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Introduction to Medical Sciences > Nerves and Muscles 1 > Flashcards

Nerves and Muscles 1 Flashcards

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USMLE® Step 1 flashcards
1
Q

How is the nervous system organised?

A

The nervous system is composed of the Central Nervous System and the Peripheral Nervous System.

The Peripheral Nervous System is subdivided into the Somatic Nervous System and the Autonomic Nervous System. The Autonomic Nervous System is then divided into the Sympathetic Nervous System and the Parasympathetic Nervous System. There is also the Enteric and Cardiac Plexus which are intimately related to the Sympathetic and Parasympathetic Nervous System.

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2
Q

What is the role of the autonomic and somatic nervous system?

A

The autonomic nervous system controls involuntary processes whereas the sympathetic nervous system is in control of voluntary processes (i.e. movement of skeletal muscles).

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3
Q

What are multipolar neurones?

A

Motor neurones. They have a single long axon and many dendrites emerging from the cell body.

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4
Q

What are unipolar neurones?

A

Relay neurones - found in sensory ganglia.

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5
Q

What are bipolar neurones?

A

Sensory neurones - found in sensory structures such as the retina.

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6
Q

What is a neurite? Give a couple of examples.

A

Projections out of the neurone cell body. Axons and dendrites are both neurites. Dendrites tend to be smaller and thicker than axons and often give rise to dendritic trees.

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7
Q

What are features of neurones?

A
  • Have high metabolic demand.
  • Do not store energy well and so require a constant supply of oxygen.
  • Have many mitochondria.
  • can often be insulated by a myelin sheath.
  • Transmit information by electrical impulses and chemical neurotransmitters.
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8
Q

Which multipolar cells have unrecognisable dendrites?

A

Pyramidal and stellate cells, These cells are found in the cerebral cortex, hippocampus and cerebellum.

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9
Q

How are cell bodies and axons arranged in the PNS?

A

Cell bodies are arranged into ganglia.

Axons are grouped in nerves.

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10
Q

How are cell bodies and axons arranged in the CNS?

A

Cell bodies are grouped into nuclei.

Axons are grouped into tracts.

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11
Q

What is grey and white matter?

A

Grey matter - Cell bodies (found in the middle in the spinal cord)
White matter - Axons

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12
Q

What are four main nuclei in the spinal cord?

A
  • Viscerosensory nuclei
  • Somatosensory nuclei
  • Visceromotor nuclei
  • Somatomotor nuclei
    The functional difference is that somatic neurons transmit information from the skin or skeletal muscles to the central nervous system while the visceral neurons transmit information from the internal organs to the central nervous system.
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13
Q

What is the dorsal root ganglia and the ventral root ganglia?

A

Dorsal root ganglia: Contains the cell bodies of the sensory fibres bringing information into the CNS.

Ventral root fibres: Contains cell bodies of motor fibres taking information out of the CNS so it can have an effect on the muscles or glands.

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14
Q

What are the two types of ganglia?

A

Sensory ganglia: Contain cell bodies of sensory afferent neurones.

Autonomic ganglia: contain the cell bodies of motor efferent neurones form the ANS.

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15
Q

What are the layers of connective tissue in peripheral nerves?

A

Endoneurium: Connective tissue around an individual nerve axon.

Perineurium: Connective tissue around a fascicle - a bundle of axons.

Epineurium: Connective tissue around the whole nerve.

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16
Q

What are the neuroglia found in the CNS?

A
  • Oligodendrocyte
  • Astrocyte
  • Microglia
  • Ependyma
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17
Q

What is the role of oligodendrocytes?

A

Myelinate neurones - one oligodendrocyte can myelinate many neurones at one time.

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18
Q

What is the role of astrocytes?

A

The most common neuroglia.

