Neurophysiology Flashcards
what is neurophysiology?
the functions of the nervous system
what are the functions of the nervous system?
- control movement and some functions (motor neurons)
- detect external stimuli (sensory neurons)
- integration of neural activity and connections (association neurons)
what cells make up the nervous system?
neurons and supporting cells
what are neurons
basic functional and structural unit of the nervous system
what do supporting cells do?
aid the functions of neurons, about 5x more abundant
association neurons
responsible for behaviour, thoughts and emotions in the CNS
what are the 3 main regions in neurons
- axon
- cell body
- dendrites
what do neurons do?
- conduct electrochemical impulses (action potentials)
- release chemical regulators (neurotransmitters)
what does the cell body of neurons do
- the “nutritional center” of the neuron, where macronutrients are produced
- in the CNS frequently clustered to nuclei
- in the PNS occur in clusters called ganglia
what do dendrites do in neurons?
- thin branched processes that receive information from sensory receptors (or from other cells) and send it to the cell body
what do axons do in neurons?
- delivers electrical signals from the cell body to another neuron or an effector organ (muscle or gland)
- conduct impulses called action potentials
what are afferent neurons
- aka sensory neurons
- conduct impulses FROM sensory receptors into the CNS
what are efferent neurons
- aka motor neurons
- conduct impulses OUT OF the CNS to effector organs (like muscles or glands)
what are inter neurons
- aka association neurons
- located entirely within the CNS, serve the integrative and associative functions of the nervous system
what are the 2 types of motor neurons?
somatic and autonomic neurons
somatic motor neurons
responsible for reflex and voluntary control of skeletal muscle
- have cell bodies in the CNS and send axons to skeletal muscles
autonomic motor neurons
involuntary control of smooth muscle cardiac muscle and glands outside the CNS
- involves 2 neurons in the efferent pathway: 1. cell body in the CNS (which synapses with the second neuron), 2. post ganglionic neuron (whose axon extends to the effector organ and its synapse targets the tissue)
2 divisions of autonomic neurons
sympathetic and parasympathetic
sympathetic neurons
controls the body’s “fight or flight” response
parasympathetic neurons
controls the bodies “rest and digest” functions
simple neural circuit
- stimulus reaches receptor connected to sensory neuron
- sensory neuron send info integration center of the association neuron
- after integration info is sent through the motor neuron
- motor neuron reaches the effector and generates a response
4 structural classifications of neurons
- pseudopolar: single, short process that branches like a T to form a pair of longer processes
- bipolar: 2 processes, one at either end, retinal and cochlear neurons
- multipolar: have several dendrites and one axon extending from the cell body - motor neurons
- anaxonic: have no obvious axon, some CNS neurons
what is a nerve
- a bundle of axons located outside the CNS, most are comprised of both sensory and motor fibres
- some cranial nerves only contain sensory fibres - the ones that serve sight, hearing, taste and smell
supporting cells in the PNS
- Schwan cells: form myelin sheaths around peripheral axons
- Ganglionic (satellite) cells: support neuron cell bodies within the ganglia
supporting cells in the CNS
- Oligodendrocytes: form myelin sheaths around CNS axons
- microglia: migrate through the CNS and phagocytose foreign and degenerated material
- astrocytes: help to regulate the external environment of neurons in the CNS
- ependymal cells: line the ventricles (cavities) of the brain and the central canal of the spinal chord
What is the difference between supporting cells in the CNS and PNS
In CNS: one oligodendrocyte forms myelin sheaths around several axons
In PNS: successive wrapping of schwan cell membrane around one axon, most of the schwan cell cytoplasm is left outside the myelin
What are astrocytes
- the most abundant glial cell in the CNS (up to 90% of nervous tissue in the brain)
- processes terminate in “end feet” at capillaries and others on neurons, therefore can influence interactions between neurons and the blood
- have other extensions adjacent to synapses between the axon terminal of one neuron and the cell body of another
7 functions of astrocytes
- take up K+ form extracellular fluid
- take up neurotransmitters released from the axon terminals of neurons
- the “end-feet” surrounding blood capillaries take up glucose from the blood
- formation of synapses in the CNS
- regulate neurogenesis in the adult brain
- induce the formation of the BBB
- release transmitter chemicals that can stimulate or inhibit neurons
why do astrocytes take up K+
- K+ diffuses out of neurons during the production of nerve impulses and ends up in the extracellular fluid
- the take-up of K+ helps maintain proper ionic environment for neurons
astrocytes taking up neurotransmitters (glutamine example)
- astrocytes can take up th eneurotransmitter glutamate and transform it to glutamine which can be released back into neurons
- the neurons can then reform glutamate to fire again
why do the “end-feet” of astrocytes surrounding the blood capillaries take up glucose from the blood
- astrocytes metabolize glucose to lactate and then release it as an energy source by neurons, which metabolize it aerobically into CO2 and H2O for the production of ATP
- PET scans and fMRIs visualize brain locations by their metabolic activities and are based on the functions of astrocytes as well as neurons
what is the purpose of blood brain barrier
to impose strict control over what can move from blood plasma to the brain
why can some substances not pass the blood-brain barrier
- they are too highly charged
- too large
- not lipid soluble
what can move through the blood brain barrier
- non-polar CO2 and O2
- organic molecules like alcohol and barbituaries
how do endothelial cells of brain capillaries contribute to the BBB
- ## endothelial cells are joined by tight junctions and there are no pores between adjacent cells so the brain cannot obtain molecules from blood plasma by a nonspecific filtering process
what components of the BBB do astrocytes influence
- the tight junctions between endothelial cells
- the production of carrier proteins and ion channels
- the enzymes that destroy potential toxic molecules
how do CNS depressants directly affect brain cells
- affect areas that inhibit behaviours, alter speech, slow reaction time and foggy memory
- reactions depend some part on dose, size, weight, gender, genetics, etc.
fetal alcohol syndrome
- when mother drinks alcohol while pregnant may result in baby having small eye openings, smooth philtrum and thin upper lip
how do astrocytes affect the BBB
- secrete neurotrophins and in turn the endothelial cells appear to secrete regulators that promote the growth and differentiation of astrocytes
Nicotine and the BBB
- in < 10 seconds nicotine molecules cross the BBB and fit like keys into locks activated by acetylcholine neurotransmitters and increase the level of several other neurotransmitters (e.g dopamine)
tobacco and the BBB
- decreases MAO activity which is the enzyme needed to break down neurotransmitters
what problem arises with prescribed drugs and the BBB
- drugs we need to treat neurodegenerative disorders can’t pass through the BBB but some infections can pass through
Rabies and the BBB
- rabies is a deadly viral infection which can penetrate the BBB
- there is no treatment after symptoms appear, but before they do rapid treatment with anti-rabies antibodies help attenuate the infection
- immune cells and antibodies cannot enter the brain therefore antibodies replicate out of control
what does dualinnervative mean
when an organ receives info from both sympathetic and parasympathetic systems