LECTURE 3: Introduction to the Nervous System

Question 1

Organisation of the Nervous System:

Answer 1

1. Central
   - Brain
   -Spinal Cord
2. Peripheral
   - Cranial Nerves
   - Spinal Nerves

Question 2

Two Cell Types; What are they?

Answer 2

1. Neurons; EXCITEABLE
2. Glia; SUPPORT

Question 3

What are the 3 Types of NEURONS?
found where? what do they look like?

Answer 3

1. Multipolar (most abundant neuron in CNS)
2. Pseudounipolar (Spinal ganglion)
3. Bipolar (Retina)

Question 4

What are the 5 types of Glia Cells (SUPPORT)?

What is their main purpose?

Answer 4

1.Oligodendrocytes/Neurolemmocytes
PURPOSE: Myelinating cells in CNS.

2. Astrocytes
   PURPOSE: Support and nurture neurons.
3. Microglia
   PURPOSE: Immune cells
4. Polydendrocytes
   PURPOSE: Stem Cells
5. Ependymal cells; Line Ventricles, separate CSF from nervous tissue.

(NO MAPE?)

Question 5

Explain the process of SYNAPTIC INPUT. (4)

Answer 5

1. Rough endoplasmic reticulum (rER) stains purple with a “Nissl stain “
   — and is called “Nissl substance”.
2. Proteins, neurotransmitters and hormones are produced in the CELL BODY.
3. and then TRANSPORTED (VIA MICROTUBULES) down the axon (ANTEROGRADE TRANSPORT) TO SYNAPSE.
4. TROPHIC FACTORS from a NEURON’S TARGET in the PHERIPERY is SHUTTLED UP the AXON (RETROGRADE TRANSPORT) TO CELL BODY.

• Survival of neurons depends on trophic support!

Question 6

What are the well-established ROLES for GLIAL CELLS? (5.)

Answer 6

1. MAINTAINING the IONIC MILIEU of NEREVE CELLS
2. MODULATING the RATE of NERVE SIGNAL PROPAGATION.
3. MODULATING SYNAPTIC ACTION by CONTROLLING the UPTAKE of NEUROTRANSMITTERS.
4. PROVIDING a SCAFFOLD for some ASPECTS of NEURAL DEVELOPMENT.
5. AIDING in and/or PREVENTING (in some instances) RECOVERY FROM NEURAL INJURY.

Question 7

Understanding Microglia in DETAIL:
origination of glial cells, microglia, function/role?

Answer 7

1. ALL Part of BRAIN’S GLIA = ORIGINATE from ECTODERMAL TISSUE

***MICROGLIA DO NOT = they originate from YOLK-SAC PROGENITORS.

2. YOLK-SAC PROGENITORS OLY POPULATE the BRAIN DURING DEVELOPMENT.
   - (reviewed in Kim and de Vellis, 2005; Kettenmann et al., 2011.)
3. Some neurobiologists PREFER TO CATEGORIZE microglial as a type of MICROPHAGE.
4. FOLLOWING BRAIN DAMAGE, the NUMBER OF MICROGLIA AT THE SITE OF INJURY INCREASES DRAMATICALLY.

Question 8

Explain the BLOOD BRAIN BARRIER (5)
What is it? It’s the purpose?
Formed how?
Structure?
Pass to and fro?

Answer 8

1. What is it? The blood-brain barrier (BBB) is a specialized structure that separates the blood circulation from the central nervous system (CNS).
   - The BBB effectively separates the blood from the neuropil (neurons and glia).
   - - The BBB helps maintain a stable and controlled environment for proper brain function.
2. FORMED BY ENDOTHELIAL CELLS that LINE theBLOOD VESSELS in the CNS.
3. The ENDOTHELIAL CELLS areCONNECTED TOGETHER VIA TIGHT JUNCTIONS= CREATING A BARRIER
4. ASTROCYTE processes (END-FEET) COVER the BLOOD FROM THE NEUROPIL SIDE = reinforcing the barrier.
5. HOW CAN THINGS PASS TO AND FRO FROM THE BBB?
   - SMALL LIPOPHILIC MOLECULES, WATER, AND GAS = PASSIVELY DIFFUSE ACROSS THE BARRIER.
   - OTHER SUBSTANCES REQUIRE = ACTIVE TRANSPORT. (Active transport involves specific carrier proteins or transporters.)

Question 9

How do Neurons communicate?

Answer 9

1. Neurons communicate with each other through a combination of ELECTRICAL AND CHEMICAL SIGNALS.
2. • ELECTRICAL SIGNALS: Neurons can generate and transmit electrical signals, known as aACTION POTENTIAL OR NERVE IMPULSES. These electrical signals are MEDIATED THROUGH THE MOVEMENT OF IONS (charged particles), ACROSS NEURONAL MEMBRANE.
3. ACTION POTENTIAL GENERATION:
4. • The resting membrane potential of a neuron is around -70 mV, with the inside of the cell being more negative than the outside.

2- STIMULUS: Excitatory inputs promote the generation of action potential
- Action potentials occur when the SUM OF EXITATORY AND INHIBITORY INPUTS = reaches the action potential threshold, typically around -50 mV.
- It TRIGGERS A RAPID BUT TEMPORARY CHANGE IN ELECTRICAL POTENTIAL OF THE NEURON.

