Week 9 - Structure of nervous tissue, nerve conduction + peripheral nerves

Question 1

What glial cells are in the central nervous system?

Answer 1

Astrocyte
Oligodendrocyte
Microglia
Ependymal cell

Question 2

What glial cells are in the peripheral nervous system?

Answer 2

Satellite cell
Schwann cell

Question 3

What are the functions of astrocytes and satellite cells?

Answer 3

• Regulate the extracellular microclimate
• Remove waste products
• Scar formation
• Help to selectively control passage of molecules between the blood stream and the nervous tissue via the BBB

Question 4

What are the functions of oligodendrocytes and schwann cells?

Answer 4

• Myelination → provides insulation of the axon.
  Prevents degradation of electrical signals and enhances conduction speeds.

NOT ALL AXONS MYELINATED

Question 5

What is the function of microglia?

Answer 5

injest pathogens - provide immune support to the CNS

Question 6

What is the function of ependymal cells?

Answer 6

Producing cerebrospinal fluid - protective cushion for brain and spinal cord

Question 7

Functions of the brain?

Answer 7

𝟭.𝗔𝘂𝘁𝗼𝗻𝗼𝗺𝗶𝗰 𝗳𝘂𝗻𝗰𝘁𝗶𝗼𝗻𝘀
heartbeat, breathing, digestion, body temp.
𝟮.𝗖𝗼𝗴𝗻𝗶𝘁𝗶𝘃𝗲 𝘀𝗸𝗶𝗹𝗹𝘀
planning, thinking, emotions + behaviours, learning
𝟯.𝗦𝗲𝗻𝘀𝗼𝗿𝗶𝗺𝗼𝘁𝗼𝗿 𝗳𝘂𝗻𝗰𝘁𝗶𝗼𝗻
sensation + movement

Question 8

What two cellular components is neural tissue made of?

Answer 8

• neurons
• glial cells

Question 9

Function of an axon

Answer 9

transmit messages away from cell body

Question 10

Function of a dendrite

Answer 10

receive messages from other cells

Question 11

What are neurones

Answer 11

→functional unit of the nervous system
→specialised cells which transmit electrical impulses
→have common structural features

Question 12

Function of axon terminals

Answer 12

form junctions with other cells

Question 13

Describe a multipolar neurone and example

Answer 13

Many branches coming from the soma.

e.g. Motor neurone

Question 14

Describe a pseudo-unipolar neurone and an example

Answer 14

One process leaving the soma.
The axon has a peripheral branch and a central branch.

e.g. Sensory neurone

Question 15

Describe a bipolar neurone and an example of it’s location

Answer 15

Have one dendritic process and one axonal process with the soma in the middle.

E.g. Retina (vision) or olfactory system (smell)

Question 16

Why is an oligodendrocyte different to a schwann cell?

Answer 16

In an oligodendrocyte, each cell provides for a number of different axonal segments on different axons.

Question 17

How does the astrocyte impact the BBB

Answer 17

It secretes growth factors - stimulate endothelial cells to create an increased number of tight junctions (see a picture).
The more tight junctions, the more effective the permeability of the BBB is to remain selective.

Question 18

What is the resting membrane potential?

Answer 18

Generated by an unequal distribution of Sodium (Na+) Potassium (K+) and Chloride (Cl-) ions.

At rest, this is around -70mV

This is due to the extracellular environment having a net +ve charge and the intracellular environment having a net -ve charge.

Question 19

What is the sodium/potassium pump?

Answer 19

→3 sodium ions bind to the pump.

→A phosphate from ATP is donated to the pump (energy used)

→Pump changes shape and releases sodium ions outside of the cell.

→2 potassium ions bind to the pump and are transferred into the cell.

→Phosphate group is released and pump returns to its original shape.

Question 20

How is an action potential generated?

Answer 20

→Stimulus triggers influx of positively charged ions, changing voltage across membrane from its resting value (-70mV) to a positive value (+30/40mV)
→DEPOLARISATION → transient rapid influx of Na+ ions followed by repolarisation.
→REPOLARISATION → delayed, sustained efflux of K+ions

Question 21

Why is an action potential an ‘all or nothing’ response?

Answer 21

An action potential cannot be generated of different strengths, it is either generated or isn’t, depending on if the threshold stimulus is met.

Question 22

What is a sub-threshold stimulus?

Answer 22

A stimulus that is too small to cause an influx of sodium ions and therefore produce an action potential.

Question 23

What is hyperpolarisation?

Answer 23

Following repolarisation.
A phase where some potassium channels remain open and sodium channels reset.
A period of increased potassium permeability results in excessive potassium efflux before the potassium channels close.

