stimulus

Question 5

What is the reflex arc?

Answer 5

The pathway of neurones involved in a reflex

Question 6

Spinal reflex

Answer 6

1. Stimulus
2. Receptor
3. Sensory neuron
4. Coordinator (intermediate neuron)
5. Motor neurone
6. Effector
7. Response

Question 7

What are the advantages of the reflex arc?

Answer 7

Increases survival, protects the body from harm.
● Involuntary - do not require brain
○ Brain is not overloaded with situations in which response is always the same.
● Fast - neuron pathway is short
○ Only one or two synapses where neurons communicate with
○ Synapses are the slowest link in a neuron pathway
● Absence of decision making - rapid action
● Effective from birth, do not have to be learnt

Question 8

What is a resting potential?

Answer 8

the potential difference across the membrane due to a difference in charge between the inside and outside of a cell when it is at rest (inside is negatively charged relative to the outside).

Question 9

What is a generator potential?

Answer 9

change in the potential difference when a stimulus is detected as the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell

Question 10

What is the threshold level?

Answer 10

the level the generator potential reaches to trigger an action potential.

Question 11

What is the action potential?

Answer 11

electrical impulse along a neurone triggered if the generator potential is big enough and reaches the threshold level. Action potentials are all one size, so the strength of the stimulus is measured by the frequency of the action potentials.

Question 12

What are Pacinian Corpuscle?

Answer 12

Pacinian corpuscles are mechanoreceptors - they detect mechanical stimuli such as pressure and vibrations

Question 13

Structure of Pacinian Corpuscle

Answer 13

● Contain the end of a sensory neurone (aka sensory nerve ending) wrapped in many layers of
connective tissue called lamellae, each separated by a gel.
● The sensory neuron ending at the centre of the Pacinian corpuscle has a special type of sodium channel in its plasma membrane, a stretch -mediated sodium channel

Question 14

Function of Pacinian Corpuscle

Answer 14

1. In its normal (resting) state, the stretch-mediated sodium channels of the membrane around the neurone of a Pacinian corpuscle are too narrow to allow sodium ions to pass along them. In this state, the neurone of the Pacinian corpuscle has a resting potential.
2. When pressure is applied to the Pacinian corpuscle, it is deformed and the membrane around its neurone becomes stretched
   3.This stretching widens the sodium channels in the membrane and sodium ions diffuse into the sensory neurone.
3. The influx of sodium ions changes the potential of the membrane (it becomes depolarised), thereby producing a generator potential.
   5.The generator potential in turn creates an action potential (nerve impulse) that passes along the neurone and then, via other neurones, to the central nervous system

Question 15

Distribution of rod and cone cells

Answer 15

➔ The distribution of rod and cone cells on the retina is uneven.
➔ Light is focused by the lens on the pan of the retina opposite the pupil (the fovea).
➔ The fovea therefore receives the highest intensity of light.
➔ Therefore cone cells, but not rod cells, are found at the fovea.
➔ The concentration of cone cells diminishes further away from the fovea.
➔ At the peripheries of the retina, where light intensity is at its lowest, only rod cells are found.

Question 16

What explains the difference in sensitivity and visual acuity in mammals?

Answer 16

The distribution of rod and cone cells, and the connections they make in the optic nerve,

Question 17

Sensitivity of Rod cells to colour

Answer 17

● Rod cells cannot distinguish different wavelengths of light
○ Therefore lead to images being seen only in black and white.

Question 18

Sensitivity of Rod cells to light

Answer 18

● Many rod cells are connected to a single sensory neurone in the optic nerve
● Rod cells are used to detect light of very low intensity.
● A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells .
● As a number of rod cells are connected to a single bipolar cell (retinal convergence), there is a much greater chance that the
threshold value will be exceeded than if only a single rod cell were connected to each bipolar cell (due to summation).
● In order to create a generator potential, the pigment in the rod cells (rhodopsin) must be broken down.
● There is enough energy from low-intensity light to cause this breakdown

Question 19

Visual acuity in cone cells

Answer 19

● Each cone cell has its own connection to a single bipolar cell
● This means that, if two adjacent cone cells are stimulated, the brain receives two separate impulses.
● The brain can therefore distinguish between the two separate sources of light that stimulated the two cone cells.
● This means that two dots close together can be resolved and will appear as two dots.
● Therefore cone cells give very accurate vision, that is, they have good visual acuity

Question 20

What does the peripheral nervous system split into?

Answer 20

• Somatic (conscious)
• Autonomic (unconscious)

Question 21

What are the two divisions of the autonomic nervous system?

