C26 - The Nervous System

Question 1

What are the 2 divisions of the nervous system?

Answer 1

The peripheral and central nervous systems.

Question 2

What are the 2 divisions of the central nervous system?

Answer 2

The brain and spinal chord

Question 3

What are the 2 divisions of the peripheral nervous system?

Answer 3

Sensory nervous system

Motor nervous system

Question 4

What are the 2 divisions of the motor nervous system?

Answer 4

Somatic nervous system

Autonomic nervous system

Question 5

What does the somatic nervous system do?

Answer 5

Carry impulses from the CNS to skeletal muscles via motor neurones.

This is responsible for voluntary actions.

Question 6

What does the autonomic nervous system do?

Answer 6

Carry impulses from the CNS to muscles in the internal organs such as the smooth muscle of gut and blood vessel walls, and to other effectors, e.g. endocrine glands and the S.A. node, via motor neurones.

This is responsible for involuntary actions.

Question 7

What type of reactions are the somatic and autonomic nervous system responsible for?

Answer 7

Somatic - voluntary

Autonomic - involuntary

Question 8

How do the somatic and autonomic nervous systems differ, in terms of the number of neurones?

Answer 8

In the autonomic nervous system, there are 2 neurones linking the CNS to the effector. They are connected via a synapse situated in a structure called a ganglion, which is outside the CNS.

In the somatic system, there’s a single neurone linking the CNS and effector.

Question 9

How do the somatic and autonomic nervous systems differ, in terms of myelination?

Answer 9

Somatic neurones are myelinated along the length of the axon or nerve fibre.

Autonomic neurones are myelinated between the CNS and the ganglion (pre-ganglionic neurone) but between the ganglion and effector (post-ganglionic neurone) they are unmyelinated.
The length of pre- and post-ganglionic fibres also differ between the sympathetic and parasympathetic branch.

Question 10

How do the somatic and autonomic nervous systems differ, in terms of neurotransmitters used?

Answer 10

Somatic: acetylcholine is always used by the somatic motor neurones at their effector.

Autonomic: the pre-ganglionic neurotransmitter in both branches is acetylcholine.
However, the post-ganglionic neurotransmitter used is different -
- The parasympathetic branch uses acetylcholine.
- The sympathetic branch uses noradrenaline (is adrenergenic.

Question 11

What are the 2 divisions of the autonomic nervous system?

Answer 11

Sympathetic system

Parasympathetic system

Question 12

What is the parasympathetic system?

Answer 12

A system/division of the autonomic system which is active under normal, relaxed conditions.
(Often described as the ‘rest and digest’ system)

Question 13

What is the sympathetic system?

Answer 13

A system/division of the autonomic system which is active under stressful situations e.g. excitement and danger.

(The neurotransmitters used are noradrenaline and acetylcholine).

Question 14

How does the parasympathetic nervous system affect the body? (8)

Answer 14

• Operates during rest/relaxation so allows digestion and increases food movement through the gut.
• Slows heart rate and dilates arteries and arterioles.
• Constricts bronchioles.
• Contracts circular muscles in iris so pupil constricts.
• Stimulates tear and saliva production
• Relaxes bladder and anal sphincters, and no effect on erector pili muscles in skin so hairs lie flat.
• No effect on sweat production
• Ganglia linking the neurones are within the target organ.

Question 15

How does the sympathetic nervous system affect the body? (8)

Answer 15

• Operates during stress-related activities and slows down movement through the gut.
• Speeds up heart rate and constricts arteries and arterioles.
• Dilates bronchioles.
• Contracts radical muscles in iris so pupil dilates.
• No effect on tear production and can make saliva thicker.
• Contracts bladder and anal sphincters and erector pili so hairs stand on end.
• Increases sweat production.
• Ganglia are close to spinal chord, not within target organ.

Question 16

What are the (8) distinct parts of the brain?

Answer 16

Cerebral hemisphere / cerebrum

Pineal gland

Hypothalamus

Cerebellum

Medulla oblongata

Spinal chord

Vertebra

Question 17

What’s an acquired brain injury, ABI?

Answer 17

Any brain injury that occurs after birth e.g. a stroke, infection, haemorrhage or anoxic injury.

