Basic Anatomy of the Somatic Nervous System Flashcards

1
Q

what is the role of the NS?

A

important in integrating information coming from our external environment AND regulating internal processes

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2
Q

describe the different divisions of the NS

A
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3
Q

what is the NS split into?

A

central nervous system
peripheral nervous system

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4
Q

what is an afferent neurone?

A

send sensory impulses from receptors in the PNS to targets in CNS (PNS –> CNS)

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5
Q

what is an efferent neurone?

A

send impulses from the central nervous system to your limbs and organs (effectors) located in the PNS (CNS –> PNS)

way to remember: EFFErent goes to EFFEctors

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6
Q

why does only efferent system divide further and not afferent?

A

afferent system is simply just a sensory system (sensory neurones).
so they don’t divide into somatic and autonomic systems.
only the efferent system does as it only makes sense that effects are voluntary and involuntary.

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7
Q

what is the somatic and autonomic NS?

A

somatic- controls voluntary movement
autonomic- controls involuntary movement

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8
Q

what does the autonomic NS divide into?

A

sympathetic- fight or flight
parasympathetic- rest and digest
enteric- NS involved in regulating your gastrointestinal tract

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9
Q

what are the anatomical, directional and functional devisions of the NS?

A

anatomical- CNS and PNS
directional- afferent and efferent (gives you direction of impulse)
functional- somatic and autonomic (voluntary/ involuntay)

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10
Q

what does the CNS consist of?

A
  • the brain and spinal cord
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11
Q

what layers of tissue cover the brain and spinal cord?

A

Meninges:
a layer of connective tissue which acts as a membrane around the brain and the spinal cord.
consists of:
- dura mater
- arachnoid matter
- pia matter.

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12
Q

what fluid is the brain and spinal cord suspended in?

A

Cerebrospinal Fluid - This is present in the subarachnoid space (between arachnoid and pia matter)

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13
Q

what is the superficial layer of the CNS?

A

Cranium (brain)
Vertebral Column (spinal cord)

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14
Q

what does the PNS do?

A
  • nervous system outside the CNS
  • connects CNS to target organs
  • connects sensory to CNS
  • so that the CNS can process information
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15
Q

what does the PNS consist of?

A
  • 31 spinal nerve pairs
  • 12 cranial nerve pairs
  • Ganglia (autonomic/sensory) - bunches of neuronal cell bodies
  • Nerve plexuses (Brachial/ lumbar/sacral) - networks of nerves that carry both afferent & efferent systems
  • Enteric nervous system - regulating gastrointestinal tract
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16
Q

what cells does the NS mainly consist of?

A
  • neurones (nerve cells) ~10%
  • glial cells (supporting cells) ~90%
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17
Q

what is the structure of a neurone?

A

the nerve cell responsible for
conducting impulses
micro-anatomy of a neurone:
cell body (perikaryon) = 1
dendrites = many
axon = usually 1
terminal bouton/ synapses=
many

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18
Q

what is an axon hillock?

A

region where an action potential is generated.
produces ‘kink’ in neurones – visible in micrographs

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19
Q

what are the 3 types of neurones?

A

Multipolar = Motor (part of efferent NS)
Bipolar = Relay or special sense
Pseudo-unipolar = Sensory

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20
Q

what is the structure of a multipolar neurone?

A
  • multiple dendrites
  • one axon that divides into multiple synapses
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21
Q

what is the structure of a bipolar neurone?

A
  • one dendritic process emerging to the cell body
  • one axon that carries impulse from cell body to synapse
    (hence bipolar)
  • mainly found in special senses ie. olfactory epithelium in nose, neuronal layers in retina
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22
Q

what is the structure of a pseudo-unipolar neurone?

A
  • one process coming off cell body and immediately branching into dendrites and axons
  • adv: info from dendrites can pass directly to the terminal synapse w/o having to go to cell body
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23
Q

what are glial cells?

A

comes form the greek term “glue”
most predominant cell type within the CNS
responsible for creating optimum microenvironment for neuronal activity

24
Q

what are the 4 main types of glial cells?

A
  • Astrocytes
  • Microglia
  • Ependymal
  • Oligodendrocytes
25
Q

what is the structure of astrocytes and what do they do?

A
  • Star shaped
  • Contribute to the blood-brain barrier- take nutrients from the blood into extracellular matrix of brain and neurones
  • Most abundant cell type
  • Provide structural and metabolic support
  • have the ability to regenerate and can form gliomas (tumour)
  • involved in removing synapses at the end of their life
  • some synapses are tripartite (3 terminals rather than 1) the 3rd terminal comes from the astrocyte - involved in up taking neurotransmitters that are released into the synaptic cleft to prevent over/ under activation of synapse
26
Q

what is the structure of microglia and what do they do?