  • Regulate ionic concentration - remove K+, a by-product of neurotransmission.
  • Role in growth of the neurone as they can produce growth factors.
  • Role in metabolism - have globe extensions that attach to blood vessels and so are thought to deliver nutrients to neurones.
  • Maintaining of the Blood brain barrier
  • Glucose metabolism - they take up glucose and convert it to lactate. They then feed this to neurones which can use lactate as an energy supply.
  • Structural - form a supportive framework
  • Can remove excess neurotransmitters from the synapse. they can inactivate them and recycle neurotransmitters.
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19
Q

What is the role of microglia?

A

They have a role in defence. They have phagocytic activity. They are therefore able to mop up debris and dead neurones.

20
Q

What is the role of ependyma?

A

Line the ventricles and the central spinal canal - they have cilia and so can waft CSF through out the nervous system.

21
Q

What are the main neuroglia in the PNS? What is their role?

A

Schwann cells: Produce myelin. They also have a phagocytic activity and clear cellular debris that allows for regrowth of neurones.
Satellite cells: Similar role to astrocytes. They regulate the external chemical environment.

22
Q

What are Nodes of Ranvier?

A

The gaps between the myelin across the axon.

23
Q

What is a mesaxon?

A

A pair of parallel plasma membranes of a Schwann cell, marking the point of edge-to-edge contact by the Schwann cell encircling the axon.

24
Q

How are non-myelinated neurones protected by Schwann cells?

A

Non-myelinated neurones are taken into channels of Schwann cells known as a mesaxon. The Schwann cell can then support the neurone. One Schwann cell can take in several neurones.

25
Q

What is the difference in method between a Schwann cell and an oligodendrocyte?

A

Schwann cells can only myelinate one neurone in one area whereas an oligodendrocyte can myelinate several neurones at once.

26
Q

What is Saltatory conduction?

A

The movement of ions can only occur at the Nodes of Ranvier as a result, the impulse jumps between these gaps. This increases the rate of transmission.

27
Q

What are the types of demyelinating disease?

A
  • Demyelinating myleinoclastic disease - secondary i.e. the myelin produced is functional but is destroyed by a toxin, infectious agent, autoimmune causes or a chemical.
  • Demyelinating leukodystrophic (dysmyelinating) - the myelin produced is dysfunctional and so quickly breaks down. Cause can be genetic or idiopathic.
28
Q

What are the consequences of demyelinating diseases?

A

A demyelinating disease –a condition that results in damage to the myelin sheath

Consequences of myelin damage: nerve impulses slow/stop, causing neurological problems

Deficiency in sensation, movement, cognition, or other functions specific to the nerves involved

Extensive myelin loss is usually followed by axonal degeneration and often cell body degeneration

29
Q

What is the pathophysiology of multiple sclerosis?

A

The astrocytes aggregate and cause the blood brain barrier to become leaky. As a result T cells can infiltrate. the T cells secrete inflammatory cytokines that are chemo attractive. Macrophages and B cells come to the site of injury. Macrophages can then digest the myelin; B cells produce antibodies against the myelin.

30
Q

What is ALS?

A

Amyotrophic Lateral Sclerosis (ALS)/Motor neurone disease - characterised by the loss of motor neurones (upper neurones in the brain and lower neurones in the brain and spinal cord). Thought to have a genetic cause as there is a change in the clusters of genes involved in protein degradation in the cytoskeleton and RNA processing. Hyperactive microglial cells in ALS - which may produce large amounts of inflammatory cytokines which affect the motor neurones.

31
Q

What is Adrenoleukodystrophy?

A

Rare X-linked disease. Excess accumulation of very long chain fatty acids in the brain and adrenal gland. It is thought to be due to a disorder of the enzymes in fatty acid oxidation. Leads to the loss of myelin in the brain and oligodendrocytes. Leads to a loss of conduction. Can lead to seizures vison loss, difficulty swallowing. In the adrenal gland, this can cause adrenal insufficiency.

32
Q

What is Guillen Beuren Syndrome?

A

Acute inflammatory demyelinating polyneuropathy.It is an ascending paralysis, from feet upwards. It is thought to have an autoimmune cause.

