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Pathophysiology 1 > Peripheral Nerves > Flashcards

Peripheral Nerves Flashcards

1
Q

Chain of peripheral nerve function

A

Sensory nerve receptors - eg, skin, joints, muscles and tendons

Along peripheral nerve

Brain and spinal cord- integration. Spinal cord takes info up to sensory cortex in front of parietal lobe. Info processed to make motor output in motor cortex. Stimulates descending pathways

Through spinal cord

Muscular system- to produce response

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2
Q

2 nervous systems

A

CNS

PNS

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3
Q

What is in the CNS?

A

Brain and spinal cord

Brain = receives and processes sensory info, produces responses + stores memories, thoughts and emotions

Spinal cord= conduct signals to and from the brain + control reflexes

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4
Q

Peripheral nervous system

A

Sensory neurones - pick up sensory info from receptors to spinal cord + CNS

Motor neurones- take info away from spinal cord to muscles or glands
Either somatic (voluntary) or autonomic (involuntary)
Autonomic is sympathetic fight and flight or parasympathetic rest and digest

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5
Q

Types of motor neurones

A

LOWER MOTOR NEURONES- Neurones with cell bodies in spinal cord or brain stem and axons innervated skeletal muscle
They are peripheral

UPPER MOTOR NEURONES- Transmit signals from brain to lower motor neurones or interneurones in brain stem + spinal cord.
CNS nerves

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6
Q

What two types of nerve in PNS.

A

Sensory nerves

Motor nerves

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7
Q

Sciatic nerve

A

Comes from L4-S3,

Along lumbosacral plexus

Exits pelvis via greater sciatic foramen

Gluteal region deep to biceps femoris in Lower thigh

Gives off branches to semitendinosus, semimembranosus, biceps femoris and adductor magnus

Upper limb has brachial plexus with sensory and motor neurones in a bundle which are peripheral nerves

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8
Q

What are cranial nerves?

A

They are peripheral nerves from the brain stem and supply muscles of face, nose etc.

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9
Q

Cranial nerves for physio

A

FACIAL NERVE 7= Supplies muscles of the face- damage to facial nerve can cause Bells Palsy, so dropping of face on one side. Inflammation of facial nerves (mimics stroke).

VAGUS NERVE 10= controls heart, lungs and gastrointestinal system , so damage impacts heart and lungs

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10
Q

Can peripheral nerves mend.

A

Peripheral nerve can mend but CNS nerves can’t

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11
Q

How many peripheral nerves and cranial nerves are there?

A

31 spinal peripheral nerves

12 cranial nerves

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12
Q

Autonomic nervous system

A

Involuntary

SYMPATHETIC - From thoracic + lumbar

Fight or flight so increase HR, breathing rate , shunts blood to muscles

PARASYMPATHETIC- cranial and sacral nerves

Rest an digest so slows HR, lower blood pressure , slow resp rate

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13
Q

What systems does ANS control?

A 
BLOOD PRESSURE 
HEART AND BREATHING RATE 
BODY TEMPERATURE 
DUGESTION 
METABOLISM 
WATER AND EKECTROLYTE BALANCE 
PRODUCING BODY FLUIDS
URINATION 
SEXUAL RESPONSE
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14
Q

Spinal cord damage and regions

A

Dorsal columns - usually sensory

Lateral and anterior = usually motor info

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15
Q

Connective layers of nerves

A

EPINEURIUM- Dense CT surrounds whole neurones. Contains vascular networks.

PERINEURIUM- Sheath of CT around fascicles of nerve fibres. Fascicles contain neurones (myelinated or unmyelinated)

ENDONEURIUM- Delicate CT around myelin sheath of axons of nerves.

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16
Q

Structure of a nerve

A

MIXED NERVE= All spinal nerves are mixed. Contain both afferent (sensory) and efferent (motor) fibres to and from spinal cord.