New AP can’t be generated until RMP is restored.

Question 24

What is propagation?

Answer 24

The AP is generated at the axon hillock and then propagates as a wave of depolarisation along the axon.
Voltage-gated Na+ channels produce regenerative current so AP retains amplitude with distance as subsequent patches of membrane are activated.

Question 25

What propagation velocity?

Answer 25

The speed at which an AP moves along axon. (range = 0.1m/sec - 100m/sec).

Question 26

How does myelin improve propagation velocity?

Answer 26

→It is a fatty substance that increases the resistance of the path across the membrane - prevents ions "leaking" out. →In myelinated axons - voltage gated Na+ ions concentrated at Nodes of Ranvier. →AP "jumps" from node to node in a process called SALTATORY CONDUCTION

Question 27

What factors (besides myelin) influence conduction velocities?

Answer 27

diameter of the axon temperature (larger diameters and higher temps. generally increase conduction velocity)

Question 28

Describe the process of synaptic transmission

Answer 28

1. AP reaches axon terminal 2. Calcium channels open 3. Ca2+ causes synaptic vesicles to release a neurotransmitter 4. The neurotransmitter diffuses across the synaptic cleft 5. Before binding to post synaptic receptors (receptor specificity) 6. Activation of receptors causes Na+ channels to open in post synaptic cell → if post synaptic potential reaches threshold, new AP generated in 2nd neurone. Active re-uptake of remaining neurotransmitter from synaptic cleft.

Question 29

What is a neurotransmitter?

Answer 29

A chemical messenger that transmits signals across a chemical synapse from one neuron to another (dopamine, serotonin, acetylcholine, GABBA, glutamate, noradrenaline etc)

Question 30

What is summation?

Answer 30

The post synaptic potentials (PSP's) produced by each active synapse can sum together - in space and/or time - to determine the behaviour of the postsynaptic neuron.

Question 31

What is spatial summation?

Answer 31

The addition of simultaneous stimuli from several conducting fibres. Excitatory potentials from many neurons trigger threshold point.

Question 32

What is wave summation?

Answer 32

Many excitatory potentials from one neuron triggers threshold point.

Question 33

What constitutes the CNS?

Answer 33

The brain and spinal cord (integration and command centre)

Question 34

What are the divisions of the peripheral nervous system?

Answer 34

Autonomic nervous system → regulates internal environment (sympathetic + parasympathetic division) Somatic nervous system → enables us to interact with the external environment (involves sensory and motor nerves)

Question 35

How does the CNS interact with the ANS?

Answer 35

The ANS uses autonomic sensory neurones to transmit information from internal organs and feed-back to the CNS. The CNS processes this information and produces a motor command for the autonomic motor neurones which transmit signals from the CNS to innervate internal organs and glands. (involuntary control)

Question 36

How does the CNS interact with the SoNS?

Answer 36

Somatic sensory neurones transmit information from the sense organs and feed-back to the CNS. The CNS processes this information and produces a motor command. Somatic motor neurons transmit signals from the CNS to innervate skeletal muscles. (voluntary control)

Question 37

Spinal cord structure?

Answer 37

→ long, delicate cord of nervous tissue → about 45cm long and between 6mm - 13mm in diameter → protected by bony structures in the vertebral column

Question 38

Spinal cord location?

Answer 38

→ lies in vertebral canal → pair of spinal nerves emerge from each spinal vertebrae level via the intervertebral foramen (easily squashed)

Question 39

Spinal cord function?

Answer 39

Responsible for transmitting nerve signals to and from brain

Question 40

How many cervical vertebrae are there?

Answer 40

7

Question 41

How many thoracic vertebrae are there?

Answer 41

12

Question 42

How many lumbar vertebrae are there?

Answer 42

5

Question 43

How many sacral vertebrae are there?

Answer 43

5 fused vertebrae

Question 44

How many vertebrae are in the coccyx?

Answer 44

4 fused vertebrae

Question 45

How many pairs of spinal nerves are there?

Answer 45

31

Question 46

How many pairs of cervical spinal nerves are there?

Answer 46

8

Question 47

How many pairs of thoracic spinal nerves are there?

Answer 47

12

Question 48

How many pairs of lumbar spinal nerves are there?

Answer 48

5

Question 49

How many pairs of sacral spinal nerves are there?

Answer 49

5

Question 50

How many pairs of coccygeal spinal nerves are there?

Answer 50

1

Question 51

What does grey matter within the spinal cord consist of?

Answer 51

Cell bodies of neurones within the spinal cord

Question 52

What does white matter within the spinal cord consist of?

Answer 52

myelinated axons

Question 53

What is the dorsal root?

