Module 2 - Nervous Systems Flashcards
Sensory neuron vs interneuron vs motor neuron structure
Sensory neuron - long axon
Interneuron - lots of dendrites to collect information and many synaptic terminals (branches off axon)
Motor neuron - many dendrites and 1 long axon from CNS to effector
What are Glia? What are the types and their roles?
- supporting cells that are vital for structural integrity and normal function of neurons
Types:
Astrocytes - in the CNS, form the blood-brain barrier and regulate extracellular concentration of ions and neurotransmitters
Oligodendrocytes (CNS) and Schwann cells (PNS) - form myelin sheaths around axons that act as insulators
What is the abundance of Glia?
10-50 times more than neurons in the mammalian brain
Resting membrane potential Na+ and K+ concentration
ECF - 5mM K+ and 150mM Na+
Cytoplasm - 140mM K+ and 15mM Na+
Rate of Na+/K+-ATPase pumping
3 Na+ ions out and 2 K+ ions in
What causes the resting membrane potential?
Many open K+ channels and few Na+ channels plus charged proteins inside the cell
Hyperpolarisation vs depolarisation
Hyper - inside of membrane becomes more negative as a result of K+ channels opening and K+ flowing out of cell
De - inside of membrane becomes more positive as a result of Na+ channels opening and Na+ ions flowing into the cell
Graded vs action potentials
Graded:
- can be hyper- or depolarisation
- vary in magnitude with the strength of stimulus
- local and die out
Action:
- depolarisation only
- reach a certain threshold and is an ‘all or nothing’ response
- travel along axons
Absolute refractory period (ARP) vs relative refractory period (RPR)
ARP - no action potential can be generated on top of the current one as Na+ channels are open and then inactive
RPR - action potential can only be generated to add to the current one if a large stimulus is applied, as some Na+ channels are closed again
Saltatory vs. smooth conduction
Saltatory: conduction of AP along axon - AP only needs to be generated at Nodes of Ranvier between Schwann cells along the axons => faster conduction
Smooth: AP generated all the way along due to no myelination
Na+ channels vs K+ channels
Na+ channels have 3 stages - Closed, open and inactive, and open very fast
K+ channels have 2 stages - closed and open, and are slower to open
Both open by depolarisation signal
What effects the speed of conduction?
- Axon diameter: larger diameter = less resistance = faster conduction
- temperature: increase temp = increase conduction speed
- degree of myelination: increase myelination = decreased loss of electrical signal = increased conduction speed (more effect than axon diameter)
Electrical vs chemical synapses
Electrical:
- rare type
- at gap junctions
- direct electrical currents between cells
Chemical:
- common type
- involve release of a neurotransmitter
- neurotransmitter released by presynaptic neuron
Excitatory vs inhibitory postsynaptic potential
EPSP - depolarisation in postsynaptic membrane, could lead to another action potential is depolarisation reaches threshold
IPSP - hyperpolarisation at postsynaptic membrane
Temporal vs spatial summation
temporal - several EPSP’s from the same synapse just after each other
spatial - two or more EPSP’s from different synpases
Postsynaptic potential vs action potential
Postsynaptic:
- excitatory (EPSP) or inhibitory (IPSP)
- graded
- local
- at the cell body or dendrites
Action:
- depolarisation
- all or nothing
- can be the result of the addition of excitatory postsynaptic potentials
- generated at the axon hillock
- travels along the axon
Types of chemical synaptic transmission and related receptor types
Direct:
- neurotransmitter opens ion channels on the postsynaptic membrane
- action via ligand-gated ion channels
Receptors: ion channel receptors
Indirect:
- neurotransmitter binds to a receptor on the postsynaptic membrane
- activates a signal transduction pathway
- involves a second messenger
Receptors: GPCR’s
4 ways to remove neurotransmitters from synaptic cleft
- Broken up by enzymes such as acetylcholinesterase (super fast, enzyme sits in cleft ready to take action)
- Diffusion (too slow for the necessary control)
- recycled by selective uptake of transporters such as NET and SERT back into the presynaptic neuron where they return to vesicles (different transport proteins for each neurotransmitter)
- Taken up by astrocytes which mop up the left overs
What animals don’t have a nervous system?
Sponges
CNS vs PNS
CNS
- brain
- spinal cord
PNS
- cranial nerves (12 pairs in mammals)
- spinal nerves (31 pairs in mammals)
Somatic vs autonomic nervous system
Both part of PNS
Somatic - voluntary control e.g. motor neurons
Autonomic
- mostly involuntary control e.g. heart rate
- 3 divisions: sympathetic, parasympathetic and enteric
Sympathetic vs parasympathetic vs enteric divisions of autonomic nervous system from PNS, and response/s of activation
Enteric - nerves to gut, very complex
Sympathetic:
- fight or flight
- bronchi dilate
- heart rate increases
- increase converstion of glycogen to glucose
- adrenaline secretion
- digestion inhibitation
- nerves arise from thoracic or lumber (middle) regions of spine
- short pre-ganglia fibre and long post-ganglia fibre
Parasympathetic:
- rest and digest
- calming
- often has opposite response to the sympathetic division
- nerves arise from cervical or sacral (top and bottom) regions of spine
- long pre-ganglia fibre and short post-ganglia fibre
Roles of cerebrospinal fluid
- protects the CNS
- clear fluid in subarachnoid space (between the skull and cortex)
- 4 ventricles and central canal
- supply nutrients and hormones
- remove waste
- blocks flow in hydrocephalus
Grey vs white matter inc. location in brain and spinal cord
Grey matter:
- dendrites, cell bodies and unmyelinated axons
- outside of brain
- inside of spinal cord
White matter:
- myelinated axons
- inside of brain
- outside of spinal cord
