Week 6: The Nervous System

What are the 3 Basic Functions of the Nervous System?

1. Sensory - Sensory receptors detect changes in the environment.

2. Integration - Input is processed so that the system (brain) can decide on what to do.

3. Motor Output - Response initiated which then activates the body’s muscles and glands.

Name and describe the Divisions of the Nervous System:

Name and Describe what the Nervous System is made of? Name the 3 Functional Neurons:

1. Neurons

   • Communication

   • Processes information

   • Control functions

2. Neuroglia (Glial Cells)

   • Supporting cells

Functional Neurons:

1. Motor Neurons - CNS sends signal to targeted muscles or glands.

2. Sensory Neurons - Send sensory information to the CNS.

3. Interneurons - Located in the CNS. They connect sensory neurons to motor neurons.

Name and describe the 6-Types of Neuroglia:

CNS

1. Astrocytes

   • Maintain blood-brain barrier.

   • Regulate nutrient and ion balance.

   • Provide structural support.

   • Repair damaged tissue (scar formation).

2. Ependymal Cells

   • Line brain ventricles and spinal cord central canal.

   • Produce and circulate cerebrospinal fluid (CSF).

3. Oligodendrocytes

   • Form myelin sheath around CNS axons.

   • Provide structural framework.

4. Microglia

   • Immune cells of the CNS.

   • Remove waste and pathogens (phagocytosis).

   • Activated during injury or disease.

PNS

5. Satellite Cells

   • Surround neuron cell bodies in PNS ganglia.

   • Regulate O2 and CO2, nutrient, and neurotransmitter levels around in ganglia.

6. Schwann Cells

   • Form myelin sheath around PNS axons.

   • Aid in axon regeneration.

Name and describe the Structures of a Neuron:

1. Dendrites - Receives electrical signal from other neurons.

2. Soma (Cell Body) - Holds the Nucleus and supports cell function.

3. Nucleus - Holds DNA and controls function and repair.

4. Axon - Long fibre that transmits electrical signal.

5. Myelin Sheath - Insulates axon and speeds process. Made from Oligodendrocytes (CNS) and Schwann Cells (PNS).

6. Axon Terminal - Releases neurotransmitter to synapse.

7. Synapse - The gap between 2 neurons.

8. Post-Synaptic Cell - The neuron (muscle or gland) receives neurotransmitter. Has receptors to detect/respond to chemical message.

What is an Electrical Synapse?

• Cytoplasmic continuity between two neurons (like a bridge). It’s called a Gap Junction (connexons).

• Fast messaging

  • e.g., reflexes

What is a Chemical Synapse?

• Instead of a Gap Junction it releases a chemical, ‘neurotransmitters’ into the Synaptic Cleft.

• Neurotransmitters float across the Synaptic Cleft and enter a post-synaptic cell.

• Slow/controlled

  • e.g., Neuromuscular Junction

Name the Structures of the Chemical Synapse:

1. Pre-Synaptic Vesicle

2. Mitochondria

3. Post-Synaptic Neuron

4. Pre-Synaptic Vesicle (Pre-Synaptic Membrane)

5. Synaptic Cleft

Describe the Process of Chemical Synapse and Name the Ion Channels:

1. In the pre-synaptic cell, the electrical signal travels via the axon to the axon terminals.

2. Action potential

3. The voltage charged Ca2+ (calcium) channels open (Active: Electrical - Voltage Channel).

4. Ca2+ enters the channels and enter the axon terminal.

5. The Ca2+ enter pre-synaptic vesicles.

6. The vesicles hold neurotransmitters.

7. The vesicles fuse with the pre-synaptic membrane for exocytosis (exit).

8. The neurotransmitters travel through the synaptic cleft.

9. The neurotransmitters enter post-synaptic receptors and bind.

10. Ion channels (Active: Chemical - Ligand Channel) open.

11. Graded Potential

What does ‘Resting Membrane Potential’ Mean?

• The neuron is at rest (not sending an electrical signal).

• Polarised - Exterior is positively charged and interior is negatively charged.

  • Uneven distribution of ions (like Na⁺ and K⁺) and the work of the sodium-potassium pump.

What are Ion Channels? Give examples:

• Tiny gates in the neuron’s membrane.

• They open and close ions like Na⁺ (sodium), K⁺ (potassium), or Ca²⁺ (calcium) pass in or out.

• When they open, they can change the charge inside the neuron.

• Passive channels

• Active channels

  • Chemically gated (ligand gated)

  • Mechanically gated

  • Voltage gated (electrical signal)

    • e.g., Ca2+ Voltage Charged Channel

What does ‘Graded Potential’ Mean? Also, Name and Describe it’s Polarisation:

• A small change in the neuron’s charge.

• Happens when a few ion channels open, usually near the dendrites or cell body.

• Can be strong or weak — the size of the signal depends on the strength of the stimulus.

• If the graded potential is strong enough and reaches the axon hillock, it may trigger an action potential (e.g., a full nerve signal).

• If a stimulus opens ion channels:

  • If Na⁺ enters → the inside becomes less negative → this is called depolarisation.

