Week 3- The Neuron

Question 1

Why do we need to know about neurons?

Answer 1

• Understanding the full complexity of human behaviour
• Neurons are the building blocks of emotions, dreams and thoughts

Question 2

Outline the parts and function of the Central Nervous System

Answer 2

Control centre, receiving and analysing information and sending instructions

• Brain
• Spinal cord

Question 3

Outline the parts and function of the Peripheral Nervous System

Answer 3

Receives information via sensory neurons, which are then passed on to the CNS

• Nerves
• Ganglia

Question 4

Outline how the CNS and PNS work together

Answer 4

The PNS sends information via the sensory systems in the body (from the organs and tissues) to the CNS and the CNS sends out instructions to the muscles and glands about what to do

Question 5

Outline the three times of neurons

Answer 5

Neurons (or nerve cells) are the basic units of the nervous system

• Sensory (afferent) neurons- transmit information to the brain
• Motor (efferent) neurons- transmit commands from the brain to the muscles and glands of the body
• Interneurons- nerve cells that connect neurons to other neurons

Question 6

Outline the purpose of the myelin sheath

Answer 6

• Insulates axon from other stimuli that might interfere with the signal
• Speeds up the transmission of nerve impulses

Question 7

Outline the two types of matter

Answer 7

• Grey matter- cell bodies, dendrites and unmyelinated axons
• White matter- myelinated axons (white matter = fat)

Question 8

Outline how signals are sent

Answer 8

At the end of the axon are the terminal buttons. Signal is sent down the axon and then sent as a signal across a gap called the synaptic cleft to the dendrite of another neuron

Question 9

How do neurons communicate with one another?

Answer 9

• Refer to the neuron as ‘firing’
• Neurons send messages electrochemically- chemicals cause an electric signal
• Chemicals in the body are “electrically charged”- when they have an electric charge they are called ions

Question 10

How do neurons fire?

Answer 10

• Neurons are surrounded by a membrane that allows some neurons to pass through and blocks some others
• Referred to as semi-permeable
• Most important ions in the NS are:
  • Sodium (Na+)
  • Potassium (K+)
  • Chloride (Cl-)

Question 11

Outline the process of resting potential

Answer 11

• When a neuron is not sending a signal, it is “at rest”
• At rest, the inside of the neuron is negatively charged relative to the outside
• The cell membrane allows only some ions to pass through channels in the membrane. At rest, potassium ions (K+) can cross through the membrane easily. Chloride ions (Cl-) and sodium ions (Na+) have a more difficult time crossing
• An ion pump moves 3 sodium ions out of the neuron for every 2 potassium ions it puts in

Question 12

Outline the result of a neuron at resting potential

Answer 12

• When all these forces balance out, and the difference in the voltage between the inside and outside of the neuron is measured, you have resting potential
• The resting membrane potential of a neuron is about -70mV (mV = millivolt)- this means that the inside of the neuron is 70mV less than the outside
• When a neuron is stimulated by another, the cell is depolarised
  • Sodium channels open
  • An influx of positive sodium ions
  • Results: the charge inside the cell becomes less negative, making it more likely to fire

Question 13

Outline the process of an action potential

Answer 13

• If the depolarising current brings the resting potential to about the threshold level of -55mV, a neuron will fire an action potential
• If the neuron does not reach this critical threshold level, then no action potential will fire
• Action potentials are the necessary action to enable communication between neurons
• If the neuron does not reach the critical threshold level, then no action potential will fire
• When the threshold is reached, the size of the action potential is fixed
• There are no big or small action potentials in one nerve cell
• The neuron either does not reach the threshold OR a full action potential is is fired. “All or none” principle

Question 14

Outline the role of the synapse

Answer 14

1. The presynaptic neuron has the message (action potential) to send. It has reached action potential, travelled down the axon to the axon terminal, which we can then refer to as the synapse
2. The synapse separates the axon terminal on one neuron from the dendrite on another neuron
3. There is a microscopic gap between the neurons called the synaptic cleft, the action potential cannot cross the synaptic cleft, instead the nerve impulse has to be carried by chemicals called neurotransmitters to the
4. Post synaptic neuron

Question 15

Outline the synapse’s role in firing an action potential

Answer 15

• Inside the terminal button are synaptic vesicles, which contain neurotransmitters
• Post synaptic neuron has receptors for the neurotransmitters
• The action potential causes the vesicles to release the neurotransmitters into the synaptic cleft
• The neurotransmitters land on receptor sites of the post synaptic neuron. If the receptor shape is compatible, it will bind, like a key in a lock. If not, it will not bind
• The shape is determined by the chemical structure of the neurotransmitter
• Those neurotransmitters that do not bind break down or drift away from the site and may be reabsorbed by the pre-synaptic neuron (reuptaken)