Question 18

What are the 2 types of brain damage?

Answer 18

Traumatic brain injury (TBI) -
occurs following a severe blow to the head.

Non-traumatic brain injury -
doesn’t involve a blow to the head/are caused by stoke, infection etc.

Question 19

What are the (5) neuro-imaging techniques used (for diagnosing brain damage)?

Answer 19

MRI

fMRI

CT scans

PET scans

EEG (electroencephalogram)

Question 20

What’s an MRI?

When’s it used?

Answer 20

Magnetic resonance imaging.

This can be used to detect tumours, strokes, areas of infarction and areas of demyelination in the CNS.

Question 21

What’s an fMRI?

When is it used?

Answer 21

A functional MRI.

It allows identification of activity in specific areas of the brain due to increased blood flow.
It relies on the fact that the magnetic properties of haemoglobin change depending on whether its oxygenated or deoxygenated.

fMRI can be used when planning brain surgery to identify specific areas.

Question 22

What’s a CT scan?

Answer 22

Computed tomography / CAT scans.

X-rays and a computer are used to construct images of the internal structures.

Further detail can be obtained by using CT perfusion, where a substance is injected to show which areas are adequately supplied (or perfused) with blood.

Question 23

What’s a PET scan?

Answer 23

Positron emission tomography.

A radioactive form of glucose (FDG) is introduced into the vein and is taken up by tissues.
The scanner then detects the positions released from the glucose to form an image.

As cancerous cells process glucose differently (compared to normal cells), this can be detected and displayed on the image as different colours.

(Useful for monitoring long term care)

Question 24

What’s a EEG?

Answer 24

An electroencephalogram.

Small electrical impulses sent from brain cells to other brain cells are detected by electrodes on the scalp.
These impulses are recorded and monitored for any abnormal readings, which may indicate conditions such as epilepsy, dementia, brain inflammation, head injury or coma.

Question 25

What’s a TBI?

Answer 25

Traumatic brain injury

Question 26

What is the cerebrum / cerebral hemisphere and where is it found?

Answer 26

It’s the largest part of the brain which is formed as two hemispheres. (Top of brain)

Its surface is covered by a layer of nerve cell bodies known as the cerebral cortex which is extensively folded.

Question 27

What does the cerebrum do?

Answer 27

It allows conscious thought processes, emotional responses, understanding and use of language and intelligent thought.

The left cerebral hemispheres receives sensory inputs from receptors on the right side of the body and controls voluntary muscles in the right side from the motor cortex.
The right hemisphere carries out the same functions for the left side of the body.

Question 28

Where is the cerebellum found?

Answer 28

It’s a structure in the brain found the back of the head below the cerebrum.

Question 29

What does the cerebellum do?

Answer 29

It controls the coordination of the muscles and non-voluntary movement, balance, and posture.

It takes in sensory inputs from the retina and other receptors such as the spindle fibres in muscle or organs in the inner ear.

Question 30

Where is the medulla oblongata found?

Answer 30

It’s a structure in the brain found in the lower centre of the head above the spinal-cord.

Question 31

What does the medulla oblongata do?

Answer 31

It controls autonomic activities in the body such as heart rate, breathing rate, blood pressure and peristalsis in the gut muscles.

Question 32

Where is the hypothalamus found?

Answer 32

It is a structure in the brain found in the centre, above the medulla oblongata and below the cerebrum and pineal gland.

Question 33

What does the hypothalamus do?

Answer 33

It’s controls body temperature, osmoregulation, and secretion of hormones via the pituitary gland.

The hypothalamus produces hormones that are secreted by the posterior pituitary, and also produce releasing factors that stimulate the secretion of hormones produced by the anterior pituitary.

Most homoeostatic mechanisms are controlled here.

Question 34

Where is the pituitary gland?

Answer 34

It’s a structure in the brain, found as a small lobe in front of the hypothalamus in the centre of the brain, below the cerebral hemisphere and pineal gland.

Question 35

What does the pituitary gland do?

Answer 35

Posterior lobe stores and secretes hormones produced by the hypothalamus, but the anterior lobe produces and secretes hormones.