A
  • immune function- phagocytosis
  • when resting, they communicate with other neurones & cells to make sure that everything is controlled (Ramified)
  • they pick up any signals from other neurones indicating that something isn’t right, hence activating them
  • maintain brain homeostasis
  • dysregulation can lead to neurological disease - through increased activation of microglia
27
Q

what is the structure of ependymal cells and what do they do?

A
  • simple ciliated epithelial cells lining the ventricles
  • cerebrospinal fluid synthesis: provides nutrients and creates perfect environment for neurone function
  • protection of brain and buoyancy
28
Q

what happens if cilia doesn’t work properly?

A

if cilia is disregulated, it can lead to conditions relating to flow of CSF e.g hydrocephalus - build up of CSF in the brain

29
Q

what is the structure of oligodendrocytes and what do they do?

A
  • cells with few processes
  • create myelin sheaths around neurones in the CNS
  • can myelinate several neurones at the same time
  • provide metabolic support and electrical insulation
30
Q

what is a glial unit?

A

when one oligodendrocyte or Schwann cell myelinates one portion of the axon

31
Q

what do Schwann cells do?

A
  • create myelin sheaths around neurones in PNS
  • provide metabolic support and electrical insulation
32
Q

what is the difference between Schwann cells and oligodendrocytes?

A

one schwann cell can only myelinated one axon but oligodendrocytes can myelinate multiple in one go
Schwann cells are found in the PNS ONLY
oligodendrocytes are found in the CNS ONLY

33
Q

what is myelin?

A

Myelin is a lipid sheath 0.5-2.5μm
its an extension of the bilayer and wraps around the axon
thick
created by glial cells which surrounds the axon of a neurone
Increases the speed of conduction, provides protection and structural support
Created by:
Oligodendrocytes in CNS
Schwann Cells in PNS

34
Q

what are the gaps between the myelin sheath called?

A

nodes of Ranvier

35
Q

what is a nodal membrane?

A

Membrane at the node of ranvier

36
Q

what is an internodal membrane?

A

Membrane at the regions that are myelinated

37
Q

what are unmyelinated neurones?

A

axons are still surrounded by schwann cells - don’t completely wrap around the axon
the schwann cells have a more supportive role

38
Q

what is the somatic NS?

A
  • specific collection of tissues of the nervous system
  • the voluntary division of NS
  • its sensations give rise to awareness of the sensory world around us– allows us to accurately localise sensations throughout the extent of the body
  • gives us awareness of our body position in 3D space– known as proprioception
39
Q

what is the role of the afferent system in the somatic NS?

A

carry sensory information from the surface of the body to the NS
its sensations give awareness to the sensory experience
gain stimuli from the PNS are transmitted to the CNS

40
Q

where is the afferent neurone found in the somatic NS?

A

sensory neurone cell bodies are found in the dorsal root ganglion of the spinal nerve

41
Q

what is the role of the efferent system in the somatic NS?

A

carries motor info of the NS (output)
convey commands from the brain to skeletal muscles only (voluntary movements)
it manifests its actions as muscle contraction

42
Q

where is the efferent neurone found in the somatic NS?

A

motor neurone cell bodies are found in the ventral horn of the spinal cord or cranial nerve nuclei in the brain stem

43
Q

what is the afferent systems involvement in processing sensation?

A

sensation taken from areas such as the skin or special sense organs
processed by relevant areas of the CNS
elicits a reaction from the efferent division

44
Q

what is the region of the brain involved in processing sensory info?

A

primary somatosensory cortex

45
Q

what is the efferent systems role in movement of muscle?

A

only synapse with skeletal muscle
(smooth and cardiac are in autonomic NS)

46
Q

how do efferent neurones transmit impulses to the muscles?

A

following AP…
synaptic vesicles containing neurotransmitters fuse with PM release neurotransmitters to synaptic cleft
in muscle cell membrane there are receptors that detect neurotransmitters and cause contraction
neuromuscular junctions
(NMJs) or motor end
plates conduct stimuli to
skeletal muscle

47
Q

what is the difference between a neurone and a nerve?

A

MANY neurones make up ONE nerve

48
Q

what is the anatomy of a nerve?

A

multiple axons are grouped together to form a fascicle
many fascicles create a nerve numerous axon bundles (fascicles) surrounded by three protective layers

49
Q

what are the protective layers that surround fascicles?

