Anatomy of the somatic nervous system Wk2

Question 1

What is the somatic nervous system?

Answer 1

• Voluntary division of nervous system - coordinates nervous system
• Accurately localise sensations throughout body e.g. heat
• Awareness of body position in 3D space - proprioception

Question 2

What is the central nervous system?

Answer 2

• Central and peripheral nervous system are functionally continuous
• Includes brain an spinal cord
• Many nerves straddle both CNS and PNS

Question 3

What is the peripheral nervous system?

Answer 3

• Nervous system outside of the CNS
• Connects CNS to target organs
• Connects sensory to CNS: where info is integrated and appropriate response
• CNS integrates information

Question 4

What does PNS include?

Answer 4

• 31 spinal nerve pairs
• 12 cranial nerve pairs
• Ganglia (collections of cell bodies) - autonomic/sensory
• Nerve plexus (nerve fibres branch and share peripheral and CNS) - brachial/lumbar/sacral
• Enteric nervous system - autonomic - GI tract

Question 5

What is the ratio of neurones to glial cells?

Answer 5

• Neurones (nerve cells) and glial cells (supporting cells) make up the nervous system
• 1:1 ratio

Question 6

What are the types of neuroglia in the CNS?

Answer 6

• Ependymal cells
• Oligandendrocytes
• Astrocytes
• Microglia

Question 7

What are the types of neuroglia in the PNS?

Answer 7

• Satellite cells

- Schwann cells

Question 8

What is the structure of a neurone from top to bottom?

Answer 8

• Dendrites: bring stimuli to cell body and branch off of cell body
• Cell body: metabolism, upkeep of cell, proteins made by ribosomes (nucleus located within)
• Perikaryon
• Axon hillock
• Axon
• Terminal boutons: distal end
• Synapses located throughout

Question 9

What are the 3 types of neurone?

Answer 9

• Multipolar : motor/efferent (cellular extensions)
• Bipolar : Relay of special sense (sight hearing smell) (1 axon, 1 dendrite)
• Pseudo-unipolar : sensory (single process - quick transfer of signal without going through)

Question 10

What are glial cells?

Answer 10

Cells which are non-neuronal and are located within the central nervous system and the peripheral nervous system.

Question 11

What are the different types of glial cells?

Answer 11

• Ependymal cells: involved in making cerebral spinal fluid which protects brain
• Astrocytes: contribute to BBB
• Microglia: immune function (like macrophages)
• Oligodendrocytes & Schwann cells: create myelin sheaths around neurones and provide support

Question 12

What is myelin?

Answer 12

• Lipid sheath 0.5-2.5 Um thick, created by glial cells which surrounds the axon of a neurone

Question 13

What does myelination do?

Answer 13

• Increases speed of conduction
• Provides protection
• Provides structural support

Question 14

What is myelin created by?

Answer 14

• Oligendendrocytes in the CNS

- Schwann cells in the PNS

Question 15

What happens with unmyelinated neurones?

Answer 15

• Axons are still surrounded by schwann cells

- The Schwann cells have a more supportive role but aren’t fully wrapped around

Question 16

What are afferent divisions?

Answer 16

• Sensory portion of the NS (input)
• Stimuli from the PNS are transmitted to the CNS
• Sensory neurone cell bodies are found in Dorsal root ganglia
• Sensation taken from areas such as skin or special sense organs, processed by relevant areas of the CNS and eliciting a reaction from the efferent division

Question 17

What are efferent divisions?

Answer 17

• The motor portion of the NS (output)
• Stimuli from the brain initiate movement of skeletal muscle
• Motor neurone cell bodies are found in brainstem/spinal cord
• Muscle types: skeletal (voluntary), cardiac (myogenic - doesn’t need initiation) and smooth (involuntary)

Question 18

What is a reflex loop?

Answer 18

Can bypass going to the brain e.g. pain - protective feature

Question 19

How do efferent divisions cause movement?

Answer 19

Neuromuscular junctions or motor end plates conduct stimuli to skeletal muscle

Question 20

What is a fascicle?

Answer 20

Numerous axon bundle

Question 21

What is a fascicle protected by?

Answer 21

Order of inside out

• Endoneurium: in between axons
• Perineurium: binds fascicle
• Epineurium