Compendium 8 Flashcards

Question

Explain satellite cells

Answer 1

Provide support and nutrition to cell bodies in ganglia Protect cell bodies from harmful substances

Answer 2

Myelinated: contain myelin sheath, have nodes of ranvier which are sections that don't contain myelin sheath Unmyelinated: no myelin sheath, may have one Schwann cell or oligodendrocytes covering more than one axon

Answer 3

Insulates, stops charges leaking out of axon, protects axon from damage, can speed up action potentials

Answer 4

Cell body and dendrites Brain outer cortex and nuclei Inner part spinal cord Ganglion

Answer 5

Axons Deeper nerve tracts of brain Outer part spinal cord Nerves

Answer 6

Action potential - an electrical signal transferring information from one part of neuron to the next When ions flow across membrane it causes change in charge (one side more negative, one more positive) which is called a membrane potential

Answer 7

1) difference in ionic conc (mostly K and Na) across membrane - number positive and negative ions in extracellular and intracellular fluid is considered electrically neutral as one same side, the number of positive and negative ions is around the same so charges cancel out --> doesn't mean charge across whole membrane is neutral 2) ability of membrane to permeable to ions - action potential results from movement of ions - cannot occur unless membrane permits this

Answer 8

Also called leak channels Open so ions can leak through at any time Each leak channel is specific to a certain ion Cell membrane has more K than Na leak channels No signal required

Answer 9

Requires signals to open, three types: 1) ligand gated: open when ligand/chemical binds to them (e.g. Neurotransmitter or hormone) 2) voltage gated: open in response to membrane potential change (voltage) 3) other gated: open in response to stimuli

Answer 10

RMP: difference in charge across the cell membrane in a resting cell caused by Na/K pump and K leak channels - inside cell more negative than outside cell - RMP=-70mV K is naturally abundant on intracellular side therefore leak through leak channels to extracellular fluid (down conc. gradient), the accumulation of K on extracellular side makes extracellular more positive Same for Na which is naturally more abundant on extracellular side, however, less of them and their leak channels so no big difference to charge is made Na/K works against conc. gradient to send 3 Na ions outside and bring 2 K inside which ensures large conc. gradient is maintained

Answer 11

Depolarisation: when membrane potential becomes more positive e.g. Could go from -70mV to -30mV Hyperpolarisation: when membrane potential becomes more negative Repolarisation: membrane potential returns to normal

Answer 12

Can lead to action potentials if the stimulus is strong enough Short lived, localised (occur in one part of membrane) changes in membrane potential Magnitude proportional to stimulus strength (strong stimulus = greater voltage change) Often occurs in dendrites or cell body Able to SUMMATE: effect produced by one gradient potential is added to effect produced by another graded potential (allows ions channels to open) Decremental: not able to transfer info over long distance (hence start of action potential)

Answer 13

When a graded potential summates and membrane potential reaches a threshold of -55mV Occurs in trigger zone of axon as it contains a large number of voltage ion chnanels

Answer 14

Resting membrane potential: all gated na and k channels are closed, K leak channels open so intracellular more negative, Na/K pump working Depolarisation: once threshold reached, cell becomes more positive, Na gated channels open so Na moves inside cell, K gated channels closed so K remains in abundance in cell Repolarisation: Na gated channels close, K gated channels open and K moves out of cell down conc. gradient so intracellular becomes more negative, less to negative membrane potential Hyperpolarisation/afterpotential: Na gated channels closed, k gated channels slowly close so K continues to leave cell to create afterpotential, membrane potential becomes very negative Resting membrane potential: Na and k gated channels closed, RMP re-established by Na/K pump, k lead channels continue to help re-establish RMP

Answer 15

Graded potential must reach threshold (-55mV) for action potential to be generated If doesn't reach then RMP returns to normal until next stimulus

Answer 16

Occurs when part of a neuron generates an action potential, so neurons cannot respond to another stimulus at same sight Absolute refractory period: stages of depolarisation and repolarisation which can't have any interruptions (Na channels open) Relative refractory period: stage where most voltage gated Na channels are closed, an action potential can occur but has to be a strong stimulus