3. VOLTAGE-GATED Na+ CHANNELS: The OPENING of voltage-gated sodium (Na+) channels, ALLOWING A RAPID INFLUX OF (+ TIVELY CHARGED SODIUM (Na+) INTO THE NEURON. (K- Inside)
4. DEPOLARISATION: The INFLUX OF Na+ IONS leads to a rapid change in the electrical potential of the NEURON = DEPOLARISED,
   - Depolarization refers to a SHIFT TOWARDS A MORE POSITIVE CHARGE INSIDE THE NEURON. This CAHNE IN CHARGE PROPOGATES ALONG NEURON = creating the electrical signal of the action potential.

Question 10

Characteristics of an ACTION POTENTIAL That TRAVELS ALONG AN AXON (3)
- how can it achieve it as well

Answer 10

As an action potential (AP) travels along an axon it must be:
1. * Unidirectional

2. • Fast (myelin + increased axon diameter helps this!)
3. • Efficient (APs are generated only at nodes of Ranvier!)

Question 11

Features of the SPINAL CORD VS SPINAL NERVES
- which system? How many?

Answer 11

SPINAL CORD = CNS
there are 5 SPINAL CORD SEGMENTS

SPINAL NERVES = PNS
there are 31 PAIRS OF SPINAL NERVES

Question 12

EXPLAIN the POSITION OF THE SPINAL CORD:
where? begin and ending? Cauda Equina?

Answer 12

1. HOUSED WITHIN THE VERTEBRAL CANAL
2. BEGINS from FORAMEN MAGNUM to L1-L2 VERTEBRAL LEVEL.
3. LUMBAR/SACRAL/COCCYGEAL NERVES FORM = CAUDA EQUINA

Question 13

EXPLAIN THE PROTECTION OF THE SPINAL CORD: 3

Answer 13

1. Spinal cord COVERED IN 3 LAYERS OF MENINGES
   - (pia, arachnoid & dura mater)
2. SURROUNDED BY EPIDURAL FAT IN THE VERTEBRAL CANAL
3. DURA MATER EXTENDS THROUGH the INTERVERTEBRAL FORAMEN to BECOME the EPINEURIUM OF SPINAL NERVE.

Question 14

EXPLAIN Spinal nerves (PNS)
- what is a mixed spinal nerve? function? Location? the issue with location? how and why?POSTEROLATERAL HERNIATIONS

Answer 14

1. ANTERIOR (MOTOR) and POSTERIOR (SENSORY) ROOTS of SPINAL NERVESCOME TOGETHER TO FORM MIXED SPINAL NERVES.
2. • MIXED SPINAL NERVES are RESPONSIBLE for both MOTOR AND SENSORY FUNCTIONS.
3. • The mixed spinal nerve is LOCATED IN INTERVERTEBRAL FORMAEN, which is the opening between adjacent vertebrae.
     - The intervertebral foramen is the space through which the mixed spinal nerve passes.
4. • The LOCATION OF MIXED SPINAL NERVE IN INTERVERTEBRAL FORMAEN MAKES IT SUSCEPTIBLE FOR COMPRESSION OR ENTRAPMENT.
5. • POSTEROLATERAL HERNIATIONS of the intervertebral disc can pose a risk to the mixed spinal nerve.
     - A posterolateral herniation OCCURS when the INNER GEL-LIKE SUBSTANCE OF the INTERVERTEBRAL DISC PROTUDES OUTWARDS TOWARDS THE POSTERIOR AND LATERAL SIDES.
     - If a herniated disc compresses the mixed spinal nerve in the intervertebral foramen, it CAN LEAD TO NERVE ENTRAPMENT.
     - Nerve entrapment can result in pain, sensory disturbances, or motor deficits depending on the affected nerve.

Question 15

Spinal nerves form into plexuses to supply the body.
What, how, why, function
examples?

Answer 15

• Spinal nerves, after exiting the vertebral column through the intervertebral foramina, combine and form complex networks called PLEXUSES.
• These plexuses are formed by the MERGING and BRANCHING of ANTERIOR RAMI (branches) of adjacent spinal nerves.
• These plexuses give rise to various nerves that distribute throughout the body, allowing for the CONTROL OF MUSCLE MOVEMENT and the TRANSMISSION OF SENSORY INFORMATION.
• The COMPLEXITY of the plexuses allows for the MIXING AND SHARING OF NERVE FIBRES fFROM MULTIPLE SPINAL LEVELS, providing REDUNDANCY and FLEXIBILITY in NERVE SUPPLY TO DIFFERENT REGIONS OF THE BODY.

The main plexuses in the body are:

1. Cervical Plexus: Formed by the anterior rami of spinal nerves C1-C4, the cervical plexus supplies motor and sensory innervation to the neck, shoulder, and parts of the head.
2. Brachial Plexus: Formed by the anterior rami of spinal nerves C5-T1, the brachial plexus supplies motor and sensory innervation to the upper limb, including the shoulder, arm, forearm, and hand.
3. Lumbar Plexus: Formed by the anterior rami of spinal nerves L1-L4, with contributions from T12, the lumbar plexus supplies motor and sensory innervation to the abdominal wall, parts of the lower limb, and the genital region.
4. Sacral Plexus: Formed by the anterior rami of spinal nerves L4-S4, the sacral plexus supplies motor and sensory innervation to the posterior thigh, leg, foot, and pelvic region.
5. Coccygeal Plexus: Formed by the anterior rami of spinal nerves S4-S5 and the coccygeal nerve, the coccygeal plexus provides innervation to a small region near the coccyx.