A

from out to within:
epineurium - sheaths the entire nerve
interfascicular bands attach adjacent nerve fascicle

perineurium - axons with common origins and common destinations will travel together forming a nerve fascicle.
perineurium ensheaths a nerve fascicle

endoneurium - ensheaths a single cell’s axon
gives it structure and isolates it

50
Q

what are some typifying characteristics of the somatic NS? (hamzah’s notes)

A

It can be said to exist in a bi-stable state
Thus, it is either
Active (awake)
or
Inactive (sleep)
It is largely paralysed during [rapid eye movement sleep]
Its effector organ is the skeletal muscle only
It is responsible for movement (via muscles) and motor tone of the body

51
Q

what are characteristic anatomical properties of neurones of the somatic NS? (hamzah’s notes)

A

Dendrites – very important as they increase the surface area of the cell’s membrane.
synaptic impulse are directed through these membranes.
Dendrites with direct connection to the cell body are known as proximal dendrites
Dendrites with no connection to the cell body are called distal dendrites
The diameter of the dendrites the lower the cross-sectional resistance to electrical impulses, so the faster the impulse travel
The Cell body has a multipolar cellular morphology – the cell body has a lot of processes radiating in multiple directions
Cell body is located in the central nervous system (Ventral horn of the spinal cord or Cranial nerve motor nuclei of the brain)
They are largely myelinated:
Alpha motor neurons (fastest) (main) innervate the highly contracting fibres that supply the muscle with its power.
Gamma motor neurons (slow) innervate slightly contract fibres – allows muscle to be sensitive to stretch, over a wide range of muscle lengths.

52
Q

describe the structure of somatic afferents/ sensory neurone? (hamzah’s notes)

A

The axon splits into two sub axons.
This is a sensory neurone so its electrical impulses are generated at the periphery end which converts electromechanical energy into electrical impulses
The impulses are then propagated along the periphery axon towards the cell body
The cell body receives a copy of the electrical impulse alerting the cell allowing it to respond metabolically to support the axon – e.g. makes sure nutrition is made available to the axon.
The impulse then moves along the axon towards the brain.
Bold cell body – Axonal terminals on the cell body would interfere with signal generated in the peripheral corrupting the signal.
This morphology is called pseudo unipolar morphology (characteristic primary sensory neurones) - one process radiating in multiple directions
Primary sensory neurones: neurones responsible for converting electromechanical energy into electrical impulses.
Cell body is located outside of the CNS they are located in ganglia.
Levels of myelination vary between functional sub-types
Some are myelinated:
Heavily myelinated (alpha) and (Beta)
Lightly myelinated (gamma)
The rest are unmyelinated:
Knows are C-fibres Or free nerve endings (largely responsible for pain sensation)

53
Q

what does the neuroglia in the PNS consist of? (hamzah’s notes)

A

Neuroglia of the PNS are:
The Schwann Cell
Main Function is myelination of Peripheral Nerve Axons
1 Schwann Cell myelinates only 1 axon segment
The Satellite Cells
Physical Support of Neurones in PNS
Microglia
(they are macrophages) Immune and Inflammatory functions

54
Q

describe the myelination of axons of the PNS in the somatic NS (hamzah’s notes)

A

Are variable in thickness & length
Some are not myelinated - Thin axons
Others are heavily myelinated -Thick axons
The level of myelination varies between neuronal types
Unmyelinated axons are only found on C fibres (responsible for pain sensation) - somatic sensory neurones
All motor neurones are myelinated
Conduction speed of electrical impulses is correlated to the level of axonal myelination
Expressed mathematically as Conduction velocity (CV) =5.8 x fibre diameter (FD)

55
Q

describe the myelinated axon in X-Section of the somatic NS
what diseases can demylinate axons? (hamzah’s notes)

A

Thickness of myelin varies between neuronal types
Myelin of thin axons can be 0.5 micrometres thick
Myelin of thick axons can be 2.5 micrometres thick
On average, a Schwann Cell wraps itself 100x around an axon
Certain diseases demyelinate axons
Multiple Sclerosis
Diabetes
Guillain Barre
Polyneuropathies
They provide insulation - increases the speed of conduction of nerve impulses
Reduces the capacitance of neurones – makes it easier for the neurone to be activated
If a nerve axon is cut and it dies away, the myelin sheath left behind maintains the tunnel where the old axon ran. This creates a path taken by a new/regenerated axon.

56
Q

what is a motor neurone? (hamzah’s notes)

A

It is an efferent neurone that supplies
Skeletal muscle - effectors of the somatic nervous system
Smooth muscle - effectors of the autonomic nervous system
Cardiac muscle are myogenic
Role of skeletal muscles:
Bring about displacement of limb (movement)
Set muscle Tone
Taken together motoneurons make up the motor system of the body

57
Q

describe the anatomy of the NMJ (hamzah’s notes)

A

It is confined to a specific area of the muscle known as the ‘nerve entry point’ or neurovascular hilum
The nerve entry point is the:
Geographical centre of any given muscle (allows contraction to be centralised)
Site of entry of a motoneuron into the substance of the muscle
Site of entry of arterial supply to a muscle
Site of exit of venous drainage of the muscle
Site of collection of nicotinic receptors of healthy muscles – that allow for electrical impulses of the nerve to produce contraction of the muscle done with production of neurotransmitter – Acetyl choline.