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17
Q

BASIC NEURONE TYPES

A

BIPOLAR
eg, interneurone that passes info from one nerve to another

UNIPOLAR
Sensory nerve

MULTIPOLAR
Motor neurone

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18
Q

Features of basic neurone

A

DENDRITES - Bring info into cell body from receptors
CELL BODY- Contains mitochondria, nucleus and nucleolus. Golgi produces neurotransmitters.
AXON- takes info from cell, body
SYNAPTIC KNOBS= Release neurotransmitters into synaptic cleft from synaptic vesicles
TELODENDRIA- End branches of neurone ends in synaptic knob
Axon covered in myelin sheath from schwann cells in PNS and fatty produce from oligodendrocytes in CNS

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19
Q

What are neuralgia?

A

Neuroglia connect nerves together for insulation + protection - cells between nerve cells.

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20
Q

Neuroglia cells in PNS

A

Satellite cells and Schwann cells

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21
Q

Neuroglia cells in CNS

A

Astrocytes, microglia and oligodendrocytes

22
Q

Astrocytes

A

In CNS, astrocytes connect neurones to blood vessels + filters blood so bad substances don’t enter brain.
Holds nerve cells together too.

23
Q

Microglia

A

In CNS, spider - like phagocytes to remove debris

24
Q

Oligodendrocytes

A

In CNS, they produce myelination, and cover + protect axons in CNS nerves

25
Q

Schwann cells

A

In PNS, Schwann cells produce myelin to wrap round axon and protect axon

26
Q

Satellite cells

A

Satellite cell function - maybe repair and provide nutrients to neurone?

27
Q

Why can peripheral nerves regenerate and CNS nerves can’t?

A

Oligodendrocytes don’t have a neurolemma but Schwann cells do have a neurolemma.

Neurolemma is a structure for the PNS nerves to regenerate if harmed

28
Q

How does someone recover from a stroke?

A

CNS nerves don’t repair but we have neuroplasticity in brain- bypassing of information so new pathways created in brain

29
Q

Nerve conduction in three simple steps

A

Dendrites transmit electrical impulse into cell body

Cell body produces action potential to pass down axon

End of axon= neurotransmitters released from synaptic vesicles in knobs

Impulse transmitted to adjacent cell

30
Q

Define nerve impulse

A

Nerve impulse is electrical current passed down dendrites or axons due to ion channels opening in the plasma membrane.

31
Q

Action potential sequence

A

Neurone at rest = inside more negative, as more Na+ outside the neurone

Membrane is polarised at -70mv resting state

Resting potential maintained by sodium-potassium pump. Potassium ions in and sodium ions out.

Stimulus disturbs dendrite plasma membrane + sodium ion channels open

Sodium ions diffuse into neurone

Membrane depolarised at -55mv and increases more so net positive charge in neurone than outside. Wave of depolarisation along the membrane.

Potential difference gets to +30mv, sodium ion channels close and K+ channels open. Repolarisation occurs.

Rapid diffusion if K+ ions out of cell to decrease potential in neurone membrane.

Potassium ion channels slow to close so many K+ diffuse out of cell.

Potential difference is more than resting potential (below -70mv) called hyperpolarisation

Sodium- potassium pump returns membrane back to resting potential and maintains it until nerve stimulated again.

32
Q

What is refractory period?

A

Time delay between one ap and the next ap.

Ion channels recover in this time and nerve cannot be stimulated in this time.

It means that:
Action potentials don’t overlap
Limit to frequency of impulses passed
Action potentials unidirectional

33
Q

All or nothing law

A

If threshold reached at -55mv, action potentials will always fire with same voltage. Sodium ion channels open and at -55mv the rest of sodium ion channels open

If threshold not reached, then action potential will not fire!

34
Q

What is spatial summation?

A

Many impulses arrive simultaneously at cell body and stimulates action potential (many short signals at many dendrites).
If they arrived separately they are weak and threshold not exceeded so no action potential.

35
Q

What is temporal summation?

A

Impulses arrive in quick succession one after the next. So series of signals at one synapse can lead to action potential.

36
Q

What ions are needed for nerve impulses ?