Answer 53

Afferent (sensory) fibres (all sensory info comes into spinal cord at the back)

Question 54

What is the ventral root?

Answer 54

Efferent (motor) fibres (all motor info leaves spinal cord at the front)

Question 55

What is the dorsal root ganglion?

Answer 55

Cluster of cell bodies - sensory neurones

Question 56

What are the grey and white rami responsible for?

Answer 56

Making connections with the ANS via the sympathetic ganglion

Question 57

What is a mixed spinal nerve?

Answer 57

Refers to the part of the nerves where both afferent (sensory) and efferent (motor) nerves are housed in the same nerve epineurium to go through the intervertebral foramen.

Question 58

What is the ventral ramus?

Answer 58

→Branches from the mixed spinal nerve. →Larger than dorsal ramus. → Carries sensory and motor info →Supplies the anterolateral parts of the trunk and limbs.

Question 59

What is the dorsal ramus?

Answer 59

→Branches from mixed spinal nerve →Carries sensory and motor info →Pass posteriorly to supply the skin and deep muscles of the back

Question 60

What is a dermatome?

Answer 60

The area of skin that is supplied by a specific spinal nerve and it's afferent (sensory) fibres. These fibres are responsible for telling the brain what is going on externally.

Question 61

What is a myotome?

Answer 61

A group of muscles innervated by a specific spinal nerve and it's efferent (motor) fibres.

Question 62

How may a spinal root/nerve issue be found through dermatomes?

Answer 62

Impaired sensation at specific dermatome region. Indicates an issue with spinal nerve/root that controls that area.

Question 63

How may a spinal root/nerve issue be found through dermatomes?

Answer 63

Changes in muscle strength within a particular myotome may indicate damage to a particular spinal nerve root.

Question 64

What movement has the strongest association with C2?

Answer 64

Neck flexion

Question 65

What movement has the strongest association with C3?

Answer 65

Lateral flexion of the neck

Question 66

What movement has the strongest association with C4?

Answer 66

Shoulder elevation?

Question 67

What movement has the strongest association with C5?

Answer 67

Shoulder abduction

Question 68

What movement has the strongest association with C6?

Answer 68

Elbow flexion with wrist extension

Question 69

What movement has the strongest association with C7?

Answer 69

Elbow extension

Question 70

What movement has the strongest association with C8?

Answer 70

Finger flexion

Question 71

What movement has the strongest association with T1?

Answer 71

Finger abduction

Question 72

What movement has the strongest association with L2?

Answer 72

Hip flexion

Question 73

What movement has the strongest association with L3?

Answer 73

Knee extension

Question 74

What movement has the strongest association with L4?

Answer 74

Ankle dorsiflexion

Question 75

What movement has the strongest association with L5?

Answer 75

Great toe extension

Question 76

What movement has the strongest association with S1?

Answer 76

Ankle plantar flexion

Question 77

What are plexus?

Answer 77

A network of nerves that enables fibres from different spinal levels to come together to form named peripheral nerves. These named peripheral nerves go on to supply the muscles and skin in periphery.

Question 78

Cervical plexus info?

Answer 78

Spinal nerves C1-C4 Creates named peripheral nerves that innervate the back of the head, the neck, the shoulders and the diaphragm. E.G. PHRENIC NERVE

Question 79

Brachial plexus info?

Answer 79

Spinal nerves C5-T1 Creates named peripheral nerves that innervate the upper limbs. E.G. MEDIAN NERVE / RADIAL NERVE / ULNAR NERVE

Question 80

Lumbar plexus info?

Answer 80

Spinal nerves L1-L4 Creates named peripheral nerves that innervate anterior + lateral aspects of the thigh. E.G. FEMORAL NERVE

Question 81

Sacral plexus info?

Answer 81

Spinal nerves L4-S4 Creates named peripheral nerves that innervate posterior aspect of the thigh and everything below the knee. E.G. SCIATIC NERVE

Question 82

Nerve root origins of the femoral nerve?

Answer 82

L2, 3, 4

Question 83

Nerve root origins of the sciatic nerve?

Answer 83

L4, 5 S1, 2 , 3

Question 84

What is the epineurium?

Answer 84

Outermost layer of dense irregular connective tissue surrounding a peripheral nerve. Provides protective surface.

Question 85

What is a fascicle?

Answer 85

A group of axons. Fascicles group together axons according to their function e.g. sensory axons together or motor axons together within a peripheral nerve.

Question 86

What is perineurium?

Answer 86

(around one fascicle) Holds a bundle of axons of a similar type together within fascicle.

Question 87

What is the endoneurium?

Answer 87

Protective tissue sleeve around each axon