Answer 17

Depolarisation of one part of neuron causes Na to move inside cell which creates current that will depolarise the area adjacent to it Occurs along the whole length of the fibre Following depolarisation each segment of axon becomes repolarised

Answer 18

Action potential generated at one node of randier which creates current that rapidly jumps to next node -- called saltatory conduction Continues along whole axon length very fast as skips large segments of axon

Answer 19

An action potential is transmitted to another neuron, cell, muscle, effector gland, ect. Electrical synapses - current Chemical synapses - chemicals e.g. Neurotransmitters and hormones

Answer 20

1) action potential arrives at pre-synaptic terminal 2) calcium channels open and calcium ions move down conc. gradient and diffuse into cell to act on vesicles 3) vesicles containing neurotransmitters, move to presynaptic membrane and fuse with it 4) neurotransmitters released into synaptic cleft via exocytosis 5) neurotransmitters diffuse across cleft 6) neurotransmitters bind to receptors of ligand gated Na channels on postsynaptic membrane 7) ion channels open allow diffusion of ions into post synaptic cell (Na moves in) - change in charge may trigger graded potential and so on 8) neurotransmitter removed from synapse by enzyme activity (must be removed or Na will keep entering cell and cause overstimulation) Enzyme activity includes: released from receptor on post synaptic membrane and diffuse away from synapse, broken down by enzymes or remains whole, reabsorbed by pre synaptic membrane so can be reused when another impulse arrives

Answer 21

Antidepressants block reuptake of neurotransmitters (feel good ones) by presynaptic membrane so will continue to stimulate post synaptic neuron producing positive moods and emotions Neurotransmitters have different effects depending on where they are released e.g. Can prevent neuron from being stimulated in one part or cause it to be active in another -alcohol increases activity of inhibitory neurotransmitters in brain so brain function is slower as inhibitory input to brain is increased

Answer 22

Facilitates transfer info from PNS to CNS and back Protected by vertebral canal, CSF and meninges Outer= white matter, inner = grey matter Anterior an posterior of spinal cord have indentations that look like they split the cord in half - anterior median fissure - posterior median sulcus White matter divides into 3 columns- dorsal (back), ventral (front) and lateral (side) Grey matter divided into horns - dorsal, ventral, lateral Middle of two halves called COMMISSURES which connects grey and white matter together Hole right in centre called central canal which contains CSF Rootlets branch directly off spinal cord which merge to from dorsal root at back and ventral root at front which merge to from spinal nerves (31 pairs arise)

Answer 23

Sensory receptor stimulated and stimulus travels along sensory neuron through spinal nerve to cell body in dorsal root ganglion Then through rest of dorsal root to dorsal horn in grey matter Can then cross synapse to an interneuron and then motor neuron of straight to a motor neuron -synapse w/ interneuron will pass to somatic motor neuron and to skeletal muscle -no interneuron will be to automatic motor neuron and then to smooth muscle or glands

Answer 24

Once in motor neuron will travel through ventral root and then through body to effector

Answer 25

Dorsal horns = interneurons Ventral horns= some neurons but mostly cell body of somatic motor neuron Lateral horns= cell body of automatic motor neuron

Answer 26

Automatic response to a stimulus that requires no contours thought Can be somatic or autonomic Homeostatic mechanism

Answer 27

The 5 components of a reflex make up a reflex arc: 1) sensory receptor 2) sensory neuron 3) internuron 4) motor neuron 5) effector The FUNCTIONAL UNIT of the nervous system Simplest arcs don't contain interneurons and are called monosynaptic (ones that do called polysynaptic) There are 3 types : stretch (monosynaotic), Golgi tension, withdrawal

Answer 28

Receptor stimulated so signal sent via sensory neuron to spinal cord Action potential synapses with motor neuron which sends action potential to effector muscle or gland Action potential is also sent to brain so it is aware something has occurred, however, response initiated by lumbar region of spinal cord and not the brain Common in knee, ankle, Achilles, tricep

Answer 29

Eye light shinned in would constrict (direct reflex), however, other eye would too (called consensual reflex) as brain communicates and links are made between nerves controlling each eye

Answer 30

Have control over Slower than a reflex -require conscious thought Can become a learned behaviour e.g. Quicker responses through repetition E.g. Burning hand on hot stove