Grey Matter

Question 1

Neurones

Answer 1

Dendrons:

Extend from the cell body of the neuron, denrons brand off even further to form the dendrites

Dendrites:

Receive signals

Cell body:

Contains nucleus and other organelles, carry out normal functions of the cell, like protein synthesis

Axon:

Carries electrical signal away from the cell body to the synapses

Synapses:

Lie at the end of the axon and pass the electrical signal on to the next cell

Myelin sheath:

Layers of fat that covers the axon

Schwann Cells:

Membrane encircles the axon many times forming the myelin sheath. Its presence increases the speed of impulse conduction. They also engulf debris and neuronal regeneration.

Nodes of Ranvier:

The gaps between the myelin sheaths

Question 2

Which direction do dendrites travel?

Answer 2

Towards the cell body.

Question 3

Which direction do axons travel?

Answer 3

Away from the cell body.

Question 4

Describe a reflex arc.

Answer 4

Rapid short-lived, automatic and involuntary Stimulus receptor sensory neurone Synapses CNS Relay neuron Synapses Motor neuron Effector

Question 5

Describe the pupil reflex.

Answer 5

Reflex Pathway Light is picked up by photoreceptors in the retina of the eye This is passed on to sensory neurons which pass the signal back to the brain Midbrain sensory neurons target a coordinator The co-ordinator changes the activity of motor neurones targeting muscles in the eye. Dark light - Contraction of radial and relaxation of circular muscles.

Question 6

Describe the resting potential.

Answer 6

-70mV. Neurones have a negative resting potential across their cell (negative inside compared to outside). So negative ions inside the cell have a tendency to leave the cell and positive ions outside the cell have a tendency to enter the cell. Resting potential is about -70mV Sodium-potassium pump Uses ATP to pump 3 sodium ions (+ charge) out of the cell and 2 potassium ions (+ charge) into the cell to maintain the resting potential. Net loss of 1 positive from inside the cell. The membrane is permeable to potassium ions through potassium channels but not to sodium. Potassium ions leave the cell through facilitated diffusion down the concentration gradient Potassium ions have an electrical gradient (into cell) and concentration gradient (out of cell).

Question 7

Describe an action potential (depolarisation, repolarisation and hyperpolarisation).

Answer 7

Depolarisation (positive feedback)

If a sodium channel opens then there is an influx of sodium ions and the membrane potential is reduced. This then causes more voltage-gated sodium channels to open. If the membrane potential exceeds the threshold potential then action potential will occur. This causes all the gates of the sodium channel to open (all or nothing principle) causing the membrane polarity to reverse.

Repolarisation

When the axon becomes positive,voltage-gated potassium channels open (at +40). Voltage-gated sodium channels close. Potassium ions leave the cell and therefore reduce the membrane potential. The potassium channels remain open and leads to the undershoot

Hyperpolarisation

There is a high amount of potassium outside the cell and high amount of sodium inside the cell. The action of the sodium potassium pump restores the ion concentrations back to its resting potential.

Refractory period

In this period it is impossible to initiate another action potential as the axon can’t be depolarised. Allows the action potential to only travel in one direction Action potentials are discrete (only one after the other can occur)

Question 8

Refractory period

Answer 8

It is impossible to initiate another action potential as the axon is unable to be depolarised. - Action potential only one direction - Action potential discete

Question 9

Action Potential Graph

Answer 9

Question 10

What does the size of a stimulus affect?

Answer 10

Frequency of impulses. Number of neurons in a nerve conducting impulses.

Question 11

Define saltatory conduction.

Answer 11

Myelin sheaths increase the speed of conduction because action potential can’t occur where the myelin sheath is present. So the action potential jumps between the nodes of Ranvier.

Question 12

Describe speed of conduction.

Answer 12

Determined by the diameter of an axon. Speed is quicker for normal squid but slower for a giant squid. The myelin sheath acts as an electrical insulator and the depolarisation occurs in the nodes of Ranvier.

Question 13

Synapses workings

Answer 13

• action potential reaches the synaptic nob
• calcium channels open and calcium (from the synaptic cleft) in to the pre-synaptic nob
• the the vesicles with the neurotransmitters moves to the cell membrane and the transmitter is release through exocytosis
• neurotransmitters move to the post-synaptic through the cleft and binds to the receptors on the post synaptic membrane
• neurotransmitter stimulates action potential through depolarizing (sodium channels open)

Question 14

How are neurotransmitter are removed from the synapse

Answer 14

The neurotransmitter breaks down at the receptors and there is a large concentration gradient causing the parts to move back to the pre-synaptic nob and form vesicles so the NT are ready to be used again.

Question 15

What are synapses used for?

Answer 15

Control of nerve pathways. Integration of information from different neurons.

Question 16

Acetylcholine

Answer 16

Found in all nerves of the voluntary and the parasympathetic autonomic system

Question 17

Describe excitatory synapses.