Answer 21

.The sympathetic nervous system – this stimulates effectors and so speeds up any activity. It controls effectors when
we exercise strenuously or experience powerful emotions. Helps us to cope with stressful situations by heightening our
awareness and preparing us for activity (fight or flight response).
.The parasympathetic nervous system– this inhibits effectors and so slows down any activity. It controls activities
under normal resting conditions. It is concerned with conserving energy and replenishing the body’s reserves. (Rest and
The parasympathetic nervous system digest).

Question 22

What are the actions of the sympathetic and parasympathetic nervous system?

Answer 22

Antagonistic

Question 23

Cardiac muscle is myogenic. What is meant by this?

Answer 23

Self stimulation from inside muscle rather than outside

Question 24

What structures control, by electrical activity, the rate of contraction?

Answer 24

● Sinoatrial node (SAN) (pacemaker) – distinct group of cells within the wall of the right atrium of the heart. It is from
here that the initial stimulus for contraction originates. Controls rhythm of heartbeat by sending out regular waves of
electrical activity to atrial walls, causing them to contract simultaneously.
● Atrioventricular node (AVN) – group of cells in walls of right and left ventricle. They receive electrical activity from
the SAN. Slight delay so that ventricles cn fill with blood before contraction.
● The Purkyne fibres – specialised muscle fibres in the walls of the ventricles that convey electrical activity to the
apex of the heart.
● The bundle of His – Purkyne tissue collectively make this up which runs through the septum in the walls of the ventricles that convey electrical activity to the apex of the heart

Question 25

How do these structures control heart rate?

Answer 25

1. The SAN sends a wave of electrical excitation/depolarisation to the atrial walls, causing them to contract simultaneously.
2. A layer of non-conductive collagen tissue (atrioventricular septum) prevents the wave crossing to the ventricles .
3. Instead, the wave of excitation/depolarisation enters the AVN, which will lies between atria.
4. After a short delay (beneficial allowing enough time for the atria to fully pump all the blood into the ventricles before
   ventricles contract) the AVN passes the wave of electrical excitation/depolarisation between the ventricles along the bundle of His.
5. The bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the
   bundle branches into smaller fibres of Purkyne tissue in the right and left ventricle walls.
6. The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly and simultaneously from the bottom of the heart upwards.
7. The cells then repolarise, and the cardiac muscle relaxes

Question 26

What region of the brain controls changes to the heart rate?

Answer 26

Medulla Oblongata

Question 27

What are the roles of the sympathetic and parasympathetic nervous system in controlling heart rate?

Answer 27

● Sympathetic nervous system - increases heart rate
● Parasympathetic nervous system - decreases heart rate

Question 28

Control of HR in response to high blood O2/Low blood CO2/high PH

Answer 28

1. Chemoreceptors in carotid arteries detect blood has a lower than normal concentration of CO2.
2. Increase the frequency of nervous impulses along sensory neurone to medulla oblongata.
3. This increases frequency of nervous impulses along the parasympathetic neurones to the SAN.
4. The parasympathetic neurones secrete acetylcholine which binds to receptors on the SAN
5. Less impulses released by SAN
6. Heart rate decreases to return levels back to normal

Question 29

Control of HR in response to low blood O2/low blood CO2/high pH levels

Answer 29

1. Chemoreceptors in carotid arteries detect blood has a higher than normal concentration of CO2.
2. Increase the frequency of nervous impulses along sensory neurone to medulla oblongata.
3. This increases frequency of nervous impulses along the sympathetic neurones to the SAN.
4. The sympathetic neurones secrete noradrenaline which binds to receptors on the SAN
5. More impulses released by SAN
6. Heart rate increases to return levels back to normal

Question 30

Control of HR in response to high blood pressure

Answer 30

1. Baroreceptors in carotid arteries detect blood has a higher than normal blood pressure.
2. Increase the frequency of nervous impulses along sensory neuron to medulla oblongata.
3. This increases frequency of nervous impulses along the parasympathetic neurones to the SAN.
4. The parasympathetic neurons secrete acetylcholine which binds to receptors on the SAN
5. Less impulses released by SAN
6. Heart rate decreases to return blood pressure back to normal

Question 31

Control of HR in response to low blood pressure

Answer 31

1. Baroreceptors in carotid arteries detect blood has a lower than normal blood pressure.
2. Increase the frequency of nervous impulses along sensory neuron to medulla oblongata.
3. This increases frequency of nervous impulses along the sympathetic neurones to the SAN.
4. The sympathetic neurons secrete noradrenaline which binds to receptors on the SAN
5. More impulses released by SAN
6. Heart rate increases to return levels back to normal