Posterior: store and secrete
Anterior: produce and secrete

Question 36

What are the (9) components of a nerve cell / neurone?

Answer 36

Axon
Axon terminals
Nucleus
Nucleolus 
Cell body
Dendrites
Myelin sheath
Node of Ranvier
Schwann cell

(All organelles of eukaryotic cells)

Question 37

What is the structure of a neuron?

Answer 37

They have a cell body with a nucleus and all other cell organelles.
They have short branched extensions from the cell body, called dendrites, which provides an increased surface area to receive the impulses from the other nerve cells.

They have an axon – single long extension from the cell body that carries the impulses away from the cell body.
The axon is usually surrounded by Schwann cells.

Schwann cells are flattened cells that are rolled around the axon as they develop. The plasma membrane of the Schwann cells formed many layers surrounding each axon, forming the myelin sheath.

Question 38

What is the myelin sheath made of (around axons)?

Answer 38

It’s consists of Schwann cells and has high electrical resistance so ensures electrical impulses are passed quickly.

Question 39

What are the three types of neurons?

Answer 39

Sensory

Relay

Motor

Question 40

What do sensory neurons do?

Answer 40

Carry impulses from receptors to the central nervous system.

Question 41

What is the structure of a sensory neuron?

Answer 41

The dendrites join together into a single process, a long myelinated dendron, which carries the impulses to the cell body.

The axon carries the impulse from the cell body, so the cell body is found part way along the neuron and to one side.

Question 42

What do you motor neutrons do?

Answer 42

Carry impulses from the central nervous system to effectors.

Question 43

What’s the structure of the motor neuron?

Answer 43

There are many short dendrites surrounding the cell body and a single long axon that connects to the effector or to other neurons.

Question 44

What is the resting potential difference within the axon membrane?

Answer 44

-65 mV

Question 45

What causes a nerve impulse?

Answer 45

Temporary changes (in Na and K ion concentrations) across the axon membrane.

This causes the electrical potential difference across the membrane to change and become depolarised. The resting potential is re-established once the wave of depolarisation (the action potential) has passed.

Question 46

How is a resting potential established across the axon membrane?

Answer 46

At rest, the inside of the axon membrane has a negative charge compared to the outside of the membrane. (p.d. of -65 mV / negative as the inside is more negative).
The membrane is said to be polarised.

This p.d. is caused by a carrier protein that uses ATP to actively pump Na⁺ ions out and K⁺ ions in to the axon across the membrane.

The active transport of Na⁺ ions out is greater than the transport of K⁺ ions in, since 3 Na ions are moved out for every 2 K ions moved in.

The axon is more permeable to K⁺ ions than Na⁺, so some K ions diffuse out.

Question 47

What’s an action potential?

Answer 47

A change in the electrical membrane potential which causes the transmission of a nerve impulse.

Question 48

Why does an action potential arise (across an axon membrane)?

Answer 48

De to changes in membrane permeability to both K⁺ and Na⁺ ions.

Changes to the electrical membrane potential cause voltage-gated ion channels in the axon membrane to open or close.

This results in movement of the ions across the membrane, further affecting the membrane potential.

Question 49

How does an action potential arise (across axon membranes)?

Answer 49

Voltage-gated Na⁺ ion channels open, allowing Na⁺ to diffuse into the axon, down the concentration gradient.
This causes the membrane to depolarise (becoming more positive inside than out).

When the inside of the axon membrane reaches +40 mV, the Na⁺ ion channels close and the K⁺ ion channels open.

K⁺ ions diffuse out of the axon down a concentration gradient (repolarisation).
This causes the inside to become even more negative (hyperpolarisation) than it was at resting potential.

The K⁺ gates now close and the Na/K pump re-establishes the resting potential.

Question 50

What’s propagation?

Answer 50

The transmission of a nerve impulse along an axon.

As one region becomes depolarised it stimulates the following region to become depolarised.

Question 51

What’s the refractory period?

Answer 51

The short period of time after firing during which it is more difficult to stimulate a neurone.

(Time for ions to be re-balanced after hyperpolarisation).

Therefore impulses can only travel forwards.

Question 52

What’s the ‘all-or-nothing’ rule?

