The nervous system and brain Flashcards
What does the CNS consist of?
Brain
Brain stem
Cerebellum
Spinal cord
What does the PNS consist of?
Cranial nerves and their branches, spinal nerves and their branches, ganglia, enteric plexuses and sensory receptors
How many pairs of cranial nerves are there?
12
How many pairs of spinal nerves are there?
31
What are the three main functions of the nervous system?
Sensory
Integrative
Motor
What are the subdivisions of the PNS?
Somatic nervous system (SNS)
Autonomic nervous system (ANS)
Enteric nervous system (ENS)
What are some effects of the parasympathetic nervous system?
‘Rest and digest’
-Decreased heart contractility
-Increased salivation and gastric/pancreatic juice secretion
-Contraction of smooth muscles of viscera
-Bronchospasm
-Pupil constriction
What are some effects of the sympathetic nervous system?
‘Fight or flight’
-Pupil dilation
-Increased sweating
-Vasoconstriction of some blood vessels
-Vasodilation of skeletal muscle and liver blood vessels
-Increased heart rate
-Increased cardiac contractility
-Relaxation of the smooth muscles of the viscera
-Bronchodilation
-Skeletal muscle contraction
-Glycogenolysis
-Thermogenesis
What is the function of neuroglia (glial cells)?
Supporting, nourishing and protecting neurons and maintaining their interstitial fluid
What subdivision of the PNS can function with or without input from the CNS?
The enteric nervous system
Where are cell bodies of the the grey matter found?
Periphery of the brain and centre of the spinal cord
What are ganglia?
Collections of neuronal bodies found in the PNS. Act as synaptic relay stations between neurons
What does grey matter mainly consist of?
Neuronal cell bodies (soma)
What does white matter mainly consist of?
Myelinated axons
What membrane surrounds axons?
Axolemma (the plasma membrane of the axon)
Is transmission speed faster in myelinated or unmyelinated neurones?
Myelinated
(Unmyelinated neurones range from 0.5-10m/s in speed compared to up to 150m/s in myelinated neurones)
What is the structure of myelin sheaths?
Several Schwann cells along the length of the axon. Each Schwann cell curled around the axon (like thin dough wrapped around a rolling pin) to create several layers of Schwann cell cytoplasm.
Where is white matter located?
The centre of the brain and periphery of the spinal cord
What is resting membrane potential?
-70mV
What happens during the initial phase of depolarisation of neurone action potential?
Voltage gated Na+ channel activation gates are opened
When is the depolarisation phase of action potential started?
When a stimulus alters the potential above the threshold (-55mV)
What happens during the depolarisation phase of action potential?
Na+ are opened initially, followed by voltage gated K+ channels being opened, towards the end Na+ channels are inactivating.
What happens during the repolarisation and after-hyperpolarisation phase of action potential?
Voltage gated K+ channels are still open and Na+ channels are still inactivating. Then Na+ channels fully return to the resting state whilst Voltage gated K+ channels remain open.
During neuron resting state what ions are in a higher concentration outside the cell?
Na+, Ca++ and Cl-
During neuron resting state what ions are in a higher concentration inside the cell?
K+, organic phosphates (-ve) and amino acids (-ve)
Are voltage-gated channels active or passive?
Active
What is threshold membrane potential?
-55mV
What initial ion movement occurs to depolarise the cell?
Sodium channels open and flood the cell with sodium
What ion movement occurs once peak membrane potential is reached?
Potassium channels open causing K+ to flood outside of the cell, sodium channels close stopping Na+ inflow.
(Repolarisation)
When does a hyperpolarising phase occur?
When, while potassium channels are still open, outflow of K+ is high enough to cause the membrane potential to dip below the normal resting level (to about -90mV)