Neurology Flashcards
How is the nervous system split?
Nervous System is split into Central, Peripheral and Enteric
Central = brain and spinal cord
Peripheral = nerves and the rest of the body
Enteric = involved in the gut
How is the Peripheral Nervous System split?
Split into Sensory and Motor:
Sensory = sensing the environment and feeding that back into the CNS
Motor = movements, split into Autonomic and Somatic
Somatic = can control the movement of skeletal muscles
Autonomic = no conscious control (automatic), split into sympathetic and parasympathetic
Sympathetic = fight or flight, prep for movement - outflows throughout the spinal cord
Parasympathetic = rest and digest - outflows at the cranial (head/neck) and sacrum (by pelvis)
Resting Membrane Potentials (Na+/K+ pump)
1) Na+/K+ pump uses ATP hydrolysis to pump 3 Na+ ions out and 2 K+ ions in to the cell constantly
2) Both Na+ and K+ channels are always open, but there are more K+ channels, so the axon membrane is more permeable to K+ ions
3) K+ ions diffuse down the gradient through K+ channels
4) Na+ ions diffuse into the cell through the Na+ channels down their concentration gradient
5) This maintains a difference in the concentration gradients
Action Potentials - Na+ ions
1) Voltage gated Na+ channels are closed at rest. High Na+ outside the cell and low inside the cell
2) When a neurone is stimulated, there is a wave of depolarisation through the neurone
3) Depolarisation causes the voltage gated Na+ channels to open and Na+ enters the cell down its concentration gradient
4) Once the threshold value (-55mV) is reached, an action potential is triggered
5) Eventually, the voltage gated Na+ channels become inactivated and then close
Action Potentials - K+ ions
1) K+ channels open so K+ ions can diffuse out of the cell down the concentration gradient
2) Membrane repolarises
3) The membrane may become too negative
Action Potentials - the Refractory Period
1) Hyperpolarisation in the membrane drops the membrane voltage below -70mV
2) Both the Na+ AND K+ voltage gated channels remain closed, so another action potential can’t pass down the cell - this is the refractory period
Synaptic Transmission
1) Action potential reaches the pre-synaptic knob
2) Depolarisation causes the voltage gated Ca2+ channels to open, and Ca2+ diffuses in down the concentration gradient
3) Ca2+ binds to vesicles and induces their movement down the pre-synaptic knob
4) Vesicles fuse with the pre-synaptic membrane, releasing the neurotransmitter into the synaptic cleft
5) Acetylcholine diffuses across the cleft and binds to ligand-gated Na+ channels
6) This induces the opening of the Na+ channels, so Na+ ions diffuse into the post-synaptic neurone
7) This depolarises the post-synaptic membrane and will eventually go on to trigger an action potential
Ionotropic Receptors
Ligand-gated ion channels
Neurotransmitter binds directly to the ion channel
This allows selective movement of ions into or out of the cell
This is very fast
Metabotropic Receptors
G-protein coupled receptors
Neurotransmitter binds to the G-protein receptor
This triggers an intercellular cascade that eventually activates transcription of DNA
This is very slow
Ganglions
Collection of neurones found in the PNS
Thought to act like synaptic relay stations
Myofibril
Cylindrical organelle running the length of the muscle fibre, containing actin and myosin filaments
Sarcomere
Functional unit of the myofibril
Divided into I, A and H bands
Actin
Thin, contractile protein filament
Myosin
Thick contractile protein filament with protrusions known as myosin heads
Tropomyosin
Actin-binding protein that regulates muscle contraction
Troponin
Complex of 3 proteins attached to tropomyosin
Skeletal Muscle
Under conscious control
Located in muscles attached to the skeleton
Striated
Smooth Muscle
Not under conscious control
Located in walls of internal organs, e.g. liver, pancreas and intestines
Not striated
Microanatomy of Skeletal Muscle
Muscle fibres are made up of many myofibrils
Sarcolemma surrounds muscle fibres
Transverse tubule is an extension of the sarcolemma that penetrates the centre of the muscle fibres
Transverse tubule connects to the sarcoplasmic reticulum
Function of Skeletal Muscle
A band = dark area, where actin and myosin overlap
I band = light area, contains only actin
Z line = holds actin filaments in position, zigzag shape
H zone = contains myosin only
Receiving a Signal
Signal travels down T-tubules that extend into the muscle fibre
Action potential passes down the sarcolemma
Causes voltage gated Ca2+ channels to open and Ca diffuses out of the T-tubules
Ca binds with Ca channels of sarcoplasmic reticulum (SR), causing them to open
Ca diffuses into SR and then leaves SR into muscle filaments
Now muscle contraction can begin via the sliding filament theory
Sliding Filament Theory
Sliding of actin past myosin generates muscle tension
Troponin-tropomyosin complex
- consists of troponin T, C and I
- in the relaxed state, the complex covers the myosin binding site
- troponin C binds with Ca2+ ions causing a conformation change and the myosin binding site is exposed
Varicosity
Bump found along the axon which contains a high concentration of neurotransmitters
Single Unit
When one smooth muscle cell depolarises, all the cells depolarise
Multi Unit
Smooth muscle cells separated from each other
Structure of Smooth Muscle
Spindle shaped
Centrally located nucleus
Dense body serves as anchor to thin filaments
Thick and thin filaments
Not striated
Can be single unit or multi unit
Multipolar neurones
Make contact with lots of cells and pass that information back
Unipolar neurones
Connect to one cell
Bipolar neurones
Connect to two cells
Sensory Impulses
Enter the spinal nerve at the posterior root, which is the afferent pathway
Motor Impulses
Enter at the anterior root, which is the efferent pathway
Myelin
Insulates the axon and makes the action potential travel faster through saltatory conduction
Saltatory Conduction
Node to node depolarisation of the neurone, meaning impulses are conducted faster along a myelinated neurone
Allows for more frequent impulses due to faster conduction
What is the myelin sheath made of in the PNS?
Schwann cells
Neurones
Send signals to and from the body and the brain
Can be myelinated or non-myelinated
Glial Cells
Cells other than neurones in the brain that maintain the environment
Astrocytes
Takes nutrients from the bloodstream and pass to other cells in the brain
Microglial cells
Part of the immune response in the brain
Ependymal Cells
Separates the brain from the cerebrospinal fluid
