Lecture 8: Introduction to Neural Function

Question 1

Organisation of Nervous System?

Answer 1

1. Central Nervous System (CNS)
   - Brain and Spinal Cord
   - spinal cord;
   interneuron: axon terminal, cell body
2. Peripheral Nervous system;
   - nerves and ganglia
   - Afferent Neuron: Sensory receptor, peripheral axon (afferent fiber), cell body,central axon,
   - Efferent neuron - cell body, axon (efferent fiber), axon terminals, effector organ (muscle or gland)

Question 2

Organisation of the Nervous System

Answer 2

CNS
- Brain and spinal cord

PNS
Afferent Division (Input to CNS from periphery)
1. Sensory stimuli
2. Visceral stimuli

and

EFFERENT DIVISION (output from CNS to periphery)
1. SOMATIC NERVOUS SYSTEM =
- Motor neurons –> SKELETAL MUSCLES

2. AUTONOMIC NERVOUS SYSTEM
3. Sympathetic NS = Smooth muscle, cardiac muscle, some endocrine glands and Exocrine glands.
4. PARASYMPATHETIC NS = Smooth muscle, cardiac muscle, some endocrine glands and Exocrine glands.
5. ENTERIC NERVOUS SYSTEM
   Stimuli in digestive tract input — output = digestive organs

Question 3

Visceral Afferents = 3

Answer 3

• Blood Pressure
• Pain
• Osmolarity

Question 4

Somatic Afferents = 3

Answer 4

1 * Touch/pain/temp.
2 * Proprioception
3 * Balance

Question 5

Special senses = 4

Answer 5

1 * Vision
2 * Hearing
3* Taste
4 * Smell

Question 6

Types of Cells in Nervous System = 2

Answer 6

1. Neurons
   * main signalling cells
   * humans ~1011 neurons
2. Glial Cells
   *support cells (Greek glia,“glue”)
   * outnumber neurons 10-50x

Question 7

Myelin

Answer 7

lipid rich impermeable to ions

Question 8

Nodes of Ranvier

Answer 8

not covered by myelin

Question 9

Types of Glial cells

Answer 9

1. Microglia
   * Phagocytes
   * Arise from macrophages outside NS
   * Embryologically unrelated to other NS cells
2. Macroglia
   1 * Oligodendrocytes (formation of myelin sheaths CNS)

2 * Schwann cells (formation of myelin sheaths PNS)

3 * Astrocytes (blood-brain barrier, reuptake transmitters)

4. Ependymal cell

Question 10

Function of Glial Cells =7

Answer 10

1 ➢Structural support and insulation of neurons

2 ➢Myelin sheaths - Oligodendrocytes & Schwann cells

3 ➢Scavenging dead cells - microglia

4 ➢Uptake of released neurotransmitters, buffer for excess K+

5 ➢Blood brain barrier- astrocytes + endothelial cells

6 ➢Glia direct migration of developing neurons

7 ➢ Trophic support for neurons

Question 11

Typical NEURON structure AND ROLE.

Answer 11

1. Dendrites = input
2. Soma = Integrative
3. Axon = conductile
4. Axon terminals = output

SECRETION

Question 12

How to — Classification of Neurons = 6

Answer 12

1 * Number of neurites
2 * Size
3 * Shape
4 * Neurochemistry
5 * Location
6 * Connectivity

Question 13

Morphological Variations

Answer 13

1. Unipolar cell
   - dendrite
   - axon
   - cell body
   INVERTEBRATE NEURON
2. Pseudo-unipolar cell
   - dendrite, central axon, single process, cell body, peripheral axon to skin and muscle
   DORSAL ROOT GANGLION CELL
3. BIPOLAR CELL
   - dendrites, cell body, axon,
   RETINAL BIPOLAR CELL
4. 3 TYPES OF MULTIPOLAR CELLS
5. Spinal motor neuron
6. Hippocampal pyramidal cell
7. Purkinje cell of cerebellum

Question 14

Structure of Nerve Cells = 7

Answer 14

1 ➢Nerve cells are NEURONS

2 ➢ The cell body is called the SOMA

3 ➢Projections from the soma are NEURITES

4 ➢DENDRITES are neurites which receive input

5 ➢AXONSs transmit signal long distances

6 ➢ TERMINALS are where neurotransmitters are released from

7 ➢ NEUROTRANSMITTERS are the chemicals that signal between nerve cells

Question 15

UNDERSTANDING Neural Signalling = 3

Answer 15

1. Nerve to nerve connection is a SYNAPSES
2. Neve to gland or muscle is a JUNCTION
3. very close contacts between axon terminals and target cell