Answer 17

Post-synaptic membrane is more permeable to Na+ ions.

Question 18

Describe inhibitory synapses.

Answer 18

Less likely for there to be an action potential. Cl- and K+ channels are opened. Greater potential difference leads to hyperpolarisation.

Question 19

What are the differences between nervous and hormonal control?

Answer 19

Nerves transmit signals electrically, hormones transmit signals chemically. Nerves are fast acting, hormones are slow acting. Nerves create short-term changes, hormones create long-term changes. Nerves are transmitted in action potentials, hormones are transported in blood. Nerves have a local response, hormones have a widespread response.

Question 20

Rod cells at rest

Answer 20

Sodium diffuse in through open cation channels

The sodium moves down the concentration gradient to the inner segment

The sodium is actively pumped out causing it to be depolarised to -40mV

The membrane is slightly depolarised which triggers a neurotransmitter (glutamate) to be released.

This diffuses across the synaptic cleft to a bipolar cell, preventing it from depolarising,

Question 21

Rod cells detect light

Answer 21

Light is absorbed by rhodopsin in the rod cell.

Rhodopsin breaks down into opsin and retinal.

Cation channel to close.

This means that the inner segment continues to pump sodium ions out of the cell so the membrane becomes hyperpolarized.

So glutamate is not released across the synapse so an action potential forms and is transmitted to the brain.

The information from the optic nerve is processed by the brain in the visual cortex.

Question 22

How does auxin work?

Answer 22

Stimulates growth in response to cell elongation.

Light –> Found at the shaded side so grows to the sun

Gravity –> Found against gravity so it grows down

Question 23

Describe phytochromes.

Answer 23

Pr absorbs red light. Pfr absorbs from infrared light.

Pr inhibits growth

Pfr promotes growth

Question 24

Phytochrome and Germination

Answer 24

Phytochromes are first synthesized in the young seed at the inactive Pr form.

Exposed to light, Pr is converted to Pfr

The Pfr form allows chlorophyll molecules to be synthesized so the growing seed can start to photosynthesise.

The Pfr form also promotes growth and flowering by active as a transcription factor

Question 25

Phytochrome and Flowering

Answer 25

The balance of the two forms of phytochromes are affected by the varying period of light and dark

At night, the Pfr is converted back to Pr slowly as there is no light (Pr high levels)

In the day there is lots of red light so Pr is converted to Pfr quickly (Pfr high levels)

Long days results in Pfr building up

Short days results in Pr building up

Question 26

Describe the consequences of a stroke.

Answer 26

Problems with speech, understanding, reading and writing.

Question 27

What leads to recovery from a stroke?

Answer 27

Neural plasticity.

Question 28

Describe how PET scans help diagnose Alzheimer’s.

Answer 28

The accumulation of beta amyloid is a sign of Alzheimer’s. Synapses become blocked by beta amyloid proteins. This can be tracked with an amyloid tracer.

Question 29

What is the role of the thalamus?

Answer 29

Routes sensory information correctly.

Question 30

What is the role of the hypothalamus?

Answer 30

Thermoregulation, sleep, thirst and hunger.

Question 31

What is the role of the hippocampus?

Answer 31

Long-term memory.

Question 32

What is the role of the basal ganglia?

Answer 32

Selects and initiates stored programmes.

Question 33

What is the role of the cerebellum?

Answer 33

Balance, movement, motor skills.

Question 34

What is the role of the midbrain?

Answer 34

Relays information.

Question 35

What is the role of the medulla oblongata?

Answer 35

Regulates processes that are not consciously controlled.

Question 36

What is the role of the frontal lobe?

Answer 36

Higher brain functioning, association, primary motor cortex.

Question 37

What is the role of the parietal lobe?

Answer 37

Orientation, movement, sensation, calculation, recognition and memory.

Question 38

What is the role of the temporal lobe?

Answer 38

Processing auditory information.

Question 39

What is the role of the occipital lobe?

Answer 39

Processing information, involed in vision and intepreting signals coming from the retine

Question 40

Describe a CT scan.

Answer 40

Uses X-rays to assess brain damage, the x-ray beams are through the patient and picked up with a detector on the opposite side.

Exposes the patient to harmful radiation

Question 41

Describe an MRI scan.

Answer 41

Uses a magnetic field to image the structure in the brain

Forms higher quality images than CT scan

Used for diagnosis of medical problems as tumour cells respond differently to a magnetic field

Question 42

Describe an fMRI scan.

Answer 42

Follows areas of the brain by following uptake of oxygen. Deoxyhaemoglobin absorbs radio waves.

Question 43

Describe a PET scan.

Answer 43

Uses radioactive decay of certain isotopes to image brain activity. This builds up a map of radioactivity in the brain.

Very detailed and can be used to investigate both structure and the function of the brain in real time.

These scans can show if areas in the brain are unusually inactive or active. So useful for studying disorders (Alzheimer’s disease)