Week 2 - 3: Nervous System (Part 2)

Front 1

How does a nerve Transmit and impulse between the input of the cell and the exit point?

Back 1

1. Resting membrane is polarized. In the resting state the external face of the membrane is slightly positive. It's internal face is slightly negative. The chief extracellular ion is sodium (Na+), whereas the chief intracellular ion is potassium (K+). The membrane is relatively impermeable to both ions.

2. Stimulus initiates local depolarisation. A stimulus changes the permeability of local "patch" of the membrane, and sodium ions diffuse rapidly into the cell. The changes the polarity of the membrane at the site.

3. Depolarisation and generation of an Action Potential. If stimulus is strong enough, depolarisation causes membrane polarity to be completely reversed, and an action potential is initiated

4. Propagation of the Action Potential. Depolarisation of the first membrane patch causes permeability changes in the adjacent membrane, and events described in step (2) are repeated. Thus action potential propagates rapidly along the entire length of the membrane.

5. Repolarisation. Potassium ions diffuse out of the cell as the membrane permeability changes again, restoring the negative charge on the outside of the membrane and the positive charge on the outside surface. Repolarisation occurs in the same direction as depolarisation.

6. Initial ionic conditions restored. The ionic conditions of the Resting state are restored later by the activity of the sodium-potassium pump. 3 sodium ions are ejected for every 2 potassium ions carried back into the cell.

Front 2

Role of sodium-potassium pump in maintaining cell membrane resting potential

Back 2

The sodium-potassium pump restores the initial concentrations of the sodium and potassium ions inside and outside the neurons. The pump uses ATP (cellular energy) to pump excess sodium ions put of the cell and to bring potassium ions back in. Until repolarisation occurs, a Neuron cannot conduct another impulse.

Front 3

Conditions for cellular membrane resting potential

Back 3

The ionic conditions of the resting state are restored later by activity of the sodium-potassium pump. 3 sodium ions are ejected for every 2 potassium ions carried back into the cell.

Front 4

Electrochemical events of neuronal depolarisation (including transmission of an action potential)

Back 4

If stimulus is strong enough, depolarisation causes membrane polarity to be completely reversed, and an action potential is initiated. (Propagation of the Action Potential) Depolarisation of the first membrane patch causes permeability changes in the adjacent membrane. Changes in polarity of the membrane, progpogates action potential rapidly along the entire length of the membrane

.

Front 5

Electrochemical events of neuronal repolarisation

Back 5

Potassium ions diffuse out of the cell as the membrane permeability changes again, restoring the negative charge on the outside of the membrane and the positive charge on the outside surface. Repolarisation occurs in the same direction as depolarisation.

Front 6

Action potential at a typical axon terminal

Back 6

When an action potential reaches the Axon terminal, it depolarises the membrane and opens voltage gated sodium ions channels. Sodium ions enter the cell, further depolarising the presynaptic membrane.

Front 7

Fate of neurotransmitters released into synaptic cleft

Back 7

When actional potential reaches an axon terminal, the electrical change opens calcium channels. Calcium ions cause the tint vesicles containing Neurotransmitters to fuse with axonal membrane, and pore-like openings form releasing the neurotransmitter into the synaptic cleft.

The neurotransmitter molecules diffuse across synaptic cleft and bind to receptors on the membrane of the next Neuron.

If enough neurotransmitter is released generates graded potential and eventually a nerve impulse. Electrical changes prompted by neurotransmitterms binding are brief because neurotransmitters quickly released from synaptic cleft either by diffusing away, re-uptake into axon terminal or enzymatic breakdown.

Neurotransmission at a chemical synapse begins with the arrival of an action potential at the presynaptic axon terminal.

Front 8

Typical forms of stimulus for cellular depolarisation

Back 8

A stimulus changes the permeability of local "patch" of the membrane, and sodium ions diffuse rapidly into the cell. This changes the polarity of the membrane at the site. Depolarisation and generation of an Action Potential. If stimulus is strong enough, depolarisation causes membrane polarity to be completely reversed, and an action potential is initiated

Front 9

6 common neurotransmitters

Back 9

1. Serotonin

2. Dopamine

3. Glutamate

4. Epinephrine

5. Norepinephrine

6. Endorphins

Front 10

What is a Reflex Arc?

Back 10

Reflexes are rapid, predictable and involuntary responses to stimuli. It always goes in the same direction.

Reflexes occurs over neural pathways called Reflexes arcs and involve both CNS and PNS structures.

Front 11

Purpose of reflex arcs

Back 11

A reflex arc is a pathway that a nerve impulse follows during reflex action. Reflex arc are highly beneficial in situations that require a quick response and do not involve conscious thought.

A reflex arc is a pathway that a nerve impulse follows during reflex action. Reflex arc are highly beneficial in situations that require a quick response and do not involve conscious thought.

A reflex arc is a pathway that a nerve impulse follows during reflex action. Reflex arc are highly beneficial in situations that require a quick response and do not involve conscious thought.

A reflex arc is a pathway that a nerve impulse follows during reflex action. Reflex arc are highly beneficial in situations that require a quick response and do not involve conscious thought.

Front 12

Example of regulatory reflex arc

Back 12

E.g.

-Secretion of saliva (salivary reflex)

- Change in the size of the eyes pupil (pupillary reflex)

* not 100% sure on this one, so please confirm and I can update*

Front 13

5 components of a typical Reflex Arc

Back 13

1. Sensory (stretch) receptor - responds to stimuli

2. Sensory (afferent) Neuron -

Connection pathway for receptor and effector

3. Interneuron (integration centre)

Acts as a link between sensory and motor neurons

-

4. Motor (efferent) neuron - Connection pathway for stimuli from sensory to interact with effector organ

Connection pathway for stimuli from sensory to interact with effector organ

5. Effector Organ-

Muscle or gland eventually stimulated

Front 14

2 types of physiological reflex arcs

Back 14

1. Somatic Reflexes- All reflexes that stimulate skeletal muscles. Still classed as involuntary

2. Autonomic Reflexes- regulate activity of smooth muscle, heart and glands. Regulate body functions such as digestion, elimination, BP, sweating