A

Sodium
Potassium
Calcium

37
Q

Describe myelinated peripheral N

A

Myelin sheath around axon - electrical insulator

Sheath is made of Schwann cells with small gaps called nodes of ranvier.

Saltatory conduction- cytoplasm conduct electrical charge to depolarise next node + impulse jumps from node to node

Rapid !

38
Q

Describe unmyelinatwd neurone

A

Impulse travels as wave of depolarisation the whole length of axon

Slower than myelinated

39
Q

Define synapse

A

The junction between a neurone and another neurone or effector cell

40
Q

Can neurotransmitters be recycled ?

A

YES

they’re re up taken into presynaptic neurone to be used again

Enzymes can break neurotransmitters down and components re enter the presynaptic neurone

41
Q

Define neurotransmitters

A

Proteins that pass a chemical signal from one neurones axon to next cell

42
Q

Synapse

A

Action potential at end of neurone

Calcium ion gated channels open on ore membrane

Calcium ions enter synaptic knob

Influx of calcium stimulates synaptic vesicles to fuse to pre membrane

They release neurotransmitters into cleft

Neurotransmitters bind to receptors on post synaptic membrane

Action potential stimulated in next cell as excitatory or inhibitory

43
Q

Examples of neurotransmitters

A

ACETYLCHOLINE - excitatory at neuromuscular junctions - muscle contraction occurs

SEROTONIN- more serotonin in brain, less chance of depression

DOPAMINE- Lack of dopamine causes Parkinson’s . Too much dopamine is schizophrenia

NOREPINEPHRINE- neurotransmitter and also a stress hormone

GABA- neurotransmitter to reduce activity of brain neurones and CNS. Increases relaxation, reduces stress, boosts sleep, produces calmer mood and alleviates pain.

44
Q

Excitatory neurotransmitters

A

They will excite next membrane producing AP, by depolarisation

Inhibitory will hyperpolarise membrane to prevent action potential in post synaptic membrane

A stroke patient may have too many excitatory transmitters so high tone and spasticity.
OR too many inhibitory neurotransmitters so weakness and less excitation of muscles

45
Q

CNS DAMAGE

A

CNS neurones can’t repair

Clean up slow, oligodendrocytes inhibit regeneration + environment poor

Neuroplasticity - forms new pathways in brain

46
Q

Structural neuroplasticity

A

Strength between neurones in the brain are changed

47
Q

Functional neuroplasticity

A

Permanent changes in synapses due to learning and development

48
Q

PNS REGENERATION

A

Some regeneration

Clean up of damage quicker by macrophages
Schwann cells assist regeneration

Myelinated neurones have neurolemma so can repair, regenerate the axon etc, only if cell body and Schwann cells intact.

49
Q

How does PNS regenerate?

A

24-48 hrs chromatolysis so cell body swells

Wallerian degeneration - distal part of axon degenerates and macrophages engulf degraded axon and Schwann cells.

Neurolemma cells divide + form regeneration tube.

Axon sends buds into network of Schwann cells.

Axon grows along cord of Schwann cells

Axon regenerate by wallerian regeneration

50
Q

PERIPHERAL NERVE INJURIES

A

Tea with (NaN)

TRANSIENT ISCHAEMIA- lack of oxygen to area supplied by that nerve eg, laying on arm and getting spins and needles in the hand

NEUROPRAXIA - Compression of nerve so blocks nerve conduction. Loss of sensory and motor function for 6-8 weeks. Numbness tingling and vibration.
Usually due to trauma to body but axon not damaged and ANS not damaged.

AXONOTMESIS- commonly in car crash.
Injury to peripheral nerve at an extremity of the body. Axon and myelin sheath damaged but Epi,peri and endo neurium intact. No nerve conduction distal to site of injury for 3-4 days. Some wallerian regeneration but may require surgery.

NEUROTMESIS- Total severance to entire nerve eg, industrial accident. Axon and sheath separated and surgery is needed. Potentially some regeneration but not all.
Complete loss of sensory and motor function

Pathophysiology 1 (22 decks)

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