Lecture 2 -Intro to neurophysiology

Question 1

What is the importance of the nervous system in terms of homeostasis?

Answer 1

All the different parts of the body work to maintain a constant internal environment that is suited to the nervous cells. It is the brain that controls all these processes/ body parts.

Question 2

In addition to homeostasis what is the nervous system responsible for?

Answer 2

Thoughts, feelings, memories, emotions, sensations, perception, species senses, pain, movements (both voluntary and innate), reproductive function.

Question 3

What does the central nervous system consist of? (Think flow chart)

Answer 3

The brain and the spinal chord. Both of these are incased in bone (the skull + the spinal column).
The brain and spinal chord then consist of two cells types neurons and gila.

Question 4

What does the peripheral nervous system consist of? (Think flow chart)

Answer 4

Consists of peripheral nerves + ganglia

These are then composed of two general cell types (neuron + gila)

Question 5

True or false the peripheral nervous system includes the enteric nervous system?

Answer 5

True

Question 6

What are the different zones of a neuron and their roles?

Answer 6

• Input zone= The dendrites + cell body. Receives chemical signals from other neurons
• Summation zone= The axon hillock/ initial segment. Inputs are summated and may or may not reach threshold to generate an action potential (electrical signal)
• Conduction zone= axon (can be long). Carries electrical signal to wherever it is going.
• Output zone= axon terminals where they have contact with other neurons or effector cells. The release of a neurotransmitter is a chemical signal.

Question 7

How does the signal change throughout the neuron?

Answer 7

Starts chemical in the input zone, turns electrical at the summation zone + conduction zone, then goes back to chemical at the output

Question 8

What is the function of dendrites?

Answer 8

They increase the surface area of the cell body for optimum input from other neurons

Question 9

An axon bundle=

Answer 9

A nerve

Question 10

How does myelination differ in the peripheral nervous system as opposed to the central?

Answer 10

Central nervous system myelination= oligodendrocytes

Periphery nervous system myelination= Schwann cells

Question 11

What is the purpose of myelination?

Answer 11

It increases the speed of action potential propagation down the axon

Question 12

Name the four types of glia and their functions…

Answer 12

1. Astrocytes= maintain the extracellular environment and thus supply nutrients to neurons. Unsheathe blood capillaries. Provide an injury response.
2. Microglia= the immune cells of the CNS thus providing the main injury response. They engulf microorganisms and debris.
3. Ependymal cells= line fluid filled spaces of the brain and spinal cord. The ones in the choroid plexus produce CSF and the cells have cilia to circulate this.
4. Oligodendrocytes= support nerve cells. And in the CNS ensheath them will myelin.

Question 13

What is the function of CSF?

Answer 13

Its a fluid that exists in and around the ventricles. It provides a buffer for the brain.

Question 14

How come the CNS requires its own immune cells?

Answer 14

The immune cells in the blood don’t have access to the brain (kept separate via a barrier)

Question 15

What are electrical synapses like?

Answer 15

These are gap junctions where the unmoderated flow of ions directly from cell to cell (exist close together) results in rapid communication. Not used very much in the nervous system.

Question 16

What are chemical synapses?

Answer 16

This is a much slower way of transferring a signal relying on a series of steps but is a lot more controlled/ selective and is therefore preferred in the nervous system. Neurotransmitters exist in vesicles which then release their contents at the cleft (space). The neurotransmitters then have to cross and bind with post synaptic receptors. Causing an open of voltage gated ion changes and Depolarisation/ an electrical signal.

Question 17

Where is the primary somatosensory cortex? How is this organised?

Answer 17

Post-central gyrus.

There is a map whereby specific regions of the cortex receive sensory information from specific regions of the body.

Question 18

Where is the primary motor cortex located? and how is this arranged?

Answer 18

Pre-central gyrus
Like the somatosensory cortex there exists a map where specific regions correspond to the specific areas of the body that will receive efferent information.

Question 19

Why is the primary somatosensory cortex and the primary motor cortex arranged similarly?

Answer 19

Areas corresponding to the same regions of the body are close together so that the afferent and efferent information can interact and feed off each other in a loop

Question 20

How is efferent information divided?

Answer 20

• Somatic (known actions) e.g. skeletal muscle

- Autonomic (unconscious actions) e.g. sympathetic or parasympathetic

Question 21

Compare and contrast the parasympathetic and sympathetic divisions of the autonomic efferent nervous system….

Answer 21

• Parasympathetic= ‘rest + digest’. Cell bodies sit in the brain stem + Sacro part of spinal chord (CNS). The preganglionic axon is then long as it reaches a parasympathetic ganglion that is close to the effector. The post ganglionic axon is therefore short. At both synapses acetylcholine is the neurotransmitter.
• Sympathetic= ‘fight or flight’. Cell bodies sit in the thoracic + upper lumbar parts of the spinal chord (still CNS). However, the preganglionic axon is a lot shorter than in parasympathetic. The post ganglion axon is therefore much longer. At the first synapse acetylcholine is used (consistent) however, at the second noradrenaline is the neurotransmitter.

Question 22

Information is transmitted through….

Answer 22

changes in membrane potentials

Question 23

What are electrical signals called before meeting threshold and what are they afterwards?

Answer 23

Before= excitatory or inhibitory potentials. 
After= if the sum of both EPSP and IPSP is above threshold then an action potential can be generated (all or none)

Question 24

What are electrical signals called before meeting threshold and what are they afterwards?

Answer 24

Before= excitatory or inhibitory potentials. 
After= if the sum of both EPSP and IPSP is above threshold then an action potential can be generated (all or none)

Question 25

Describe the events occurring at a cholinergic synapse….

Answer 25

1) action potentials generate the opening of voltage gated calcium channels
2) calcium ions diffuse into the axon terminal (because calcium levels are much lower inside than outside) and trigger synaptic vesicles to release acetylcholine via exocytosis (membranes merge)
3) Acetylcholine diffuses across the synaptic cleft binds to acetylcholine gated sodium ion channels in the postsynaptic membrane and produces a graded Depolarisation.
4) Depolarisation ends as acetylcholine is broken down to acetate and choline by acetylcholinesterase.
5) The axon terminal reabsorbs choline from the synaptic clef and uses it to resynthesize ACh

Question 26

Acetylcholinesterase is given what collection of letters to shorten it’s name?

Answer 26

AChE

Question 27

The post-synaptic receptor that receives acetylcholine is described as…

Answer 27

ligand gated (open to allow ions through)

Question 28

How does Botox work at the synaptic terminal?

Answer 28

It stops the binding of calcium to vesicles meaning acetylcholine can’t be released at the synaptic clef. It is essentially causing paralysis.

Question 29

Where do nerve agents like sarin and novichok act in terms of the synaptic terminal? What is a symptom?

Answer 29

Inhibits the action of AChE meaning acetylcholine can’t be broken down and continuous depolarisation occurs. A symptom is salivation, a function of the parasympathetic nervous system, as acetylcholine continues to bind to receptors just like it does in this response.