Question 16

NEURAL SIGNALLING = PRE-SYNAPTIC VS POST-SYNAPTIC

Answer 16

Pre-synaptic cell sends the signal

Post-synaptic cell receives the signal

Question 17

Signalling Between Neurons

Answer 17

1. Axosomatic synapses
2. Axodendritic synapses
3. Axo-axonic synapse

Question 18

Neuronal Signalling = RESTING MEMBRANE POTENTIAL (-60 TO -70 mV)

WHY = 2

Answer 18

Resting membrane potential (-60 to -70 mV)

DUE TO
1 * unequal distribution electrically charged ions

2 * selective permeability of membrane these ions

Question 19

In nerve cells membrane potential can be quickly altered by

Answer 19

changes in permeability to certain ions.

Question 20

Recording Membrane Potential

Answer 20

Intracellular recordings enable measurement of membrane potential

Amplifier and oscilloscope – extracellular electrode

y axis = Vm (mV)
x axis = time

Passive vs Active response

Question 21

Understanding PASSIVE SIGNALS
GRADED VS ACTION POTENTIALS

Answer 21

—Changes in potential are used to transmit information within the nervous system

GRADED POTENTIALS signal over short distances
- ACTION POTENTIALS signal over long distances

Question 22

Understanding PASSIVE SIGNALS = 3

Answer 22

1. Vm decays due to leakage of electrically charged ions.
2. Distance at which Vm has decayed to 37% of original value at current injection defines length constant (λ).
3. λ is a measure of efficiency of passive spread.

“Because changes in potential “die out” over short distances (few mm) they only signal over short distances”

Question 23

UNDERSTANDING AXON HILLOCK = 4

Answer 23

The axon hillock is the region of a neuron that controls the initiation of an electrical impulse based on the inputs from other neurons or the environment.

1. THRESHOLD for action potential lowest at AXON HILLOCK
2. Axon hillock highest density of Na+ channels
3. Effectiveness of synaptic connection depends on the distance length constant
4. Integration of all EXCITATORY and INHIBITORY inputs

Question 24

Summation

Answer 24

The less a passive signal decays, the more likely it is to generate an AP

Temporal vs Spatial summation
- Synaptic current,
- Synaptic potential,
-long time constant (100msec) vs long length constant (1nm)
- short time constant (20 msec) vs short length (0.1 nm)

Question 25

Neuronal Connectivity = 2

Answer 25

1. Divergence
   - Convergence Excitation and excitation (E)
2. Convergence
   - Convergence excitation (E) and Inhibition (I)

Question 26

Interneurons: Feed forward inhibition

Answer 26

1. Afferent neurons innervating extensor muscles
2. Extensor motor neuron to extensors

or

1.Afferent neurons innervating extensor muscles
2. Inhibitory interneuron
3. Afferent innervating flexor muscles
3. flexor motor neuron
4. flexors

Question 27

INTERNEURONS: Feedback inhibition

Answer 27

1.Afferent neurons innervating extensor muscles
2. Extensor motor neuron

or 1.Afferent neurons innervating extensor muscles
2. Inhibitory interneuron

Question 28

INTERNEURON = GATING INTERNEURONS

Answer 28

1. SELECTABLE INPUT
2. DESCENDING CONTROL SIGNAL
3. INTERNEURON
4. MOTOR NEURON
   - + other inputs

Question 29

interneuron = Gating by presynaptic inhibition

Answer 29

1. selectable input
2. descending control signal
3. interneuron or motor neuron

Question 30

Summary = 7

Answer 30

1 ➢ The nervous system has central and peripheral components with afferent and efferent neurons.

2 ➢ Nerve tissue contains both neurons and glial cells

3 ➢ Signalling occurs between neurons at synapses

4 ➢ Signals can cause either excitation or inhibition of the post synaptic cell

5 ➢ Signals received at the dendrites and soma are integrated at the axon hillock where action potentials are generated

6 ➢ Action potentials are regenerated signals that travel the length of the axon

7 ➢ Neural pathways show both divergence and convergence