33
Q

What is the difference between the motor efferent neurone of the SNS and the ANS?

A

In the SNS, there is only one motor neurone. In the ANS, there is two neurones - a pre-ganglionic neurone and a post-ganglionic neurone. The pre-ganglionic neurone has a cell body that lies in the CNS, the axon synapses onto a post-ganglionic neurone whose cell bodies lies in the autonomic ganglion.

34
Q

How are the efferent and afferent neurones organised in the SNS?

A

Afferent: The nerve ending lies at the receptor, the cell body lies in the PNS and the axon lies in the CNS.

Efferent: The cell body lies in the CNS. The axon travels through the PNS to the target tissue.

35
Q

What are the differences between the parasympathetic nervous system and the sympathetic nervous system?

A
  1. The pre-ganglionic neurone in the SNS is short and myelinated. It is however long and myelinated in the PNS.
  2. The post-ganglionic neurone in the SNS is long with many branches. In the PNS it is short with few branches.
  3. The ganglia in the PNS is near to the target tissue and far from the target tissue in the SNS.
  4. The pre-ganglionic neurotransmitter in both the PNS and SNS is acetylcholine. The post-ganglionic neurotransmitter in the PNS is acetylcholine but noradrenaline in the SNS.
  5. The PNS is active when at rest or sleep. The SNS is active in the fight or flight mode - in stress and exercise.
  6. The PNS slows things down however the SNS speeds things up.
36
Q

Howe are nerves classified?

A

Erlanger Gasser Classification - A, B or C. Motor fibres and non-muscle sensory neurones are classified according to speed of transmission where A is the fastest and C the slowest.

Numerical system - I, II, III - this system classify sensory muscle fibres according to speed of transmission.

These systems are applied to both the SNS and ANS now and often used interchangeably. For example slow, non-myelinated sensory neurones cab be referee to as type C as well as type IV.

37
Q

What is the relationship between neurone diameter and how fast an impulse is transmitted?

A

Directly proportional. As an axon increases in diameter - due to increased myelination - the rate of transmission increases.

38
Q

What are sensory modalities?

A

A sensory modality - is an aspect of a stimulus or what is perceived after a stimulus. The term sensory modality is often used interchangeably with sense. The basic sensory modalities include: light, sound, taste, temperature, pressure, and smell.

39
Q

How are receptors classified according to location?

A

Externo-receptors - external surface
Interno-receptors - internal organs
Proprioceptors - internal receptors concerning the placement/potion of muscles, tendons and joints

40
Q

How are receptors classified according to stimulus?

A 
Mechanoreceptors - pressure, touch, vibration, stretch
Thermo-receptors - Temperature 
Photoreceptors - Light 
Chemoreceptors - chemicals 
Nociceptors - pain (usually chemical)
41
Q

What are muscle spindles?

A

Receptors that detect the stretch of muscles. They are non-adapting.

42
Q

What is the Pacinian Corpsule?

A

Receptors found in the deep dermis, tendons, joints and genitalia. It detects vibration and deep pressure. They are fast adapting.

43
Q

What is Meissner’s/Krause’s bulb?

A

Receptors that detect touch, vibration, light and pressure. They are rapid detecting. They are found in the oral mucosa, lips, genitalia and fingertips.

44
Q

What are Ruffini organs?

A

Found in the deep dermis, ligaments, joint capsules and detach stretch and deep pressure. They are slow adapting.

45
Q

What is the spinal cord reflex pathway?

A
  1. The receptor is stimulated.
  2. The sensory afferent neurone transmits the information to the CNS via the dorsal root ganglion, dorsal root and to the dorsal horn.
  3. Inter-neurones in the dorsal horn project axons down to the motor neurone cell bodies located in the ventral horn.
  4. The efferent axons leave via the ventral root and enter the spinal nerve, to supply the motor endings.
  5. The efferent neurone transmits the information to the effector to bring about a response.

Introduction to Medical Sciences (43 decks)

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