Week 3 - Central Nervous System Flashcards
4 functions of the central nervous system
1) Control of the internal environment - coordinated with the endocrine system (Hypothalamus-Pituitary Axis), perceiving and responding to events in the internal/external environment.
2) Voluntary control of movement
3) Spinal cord reflexes (rapid unconscious movements such as touching hot pan)
4) Assimilation of experiences necessary for memory and learning
Draw and outline the anatomical division of the NS.
Central NS: brain and the spinal cord (protected by skull and vertebrae)
Peripheral nervous system (PNS): neurons outside the CNS. This can be divided into sensory division and motor division.
Sensory division: detects stimuli and afferent fibers transmit impulses from receptors to CNS. Can be broken down into somatic, visceral and special sensory.
Motor division: efferent fibers transmit impulses from CNS to effector organs. Broken down into somatic and autonomic.
Autonomic: parasympathetic and sympathetic NS
Describe the role of dorsal root and ventral roots and how they differ?
To connect the nerve fibers from the PNS to the CNS
Dorsal roots are afferent - meaning they carry sensory information to the CNS (spinal cord) from the PNS
Ventral roots are efferent - meaning they carry motor information from the CNS (spinal cord) to the PNS
They both make up 31 pairs of spinal nerves in the PNS.
Define somatic sensory and visceral sensory.
Somatic - sensory input consciously perceived from receptors like the eyes, skin…
Visceral - sensory input that is not consciously perceived from receptors of blood vessels and internal organs such as the heart (e.g. increased HR).
Define autonomic and somatic NS.
Autonomic - motor output that is involuntarily controlled; effectors are cardiac muscle, smooth muscle and glands.
Somatic - motor output that is voluntarily controlled; effectors is skeletal muscle.
Dendrites
extend from the cell body and receive information from the synaptic terminals of adjacent cells
What is the role of myelin?
it enhances the conduction of an AP along a nerve fiber + insulates the axon and reduces the loss of the electrical impulse.
Axon
carry electrical messages (APs) away from the cell body
What is the role of Schwann cells in the structure of a neuron?
The cell membrane of Schwann cells is responsible for the myelination of axons.
What two factors are responsible for a greater speed of neural transmission (conduction velocity)?
- The diameter of the axon
- The amount of myelin sheath
Resting membrane potential
the electrical charge difference in the cell (intracellular) and outside the cell (extracellular)
there is a negative charge inside the cell in respect to the charge outside the cell at rest
What is the magnitude of the resting membrane potential determined by?
- Permeability of plasma membrane to ions - when channels are open ions go from an area of high conc to low conc, membrane far more permeable to K+.
- Difference in ion concentrations across the cell membrane (Na+ greater outside cell, K+ greater inside cell)
Why do we have a negative membrane potential in the cell/neuron at rest?
- Diffusion of potassium out the cell.
- Higher permeability of the plasma membrane for potassium compared to sodium
At rest, most of the sodium channels are closed whereas the potassium channels are open. Therefore, potassium ions move from high conc (in the cell) to low conc (extracellular fluid) and this net loss of positive charge leads to a negative charge which is the resting membrane potential.
How do we maintain this negative resting membrane potential?
Sodium-potassium ATPase pump
What does the sodium-potassium pump do?
Uses energy from ATP to maintain this intracellular and extracellular environment by pumping 3 Na+ OUT of the cell and 2 K+ IN the cell.
When does an action potential occur/fire? What does this result in?
It occurs/fires when an excitatory stimulus of sufficient strength (causes membrane potential increase to -50mV) depolarizes the cell by opening sodium channels.
Therefore, sodium diffuses into the cell which makes the cell more positive (depolarizing it).
K+ channels also open but K+ permeability is relatively smaller and lasts longer.
What is the threshold potential for an AP to fire?
-50mV is the voltage at which Na+ channels open to initiate AP
Repolarization
return to resting membrane potential - potassium leaves the cell rapidly and sodium channels close.
All-or-none law
Once a nerve impulse (AP) is initiated, it will travel the whole length of the axon. When the AP reaches the end, a neurotransmitter is released into the synpase.
a) Membrane potential depolarizes from -.. mV to +.. mV
b) Membrane potential repolarizes from +.. mV to -.. mV
c) The RMP of a healthy neuron is usually in the range of -..mV to -..mV.
a) -70mV to +30mV
b) +30mV to -70mV
c) -70mV to -80mV
Synapse
gap between the presynaptic neuron and the dendrites of the postsynaptic neuron
Neurotransmitters
Chemical messengers released from presynaptic membrane (in vesicles) into the synaptic cleft.
They bind to receptors on the postsynaptic membrane which causes the depolarization of the postsynaptic membrane if sufficient amounts of the neurotransmitter is released (threshold point met)
Two types of neurotransmitters
1) Excitatory neurons that produce excitatory postsynaptic potentials (EPSP) (e.g. Glutamate)
2) Inhibitory neurons that send inhibitory postsynaptic potentials (IPSP) (e.g. GABA)
What are the two ways that EPSPs can promote neural depolarization?
1) Temporal summation: rapid, repetitive excitation from a single excitatory presynaptic neuron
2) Spatial summation: summing EPSPs from several different presynaptic neurons