HES 202 EXAM QUESTIONS AND ANSWERS LATEST
UPDATE
what is a motor unit and how is force graded?
Alpha motor neurons and all skeletal muscle fibres innervated by its axon
MU are fundamental functional unit of contraction
Force is controlled either by
1) recruitment/de- altering the number of active MU
2) rate coding- changing the frequency of activation (motor unit discharge rate)
Draw a motor neuron
Axon hillock
is the component of the MN where the excitatory post synaptic potentials summate to
generate an ap
Depolarization
NT bind to receptors on dendrites, voltage gated ion channels open. Positive ions flood
interior neuron and depolarize the membrane. Decrease the difference in voltage
between inside and outside
A stim from sensory cell or another neuron depolarized the target neuron to its threshold
(-55mv), na channels in axon hillock open starting AP. once na channels open neuron
depolarizes to membrane potential 40mv. the ap travels down neuron as na channels
open
Hyperpolarization
na channels close --> refractory period
- same time k channels open and k leaves the cell, as k leaves the membrane potential
becomes more negative
- sodium returns to resting state
- eventually k+ ions diffuse out of the cell through potassium leakage channels,brinigng
the cell to hyperpolarized state
What does myelin do?
insulates the axon and prevents movement of ions across membrane
note: the speed of the AP is influenced by axon diameter and if it is myelinated or not
ions move readily at gaps in the myelin sheath (nodes of ranvier) so an AP at one node
brings the next node to a threshold and initiates an AP
saltatroy conduction
Saltatory conduction- is the propagation of action potentials along myelinated axons
from one node of Ranvier to the next node, increasing the conduction velocity of action
potentials.
botox
prevents release of ACh
UPDATE
what is a motor unit and how is force graded?
Alpha motor neurons and all skeletal muscle fibres innervated by its axon
MU are fundamental functional unit of contraction
Force is controlled either by
1) recruitment/de- altering the number of active MU
2) rate coding- changing the frequency of activation (motor unit discharge rate)
Draw a motor neuron
Axon hillock
is the component of the MN where the excitatory post synaptic potentials summate to
generate an ap
Depolarization
NT bind to receptors on dendrites, voltage gated ion channels open. Positive ions flood
interior neuron and depolarize the membrane. Decrease the difference in voltage
between inside and outside
A stim from sensory cell or another neuron depolarized the target neuron to its threshold
(-55mv), na channels in axon hillock open starting AP. once na channels open neuron
depolarizes to membrane potential 40mv. the ap travels down neuron as na channels
open
Hyperpolarization
na channels close --> refractory period
- same time k channels open and k leaves the cell, as k leaves the membrane potential
becomes more negative
- sodium returns to resting state
- eventually k+ ions diffuse out of the cell through potassium leakage channels,brinigng
the cell to hyperpolarized state
What does myelin do?
insulates the axon and prevents movement of ions across membrane
note: the speed of the AP is influenced by axon diameter and if it is myelinated or not
ions move readily at gaps in the myelin sheath (nodes of ranvier) so an AP at one node
brings the next node to a threshold and initiates an AP
saltatroy conduction
Saltatory conduction- is the propagation of action potentials along myelinated axons
from one node of Ranvier to the next node, increasing the conduction velocity of action
potentials.
botox
prevents release of ACh