Answer 52

A stimulus has to be of a particular intensity in order to generate an action potential (the threshold).

The larger the intensity, the more frequent the action potentials.

Question 53

What’s the purpose of the myelin sheath?

Answer 53

To provide electrical insulation.
In myelinated neurones, ions can’t pass through the myelin sheath.

Depolarisation occurs at the gaps between Schwann cells, where voltage-gated Na and K ion channels are found, known as nodes of Ranvier.

The action potential jumps from node to node by saltatory conduction. This speeds up transmission of impulses.

Question 54

How do impulses travel in unmyelinated neurones?

Answer 54

As a wave of depolarisation.

Question 55

What does the structure of a synapse consist of?

Answer 55

A synaptic gap between pre and post synaptic neurones.
In the cytoplasm of the synaptic knob of the presynaptic neurone, there are many vesicles containing a neurotransmitter (usually acetylcholine).

The synaptic knob also contains SER and many mitochondria.
The plasma membrane of the knob has high-voltage gated Ca ion channels.

The post synaptic membrane has chemical-gated Na ion channels that carry receptor sites for acetylcholine.

Question 56

What’s saltatory conduction?

Answer 56

The mechanism by which an impulse is transmitted along a myelinated nerve cell.

Question 57

What happens during propagation of an action potential?

Answer 57

The axon is initially in resting state.

Depolarisation of the membrane causes Na ions to flow into the neurone (inside becomes positive).

The inflow of Na ions causes a wave of depolarisation to spread along the membrane.

This process repeats itself along the axon.

Question 58

What happens when an impulse crosses the gap of a (cholinergic/acetylcholine) synapse?

Answer 58

1) An action potential arrives in the presynaptic neurone.
This causes Ca ion channels to open and Ca ions to enter the synaptic knob.

2) The Ca ions cause vesicles of acetylcholine to fuse with the presynaptic neurone membrane.
Acetylcholine is released into the synaptic cleft and diffuses across to the postsynaptic membrane.

3) Acetylcholine binds to specific receptor sites on the Na ion channels in the post synaptic membrane. This causes the Na ion channels to open, allowing Na ions to enter the neurone.
4) If enough Na ions enter to overcome the threshold value, an action potential is generated in the postsynaptic neurone.

5) An enzyme called acetylcholinesterase hydrolysed acetylcholine. The breakdown products diffuse back across the cleft and into the synaptic knob.
Na ion channels close once the acetylcholine is broken down.

6) ATP produced in the mitochondria is used to re-form acetylcholine from the breakdown products.
This is stored in vesicles in the synaptic knob until needed again.

Question 59

What do excitatory postsynaptic potentials (EPSP) do?

Answer 59

Increase the likelihood of an action potential occurring in the postsynaptic neurone.

This is because the neurotransmitter causes the membrane potential to become less negative and closer to the threshold.

Question 60

What do inhibitory postsynaptic potentials (IPSP) do?

Answer 60

Decrease the likelihood of an action potential occurring in the postsynaptic neurone.

This is because the neurotransmitter causes the membrane potential to become more negative and further from the threshold.

Question 61

What’s a reflex arc?

Answer 61

The simplest nerve pathway, necessary for rapid, protective mechanisms of the body, without involving the conscious part of the brain.

Question 62

What’s a spinal and cranial reflex?

Answer 62

Spinal - one involving the spinal cord as the coordinating part of the CNS. E.g. knee jerk or moving hand from heat.

Cranial - one involving lower centre of brain as coordinator. E.g. iris reflex, blinking or salivation.

Question 63

How is the plantar reflex used (by doctors)?

Answer 63

As a diagnostic tool.
This occurs when the sole of the foot is stimulated with a blunt instrument or finger.

In normal individuals, the plantar reflex causes the foot to flex downwards.

In individuals suffering from spinal diseases, the reflex causes the foot to flex upwards.

Question 64

What diagnostic reflexes are used (as diagnostic tools by doctors)?

Answer 64

• Plantar reflex on the soles of foot. Normal response is for foot to flex downwards, not up.
  This can be done to specific nerves in leg too.
• Reflex responses of pupils. Both pupils should constrict in response to light shone in one eye. Different pupil sizes indicates nerve damage.
• Blink reflex. If absent, indicates the person is in a coma.

