Nerve Cells & Connections Flashcards
(20 cards)
Types of Neurons
Afferent (sensory) neurons PNS
- bipolar, pseudeuniport
Inter-neurons CNS
- Multipolar, Anaxanic
Efferent (motor) neurons PNS
- Multipolar
Types of Gila
Astrocytes - maintain external environment and surround blood vessels and form BBB
Oligodendrpcytes - form mylein sheath in CNS
Microglia - macrophages of the CNS
Ependymal - produce the corebrospinal fluid
Schwann cells - form myelin sheath in PNS
Satelite cells - support neuron cell bodies in PNS
Membrane potentials
Action potentials - transmit signals over long distances
Graded potentials - decide when an axon potential should be fired - only useful over short distances
Resting membrane potential - keeps cells ready to respond
Creating a resting membrane potential
Phospholipid bilayer impermeable to water and ions. Balanced - no membrane potential
Addition of leaky K-channels - k leaks out down concentration gradient, this build up electrical gradient. Equilibrium is reached when electrical gradient is equal and opposite to the concentration gradient
Small concentrational gradient = small resting potential
Large resting potential = requires lots of leaky K out of cell to reach equilibrium
Ionic basis of graded potentials
EPSPs - generated by Na/K channels or closely leaky K channels
IPSPs - generated by opening Cl channels or K channels
Properties of an action potential
- threshold
- all-or-none
- self-propagation
- have refractory periods
- travel slowly
- only encoded stimulus intensity in firing frequency, no amplitude
Action potential - role of NA and K
Voltage-gated Na channels medicate the depolarising phase
Voltage-gated K channels mediate the repolarising and depolarising phase
Explain large axons
- Electric current flows more easily down a large axon then a small axon
- Allows the Na channels to be more spaced out along membrane
Explain myleination
Shwann cells (PNS) and Oligodendrocytes (CNS) wrap layers around axons. Increased membrane resistance (less current leaks out) Decreased membrane capacitance (less current wasted charging up membrane) Action potential spreads passively from node to node and still reach threshold - saltatory conduction
Explain the neurotransmitter junction
- Action potential in motor neurons
- opens voltage-gated Ca channels in synaptic terminal
- Fussion of vesicles
- ACh diffuses across synaptic cleft
- ACh binds to ACh receptors
- Opens ligand-gated Na/K channels
- Evokes end plate potential (graded potential)
- (always) depolarises membrane to threshold
- Opens voltage-gated Na channels
- Evokes action potential
- Muscle contrasts
- Ach cleared up
Types of postsynaptic potentials in CNS
- Fast EPSPs (ionictrophic)
- Slow EPSPs (metabotrophic)
- Fast IPSP (ionictrophic)
- Slow IPSP (metabotrophic)
Explain CNS synapse anatomy
- Axo-dendrites
- Axo-somatic
- Axo-axonal
Difference between Monosynaptic reflexes ans Polysynaptic reflexes
Monosynaptic:
Sensory (afferent) neurons and motor (efferent) neurons
Polysynaptic:
Sensory (afferent) neurons, interneurons, and motor (efferent) neurons
Explain muscle spindle (stretch) reflex
Sensory stretch receptor = muscle spindle
alpha motor neurons innvate extrafusal muscle fibres, causing the muscle to stretch, stretching muscle activates the muscle spindle, this stimulates alpha motor neurons and leads to the muscle contracting
This is a negative feedback system - detecting stretch of muscle.
Differences between Extrafusal fibres and Intrafusal fibres
Extrafusal fibres:
is from the main bulk of muscle, are innervated by alpha motor neurons and lie parallel with sensory muscle spindles
Intrafusal fibres:
from very minor part of muscle, are innervated by gama motor neurons and lie in series with snesory muscle spindles
Co-activation of alpha and gama motor neurons allows the muscle to stretch whatever the length of muscle.
Explain excessive tension in the Golgi
- Golgi tendon activated by excessive tension
- Afferent fibres activates inhibitory interneurons in the spinal cord
- inhibits motor neurons supplying the muscle
- muscle relaxes to prevent damages
- polysynaptic reflex
Flexion (and crossed extensor) reflex
Flexion is the mechanism to remove a limb from damage/potentially damaging stimulus
Stimulus detected by nociceptors, this activates interneurons that activate motor neurons supplying ipsilateral flexers, and inhibit motor neurons supplying ipsilateral extensors = crossed extensor reflex (withdrawal), also activates interneurons that inhibit motor neurons supplying contralateral flexors, and activate motor neurons supplying contralateral extensors = crossed extensor reflex
Difference between Somatic and automatic nervous system
Somatic:
Only one axon goes all the way to target, is present in skeletal muscle, has been specialised, ionictrophic receptors, always excites target
Automatic:
pre-ganglion fibre (small myelinated), post-ganglion fibre (unmylienated), present in smooth and cardiac muscle, Metabotophic receptors, may or may not excite target
Difference between Sympathetic and Parasympathetic
Sympathetic:
outflow is from lumber regions, ganglion lie close to spinal cord in sympathetic chain, or in collateral ganglion, release neurodrenaline
Parasympathetic:
outflow is from carnial and sacral regions, ganglion lies close to or within the target. Releases ACh
How sympathetic and parasympathetic influence systems
Eyes - Sympathetic, alpha receptors on radial muscle of iris (pupils increase). Or beta receptor on ciliary muscle (focus far away) Parasympathetic, muscorinic receptor on sphicter muscle (pupils smaller). Or receptor in ciliary muscle (focus up close)
The heart - sympathetic increases heart rate and strength of contraction. Parasympathetic decreases heart rate and little effect on strength of contraction.
The lungs - Sympathetic relax and dialtes airways. Parasympathetic contrast and castriel airways.