Question 16

Outline the effects of neurotransmitters

Answer 16

• Either increase (excitatory neurotransmitters) neural firing- hyperpolarisation
• Or decrease neural firing (inhibitory neurotransmitters)- depolarisation

Question 17

Outline the process of summation

Answer 17

• Process of summation occurs at the axon hillock]
• Neurotransmitters produce stronger effects through summation
• Can be temporal summation- involves a single presynaptic neuron rapid-firing signals to a postsynaptic neuron
• Can be spatial (or partial) summation- multiple postsynaptic potentials all occurring simultaneously at different receptor sites

Question 18

Outline long term potentiation

Answer 18

• When a synapse is repeatedly activated, each activation strengthening neural pathways
• Increased sodium channels, so sodium can enter cell, making action potentials more likely to happen
• More synapses grow between neurons

Question 19

Define multiple sclerosis and outline the process of demyelination

Answer 19

• A person’s immune system is attacking its own tissue
• Immune system attacks myelin, affecting neurons in many ways. Inflammation on myelin, damaging it to the extent that it deteriorates (demyelination)
• When demyelination occurs, transmission of electrical signals along the axon is impaired. Possible to repair damaged myelin in remyelination, after inflammation is reduced
• If demyelination perseveres, MS lesions are observed. Scarring is visible on MRI tests. Depending on where lesions occur, will result in different types of function impairments
• Absence of myelin sheath would likely stop action potential completely

Question 20

Outline symptoms of multiple sclerosis

Answer 20

• Central
  
  • Fatigue
  • Cognitive impairment
  • Depression
  • Anxiety
  • Unstable mood
• Visual
  
  • Nystagmus
  • Optic neuritis
  • Diplopia
• Speech
  
  • Dysarthria
• Musculoskeletal
  
  • Weakness
  • Spasms
  • Ataxia
• Sensation
  
  • Pain
  • Hypoesthesia
  • Paraesthesia
• Bowel
  
  • Incontinence
  • Diarrhoea or constipation

Question 21

Outline the role of acetylcholine and associated disorders

Answer 21

• Widely distributed excitatory NT
• Triggers muscle contraction and stimulates excretion of certain hormones
• Involved in wakefulness, attentiveness, anger, aggression, sexuality and thirst etc
• Lack of acetylcholine in certain parts of the brain is associated with Alzheimer’s disease

Question 22

Outline the role of dopamine and associated disorders

Answer 22

• Involved in controlling movement and pressure
• Modulates mood
• Plays a central role in positive reinforcement and dependency
• Lack of dopamine in certain parts of the brain causes muscle rigidity typical of Parkinson’s disease

Question 23

Outline the role of GABA (gamma-aminobutyric acid) and associated disorders

Answer 23

• Inhibitory neurotransmitter widely distributed in the neurons of the cortex
• Contributes to motor control, vision and many other cortical functions
• Regulates anxiety
• Some drugs that increase the level of GABA in the brain are used to treat epilepsy and to calm the trembling of people suffering from Huntington’s disease

Question 24

Outline the role of glutamate and associated disorders

Answer 24

• Major excitatory NT
• Association with memory and learning
• It is also thought to be associated with Alzheimer’s disease, whose first symptoms include memory impairments

Question 25

Outline the role of serotonin and associated disorders

Answer 25

* Contributes to various functions, e.g. regulating body temperature, sleep, mood, appetite and pain * Depression, suicide, impulsive behaviour and aggressiveness all appear to involve certain imbalances in serotonin

Question 26

Outline the role of norepinephrine and associated disorders

Answer 26

* Important for attentiveness - Emotions - Sleeping - Dreaming - Learning * Released as a hormone into the blood * Causes blood vessels to contract and heart rate to increase * Norepinephrine plays a role in mood disorders such as bipolar disorder

Question 27

Outline the role of the endocrine system

Answer 27

* Endocrine glands release hormones into the bloodstream * Hormones travel through the bloodstream, they can simultaneously activate diffused target sites * Hormones can have an organisational effect- facilitate a permanent change in the structure and function, e.g. androgens which permanently lower the voice

Question 28

Outline the structure and function of the somatic nervous system

Answer 28

* Consists of peripheral nerve fibres that send sensory information to the central nervous system, AND motor nerve fibres that project to skeletal muscles * Mostly involved in intentional actions (and as such is referred to as the voluntary nervous system) * Also involved in some involuntary or automatic actions such as balance

Question 29

Outline the structure and function of the autonomic nervous system

Answer 29

* Regulates the function of our internal organs and controls basic life processes e.g. respiration * Consists of two part - Sympathetic system: the emergency system (fight, flight or freeze) - Parasympathetic system: carries out routine activities that maintain our energy resources