Question 65

What statistical test can be used to investigate reflex time (by catching a falling ruler)?

Answer 65

Unpaired t-test.

Question 66

What are the effects of brain damage?

Answer 66

It depends on the region of the brain affected.

• Damage to the speech centre causes speech impairment.
• Damage to the motor area of the cerebral cortex can affect the ability to control certain voluntary muscles.
• Damage to the hypothalamus or pituitary gland causes the production and release of large numbers of hormones (which control homeostatic mechanisms).
• Can cause vegetative state.

Question 67

How are drugs used to modify brain activity?

E.g. with Alzheimer’s

Answer 67

• Cholinesterase inhibitors inhibit the enzyme ‘cholinesterase’ from hydrolysing acetylcholine.
  The increase in acetylcholine restores some of the brain’s lost function.
• Some brain damage may be prevented with anti-inflammatory drugs e.g. aspirin and ibuprofen.
  They reduce swelling in the brain and inhibit the formation of cell signalling molecules that are involved in the inflammation response.
  They can also block pain and reduce fever.

Question 68

How are drugs used to treat Parkinson’s disease?

Answer 68

(Parkinson’s disease is due to loss of brain cells which produce dopamine. Dopamine helps control muscle movements therefore, if less is produced, it results in tremor, rigid joints and slow movements.)

Therapeutic drugs (e.g. levodopa which is metabolised to dopamine), dopamine agonists (which mimic dopamine) and monoamine oxidase inhibitors (MAO-B which inhibit the enzyme that breaks down dopamine in neurones) are given.

Question 69

How does alcohol effect the body/brain?

Answer 69

It affects coordination and motor skills by inhibiting neurotransmission across the synapses of some neurones.

• Alcohol binds to GABA receptors. GABA is an inhibitory neurotransmitter which opens chloride ion channels (which causes a negative change shortly inhibits further transmission).
  When alcohol binds to GABA receptors, the on channels remain open for longer causing hyper-polarisation, prolonging inhibition.
• It also binds to glutamate receptors at synapses, preventing glutamate (an excitatory neurotransmitter) from binding to and exciting the cell.

Question 70

How does heroin effect the body/brain?

Answer 70

It’s an example of an opioid.
It causes clouded cognitive function, slowed heart rate and reduced breathing rate.

It’s converted to morphine in the brain and binds to the opioid receptors.
It inhibits dopamine inhibition so dopamine floods the synapse (producing happy feeling).

Question 71

How does marijuana effect the body/brain?

Answer 71

It contains chemical THC which resembles anandamide, a natural cannabinoid, which when produced by the body, stimulates a temporary release of dopamine.

However THC doesn’t break down as rapidly as anandamide so dopamine is present in the body in large amounts for longer periods.

THC blocks the action of the inhibitory neurotransmitter GABA, which normally prevents dopamine release.

Question 72

How do methamphetamines effect the body/brain?

Answer 72

They’re a group of drugs that affect the excitatory synapses in neurones by increasing levels of dopamine released at synapses.

It mimics dopamine and is taken into neurones by dopamine transporters.
Once within, meth enters the dopamine vesicles, forming them out.
Excess dopamine causes transporters to work in reverse, pumping dopamine out. The excess dopamine becomes trapped in the synaptic cleft and repeatedly bind to receptors, causing overstimulation.

The drug is slow to be broken down, so the stimulatory affect of dopamine is prolonged.

Question 73

What’s the lambic system?

Answer 73

The part of the brain that is associated with long term memory, behaviour and emotions.

It influences both the endocrine system and autonomic nervous system, acting as the brains reward system.

Dopamine is released by the hypothalamus, which is part of the limbic system.

Question 74

What’s the purpose of dopamine?

Answer 74

Dopamine is released by the hypothalamus, which is part of the limbic system.

It plays an important part in reward motivation behaviour or activities e.g. exercise, which increase dopamine levels in the brain (happy feeling). (This is also the basis of dependency of some addictive drugs).

Question 75

What are the main reasons for drug dependency?

Answer 75

Psychological

Physical

(Initially from peer pressure, anxiety, depression etc.)