  • If Cl⁻ (chloride ion) enters or K⁺ leaves → the inside becomes more negative → this is hyperpolarisation.

• These changes are temporary and vary in strength — hence the term graded.

What does ‘at rest’ Mean?

• Polarised

• The inside of the neuron is more negative than the outside.

• Both Na+ and K+ channels are closed.

• The neuron is ready to fire but not active (action potential).

What is Depolarisation?

• The inside becomes less negative and more positive.

• Na+ channels open allowing Na+ entry, K+ channels are closed.

• Can lead to an action potential if it reaches the threshold.

What is Hyperpolarisation?

• The inside becomes more negative than the resting state.

• Caused by K+ leaving or Cl- entering the cell.

• Makes the neuron less likely to fire.

What is Repolarisation?

• The neuron returns to its resting state after depolarisation.

• K+ leaves the cell to restore the negative charge inside.

• Happens after an action potential to reset the membrane.

What are Ions? Give some Examples:

• Positive charged particles.

• Can change the charge of a neuron.

  • e.g.,

    • Na+ (Sodium)

    • K+ (Potassium)

    • Ca2+ (Calcium)

Name and Describe the Protective Mechanisms of the Brain?

1. Bone Exterior: Skull and Vertebral Column

   Skull:

   • Hard

   • Boney

   • Encases the Brain.

   Vertebral Column:

   • Protects Spinal Cord

2. Meninges (3-Layers)

   1. Dura Mater

      • Tough and thick outer layer.

      • Attached to the inner surface of the skull.

   2. Arachnoid Mater

      • Web-like middle layer.

      • Contains spaces where (cerebrospinal fluid) CSF flows.

   3. Pia Mater

      • Thin, delicate layer that clings tightly to the brain surface.

      • Carries blood vessels into brain tissue.

3. Cerebrospinal Fluid (CSF)

   • Clear fluid that circulates the arachnoid and pia mater, and within the brain’s ventricles.

   • Cushions the brain.

   • Removes waste and delivers nutrients.

4. Blood-Brain Barrier (BBB)

   • Selective filter made of tight junctions between brain capillary cells.

   • Protects the brain from pathogens.

   • Allows essential molecules to pass through (e.g., oxygen, glucose, medications).

Identify and Describe the Meninges:

2. Meninges (3-Layers)

   1. Dura Mater

      • Tough and thick outer layer.

      • Attached to the inner surface of the skull.

   2. Arachnoid Mater

      • Web-like middle layer.

      • Contains spaces where (cerebrospinal fluid) CSF flows.

   3. Pia Mater

      • Thin, delicate layer that clings tightly to the brain surface.

      • Carries blood vessels into brain tissue.

Identify and Describe (Positioning) the Structures of the Brain:

1. Frontal Lobe

   • Judgement

   • Reasoning

   • Personality

   • Voluntary Movement - contains Primary Motor Cortex

     • Anterior surface of the brain.

     • Anterior to Central Sulcus.

2. Parietal Lobe

   • Sensory information (e.g., pain ,touch, temperature).

     • Superior surface

     • Posterior to Frontal lobe.

     • Posterior to Central Sulcus.

3. Occipital Lobe

   • Interpretation of visual patterns (eyes).

     • Most posterior aspect of the cerebrum.

4. Temporal Lobe

   • Hearing

   • Language

     • Lateral surface of Cerebrum.

     • Inferior to Lateral Sulci.

5. Cerebellum

   • Coordinating movement

   • Balance

   • Posture

     • Inferior and posterior to the Occipital Lobe

6. Central Sulcus

   • Separates the Frontal and Parietal Lobes.

   • Defines the Primary Motor Cortex (skeletal muscle) and Primary Somatosensory Cortex (senses).

Name and Describe the Brain’s Structures:

1. Cerebellum: Balance, posture, and fine motor movement.

2. Hypothalamus: Homeostasis and links the Nervous System and Endocrine System via the Pituitary Gland.

3. Pons: Breathing regulation and communication between the cerebrum and cerebellum.

4. Medulla Oblongata: Vital automatic functions (e.g., heart rate, breathing).

5. Corpus Callosum: Thick band of fibres that connect the left and right cerebral hemispheres.

6. Thalamus: Sends sensory signals to the right areas of the cerebral cortex.

What is Grey and White Matter?

Grey Matter:

• Made up of neuronal cell bodies, dendrites, and synapses.

• Processing and decision-making (e.g., thinking, memory, sensory input).

White Matter:

• Made up of axons covered in myelin (makes it look white).

• Carries signals between grey matter regions.

Name and Describe the Spinal Cord:

7. Dorsal Root Ganglia: Processes incoming sensory information (e.g., touch, pain).

8. Dorsal Root: Carries sensory information into the spinal cord.

9. Ventral Root: Carries motor information (voluntary) out of the spinal cord.

Classification of Neurons

Describe the Differences of the Somatic and Automatic System:

Somatic:

• Voluntary

• Motor Cortex

• Skeletal muscle

Autonomic:

• Involuntary

• Hypothalamus, brain stem

• Smooth, cardiac muscle, glands.